TRACING NITROGEN AND PHOSPHORUS THROUGH TREATMENT PROCESSES

Abstract

Eutrophication results in the deterioration of water quality due to luxuriant growth of plant life and affects ecological balance of the waters. Although there is considerable literature on nitrogen and phosphorus removal in different wastewater treatment processes, information on nitrogen and phosphorus fractions in wastewater at. different stages of wastewater treatment processes in scanty. Some information on the nitrogen and phosphorus fractions in wastewater and their seasonal variation is available. Tracing of nitrogen and phosphorus through a treatment plant assists in understanding the mechanisms of transformations of the various forms of nitrogen and phosphorus. Wastewater contains phosphorus in the form of organic, ortho and polyphosphates which occurs both in filtrable (dissolved) and particulate (suspended) form. During the treatment process most of the organic phosphorus and polyphosphates are decomposed to inorganic orthophosphate. Which is preferably taken up by free living microorganisms and algae. In the course of the present study, variations of various forms of nitrogen and phosphorus at different stages of selected treatment processes were studied. Wastewaters were collected from different stages of ASP (I8MLD), Kankhal; oxidation ponds (6MLD), Lakkarghat ; ASP in series (Bench - scale, 3.5LD), Env. Engg. Lab. ; UASB reactor (Bench - scale, 37.3 5LD), Env. Engg. Lab. The samples were analysed for reactive phosphorus, acid - hydrolyzable phosphorus, total phosphorus, ammonical nitrogen, nitrite and nitrate. Both Haridwar and Rishikesh wastewaters had approximately 60-62 % dissolved phosphorus, which was reduced to approximately 48% during aerobic treatment iii indicating better removal rate for dissolved fraction compared to suspended fraction. Of all the fractions maximum rate of reduction was recorded for dissolved organic phosphorus. In oxidation ponds a uniform rate of removal of suspended fractions was noticed while concentration of dissolved fractions decreased more rapidly with travel of wastewater. Overall, final effluent from both the plants contained more phosphorus than suggested value of I mg/L for control of eutrophication. In the sludges most of the phosphorus was found in suspended form. The wastewaters coming from Haridwar and Rishikesh were having the same concentration of ammonical nitrogen and nitrate nitrogen. During the treatment of domestic wastewaters, the ammonical nitrogen decreased by about 25% and nitrate nitrogen increased by about 61%.