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CKD USE AS A SLUDGE STABILIZING, DEWATERING AND DISINFECTION AGENT IN IRAQ

Salah F. A. Sharif a,b,*, Sabah U. Shadeedc,**,

a- A Prof, Building and Construction Department, University of Technology, Iraq

b-Research Fellow, College of Engineering, UNITEN, Malaysia,

** E-Mail: dr.salahfarhan@yahoo.com, HP: (+9647901497563), (+60147315069)

c- Local Environmental Council Chairman, Al-Anbar Province, Iraq

**, E-Mail: sa_shadeed@yahoo.com, HP: (+964792354118)

ABSTRACT

Hundreds of thousands of tons of cement kiln dust (CKD) as well as other emissions are generated annually from existing cement plants in Iraq. Most plants dispose of CKD near or around the plants site as uncovered mounds and piles with significant economic and environmental impacts. The amount of generated CKD is found to be variable among different cement plants. It can be estimated that the generated CKD on the average is about (8-33) % of the production output depending on the conditions of each plant.
An experimental laboratory work on one of the beneficial uses of CKD was carried out in this study. CKD was mixed with sewage sludge as dry alkaline stabilizing agent. Sludge treated with CKD was found to meet the class A requirements (fecal coliform density less than 1000 MPN/g solid) as set by USEPA. In this study, the fecal coliform density of
thickened sludge treated with 20 % CKD was reduced from 2.43×108 MPN/g to 410
MPN/g, while; for dewatered sludge treated with 30 % CKD, it was reduced from 8.75×107
MPN/g to 220 MPN/g. CKD was successfully applied to destroy pathogens, reduce vector attraction and bring the sludge to a manageable form.

Keywords: Cement Kiln Dust (CKD), Iraqi Cement Plants, Sanitary Sludge Stabilizing.

1- Introduction

Although sanitation in Iraq cities is not yet as required level, but a huge amounts of sludge expected to be rejected and disposed to the environment in the near future. Conjunction
with lack of available sludge treatment technology, several problems could be created due

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to high water content and pathogens of disposed sludge. Many studies and research works where performed by Iraqi engineers and researchers to solve this problem. Apart of them concentrates to use the disposed CKD from cement manufacturing plants.
The physical characteristics of fresh CKD are a fine, dry alkaline dust that readily absorbs water. CKD particle sizes generally vary by kiln process type and range from 0-5 micrometers (µm) (approximately clay size) to greater than 50 µm (silt size). The chemical composition of the primary bulk constituents in CKD (those found in quantities greater than 0.05 percent by weight) are silicates, calcium oxide, carbonates, potassium oxide, sulfates, chlorides, various metal oxides, and sodium oxide. Also that variability in raw feed, fuels, process types and product specifications may influence CKD chemical characteristics.
There are many existing plants of cement production working in Iraq which are generating thousands tons yearly of by-product (CKD) which by current practices of managing and disposing have caused, and may continue to cause contamination of air, nearby surface water and ground water, also pose a danger to human health and environment and it may do so in the future.
One of the most important options for making use of CKD is mixing it with sludge resulting from sewage treatment plants as stabilizing/solidifying agent. Where absorptive capacity and alkaline properties of CKD can reduce the moisture content and provide an alkaline environment for waste materials (sludge) (Naik et al., 2003; USEPA, 1993). This approach to wastes utilization allows not only saving natural resources, but also avoiding the negative environmental impact of waste disposal and land filling (Paulauskas et al.,
2006). A laboratory study was conducted to determine if CKD could be used as dry- alkaline stabilization agent to stabilize the sewage sludge in accordance with EPA criteria for PSRP. This study was applied on a sewage sludge produced at Al-Rustamiyah sewage treatment plant. Usually, effluent and disposal sludge from this plant are used for land application. At Al-Rustamiyah sewage treatment plant, the sludge passes to the drying bed without significant stabilization of organic matter. Due to the function absence of plant's
digesters which are out of service from many years ago, the sludge on the drying beds

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becomes septic again which creates serious troubles (Al-Najjar, 2001), as well as having high densities of fecal coliform bacteria as shown later.
Dry alkaline stabilization of sewage sludge by using CKD is a treatment intended to destroy pathogens, reduce vector attraction and odors, and bring the sludge to a manageable form for land application. Fecal coliforms bacteria tests are used as an indicator or measure of the effectiveness of stabilization process in reducing microbial densities in sludge (Christine et al., 2007).

2- Quantity and Quality of CKD in Iraq

The survey of the sixteen cement plants which are grouped into three regional companies of cement was prepared as data collection worksheet and distributed to all plants. Approximately, more than 85 percent of the cement plants have been responsive to the survey. Some of the responses may not provide accurate or complete data for many reasons. To minimize the non-response and the lack of data, information submitted by plants in response to the survey was supplemented and evaluated against data obtained from other sources. These other sources include sampling and measurement activities, data collection from documents and reports; site visits observations and utilizing the published international experience in this field.
The production capacity of Iraq cement industry which is distributed over three regional state companies is shown in table (1) which consisted of (79 %) produced by dry process kilns and the remaining (21%) produced by wet process kilns.

Table (1): Production Capacity of Cement General State Companies (USAID, 2007; State Owned Enterprises Guide, 2005).

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An understanding of the issues surrounding CKD requires knowledge of both the raw
materials and the fuels (process input) used in cement kiln systems, because these inputs in conjunction with the manufacturing process determine the characteristics and quantities of CKD generated. Fuel inputs can significantly influence CKD chemical characteristics especially sulfur level. Table (2) shows the characteristics of heavy fuel oil used as a source of heat required in cement manufacturing process at all cement plants. The designed and actual heat consumption is shown in Table (3) for all cement plants of the three cement companies. While table (4) is showing the designed and interdependent conversion factor (the quantity of raw materials required to produce unit of product) for all cement plants.

Table (2): Characteristics of Heavy Fuel Oil Used for the Burning in Cement Rotary

Kilns (from Documents and Reports of Cement Plants (DAROCP)).

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Table (3): Fuel Consumption for Iraqi Cement Plants, from (DAROCP).

Table (4): Conversion Factor for Cement Plants, from (DAROCP).

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In Iraq, specific data on CKD waste were sparse. A sampling and analysis program was conducted to determine the specific characteristics of CKD at different sources and to integrate the results with available data from plants documents and reports. In addition, dust emission measurements were carried out at different plants to determine the concentration of dust emitted from stacks.
Method and instruments used to quantify and qualify the CKD were as follows:
- Dust emission from stacks was measured according to ASTM D 2928-71; standard method for sampling stacks for particulate matter. The tests were carried out by using FLS miljo mini-sampTM equipment.

 Particle size distribution specified by using soil hydrometer, 152 H-62 ASTM, 0 – 60 g/l.

 Chemical analysis of cement and CKD were done according to ASTM C-114. Also, this method determines the oxides of silica, aluminum, iron, calcium, magnesium, sulfur.

 Alkali materials (sodium and potassium oxides) measured according to ASTM C-114 using flame photometer model JENWAY – PFP7.

 pH measured by using pH-meter according to ASTM D-4972.

 Water holding capacity measured according to ASTM D-2216.

The mean of chemical analysis of CKD which generated is shown in table (5), and the particle size distribution and other physical properties are shown at table (6) for different
cement plants of the three cement companies.

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Table (5): Chemical analysis of CKD.

Northern cement plant's samples

Iraqi cement plant's samples

Southern cement plant's samples

omponents

(wt%)

ample No. 1 adoosh)

ample No.2

Sinjar)

ample No.3 amm-am

l Aleel)

Sample No. 1 l Qaim)

ample No. 2

Kirkuk)

ample No. 3

Falluja)

Sample No. 1 (Kufa)

ample No. 2

Muthana)

ample No. 3 erbala)

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Table (6): CKD Particle Size Distribution and Other Physical Properties.

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3- Experimental Work

3-1. Materials: Thickened and dewatered sludge were used in this study. Thickened sludge (raw sludge) from outlet of thickening unit and dewatered sludge from the drying bed from Al-Rustamiyah sewage treatment plant/ Baghdad were taken as samples. Before CKD addition, the two sludge types were tested for pH, total solid (TS), volatile solid (VS) and fecal coli-form densities (FC). Results are shown in table (7). The properties of CKD which is used as alkaline agent are shown in table (8).

Table (7): Characteristics of Thickened and Dewatered Sludge before CKD Addition.

Table (8): Characteristics Of CKD Added To Sludge.

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3-2. Experimental Procedure: Before CKD addition, characteristics of thickened and dewatered sludge were examined as shown previously in table (7). Then, six samples of thickened sludge and six samples of dewatered sludge were mixed with different doses of CKD in order to obtain stabilized sludge. The dosages ranged between (5-40) gm of CKD to 100 gm sludge (5-40 % weight/weight). Sludge and CKD were mixed manually with a glass rod in the glass bowls to obtain good homogeneity. A screening test was then carried out to determine which mix proportions produced the required pH (at least pH ≥ 12 for the first 2 hours and pH ≥ 11.5 for the next 22 hours). The resulting mixtures of sludge and CKD were conveyed after 6 hours into the perforated bottom cylinders of experimental lab apparatus which was constructed to accelerate the drying process of treated sludge by supplied air. The mixtures of thickened and dewatered sludge with CKD which satisfied the initial pH requirement were monitored at different time intervals. Further tests involving TS, VS, moisture content, and FC densities were also measured at different time intervals (0, 2, 12, 24, 48, 72, 96, 120, 144 and 168 hours).

3-3. Apparatus of Drying: A small scale drying apparatus, as shown in figure (1), was constructed to accelerate drying of stabilized sludge samples. This apparatus consists of multi cylinder tubes (with 10 cm diameter and 20 cm in height) welded at the ceiling of steel box structure (10 cm high, 30 cm wide and 50 cm long). The ceiling plate of box which represents the bottom of the cylinder tubes was perforated at each one. An air blower (BBC, Type QUXY 90 L 2 AAT, 0.75 kw, 2860 rpm) was used to supply air to the system (connected to the box) during the experiments. The air supplied was released from the box through perforated plate to the cylinder tubes which contain a mixture of stabilized sludge to accelerate drying. If the resulting mixtures were in the cake form, the air drying process was initiated. However, if the resulting mixtures were in liquid form, it was left in the tubes to drain well through the bottom perforated plate to an intermediate solid level to produce a

cake material.

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Figure (1): Lab apparatus used for treated sludge drying

3-4. Determination of pH: The pH of the sludge and the alkaline stabilized sludge were determined at specified time intervals. A portable pH meter (Corning Model Check- Mate

90 with a glass electrode) was used for the analysis. Table (9) shows the pH values of treated sludge with different CKD addition at different time intervals for both thickened and dewatered sludge.

Table (9): pH Values of Treated Sludge.

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3-5. Determination of Total and Volatile Solids: The total solids and the volatile solids concentrations of the sludge were determined by placing a known volume of each sludge type in an evaporating porcelain dish and following the procedures established in the Standard Methods. Total solids are those remaining after the water is driven off by heating

the sludge sample at (103-105) oC.
Total solids percent are calculated by the following equation (APHA, 1995):
%TS 

A  B 100

C  B

.......................................... (a)
Where:
A = weight of dish plus dried sample, g. B = weight of dish, g.
C = weight of dish plus wet sample, g.
Moisture content is a measure of water in sludge. Percent of moisture content is equal to (1-
% TS). After the total solids were determined, the dried residue was placed in a 550 oC furnace for sixty minutes to drive off the volatile solids. Volatile solid is a measure of the organic matter content of the sludge (Vesilind, 1979). Volatile solid content is usually
quoted as a percentage of the total solide residue as follow (APHA, 1995):

%VS  WVS

WTS

100
………………………….. (b)

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Where:
WVS = weight of volatile solid and
WTS = weight of dry solid.
Table (10) shows the moisture content, total and volatile solids percent for both thickened and dewatered sludge treated with 20 % and 30 % CKD, respectively at different time intervals.

3-6. Analytical Procedure for Fecal Coliform Determination: Bacterial analyses performed in this study included fecal coliforms (FC). Fecal coliform tests were performed according to standard method (SM 9221E) by using the multiple tube procedure (USEPA,

1999). Concentrations of fecal coliform bacteria were reported as the MPN per 100 ml or MPN per gram dry solid. The MPN value is determined from the number of positive tests in a set of five replicate made at three different dilutions. A series of test tubes as shown in figure (2) containing (LTB) broth were inoculated with sewage sludge and incubated for 24

± 2 hours at 35 ± 0.5 oC.

Table (10): Total Solid, Volatile Solid and Moisture Content Of Treated Thickened and Dewatered Sludge.

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After incubation, the presence of turbidity and gas constitutes a positive presumptive test for coliforms. The absence of turbidity and gas requires a second incubation for 24 ± 2 hours at 35 ± 0.5 oC. Failure to produce turbidity and gas (i.e. shades of yellow color) within 48 hours ± 3 hours indicates fecal coliforms are not present. Combination number of positive tubes of the highest dilution and the next two higher dilutions are used to determine the MPN index/100 ml value from a table. This index value is used to compute the MPN /g dry solid according to the following equation (USEPA, 1999; USEPA, 2005):
MPN/g solid = (10×MPN index/100 ml)/(largest volume×% dry solid) ------- (c)

Figure (2): Fecal Coliform Inoculated Test Tubes.

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The results of fecal coliform densities with time for mixes proportion which satisfy the required pH are presented in table (11).

Table (11): Fecal Coliform Densities of Treated Thickened and Dewatered Sludge.

4- Results and Discussion

4.1- This work was conducted to examine the stabilization potential of sewage sludge. Sludge stabilization was performed using CKD as alkaline agent which is an inorganic waste material resulting from the cement industry. The results obtained from this study were analyzed in accordance with the requirements of part 503 of the 40 CFR regulation of the U.S. EPA. The part 503 rule defines two types of biosolids (sludge) with respect to

pathogen reduction: Class A, where, the density of fecal coliform in the sewage sludge

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should be less than 1000 most probable number (MPN) per gram of total solids and class B, where the density of fecal coliform in the sewage sludge should be less than 2 million (MPN) per gram of total solids. Both classes are safe, but additional requirements are necessary with class B materials (USEPA, 2000).
4.2- The pH of the sludge/alkaline materials mixture must be above 12 for 2 hours and subsequently maintained above 11.5 for 22 hours to meet pathogen and vector attraction reduction requirements by alkaline addition. The importance of measuring the pH during alkaline stabilization is based on the relationship of this parameter to pathogen destruction (USEPA, 1999).

4.3- The pH levels of six mixes, of each sludge, have treated with different ratio addition of CKD were monitored at 2, 12, 24, 72, 120 and 168 hours. At 2 hours, the mixes containing thickened sludge with a minimum of 15 % CKD and mixes containing dewatered sludge with a minimum of 25 % CKD attained an initial pH of ≥ 12. At 24 hours, the mixes containing thickened sludge with a minimum of 20 % CKD and mixes containing dewatered sludge with a minimum of 30 % CKD were able to maintain required pH values of ≥ 11.5.

4.4- As shown in figure (3), rapid increases in pH values for both thickened sludge treated with 20 % CKD and dewatered sludge treated with 30 % CKD were occurred during short period of time at the beginning of sludge treatment due to the alkaline CKD addition. The pH of the treated sludge must be maintained at the required level for an adequate time, as mentioned above, to destroy pathogens. The chemical added must provide enough residual alkalinity to maintain a high pH until the product used or disposed of because high pH prevents growth or reactivation of odor-producing and pathogenic organisms. Drop in pH, referred to as pH decay, occurs due to water filtration (leach out) which is the washing out the mixture's residual alkalinity through perforated plate of cylinders' bottom of drying apparatus at drying stage, allowing the pH to drops to 11.5 then gradually decrease to about 11.

4.5- Treating sewage sludge by the addition of sufficient quantity of CKD to raise the pH level to achieve reduction in pathogen resulted in an increase in solid content of the

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sludge. It was necessary to dry the stabilized sludge to moisture content preferably less than
10 % to prevent pathogen re-growth in conjunction with alkaline environment (WEF,

2006). Drying method used in this study consisted of applying air to the resulting mixture. A constructed lab apparatus, as shown previously in figure (1), was designed to this purpose. Where, after conveying sludge mixtures to the cylinders of apparatus, the bottom perforated plate permit sludge dewatering to an intermediate solid level as a cake material. Then, the air which was supplied for 6-8 hours per day was vented through the mixtures of

treated sludge to accelerate drying and contribute to the oxidation of volatile solids.

14

pH

Treated thickened sludge

Treated dewatered sludge

12

10

8

6

0 24 48 72 96 120 144 168

Time (hours)

Figure (3): Ph Versus Time for Thickened Sludge Treated With 20% CKD And

Dewatered Sludge Treated With 30% CKD.

4.6- Vectors which include flies, mosquitoes, rodents, and birds, can transmit pathogens to humans physically or through playing a specific role in the life cycle of a specific pathogen. Reducing the attractiveness of processed solids to vectors reduces the potential for transmitting diseases. Sewage sludge is considered to have undergone adequate vector attraction reduction if sufficient alkali is added to raise the pH level to at least 12 and

maintain it for two hours or maintain a pH of at least 11 for 22 hours (USEPA, 1999).

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Thickened sludge treated with 20 % CKD and dewatered sludge treated with 30 % CKD as shown in table (10) could met the vector attraction requirements with regard to pH level.
Reduction of vector attraction is achieved if the mass of volatile solids in the treated sludge is reduced by at least 38 % (USEPA, 1999). Volatile solids content of sludge is an indication of sludge stability; hence, reduction of volatile solids is used for assessing the effectiveness of a process in stabilizing sludge. Figure (5) shows the change in volatile solid content as percent to the total solid with time for thickened sludge and dewatered sludge treated with 20% and 30% CKD respectively. As shown the rapid decrease in volatile solids percent is due to the CKD addition which is an inorganic solid material. Then, a slow decay in volatile solids percent is observed as a result of oxidation of organic
matter by vent air used for sludge drying.

100

100

90 90

80 80

70 70

60 TS % AND MC % 60

MC % of dewatered sludge

50 TS % of dewatered sludge 50

MC % of thickened sludge

40 TS % of thickened sludge 40

30 30

20 20

10 10

0 0

0 24 48 72 96 120 144 168

Time (hours)

Figure (4) Total Solid Percent and Moisture Content Variation with Time

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90

Percent of Volatile solid

80

Treated thickened sludge

Treated dewatered sludge

70

60

50

40

30

20

10

0

0 24 48 72 96 120 144 168

TIME (hours)

Figure (5): Variation Trend of Volatile Solid Percent versus Time.

4.7- Alkaline amendments using CKD instead of lime have been applied as a dry dust in sufficient quantities to raise the pH level and decrease the moisture content of the sludge to a low level which impedes microbial growth. The EPA part 503 regulations require that fecal coliform density may not exceed 1000 MPN/g of solids if the sludge is to

partially qualify as class A sludge, or less than 2×106 MPN /g of solids if the sludge is to
qualify as class B sludge. These standard limits were compared with the experimental results to determine the CKD dose (addition) needed to meet these criteria.
Fecal coliforms are a group of bacteria that are defined by their ability to use lactose for growth when incubated at elevated temperatures. With respect to biosolids, fecal coliforms are also used as indicators or measure of process effectiveness in reducing microbial densities (WEF, 2006).
Before CKD addition, the fecal coliform densities as illustrated in table (3.10) were
2.43×108 MPN/g of solids for thickened sludge and 8.75×107 MPN/g of solids for dewatered sludge. After CKD addition, the mixes proportion which satisfy the required pH

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were further monitored for fecal coliform densities with time and the results are presented in table (3.14). MPN of fecal coliform per gram of solid have been calculated by the combination of positive tubes for a series of dilutions. About 99 % decrease in fecal coliform count was observed as shown in figure (4.10) after 12 hours upon mixing the samples of sludge with CKD.
Thickened and dewatered sludge treated with 20 % and 30 % CKD, respectively met the requirements for class B after 12 hours. Where, the MPN of fecal coliform was 6.22×105 and 4.0 ×105 per gram of solid for thickened sludge treated with 20 % CKD and dewatered sludge treated with 30 % CKD, respectively. At 120 hours, thickened and dewatered sludge amended with 20 % and 30 % CKD, respectively, met class A requirements with fecal coliform densities about 1000 MPN/g of solid and 850 MPN /g of solid for thickened and
dewatered sludge, respectively.

1000000000

100000000

MPN/g solid

Treated thickened sludge

Treated dewatered sludge

10000000

1000000

Upper limit of class B sludge

100000

10000

1000

Upper limit of class A sludge

100

10

0 24 48 72 96 120 144 168

TIME (hours)

Figure (6): Variation of Fecal Coliform Densities of Treated Sludge with Time.

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Examination of thickened sludge treated with 15 % CKD and dewatered sludge treated with 25 % CKD after 24 hours of treatment showed that the fecal coliform densities of treated sludge achieve class B requirements. Where the fecal coliform density was 5.4×105
MPN/g solid for thickened sludge and 3.72×105 MPN/g solid for dewatered sludge, the
dose needed to meet the pH criteria is higher than the dose needed to reduce the density of fecal coliform, which guarantees that the pH-time criteria set by the US EPA are adequate to meet the fecal coliforms requirement.
Examination of final sludge produced at Al-Rustamiyah treatment plant as illustrated in table (12) which was treated by sun on drying bed shows that the average value of fecal coliform density is 1.49×106 MPN per gram of solid which met the class B sludge according to the US EPA requirements.

Table (12) Characteristics Of Final Sludge Produced At Al-Rustamiyah Plant.

Comparison between fecal coliform densities in treated sludge with CKD and sludge produced at Al-Rustamiyah plant with pathogen reduction requirement of class A and B is shown in figure (7). This figure indicates that treating sludge with CKD could achieve class A requirements while sludge produced at Al-Rustamiyah plant achieve class B
requirements.

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comparison of fecal coliform densities

Treated thick sludge

Treated dewatered

sludg

Class B

Class A

7

6

5

4

3

2

1

0

Alrustamyah

final sludg

Figure (7) Comparison of Log Values of Fecal Coliform Densities

REFERENCES:

1- Al-Najjar, Abdulfattah Ahmed Ameen, (2001), " Evaluation of Sludge Treatment in Al- Rustamiyah Sewage Treatment Plant-3rd Extension", MSc. Thesis, University of Technology.
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4- Burnham, C. Jeffry, Hatfield, Nancy, Bennett, F. Gary and Logan, J. Terry, 2000, " Use of Kiln Dust With Quicklime for Effective Municipal Sludge Pasterization and Stabilization With the N-Viro Soil Process ", www.patentstorm.us/patents/5997599.

5- Christine, L. Bean; Jacqueline, J. Hansen; Aarone, B. Margoline and Giovanni Widmer, (2007), " Class B Alkaline Stabilization to Achieve Pathogen Inactivation", Int. J. Environ. Res. Public Health, Vol. 4, No. 1, www.mdpi.org/ijerph/papers/ijerph2007010009.pdf.
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7- Investment Department, 2007, " Investment Opportunities to Implement New Cement
Plants in Iraq", Ministry of Industry and Minerals, Republic of Iraq.
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16- USEPA, 2000, " Biosolids Technology Fact Sheet – Alkaline Stabilization of Biosolids", www.epa.gov/region8/biosolids/biosolidsdown/BiosolidsTechSheetAlk.pdf.
17- USEPA, 2005, " Method 1680: Fecal Coliforms in Sewage Sludge by Multiple Tube Fermentation Using Lauryl Typtose Broth (LTB) and EC Medium", EPA-821/R-04-026, Office of Water, USEPA.
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