The harvest of microalgae from the effluent of a sewagefed high rate stabilization pond by Tilapia nilotica

Abstract

Abstract There was a linear relationship between maize yield and total nitrogen applied, irrespective of the source of the nutrient: organic (raw sewage, fish pond effluent) or inorganic (commericial fertilizer). An absolute relationship between maize yield and total nitrogen applied could not be developed due to differences in soil fertility (in the experiment apparently due largely to soil physical characteristics). The effluent from the fish ponds contravened the WHO standard of 2 faecal coliforms/100 ml for waste-water reuse for crops eaten cooked and for fish culture. The land required to treat and recycle domestic sewage from a hypothetical city of 100 000 people (design criteria: 40 g BOD 5 and 701 water consumption/person/day i.e., sewage strength 570 mg BOD/1) was estimated at 63 ha. The land area ratios were 1.86 : 1 : 10.25 for the high rate stabilization pond, fish pond, and maize plot, respectively. It is suggested that where land is available in the tropics, wastewater be recycled in a system of conventional stabilization ponds modified for fish cultivation as well as waste treatment. Particular emphasis must be given to public health, pollutants as well as pathogens, in recycled wastewater. Perhaps the only rational way to use a high rate stabilization pond is to harvest the phytoplankton directly from the effluent for use as animal feed.