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An anaerobic floating drum digester was used in treating domestic sewage. The volumetric capacity of the digester plant was estimated as 258.99 litres with a 250 litre-gas holder tank. The gas holder tank was fitted into the digester tank with a clearance of about 2cm to allow the former rise freely when biogas is generated in the digester tank. An inlet pipe was introduced for loading the wastes into the digester and an outlet pipe for dislodging, with an overflow pipe which indicates the maximum extent to which the digester could be filled. A gas valve was incorporated at the top of the dome-shaped gas holder to control the gas flow. With the aid of a thermocouple wire fitted into the digester and a multimetre, the temperature of the sewage was monitored at a succession of 4 hours for a hydraulic retention period of 42 days. Sewage was obtained from a freshly dug soak away and fed into the bio-digester through the inlet pipe. Physical, chemical and bacteriological analyses were carried out before and during digestion process on daily basis. Results show that Biochemical Oxygen Demand (BOD) of the sewage before and after treatment was 96.50 mg/l and 55.50 mg/l respectively. The Chemical Oxygen Demand (COD) was 81.60 mg/l and 59.00 mg/l, before and after treatment respectively. The dissolved oxygen (DO) reduced from 124.80 mg/l to 84.30mg/l after a hydraulic retention period of 42 days. These results of the resulting treated water agreed to a reasonable level with the standards slated in the World Health Organisation (WHO, 2006) standards for safe disposal of wastewater.
Keywords: Anaerobic bio-digester, domestic sewage, dislodging, thermocouple.