하수처리장에서의 총인 분석 및 처리효율 평가

Abstract

This study was conducted to assess removal efficiency and develop improvement plans for a T-P treatmentplant in the 1st sewage treatment plant in Gwangju. The findings of this study are as follows: among all processes,the T-P removal process achieved the highest efficiency (84%), whereas the T-N removal processshowed the lowest (1.2%). About 77% of the 84% T-P removal efficiency was credited to the sedimentationbasin, indicating that coagulant injection is essential. Comparing coagulants using jar tests found that the optimalPAC input was 20~25 ppm and its T-P removal efficiency was 94~95%, whereas the optimal LAS inputwas 25~30 ppm with T-P removal efficiencies of 84~89%. This shows that PAC can achieve a better removalefficiency than LAS. Although the jar tests suggested the best PAC input of 20~25 ppm, the actual input atthe plant was 28~36 ppm, about 8~11 ppm higher. This may be attributable to the significantly shortened retentiontime in the sedimentation basin due to the high-rate coagulation of an inclination plate settler using microsand. The degrees of coagulation by rapid mixing were measured, and zeta potentials were found moderateranging between -8.44~-8.40 mV. This indicates that a pump injection method should be adopted for the bestcoagulation (zeta potential: 0~+3 mV). Replacing the four existing rapid-mixing coagulant injectors (powerconsumption: 85.6 kW/h) with one device using pump injection (power consumption: 1.5 kW/h) may not onlyimprove T-P removal efficiency but also reduce the annual electricity cost by 60 million won.