Microbiological aspects of anaerobic filter treatment of septic tank effluent at low temperatures

Abstract Laboratory scale anaerobic filters packed with plastic ballast rings were used to treat low strength septic tank effluent. After an initial warm start‐up, each of the three filters (filters 1, 2 and 3) were operated at 10°C, 5°C and 20°C respectively. BOD removals increased in proportion to temperature and HRT. The filters achieved partial (approximately 90%) removal of coliforms, but the effluent coliform populations remained too high to allow a direct discharge of the effluent into a water course. Faecal coliform removals were greater at 10°C and 20°C than at 5°C while little differences were noted for the total coliform rates of removal. The rates of attachment and colonization were greatest at lower temperatures, and more bacteria formed tighter attachments at the lower temperatures.