dr. mohammed hamoda - composting of mixtures of municipal solid wastes and sewage sludge in kuwait

Composting of Mixtures of Municipal Solid Waste and Sewage Sludge in Kuwait

M.F. Hamoda , Ph.D., P.EngM.F. Hamoda , Ph.D., P.Eng..

Professor of Environmental Professor of Environmental EngineeringEngineering

Kuwait University, KuwaitKuwait University, Kuwait

ContentsContents

IntroductionIntroduction Materials and MethodsMaterials and Methods Results and DiscussionResults and Discussion ConclusionConclusion

IntroductionIntroduction

MSW quantities increase by about 5% every MSW quantities increase by about 5% every year.year.

High organic content of MSW (food component High organic content of MSW (food component about 55%).about 55%).

Excessive production of municipal wastewater Excessive production of municipal wastewater sludgesludge

High cost of land and limited suitable sites for High cost of land and limited suitable sites for landfilling.landfilling.

Increased recycling of metals, plastics and Increased recycling of metals, plastics and glass.glass.

Potential market for compost to reclaim desert Potential market for compost to reclaim desert land in the GCC countries.land in the GCC countries.

Composition of MSW in KuwaitComposition of MSW in Kuwait

Food 55%

10%

Paper 8%

5%

Glass 4 %

9%

Materials and MethodsMaterials and Methods

Waste CharacteristicsWaste Characteristics MethodsMethods In-Vessel UnitsIn-Vessel Units Experimental Set-UpExperimental Set-Up

Characteristics of mixed MSW Characteristics of mixed MSW and Sewage Sludgeand Sewage Sludge

Highly organic ( 75%)Highly organic ( 75%) MSW is mainly food waste (55%)MSW is mainly food waste (55%) Sewage is primarily domestic and Sewage is primarily domestic and

sludge is thickened (15 % solids)sludge is thickened (15 % solids) MSW is shredded and screened MSW is shredded and screened

(particle size : 5mm)(particle size : 5mm) Moisture content ( M.C.=60%)Moisture content ( M.C.=60%) Carbon/Nitrogen ratio (C/N=20)Carbon/Nitrogen ratio (C/N=20)

ParameterMean ValueStandard

Error of the

Mean

pH7.70.15

Moisture Content (%) 54.12.24

Organic Matter @ 550 oC

(%)

61.518.67

Total Organic Carbon

(%)

34.20.63

Total Kjeldahl Nitrogen

(%)

6.10.12

C:N Ratio5.60.15

Table 1. Chemical composition of dewatered MSS sample


Error of the

Mean

pH7.70.15



(%)

61.518.67


(%)

34.20.63


(%)

6.10.12

C:N Ratio5.60.15

Table 1. Chemical composition of dewatered MSS samples


Error of the

Mean

pH5.30.23



(%)

77.933.10


(%)

45.21.80


(%)

2.470.28

C:N Ratio18.33.09

Table 2. Chemical composition of MSW samples

MSW : MSS ( Ratio)

Moisture Content (%)

C/N (Ratio)

Volatile Solids (%)

1:1

54.0615.2571.28

2:1

56.7816.3372. 35

4:1

58.1217.3674.12

Table 3. Characteristics of mixtures of municipal solid wastes and sewage sludges

In-Vessel Experimental UnitIn-Vessel Experimental Unit

In-vessel UnitsIn-vessel Units

Four identical in-vessel units were used. Each Four identical in-vessel units were used. Each unit was made of a double wall, 364 grade unit was made of a double wall, 364 grade stainless steel, cylindrical shape drum and stainless steel, cylindrical shape drum and was supported horizontally by 1100 mm was supported horizontally by 1100 mm height steel frame. The dimensions of each height steel frame. The dimensions of each vessel were 600 mm inside diameter, 764 mm vessel were 600 mm inside diameter, 764 mm outside diameter, and 1000 mm length with outside diameter, and 1000 mm length with capacity of 200 L. Each drum was capacity of 200 L. Each drum was electrically- driven by a motor and was electrically- driven by a motor and was insulated by a water jacket which was heated insulated by a water jacket which was heated with four 1200 watt heating bars, two from with four 1200 watt heating bars, two from each side. Each cylindrical vessel was fully each side. Each cylindrical vessel was fully insulated along its circumference with insulated along its circumference with rockwool insulation to minimize heat loss.rockwool insulation to minimize heat loss.

In-vessel unitsIn-vessel units

The composting vessels were connected to an air The composting vessels were connected to an air compressor through an air flow meter and regulating compressor through an air flow meter and regulating valve to control the air flow. The air was supplied into valve to control the air flow. The air was supplied into the vessel via an air pocket made of 3 mm opening the vessel via an air pocket made of 3 mm opening grill in the bottom of the vessel to ensure proper air grill in the bottom of the vessel to ensure proper air distribution throughout the vessel and was vented distribution throughout the vessel and was vented through an outlet 25 mm diameter pipe. The contents through an outlet 25 mm diameter pipe. The contents of the reactor were mixed by rotating the drum once of the reactor were mixed by rotating the drum once a day for 15 minutes (6 rotations/minute) and were a day for 15 minutes (6 rotations/minute) and were mixed manually before sample withdrawal. The mixed manually before sample withdrawal. The temperature of the material inside the vessels was temperature of the material inside the vessels was continuously monitored by a thermocouple inserted continuously monitored by a thermocouple inserted inside the center of the material and was recorded by inside the center of the material and was recorded by an on-line computer system. an on-line computer system.

Windrow Composting PileWindrow Composting Pile

Experimental Set-upExperimental Set-up

WaterCooler

Computer

Compressor

Water Pump

In-vessel Composting Unit

Sludge Temp. Probe

Air Vent

Air Filter / umidifier

ElectricalHeaters/Off

Results and DiscussionResults and Discussion

Process performance was evaluated as Process performance was evaluated as follows:follows:

Reductions in: VS and OCReductions in: VS and OC Other Parameters: pH, C/NOther Parameters: pH, C/N Kinetic AnalysisKinetic Analysis Statistical AnalysisStatistical Analysis

3.1 Reduction in Volatile Solids 3.1 Reduction in Volatile Solids during Composting of MSWduring Composting of MSW

3.2 Reduction in Volatile Solids 3.2 Reduction in Volatile Solids during Co-composting of Mixtures during Co-composting of Mixtures

of MSW: MSS (2:1)of MSW: MSS (2:1)

3.3 Reduction in Volatile Solids 3.3 Reduction in Volatile Solids during Co-composting of Mixtures during Co-composting of Mixtures

of MSW:MSS (4:1)of MSW:MSS (4:1)

3.4 Reduction in Organic Carbon 3.4 Reduction in Organic Carbon during Composting of MSWduring Composting of MSW

3.5 Reduction in Organic Carbon 3.5 Reduction in Organic Carbon during during

Co-composting of Mixtures of Co-composting of Mixtures of MSW:MSS (2:1) MSW:MSS (2:1)

-12

0

12

24

36

0 5 10 15 20 25 30

Time, Days

Av

. OC

Re

d.,

%

Temp. 45 C

Temp. 65 C

Windrow ≈ 35 ºC

3.6 Reduction in Organic Carbon 3.6 Reduction in Organic Carbon during during

Co-composting of Mixtures of Co-composting of Mixtures of MSW:MSS (4:1)MSW:MSS (4:1)

3.73.7 Variations in C/N Ratio during Variations in C/N Ratio during Composting of MSWComposting of MSW

3.8 Variations in C/N Ratio during3.8 Variations in C/N Ratio duringCo-composting of Mixtures of Co-composting of Mixtures of

MSW:MSS (2:1)MSW:MSS (2:1)

3.93.9 Variations in C/N Ratio during Co-Variations in C/N Ratio during Co-composting of Mixtures of MSW:MSS composting of Mixtures of MSW:MSS

(4:1)(4:1)

Kinetic Analysis of VS ReductionKinetic Analysis of VS Reduction

To waste biodegradability and to measure the loss of organic To waste biodegradability and to measure the loss of organic matter, expressed as volatile solids during composting , it was matter, expressed as volatile solids during composting , it was necessary to determine process kinetics using data obtained in necessary to determine process kinetics using data obtained in this study under controlled temperature. The plots shown in this study under controlled temperature. The plots shown in the following figures and the correlation coefficient (Rthe following figures and the correlation coefficient (R22) ) obtained as shown in Table suggest that the degradation of obtained as shown in Table suggest that the degradation of organic matter during MSW composting at the mesophilic organic matter during MSW composting at the mesophilic temperature range as a function of time follows a first-order temperature range as a function of time follows a first-order kinetics expressed as:kinetics expressed as:

dC/dt = -kCdC/dt = -kC where C is the biodegradable volatile solids at any time, t is where C is the biodegradable volatile solids at any time, t is

the time in days, k is the reaction rate constant (day-1)the time in days, k is the reaction rate constant (day-1) By integrating this equation and letting C = Co at time = 0 By integrating this equation and letting C = Co at time = 0

gives:gives:

ln C/ Co = - ktln C/ Co = - kt

3.10 Kinetic Analysis for In-Vessel 3.10 Kinetic Analysis for In-Vessel VS Reduction of MSW at 15 VS Reduction of MSW at 15 ooCC

3.11 Kinetic Analysis for In-Vessel 3.11 Kinetic Analysis for In-Vessel VS Reduction of MSW at 45 VS Reduction of MSW at 45 ooCC

3.12 Kinetic Analysis for Windrow 3.12 Kinetic Analysis for Windrow VS Reduction of MSW at 20 VS Reduction of MSW at 20 ooCC

Table 4. Kinetic rates (k) for VS reductions during in-vessel composting of MSW

Temp, ºC

1 5

2 5

3 5

4 5

k, d-1

0.0042

0.0052

0.0063

0.0103

R 2

0.882

0.878

0.911

0.958

k = first-order kinetic rate constant R2 = correlation coefficient

ConclusionsConclusions

1. Co-composting of mixtures of MSW and MSS at various proportions was more effective than composting of these wastes when treated separately. Reductions of up to 38% of VS were obtained during 30 days of co-composting of MSW and MSS mixtures .2. In-vessel composting of wastes at controlled temperatures is more effective than windrow piles where temperatures can not be controlled effectively.3. Optimum operating conditions for temperature is 45 oC and for MSW:MSS mixture is 2:1.4. A first-order model was suitable to describe the composting process kinetics.

dr. mohammed hamoda - composting of mixtures of municipal solid wastes and sewage sludge in kuwait

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