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WASTE 2004, UK

Faculty of Environmental Sciences and Process Engineering Chair of Management Bernard Fei -Baffoe , G ünter Busch, Marko Sieber Brandenburg University of Technology, Siemens -Halske -Ring 8, 03046, Cottbus , Germany

ANAEROBIC DIGESTION OF UNSORTED

Motivation In low -income economies, the possibility of having waste being sorted a t source to facilitate effort seems impossible. However, in organized and high income residential communities th is practice may have a high chance of success, but the waste genera ted from these areas constitutes a small fraction compared to th at from low and middle -income residential communities. Landfilling is either an unacceptable or at best a temporary solution to dispos al of these . Results of a systems analysis of this proble m suggest that conversion of the biodegradable fraction of thes e waste via coupled with gasification represents the mos t economic and environmentally attractive option for their treat ment.

Main objective Value Parameter Expt Expt Expt For the three repeated tests carried To utilize organic potential of unsorted municipal solid waste t o produce 1 2 3 out, the organic material and reduce organic matter in the bulk waste to minimize Total solids (% ) 60.69 60.99 48.94 (biodegradable, plastics etc) was in environmental pollution caused by (dumping sites). Ignition loss (% TS) 55.13 40.47 44.72 the range of 40 – 60 % of the total C:N 41.78 39.48 32.88 solid of the solid waste used for the pH 5.84 6.45 5.74 experiments. This fraction constitutes Investigation the biodegradable part of the waste, Good biodegradable (%TS) 40.77 25.04 28.54 To realize the above objective, it is essential to carry out the following investigations which was 25 – 42% TS (Table 2). Organic total solids (%) 33.45 24.68 21.89  Biogas production from the organic fraction in the presence of other impurities in a single stage batch anaerobic digester. And reliability of the digestio n process. Table 2 Characteristics of UMSW used in the experiment  Testing the Effect of inoculum – substrate composition on digestion of the organic fraction of the waste 70 60  Performing quantitative and qualitative study on biogas producti on 50 40 According to the se compositions three separate experiments (repeated) were 30 Snapshot view composition (dry 20 basis) of the mixed waste obtained carried out (Table 2 ). Percentage carried out (Table 2 ). 10 through manual sorting (Figure 3). 0 Rest Paper Plastic Glass Metal Experiments Seed material Feedstock Fraction 1 Fresh inoculum Fresh unsorted solid waste Bioleachate from 2 previous test Fresh unsorted solid waste Figure 3 Waste composition 800 Ex pt 1 Bioleachate from Part of digestate from previous test + Ex pt 2 3 previous test fresh unsorted solid waste (1:4) 600 Ex pt 3

Table 1 Characteristics of each experiment The methane yields from the experiments 400 carried out are between 190 and 680 l/kg Anaerobic Digestion and Operation good biodegradable (Figure 4). 200 biodegradable) The system is a one -stage process having the entire processes, hydrolysis/ and the

The system is a one -stage process having the entire processes, hydrolysis/ acidogenesis and the (l/kg good Methane acetogenesis /methanogenesis taking place simultaneously in one reactor. 0 The hydrolysis/ acidogenesis and acetogenesis /methanogenesis processes takes place within the 1 3 5 7 9 11 13 15 17 19 21 23 waste bed and in the leachate . The hydrolysis is achieved by spraying the waste bed with Time (day) biologically active liquid. The waste is acidified and the soluble components are l eached out. Figure 4 Methane production rate The resulting percolate is recycled over and over the waste be d to promote further leaching 60 1400 and sufficient moisture for bacterial growth thereby increasing degradation. Exp t 1 Exp t 1 Exp t 2 1200 50 Exp t 2 Expt 3 1000 Exp t 3 40 800 30 600 20 400 biodegradable) Biogas (l/Kg TOS) (l/Kg Biogas (l/kg good Biogas 10 200 0 0 1 3 5 7 9 11131517 192123 1 3 5 7 9 11131517192123 umsw Time (day) Time (day)

Figure 5 Gas production rate through time at three digester compositions leachate Gas production rate of 200 – 1200 l biogas per unit mass of good biodegradable and 10 – 60 l gas flow pressure meter pump biogas per unit TOS respectively of organic waste demonstrates t he efficiency of the system (Figure 5). The unsorted solid waste used in the study , contains non degradable volatile materials such as perforated plastics which will contribute to the volatile solid content of the waste, but will not yield any gas. plate Figure 1 Schematic representation of the single -stage batch reactor Conclusion Energy recovery can play very vital role in the management and the disposal of unsorted municipal Results and Discussion waste. Energy recovery will produce a reduced stabilized residue where the non -degradable Due to non -availability of anaerobically degraded (stabilized ) waste at the start of the fractions like plastics , glass and metals can be removed and the resulting residue be used for land experiments, the first batch of unsorted waste was degraded by mixing with sludge from application after short aerobic post treatment . mesophilic pig dung digester in the ratio of 1:2 by weight. Part of the stabilized waste from this The single -stage process was investigated as a means of starting up anaerobic degradation of experiment was used to start up the degradation of subsequent fresh bed of waste as described in unsorted municipal solid waste. The single stage digester was chosen because it is a simple table 1. The kinetics of degradation progressively increased during the first three experiments technology which could be feasibly be scaled up simply using affordable materials. The study carried which it reached a maximum . Subsequent experiments exhibited similar maximum kinetics . Plots out have demonstrated that the process enables rapid start up of the degradation. At the end of of the gas production rate of the runs during the period when the degradation kinetics was digestion, the biogas potential of the remaining digestate has been reduced drastically. increasing are shown in figure 4 and 5. Table 2 and figure 3 lists the chemical and physical The results obtained shows the need for further improvement in weight loss through pretreatment of characteristics of the solid waste before degradation. the waste to optimize gas yield.

Further Information: BTU Cottbus, Siemens -Halske -Ring 8, 03046, Cottbus, Chair of , Fei -Baffoe Bernard, E -mail: [email protected]