Faecal coliform die-off in wastewater storage and treatment reservoirs

This paper describes faecal coliform (FC) removal in pilot-scale Wastewater Storage and Treatment Reservoirs (WSTR) in northeast Brazil. FC decay during the filling phase of WSTR was very reduced, suggesting that these reactors should be filled as quickly as possible, and subjected to the highest organic loading that will not cause odour emissions. The highest loading employed in this study was 659 kg BOD5/ha.d, causing no nuisance conditions. During the resting phase, FC decay rate decreased exponentially and Chick's law was modified. The time into the resting phase for FC to reach 10(3) cfu/100 mi ranged from 15 to 25 days as WSTR depth varied from 2.00 to 6.50 m. The performance of sequential batch-fed waste stabilization ponds (SBFWSP) in removing FC was compared to that of waste stabilization ponds (WSP) operated in series. In general, SBFWSP ware cheaper than WSP in series. When provision of volume to store the winter effluents is considered. a WSP system presents a higher benefit/cost ratio than a hybrid WSP-WSTR system, but the adoption of the latter can double the annual net return for a rainy season of 5 months for instance.