Performance of silver carp (Hypophthalmicthys molitrix) dominated integrated post treatment system for purification of municipal waste water in a temperate climate

The stabilization of municipal waste water by the combination of a UASB reactor and waste stabilization ponds is a low cost solution and could satisfy discharge standards with regards to physicochemical and biological parameters. Domestic wastewater was treated on a pilot scale (2.6 m3 d−1 sewage to the ponds and 20 days overall retention time) by the combination of a 6 m3 UASB reactor followed by two ponds, the second pond serving as a maturation pond and stocked with common carp and silver carp. Although climatic conditions were far from ideal, the system achieved 30–35% organic pollutant and 30–80% nutrient reduction along with 97–99% faecal coliform reduction. The result of this study clearly indicates that if the climatic condition is unfavourable, even at low flow rates chances of mass mortality of fish are quite high due to high O2 depletion and high ammonia concentration in the water. It is recommended that monitoring of the oxygen demand of the maturation pond is necessary for intensifying fish production.