The effect of moisture content and alkalinity on the anaerobic biodegradation of pit latrine sludge A. A.-L. Couderc, K. Foxon, C. A. Buckley, C. F. Nwaneri, B. F. Bakare, T. Gounden and A. Battimelli ABSTRACT A. A.-L. Couderc Universite ´ P. Ce ´ zanne, Avenue Escadrille Normandie-Niemen, 13397 Marseille, France K. Foxon C. A. Buckley C. F. Nwaneri B. F. Bakare School of Chemical Engineering, Pollution Research Group, University of KwaZulu-Natal, Durban 4041, South Africa E-mail: foxonk@ukzn.ac.za T. Gounden eThekwini Water and Sanitation, P.O. Box 1038, Durban 4000, South Africa E-mail: teddygo@dmws.durban.gov.za A. Battimelli Laboratory for Environmental Biotechnology, National Institute for Agronomic Research (INRA), Avenue des Etangs 11100, Narbonne, France E-mail: battimel@supagro.inra.fr This study investigated the effect of additional moisture and/or alkalinity on the rate of anaerobic digestion in samples of material obtained from pit latrines. In modified serum bottle tests it was shown that poor gas production rates were observed from all experiments with material collected at the lower part of one pit. Using material from the top layer of a second pit it was shown that experimental bottles produced significant amounts of gas for all treatments. Analysis of data indicated that treatment with additional alkalinity had no discernible effect on anaerobic gas production rates, but that there was some correlation between moisture content and gas production rate. These results did not support the hypothesis that low pH buffering capacity was a limiting factor in the rate of digestion of pit latrine sludge, but confirmed that low moisture content could reduce the rate of stabilisation. This implies that increasing the moisture content in a pit latrine has the potential to increase biological stabilisation rates in the pit when the material is not already well-stabilised. Key words | alkalinity, anaerobic degradation, biogas, buffering capacity, pit latrine, VIP INTRODUCTION Ventilated improved pit (VIP) latrines are recognized as a minimum level of acceptable sanitation in South Africa. VIP latrines consist of a pit, cover slab, pedestal, and a superstructure provided with a ventilation pipe with fly screen (Mara 1984) to reduce odours and flies relative to those experienced with rudimentary or unimproved pit latrines. The liquid fraction (urine, water) infiltrates into the surrounding soil. The solid fraction (human excreta) is decomposed under aerobic and anaerobic conditions by producing biogas and soluble products which may leach into the soil. Grey water from sinks, washing dishes, showering etc. is often added by householders into pits. This practice increases the flow of soluble compounds into the surrounding soil and may decrease the rate at which the pit fills. An increase in the decomposition rate is a key factor to balance the system and limit the sludge accumulation thereby reducing the frequency with which the pit requires emptying. This study aimed to investigate some of the factors which may influence the decomposition rate and thus decrease the emptying costs. The eThekwini Municipality serves the metropolitan area of Durban in KwaZulu-Natal on the east coast of South Africa. The municipality provides a free basic sanitation service that includes a programme to empty full pit latrines within the municipal area every five years. There are a total of about 150,000 pit latrines in the eThekwini doi: 10.2166/wst.2008.449 1461 Q IWA Publishing 2008 Water Science & Technology—WST | 58.7 | 2008 Downloaded from https://iwaponline.com/wst/article-pdf/58/7/1461/436427/1461.pdf by guest on 06 June 2020