Biological removal of nitrogen and phosphorus from wastewater by a single sludge reactor

Abstract

A new biological process in a single sludge reactor containing the combined anaerobic-anoxic-aerobic zones and a clarifier is tested to check continuous removal of organic substances, nitrogen and phosphorus from wastewater. Attempts have been made to delineate organic substances, nitrogen and phosphorus removal mechanisms and to evaluate the removal efficiencies of these constituents with different internal recycle ratios and COD/TKN ratios. The removal efficiencies of TOC, BOD and COD were observed to be higher than 95%, 95% and 90% in all runs, respectively. In the case of aerobic recycle ratios, higher removal efficiencies were attained with the aerobic recycle ratio of 100% than with that of 50% and 200%. The removal efficiencies are 88% for T-N(Total-Nitrogen) and 87% for PO4-P with the aerobic recycle ratio of 100%. Large differences in the removal of T-N and PO4-P with COD/TKN ratios were observed: at influent COD/TKN of 4.8, 6.6 and 9.8, removal efficiencies for T-N are 69%, 80%, and 88% and those for PO4-P are 50%, 75% and 88%, respectively. The removal efficiencies decreased with the increase in nitrogen loading in wastewater.