Seasonal and diurnal variations of temperature, pH and dissolved oxygen in advanced integrated wastewater pond system treating tannery effluent.

Abstract Seasonal and diurnal fluctuations of pH, dissolved oxygen (DO) and temperature were investigated in a pilot-scale advanced integrated wastewater pond system (AIWPS ® ) treating tannery effluent. The AIWPS ® was comprised of advanced facultative pond (AFP), secondary facultative pond (SFP) and maturation pond (MP) all arranged in series. The variations of pH, DO and temperature in the SFP and MP followed the diurnal cycle of sunlight intensity. Algal photosynthesis being dependent on sunlight radiation, its activity reached climax at early afternoons with DO saturation in the SFP and MP in excess of over 300% and pH in the range of 8.6–9.4. The SFP and MP were thermally stratified with gradients of 3–5°C/m, especially, during the time of peak photosynthesis. The thermal gradient in the AFP was moderated by convective internal currents set in motion as a result of water temperature differences between the influent wastewater and contents of the reactor. In conclusion, the AFP possessed remarkable ability to attenuate process variability with better removal efficiencies than SFP and MP. Hence its use as a lead treatment unit, in a train of ponds treating tannery wastewaters, should always be considered.