Hydrobiological studies of some waste stabilization ponds and aspects of fish culture

Abstract

A comparative hydrobiological study of the waste stabilization ponds at Blenheim, Carterton and Masterton with a triple purpose of comparing the efficiency of waste treatment, investigating the interrelationships of some ecological factors and furnishing a qualitative study of micro-organisms was carried out between March 1971 and November 1972. Some aspects of fish culture in sewage-enriched water were also investigated. Masterton 3-ponds system was more efficient in waste treatment than the Carterton 2-ponds plus Imhoff tank system and the Blenheim single-pond system due to its exceptionally high percentage reduction in effluent BOD and bacterial counts. The inferior performance of the Carterton and Blenheim pond systems was considered to be due to the high sewage loading in the former and wind generated short-circuiting effect in the latter and low percentage reduction of effluent BOD and bacterial counts in both. Series type ponds without overloading were essential for proper waste treatment. Linear regression analysis of the measured environmental data gave moderate to high correlation between air and water temperatures, water temperature and faecal coliform count, secchi disk transparency and phyto-plankton population, pH and total carbon dioxide concentration, dissolved oxygen concentration and percentage saturation of dissolved oxygen etc. Qualitative study of bacteria, protozoa, and phytoplankton and zooplankton were aimed to lay a foundation to the above studies. Fish culture studies indicated that temperature, pH, dissolved oxygen and food were essential for the successful culture of Carassius auratus, Salmo gairdneri and Retropinna retropinna in an experimental pond at Blenheim. The studies also indicated that predatory fish like Carassius auratus may be introduced into stabilization ponds to maintain ecological stability by controlling the over-population of some zooplankton like Daphnia sp.