design of an integrated waste management facility for the dublin region

BSEN40320 – WASTE TO ENERGY PROCESSES AND TECHNOLOGY

Integrated WasteManagement

Facility for the Greater Dublin Region

Martin, L. McKeirnan, D. Kumar-Singh, A. Priyadarshan-Kale, A & Hemant-Karmarkar, M.

11/28/2014

The feasibility of developing an integrated waste management facility to cater for the greater Dublin region was investigated. A suitably-sized site was located with 18km of the city and was designed to include a landfill, incinerator, anaerobic digester and composting facility. The cost of developing the site was estimated to be in the region of €157million however the initial investment is expected to be paid back through the generation of heat and electricity from on-site processes in addition the economies of scale. Overall such a facility is viewed as a worthwhile investment for the sake of upgrading Irelands waste management system to a sustainable entity whilst minimizing the environmental damage associated with waste disposal.

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Contents Section 1: Introduction ........................................................................................................................... 5

Section 2: Site Selection .......................................................................................................................... 6

Section 3: Site Layout ............................................................................................................................ 11

.......................................................................................................................................................... 13

Section 4: Landfill .................................................................................................................................. 14

Site Infrastructure ............................................................................................................................. 14

Landfill Design ................................................................................................................................... 15

Liner Design ....................................................................................................................................... 15

Leachate ............................................................................................................................................ 16

Gas .................................................................................................................................................... 17

Ground Water and Surface Water .................................................................................................... 18

Section 5: Incineration .......................................................................................................................... 20

Incinerator types: .............................................................................................................................. 21

1. Moving Grate: ....................................................................................................................... 21

2. Rotary Kiln: ............................................................................................................................ 22

3. Fluidised Bed: ........................................................................................................................ 22

State of the art moving grate incinerator: ........................................................................................ 23

Incinerator Efficiency: ....................................................................................................................... 25

Section 6: Anaerobic Digestion: ............................................................................................................ 27

Importance of AD: ............................................................................................................................. 28

Feedstock for AD ............................................................................................................................... 29

Chemical Reactions in AD ................................................................................................................. 30

Variable Parameters in AD ................................................................................................................ 31

Temperature ................................................................................................................................. 31

Redox potential ............................................................................................................................. 31

C:N ratio ........................................................................................................................................ 31

pH .................................................................................................................................................. 32

Inhibitory Substances .................................................................................................................... 32

Types of AD ....................................................................................................................................... 32

Single stage and Two-stage digesters ........................................................................................... 32

High Solid or Dry Anaerobic Digestion and Low solid or Wet Anaerobic Digestion ..................... 33

Planning and Financial viability ..................................................................................................... 33

Planning Regulations (SEAI: Application guidelines) ......................................................................... 34

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Section 7: Composting .......................................................................................................................... 35

Composting in Ireland ....................................................................................................................... 35

Site layout ......................................................................................................................................... 36

Windrow (mechanical aeration) ....................................................................................................... 36

Type of Wastes Used for the Composting process ........................................................................... 37

Requirements for Composting : ........................................................................................................ 37

Carbon: Nitrogen ratio .................................................................................................................. 38

Moisture Content .......................................................................................................................... 38

Oxygen .......................................................................................................................................... 38

pH .................................................................................................................................................. 38

Temperature ................................................................................................................................. 39

Particle size ................................................................................................................................... 39

Conclusion ......................................................................................................................................... 39

Advantages of composting................................................................................................................ 40

Section 8: Discussion and Conclusions.................................................................................................. 41

References: ....................................................................................................................................... 42

Appendix 1: Incineration efficiency calculations .............................................................................. 47

Appendix 2: Methane production rates from landfill equations ...................................................... 48

Appendix 3: Distribution of workload ............................................................................................... 49

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List of figures:

Figure 1:Waste Management Hierarchy (EPA, 2004) 5

Figure 2: Dublin Recycling rates 2000-2010 (Dublin Local Authorities, 2012) 6

Figure 3: Potential locations for waste treatment facility (Google Maps, 2014) 7

Figure 4: The composition of Irish MSW 8

Figure 5: Layout of the various waste treatment technologies and the site in Mayne, Co. Meath 13

Figure 6: Liner System Design showing both soil layer and synthetic layer 15

Figure 7 Vertical gas collection system for proposed landfill 17

Figure 8: Methane emissions and uses from 1990-2008. 18

Figure 9: Waste management strategies of different E.U countries. (Eurostat, 2012) 20

Figure 10: Moving Grate Incinerator (igniss.pl, 2014) 21

Figure 11: Rotary Kiln Incinerator (infohouse, 1996) 22

Figure 12: Fluidized bed incinerator (infohouse, 1996) 22

Figure 13: Typical design of a MSW incinerator (Murdoch University, 2014) 23

Figure 14 Figure1. Anaerobic digestion installed capacity in Europe 27

Figure 15: Complete flow Cycle of AD (Photo Courtesy: Pagels Ponderosa; Utah State University): 29

Figure 16 Figure3. Chemical Reactions in Anaerobic Digestion (www.wastewaterhandbook.com,2014) 31

Figure 17: Lemvig biogas plant overview (Source: www.lemvigbiogas.com) 33

Figure 18: Locations of the composting facilities in Ireland (Herity 2013) 35

Figure 19: Diagram of Windrow (Harvest Quest, 2014) 37

Figure 20: Market for Compost in Ireland. McGovern (2012) 40

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List of tables:

Table 1: Criteria for site selection (Leão et al, 2004) 10

Table 2: Capital costs of the integrated waste facility 12

Table 3: Products from AD 28

Table 4: Constituents of Biogas (Source: SEAI & Teagsac) 28

Table 5: Potential Feedstock for Electricity Production in Ireland ( teagasc 2013) 30

Table 6: Variable Parameters in AD (Zupan & Grilc, 2007) 32

Table 7: Specification for AD plant in Dublin 34

5

Section 1: Introduction Traditionally in the times of more relaxed environmental laws, landfilling was the preferred

option of waste disposal which up until recently appeared to be the most economical means

of waste disposal

(Daskalopoulos et al, 1998).

In Europe, this archaic

method of waste disposal is

becoming less and less

favoured due to EU

legislation which insists on

countries diverting their

waste from landfill and

devising more

environmentally responsible

waste management plans. Ireland’s interpretation of which is expressed in the “Waste

Management Act, 1996” and promotes the use of the hierarchy outlined in figure 1.1.

Despite the introduction of this act and a rigorous recycling campaign, the majority of the

country’s waste still ends up in landfill. As trends of rapid economic growth looks set to

continue landfills will reach capacity soon and unless Ireland develops a more sustainable

waste management plan there could be a waste crisis on the country’s hands (Davies, 2004).

According to Stehlik et al (2009) the development of Waste-To-Energy-Centres (WTEC’s)

along with new developments in waste-to-energy processes (WTE), can help rapidly growing

countries reach their waste and emissions reduction targets. Ireland’s susceptibility to

NIMBYism is hindering our capability to deal with waste adequately (Davies, 2004) and

causing the country to fall way behind in meeting emissions reductions in comparison to our

European counterparts such as Denmark (Hjelmar, 1997) and Belgium (Van Gervan, 2005).

There is ample evidence that the combination of waste sorting and recycling, composting,

anaerobic digestion, incineration and finally landfill with biogas recovery is the most

efficient way to treat waste with respect to environmental impact and land use reduction

(Cherubini et al, 2009; Daskalopoulos et al, 1998; Mendes et al, 2004). The aim of this study

is to investigate the feasibility of siting an integrated waste management centre to deal with

the municipal solid waste of the greater Dublin area. This centre will incorporate

Figure 1:Waste Management Hierarchy (EPA, 2004)

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an anaerobic digester and a composting system for the treatment of organic

materials,

an incinerator with energy recovery for the treatment of inorganic materials,

a landfill with biogas recovery.

Section 2: Site Selection Dublin is the capital city of Ireland with a population of 1.27 million as of 2014. According to

the central statistics office this is set to increase to somewhere in between 96,000 and

286,000 by 2021. The city produced almost 1.2 million tonnes of municipal solid waste

(MSW) in 2010 with this annual figure expected to rise steadily to 1.4 million tonnes by 2020

(Dublin local Authorities, 2012). According to figure 2 the rigorous recycling campaign

implemented by the Dublin councils appears to be successful with targets being exceeded in

2010.

However the remaining proportion of waste is still being sent to landfill. Setting aside the

emissions from this method of waste disposal for a moment the main issue with this in

Dublin’s case is a spatial one. According to Tammemagi (1998) even countries with

seemingly endless amounts of space cannot afford to waste land on landfills. In Dublin most

of the surrounding area outside the city limits consists of valuable agricultural land.

According to DoELG, (1999) the main aim of the 1996 Act is to reduce the amount of waste.

The development of an integrated waste facility can significantly reduce the amount of

space required to store waste whilst simultaneously using that waste as a resource to

generate energy from biogas or refuse derived fuels. When selecting a site there are a vast

number of criteria which must be satisfied in order to minimise environmental impact and

Figure 2: Dublin Recycling rates 2000-2010 (Dublin Local Authorities, 2012)

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human health concerns. Figure 3 shows the final sites considered for the waste

management plan.

Figure 3: Potential locations for waste treatment facility (Google Maps, 2014)

The final three sites considered are roughly 20-30 km form the city centre ranging from 27

hectares to 40 hectares in size. Using the following equations, taken from Kiely (1997) along

with population and waste generation estimates from the Dublin local authorities (2012) the

optimum sized site was calculated.

Assuming a required lifespan of 20 years for a projected population of 1.4 million

(CSO,2012) with an average of 3.5 people per household, this gives us a density of 285kg of

waste per household per week with an assumed density of 500 kg/m².

A) 𝐖𝐚𝐬𝐭𝐞 𝐠𝐞𝐧𝐞𝐫𝐚𝐭𝐞𝐝 =Total population

persons per house∗

household waste per week

10³

=1,400,000

3.5∗

285

103= 11,400 𝑡𝑜𝑛𝑛𝑒𝑠 𝑝𝑒𝑟 𝑤𝑒𝑒𝑘

= 592,800 𝑡𝑜𝑛𝑛𝑒𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟

B) 𝟖𝟓% 𝐕𝐨𝐥𝐮𝐦𝐞 𝐫𝐞𝐝𝐮𝐜𝐭𝐢𝐨𝐧 𝐝𝐮𝐞 𝐭𝐨 𝐢𝐧𝐜𝐢𝐧𝐞𝐫𝐚𝐭𝐢𝐨𝐧, 𝐫𝐞𝐜𝐲𝐜𝐥𝐢𝐧𝐠, 𝐛𝐢𝐨 𝐭𝐫𝐞𝐚𝐭𝐦𝐞𝐧𝐭 = 592,800 ∗.15 = 88,920 tonnes per year

C) 𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐥𝐚𝐧𝐝𝐟𝐢𝐥𝐥 =88,920∗103

500kg/m²(density of waste)=177,840m³ per year

𝐇𝐞𝐢𝐠𝐡𝐭 𝐫𝐞𝐬𝐭𝐫𝐢𝐜𝐭𝐢𝐨𝐧 𝐨𝐟 𝟏𝟐. 𝟓𝐦 =177,840

12.5= 14227.2𝑚2 = 1.4ℎ𝑎

8

D) 𝐀𝐫𝐞𝐚 𝐫𝐞𝐪𝐮𝐢𝐫𝐞𝐝 𝐟𝐨𝐫 𝟐𝟎 𝐲𝐞𝐚𝐫𝐬 =

1.4ha ∗ 20(years) ∗ 1.5(extra space for infrastructure) = 42ha

Figure 4: The composition of Irish MSW

Fig. 4 shows the approximate composition of MSW derived from the Dublin Local

Authorities (2012). This is important for determining the size of treatment facilities such as

composting, anaerobic digestion and incineration.

The projections of these equations suggest that for a 20 year lifespan, the ideal size required

would be 42 hectares. At 40hectares, Site A, Mayne is closest to this spatial requirement.

Looking at table 1, this site holds a number of advantages over sites B and C located closest

to the city centre (18km) but furthest from residential areas (>0.5km). In addition, site A is

approximately 2km from the M3 and lies at least 3km from the nearest amenities.

Although the population density of this area is low, there are

likely to be a number of objections to the development of a waste management centre at

this location especially from farmers from the surrounding area, nearby residents,

environmental groups and commercial property owners in the area. The Irish public in

general has a tendency to object to any kind of new development suggested by the

government. Cavazza (2013) suggests that a general lack of public trust in local authorities

hinders the development of any kind of new waste technology. It appears that Ireland’s

history of cloak and dagger politics is severely impeding the upgrading of its waste

management facilities. These concerns could be alleviated by:

Glass(9%)

Metals(8%) Textiles(2%)

Plastic(11%)

Organic (21%) Other(17%)

Paper(32%

MSW Compostion in Ireland

9

Compensating property owners within a defined radius of the facility with heat and

power generated from the on-site facilities.

Carrying out the development with complete transparency, outlining the overall

benefits of this facility such as emissions reduction, spatial reduction and jobs.

Encouraging public participation in the planning process. Patel-Tonra (2010),

recommend formally inviting any landowners within 1km of the development to an

information and Q&A seminar whilst posting newspaper adverts to notify any other

interested parties.

Take measures taken to reduce odour, noise and aesthetic pollution such as

incorporation of a green buffer region and designated slip road from the motorway

for refuse lorries.

The biggest drawback of this site is that it borders a tributary to the River Tolka which feeds

right into Dublin city (biodiversityireland.ie, 2014) however this issue can be addressed by

infrastructural safety measures such as the inclusion of leachate barriers into landfill design.

The fine loamy drift soil-type is composed of a 40:40:20 ration of sand, silt and clay

(Teagasc, 2014). A higher clay composition would be more ideal to assist in the absorption

of odours and leachates thus the landfill design will have to ensure alternative solutions to

these issues.

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Table 1: Criteria for site selection (Leão et al, 2004)

Site A Site B Site C

Name of site

Mayne Athgoe Slate Quarries (Rathmore )

Size 40 Hectares 32 Hectares 27.9 Hectares

Cost (Euro)

1.3 Million 1 Million 485,000

Distance from Dublin

18km 20km 27.3km

Distance from Road Network

2 km from M3 2 km from N7 1.5 km from N81

Residential Distance

>0.5km <0.4km >0.5km

Slope <5° >20° 5°<x>20°

Soil Type Fine Loamy Drift with Limestone Fine Loamy Drift with Limestone Fine Loamy over Shale/Slate

Current Land Use

Agricultural Agricultural Agricultural

Distance from Amenities

>3km <2km >3km

Water bodies

Borders tributary to R. Tolka <0.5 km from a drainage ditch <0.5km from a drainage ditch

Links to the property

http://www.myhome.ie/commercial/brochure/mayne-clonee-meath-approx-100-acres/2488626

http://www.myhome.ie/commercial/brochure/athgoe-newcastle-co-dublin-lands-approx-80-acres-newcastle-dublin-county/2682926

http://www.myhome.ie/commercial/brochure/farm-c-69-acres-slate-quarries-rathmore-naas-kildare/2913312










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Section 3: Site Layout

Fig. 5 shows a plan view of the chosen site for the proposed waste to energy centre at

Mayne, Co. Meath. An access road of approximately 200m in length will be constructed to

connect the WTEC to the Bracetown business park road which is approximately 500m from

N3 road. At the site entrance a weigh bridge will be constructed to quantify the amount of

waste delivered to the facility. Located immediately after the site entrance are the

administration buildings covering an area of 100m². A permanent roadway will be

constructed to connect the various waste treatment facilities. To the right of the access

road, a sorting centre will be erected. All four municipalities of Dublin are serviced with

separate collections of organic waste (brown bins), recyclables (green bins) and unsorted

refuse (black bins) meaning the majority of waste is pre-sorted upon arrival. Hence this area

need not cover too much area. The anaerobic digester will be located to the north of the

site as indicated in fig.5. In accordance with SEAI guidelines (2008) the digester is at least

250m from any residential accommodation in this location taking up approximately 0.5

hectares. The mass burn incinerator will be located to the south of the site to satisfy DEFRA

(2010) guidelines of siting the facility at least 500m from residential accommodation and

takes up approximately 3ha of site space. This point is the optimum location this site allows

with the nearest residences located >600m away to the East of the site. It is proposed to

build a CHP plant between these two units. Here electricity and heat can be generated and

used for:

supplying electricity and heat for on-site processes

supplying electricity and heat to the nearby industrial estates consisting of

Bracetown on the site perimeter and Damastown located 2km to the south east of

the site.

Exporting remaining power to the national grid.

The landfill will be located in the south east of the site. Even with the mass reduction of

wastes exhibited in the treatment processes, the landfill still requires the most substantial

space. Fig.5 shows a punnet square of intended development over the 25 year lifespan of

the site. This is a worst case scenario as the development would inevitably bring the landfill

closer to residential areas. The optimum scenario is that the land indicated by the shaded

12

area to the south of this site will come available on the market within 5 years of the

commencement of waste management activities; and landfill development will be

concentrated in this direction, maintaining safe distances from residences. The owner of this

property will be more inclined to sell this site considering that its value will depreciate

significantly due to the presence of the waste facility in its vicinity. The composting facility,

consisting of 3 windrows and a grinding unit will be located to the north of the site taking up

0.2ha for recommended windrow width and separation along with the grinding unit area.

This satisfies the minimum distance requirement outlined by Forgie et al, (2004) of 400m

away from residential units. Initial use of the compost generated from this facility will be

applied as fertilizer to the proposed green buffer zone to facilitate growth. It is proposed

that rapid-growing coniferous trees will be planted in the outlined area to obscure the

waste treatment facilities on-site from public view.

Property/Technology Capital Cost (€)

Site 1.3 million

Incinerator 150 million

Anaerobic Digester 4 million

Composting Technology 120,000

Administration buildings 70,000

CHP Plant 350,000

Machinery for site maintenance 400,000

Potential site expansion 750,000

Total building Cost 156,990,000

Table 2: Capital costs of the integrated waste facility

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Figure 5: Layout of the various waste treatment technologies and the site in Mayne, Co. Meath

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Anaerobic Digester

Weigh-bridge

Access Road

Administration

Sorting Centre

CHP Plant Composting Grinder

and Windrows

Incinerator

Proposed Site

Expansion

Landfill N3

Dublin City Centre 18km

Site Boundary (40ha)

Green Buffer Zone

Damastown Industrial

Estate 2 km

14

Section 4: Landfill

Daire McKiernan

Since July 2009, there has been a significant improvement in the operation of MSW landfill

sites in Ireland (EPA, 2010). This is due to the regulations which have been enforced and

monitored by the EPA. It is imperative that as much biodegradable municipal waste (BMW)

as possible is diverted away from the proposed landfill. Article 5 of the Landfill Directive

requires that Ireland reduces the amount of BMW being landfilled to 0.427 million by 2016.

As landfill has been the cheapest form of waste disposal, it has been the traditional form of

waste management. However, in recent years, there has been an increased shift to

integrated waste management and the sustainable disposal of our waste.

The aim of the EPA, under directives from the European Union, is to reduce the impacts of

and reliance on landfill and to promote an integrated management approach to waste

disposal (Cummins et al, 2002). The landfill is required to operate in accordance with the

Landfill Directive and its main objectives are to prevent or reduce any negative effects on

the environment or human health that are associated with the landfilling of waste (EPA,

2010). Under Statutory Instrument No.194 of the Waste Management (Landfill Levy)

Regulations 2013, landfill costs are set at €75 per tonne of waste.

Site Infrastructure

Site facilities such as weighbridge, office and staff buildings and storage facilities for small

amounts of oils and chemical wastes have been accounted for in a previous section. A

garage or workshop is needed for machinery directly associated with the landfill such as

compactors and excavators. The location of this building can be seen in figure 5. A

permanent internal road which allows access to the landfill can also be seen. Temporary

roads associated with the landfill which lead to the current working cell can be constructed

using debris from nearby construction sites.

The public’s knowledge of the daily activities which take place in the landfill should be kept

to a minimum. This can be carried out by erecting embankments along the perimeter of the

site which act as a green buffer zone. Coniferous trees and shrubs should also be added to

ensure a permanent green buffer zone for screening of the site and control of air pollution

15

also. In the initial phases of the landfill, temporary mobile fences may be necessary to

screen the cells which are being worked on a daily basis.

Landfill Design

The primary goal of the landfill design is to reduce as much as possible the negative effects

the landfill can have on the environment. This is a containment site, where the leachate and

gas are surrounded from the surrounding environment (Kiely, 1997). It is proposed that this

landfill occurs in 6 separate phases. Phasing allows the progressive use of the landfill area in

terms of filling and restoration being carried out at different locations within the site. This is

a ground level landfill and following topsoil removal, waste will be deposited on the surface

up to a height of 12.5m. This type of landfill requires the import of daily and intermediate

covers which can be constructed using up to 1m of compacted soil to prevent

As it is a difficult task to select a location which will have no negative impact or conflicting of

interests, the best compromise location has been selected which minimises the impact on

the environment and the public also.

To ensure minimum pollution and environmental degradation due to the landfill and its

operations, a number of landfill designs should be taken into account. These include liner

design, leachate and gas management and monitoring of the surrounding ground- and

surface water and air quality.

Liner Design

According to Annex I of the Landfill Directive, protection of soil, groundwater and surface

water is to be achieved by the combination of a

geological layer and a bottom liner (EPA, 2010).

Liners are designed to protect the surrounding

water sources by preventing leachate from

seeping out of the contained landfill (EPA, 2000).

To minimize the impact of leachate, a protective

layer called a lining system must be implemented.

As this site has a soil composition ratio of 40:40:20, sand,

silt and clay (Teagasc, 2014), another protective layer must

Figure 6: Liner System Design showing both soil layer and synthetic layer

16

be added to minimize run off. It is recommended that imported clay of depth 0.5m and

compacted in layers of not more than 20cm should be applied.

The soil should have a very low hydraulic conductivity of <10-9 m/s. Along with this, a

synthetic lining system should be utilized due to the close proximity to the underground

tributary to the Tolka River. The various leachate control methods can be seen in fig.6.

These are usually made out of polyethylene and up to 2.0mm in thickness (Kiely, 1997). A

layer of about 1m of waste should be placed on top of the liner before machinery start to

compact the waste.

Leachate

Leachate is a water-type liquid that is commonly found in landfills that can consist of a

number of chemicals. Leachate generally occurs due to rainfall combined with the moisture

fraction of the waste. As a result, leachate contains organic material and heavy metals and is

toxic to the environment (Kiely, 1997). To collect this leachate, a drainage system must be

constructed which consists of a series of wells and pumps. The leachate is then pumped to

an onsite storage tank where it is treated in an effluent balance tank which has a series of

aerators to agitate the leachate and encourage aerobic conditions. Another method of

reducing the potentially toxic composition of leachate is by recirculating through the landfill

which dilutes the leachate to acceptable levels.

As leachate is produced, it must be collected and removed from the landfill liner. Leachate

collection pipes collect this waste which builds up along the landfill liner. These drainage

pipes then lead to a leachate collection pond where it can be treated by either biological or

physical-chemical methods (EPA, 2000). All active cells should have at least 2 leachate

monitoring points with one located at the leachate collection point.

Monthly, quarterly and annual monitoring of leachate are requirements as part of the

Landfill Directive. Parameters such as leachate level, pH, conductivity, temperature,

ammonia, chloride, BOD/COD, total oxidised nitrogen, total phosphate, metals, sulphates

and fluoride must be monitored at the aforementioned frequencies (EPA, 2010).

17

Gas

Landfill gas is a product of biochemical reactions which occur within the landfill under

anaerobic conditions (Kiely, 1997). The composition of the gas is dependent on a number of

conditions such as the type and age of the waste. Landfill gas can have a calorific value of 15

to 21 MJ/m3 with the gas consisting of up to 60% methane and 39% CO2 (EPA, 1997, 2000)

and is therefore a possible greenhouse gas and environmental risk. In 2009, it accounted for

71% of all complaints in relation to landfill sites.

There are four phases which lead to the production of gas in a landfill:

1. Initial Aerobic Phase – Generally takes days to weeks and O2 is used up as the more

easily degradable organic waste is broken down. This results in elevated

temperature and CO2 production.

2. First Transition Phase – Lasts from weeks to months as anaerobic and acidic

conditions begin to develop due to O2 being completely used up and a drop in pH 6-

4. Hydrogen and CO2 are produced in this stage.

3. Second Transition Phase – This stage takes 3-5 years and involves methanogenic

bacteria activity which convert simple acids like acetic and formic acids to methane

and methanol. Requires a pH 6-7 to effectively work.

4. Methane Phase – A stable process due to all the organic acids being used up by the

methanogenic bacteria.

A gas management system must be put in

place to reduce impact on air quality,

minimise risk of gas migration to other sites,

permit effective control of gas emissions and

if possible to maximise energy recovery. A

landfill gas collection system made up of gas

wells, wellheads and collection pipes can be

used to actively collect and utilise this

resource or to dispose of it through flaring.

Fig.7 shows how gas is collected by means of

vertical gas collection system. This process

can offset some of the costs of control as the gas can be used to make electricity which can

Figure 7 Vertical gas collection system for proposed landfill

18

then be used onsite or sold to local businesses. However, a minimum of 200,000 tonnes of

waste is needed to sustain a commercially viable gas electricity scheme (Department of

Trade and Industry, 1995). As only 88,920 tonnes/year are expected to go to landfill it will

be a number of years before the biogas plant can produce 1MW of electricity. The volume

of gas produced from the landfill has been calculated as 435.76L CH4/kg of wet waste

(Appendix 2).

If the quality of the gas is too low to be collected and used for energy production, it must be

disposed of through flaring. At landfill sites across Ireland this is the most common type of

disposal of landfill gas with all 31 open landfill sites in 2008 utilising flaring (EPA, 2010). Only

20,000 tonnes of methane produced by landfills in 2008 was utilised through energy

recovery with 58,000 tonnes being disposed of through flaring.

Figure 8: Methane emissions and uses from 1990-2008.

Ground Water and Surface Water

The Landfill Directive (EPA, 1999) requires that all ground and surface water be monitored.

Monitoring must be carried out to test the quantity and quality of surface and ground water

on a period basis. This is done to ensure that any impacts the landfill is having on the

environment can be controlled and prevented. Council Directive 80/68/ECC was

implemented through the Waste Management Act of 1996 to prevent pollution of ground

waters and eliminate the effects of the pollution which has already occurred.

19

To assess for risks to groundwater, information regarding water table height, location of

various groundwater features, ground water quality and groundwater vulnerability should

be collected.

Surface water management is essential to reduce the amount of leachate produced and

minimise the transport of chemicals from the landfill. This can be done by designing a

surface water collection system. This collection system allows the collection and

transportation of run off to a settlement pond away from the landfill operations. This is

done by constructing a series of drainage pipe systems (EPA, 2000).

20

Section 5: Incineration

Luke Martin

The incineration of MSW is easily the most controversial waste management process to be

incorporated into the proposed waste to energy centre (WTEC) at Mayne. Much to the

annoyance of the E.U, Ireland has been slow to adapt their waste management strategy to

include modern, environmentally-friendly waste treatment methods (Davies, 2004).

Figure 9: Waste management strategies of different E.U countries. (Eurostat, 2012)

Fig.9 shows Ireland’s favoured waste disposal methods in relation to the rest of Europe.

These figures show the country performs reasonably well in recycling and composting waste

with approximately 49% waste diverted by these methods; however a massive percentage

of Irelands waste is still being disposed of in landfills. The countries which perform best in

minimizing their reliance on landfill, the likes of Denmark, Sweden and the Netherlands,

have all invested in the thermal treatment of their waste. Up until 2011, Ireland has resisted

the use of incinerators largely due to the factors discussed in section 2 such as “NIMBYism”

and lack of trust in planning authorities (Davies, 2004; Cavazza, 2013). The completion of

the Indaver WTEC accounts for the 8% of waste which Ireland treats via incineration in

figure 1. Contrary to public opinion, the health risks associated with incineration are

estimated to be five times lower than those associated with landfill (Moy et al, 2008). In a

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Was

te T

reat

me

nt

Pre

fere

nce

s

E.U Country

Management of MSW in E.U Countries 2012

Landfilled

Recycled/Composted

Incinerated

21

similar study, Cangialosi et al (2008) has claimed that the health impacts which may arise

from inhalation, dermal contact or soil and food ingestion of PCDD’s and PCDF’s emitted

from incinerators are well below the background levels of these carcinogens. In addition,

Sabbas et al (2003) report that incineration can reduce waste to one-tenth its initial volume

meaning less space is required for final disposal. This observed 8% towards incineration is a

step in the right direction for Irelands waste management plan. Another argument

specifically in opposition to incineration is that a move to this technology will discourage the

more environmentally-friendly practice of recycling due to the constant demand of

feedstock’s for these devices (Snary, 2002). However this argument barely holds water

considering 43% of waste in Ireland is going towards landfill despite rigorous recycling

campaigns. There is more than enough feedstock composed of non-recyclable material to

justify the development of an incinerator.

Incinerator types:

There are three main types of incinerators classified by the method used to manoeuvre

waste through the various heating zones.

1. Moving Grate: This involves a system

of moving grates which facilitate the

movement of waste through the

furnace (Fig.10). The waste goes

through three stages of heating. The

drying stage at <100°C (A); the

pyrolysis stage in which waste is

heated in the absence of oxygen at

<700°C (B); and the combustion stage

at 700-1000°C (C). Flue gas is directed

towards a scrubber at 850°C for MSW and 1100°C for hazardous waste to ensure

chemical bonds of harmful molecules are broken (DEFRA, 2010). Air is drawn in from

below for two functions; to induce combustion and to cool the grates. Grates are

arranged at angles to allow waste to proceed through the furnace via gravity.

Bottom ash, recovered at the end of the process is roughly 10% the initial volume of

the waste. According to Nixon et al (2013) this class of incinerator is the most

Figure 10: Moving Grate Incinerator (igniss.pl, 2014)

22

popular in the U.K as most operators identify moving grate as most reliable

technology for heat recovery from waste.

2. Rotary Kiln: This type of

incinerator consists of an

inclined rotating drum

(Fig.11). This is a modular

design type consisting of

two heating zones; a

pyrolysis zone and a

combustion zone. The

action of rotation on an

incline shifts waste slowly

through the pyrolysis chamber,

where solid waste is volatilized into various gases. The combustion chamber

completes the phase change of pyrolysis gases into simpler molecules. This design

type is less expensive to build than moving grate and is suited to small scale,

specilized treatment plants located in close proximity to the sources of waste (Nixon

et al, 2013).

3. Fluidised Bed: This design involves

waste being fed through a waste feeder

and being immersed in violently moving

red-hot sand (fig.12). Waste burns

instantaneously on contact with with the

sand resulting in a high incineration ratio

per unit area. This type of incinerator

cannot support the combustion of non-

uniform sized material meaning pre-

treatment methods such as shredding

are required. These systems are easiest

Figure 11: Rotary Kiln Incinerator (infohouse, 1996)

Figure 12: Fluidized bed incinerator (infohouse, 1996)

23

to operate with lower start-up and stop times however they require upto 50%

higher power demand than moving grate incinerators. According to Nixon et al

(2013) the greatest advantage to these systems is that quantities of bottom are

significantly reduced.

Considering the proposed WTEC is designed to cater for the municipal solid waste from the

greater Dublin area, the moving grate incinerator is deemed as the most appropriate

technology for this facility. With over 250,000 tonnes of waste expected per year at this

facility (Equation 1(B) minus 49% for recycling), efficiency is key. Moving grate incinerators

can accept a continuous flow of non-homogenously sized waste without enlisting in the use

of pre-treatment methods. This limits the likelihood of malfunctions which, in turn boosts

the efficency of collection systems.

State of the art moving grate incinerator:

Fig.13 shows a schematic of the overall layout of the on-site incinerator including

connections to boilers and turbines along with scrubbers to limit the emission of harmful

gases and particulates.

Figure 13: Typical design of a MSW incinerator (Murdoch University, 2014)

24

The system begins with the deposition of municipal solid waste into a storage bunker (a).

Ideally only unsorted refuse waste will be fed into the storage pit. Waste can be further

sorted by a grabber (b), to avoid placing hazardous materials into the hopper(c) or to

retrieve non-ferrous metals. The hopper then gradually releases waste into the moving-

grate incinerator (d). Waste is shifted through the various heating stages outlined in fig.10

(A, B & C) steadily via the moving grates (e). Temperature must be increased gradually to

inhibit the development of cold pockets or gas channelling (DEFRA, 2010). Bottom ash exits

the system via the ash chute (f) and is transported via conveyor belt to a slag removal

system (g), or a magnet to remove any non-ferrous metal residue (not illustrated in this

diagram). Forteza et al (2004) has shown that after a minimum storage time of one month,

the leachates within bottom ash stabilize sufficiently to enable environmentally sound usage

of these residues in road and pavement construction. Flue gases rise through the

combustion chamber (h) at temperatures of 850-1100°C to facilitate the “cracking” of the

strong molecular bonds exhibited in furans and dioxins. The breakdown of these bonds

leads to the creation of another hazardous compound in Nitrous Oxide. Zandaryaa et al,

(2001) recommend the injection of ammonia into the combustion chamber at this stage

which acts as a reagent, reducing the harmful NOᵪ into harmless molecular nitrogen and

water vapour (process known as selective non-catalytic reduction). At least one auxiliary

burner linked to a temperature sensor must be present in this chamber to ensure these

temperatures are maintained throughout the entire process followed by rapid quenching of

the material (DEFRA, 2010). Failure to do so may allow hazardous compounds to reform (de

novo synthesis) in the 400-250°C temperature range.

Flue gases continue out of the after-burn chamber to heat the boiler system (i) which

generates steam to be exported to an on-site turbine. DEFRA (2010) recommends the use of

combination of the following four technologies to maximise energy recovery;

Boiler system to utilize waste heat,

Turbines powered by steam from these boiler to generate electricity,

Combined heat and power (CHP) scheme to utilize exhaust steam,

Internal heat exchangers for flue reheating.

Suggestions on where to incorporate such features are discussed in section 3 (site

selection). Upon passing the boiler system; flue gases proceed to the economizer (j) where

25

heat is recycled for on-site usage either for supplementary heat supply to the incinerator

itself, or for water and space heating. It is important to locate these heat recovery features

at this point in the cycle, straight after combustion because flue gas temperatures are at

their highest but also require rapid quenching.

After the heat recovery stage, flue gases are now at temperatures of approximately

160°C. It is at this point where the secondary processes associated with gas clean-up begin

in order to ensure minimal harmful emissions to the outside environment. Under E.U

legislation, all modern incinerators must limit their daily average emissions of HCL and TOC

(10mg/m³), HF (1mg/m³), SO₂ (50mg/m³) along with other chemicals such as mercury

(DEFRA, 2010). In order to remove these components safely, gases are first treated in a wet

scrubber (k) which utilizes reagents which target these specific molecules. These scrubbers

also capture fractions of dust simply due to water droplets encapsulating these small

particles. Gas is then further treated in a highly efficient filtration device known as an

electrostatic precipitator (l). This system utilizes an electro-static charge to which designed

to extract the finest portion of particulate matter from the gas. Considering dioxin and furan

pollutants are at the centre of most incinerator objections (Davies, 2004), it is necessary to

include a further, pre-cautionary filtration system in place to prevent their release. Hence

gas passes through a final dioxin filtration system (m) consisting of a catalytic fibre which

oxidises dioxins to form CO², HCL and H₂O (Gore Creative Technologies, 2001). The chimney

stack (n) should be 70m in height for this plant considering 250,000 tonnes of waste are

expected per year (DEFRA (b), 2007).

Incinerator Efficiency:

According to CEWEP (2012), larger incinerators (intake of 250,000 tpa) in northern Europe

tend to have the most favourable R1 value of approximately 0.77. This R1 value is a way of

expressing the energy efficiency relative to conventional power plants hence are suitable for

heat recovery (European Commission Directive, 2008/98/EC). With heat available in the

flue gas in this moving grate incinerator of 8582GJ/day, overall efficiency of this system is

estimated at 80% (Kiely, 1997) [Calculations shown in Appendix 1]. Tolis et al, (2010) has

calculated payback periods of MSW incinerators to be 26-28 years. Gasification yields

greater energy from substrates and has much lower payback periods than mass burn

incineration (8-10 years) so one might argue why invest in incineration? According to

26

Asadullah (2014) these technologies have not yet been successfully up-scaled to deal with

the volumes of waste this site will intake nor are the suited to the heterogeneous sizes for

MSW. Hence the inferior efficiencies of this incinerator is over written by its versatility in

accepting different waste types.

27

Section 6: Anaerobic Digestion:

Anant Kumar Singh

Anaerobic digestion is defined as the controlled breakdown of complex organic matter into

simpler compounds by anaerobic or facultative bacteria in the absence of oxygen.

Anaerobic digestion (AD) is one of the most efficient waste treatment technologies. There is

a recent surge in the installation of AD in Europe due to EU attention towards sustainable

waste management. The technological advancement in better control and optimization of

the anaerobic digestion process is making it financially viable option for waste treatment.

More than 80% composting plants in Netherlands and Belgium will have an anaerobic

digestion facility installed by 2015 as primary treatment.

The economic value associated with syngas makes the AD process more financially feasible

than landfill. The proper waste collection and segregation mechanisms are helping the AD to

run on specific mixture of waste or residue and improving plant operational condition and

reduction of variability. (Baere & Mattheeuws, 2012)

Figure 14 Figure1. Anaerobic digestion installed capacity in Europe

28

Type of product Concentration by mass Uses

Biogas 2-4% For power generation or as cooking gas.

Fiber 7-25% Nutrient rich can be used as soil conditioner

Liquor 75-93% Liquid Fertilizer

Table 3: Products from AD

Component Concentration (by volume)

Methane (CH4) 50-75%

Carbon dioxide (CO2) 25-45%

Water vapor (H2O) 2-7%

Oxygen (O2) <2%

Nitrogen (N2) <2%

Ammonia (NH3) <1%

Hydrogen (H2) <1%

Hydrogen sulphide (H2S) 20-20,000ppm

Table 4: Constituents of Biogas (Source: SEAI & Teagsac)

Importance of AD:

( Baere & Mattheeuws, 2012; Jenkins et al., 2008)

1. It reduces future environmental impacts of waste by degradation into simplest

molecules.

2. AD reduces the spread of harmful diseases and weed seeds.

3. Better control of methane emissions than landfill.

4. Waste water treatment and potential application of liquor in the farm as liquid

fertilizers.

5. To meet the EU environmental regulation and increase of the renewable energy

share.

6. Odour reduction and limited space requirement.

29

7. Better application of nutrient in the soil and reduction of nitrate run-off into water

bodies.

Figure 15: Complete flow Cycle of AD (Photo Courtesy: Pagels Ponderosa; Utah State University):

Feedstock for AD

Waste or agricultural residual having moisture content more than 80% can be used as

feedstock for AD. Any type of easily biodegradable waste like grass, MSW, agricultural waste

from farm can be used as a feedstock.

30

Animals Population Wet tonnes

available

MWh/tonne Potential

Electricity MWh

Cattle 6.4m 32m 0.04 1,280,000

Pigs 1.4m 2.4m 0.024 57,600

Grass 3.4m hectares 204m 0.250 51m

Poultry 13.9m 0.2m 0.180 36,000

Table 5: Potential Feedstock for Electricity Production in Ireland (Teagasc 2013)

Chemical Reactions in AD

A group of bacterium accomplices the task of anaerobic digestion of organic matter in

synergistically.

1. Hydrolysis- The degradation of complex organic matter takes place. Like

Carbohydrates, starch, protein, fats into smaller compounds. It is a rate limiting step if

cellulose is present in higher amount due to slow degradation of cellulose.

Pretreatment of the feedstock is required to improve the hydrolysis.

2. Acidogenesis- These compounds are further broken down into lactic, butyric, propionic,

and valeric acid.

3. Acetogenesis- These short chain molecules are further broken down into produce

carbon dioxide, Hydrogen and acetic acid by fermentation. This can be rate limiting step

if high amount of fat rich substrate is present in the feed.

4. Methanogenesis- This is the last step of biogas production. Different biochemical

pathways used by methanogenic bacteria to produce methane, CO2 and other gases.

Acetotrophic methanogenesis: It uses acetic acid to produce methane. It is the main

producer of methane.

4 CH3COOH 4 CO2 + 4 CH4

Hydrogenotrophic methanogenesis: A small amount of methane is produced by

utilizing CO2 and H2.

CO2 + 4 H2 CH4 + 2 H2O

Methylotrophic methanogenes: It uses methanol to produce methane.

4 CH3OH + 6 H2 3 CH4 + 2 H2O

31

Figure 16 Figure3. Chemical Reactions in Anaerobic Digestion (www.wastewaterhandbook.com,2014)

Variable Parameters in AD

Temperature

Anaerobic digestion works in a variety of temperatures based on the nature of the bacteria.

Generally, physchrophilic bacteria (15-20°C), mesophilic bacteria (25-40°C) and thermophilic

bacteria (50-60°C) are the main types of bacteria identified in anaerobic digester. Higher

temperature increases the rate of digestion. Mesophilic bacteria are used in AD because it

can sustain variation in temperature and require low heat.

Redox potential

Methanogenic bacteria can work at a redox potential of -300mV to -330mV. Low redox

potential is required for the electron transfer in AD.

C:N ratio

For successful AD operation, the C:N ratio should be from 3:1 to 30:1. But, any further

increase in C:N ratio leads to slow growth of bacteria due to absence of nitrogen for the

http://www.wastewaterhandbook.com/

32

growth. But, a C:N ratio lowers than 3:1, cause ammonia formation which is toxic to bacteria

in high concentration at higher pH.

pH

The AD works in the pH range of 6.5-7.5. A reduction in the pH below 6.5 due to more acid

production has a toxic effect on methnogenic bacteria. The pH reduction below 6.9 is

considered as an indication of pH change and proper treatment and buffering system is

applied. There are two different buffering systems are applied in the AD to maintain the pH.

1. Carbon dioxide – hydrogen carbonate–carbonate buffering system.

2. Ammonia–ammonium buffering system.

Inhibitory Substances

Inorganic salts (like sodium, potassium, calcium, Magnesium), heavy metals (lead, cadmium,

copper, zinc, nickel and chromium) have inhibitory effect on bacteria in high concentration

and simulating effect on low concentrations.

Parameter Hydrolysis/

Acidogenesis

Methanogenesis

Temperature Mesophilic: 25-30°C Mesophilic: 30-40°C

Thermophilic: 50-60°C

pH value 5.2-6.3 6.7-7.5

C:N:P:S ratio 500:15:5:3 600:15:5:3

Trace elements --- Ni, Co, Mo, Se

Table 6: Variable Parameters in AD (Zupan & Grilc, 2007)

Types of Anaerobic Digestion

Single stage and Two-stage digesters

In single phase AD, all the reactions take place in a single compartment. These are simple to

design, build, and operate and less capital expensive. These digesters depend on the ability

of methanogenic organisms to tolerate a decline in pH by the formation of acidic

compounds. More than 80% of the digesters in Europe are based on single stage digesters.

The methanogenesis stage is separated from the initial hydrolysis or acidogenesis stage in

two stage digesters. The production of biogas is higher and better process control. But,

these are capital expensive. (Jenkins et al., 2008; Sinpaisansomboon et al. , 2007; Zupan &

Grilc, 2007)

33

High Solid or Dry Anaerobic Digestion and Low solid or Wet Anaerobic Digestion

The solid content is more than 15% of the total feed and rest is water. The substrate and

biomass are in presoaked solid form. Due to lesser amount of water, the reactor volume is

less and more production of methane. There is reduced inhibitory effect of ammonia in this

process. But, the transportation of substrate is energy intensive process. Low solid digesters

generally have solid content from 5-15%. These are either batch or continuous based on the

plant requirement. (Jenkins et al., 2008; Sinpaisansomboon et al., 2007; Zupan & Grilc,

2007)

Planning and Financial viability

AD is financially viable and great income source if it is managed properly and constructed on

a large scale. As a part of the integrated waste facility, a consistent supply of feedstock is

always available.

Main revenue sources are biogas sale, heat, liquor production and direct electricity sale.

Liquor and fiber is separated in separator and liquor goes to heat exchanger to preheat the

cold incoming slurry. Around 20-30% heat generated by the digester is used in the anaerobic

digestion process.

Figure 17: Lemvig biogas plant overview (Source: www.lemvigbiogas.com)

34

Specification Proposed plant for Dublin City Lemvig Plant (Case study)

Land Area 1 hectare >1 hectares

Installed biogas capacity 7100m3 14300m3

Input substrate Around 300t/day≈109500 t/yr

20% industrial waste + 20-30%

MSW from home + 50% Slurry

Around 615 ton/day (83%

manure and 17% organic

waste)

Conditions Thermophilic Thermophilic

Installed Power 1.5MW 3MW

Investment 4m (1-2m subsidies from EU) 10.2m (1.2m subsidies from EU

& cost included land)

Positive factors Free heat to public Cheaper biogas rates and heat-

good public perception

Operating cost 40,000 40,000-50,000

Payback period 5-6 years 4 years

Table 7: Specification for AD plant in Dublin

Planning Regulations (SEAI: Application guidelines)

1. All waste storage and treatment must not be within 10m of any watercourse or

250m from any spring well or borehole.

2. Biogas must be burnt in an appliance with a net rated thermal input of less than

3MW.

3. Permitted waste types comprise sludges, plant tissue waste and manure from

agriculture, horticulture, forestry and fishing and some wastes from the dairy

products industry.

4. A Standard Rules Environmental Permit for off-farm anaerobic digestion is that the

distance to any off site building used by the public must be 250m or greater.

35

Section 7: Composting

Aneesh Priyadarshan Kale and Mugdha Hemant Karmarkar

Composting is the natural degradation of organic material by micro-organisms and its

conversion into a stable earth like material called humus. This process is accomplished in an

aerobic environment. This material can be used in soil so as to increase it’s the overall

fertility (Curran, 2014). The micro-organisms break down the raw organic matter and get

energy which is used up by them for the process of reproduction. (Composting Council of

Canada, 2014)

The decomposed matter that is left consists of dead and living micro-organisms along with

non-degraded organic matter is called as "Compost".

Composting in Ireland

As seen there are lists of composting facilities in the country. In Ireland, mostly windrows

are used for composting technology followed by in-flow and aerated systems. This is

because windrows require low maintenance costs, low initial costs (Herity, 2003).

Figure 18: Locations of the composting facilities in Ireland (Herity 2013)

36

Site layout

There would be a network of roads connecting the rest of the facility as well as small roads in

between the composting unit for movement of machinery and vehicles to carry the compost.

There is a grinder located next to the composting unit to reduce waste particles to the

required size. For the waste facility windrow composting is been proposed.

Windrow (mechanical aeration)

Windrows are basically long rows of piles of organic waste. These are turned frequently either

manually or mechanically over a period of time so to facilitate movement of air (EPA, 2014).

The site is to have a pair of windrows. Preferably the piles are around 1 to 3 meters tall .The

width would be around 2-5m. It is kept in such a way that there is enough air flow in it so as

to maintain the temperature. There are a number of machines that are used to mix the waste

such as front end loaders (EPA, 2014).

A series of pipes are to be installed below the composting unit so as to catch the leachate,

which can be treated in a small unit next to the composting site. This will help to nullify any

soil or ground water pollution from happening. There can also be presence of detachable

rooftop, to offer protection from rain and control the temperature. Turning at frequent

intervals maintains temperatures.

Windrow composting tends to have many benefits over other conventional methods. Since

there is frequent turning there is good amount of air exchange that takes place. It also helps

to maintain the desired temperature range. Constant and hard-core mixing helps grinding the

particles to as small as possible thus increasing microbial activity and at the same time

reducing the time.

37

Figure 19: Diagram of Windrow (Harvest Quest, 2014)

Type of Wastes Used for the Composting process

Most of the wastes used for the composting process, are biodegradable garden and park

wastes, food and kitchen wastes from kitchens, restaurants, fast food joints, caterers, wastes

from food processing plants. (Curran 2014)

According to ABP 2002 regulations, Category 2 and 3 could be used for composting. Under

category 2, manure and gut contents can be used directly in a compost plant. In Category 3,

food of animal origin, catering waste is suitable for composting. (Curran 2014)

Category 3 before submitting to a compost plant, it should be ssubjected to a treatment

(Curran, 2014)

It is a highly popular technique as it yields high quality product at the same time it requires

less investment as well. The space available in the proposed facility is sufficient enough to

have an installation of two windrows.

As the final product is of good standard, it can be sold off as high quality compost.

Requirements for Composting :

The process of composting is carried by diverse population of micro-organisms. To make the

process more effective, the system should be managed properly by supplying a sufficient

proportion of the parameters required by the micro-organisms (Curran, 2014).

38

Carbon: Nitrogen ratio

Main nutrients required for the composting process is Carbon and Nitrogen. Proper

amounts of carbon and nitrogen will help in carrying out the process effectively (Hattemer &

Stettler,2000).

If the carbon levels are high and decrease in the nitrogen level, the microbial activity will

slow down, since, nitrogen is required to break the carbon sources. This will have an adverse

effect on the process. If the carbon is less and more amount of nitrogen, excess of carbon

will be broken down and nitrogen will be easily lost in the atmospheres in the form of

ammonia gas. Thus, the process will be affected in a negative way on the environment

resulting in bad composting process. The optimum range of C:N will be 25:1 to 35:1(Earth

easy, 2014). When the ratio decreases to 12-20:1, this means that the process is finished

(Hattmar & Stettler, 2000).

Moisture Content

With the help of moisture, the micro-organisms move and transport materials. It is also

essential for all the chemical reactions taking place during the process.

The optimum moisture content range should be 50-60%. (Curran, 2014). If the moisture

content exceeds 60%, the microbes will not thrive. Also, if the content reduces below 15 %,

the microbial activity will stop. (Hattemer & Stettler,2000)

Oxygen

Lack of oxygen can result in anaerobic decomposition which will lead to inefficient compost

and undesirable odours. It should be well supplied to the entire pile. The concentration of

oxygen required is minimum 5% (Curran, 2014). Despite of the aeration, the amount of air

do not reflect the amount of oxygen reaching the microorganism. This is because, most of

the micro-organisms require aqueous environment for them to sustain (Hattemer &

Stettler, 2000).

pH

The ideal pH range for the microbial activity is between 6.5 to 8.0 (Hattemer & Stettler,

2000) Acidic pH has a negative effect on the compost. Bacterial growth is significant in such

conditions, thus, slowing down the process (Composting Council of Canada, 2014). pH

should be considered when some materials are rich in nitrogen. This material will increase

39

the alkalinity of the compost forming ammonia. This ammonia results in the loss of nitrogen

through volatilization. This affects the environment in a negative way (Hattemer & Stettler,

2000).

Temperature

During the process wherein the micro-organisms break down the materials there is release

of heat in the compost. This increases the temperature. It indicates that the process is

taking place in a proper manner (Composting Council of Canada, 2014). On the other hand,

if the temperature fails to increase, this indicates insufficient amount of nitrogen and

moisture content. Temperature is to be maintained around 40-60 degree Celsius (Friesen,

2002).

Particle size

Different materials used in the compost, have different particle size. The maximum size of

the particles should be 12mm.Good particle size leads to good air flow, (Earth Easy, 2014).

Conclusions

In 1998, the Irish Government policy of waste management aimed to reduce the amount of

biodegradable waste dumped in landfills over a period of 15 years. These targets included

50% diversion of the house hold waste to landfills(Citizen Information Board, 2010). Thus a

composting unit will not only serve the purpose, but also the compost that is obtained be

sold in the Irish market. According to McGovern (2012), the price of compost directly from

the site can fetch anywhere between 10-40Euros per m3 of compost. If this is to be further

treated and bagged the price of compost is seen to go high as 180 Euros.

According to McGovern (2012) the main markets for compost are highlighted in the figure

below.

http://www.agric.gov.ab.ca/app88/loaddetail?uid=marlene.friesen&action=7&search=Friesen

40

Figure 20: Market for Compost in Ireland. McGovern (2012)

Since there is a potential market that is available for the compost, it can serve as a source of

revenue for the waste facility.

Advantages of composting

According to U.S Environmental Protection Agency, (2014) composting has many benefits.

Good quality of compost tends to improve soil quality.

It thus helps reduce dependency of chemical fertilizers on agricultural land by

improving crop yield.

Compost has also been known in helping pest and plant diseases.

The compost process tends to absorb odour and treat semi volatile and volatile

The trend of composting tends to move away waste from landfills and incinerators,

thus reducing the stress on them as well as bring down the pollution levels

associated with them.

The compost obtained when spread on soil tends to arrest soil erosion.

Use of compost means use of less water, fertilizers and pesticides. It is an economic

commodity and a low cost option to landfill and other methods.

41

Section 8: Discussion and Conclusions

Overall the task of siting an integrated waste management facility within a reasonable

distance of Dublin is feasible. The city provides a more than adequate feedstock to justify

the construction of these technologies. Despite exorbitant initial capital costs in the region

of 157 million the project is entirely worth undertaking due to the following reasons:

The majority of on-site processes have payback periods within the 25 year lifespan of

the site due to power generation (incinerator and AD) as well as commercial

ventures (composting, ash for road construction).

These processes reduce the environmental impact of waste disposal considerably by

converting waste in controlled environments, capturing harmful emissions before

they reach the outside environment thus limiting the emission of GHG’s and other

harmful chemicals.

Incineration and AD can generate power, offsetting fossil fuel use by supplying up to

25,000 homes with electricity whilst simultaneously providing the site with power

and heat. Nearby industrial estates could avail of this power also.

These processes can enable the recycling of post-treatment residues such as non-

ferrous metals from incineration, pathogen-free compost and raw materials which

can subjected to the Fischer-Tropsch cycle to make synthetic fuels.

These processes divert a massive amount of waste from landfill; In the case of

incineration, 80-90% of the initial volume of the waste can be diverted hence less

space is required for the landfill.

Economies of scale; by integrating all these process on one site, many savings can be

made from on-site vehicles and by building just one large CHP plant as opposed to a

few on a number of sites.

In addition, transport costs and emissions can be reduced by eliminating residue

transport to distant sites. Further transport costs can be made by the fact that

Ireland would no longer have to export waste to Germany and other countries in

Europe to be disposed of appropriately.

42

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47

Appendix 1: Incineration efficiency calculations R1 formula for Efficiency of MSW incinerator in relation to conventional power plants (European

Commission Directive, 2008/98/EC) :

𝐸𝑛𝑒𝑟𝑔𝑦 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =𝐸𝑝 − 𝐸𝑓 + 𝐸𝑖

0.97 ∗ (𝐸𝑤 + 𝐸𝑓)

Where : Ep is annual energy produced as heat/electricity

Ef is the annual energy input to the system via fuels for production of steam.

Ew is annual energy contained in waste by Net calorific value (GJ/year)

Ei is annual energy imported excluding Ew and Ef (GJ/reay)

0.97 is a factor accounting for bottom ash+ radiation energy losses

Mass/Balance calculations for incineration (Kiely, 1997):

Assumptions:

MSW: 685,000kg/day of MSW; 374,010 combustible(54.6%); 164,400 non-combustible(24%);

146,590 water(21.4%)

Heating Value: 11,780 kJ/kg

5% unburned Carbon in residue with LHV of: 32,564

Total losses of heat (excluding C in residue): 1.66x10⁸kJ/day

Boiler efficiency: 85%

Calculations:

Gross heat input = (685,000kg/day) x (11780kJ/kg)= 8.7x10⁹ kJ/day

Heat loss due to unburned C = 164,400kg/0.95 = 173,053 kg/day

Unburned C in residue = 173,058kg/day x (0.05) = 8652.65 kg/day

Heat Loss in unburned C = (8653kg/day) x (32,564 KJ/kg) = 281,776,292 kJ/day

Heat available in flue gas = Gross heat input – (losses due to unburned C + total losses of heat) =

(8.7x10⁹ kJ/day – (281,776,292 + 1.66x10⁸) = 8252GJ/day

Combustion efficiency = Net available heat/Gross heat input x 100 =

8,252,223,708/8.7x10⁹ x 100 = 94.85%

Overall efficiency = (0.9485) x (0.85) = 80%

48

Appendix 2: Methane production rates from landfill equations Methane production rate of landfill without sulphur but including water is (C70H150O70N) (Adapted

from Kiely (1997)).

Assumptions

CHON is 30% of the wet weight of waste going to landfill.

a = 150 (number of atoms in hydrogen molecule)

b = 70 (number of atoms in oxygen molecule)

c = 1 (number of molecules in nitrogen molecule)

d = 4n + a – 2b – 3c 𝑑 = (4 𝑥 70) + 150 − (2𝑥70) − (3𝑥1) = 287

e = 0.96 (fraction of waste converted to biomass)

n = 70 (number of atoms in carbon molecule)

Solution:

𝑉𝑜𝑙𝑢𝑚𝑒 (𝐿)𝑜𝑓 𝐶𝐻4/𝑘𝑔 𝑤𝑎𝑠𝑡𝑒 =(

𝑑𝑒8 ) 𝑉𝑜𝑙𝑢𝑚𝑒 𝑆𝑇𝑃

𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒/𝐶𝐻𝑂𝑁

𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑊𝑒𝑖𝑔ℎ𝑡 = (70𝑥12) + (150𝑥1) + (70𝑥16) + (1𝑥14) = 2124𝑔/𝑚𝑜𝑙𝑒

𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝐻4 𝑝𝑒𝑟 𝑚𝑜𝑙𝑒 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒 =𝑑𝑒

8=

287𝑥0.96

8= 34.5

𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑒𝑡ℎ𝑎𝑛𝑒 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒 (𝐿

𝑘𝑔) =

34.5𝑥88920

2124/0.3

= 435.76𝐿 𝐶𝐻4/𝑘𝑔 𝑜𝑓 𝑤𝑒𝑡 𝑤𝑎𝑠𝑡𝑒

49

Appendix 3: Distribution of workload

Abstract, table of contents, introduction, site selection, incineration, conclusions and reference list –

Luke Martin.

Table of figures/tables, Site Layout, Site Map, landfill and proof-reading – Daire McKeirnan.

Site Layout and Anaerobic Digestion – Anant Kumar Singh

Composting – Aneesh Priyadarshan Kale

Composting - Mugdha Hemant Karmarkar

design of an integrated waste management facility for the dublin region

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