Appropriate Rural Technology Institute Tanzania (ARTI-TZ) Anaerobic Digestion of Canteen Waste at a Secondary School in Dar es Salaam, Tanzania Tenzing Gyalpo, March 2010 Supervised by Yvonne Vögeli (Eawag), Prof. G. Kassenga and Dr. S. Mgana (both Ardhi University) Tenzing Gyalpo [email protected] Eawag (Swiss Federal Institute of Aquatic Science and Technology) Sandec (Department of Water and Sanitation in Developing Countries) P.O. Box 611 8600 Dübendorf Switzerland Tel. +41 (0)44 823 52 86 Fax +41 (0)44 823 53 99 Internet: www.eawag.ch; www.sandec.ch Bibliographic reference: Gyalpo T (2010). Anaerobic digestion of canteen waste at a secondary school in Dar es Salaam, Tanzania. Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland. Cover pictures: Project information (top left), Institutional ARTI biogas plants (top right), Open dumping site at the school (bottom left), Biogas stove with stiff maize paste (bottom right) (Pictures: Tenzing Gyalpo) Table of Content SUMMARY I ACKNOWLEDGEMENT III LIST OF FIGURES IV LIST OF TABLES V ABBREVIATIONS VI 1 INTRODUCTION 1 1.1 OBJECTIVES 1 1.2 COMPACT BIOGAS SYSTEMS AT AZANIA SECONDARY SCHOOL 2 2 MATERIALS AND METHODOLOGIES 3 2.1 OPERATION OF THE BIOGAS PLANTS AT AZANIA SECONDARY SCHOOL 3 2.2 GAS PRODUCTION AND COMPOSITION 3 2.3 SAMPLE COLLECTION 4 2.4 ANALYSIS OF FOOD WASTE AND EFFLUENT 4 2.5 MONITORING OF THE COOKING PRACTICE 5 2.6 COST-BENEFIT ANALYSIS 5 2.7 INTERVIEWS WITH OTHER INSTITUTIONS WITH ARTI BIOGAS PLANTS 5 3 RESULTS 6 3.1 OPERATION OF THE AZANIA PLANTS 6 3.2 GAS COMPOSITION, PRODUCTION, AND AVAILABILITY 6 3.2.1 BIOGAS COMPOSITION 6 3.2.2 BIOGAS PRODUCTION 7 3.2.3 BIOGAS AVAILABILITY 8 3.3 MONITORING OF THE COOKING PRACTICE IN THE KITCHEN 9 3.3.1 TIME AND ENERGY CONSUMPTION 11 3.4 WASTE PRODUCTION 12 3.5 DECOMPOSITION OF ORGANIC WASTE 13 3.6 INDICATORS OF PROCESS STABILITY 14 3.7 EFFLUENT QUALITY 15 3.8 OPERATIONAL PARAMETERS 17 3.9 COST-BENEFIT ANALYSIS 18 3.10 INSPECTION OF OTHER INSTITUTIONAL PLANTS 20 4 DISCUSSION 22 4.1 ON-SITE MEASUREMENTS 22 4.2 LABORATORY RESULTS 22 4.3 COMPARISON WITH LOHRI (2009) 22 4.4 TECHNICAL ASPECTS 23 4.5 ECONOMIC ASPECTS 25 4.6 SOCIAL ASPECTS 25 5 CONCLUSIONS AND RECOMMENDATIONS 27 5.1 CONCLUSIONS 27 5.2 RECOMMENDATION FOR AZANIA AND OTHER INSTITUTIONS 28 REFERENCES 30 APPENDIX 31 A AZANIA SECONDARY SCHOOL 31 A.1 TEST OF A DIFFERENT GAS BURNER 31 A.2 IMPLEMENTATION OF NEW PIPE SYSTEM 32 B ARTI TZ 34 B.1 CURRENT ACTIVITIES CONCERNING BIOGAS PLANT PROMOTIONS 35 B.2 FOLLOW UP ON RECOMMENDATIONS MADE BY CHRIS LOHRI IN 2008 36 B.3 CBS MANUAL FOR THE INSTITUTIONAL PLANT (4000L/3000L) 39 B.4 PRICE LIST OF THE BIOGAS PLANTS AND EQUIPEMENTS 43 C QUESTIONNAIRE REGARDING ARTI COMPACT BIOGAS PLANT 44 D LABORATORY DATA 46 Summary Inadequate solid waste management is gaining importance as one of the most important threats to public health and environmental quality in economically developing countries. As the organic fraction accounts for the larger part of the municipal solid waste, anaerobic digestion thereof would be an appropriate solution to reduce the amount of waste dumped and/or landfilled. After the evaluation of the suitability of the ARTI Compact biogas system for kitchen waste on household level by Lohri (2009), this study focuses on the technical and operational aspects of institutional biogas plants. Azania is the first secondary school in Tanzania which is equipped with three ARTI biogas plants to treat their food waste (digester tank 4000 L, gas holder 3000 L). These plants as well as the training of the operators and cooks were funded by Costech (8’850’000 TShs, 6’404 US Dollars, 18.03.10). The unstirred floating-dome digesters were fed with the canteen waste (26% TS, 92% VS). Two biogas plants (plant 2 and 3) were fed with 8 kg food waste per day whereas for one biogas plant (plant 1) the daily load should be increased from 8 kg/d to 20 kg/d. Though, 20 kg/d could not be reached due to lack of food waste. The analysis showed that the reduction in organic waste for both, plant 1 and plant 2, was very high. The effluent contained around 90% less TS, VS, and COD compared to the influent. The ammonium and phosphate concentrations in the effluent were on average 280 mg/L and 33 mg/L, respectively. The anaerobic bacterial decomposition resulted in a mean gas production of 426 L/kg VS (= average of plant 1 and plant 2). This refers only to the gas which finally is used for cooking. Gas losses occurred due to loose fit of the gas holder and the digester tank (about 17.5%) which is not accounted in the daily gas production. The methane contents for plant 1 and 2 were 55 and 58 vol%, respectively. The hydraulic retention times were about 53 and 59 days, the solid retention times 163 and 143 days, and the organic loading rate 0.97 and 0.48 kg VS/(m3*d) digester tank for plant 1 and plant 2 respectively. The average air temperature for the study period (1.10.2009 – 25.01.2010) was 28.8 °C and the average biogas pressure was 2.25 mbar above air pressure in Dar es Salaam. The maximum usable gas amount of one gas holder was found to be about 1800 L. If all three gas holders were full and used simultaneously, the gas lasted for 6 hours of cooking which replaces up to 35 kg charcoal per week. With an average charcoal consumption of 44 kg/d at Azania, the amortisation period is 10.5 years when fed with 8 kg/plant*d. By increasing the feedstock to 16 kg/plant*d, the amortisation period can be reduced to only 4 years. Visiting other institutional plants in Dar es Salaam and interviews with the responsible persons revealed that the expectations of customers did not correspond with the specifications given by ARTI-TZ. This showed that the burning duration announced depend on several factors which have to be considered individually from institution to institution. Also, a lack of canteen waste for a constant feeding at high level reduces both the optimal biological and economical performance for a biogas plant. This study showed that the recommended feeding rate by ARTI-TZ given for the Azania plants can be doubled without impairing the digester activity. Though, this amount of food waste is not available at Azania. Therefore, new sources of food waste, e.g. from other schools or restaurants, have to be considered in order to increase the performance of the plants and finally reduce the charcoal consumption significantly. The willingness of the cooks for using biogas is present, though the time for cooking is slightly longer and the gas supply not always guaranteed. For future projects, emphasis has to be put on the estimation of daily available food waste, design of the gas burner and gas stove and intensive trainings of the people working with the biogas plants in order to use a biogas plant to its full capacity. Tough it seems yet a big challenge to fully change from charcoal to biogas, it is certainly a very good option for a partial substitution which finally will lead to a successful organic waste management and reduction in unsustainable energy consumption. ii Acknowledgement I would like to express my sincere thanks to my supervisors Yvonne Vögeli from Sandec, Prof. Gabriel Kassenga and Dr. Shaaban Mgana from Ardhi University for their valuable and constructive advices and comments to my work. I would like to thank Costech for their permission of conducting this research. Further I am grateful to Prof. Urs Baier form ZHAW, Dr. Mbuligwe and Minza Selele from Ardhi University for their helpful suggestions and support during the work. It is a pleasure to thank Mr. Ndimbo and Mr. Ramadhani for their support in the laboratory works. Without the help of the six Azania students, namely Aby, Edgar, Abel, Aminiel, Allen and Levocatus, who volunteered themselves to feed the biogas plants at their school, this project would not have been possible. I would like to thank them very much. This also holds true for the cooks, namely Margret, Rose, Antony and Stella. Their readiness to cook with biogas made it possible to collect data. Also, I would like to thank Mr. Ayubu, teacher and patron of the students, and Mr. Ngozye, the head of Azania Secondary School. Also, I would like to show my gratitude towards ARTI Tanzania, its employees and especially its directors Dennis Tessier and Nachiket Potnis for welcoming me to Dar es Salaam, for interesting discussions about biogas and for being open to improvements and realizing them at the Azania plants. Many thanks go to Christian Lohri for his help in the beginning of the work and sharing his experience in the field. Moreover, I wish to thank the Swiss Agency for Development and Cooperation (SCD), the NCCR North-South research programme, the Swiss Federal Institute of Aquatic Science and Technology (Eawag) as well as the Swiss Federal Institute of Technology Zurich (ETH Zürich) for their financial support. Finally, I am indebted to many others which I have not mentioned but nevertheless every one of them contributed to this work in their own way and made my stay in Dar es Salaam unforgettable. iii List of Figures Figure 1: Three ARTI Compact Biogas Systems at Azania Secondary School................2  Figure 2: Open dumping of waste produced at Azania Secondary School.......................2  Figure 3: Scaling of the gas amount in the gas holder.....................................................3  Figure 4: Gas meter provided by Erdgas Zurich (left), gas meter connected to the biogas stove (right)..............................................................................................5  Figure 5: Development of the methane content of plant 1, 2, and 3 during the whole monitoring period.................................................................................................7  Figure 6: Mean gas compositions of plant 1, 2, and 3. O , H S and NH accounted for 2 2 3 less than 1 vol% of the gas volumes...................................................................7  Figure 7: Biogas loss due to loose fit of the tanks.............................................................1  Figure 8: Gas holder at its full capacity..............................................................................9  Figure 9: Gas holder when cooking with biogas was finished...........................................9  Figure 10: Three charcoal stoves in the Azania kitchen..................................................10 Figure 11: Consecutive phases (blue arrows) interrupted with actions (green boxes) describing the cooking procedure for one charcoal stove……………………..11 Figure 12: Food waste bucket near kitchen.......................................................................1  Figure 13: Effluent in overflow bucket. Undigested food particles are swimming on top.13  Figure 14: pH development of plant 1, 2, and 3...............................................................14  Figure 15: Development of the redox potential plant 1, 2, and 3.....................................14  Figure 16: Temperature of the water table of plant 1, 2, and 3.......................................15  Figure 17: Results of A/TIC Kapp titration........................................................................15  Figure 18: NH +-N and PO 3--P concentrations in the effluents of plant 1 and plant 2....16  4 4 Figure 19: NH +-N concentration in effluents of plant 1 and 2 plotted against pH at 4 top of the digester tanks..................................................................................16  Figure 20: Schematic scheme of the digester tank with the separation line between sludge and water at 51, 31, 38 cm for plant 1, 2, and 3, respectively. One section is indicated by the length of a double arrow.......................................18  Figure 21: Three samples of each plant (3, 2, 1) in sequence of C, B, A (from left to right).............................................................................................18 Figure 22: Total carbon fluxes for plant 1 and 2 for the period 9.11.09 - 13.12.09……...19 Figure 23: Hanging pipes for the gas transfer....................................................................1  Figure 24: Hanging pipes for the gas transfer....................................................................1 Figure 25: Biogas stove, arrows showing space for heat loss and broken bricks……….24 iv List of Tables Table 1: Intended feeding plan for the Azania biogas plants.............................................3  Table 2: Parameter analyzed.............................................................................................4  Table 3: Waste characterization.........................................................................................6  Table 4: Mean values of daily TS, VS, and COD input and the biogas production with tot and without loss respectively (value adjusted to norm litres in brackets)............8  Table 5: Specific gas production in dependence to daily wet weight (ww), TS, VS, and COD for plant 1 and 2 (value adjusted to norm litres in brackets)....................8  tot Table 6: Theoretical maximal biogas potential (adjusted to norm litres in brackets)........8  Table 7: Menu plan of the Azania canteen.......................................................................10  Table 8: Food rations per student per day.......................................................................10  Table 9: Distribution of meals prepared among the three charcoal stoves.....................11  Table 10: Mean biogas and charcoal consumption per meal............................................1  Table 11: Mean time consumption per meal with charcoal and biogas...........................12  Table 12: Mean TS, VS, COD , COD loads per day and their reduction rate for tot dis plant 1...............................................................................................................13  Table 13: Mean TS, VS, COD loads per day and their reduction rate for plant 2.........13  tot Table 14: Heavy metal concentrations in effluents of biogas plant 1 and 2....................16  Table 15: Hydraulic retention time for different feeding amount of plant 1, 2, and 3......17  Table 16: Solid retention time of plant 1, 2, and 3 for different feeding amount..............17  Table 17: Organic loading rate of plant 1, 2, and 3 for the different feeding amount......17  Table 18: Analysis of the digester contents of plant 1, 2 and 3.......................................18  Table 19: Summary of the interviews conducted with the head master of the institutions, the cooks, and the operators of the biogas plants (to be continued)..............20  Table 20: Comparison with Lohri (2009)..........................................................................22  Table 21: Comparison of the biogas production from literature with this study...............24  Table 22: Amortization periods in years for 8 and 16 kg/plant*d.......................................1  v Abbreviations AD Anaerobic Digestion ARTI Appropriate Rural Technology Institute A/TIC Acids/Total Inorganic Carbon C Carbon CBS Compact Biogas System CH Methane 4 CO Carbon Dioxide 2 COD Chemical Oxygen Demand COD Dissolved Chemical Oxygen Demand dis COD Total Chemical Oxygen Demand tot Costech Tanzania Commission of Science and Technology DSM Dar es Salaam DW Dry weight Eawag Swiss Federal Institute of Aquatic Science and Technology FW Food Waste H S Hydrogen Sulphide 2 HRT Hydraulic Retention Time MC Moisture content NH Ammonia 3 NH + Ammonium 4 NH +-N Ammonium-Nitrogen 4 NL Norm Litre O Oxygen 2 OLR Organic Loading Rate PO 3- Phosphate 4 PO 3--P Phosphate-Phosphorus 4 P Phosphorus total total Sandec Department of Water and Sanitation in Developing Countries SRT Solid Retention Time SW Solid Waste SWM Solid Waste Management TKN (N ) Total Kjeldahl Nitrogen total TS Total Solids TZ Tanzania VS (Total) Volatile Solids (tot) ww Wet Weight vi