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6.0 SEPTIC TANK SLUDGE COMPOSTING

Septic tank sludge represents an ideal material for composting to produce a soil

amendment for use in reforestation programs, as a landfill cover material or for orchards.

A pilot-scale trial was conducted as an aid to determine the feasibility of this type ofcomposting for Montserrat.

6.1 SLUDGE ARISINGS IN MONTSERRAT NATURE AND QUANTITY

At present, data from Montserrat Water Authority show that approximately 1,050,000

litres per year or 3000 litres per day of wastewater treatment plant sludge and septage

removed from residential homes, are deposited in the sludge lagoons at New

Windward300. At present the septic tank emptying service is free, and this tends to

encourage householders to make maximum use of the service. In fact, some new houses

are being built with undersized septic tanks, due to the ready availability of tank

emptying services. There are two small package wastewater treatments in Montserrat,

each of which supplies about 250 homes.

The septage and the wastewater treatment plant sludge are discharged into an unlined

lagoon at New Windward. The overflow from this lagoon flows to a second lagoon,

which represents a second stage of treatment before the overflow is discharged into the

subsoil.

Figure 6.1: Septage and sewage sludge are discharged into an unlined lagoon at New Windward. The first lagoon discharges into asecond lagoon (pictured) and the overflow from the second lagoon (pictured in top left of the photograph) discharges into the subsoil.The lagoon supports a large algal population. The photograph was taken in July, towards the end of the dry season, when the liquidlevel in the lagoon is low due to a high evaporation rate and low rainfall.


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Figure 6.3: A sludge scoop was fabricated using materials scavenged from the New Windward landfill.

Septic tank sludge was scooped out of the bottom of the lagoon, where the sludge is thicker. (Photo creditfor second photograph: Pete Hobbis, 2001)

Figure 6.4: Sludge and green waste being mixed together, to determine which proportions would give amixture with a suitable moisture content and structure.


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Figure 6.5: After thoroughly mixing the sludge and green waste, a homogeneous mass was obtained. Themixture was damp but not wet.

Figure 6.6 A compost bin was constructed from pallets scavenged from the landfill. A sign was made andaffixed to the bin explaining the trial and cautioning members of the public against touching thecomposting sludge. The bin was positioned in an isolated location near the landfill site, in a small clearedarea but hidden from public view.


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It was determined that the best ratio of green waste to sludge to ensure a mixture with the

correct moisture content was 4:1.

A compost bin was fabricated of pallets scavenged from the landfill. Green waste was

collected at the New Windward site and shredded. This green waste primarily consisted

of Acacia trees. The shredded green waste was added to the compost bin and the sludge

was poured over it, maintaining the ratio of 4 parts green waste to one part sludge, using a

plastic bucket scavenged from the landfill to measure volume. The shredded green waste

was weighed using a spring balance. The buckets of sludge were unable to be weighed as

the mass of one bucket exceeded the capacity of the spring balance. (The mass of the

septic tank sludge added can be estimated as the mass of the equivalent volume of water).

Figure 6.7: Green waste being shredded for mixing with sludge. This is the only shredder available in thewhole country, and is a small HP model.


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Figure 6.8: Buckets of green waste were weighed prior to adding to the compost heap. Sludge could not beweighed due to its high density, the mass of one bucket exceeds the maximum capacity of the springbalance.

Figure 6.9: Green waste mixed with sludge in the ratio of 1 part sludge to 4 parts green waste. Thisphotograph illustrates the consistency of the initial mixture. The compost heap was covered with a finallayer of dry green waste to ensure that no sludge was exposed, to prevent a health risk to any curious peoplewandering by.


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Figure 6.10: This photograph illustrates the condition of the sludge compost after one week of composting.

Some white patches indicate the presence of actinomycetes.

Figure 6.11: Septic tank sludge compost being turned after several weeks. The white patches indicate thepresence of Actinomycetes. It can be noted that the compost is extremely dry.


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The sludge compost was turned and watered once per week for several weeks. At least

two full 20-litre buckets of water were added each time. However, it was noted that this

was insufficient, at the end of the week the sludge compost was far too dry. The sludge

compost bin had been located in an area where the ground was cleared and flat, but the

bin was well hidden from public view. Unfortunately, this meant that the distance from

the water tanks near the landfill gate to the compost bin was quite large, and the slope

was very steep. To add two full buckets of water to the compost necessitated making six

trips carrying one third of a bucket each time. Due to the time-consuming nature of this

sludge-watering activity, it was not feasible for more than two 20-litre buckets of water to

be added to the sludge compost weekly.

Figure 6.12: There is no running water on site at New Windward. The only available water on site is thatwhich is delivered by the Water Authority to these two tanks, which have an estimated storage capacity of10,000l each.

If the septic tank sludge composting trial is to be scaled up to a full size operation, the

shortage of water at New Windward would have to be addressed. The nearest piped water

supply is at Lookout, a distance of some 3 km away. The cost to extend the water supply

is approximately $200EC per metre301

. Each time a water tanker transports water to refill


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the tanks at New Windward, it costs $145EC. Either way, supplying water to New

Windward is very expensive. There are some springs in the surrounding area which are

presently untapped.

6.3 TECHNICAL FEASIBILITY OF COMPOSTING BASED ON

EXPERIMENTS

A temperature datalogger was used to record temperatures in the centre of the pile of

septic tank sludge compost, for a period of one fortnight. The compost trial commenced

one week prior to the installation of the datalogger in the centre of the compost heap.

The maximum temperature attained during this period was 52.7C.

A graph of the logged temperatures is illustrated below. Refer to figures 6.13 (detailed)

and figure 6.14 (simplified):

Figure 6.13: Temperatures recorded in centre of pile of septic tank sludge compost, from 20/06/01 to06/07/01.


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Variation in temperature with time for one-week-old Septic

Tank Sludge Compost for a period of a fortnight

0.00

10.00

20.00

30.00

40.0050.00

60.00

20/06/01

21/06/01

21/06/01

22/06/01

23/06/01

23/06/01

24/06/01

25/06/01

26/06/01

26/06/01

27/06/01

28/06/01

28/06/01

29/06/01

30/06/01

30/06/01

01/07/01

02/07/01

03/07/01

03/07/01

04/07/01

05/07/01

Date and Time

Temperature(

oC)

Figure 6.14: Temperatures recorded in centre of pile of septic tank sludge compost, from 20/06/01 to06/07/01.

The average temperature over the two-week monitoring period was 37.94 C. A

maximum temperature of 52.7 C was reached on 23/06/01, approximately ten days after

the beginning of the composting process. A temperature of 55C was not exceeded at any

stage during the monitoring period. This raises the question of whether adequate

pathogen destruction is likely to have occurred, especially given the high prevalence of

gastrointestinal diseases (hepatitis, typhoid and whipworm) in Montserrat. However, as

discussed in section 4.5, pathogen reduction is caused not only by heat, but also by

micro-organisms in the compost, and adequate pathogen destruction can occur at lower

temperatures, provided that these temperatures are exceeded consistently over a longer

period of time. Slightly lower temperatures have also been found to lead to faster rates of

decomposition of sewage sludge compost. 302

The USEPA standards for sanitisation of sewage sludge compost303 require a temperature

of 40C to be attained for at least 5 days to significantly reduce pathogen levels in

compost, with the temperature exceeding 55C for at least 4 hours during this 5-day

period. To further reduce pathogens, it is recommended that temperatures of 55C should

be attained for at least 3 days. The septic tank sludge compost would not meet the


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USEPA standards. However, nevertheless testing carried out by the Montserrat Water

Authority showed that significant levels of pathogen destruction had in fact been

attained.

The pathogen content of both the sludge at the bottom of the lagoon and a sample of

sludge compost were tested at the Montserrat Water Authority Laboratory, using a

standard membrane filtration procedure, testing for faecal coliforms which are widely

used as indicator organisms. While the sludge had a pathogen content of 1.9 x 108

faecal

coliform colony forming units per gram, no pathogens were detected in the sample of

compost. Refer to Table 6.1 below:

SAMPLE TYPE DATE FAECAL COLIFORMS (cfu/g)

Sludge 4/7/01 1.9 x 108

Compost 4/7/01 ND

Table 6.1: Pathogen content of sludge and compost.

The septic tank sludge compost appeared to be composting well throughout the

demonstration period, with no problems with odour or vermin, however it reduced in pile

height only approximately 3 cm over a period of four weeks. This is believed to have

been primarily due to insufficient moisture, a problem which was difficult to rectify with

the resources available for the trial.

A Solvita test was carried out using the method described in section 4.5, on 10/07/01,

when the compost was approximately four weeks old. The NH3 rating was found to be 5

and the CO2 rating was 2, giving a compost maturity index of 2. This indicates that

possibly the C:N ratio is too high or the compost is too acidic. Acidic compost is of

concern, as Montserrats volcanic soils are already acidic. A Solvita result of 2 indicates

a raw compost, a very active, putrescible fresh compost; high respiration-rate; needs

veryintensive aeration and/or turning This is usually associated with a stage of II in theDewar self-heating test. Material in this class is comparable to raw-waste and mostmanures, and is suitable for raw feedstock for making mushroom compost, landspreading

on fallow soil or farm-row crops and field cultivation304

.


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The Solvita test result is not a serious cause for concern as the compost was only 4 weeks

old at the time of testing. It is quite likely that the C:N ratio was indeed too high as it was

necessary to add four parts green waste to one part sludge to achieve the correct

consistency of the initial mix, given that there are no facilities for sludge dewatering. The

problems of high C:N ratio and low moisture content could both be resolved by adding

moisture to the compost in the form of sludge rather than clean water, an ideal solution

given the severe shortage of water at New Windward. This would obviously affect the

pathogen content of the sludge, by reinjecting a new batch of contaminants every time the

compost is watered, however provided that the compost is restricted to use for forestry

applications, orchards and landfill cover, it should not be dangerous to human health, and

in any case it will certainly not pose any greater risks than the original sludge from which

the compost was derived. If this recommendation for sludge watering is implemented,

then there should be no technical barriers to septic tank sludge composting in Montserrat.

6.4 DESCRIPTION OF THE SLUDGE COMPOSTING PROCESS

The composting process for septic tank sludge is similar in principle to that which was

described in Chapter 3 for composting at a household level, for different feedstocks, in

that the essential ingredients of oxygen and moisture must be maintained at adequate

levels. For very small quantities of sludge compost, this is ensured by manually turning

and watering, whereas for larger scale composting, agricultural machinery, electric

blowers or purpose-built windrow turners are used to maintain oxygen, and water may be

automatically dispensed when moisture level detection equipment highlights a drop

below the acceptable minimum level. For small quantities of sludge compost such as

those involved in the present trial, a simple timber bin can be used, however for larger

quantities large windrows, or aerated static piles are used to ensure that the compost

assumes a shape which enables it to reach the appropriate temperature and compostsuccessfully. It is even possible to use in-vessel technologies, although this is less

common. For successful composting of septic tank sludge, large quantities of a bulking

agent such as woodchips or shredded green waste must be added to the sludge.


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As with all composting processes, septic tank sludge composting occurs in two stages305.

Firstly the waste decomposes rapidly, due to the action of micro-organisms who carry out

decomposition, consuming oxygen, reducing the volume of the waste and giving off heat.

Following this period of rapid decomposition is the maturation or curing phase where

only very limited decomposition occurs, at a very slow rate with little heat being

produced and so little oxygen consumption that it is no longer necessary to turn or aerate

the compost306

.

Some of the characteristics of the feedstocks, septic tank sludge and wastewater treatment

plant sludge, are tabulated below. Refer to Tables 6.2 (septic tank sludge)307

and 6.3

(wastewater treatment plant sludge)308

.

Characteristics of septageMEASURED

PARAMETER

MEAN + STANDARD

DEVIATION

Total solids percent 1.47 1.52Total volatile solids percent 0.866 0.984

Total Kjeldahl Nitrogen mg/l 375 248

Ammonia-N mg/l 99.6 45.5Phosphorous ppm 7520 1820

Sodium ppm 103000 63,200

Potassium ppm 10300 6470Calcium ppm 45300 10600

Magnesium ppm 8300 3300

Fecal streptococcus organisms/100ml 3.5 x 106 11.7x 10

6

Fecal coliforms organisms/100ml 5.84 x 106 19.8 x 106Table 6.2: Some typical characteristics of septage (Anderson and Machmeier, 1988).

Characteristics of wastewater treatment plant sludgeC:N RATIO,

NUTRIENTS

STRUCTURE,

POROSITY

MOISTURE

CONTENT

DEGRADABILITY TREATMENT

REQUIRED

CAUTIONS


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There are three main types of technologies used for septic tank sludge composting: the

simple windrow composting system, the aerated static pile and in-vessel composting

systems. For in-vessel technologies, vertical or horizontal flow reactors may be used,

with the reactor being an agitated or stationary bed. Circular or rectangular bins may also

be used.

The simple windrow composting system consists of a number of long and narrow

compost heaps (windrows) approximately 2-4.3 m wide and 1-2 m high309

. The length

of the windrow depends on the available land and the quantity of incoming waste, as well

as the type of equipment used for windrow formation and turning. The windrows are

mixed and turned periodically, usually at least five times during the composting period

of 21 to 28 days. An example of a simple windrow composting system for wastewater

treatment plant sludge composting is illustrated below:

Figure 6.15: Windrow composting system for sewage sludge at Esholt, UK.

An aerated static pile composting system consists of a mixture of sludge and a bulking

agent (such as woodchips), arranged in piles, underlain by a series of pipes through

which air is passed. Air maybe blown through the piles using positive pressure or

alternatively negative pressure may be used to suck the air through. The pile height is

usually about 2-2.5m and the piles are often covered with a layer of finished compost for


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insulation. After a composting period of 21 to 28 days, and a maturation period of 30

days, the compost is usually screened to recover some of the bulking agent for re-use310.

In-vessel composting systems provide very careful process control. These systems use

forced aeration, stirring or tumbling to provide controlled aeration311, as well as providing

temperature and moisture content control. Some systems operate as plug-flow systems,

whereas others use an agitated bed.312

These in-vessel systems produce compost faster

than either the windrow or the aerated static pile, and they do not require a large area of

land, as well as minimising odour nuisance. They can consistently produce compost of a

very high quality. However, in-vessel composting systems have very high capital costs

and also high maintenance costs.

A comparison of the three main types of sludge composting technologies is given

below313

:

Comparison of Composting TypesADVANTAGES/DISADVANTAGES COMPOSTING PROCESS TYPE

ASP Windrow In-Vessel

High Capital Costs

Moderate Capital Costs

Low Capital CostsHigh Pathogen Destruction

Good Odour Control

Good Product Stabilisation

High Land Requirement

Operation Weather-Affected

High Labour Requirements

Capacity to handle high BiosolidsVolume

High Equipment and Maintenance Cost

Best Process Control

Odour Generation ProblemsBest Operation Reliability

Table 6.4: Comparison of Aerated Static Piles, Windrows and In-Vessel Composting Systems for SludgeComposting (Spellman, 1997).


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In deciding which type of technology to use, the important factors to consider are the

cost, the speed and efficiency of the process, and whether any significant environmental

impacts are associated with the technology. From Table 6.4 it can be seen that the

windrow system is an excellent choice, apart from the potential for odours, and although

it does not give the best possible process control for the small volumes of sludge arisings

available on Montserrat it is considered to be highly acceptable. Odour is unlikely to be

an issue for Montserrat as the New Windward landfill is at least 3 km away from the

nearest residential area at Lookout.

6.5 BENEFITS AND DRAWBACKS OF SEPTIC TANK SLUDGE

COMPOSTING IN MONTSERRAT

The benefits of septic tank sludge composting are very similar to those described in

Chapter 3 for composting in general, i.e. soil conditioning, possibly some plant disease

suppression and pathogen destruction. However, septic tank sludge or municipal solid

waste compost may be even more beneficial than other types of compost such as green

waste compost, because of its higher nitrogen content314. Nitrogen is particularly useful

for leafy plants such as lettuce, spinach, celery and radishes315.

While the application of compost has generally been found to provide protection from

plant diseases (refer to Section 4.2), the higher nitrogen content of sludge compost is a

mixed blessing as some of the plant diseases are not suppressed by sludge compost as

they would be for composted bark or some other type of waste. In fact, some plant

diseases such as fireblight, Erwinia amylovora, Fusarium316

317

318

(prevalent in the West

Indies) and Phytophthora319

(also found in the Caribbean) may actually be promoted by

the high nitrogen content of sludge compost.

One of the obvious benefits of turning septic tank sludge into a useful product is that it

solves the as yet unanswered question of what to do with the sludge when the two

lagoons at New Windward become full and present a danger of overflowing. The sludge

has to go somewhere. Allowing it to overflow and run downhill into the sea is not the


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most environmentally acceptable option. Even if the volume of incoming waste is of such

a level that the lagoons do not overflow, over a period of years the lagoons will fill with

sludge which will build up on the base, and they will require desludging.

Composting is not without its share of problems, however. The most significant potential

drawback of septic tank sludge composting is its high cost, a cost which could perhaps be

avoided by applying the sludge directly to land in an area which is unlikely to be

accessed by members of the public. The production of leachate and contaminated runoff

must be allowed for in the design of any sludge composting operation. Most sludge

composting facilities also have potential problems with odour, machinery and vehicle

noise, visual pollution and dust. However, in Montserrat, the obvious choice of location

for a septic tank sludge composting facility is at New Windward landfill, in close

proximity to the sludge lagoons. This site is at least 3 km away from the nearest

residences at Lookout and is far enough away not to cause any public nuisance.

Sludge composting can be a lot more problematic than other types of composting, due to

the fact that most compost feedstocks are solid and have a low to medium moisture

content, whereas sludge is liquid and has an extremely high water content. The

concentration of solids in the sludge from the lagoons in Montserrat is not known at

present, however from its appearance it is considered unlikely that the sludge contains

more than about 1% dry solids. Sludge is lacking in porosity and sludge compost has a

tendency to compact320. If the moisture content of the sludge is not carefully controlled

by the appropriate addition of dry bulking agents, then there can be problems with

reduced composting temperatures and the thermodynamic balance will be affected321. If

the moisture content of the compost drops below about 30 to 35%, then the final product

will turn to dust, due to the sludges fine particulate consistency.

Is it better to compost septic tank sludge in Montserrat or to apply the sludge or septage

directly to the soil? While septic tank effluent or wastewater treatment plant sludge do

contain high levels of nutrients (as described in Tables 6.2 and 6.3 ) which are readily and

immediately available to plants, sludge compost has been found to release its nutrients

slowly over a longer period of time. During the wet season in Montserrat, the nutrients in


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septic tank sludge could easily leach out of the soil, not only failing to benefit plants but

also potentially contaminating the groundwater. Composting the sludge and septage

would avoid this problem. Compost has also been found to provide greater improvements

to the physical, chemical and biological properties of the soil, compared with

uncomposted sludge322.

Composted sludge helps to improve soil structure and water retention capacity, correct

soil pH, and promote beneficial soil micro-organisms, benefits which would not be

realised if sludge or septage was directly applied323

. The grease and fat content of

uncomposted sludge has also sometimes been found to cause problems, because it can not

be absorbed by soil and it causes the soil to become impervious324

, possibly causing

moisture to run off the soil surface. Unstabilised raw sludge is likely to be broken down

by the soil microflora, who will produce intermediate metabolites which are not

conducive to plant growth. The soil microflora will compete with the plant roots for

nitrogen from the sludge and ammonia will be produced as part of the process325

.

Unstabilised sludge will also exert an oxygen demand as it is broken down in the soil326.

These problems are avoided if the sludge is composted before use.

If septage or sludge was to be applied directly to land in Montserrat without any degree

of pre-treatment, it would have to be applied to an area which was unlikely to be accessed

by members of the public, to avoid causing a health risk. The only such suitable area

which springs to mind is Silver Hill, where septage or sludge would provide essential

nutrients for reforestation. However, the gradient of this area is very steep, and vehicle

access is very limited. It is impossible to envisage the Public Works Departments sludge

wagon as being capable of applying septage or sludge to the steeply sloping land of the

silver hills. However, bagged compost could easily be transported on foot, or, preferably,

by horse, to this area, as well as being able to be constructively used on other parts of the

island without posing the same level of health risk and potential odour nuisance as the

raw sludge.


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How does composting compare with other methods of processing sludge, such as air

drying, anaerobic digestion or lime stabilisation? The main benefit of composting is that

it is much more effective in destroying or reducing pathogens than other sludge

stabilisation methods. Anaerobic digestion is primarily of value for recovering the energy

from digesting sludge, which is not feasible in Montserrat where MONLEC has a

monopoly on the energy supply. Air drying requires the construction of expensive sludge

drying beds, and does not solve the problem of final disposal of the sludge. Lime

stabilisation also does not in itself provide a use for the sludge, and is an expensive way

of treating sludge, without providing a product of the same value as compost. In short,

composting is the only sensible sludge treatment technology for Montserrat.

6.6 APPLICATION OF SLUDGE COMPOST

Given the great need for compost in Montserrat to reduce soil erosion, improve the soils

organic content and suppress plant diseases, it would be a great shame if septic tank

sludge compost was produced in Montserrat and then used as a landfill cover only, when

it could be diverted to other more worthwhile uses. Nevertheless, landfill cover material

is in short supply on Montserrat327, and if the landfill is to be covered then the cover

materials must come from somewhere.

Compost has been found to be particularly useful for reducing methane from landfills.

Some microbial methane oxidation occurs in all soils used as landfill cover materials,

however this effect is particularly pronounced for cover materials which contain a high

proportion of organic matter328. Compost can be used for restoration of a landfill site as

well as being used as a daily landfill cover material. For long-term restoration of a

landfill area, compost should be applied at the rate of 25-50 tonnes/ha, incorporated to a

level of 15cm in depth and then seeded with grass or clover 329. It will be at least a decade,

however, before New Windward landfill s capacity is exceeded and restoration of the

entire site is needed.


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Ideally, septic tank sludge compost produced in Montserrat should be used for forestry.

For this type of end use, application rates of up to 200t/acre have been found to be

beneficial330. A typical compost produced from sewage sludge will have a nutrient

content of as much as 2% phosphorous, 2% nitrogen and 1% potassium, as well as trace

elements which are essential plant micronutrients331. Septic tank and sewage sludge in

Montserrat are unlikely to contain high levels of heavy metals, hence nitrogen is most

likely to be the limiting factor for sludge compost application. The MAFF Code of Good

Agricultural Practice (1994)332

specifies a maximum limit of 250 kg ha-1

y-1

to protect

groundwater from nitrate pollution, in accordance with the EC Nitrate Directive (1991).

A sludge compost containing 2% nitrogen could thus be applied at the rate of 50 kg ha-1

y-1

without causing significant nitrate contamination of groundwater. In Montserrat,

groundwater is not being abstracted at present, and in theory higher application rates

could be used, however higher application rates are unlikely to be achieved as the

availability of shredded green waste to make sufficient sludge compost will be the

limiting factor.

6.7 BARRIERS AND INCENTIVES FOR SLUDGE COMPOSTING

The main barrier to composting in Montserrat is that the Montserratians do not want it! It

is in some respects a solution in search of a problem. The present sludge composting trial

is essentially something which has been foisted on the Montserratian public for their

own good and because they ought to do it. In spite of its obvious potential benefits,

there is no keenly felt need for sludge composting in Montserrat at present. Nevertheless,

it would be a shame if no thought was given to final disposal of the sludge, until one day

when the lagoons overflow into the sea!

Most Montserratians have a healthy aversion for septic tank sludge. Public reaction to the

use of septic tank sludge compost is likely to be unfavourable. Concerns raised by the

public would have to be addressed by appropriate restrictions on the use of the compost,

as well as extensive public education and public relations prior to its introduction. The

septic tank sludge composting facility itself, if located at New Windward landfill, is


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unlikely to be of concern, it is the use of the compost which will not be highly regarded.

To make the use of sludge compost acceptable, it may be necessary to apply it to

restricted areas only, even though laboratory testing for pathogens may indicate that it is

suitable for use anywhere in Montserrat. Demonstration projects where the public would

be able to see sludge compost in use may also be helpful 333.

In industrialised countries such as the United States and the United Kingdom, the heavy

metal content of wastewater treatment plant sludges (and hence of any compost produced

from them) is of major public concern. However, this is much less likely to be a problem

in Montserrat, where there are no major industries and the two small package treatment

plants cater for residential populations only. The sludge composting process has been

found to bind the metals present in the sludge, preventing them from being leached into

groundwater and reducing the amounts taken up by plants334

.

As discussed previously, the absence of a suitable water supply at New Windward

landfill is a major disincentive to the implementation of any type of large or small scale

composting at this otherwise ideal location. There is also no electric power available on

site. The water requirements for composting can be quite high, up to 300 gallons per

cubic yard of finished compost, over the entire composting period335. The nearest piped

water supply is at Lookout, which is supplied from Brimms Ghaut and Hillsgate.336 The

cost to extend the water supply from Lookout is approximately $600,000 EC. Water can

be delivered to New Windward, for a fee of $145 EC per trip337.

There are two presently untapped springs which could potentially supply water to New

Windward, at Big River and Bottomless Ghaut, and one spring at Gingerground which

was used prior to the volcano crisis338, however these springs are still a distance of at

least 2.5 km away (refer to figure 1.2). There are also two wells at Blackburne airport,

very close to New Windward, however, they are in the exclusion zone, and probably

could not be safely accessed for monitoring or maintenance. The water supply problem

could be ameliorated by using sludge to water the compost.


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The availability of suitable materials to use amendments or bulking agents is likely to be

a limiting factor for sludge composting in Montserrat. While 3000 litres of sludge per day

are available, for a ratio of four parts green waste to one part sludge by volume,

approximately 12 tonnes/day of shredded green waste or equivalent would be needed, to

turn all of the sludge into compost (Not allowing for the use of some sludge instead of

clean water, for compost watering). Even 2 or 3 tonnes/day of shredded green waste will

be difficult to procure in Montserrat. The Public Works Depot, the only potential large

supplier of shredded green waste in Montserrat, have expressed greater interest in

delivering their green waste to three decentralised locations at St Peters, Lookout and

Davy Hill, to be used for community composting or backyard composting schemes by

residents of these communities. Apart from shredded green waste, there is no other

suitable amendment material available in Montserrat. Woodchips, straw or rice hulls do

not exist in Montserrat, and as most timber and furniture is imported there is not likely to

be a substantial quantity of sawdust available. Screening will definitely be necessary for

any sludge compost produced in Montserrat, to recover as much as possible of the very

scarce amendment material.

6.8 FEASIBILITY OF SEPTIC TANK SLUDGE COMPOSTING IN

MONTSERRAT

If septic tank sludge composting was to be carried out in Montserrat, then it would have

to be carried out at a low cost, otherwise it would be economically unjustified and the raw

sludge should be used directly instead, after some other type of pathogen destruction

process such as lime stabilisation. It is impossible to envisage that the economic value of

septic tank sludge compost could ever exceed the cost of expensive equipment such as

blowers and windrow turners, especially given the small volume of sludge arisings. A

manual system of windrow formation and turning similar to that used in Coimbra,

Brazil339

is more likely to be affordable, and would create employment.

How much sludge compost could feasibly be produced in Montserrat? A green waste

availability of 40kg/day is likely to be a very generous estimate. This would allow


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approximately 10 kg/day of sludge to be composted. Assuming a compost yield factor of

0.2 (lower than for MSW composting due to the higher moisture content of the sludge

feedstock), 10 kg/day of sludge compost would be produced or 3.65 tonnes/year. This

volume is much to small to meet the likely demand for compost in Montserrat, however it

could profitably be used for reforestation of the Silver Hills.

In other countries with larger quantities of sludge and waste arisings, and a very different

set of environmental problems from those which face Montserrat, it is customary to

compost sludge and municipal solid waste together. For Montserrat, this would be far

more trouble than its worth and is not even worth considering.

6.8.1.Factors Affecting The Design

Factors affecting the design of any sludge composting plant include cost, availability and

appropriateness of different composting technologies, legislation, market or end use for

the compost, environmental issues, worker health and safety, impact on the community,

operation and maintenance requirements and product quality.

As discussed in section 6.4, the only suitable choice of technology for Montserrat is a

simple windrow composting system. There is no need for specialised compost turning

equipment, a bulldozer or even manual labour is more appropriate.There will be no needfor marketing the compost as the compost will be used for forestry applications only,

primarily for reforestation of the Silver Hills. The Forestry Department would need to

agree to sludge compost being used for this purpose.

Any new composting plant in Montserrat would require planning permission from the

Development Control Authority in accordance with the Town and Country Planning

Ordinance (No. 27, 1975) and the Land Development Authority Ordinance (No. 9, 1971).

The plan would have to be designed to comply with other legislation such as the Public

Health Ordinance (No. 16, 1981), Public Health (Nuisances) Regulation (No. 12, 1983)

and the Underground Water Ordinance (No. 7, 1967).


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There will be few adverse environmental impacts resulting from the sludge composting

facility, as it will be located at New Windward, at least 3 km away from the nearest

residence at Lookout. Product quality is likely to be quite acceptable for use in forestry

applications, even if the process is not carefully controlled. Certainly it will be no worse

than applying the original uncomposted sludge. An extensive public relations campaign

will have to be carried out prior to the use of compost from the facility, even though few

members of the public will come into contact with it, because of the local prevailing

feeling of distaste for septic tanks and sludge. Operation and maintenance, as well as

worker health and safety, are discussed in section 6.8.4 below.

6.8.2 Design Details

Site selection is an important part of the design of any new composting plant. As the

sludge lagoons are located at New Windward landfill, a site which is at least 3 km away

from the nearest residence at Lookout, the landfill site is the obvious choice for a sludge

composting facility. New Windward covers an area of 25 acres and its life span is

predicted to be 15-20 years340. Land in Montserrat is expensive at $1.50-$2.00 EC per

square foot341, however it is likely that there is land available. The area required for a

composting plant is not more than about 1500m2, which is only 1.5% of the total area of

land at New Windward. If land had to be purchased in the area adjacent to New

Windward landfill, the cost would be approximately $50,000EC. A map of the New

Windward landfill site is illustrated overleaf342.

A process flowchart for the basic windrow composting process is illustrated below343:

Figure 6.16: Flowchart for the windrow composting process (Benedict, 1988).


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The process used will be identical to that shown in Figure 6.16 with the exception that the

sludge will not be dewatered prior to mixing with the shredded green waste amendment.

This dewatering is not only considered an unnecessary expense, but also it would only

exacerbate the problems caused by a shortage of water at the landfill site.


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Figure 6.17: Map of New Windward landfill showing the approximate location of the proposed sludge

compost facility (Lands and Survey Department, 2001)


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The area chosen for the sludge composting facility would need to be levelled and a

cement slab would be needed to allow any leachate or runoff produced during the wet

season to be collected. It is recommended that one or more 10,000 litre tanks (similar to

the existing water tanks) be purchased for storage of any leachate collected during the

wet season to use for compost watering during the dry season. As there is no electric

power supply on site it is recommended that a solar powered water pump be purchased

for this leachate collection and recirculation. Note that due to the problem of wandering

livestock, the solar pump, and indeed the entire composting site, would need to be

appropriately fenced. A suitable fence would also help to discourage vermin.

Figure 6.18 A renewable power supply installation adjacent to New Windward landfill is enclosed in abuilding and elevated where it is in no danger of being destroyed by the wandering cow pictured at right. Asimilar degree of protection is needed for any power supply used for the sludge composting facility.


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Preliminary design calculations for sizing of a sludge composting facility have been

carried out using a spreadsheet developed by Professor E.I. Stentiford of the University of

Leeds. The design details are tabulated overleaf. A solids content of 35% has been

assumed, as well as a bulk density of 0.6 t/m3 for the shredded green waste. A pile height

of 1.6m and width of 3m has been chosen for the windrows as it is most likely that they

will be turned manually due to a shortage of suitable plant at affordable prices. A volume

reduction factor of 0.5 and a compost yield factor of 0.4 have been assumed. A

composting time of 8 weeks and a maturation period of 4 months have been chosen to

ensure adequate pathogen destruction, with extra time being allowed to make up for high

evaporation rates during Montserrats dry season, which are believed to be the cause of

lowered composting temperatures. The University of Leeds spreadsheet includes

provisions for sizing of a biofilter however this will not be necessary in Montserrat due to

the low potential for odour nuisance.

These preliminary design calculations show that an area of approximately 726 m2

is

needed for the composting windrows, with only an additional 0.4m2

required for storage

of the compost during the maturation period. An additional 775m2

will be allowed for

operator facilities and equipment storage, bringing the total land area required for the

facility to approximately 1500 m2.

It is not considered necessary for the composting area to be roofed, this would merely

represent an unnecessary expense. A shredder and a screen will need to be purchased or

procured. A front end loader or bulldozer can be hired from Wall Trading by the day, but

this is prohibitively expensive and it would be cheaper to purchase from elsewhere. To

reduce costs, manual labour can be used for windrow formation and turning. A

McCullough 1600 W shredder344 or equivalent is suitable for use at New Windward for

an approximate cost of $199USD. A Morbark 627 Trommel screen345

or equivalent couldbe purchased, although it is slightly oversized and a custom built timber and mesh screen,

similar to that which is used at the National Trust for the preparation of potting mix,

would be far more appropriate. Plans for building a simple compost screen are available

on the internet346

at the following website URL: http://www.bra.org/screen.htm .


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A storage area of 5m x 10m = 50m2 will be allowed for stockpiling shredded green waste.

The waste will be screened before maturation to minimise the area needed for storing

compost while it is curing. A roofed building of 10m x 5m = 50m 2 will be provided for

facilities for the operators, storage of the shredder and screen when not in use and storage

of batteries etc. for the sites power supply.

Using a cement slab is necessary to allow year round access for vehicles such as

bulldozers347

which may be used for form windrows, or even to allow manual windrow

turning without the operators wading up to the knees in mud. The cement slab for the

compost facility will be graded with a slope of 1:100, with small grooves or channels

marked on it to enable collection of the leachate. The windrows will be constructed along

the length of these grooves to prevent the leachate from ponding. There is no need for a

walled building for the composting or maturation areas as there are no neighbours to

experience an odour nuisance.

A small pond will be needed to collect leachate which runs off the slab. As the cement

slab has an area of 1833m2 and the mean daily rainfall is approximately 5.03mm348, a

lagoon with a volume of at the very least 9.220 m3 or 9220 litres would be needed. Using

a design factor of 2.0 to allow for differences between the wet and dry season and

rounding up, a volume of 18,500 litres is needed. Using a depth of 3m and allowing 25%

extra for the lagoons sloping sides, the lagoon will be 5m x 1.85m x 3m deep.

This brief outline of the design process has been provided solely to determine the

feasibility of septic tank sludge composting, to decide whether the concept can be

discarded in the early stages or is worth pursuing. Prior to the implementation of a full-

scale sludge composting plant, a much more accurate detailed design would have to be

undertaken. Please note also that no provisions have been made for future expansion

when the population of Montserrat increases.

6.8.3 Plant Layout

A diagram of a suggested plant layout is illustrated overleaf.


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Green wastestorage area

Water

storage

Shredding area for

shredding

green wastes

Operator facilities, power

supply, storage of shredder

and screen when not in use

Leachate lagoon

0 Prevailing wind direction

Direction of work flow Di

Existing Sludge Lagoons

1 in 100 Windrows

Active Composting Area

Direction of work flow

Sc

Figure 6.19 LAYOUT OF SEPTIC TANK SLUDGE COMPOSTI


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6.8.4 Operation And Maintenance

Routine operation of the sludge composting plant will include forming and turning

windrows, and monitoring temperature, dissolved oxygen, moisture content and pathogen

levels. Records would have to be kept of compost production, monitoring results and

equipment maintenance. A detailed operational plan would have to be devised prior to the

introduction of the facility, including provisions for worker health and safety and

minimising the plants environmental impact. All workers at the plant would be expected

to comply with the requirement to use personal protective equipment such as dust masks,

overalls, boots and hearing protection (when operating noisy equipment).

It is not envisaged that there will be enough work for more than two employees. The site

will operate five days a week only and is likely to close down at lunchtime on a Friday in

accordance with local customs.

The initial C:N ratio of the green waste/sludge mix used for composting should be about

30:1. The Solvita test carried out on the pilot scale sludge compost trial indicated that for

a mix of 4 parts green waste to 1 part sludge, the C:N ratio may be too high. It may be

necessary to reduce the green waste content of the sludge to give an initial ratio of 3:1, if

the composting process appears to be too slow. Further experimentation is needed to

determine whether this will raise the moisture content of the mixture too much.

During the dry season in Montserrat, when the evaporation rate is high, the moisture

content of the sludge will have to be carefully controlled. Usually, the moisture content

should be maintained in the range 35-40% by mass. As the moisture content decreases

below about 45%, biological activity declines, and below about 12%, microbial activity

ceases altogether. If the sludge windrows have a low moisture content, they will be

physically stable but biologically unstable349

. The oxygen level of the compost should be

maintained above approximately 20%, by turning as frequently as necessary to exceed

this level. This will ensure that the process does not become anaerobic. Operating

temperature should be maintained in the range from 55 to 60C, if possible. Temperatures


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of less than 55C may not be adequate to ensure pathogen destruction, and temperatures

above 60C will result in reduced microbial activity.

A bulldozer or front end loader may be needed to form and possibly turn the windrows,

unless this process is done manually. First the green waste is stacked in piles, then the

sludge is extracted from the lagoon, measured and poured over the green waste. The

green waste and the sludge are turned and mixed together, and then windrows are formed.

Usually, the optimum height of the windrow is from 1.0 to 2.0m, with a base of 2 to 4.3

m. For the present design, a width of 3m and a height of 1.6m has been chosen. This

should hopefully still be manageable, even if it is necessary to use manual labour for

windrow turning. The windrows should be made trapezoidal in shape. While trapezoidal

windrows lead to slower composting and slightly less uniform temperatures than

triangular or delta windrows350, trapezoidal windrows are better at allowing excess

rainwater to run off the compost, which will be very important in Montserrats wet

season. During the dry season, a trapezoidal shape can still be used, however the top

should be slightly concave to allow the little rain that falls to be retained as much as

possible to moisten the compost.

If compost is turned 2-3 times per week, compost can be formed from sludge in as littleas 3-4 weeks, however to ensure adequate pathogen reduction it is recommended that the

composting process continue for 8 weeks in total, followed by 4 months of maturation.

This should not cause any problems, as there is no keenly felt need for the compost

product as yet, and there is likely to be sufficient land available in the New Windward

area for storage.

The finished product will be screened before use to recover as much as possible of the

green waste, which is difficult to procure and requires the use of the islands only

shredder. It is recommended that a shredder be purchased for the exclusive use of the

septic tank sludge compost, if this project does in fact proceed. The compost should be

left to dry before screening, as a moisture content of less than 50% has been found to

greatly improve the screening process, with certain types of screens351.


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It is recommended that periodic testing for pathogens in the compost be carried out, at

least once a week provided that the Montserrat Water Authority have the resources and

agree to take on this monitoring task. It would be desirable to carry out occasional

monitoring of the finished compost for heavy metal content or other potentially toxic

elements, especially if it will be used for applications other than forestry, however this

will necessitate the sample being shipped to a laboratory in St Lucia and the expense may

not be justified.

Usually variations in sludge loading and moisture content must be taken into account

when operating any sludge composting facility352

. However, as the sludge will be

obtained from the nearby lagoon, which has a large storage capacity and acts as an

equalising tank, this is unlikely to be an issue for Montserrat.

All equipment used on site should be maintained in accordance with the manufacturers

specifications. If the composting facility employees are not trained to carry out

maintenance activities, then this job should be outsourced to the Public Works

Department (PWD).

6.8.5 INDICATIVE COSTS

The capital cost of this system is likely to be fairly low unless it is decided to extend the

water supply from Lookout. It will be necessary to install power on site for operation of

an electric shredder and for operator facilities. The primary component of operating costs

will be labour353. Other operational costs will include equipment maintenance (if

outsourced to PWD) and transport of the finished compost to Silver Hill for application.

To give an idea of the order of magnitude involved, larger windrow sludge composting

systems in the United States have incurred capital costs in the range $50,000-$8 million

USD. This works out to $2.15 to $245 /dry ton354. A few preliminary calculations have

been carried out using a spreadsheet developed by Professor Ed Stentiford of the


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University of Leeds for costing of green waste composting. This spreadsheet has been

modified to reflect local conditions (e.g. construction of a shredder rather than purchase)

and local costs, where these are known (e.g. labour on Montserrat costs approximately

$15 per hour with 10% added for social security,355 cost to hire a D8 bulldozer is $3120

ECD/day356). The spreadsheet calculations represent a worst case purchase of

equipment such as a front end loader, and the use of 10,000 litres per week of water,

trucked in rather than piped to the site. Based on the assumptions made, capital costs for

the sludge composting facility should not exceed $425,000 ECD, and annual operating

costs should not exceed approximately $145,000 ECD. The cost of production is

approximately $145,000 ECD per tonne of finished compost (using a front end loader

instead of manual labour), however the use of manual labour reduces this cost to only

$130,000, still an exorbitant sum. Calculated values from the spreadsheet are tabulated

on page 156 (Table 6.6).

Only costs have been calculated, not revenue, as the product will not be sold but will be

used for reforestation of the Silver Hills. It will not be replacing any existing product, and

the benefits or reduced soil erosion cannot be easily quantified, as new topsoil cannot

simply be purchased to replace that which would erode away without the septic tank

sludge compost. Compost in the US retails for approximately $25USD per cubic yard357,

which is $67.50ECD per cubic yard, $88.30 per cubic metre or $176.60 ECD per tonne,

which appears to be very much cheaper than the cost calculated above. Thus even

allowing for import duties and shipping costs, it may actually be very much cheaper to

import compost from overseas.

It must be stressed that these costs are based on very preliminary investigations only, and

before a full scale plant is built these calculations should be revisited, looking at costs of

earthworks, concreting, equipment availability for hire, availability of skilled personal

and training costs etc. Time has not permitted such a detailed examination in the present

case, nor is it appropriate for a feasibility study, and of course a detailed costing exercise

would be a waste of resources until after extensive public education and promotion of

sludge composting, and market research, indicates that there is indeed both public


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acceptance of the product and a genuine need is perceived by the people themselves, not

imposed by foreign experts. While it has been shown the septic tank sludge composting

is indeed technically feasible in Montserrat, the calculated indicative costs of a small

plant are quite substantial, due to the unique circumstances of Montserrat and the small

volumes involved, and it appears highly unlikely that the government of Montserrat

would place a high priority on such a project and allocate resources to it.


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6.8.6 CONCLUSIONS

Considering the results obtained from the experiments on the sludge composting trial, and

the small area of land needed for a full scale plant, it is considered that the introduction of

a septic tank sludge composting facility is technically feasible. However, a preliminary

costing indicates that the construction of a sludge composting facility cannot really be

justified on economic grounds. In fact, it may actually be cheaper to import compost and

find an alternative means of final disposal of septic tank sludge. If political will exists to

divert funds from other areas, then the facility can be constructed. However, given

Montserrats current problems and priorities, it seems unlikely that such a plant will

eventuate for some years into the future (if at all), perhaps after the sludge lagoons have

started to visibly overflow into the sea.

Due to the likely public opposition to the introduction of septic tank sludge compost,

even for forestry applications, the plant should not be introduced without extensive

promotion and marketing, where this can be found to influence public opinion in favour

of sludge composting. Without public support and recognition of the need for septic tank

sludge composting, it should not be introduced.


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300 Tonge, Bill, Montserrat Water Authority, personal communication, 2001.301 Montserrat Water Authority administration, personal communication, 2001.302 URL: http://www.weblife.org/humanure/chapter3_10.html The Humanure Handbook Chapter 3Compost Biodiversity303 URL: http://muextension.missouri.edu/xplor/envqual/wq0424.htmWQ424 Biosolids Standards forPathogens and Vectors.304 URL: http://www.woodsend.org/solvita.htmSolvita Compost Maturity Test305 URL:http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099Composting Yard Trimmings and Municipal Solid Waste306 Dougherty, Mark, Field Guide to On-Farm Composting, Ithaca, New York, Natural ResourceAgriculture and Engineering Service, 1999.307 Anderson, J.L. and Machmeier, R.E., Establishment of State Rules for Land Application and Utilizationof Septage, chapter in American Society of Agricultural Engineers, Onsite Wastewater Treatment, vol. 5:Proceedings Of The Fifth National Symposium on Individual and Small Community Systems, December14-15, 1987, St Joseph, American Society of Agricultural Engineers, 1988.308 Dougherty, Mark, Field Guide to On-Farm Composting, Ithaca, New York, Natural Resource

Agriculture and Engineering Service, 1999, page 29.309 Metcalf &Eddy, Wastewater Engineering, Treatment, Disposal and Reuse, New York, McGraw Hill,1991.310 Metcalf &Eddy, Wastewater Engineering, Treatment, Disposal and Reuse, New York, McGraw Hill,1991.311 Rynk, Robert, On-Farm Composting Handbook, Ithaca, New York, Natural Resource Agriculture andEngineering Service, 1992.312 Metcalf &Eddy, Wastewater Engineering, Treatment, Disposal and Reuse, New York, McGraw Hill,1991.313 Spellman, Frank R. Wastewater Biosolids to Compost, Lancaster, PA, Technomic Publishing Co. 1987.314 URL: http://www.clw.csiro.au/publications/technical99/tr23-99.pdfWaste-free: Vermicompost toimprove agricultural soils.315 Spellman, Frank R. Wastewater Biosolids to Compost, Lancaster, PA, Technomic Publishing Co. 1987,

page 48.316 Kato, K., Fukaya, M, and Tomita, I., Effect of successive applications of various soil amendments ontomato Fusarium wilt. Re. Bull. Of the Aichi Agric. Res. Center , 1981, vol 13, pp 199-208, cited inHoitink, H.A.J., Boehm, M.J. and Hadar, Y.,Mechanisms of Suppression of Soilborne Plant Pathogens inCompost-Amended Substrates, in Science and Engineering of Composting: Design, Environmental,Microbiological and Utilization Aspects, Worthington, Ohio, Renaissance Publications, 1993.317 Lumsden, R.D., Lewis, J.A. and Millner, P.D.,Effect of composted sewage sludge on several soilbornepathogens and diseases, Phytopathology, 1983, Vol. 75, pp. 1543-1548, cited in Hoitink, H.A.J., Boehm,M.J. and Hadar, Y.,Mechanisms of Suppression of Soilborne Plant Pathogens in Compost-AmendedSubstrates, in Science and Engineering of Composting: Design, Environmental, Microbiological andUtilization Aspects, Worthington, Ohio, Renaissance Publications, 1993.318 Hoitink, Harry A.J. and Fahy, Peter C., Basis for the control of soilborne plant pathogens with compost,Annual Review of Phytopathology, 1986, Vol. 24, pp.93-114, cited in Hoitink, H.A.J., Boehm, M.J. and

Hadar, Y.,Mechanisms of Suppression of Soilborne Plant Pathogens in Compost-Amended Substrates, inScience and Engineering of Composting: Design, Environmental, Microbiological and Utilization Aspects,Worthington, Ohio, Renaissance Publications, 1993.319 Hoitink, H.A.J., Watson, M.E. and Faber, W.R., Effect of nitrogen concentration in juvenile foliage ofRhododendron on Phytophthora dieback severity, Plant Disease, vol.70, no.4, pp 292-294, 1986 cited inHoitink, H.A.J., Boehm, M.J. and Hadar, Y., 1993, ibid.320 Engers and Coppola, 1986, cited in Ng, Mee Weng, Potential use of Composting for Sludge Treatment,MSc Dissertation, Leeds, University of Leeds, 2001.


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321 Haug, R.T. , Compost Engineering Principles and Practice, Arbor Science, Michigan, 1980, cited in Ng,Mee Weng, Potential use of Composting for Sludge Treatment, MSc Dissertation, Leeds, University ofLeeds, 2001.322 URL:http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099BiosolidsGeneration, Use and Disposal, in the United States.323 URL:http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099BiosolidsGeneration, Use and Disposal, in the United States.324 Spellman, Frank R. Wastewater Biosolids to Compost, Lancaster, PA, Technomic Publishing Co. 1987.325 De Bertoldi, M, Vallini, G. and Pera, A. (1984), Technological Aspects of Composting IncludingModelling and Microbiology, in Gasser, J.K.R. (ed), Composting of Agricultural and Other Wastes,Agricultural and Food Research Council, Elsevier Applied Science, London, cited in Ng, Mee Weng,Potential use of Composting for Sludge Treatment, MSc Dissertation, Leeds, University of Leeds, 2001.326 Kuai,L., Doulami, F. and Vestraete, W. (1999) Sludge Treatment and Reuse as a Soil Conditioner forSmall Rural Communities, Bioresource Technology, Vol. 73, No.3, 213-219, July 2000 cited in Ng, MeeWeng, Potential use of Composting for Sludge Treatment, MSc Dissertation, Leeds, University of Leeds,

2001.327 Rigby, Jenny, Report. Waste Management Sector Review, Montserrat, May 2000.328 Jones and Nedwell, cited in Warren Spring Consultancy, Shanks and McEwan (Energy Services) Ltd,and David Border Composting Consultancy, The Technical Aspects of Controlled Waste ManagementMarkets and Quality Requirements for Composts and Digestates for the Organic Fraction of HouseholdWastes, Report No. CWM 147/96, Department of the Environment, December 1996.329 Dunn, Roger, Nortcliff, Steve, Baker, R. Martin, Kendle, Tony, Pickering, Jon and Hadley, Paul, TheTechnical Aspects of Controlled Waste Management Horticultural and Landscape Use of Municipal andGreen Waste Compost, Report No. CWM/124/94, Wastes Technical Division, Environment Agency, 1994.330 Warren Spring Consultancy, Shanks and McEwan (Energy Services) Ltd, and David Border CompostingConsultancy, The Technical Aspects of Controlled Waste Management Markets and Quality Requirementsfor Composts and Digestates for the Organic Fraction of Household Wastes, Report No. CWM 147/96,Department of the Environment, December 1996.331

Spellman, Frank R. Wastewater Biosolids to Compost, Lancaster, PA, Technomic Publishing Co. 1987.332 MAFF, Code of Good Agricultural Practice for the Protection of Soil, London, Ministry of Agriculture,Fisheries and Food, Welsh Office Agriculture Department, 1998, cited in Warren Spring Consultancy,Shanks and McEwan (Energy Services) Ltd, and David Border Composting Consultancy, The TechnicalAspects of Controlled Waste Management Markets and Quality Requirements for Composts and Digestatesfor the Organic Fraction of Household Wastes, Report No. CWM 147/96, Department of the Environment,December 1996.333 URL:http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099BiosolidsGeneration, Use and Disposal, in the United States.334 USEPA, Compost-New Applications for an Age-old Technology, Office of Solid Waste and EmergencyResponse, EPA503-F-97-047, October, 1997, cited in URL:

http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099 BiosolidsGeneration, Use and Disposal, in the United States.335 URL: http://www.weblife.org/humanure/chapter3_6.htmlThe Humanure Handbook Chapter 3 FourNecessities for Good Compost336 Mappie (Philemon Murrain) Botanical Gardens Manager, Montserrat National Trust, personalcommunication, 2001.337 Montserrat Water Authority, personal communication, 2001.338 Montserrat Water Authority, Montserrat Water Authority Silver Anniversary 25 years 1972 1997,Sweeneys, Montserrat, Montserrat Water Authority, 1997, Page 14.


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339 Solid Waste in Brazil, videotape from BBC television program, undated.340 Helen Meekings, DFID, personal communication, 2001.341 West Indies Real Estate, personal communication, 2001.342 Montserrat Lands and Survey Department, 2001.343 Benedict, Arthur H., Epstein, Eliot and Alpert, Joel, Composting Municipal Sludge A TechnologyEvaluation, Pollution Control Review No. 152, Park Ridge, New Jersey, Noyes Data Corporation, 1988.344 URL: http://www.composters.com/docs/acc.htmlElectric chipper/shredder345 URL: http://www.morbark.com/equipment_specs/627trommel.htmEquipment Specs 627 TrommelScreen346 URL: http://www.bra.org/screen.htmThe Compost Screen347 URL: http://www.cityfarmer.org/paulcomp66.html#Vanccompost City of Vancouver CompostingInitiatives348 Delaney, Rosemary Pauline, Foxs Bay Wetland Montserrat: Ecology, Hydrology, and Water Quality.Implications for Management, Master of Science Thesis, Department of Biology, University of the WestIndies, Barbados, 1995.349 Ng, Mee Weng, Potential use of Composting for Sludge Treatment, MSc Dissertation, Leeds, Universityof Leeds, 2001, p. 25.350 Friends of the Earth, Compost! Friends of the Earths Guide for Local Authorities, London, Friends ofthe Earth, March 1993.351 Haug, R T., Compost Engineering Principles and Practice, Michigan, Arbor Science, 1980, cited in Ng,Mee Weng, Potential use of Composting for Sludge Treatment, MSc Dissertation, Leeds, University ofLeeds, 2001.352 Benedict, Arthur H., Epstein, Eliot and Alpert, Joel, Composting Municipal Sludge A TechnologyEvaluation, Pollution Control Review No. 152, Park Ridge, New Jersey, Noyes Data Corporation, 1988.353 Benedict, Arthur H., Epstein, Eliot and Alpert, Joel, Composting Municipal Sludge A TechnologyEvaluation, Pollution Control Review No. 152, Park Ridge, New Jersey, Noyes Data Corporation, 1988.354 URL:http://navigation.helper.realnames.com/framer/1/0/default.asp?realname=EPA+Office+of+Solid+Waste&url=http%3A%2F%2Fwww%2Eepa%2Egov%2Fosw&frameid=1&providerid=0&uid=10264099BiosolidsGeneration, Use and Disposal in the United States355 Meekings, Helen, Department for International Development, personal communication, 2001.356 Wall Trading, personal communication, 2001357

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chapter 6 tri sh morrow dissertation 2001

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