Study on self-purification capacity for organic pollutants in stagnant water

Polluted water is abandoned or stored untreated in many places. Especially, small water bodies such as ditches, ponds, wastewater tanks, etc. have not yet well been considered. The self-purification stabilizes the wastewater, but oxygen supply limits the biodegradation process. In the natural environment, approximately 3 g oxygen can be dissolved per m2 per day if the water is completely deprived from dissolved oxygen; this is the magnitude of self-purification capacity. To improve the quality of polluted water with higher oxygen demand than natural reaeration capacity, enhanced aeration is required. The laboratory experiment disclosed that water trickling onto the water surface or shallow stirring of water less than 10 mm in depth increased the mass transfer rate significantly. At the same time, the methods were found more efficient than bubbling aeration of large-scale treatment plant in terms of energy input against oxygen supply. Though it is an efficient method, elaborate application will be necessary since the mass transfer rate is not as high as bubbling aeration.