beneficial use analysis of alum sludge from drinking-water

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Beneficial Use Analysis of Alum Sludge from Drinking-water Treatment Plants for

Portland Cement Manufacturing in Holly Hill, South Carolina

By

Adam Mims

April 25, 2017

Proposal Approved By:

____________________________________________

Prof. Dalia Patino Echeverri

Nicholas School of the Environment and Earth Sciences

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Disclaimer:

This 2018 student paper was prepared in partial completion of the graduation

requirements for the Master in Environmental Management at the Nicholas School of

the Environment at Duke University. The research, analysis, and recommendations

contained in this paper are the work of the student who authored the document, and

do not represent the official or unofficial views of the Nicholas School of the

Environment or of Duke University. The author may have relied in many instances on

data provided by different unpublished sources and cannot guarantee its accuracy.

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Table of Contents

Section 1 – Introduction 4

1. Trends and prospects in the production and utilization of CCRs and the need for exploring

alternative sources of needed materials for the cement industry. 6

2. Obtaining CCR-like materials from water-treatment plants 11

Section 2 – Alum Sludge Characteristics 13

1. Disposal Alternatives 14

2. Beneficial Use of Portland Cement 14

3. Other Uses of Waste in Portland Cement 16

Section 3 - Case study: Assessing the technical, economic feasibility of using aluminium sludge from

a water-treatment plant in SC in a local cement production facility 17

1. SC Water Treatment Plant 18

2. Alum Sludge Process from RWS and CWS 18

Section 4 - Case study: Assessing the environmental implications of using aluminium sludge from a

water-treatment plant in SC in a local cement production facility 19

1. Cost Benefit Analysis of Alum Sludge Disposal and Beneficial Use 21

2. Environmental Impacts 25

Section 5 – Lessons from Case Study 27

Section 6 - Final discussion on the viability of the use of alum sludge for Portland cement – general

insights from case study to the U.S. landscape and needs for future research 28

References 30

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1 Introduction

One way to reduce the negative environmental impacts of coal-fired electric power plants is

through beneficial use programs that support re-utilization of its solid waste streams, also known as coal

combustion residuals (CCRs). CCRs are captured and reprocessed for alternative utilizations such as

Portland Cement manufacturing or wallboard manufacturing. However, environmental and energy

regulations, natural gas prices, declining costs for renewables, tax incentives, and market developments

have resulted in retirements of coal-fired power generation capacity and in the associated reduction on the

production and capture of CCRs. These reductions in CCR availability come at the same time demand for

it is increasing. As developing countries industrialize and become more urban, overall demand for

construction materials such as cement and concrete increase. Reduction in CCRs for cement production

will continue as the electric power sectors transition to increased use of cleaner energy sources in an

effort to reduce carbon emissions to mitigate climate change impacts. As the sub-products of coal

combustion become more limited, the opportunity to explore the feasibility of using alternative materials

to support the cement industry’s needs appears.

This project explores the feasibility of using CCR-equivalent materials necessary to meet the

cement industry’s needs, from the waste generated at local water treatment facilities. It provides an

overview of the current and future needs for CCR-like materials and the availability of alum sludge from

water-treatment plants in the U.S. and, it assesses the technical and economic feasibility of this

alternative. In doing so it evaluates the potential of using alum-sludge for cement production both as a

source of a raw material whose supply is declining, and also as an alternative use of a by-product whose

disposal currently imposes economic costs to water-treatment plants.

This document is organized as follows: section 1 discusses the declining production of CCRs and

increasing need for cement raw materials; section 2 explores the availability of CCR-like materials in the

sludge of water treatment plants across the U.S.; section 3 describes a case study of a water –treatment

plant in S.C. and analyses in detail the technical and logistical challenges of using alum-sludge from the

RWS water treatment plant in Santee as a cement input to the Lafarge/Holcim facility; section 4 looks in

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detail at the economic implications; section 5 provides information that can later be used for estimating

the life cycle environmental impacts of beneficial use. This analysis takes a gate to grave approach,

looking at the energy, water and material requirements, and associated emissions to soil, water and air,

from the moment alum sludge is produced as a by-product of water treatment, to the moment it ends in a

landfill, or in a building. Section 6 provides recommendations for the companies involved and for public

decision makers in charge of environmental protection.

The work will follow these steps:

1. Portland Cement data collection and analysis: This data will be used to determine the

feasibility of using alum sludge as a raw material for Portland Cement manufacturing. This

will include listing and analysing all regulated metrics that Holcim must comply with under

ASTM (American Society for Testing and Materials) and DOT (Department of

Transportation) standards for concrete use. Information from testing from Holcim analytical

labs will be evaluated and compared to existing products for benefits and impacts.

2. Cost Benefit Analysis (CBA): The CBA will assess the costs and benefits of beneficial use of

alum sludge at RWS and Holcim. The costs will be based on a mean price derived from steps

one and two, converted into present value terms using an appropriate discount rate. The

benefits will factor into monetary terms in savings from foregoing landfill disposal tipping

fees and raw material procurement costs. The CBA will be carried out however long as each

facility is available and a sensitivity analysis will be applied to determine the relative impact

of increases in energy costs (fuel costs for transportation and furnace operation). The CBA

will show whether beneficial use can be cost effective for the RWS and Holcim. If the CBA

does not show any benefits, it will be necessary to consider other beneficial use options.

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1. Trends and prospects in the production and utilization of CCRs and the need for

exploring alternative sources of needed materials for the cement industry.

The United States Energy Information Administration (USEIA) provides outlooks on annual

energy production and consumption. It evaluates critical drivers and identifies uncertainties when making

projections1. Their evaluations of the energy markets include assumptions of macroeconomic growth,

world oil prices, technological progress, and energy policies1. It is important to note that these are

projections that are modelled of what may happen, not predictions of what will happen1. Its model for

energy consumption projects an increase by 5% between 2016 and 2040 as shown in Figure 11 from the

USEIA 2017 Annual Energy Outlook.

Figure 1 – Energy Consumption Varies Minimally Across All Annual Energy Outlook Cases1

When reviewing energy consumption by fuel mix, it shows a future of increased natural gas and

renewable energies and a decline in coal generation1. Figure 2 of USEIA’s 2017 Annual Energy Outlook

shows how coal is losing market share to natural gas and renewable energy generation, mainly in the

electric power sector1.

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Figure 2 – Fuel Mix of Energy Consumption1

The USEIA projects continued decline of coal generation in part caused by local, state and even

federal regulations (such as the Clean Power Plant CPP) limiting carbon emissions from electricity

producers1. As energy consumption increases, and coal-fired power plants are retired, alternative energy

sources such as natural gas and renewables may slowly displace coal and become the major resource for

the power generation fleet.

Given the USEIA projections for the future of coal-fired power generation, a key question

remains: how will this impact CCR generation and beneficial use markets such as cement manufacturing?

The American Coal Ash Association (ACCA) surveys CCR producers and marketers every year and

releases an annual report with information on production and utilization rates of each CCR2. The 15 year

production and use graph released by ACCA projects a reduction in fly ash but an increase in its

utilization as shown in Figure 32.

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Figure 3 – Fly Ash Production and proportion of Use 2

Since 2010, fly ash production has been decreasing steadily. Until year 2015, the proportion of

fly ash used for beneficial purposes stayed at less than 50% of that produced, but this proportion has

exhibited a growing trend, which if continued, would result in a deficit of this material. Indeed the

increases in proportional use of fly ash coincide with those reported by the USEIA at times when coal use

for electric power generation was replaced by natural gas and renewables.

A report by Caltrans Rock Products, focusing on concrete, dives deeper into the future of CCR

production and its availability. Responding to a fly ash shortage in the winter and spring of 2016,

Caltrans organized a committee to investigate fly ash shortages3. They noted in their executive summary

that the reason behind the shortfalls were the following: lower electric power demand due to

unseasonably warmer weather, seasonal shutdowns for large maintenance projects at coal-fired power

plants, economic shutdowns of coal-fired power plants due to lower electricity prices from natural gas

burning power plants, shutdowns of coal-fired power plants from environmental regulations, and large

snow volumes leading to an increased availability of hydro power3. The USEIA also noted the increase in

natural gas consumption and the decline in coal generation due to environmental regulations. The

Caltrans noted variability in scheduling and climate has reduced the need for coal fired generation due to

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lower cost alternatives for electricity generation, warmer winters that reduce residential electricity

demand, and an abundance of snowmelt that increases availability if low-cost, clean electricity from

hydroelectric dams 3. These factors continue to drive the current trend of reductions in coal use and CCR

production. The report also noted that due to the uncertainty in the timing and stringency of climate-

related regulations it is difficult to predict impacts of CO2 emissions rules on coal use and CCR

production. Existing rules such as the United States Environmental Protection Agency’s Mercury Air

Toxic Standards Rule (USEPA MATS) have already caused massive closures of coal-fired power plants3.

Also, having been issued before the CPP was stayed by the United States Supreme Court for judicial

review3, the Caltrans report looked at the effects of this rule and estimated a reduction of 400 million tons

on coal use during the period 2022-2030. Figure 4 provides an interesting energy outlook reviewing coal

supplies with and without the CPP that would greatly reduce the availability of CCRs.

Figure 4 – Coal Supply Region changes with CPP Implementation3

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According to the Caltrans’ analysis, CCRs that are not utilized for beneficial use are most likely

to be landfilled or sluiced to CCR impoundments for waste storage, and hence, reclaiming this waste for

posterior beneficial use requires additional handling, repurposing, and drying costs that can be high3.

Also, if the CCRs are not separated during disposal, this may make them unusable for particular

beneficial uses such as cement3. This also raises the alarm to prepare for future shortages and alternatives

to CCRs for cement manufacturing.

The United States Geological Survey (USGS) provides a mineral commodities summary for the

United States and global uses of a variety of minerals annually4. The section on cement in their 2017

outlook report shows an increase from 2012 to 2016 an 11 million metric ton increase as shown in Table

14.

Table 1 – USGS Cement Commodity Summary 2017 Report4

Salient Statistics - United States:a

2012 2013 2014 2015 2016

e

Production:

Portland and masonry cement

b

74,151 76,804 82,600 e83,700 85,400

Clinker

67,173 69,420 74,372 e76,000 77,000

Shipments to final customers, includes exports 79,951 83,187 90,070 93,340 96,300

Imports of hydraulic cement for consumption 6,107 6,289 7,584 10,376 12,000

Imports of clinker for consumption

786 806 720 942 1,700

Exports of hydraulic cement and clinker

1,749 1,670 1,397 1,294 1,100

Consumption, apparentc

77,900 81,800 89,200 e93,300 96,200

Price, average mill value, dollars per ton

89.50 95.00 100.50 e105.50 111.00

Stocks, cement, yearend

6,900 6,570 6,140 e5,600 5,700

Employment, mine and mill, numbere

10,500 10,300 10,000 10,000 9,500

Net import relianced as a percentage of apparent

consumption 7 7 8 11 13

eEstimated.

aPortland plus masonry cement unless otherwise noted; excludes Puerto Rico

bIncludes cement made from imported clinker

cProduction of cement (including from imported clinker) + imports (excluding clinker) - exports + adjustments for stock changes.

dDefined as imports (cement and clinker) - exports

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Reviewing Figure 4’s information, cement production is trending up. Notably, imports for

clinker are also increasing which coincides with the decrease in CCR production and availability as noted

by Caltrans’ report and the USEIA. CCRs such as fly ash are a substitute raw material for clinker

production. Imports can be expensive and can be limited on storage, transportation, and global politics.

Finding domestic alternatives to fly ash to supply the necessary raw materials to clinker cement, would

benefit the cement manufacturers, and would be a win-win for the economy and the environment.

2. Obtaining CCR-like materials from water-treatment plants

Water treatment plants that utilize aluminum sulfate may provide a source for coal ash

replacement. Their alum sludge waste can provide chemical substitutes to the fly ash found in CCRs.

The 2011 USEPA’s technical report on the management of drinking water treatment residuals listed a

number of water treatment plants and characteristics providing useful information for identifying potential

markets, determining logistical challenges, and assessing the economic viability of using their sludge as

an alternative to CCRs5. Figure 6 displays Table 7-1 from USEPA’s technical report provides sludge

volumes available based on water plant treatment flows.

Figure 6 – Typical Chemical Coagulation Sludge Volumes5

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Depending on the location, sludge may be available and a likely substitute for fly ash

replacement. According to Caltrans, the California market alone demands between 800,000 and 1.3

million tons of fly ash per year3. Hence, for this state, sludge may not be the sole provider of a viable

substitute, but it may mitigate shortages. However in South Carolina’s (SC) market, cement plants can

use a much smaller quantity; between 100,000 and 250,000 tons per year. The 10 largest water treatment

plants in South Carolina are producing about 565 million gallons per day (GPD) according to the South

Carolina Department of Natural Resources (SCDNR)6. Their production values for 2005 state an average

production rate of 310 million gallons per day (MGD) for the 10 largest water treatment plants which

would equate to an average sludge production between 231,000 and 473,000 gpd according to the

USEPA’s Typical Chemical Coagulation Sludge Volumes in Figure 66,7

. Depending on how cement

plants can utilize the water sludge waste in comparison to ash utilization, it may be possible for water

sludge waste to compensate 5% to 20% of its share. Assuming the gpd of the sludge generated contains

2% to 5% solids, the alum sludge available for cement use would be between 4,620 tons and 23,650 tons

annually if we were to extrapolate the % solids from the sludge production range for 310 MGD

produced.. More importantly, the SCDNR provides a map of the largest water treatment plants in South

Carolina which provides valuable information for exploring the availability and logistics of sludge

utilization 6. Figure 7 provided by SCDNR’s report displays the locations of South Carolina’s largest

public water supply systems.

Figure 7 – Public Water Supply Systems6

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2 Alum Sludge Characteristics

Alum sludge is classified as an industrial waste and is typically disposed at municipal landfills5.

The cost to dewater and transport the material is relatively low but the disposal fees are high7. Other

alternatives for alum sludge are agriculture land applications, land reclamation, sanitary land filling, and

incineration8. Land applications cause environmental concerns due to the large volumes of metals that

can leach out7. Also, extensive use may allow metals to impact groundwater tables

7. Incineration of

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sludge only removes the organic material and hence, the remaining inorganic materials must be captured

and handled8. Typically the inorganic material is captured and hauled to a landfill for disposal

8.

Historically, alum sludge disposal has been an important challenge to water-treatment facilities 5.

Besides its high handling and dewatering costs, it poses the risks of environmental violations and

corresponding fines 8. If not handled properly, it can violate storm water runoff permits which constitutes

a NPDES (National Pollution Discharge Elimination System) violation5.

According to the EPA, 1.48 million pounds of aluminum are discharged to water systems

primarily from coagulation/filtration plants5. Aluminum discharges can be toxic to the aquatic

environment impacting fresh water fish, invertebrates, bacteria, and algae at pH conditions less than 65.

Finding alternative disposal options such as beneficial use can alleviate the environmental

impacts caused by alum sludge.

1. Disposal Alternatives

Current disposal options allow for alum sludge to be disposed by incineration, landfilling, land

application, and aluminum extraction5. Each disposal alternative imposes handling requirements for the

water treatment plant and associated costs. Storing and handling the alum sludge can cause additional

costs and create unintended environmental consequences5, 8

. Landfilling the waste incurs transportation,

dewatering, chemical treatment, and tipping (landfill fees) costs5. Land application requires extensive

permitting, monitoring, and testing costs5. Incineration methods create environmental issues that need to

be handled with additional pollution prevention equipment along with additional handling and

transportation costs8. Extraction methods for aluminum require expensive retrofitting to existing

equipment and additional chemicals.

Identifying alternatives to alum sludge disposal can provide potential cost reductions and

benefits to water treatment plants.

2. Beneficial Use for Portland Cement

The manufacturing of Portland Cement utilizes several chemicals, with the primary components

being calcium, silicon, aluminum, and iron9. Table 2 from Northwestern University’s monograph offers a

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list of sources for each component. Table 3 from Northwestern University’s monograph provides a list of

weighted proportions for each component.

Table 2 - Examples of raw materials for Portland cement manufacture9

Calcium Silicon Aluminum Iron Limestone Clay Clay Clay

Marl Marl Shale Iron ore

Calcite Sand Fly ash Mill scale

Aragonite Shale Aluminum ore refuse Shale

Shale Fly ash Blast furnace dust

Sea Shells Rice hull ash

Cement kiln dust Slag

Table3 - Oxide Composition of Portland Cement9

Oxide Range (wt%) Cement #135 (wt%)

CaO 60.2 – 66.3 63.81

SiO2 18.6 – 23.4 21.45

Al2O3 2.4 – 6.3 4.45

Fe2O3 1.3 – 6.1 3.07

MgO 0.6 – 4.8 2.42

P2O5 -- 0.11

TiO2 -- 0.22

Na2O 0.05 – 1.20

(Na2O equiv)

0.20

K2O 0.83

SO3 1.7 – 4.6 2.46

Loss on Ignition -- 0.81

Insoluble residue -- 0.16

Free CaO -- 0.64

The Portland Cement manufacturing process blends these chemicals into a composited raw feed10

.

Depending on the source, the material is ground and conveyed into the furnace10

. The furnace burns off

moisture and other elements to form a new substance called clinker10

. The clinker is then released to be

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cooled and grounded further10

. Additional chemicals are added at the final stage to produce a fine

material for concrete use10

.

Alum sludge has the ability to provide multiple chemicals to the cement process. It is composed of

primarily aluminium, silicon, and iron as listed5. Table 4 highlights an x-ray diffraction analysis of the

alum sludge in question and their highest % results.

Table 4 – XRD of Alum Sludge Provided by Regional Water System

Element *Concentration (%)

Aluminum 39.35

Silicon 31.26

Iron 24.35

Sulfur 1.385

Titanium 0.8168

Phosphorus 0.6058

*Additional elements below 0.5% were not listed

3. Other Uses of Waste in Cement Plants

The International Finance Corporation (IFC), a part of the World Bank Group, has a report

focusing on increasing the use of alternative fuels at cement plants and provides a best practice with case

study examples11

. The IFC discusses the need for cement in current and emerging development

throughout the world as well as the emission challenges associated with its production11

. Part of their

recommendations focus solely on utilizing alternative fuels that can reduce the need for current fossil fuel

choices such as coal and oil11

. Alternative fuel recommendations include municipal waste, biomass, non-

hazardous industrial and commercial waste, and other unclassified alternative fuels11

. Lafarge/Holcim

currently utilizes alternative fuels in these areas to reduce emissions and maximize their operational

benefits. Figure 8 from the IFC report provides an example of what Lafarge/Holcim and other cement

plants have been utilizing.

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Figure 8 – Alternative Fuels Utilized by Large Cement Plant18

Cement plants globally have been utilizing alternative methods to fuel and feed their

manufacturing processes to compete efficiently and economically. Evaluating a similar opportunity in

South Carolina will provide additional information to support the need to continue to be flexible and

forward thinking in Portland cement manufacturing.

3 Case study: Assessing the technical, economic feasibility of using aluminium sludge

from a water-treatment plant in SC in a local cement production facility

The trending reduction in coal generation and CCR’s, the increase in demand for fly ash in

cement production, and the growing need for substitutes opens the opportunity for a potential substitute

through water treatment plants. Evaluating the sludge characteristics, location, logistics, technical

viability, and long term economics will provide useful information to propose a solution for a growing

market with a diminishing supply source. We will review these dynamics in the context of a case study in

SC where we evaluate the feasibility of using alum sludge from a water plant in Berkeley S.C in a local

cement plant in Dorchester/Orangeburg S.C. This analysis seeks to shed light on the following questions:

Is utilizing alum sludge at the local cement production facility, Lafarge/Holcim, technically viable? Can

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this waste be used as a component in their cement in a way that allows Lafarge/Holcim to continue

meeting concrete standards, and manage increased furnace operations and raw material management? Can

the local water-treatment plant RWS provide alum sludge with consistent chemical characteristics as

required by Lafarge/Holcim?

1. SC Water treatment plant

The Regional Water System (RWS) located in Moncks Corner, South Carolina (Moultrie Plant)

and Santee, South Carolina (Marion Plant) provides over 40 million gallons per day of clean drinking

water to over 160,000 customers12

. As each gallon of water is treated with aluminium sulfate, alum

sludge is produced. Properly disposing of this sludge requires a multi-step process that generates

economic costs for the RWS and also for the neighbouring Charleston Water System (CWS). The CWS

produces almost three times as much aluminium sludge as RWS and it operates to supply 114 million

gallons of drinking water13

to its customers. As stated in the introduction, this Masters Project analyses an

alternative to both lower the disposal costs of aluminium sludge and its impacts to the environment from

RWS and CWS: utilizing the resulting alum waste into the production of Portland Cement.

2. Alum Sludge Process from RWS and CWS

At the RWS, the alum sludge is mechanically transported to a thickener where it is stored and

prepared for dewatering. After the water is physically removed, the remaining solid waste is conveyed

outside to a concrete pad where it stays until ready for transport. The material is then loaded into an 18

wheel truck and trailer for disposal at a class 3 landfill located in Cross, South Carolina. Each step in

handling the waste increases the cost of the RWS overall operations.

A few miles down the road the Charleston Water System also utilizes aluminum sulfate. Instead

of using an internal landfill, the alum sludge waste is transported to the Berkeley County Municipal Solid

Waste Landfill. The Charleston Water Systems pays for the waste dewatering and handling,

transportation, and tipping fees for each ton produced. The tipping fees alone are $65 per ton14

. For a

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production of 15,000 tons of alum sludge annually, there is a total of $975,000 just in tipping fees. This

does not include dewatering and handling costs or the transportation costs.

Lafarge/Holcim Cement located in Holly Hill, SC has agreed to test the alum sludge as another

source for its raw feed material needs15

. They currently utilize various sources of waste for both raw feed

materials and alternative fuels15

.

Because alum sludge is a new source for Holcim a rigorous process of testing and trials is

necessary to ensure the sludge moisture, odour and other characteristic are compatible with the cement

production process. It is known that the sludge’s large moisture content will impact the efficiency of the

furnaces. Also, the sludge has an odour that may or may not be transferred to the final product and has

other biological characteristics that may impact handling methods and employee health. Finally, to

ensure efficiency and quality of the cement manufacturing process, the chemical composition of sludge

needs to stay consistent to avoid affecting raw feed blends and ensuring compliance with the regulated

standards for cement in concrete utilization.

4 Case study: Assessing the environmental implications of using aluminium sludge from a

water-treatment plant in SC in a local cement production facility

This section presents estimates of the potential environmental benefits, costs and risks of utilizing

the alum sludge at Holcim, taking into account that transportation costs and associated emissions from

RWS will increase if sludge is hauled to Holcim instead of taken to the landfill located in Cross, SC.

The Lafarge/Holcim’s cement plant in Holly Hill, SC which includes a 12-foot diameter wet kiln

and two small finish mills16

was constructed in 1966. In 2003, the old plant was demolished and a new

plant was constructed consisting of a new preheater/pre-calciner kiln and associated crushing, storage,

and grinding equipment16

. After the new equipment and plant construction upgrades the plant is capable

of producing 2.2 million metric tons a year 16

. The plant recycles alternative raw materials and fuels such

as hazardous liquid waste and can recycle more than 400,000 tons of material per year16

. It incorporates

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fuel blending and storage systems and maintains capacity for loading and unloading tankers and railcars16

.

Additionally it utilizes ancillary processing equipment such as grinders and pumps to handle the

alternative raw materials and fuels16

. The plant is a suitable partner in evaluating the aluminium sludge

waste material from the RWS in assessing its characteristics for Portland Cement production. The plant

currently utilizes fly ash wastes recovered from ash impoundments, mill scale from steel producers, and

recycled used oil from local collection centers. Their expertise would provide additional benefits in

handling and evaluating the waste as a possible alternative raw material.

The plant at maximum output can utilize 400 tons of raw material feed per hour. Typically, the

plant replaces about 40% of the raw material with an alternative material such as fly ash and mill scale

depending on their chemical needs. This equates to about 160 tons per hour of the raw feed containing

alternative materials, or 1.4 million tons per year assuming 24 hours of operations, 7 days a week. As it

will be discussed below, this implies that the plant has a processing capacity of alternative materials that

exceeds by more than 300 times the quantity of alum sludge being generated at the RWS.

The alum sludge generated in 2017 was stored and prepared for loading to be disposed of as

normal operations in a class 3 landfill. Approximately 2,500 tons were disposed and 107 tons were

utilized for the trial by Lafarge/Holcim. Two trials were executed on July 24, 2017 and November 6,

2017. The first trial utilized 19.09 tons and the second trial utilized 88.54 tons total. The trials were

documented by Lafarge/Holcim personnel, who provided the information contained in this analysis.

The first trial utilized only 5% of total alternative material raw feed. It was blended in with other

alternative materials such as fly ash and fed into the kiln for clinker formation. During the trial, no

negative impacts were observed during handling and kiln feeding. The end product also showed no signs

of negative or positive impacts to structural and chemical characteristics.

The 2nd

trial utilized over 20% of the alternative raw material feed which caused severe

difficulties. The alum sludge was wet and did not blend well with the other alternative materials. It was

also difficult to handle with blending equipment and employees complained of an unpleasant odour. The

material once blended also impacted kiln feed processes, affected intermediate production outputs and

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furnace effectiveness for clinker formation. However, despite the difficulties handling and processing

resulting from adding sludge, the final product was not impacted negatively or positively by the increased

blend. Table 5 highlights the impacts of the alum sludge material during the two trials.

Table 5 – Alum Sludge Impacts during Trial

Raw Feed Blend 5% 20%

Handling No impact Negative impact – high moisture

Kiln Feed No impact Negative impact – feed rate slowed, heat rate

reduced (required additional energy)

Odour No observation Observed – nauseating

Feed Blending No impact Negative Impact – increased activity

A third trial is scheduled for May, 2018 after the plants’ scheduled maintenance outage and after

an evaluation of the initial results of the prior alum sludge feed blending experiments. However, the trial

was postponed until May due to recent rainfall events delaying dry use of the alum sludge. A raw feed

blend between 5% and 20% will be targeted to reduce handling, kiln feed, and feed blending impacts as

well as physiological impacts from the odour. Also, special attention will be paid to the effects of rainfall

and inclement weather on the alum sludge material given that the RWS does not currently cover this

material once dewatered. It is expected that increased moisture from any rainfall will increase the

difficulty of incorporating the alum sludge in the process. Prior to the second trial, a rainfall event prior

to delivery of material to Lafarge/Holcim added additional moisture that may have led to the observed

negative impacts.

1. Cost Benefit Analysis of Alum Sludge Disposal and Beneficial Use

After review of the trials from a handling and operational perspective, information regarding

costs for disposal, transportation, beneficiation fees, loading, and budgets were compiled to evaluate the

costs/benefits of the potential use of alum sludge as an alternative material for Portland Cement

manufacturing. All information in regards to this analysis was provided by both Lafarge/Holcim and the

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RWS. Currently, the RWS disposes of all alum sludge waste at a class 3 landfill located in Pineville, SC.

The RWS will also pay costs associated with loading and hauling that vary based on fuel costs and

equipment used which are outlined in Table 6.

Table 6 – Cost of disposal of Alum Sludge

Activity Cost $/ton

Loading $1.00 - $1.50

Transportation – Open Trailer Freight Truck –

Diesel Fuel

$4.00 - $5.00

Disposal Fee (includes placement, handling, and

construction)

$14.00

Total $19.00 - $20.50

The RWS disposed over 2,500 tons of alum sludge in 2017. Based on the costs listed in Table 5,

the total cost for disposal is over $47,500. In 2016, over 3,600 tons were disposed at a cost over $68,400.

Depending on the RWS sludge production volumes; they can plan to expect disposal costs between

$47,000 and $68,000 annually. The current forecast for water sales is listed in the Table 7 for the next 3

years.

Table 7 – RWS Observed and Forecasted Annual Water Sales in millions of gallons (MG)

Year 2016 2017 2018 2019 2020

Moultrie 6,856 6,807 7,289 7,625 7,953

Marion 299 321 310 683 883

Total 7,155 7,128 7,599 8,307. 8,837

The RWS thickens and dewaters the sludge to produce the alum sludge with lower moisture

levels and higher solids concentrations. The proportion of solids in the RWS alum sludge is on average ~

4E-07

%. Hence, based on the RWS 2016 and 2017 production data, it is possible to estimate the volume

of sludge that will be generated in future years. Based on the 2016 and 2017 sludge production volumes,

we estimated the sludge production per gallon of water sold which was 3E-07

% in 2016 and 5E-07

% in

2017. These values was then used in combination with the forecast of water sales to estimate expected

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sludge volumes as a range from lowest and highest production volumes. The forecasted sales are

increasing each year and so will the sludge production. Table 8 displays the estimates of sludge volumes

and associated disposal costs for each year. Disposal costs were set at $19 - $20.50 per ton.

Table 8 –Observed and Forecasted Sludge Production Volumes and Annual Disposal Costs 2016 -

2020

Year 2016(1)

2017(1)

2018(2)

2019(2)

2020(2)

Sludge

Produced

(ton)

3,681 2,611 2,784 – 3,910 3,043 – 4,275 3,064 – 4,305

Disposal Cost

$19

$69,951 $49,618 $52,895 -

$74,297

$57,824 -

$81,220

$$58,235 -

$81,798

Disposal Cost

$20.50

$75,473 $53,535 $57,071 -

$80,163

$62,389 -

$87,632

$62,832 –

$88,255

(1) Volumes and costs for 2016 and 2017 are as reported by the RWS5 (ref)

(2) Projections of volume and costs for years 2018-2020 are obtained based on the forecasted water volumes produced by the RWS in those years and the assumption

that the sludge production rate per gallon of water observed in 2016 and 2017 will remain unchanged

The net present value of the cost range for the 3 years of the forecast assuming a 5% discount rate

is $153,129 - $215,088 at $19/ton and $165,219 - $232,068 at $20.50 per ton.

If Lafarge/Holcim were to utilize 100% of the alum sludge produced annually (not replacing 40%

of the raw feed material at one time but instead using lower proportions throughout the year), the RWS

would avoid the cost of disposal of this material in a landfill. Instead, the RWS would incur the costs

associated with beneficial use of alum sludge for Portland Cement which includes loading, transportation,

and a beneficial use fees presented in Table 9.

Table 9 – Beneficial Use Cost per Activity for Portland Cement Manufacturing

Activity Cost $/ton

Loading $1.00 - $1.50

Transportation – Open Trailer Freight Truck -

Diesel Fuel

$6.15 - $7.15

Beneficial Use Fee $2.60

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Total $9.75 - $11.10

The beneficial use option removes the landfilling disposal cost of $14 and replaces it with a

beneficial use fee of $2.60, resulting in savings of $11.40 per ton for the RWS. Because the

transportation costs associated to beneficial use are $2.15/ton - $3.15 higher than the transportation costs

to the landfill the net savings for the RWS are $9.25 - $10.25 per ton. Table 10 presents the total RWS

sludge disposal costs associated to beneficial use. Assuming a discount rate of 5%, the costs for the three

year period 2018-2020 is estimated to be $78,580 - $110,374 at $9.75 per ton and $89,460 - $125,657 at

$11.10/ton.

Table 10 – Estimated Annual cost of Beneficial Use of all Alum Sludge produced 2016 – 2020

Year 2016 2017 2018 2019 2020

Beneficial Use

Cost $9.75

$35,896 $25,462 $27,143-

$38,126

$29,673 -

$41,679

$29,884 -

$41,975

Beneficial Use

Cost $11.10

$40,498 $28,726 $30,902 -

$43,405

$33,781 -

$47,450

$34,021 -

$47,787

The difference in annual costs between the two alum sludge disposal options is presented on

Table 11

Table 11 – Estimated Total Annual Savings from Beneficial Use 2016-2020

Year 2016 2017 2018 2019 2020

Disposal

$19.20

$69,951 $49,618 $52,895 -

$74,297

$57,824 -

$81,220

$$58,235 -

$81,798

Disposal

$20.50

$75,473 $53,535 $57,071 -

$80,163

$62,389 -

$87,632

$62,832 –

$88,255

Beneficial Use $35,896 $25,462 $27,143- $29,673 - $29,884 -

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$9.75 $38,126 $41,679 $41,975

Beneficial Use

$11.10

$40,498 $28,726 $30,902 -

$43,405

$33,781 -

$47,450

$34,021 -

$47,787

Difference

(low)

$34,055 $24,156 $25,751 -

$36,171

$28,151 -

$39,541

$28,351 -

$39,823

Difference

(high)

$40,498 $28,726 $26,169 -

$36,757

$28,607 -

$40,182

$28,811 -

$40,468

Italic information is extrapolated – 2016 and 2017 are actual volumes

These results indicate that the RWS can save about $74,500 - $105,000 at the lower rate and

$76,000 - $106,000 at the higher rate over the three year period 2018-2020 if it stops landfilling all the

alum sludge it produces and instead takes it for beneficial use at the Portland Cement manufacturing

plant. Because transportation costs depend on fuels with volatile prices there is some uncertainty about

these savings. There is also some uncertainty about the proportion of sludge that can be handled in the

cement plant and hence more trials will need to be completed to fine tune the operational parameters and

obtain more precise estimates of the costs.

3. Environmental impacts:

Although it is premature to try to estimate the environmental impacts of replacing the current

disposal of alum sludge with the beneficial use option at the cement plant, it is possible to conduct a

preliminary analysis of the expected changes in direct air emissions, energy use, and inputs and outputs.

On one hand, because the cement plant is located further away from RWS than the class 3 landfill, air

emissions associated to the transportation of the alum-sludge will increase.

According to the USEIA, about 22.4 pounds of CO2 is produced from burning a gallon of diesel

fuel17

. . The transportation fleet utilizes a fleet of freight trucks and open trailers that consist of Peterbilt

& Kensworth, manufacturers that average a fuel rate of 6 miles per gallon (mgd) when loaded (~80,000

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pounds) and 7.5 miles per gallon(mgd) when empty (~30,000 pounds) according to the RWS haulers. The

distance to the cement plant is 34.2 miles and to the landfill is 25.2 miles. With the loaded freight, the

trip to the landfill will consume 4.2 gallons of diesel and the trip to the cement plant will consume 5.7

gallons of diesel. With each gallon of diesel consumed, the trip to the landfill will produce 94.08 pounds

of CO2 and the trip to the cement plant will produce 126.93 pounds of CO2. The load to the cement plant

will emit 0.063 tons of CO2 and the load to the landfill will emit 0.047 tons of CO2. However the

additional mileage in hauling is minimal and hence the increase in air emission are estimated as 0.016

tons or 32.85 pounds per loaded delivery. Similarly, energy use at the cement manufacturing plant may

increase if alum sludge is particularly moist, but this cannot be estimated without more trials.

On the other hand, depending on the volume of alternative materials that alum sludge will

displace, there may be a net reduction in environmental impacts (due to reduced need for mining raw

materials for cement). Currently, the materials used are clay, marl, sand, shale, fly ash, aluminium ore

refuse, iron ore, mill scale, bauxite, and blast furnace dust. If alum sludge displaced any of these

materials, environmental emissions associated with its excavation, mining, milling, processing, screening,

dewatering, grinding, drying, production, and transportation would be eliminated or reduced. For

example, according to the International Aluminum Institute, bauxite mining on average emits 100 kg of

CO2 per ton of bauxite ore18

. If the bauxite is mined 50 miles away and a 23 ton load is shipped to the

cement plant, it would emit 2.54 tons of CO2 for the mining activities and an additional 0.093 tons in

transportation for a total of 2.633 tons. However, utilizing alum sludge would only emit 0.063 tons of

CO2 and reduce or remove the bauxite emissions impact per 23 ton load shipped.

Also, the beneficial use option also eliminates the need for disposal of alum sludge in the class 3

landfill and hence may result in the potential reduction of methane and other emissions, but this depends

on the conditions at the cement kiln, which are not known without further trials. A full environmental

lifecycle assessment can be conducted once the trials at the Lafarge/Holcim plant determine the changes

in the operating conditions for different blending rates of alum sludge. Table 12 summarizes the pros

and cons of beneficial use.

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Table 12 – Alum Sludge Beneficial Use Pros and Cons

Activity Beneficial Use Landfill Disposal Comments

Reduces Water

Treatment Costs

X

Reduces Cement Mining

Operations and

Environmental Impacts

X Additional trials to verify how

much raw material is replaced to

calculate additional

environmental savings

Eliminates Environmental

Impacts to Water from

runoff

X X

Reduces Costs of

Cement’s production

process

X Additional trials needed to verify

net reduction in costs

Increases CO2 Emissions

from Cement’s

production process

X Possibly if moisture is too high

and forces plant to use more fossil

fuel

.

5 Lessons from case study.

The case study provided significant information for operational and cost/benefit analysis for the

cement plant and the RWS. The cement plant is still investigating the possibility of using alum sludge as

a component of the alternative raw material. Before committing to this transition it will conduct further

trials to ensure chemical consistency and to secure the required volumes to fulfil their production needs.

Once the cement plant has identified their alternative raw material feed blend, further investigations into

cost and benefits as well as emissions can be considered.

Based on the results obtained so far, I recommend conducting further trials to replicate initial

results trying to isolate the effects of variables such as increased moisture from rain fall. This is a

variable that can be controlled by the water-treatment plant, by covering the sludge, as it will be

recommended below. Additionally, I suggest evaluating the possibility of using material from other water

treatment plants such as the CWS. Testing the use of larger volumes of material may provide new

information than that provided by the small volume trials we have reviewed. Finally, I recommend

exploring the possibility of disposing of the aqueous waste –resulting from sludge dewatering in the same

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ways highlighted in the IFC report mentioned in section 2 above. According to the IFC, the material in

water form can be injected into the kiln through mixer injectors to help lower the thermal nitrogen oxides

produced11

.

The RWS stands to benefit economically from the beneficial use option of alum sludge. The cost

difference between the two options (disposing and beneficial use) is significant and an incentive for

supporting any necessary additional trials for success. Removing almost half the disposal cost provides

additional funds for the RWS to utilize elsewhere. I would recommend the RWS to continue to support

the trials and provide all alum sludge production to the cement plant for continued testing and

observations. I would also recommend the RWS to assess alternatives to cover dewatered alum sludge to

prevent increased moisture from rainfall and the associated increase in handling and processing costs.

This may reduce additional drying gains during warm weather with direct contact from sunlight but will

facilitate handling and blending operations in the cement plant and increase the chances of adoption of the

beneficial use alternative.

Importantly, for both participants, completing an environmental life cycle assessment will

provide vital information for understanding the impacts of each operation and disposal practices. This

will put both companies in a better position to face new and more stringent environmental regulations that

could be enacted in the near future for cement production and disposal practices.

6 Final discussion on the viability of the use of alum sludge for Portland cement – general

insights from case study to the U.S. landscape and needs for future research

The viability of the use of alum sludge for Portland cement is promising as demonstrated by the

case study discussed in this document and by the interest expressed by other countries that have been

reviewing multiple options for alternative fuels and raw material feeds, as documented in the IFC report.

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Lafarge Canada has recently partnered with Metro Vancouver to accept water filtration residuals

to be used as alternative materials for cement manufacturing19

. This deal was reported in August 2017 the

plant has committed to utilize 10,000 tons of the residuals which are avoiding the mining of 2,100 tons of

virgin materials19

. Lafarge run trials during May 2017 to evaluate the handling and blending

opportunities19

. The plant plans to produce residual added concrete which will help Lafarge/Holcim meet

its Global 2030 Sustainability Plan19

.

The most important aspect will be creating partnerships with water treatment utilities that are in

need of solutions for their disposal activities. The need for clean drinking water will continue to grow as

the population grows and parts of the world continue to develop. Cement is going to play a vital role in

supporting that development and water is necessary to maintain life and health. The partnership between

these two processes will be vital as humanity continues to deal with emissions impacting the planet’s

climate and environment. As we move to cleaner energy sources, cement’s raw material supply will

diminish and the water treatment sector has an opportunity to replace a good portion of their demand.

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beneficial use analysis of alum sludge from drinking-water

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