공공하수 처리시설 방류수 T-N 기준을 만족하기 위해서는 호기조에서 질산화가 안정적으로 이루어져야 한다. 수온 및 pH가 질산화에 민감한 영향을 주고 있음에도 불구하고 기존 하수처리장 설계 시 동절기 저수온만 고려하고 호기조 pH는 상시 7.0으로 가정하여 설계하고 있다. 이에 본 연구에서는 MLE 공법 하수처리장의 생물반응조 유입수 알칼리도를 계절별로 파악하여 시뮬레이션을 수행하고, 알칼리도 변화가 호기조 pH 및 NH3-N 농도에 주는 영향을 확인하였다. 연구대상 처리장의 계절별 일평균 생물반응조 유입수 알칼리도는 춘/추절기 190 mg CaCO3/L, 하절기 185 mg CaCO3/L 그리고 동절기 210 mg CaCO3/L로 하절기에 저농도 알칼리도가 유입되는 것을 실험을 통해 파악하였다. 시뮬레이션 결과, 동절기 MLSS 농도가 2,500 mg/L인 경우, 유입수 알칼리도 변화와 관계없이 호기조 NH3-N 농도는 10 mg/L 이상이며 알칼리제 투입을 통한 목표 호기조 NH3-N 농도 2.5 mg/L 달성이 어려운 것으로 확인되었다. MLSS 농도가 3,000 및 3,500 mg/L인 경우에는 유입수 알칼리도에 따라 호기조 NH3-N 농도는 각각 1.3-5.0 mg/L와 0.8-3.1 mg/L의 범위인 것을 파악하였다. 춘/추절기 및 하절기 생물반응조 유입수 알칼리도가 하한치가 유입되는 경우, MLSS 및 DO 농도와 관계 없이 pH와 알칼리도가 제한 인자로 작용하여 호기조 NH3-N 농도 2.5 mg/L 이하를 만족하지 못하였다. 반면 유입수 알칼리도가 충분한 조건에서는 DO 및 MLSS 농도만 제어해도 안정적인 질산화가 가능한 것으로 나타났다. 또한 춘/추절기 및 하절기에 호기조 DO 농도가 1.0 mg/L가 되어도 질산화가 발생되는 것이 확인되어 처리장 운영에 있어서 탄소 발생 저감 방안이 수행될 수 있다.

Several kinds of coagulants such as aluminum sulfate, PAC, PASS are being used to treat drinking water resulting in residual aluminum ions in the water. Recently, it has been reported that high intake of aluminum ion may cause neurological dieseases such as Alzheimer's diesease and presenile dementia. Because of the possible adverse effect, WHO and EEC recommand to regulate residual aluminum. The autorities in Korea also has plan of regulating residual alunimum from 1995. But there is not enough information about the range of residual aluminum ion concentration when the aluminum sulfate, PAC or PASS has been used as a coagulant. Therefore the study has been conducted to find out the range of residual aluminum ion concentration after using aluminum sulfate, PAC, and PASS. Furthermore the effect of turbidity and alkalinity have been investigated. The experimental results are summarized as; 1. Most of the residual aluminum ion concentrations were within $10^{-6}$ and $10^{-5}mole/l$. Three coagulants have not showed any considerable difference in the residual aluminum concentration up to 50 NTU. However PAC has showed the least residual aluminum in high turbidity water over 100 NTU. 2. The low alkalinity water having 25mg/l as $CaCO_3$ has showed less residual aluminum than the water having 50mg/l alkalinity. However, the difference was not significcant. 3. Even the lowest residual aluminum concentration was over 0.05mg/l. Therefore the process to reduce residual aluminum would be necessary in water treatment plants.

Among many types of flue gas desulfurization (FGD) facilities, wet type FGD using lime or limestone is most popular in the world because of its simplicity of operation and availability of lime and limestone. Seawater desulfurization utilizes the alkalinity of seawater, thus requires no addition of lime and limestone. The efficiency of seawater desulfurization depends on the variation of alkalinity of seawater at different locations. This study presents the effect of gas-water ratio and total alkalinity of absorbing solution on the removal efficiency of sulfur dioxide from the flue gas by means of seawater. Also this study provides an alternative way to increase total alkalinity of seawater by utilizing fly ash from coal-fired power plants. The increase of removal efficiency with increase of alkalinity was measured as 0.26 ± 0.01% per ppm of bicarbonate alkalinity from the set of experiments using seawater, underwater, and distilled water, the alkalinity of which were 111 ppm, 38 ppm, and 1 ppm, respectively. Capability to increase total alkalinity of seawater using fly ash was confirmed.