목적: 반류수를 대상으로 고형물 부하율을 측정하여 일차슬러지 제거, 재순환, 투입에 대한 제어기술을 개발하여 처리용량 증가 및 공정성능 향상을 달성하고자 하였다. 방법: 파일럿 플랜트는 실플랜트와 유사하게 일차침전지+MLE공정으로 제작하였고, 유입 고형물 부하율을 기반으로 슬러지 인발량을 제어할 수 있도록 구성하였다. 상태점 분석으로 일차슬러지에 대한 제거 하부배출속도, 전체 하부배출속도를 결정하였다. 수동인발, 자동인발, 자동인발+재순환, 자동인발+투입 방식으로 구분하여 운전하였다. 일차슬러지 제어기술에 대한 성능평가 항목은 일차, 이차침전지의 SS 제거효율과 일차슬러지 농도로 하였다. 재순환 및 투입에 의한 생물반응조 성능향상은 암모니성질소, 총무기질소(TIN), 인산염인 제거효율과 SNR, SDNR을 통해서 판단하였다. 재순환으로 변화된 아세트산 농도와 미생물 군집특성을 비교하여 성능향상 원인을 분석하였다. 결과 및 토의: 유입 반류수 SS 모니터링 평균값은 2.2 (0.7 ~ 6.3) g/L로 일차침전지는 고농도 SS와 변동에 대응한 처리가 필요하였다. 실제 침강속도에 기반한 상태점 분석이 정밀하게 일차슬러지 제거, 재순환, 투입에 대한 안정적인 운전 가능여부와 구체적인 설계 및 운영기준을 제시할 수 있는 것으로 나타났다. 유입 고형물 부하율 변화에 따라서 하부배출속도를 제어하는 자동인발은 고농도 슬러지를 안정적으로 인발할 수 있으며, SS 제거효율도 안정적으로 유지할 수 있었다. 슬러지 재순환 운전에서도 안정적 운전이 가능하며 실플랜트에서 일차침전지 처리용량을 2배 이상 증가할 수 있는 것으로 나타났다. 일차슬러지 재순환으로 생물반응조 TIN 제거효율은 24.2 ~ 52.3% 향상되었고 인산염인 제거효율은 최대 20.1% 향상되었다. 일차슬러지 투입으로 생물반응조 TIN 제거효율이 32.6% 향상되었다. 아세트산을 포함한 휘발성 유기산이 생성되고 제거효율이 향상된 것은 재순환에 의해 일차슬러지와 접촉하였고 발효 미생물 주요 종 비율이 2.0% 존재하였기 때문으로 판단된다. 유입 반류수에는 질소, 인 처리미생물 주요 종이 26.4% 존재하여, 일차슬러지 투입으로 미생물 공급이 이루어져서 제거효율을 향상시켰다고 판단된다. 결론: 반류수를 대상으로 고형물 부하율을 측정하여 일차슬러지 제거, 재순환, 투입을 제어하는 기술은 일차침전지 처리용량을 증가시킬 수 있고 생물반응조의 질소, 인 제거효율을 향상시키는 것으로 사료된다.
Objectives : By measuring the solids loading rate for the sidestream, it was intended to achieve increased treatment capacity and improved process performance by developing control technologies for primary sludge removal, recirculation, and input. Methods : The pilot plant was manufactured by the primary clarifier + MLE process similar to the full-scale plant and was configured to control the amount of sludge withdrawal based on the inflow solids loading rate. The state point analysis was used to determine removal underflow withdrawal rate and the total underflow withdrawal rate for the primary sludge. The operation was divided into manual withdrawal, automatic withdrawal, automatic withdrawal + recirculation, and automatic withdrawal + input methods. The performance evaluation items for primary sludge control technology were primary sludge concentration and SS removal efficiency for primary and secondary clarifiers. The improvement in the performance of the bioreactor by recirculation and input was judged through the removal efficiency of ammonium nitrogen, TIN (Total Inorganic Nitrogen) and phosphate phosphorus, SNR (Specific Nitrification Rate), and SDNR (Specific Denitrification Rate). The cause of the performance improvement was analyzed by comparing the acetic acid concentration changed by recirculation and the microbial community characteristics. Results and Discussion : The average value of SS monitoring of the sidestream influent was 2.2 (0.7 ~ 6.3) g/L and the primary clarifier needed treatment in response to high concentration SS and fluctuations. It is judged that the state point analysis based on the actual settling rate can accurately suggest whether the stable operation of primary sludge removal, recirculation, and input is the possible and specific design and operation standards. The automatic withdrawal that controls the underflow withdrawal rate according to the change of the inflow solids loading rate could stably draw out the high-concentration sludge and maintain the SS removal efficiency. It is believed that stable operation is possible even in the sludge recirculation operation, and the treatment capacity of the primary clarifier can be increased more than two times in a full-scale plant. By recirculation of the primary sludge, the TIN removal efficiency in the bioreactor was improved by 24.2 ~ 52.3%, and the phosphate phosphorus removal efficiency was improved by up to 20.1%. The TIN removal efficiency in the bioreactor was improved by 32.6% by the input of primary sludge. VFAs (Volatile Fatty Acids) including acetic acid was produced and the removal efficiency was improved because it was in contact with primary sludge by recirculation and the ratio of major fermentation microorganisms was present at 2.0%. It is determined that 26.4% of the main species of microorganisms treated with nitrogen and phosphorus exist in the sidestream inflow and the removal efficiency was improved by supplying microorganisms through the input of primary sludge. Conclusions : Technology that controls primary sludge removal, recirculation, and input by measuring the solids loading rate for the sidestream is believed to increase the treatment capacity of the primary clarifier and improve the nitrogen and phosphorus removal efficiency of the bioreactor.