세계적으로 하수처리장 방류수 수질기준이 강화되고 있으며 국내 또한 하수처리장 에너지 자립율을 높이기 위해 하･페수처리장 내 고효율 혐기소화조 및 소화조 전처리 설비가 도입되면서 방류수의 수질은 향상되었다. 그러나, 농축조 및 소화조 후단에서 발생하는 반류수의 농도가 지속적으로 증가하여 하･폐수처리장 내 생물반응조 운영에 악영향을 미치고 있는 실정이다. 반류수는 발생특성상 연속적으로 발생되지 않고 간헐적･주기적으로 발생되며 슬러지 처리계통에서 배출되고 있다. 반류수 발생 시 시간 최대유량 및 농도가 수처리공정 하수유입 부하 대비 100% 이상의 부하증가를 초래하는 경우도 있어 이로 인한 생물반응조의 운영에 어려움을 겪고 있는 실정이다. 이러한 반류수 유량은 유입유량의 1~3%로 적은 양으로 발생되지만 고농도로써 수처리 공정에 충격부하를 유발하기 때문에 전체 처리효율에 악영향을 주는 것으로 알려져 있다. 또한, 질소의 농도가 높기 때문에 반류수에 의한 유입수의 질소부하 증가량은 유입 질소 부하량의 15~25% 이상을 차지한다. 이러한 반류수의 처리를 위해 생물반응조 유입 전 전처리를 통해 부하를 감소시키기 위해 응집침전 방법을 선정하였다. 이에 본 연구에서는 대구 S 하수처리장의 반류수를 대상으로 유입유량 대비 반류수의 연간 유량 및 유입 부하를 파악하였고, 고농도로 유입되는 반류수의 처리를 위해 pH, 응집제 종류, 혼화 시간 및 rpm 의 인자들을 조절하여 응집실험을 진행하였으며, CODCr, T-N, T-P, SS, NH4+의 저감효율을 도출하였다.

Three hundred thousand tons per year of water works sludge are produced in Korea. End disposal of the sludge is mainly based on recycle such as supplementary material for cement kiln, raw material for construction materials and fill material. The dry clarifier sludge organic content is about 30% and the major elements determined are aluminum(about 14%), iron(about 4%), potassium(1.8%), and manganese(0.5%). The recovery of coagulant has high economic advantage and recommended as a suitable treatment option for the disposal of water works sludge. Chemically, coagulant(aluminum) recovery from the water works sludge is a simple process. This process is however, somewhat complicated by pH control in the mixture of dewatered clarifier sludge and sulfuric acid solution. Also, the thickened water works sludge(TWS), which is withdrawn from the bottom of the thickener in water works plant, is difficult to dewater. In addition coagulation is used to remove total phosphorus(T-P) from municipal wastewater in oder to strengthening discharge water quality standard for T-P in municipal wastewater treatment plant(MWTP). Nevertheless it has the drawback of producing a large amount of sludge which together with the coagulants such as alum and polyaluminum chloride used to treat T-P in municipal wastewater increases the operating cost. Reject water originates from the dewatering of digested sludge in the MWTP. It contains heavy metals and large amounts of nutrients such as phosphorus and nitrogen. Traditionally, reject water is recycled back to the main flow line on of the MWTP. Although this method seems to be simple, it also has its drawbacks. First of which is the increase in the load of the MWTP as the reject water characteristics is very much different from the normal municipal wastewater. The objective of this study is to investigate the effectiveness of thickened water works sludge as an adsorbent of phosphorus from the reject water. In this study, batches of experiments were conducted to investigate the effect of dosage of TWS for reject water on its phosphorus adsorption properties. Increasing the TWS dosage to 30%(vol/vol), T-P and COD of reject water decreased to 55% and 20% respectively. Experimental results show that the potential of the TWS as coagulant in phosphorus and organic matter immobilization, thus converting they from rejector water to a useful material in pollutant control.

To acquire preliminary data for the control of total nitrogen (TN) in S sewage treatment plant, which processes merging food waste and sewage, the effect of reject water on the total nitrogen in the effluent was examined in this study. Water quality data for the plant during the winter period were applied to calculate the mass balance. It was calculated that at least more than 231 kg/d TN should be removed to control the TN concentration in the effluent. Assuming 18 ppm as the goal TN concentration in the effluent, about 941 kg/d TN should be removed from this plant. Approximately 10% more TN should be removed than at present to achieve this result. It was observed that dewatering the filtrate had a considerably greater effect on the total nitrogen in the effluent than the reject waters. The dewatered filtrate contained 1,399kg/d TN. The contribution of the dewatered filtrate to the TN concentration in the effluent was 0.183, which was 7 to 23 times greater than the other reject waters. In addition, the amount of total nitrogen from the reject water, with the exception of the dewatering filtrate, was lower than the amount of TN that should be removed from S sewage treatment plant. Therefore, it was concluded that one of the most effective methods for controlling the TN concentration in effluent was the removal of the TN contained in the dewatering filtrate.