Disposal of Sludge with Solid Wastes in Aerobic and Anaerobic Landfill Areas

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1 CONTACT Günay Kocasoy Turkish National Committee on Solid Wastes Bogazici University 34342, Bebek, Istanbul, TURKEY Tel: Fax: Disposal of Sludge with Solid Wastes in Aerobic and Anaerobic Landfill Areas Günay Kocasoy, Gıyasettin Güneş, Turkish National Committee on Solid Wastes, Bogaziçi University EXECUTIVE SUMMARY Increase in the population as well as the personal income and the changes in habits and the way of living, industrialization and the production of new products have increased the amount and the types of the solid wastes generated. The strict regulations about the treatment of the wastewater for the protection of environment on the other hand caused the generation of huge amount of sludge which is considered as hazardous solid waste and should be handled properly. While landfilling of the municipal solid waste has been the most popular method used for the removal of the solid wastes, there are strict limitations for the disposal of sludge in the landfilling areas. In order to compare the stabilization of the municipal solid wastes by mixing with different amount and types of sludge under aerobic and anaerobic conditions and the effect of the addition of the yeast on the decomposition rates of the organic materials and the generation of the biogas. In the research conducted different types of sludge was mixed with municipal solid wastes at different ratios and loaded into the reactors simulating the anaerobic and aerobic landfills. One of the reactors in each set was loaded only with solid waste and monitored as a control reactor. Solid waste used in the research was taken from the Kemerburgaz Sanitary Landfill and the sludge used was taken from the different units such as primary, secondary clarifier tanks and the belt-press of the domestic wastewater treatment plant of Izmit city. The research was conducted at two stages. In the first stage the four aerobic reactors were operated by applying air flow and recycling the leachate generated while the other four anaerobic reactors were operated at anaerobic landfilling conditions up to 55 th day. After 55 th day, in the second stage yeast saccharomyces cerevisiae solution was added to all the reactors except the control reactors to enhance the biological decomposition.

2 The reactors were placed in two aquariums and the water inside was heated to 34 0 C. The compressors, operated 5 minutes every day, generated 2 L air per minute and distributed air in the aerobic reactors. Approximately 50 ml leachate samples were taken and analyzed every week and then 50 ml of water was added to the aerobic reactors. On the other hand 100 ml of water was added to each anaerobic reactor at every month. Leachate generated at the aerobic reactors were recycled at every two weeks depending on the determined moisture content of the mixture in the reactors. The ph and ORP were measured at every two days. The leachate samples were analyzed for COD twice a week and for alkalinity, orthophosphate, sulphate, total Kjeldahl nitrogen and chloride once a week. The biogas generated at the anaerobic reactors was followed up and the volume and the methane content of the generated gas was monitored. The results of the research indicated that the 1:4 ratio of sludge to municipal solid waste was the optimum ratio for the stabilization of the solid wastes both in the aerobic and anaerobic reactors. The volume of the leachate generated at the aerobic reactors was less than the anaerobic reactors while the decomposition and stabilization rate was higher. The cumulative gas production at the anaerobic reactors reached up to ml while the percentage of the methane of the generated gas was as high as 64 per cent. The results of the research indicate that landfilling of solid wastes with certain amount of sludge will speed up the decomposition rate of organic materials and extend the operational life of sanitary landfill acting as a bioreactor for composting wastes while the amount and the strength of the leachate generated will be low. INTRODUCTION Increase in the population as well as the personal income and the changes in habits and the way of living, industrialization and the production of new products have increased the amount and the types of the solid wastes generated. The strict regulations about the treatment of the wastewater for the protection of environment on the other hand caused the generation of huge amount of sludge which is considered as hazardous solid waste and should be handled properly. While landfilling of the municipal solid waste has been the most popular method used for the removal of the solid wastes, there are strict limitations for the disposal of sludge in the landfilling areas. The methodology applied and the results obtained are explained in the following sections. METHODOLOGY Experimental Set-up The experimental set-up consisted of four anaerobic reactors, eight gas holders, two aquariums and heating system. The set-up simulating the aerobic landfill consisted of four aerobic reactors, four air compressors and distributor pipes, two pumps, a leachate container, four air diffusers, an aquarium and a heating system. The reactors with a height of 40 cm and a radius of 40 cm were made of plexyglass and each of them had 12.5 liter usable volume.

3 The general views of the set-up of the anaerobic and aerobic reactors are given at Figures 1 and 2 respectively. F E A B C D K G H I J A : Reactor 1 F : Heaters K : Aquarium B : Reactor 2 G : Gas holder 4 C : Reactor 3 H : Gas holder 3 D : Reactor 4 I : Gas holder 2 E : Air compressor J : Gas holder 1 Figure 1 General view of the anaerobic reactors F E L K G H I J A B C D A : Reactor 1 E : Air diffuser I : Air compressor 3 B : Reactor 2 F : Heaters J : Air compressor 4 C : Reactor 3 G : Air compressor 1 K : Aquarium D : Reactor 4 H : Air compressor 2 L : Plastic cover Figure 2 General view of the aerobic reactors and air compressors Materials Used In the research raw sludge of different units (primary and secondary clarifiers, belt press) of the treatment plants of the domestic wastewater of Izmit city and the municipal solid wastes taken from the Sanitary Landfill at Kemerburgaz, Istanbul were used. The composition and the heavy metal concentrations of the solid waste taken from the Kemerburgaz Landfill area are given in Tables 1 and 2 respectively.

4 Table 1 Composition of the solid waste used in the reactors Component Value (%) organic materials 52 paper and cardboard 8.2 plastics and nylon 9.4 glass 4.2 textile 4.3 metals 2.5 baby diapers 4.7 others 14.7 moisture 61.2 Table 2 Heavy metal concentrations of the solid waste samples filled into the reactors Parameter Concentration (mg/l ) Limit Values (mg/l ) (The Ministry of Environment and Foresty, 1991) Cu Ni Pb Cd < Cr Zn As Hg < The composition and the moisture content of the sludge filled in the reactors are given at Tables 3 and 4. Table 3 Heavy metal concentrations of the sludge samples Parameter Primary Clarifier Secondary Clarifier Belt Press Limit Values ( mg/l ) ( mg/l ) ( mg/l ) ( mg/l ) Cu Ni Pb Cd Cr Zn Fe Table 4 Moisture content of the sludge samples used in the study Primary Clarifier Sludge Secondary Clarifier Sludge Belt Press Sludge Reactors (%) (%) (%) reactor reactor reactor reactor

5 The composition of the yeast solution used to improve the decomposition and to shorten the degradation period of the processes is given in Table 5. Table 5 Composition of aqueous feed solution (Barnett et al., 1989) No Compound Concentration ( mg/l ) 1 CaCl K2HPO (NH4)2SO glucose Experimental Procedure The four aerobic and anaerobic reactors were loaded with the municipal solid wastes. Sludge was added to the three reactors in the ratios according to the values suggested by EPA (USEPA, 1978). One of the reactors to which no sludge was added, was monitored as the control reactor. Water is added to each reactor according to the moisture contents of the sludge and solid wastes. No compaction was applied after the reactors were filled. The loading conditions of the reactors are given at Table 6. Reactor Table 6 Loading conditions of the reactors Sludge Type Sludge to Waste Ratio Moisture Content (%) Solid Waste Added (Wet, g) Water Added ( ml) aerobic reactor 1 no sludge aerobic reactor 2 primary clarifier sludge 1/ aerobic reactor 3 secondary clarifier sludge 1/ aerobic reactor 4 belt press sludge 1/ anaerobic reactor 1 no sludge anaerobic reactor 2 primary clarifier sludge 1/ anaerobic reactor 3 secondary clarifier sludge 1/ anaerobic reactor 4 belt press sludge 1/ The water in the aquariums in which the aerobic and anaerobic reactors were placed was heated up to 34 0 C and air diffusers circulated water in order to distribute heat evenly in the aquarium. Air compressors, operated 5 minutes every day, generated 2 liter air per minute and distributed it in the aerobic reactors. Approximately 50 ml leachate samples to be analyzed were taken from each aerobic reactor every week and then 50 ml water was added to the reactor. On the other hand, 100 ml water was added to each anaerobic reactor at every month. The leachate generated at the aerobic reactors were recycled at every two weeks, depending on the determined moisture content of the solid wastes in the reactors. After the 15 th day of the research, moisture contents of the aerobic reactors were in the range of per cent, which was sufficient for the survival of the microorganisms. After the 45 th day of the research, the moisture contents of the aerobic reactors were decreased to 40 per cent, therefore 100 ml water was added to each aerobic reactor. No buffering was made during this first stage of the research.

6 The parameters ph and ORP was measured at every two days, COD was analyzed twice a week, alkalinity, orthophosphate, sulphate, total Kjeldahl nitrogen and chloride were analyzed once a week. The heavy metal analysis were conducted twice a month and the gases generated at the anaerobic reactors were analyzed once a week. In the second stage after the 55 th day of the research, the yeast saccharomyces cerevisiae stock solution was added to the aerobic and anaerobic reactors 2, 3 and 4 to enhance the biological decomposition. After the 75 th day of the research, the moisture of the contents of the aerobic reactors were lower than 40 per cent. Therefore 100 ml water was added to each aerobic reactor again. At the end of the research, the moisture of the contents of the aerobic reactors were in the range of per cent which was enough for the survival of the microorganisms. The settlement of the wastes in all reactors were monitored during the research period. The settlement in the aerobic reactors began at the 9 th day of the research while the settlement in the anaerobic reactors were observed after the 45 th day of the research. The settlement in the aerobic reactors were faster than the anaerobic ones. The volume of the leachate generated in the aerobic and anaerobic were measured and the leachate samples were analyzed for the same parameters at the periods as it was in the first stage of the research. The analysis of the generated gas was analyzed at the end of the research period at gas chromatography. RESULTS AND DISCUSSION The results of the research can be summarized as: The ph values of the leachate of the anaerobic reactors were low because of the accumulation of the volatile acids during the first stage. After the yeast addition in the second stage, low ph values were observed in the Reactors 2, 3 and 4 until the 94 th day and then it started to increase slightly due to the conversion of the volatile fatty acids by the bacteria. The ph values of the leachate generated at the aerobic reactors having sludge are lower than the Control Reactor without sludge, because of the acid formation from the decomposition of the organic substances. By the utilization of the organic acids, the ph of the leachate of the aerobic reactors reached to neutral ph during the first stage. After the addition of yeast, the ph of the leachate started to increase slightly. The ORP values of the anaerobic reactors initially were positive indicating the aerobic conditions in all reactors. By the depletion of the oxygen, negative ORP values were observed in the reactors. After the yeast addition the ORP values continued to be negative. On contrast to the anaerobic reactors, the ORP values of the leachate of the aerobic reactors (Reactors 2 and 3) were negative indicating the existence of the anaerobic conditions. Accumulation of the organic acids and insufficient aeration were responsible for these negative values. By time the ORP values of the leachate of all aerobic reactors were increased and reached to positive values at the end of the first stage. After the addition of the yeast solution, the ORP values continuously increased till the end of the research.

7 The COD concentration of the leachate of the anaerobic Reactors 2, 3 and 4 was higher than the Control Reactor throughout the first stage of the research. No COD removal was observed during this stage. After the addition of the yeast, the COD did not change significantly until the 77 th day, and then it started to decrease continuously till the end of the study. The COD removal efficiencies of the Reactors 1, 2, 3 and 4 were 40, 60, 55 and 66 per cent respectively. The reactors to which yeast was added had a higher COD removal than the Control Reactor. In contrast to the anaerobic reactors, a decreasing trend was observed in the COD concentrations of the leachate of the aerobic reactors in the first stage. COD removal efficiencies of the Reactors 1, 2, 3 and 4 were 52, 80, 65 and 74 per cent respectively. During the second stage, the decreasing trend was continued in the COD concentrations. By the addition of the yeast, the COD removal efficiency was increased. The COD removal efficiency of the Reactors 1, 2, 3 and 4 were 67, 68, 76 and 82 per cent respectively. Aerobic reactors had higher removal efficiencies than the anaerobic reactors. The alkalinity values of the leachate of all the anaerobic reactors were high due to the presence of the high volatile acid concentrations. After the addition of the yeast, the alkalinity values of the leachate of the Reactors 2, 3 and 4 remained constant until the 79 th day and then fluctuated. Throughout the study, the alkalinity values of the leachate of the aerobic reactors were higher than the ones of the anaerobic reactors. The heavy metal concentrations of the leachate of the aerobic reactors were higher than the anaerobic reactors due to the high oxidizing conditions during the first stage. At the second stage, the metal concentrations of the leachate of the anaerobic reactors fluctuated while they, except chromium, continuously measured until the end of the research. The cumulative gas productions at the anaerobic Reactors 1, 2, 3 and 4 were 26530, 41170, and ml respectively. It was observed that the Reactor 4 had a higher cumulative gas production than the others. The initial percentage of methane of the gases generated at the anaerobic Reactors 1, 2, 3 and 4 was low during the first stage. After the yeast addition, the methane content of the gases increased gradually. The maximum methane percentage of the gases of the Reactors 1, 2, 3 and 4 were 34, 58, 56 and 64 per cent respectively. Addition of the yeast supplied the necessary substrates for the methanogenic bacteria. CONCLUSION The purpose of the study was to compare the stabilization of municipal solid wastes by mixing different ratios and types of sludge and the effect of the yeast addition on the decomposition rates of organic materials under aerobic and anaerobic conditions. The following conclusions have been obtained upon the completion of the research:

8 Co-disposal of sludge and solid waste is an effective technique for the stabilization of the solid wastes in aerobic reactors. The aerobic and anaerobic reactors with sludge had higher COD, phosphate and total Kjeldahl nitrogen removal efficiency than the Control Reactor without sludge. The stabilization of solid wastes in the anaerobic reactors takes longer time than the aerobic reactors. Anaerobic Reactor 1 which was loaded with the belt-press sludge and solid wastes at the ratio of 1:4 had maximum COD, phosphate, sulphate and total Kjeldahl nitrogen removal efficiencies. The same is true for the Aerobic Reactor 4. The highest ratio of 1:4 is the optimum sludge (belt-press) to solid waste for both the aerobic and anaerobic reactors. All aerobic reactors had higher COD, phosphate and total Kjeldahl nitrogen efficiencies than the anaerobic reactors. The highest phosphate removal was obtained at the aerobic Reactor 3 which was loaded with secondary settling sludge and solid wastes at the ratio of 1:7. Yeast addition improved the rate of biological decomposition by converting complex organic materials to simple forms by microorganisms. The heavy metal concentrations of leachate of the anaerobic reactors are lower than the heavy metal concentrations of leachate of the aerobic reactors. The methane content of the anaerobic reactors with sludge and yeast is higher than the Control Reactor without sludge and yeast. The highest methane content was observed at the gas generated from the Reactor having belt-press sludge and solid wastes in the ratio of 1:4. The settlement of the wastes in the aerobic reactors is faster than the anaerobic reactors. REFERENCES Barnet, J. A., Payne R. W., Yarrow D.; (1989); Yeasts: Characteristics and Identification; Second Ed.; Cambridge University; England. Turkish Ministry of Environment and Forestry Home Page; U.S. Environmental Protection Agency; (1978); Municipal Sludge Landfills: Process, Design Manual; EPA-625/ SW-705; Office of Solid Waste, Washington D.C.