RESUMEN
Investigations on some microbiological factors were carried out on two pond series system for three years [1979-81] treating domestic wastewater and operating at a loading of 300 lbs BOD/acre per day at a depth of 1.2 m. The study indicated satisfactory working of the ponds for monsoon [rainy], winter and spring seasons showing a removal of 58 to 72% BOD. Conditions worsened during hot summer month [May to mid July] when due to algal blooms [Oscillatoria] the pond efficiencies were restricted to 50%. The ponds also emitted odour during this period. Maximum BOD removal was recorded at light intensities varying from 45 to 49 x 103 lux, it was found that the magnitude of diurnal oxygenation is influenced more by variation in algal population than by changes in the light intensity. Euglena and other motile pond algae adopted to the varying pond conditions, these make the pond surface to appear green in the morning and grey during the period of intense radiation. It was established that presence of a few algal species indicated incomplete stabilization whereas larger varieties were indicative of complete stabilization. Daphnia species infested the ponds in the beginning of summer, their population was controlled by sprinkling lime powder on the pond dikes. It was observed that ponds with weedless dikes appeared to have an extremely high chance of free from mosquito breeding. Die-away rates for Coliform and E. Coli organism were also investigated