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Abstract
Septic tanks in most developing countries are constructed without drainage trenches or leaching fields to treat toilet wastewater and /or grey water. Due to the short hydraulic retention time, effluents of these septic tanks are still highly polluted, and there is usually high accumulation of septic tank sludge or septage containing high levels of organics and pathogens that requires frequent desludging and subsequent treatment. This study aimed to reduce sludge accumulation in septic tanks by increasing temperatures of the septic tank content. An experimental study employing two laboratory-scale septic tanks fed with diluted septage and operating at temperatures of 40 and 30°C was conducted. At steady-state conditions, there were more methanogenic activities occurring in the sludge layer of the septic tank operating at the temperature of 40°C, resulting in less total volatile solids (TVS) or sludge accumulation and more methane (CH4) production than in the unit operating at 30°C. Molecular analysis found more abundance and diversity of methanogenic microorganisms in the septic tank sludge operating at 40°C than at 30°C. The reduced TVS accumulation in the 40°C septic tank would lengthen the period of septage removal, resulting in a cost-saving in desluging and septage treatment. Cost-benefit analysis of increasing temperatures in septic tanks was discussed.
Acknowledgments
We are very thankful Dr. Somkiet Techkarnjanaruk and Ms. Nimaradee Boonapatcharone from King Mongkut's University of Technology Thonburi for their help in molecular analysis.
Funding
This paper is based on the results from the project “Stimulating local innovation on sanitation for the urban poor in sub-Saharan Africa and Southeast Asia” funded by the Bill & Melinda Gates Foundation.
Nomenclature
| BOD5 | = | Five-day biochemical oxygen demand, mg L−1 |
| DNA | = | Deoxyribonucleic acid |
| d | = | Day |
| DGGE | = | Denaturing gradient gel electrophoresis |
| h | = | Hour |
| HRT or t | = | Hydraulic retention time, h |
| kWh | = | Kilowatt hour |
| L | = | Liter |
| PCR | = | Polymerase chain reaction |
| T | = | Temperature, °C |
| TCOD | = | Total chemical oxygen demand, mg L−1 |
| TKN | = | Total Kjeldahl nitrogen, mg L−1 |
| TS | = | Total solids, mg L−1 |
| TVS | = | Total volatile solids, mg L−1 |