This study explored effects of a sludge-based biochar addition on nitrogen removal of membrane bioreactor (MBR) for wastewater treatment. The membrane fouling reduction by the biochar addition was also investigated. A dose of 3 g/L of the biochar was applied to an MBR (i.e., BC-MBR) and treatment efficiencies of organic matter and nutrient were analyzed. The MBRs with powdered activated carbon (i.e., AC-MBR) and without any additives were also operated in parallel. The average removals of COD and TN were improved with the biochar addition compared to those with the control MBR. Interestingly, operational duration was also increased with biochar addition. The CLSM analysis revealed that biomass amounts of BC-MBR and AC-MBR were reduced by more than 40%, and thickness of the biofilm attached to the membrane surface also was decreased. The physical properties of biochar surfaces were compared with a commercial powdered activated carbon. The specific surface area with 38 m2/g and pore volume with 0.13 cm3/g of the biochar were much smaller than those of the powdered activated carbon, which were 1100 m2/g and 0.67 cm3/g, respectively. Manufacturing conditions for the biochar production needs to be further investigated for enhancing physical properties for adsorption and biological improvement.

Application of the membrane process to wastewater treatment and reuse has been increasing due to water shortage, water pollution and an increase in water demand. Membrane fouling including biofouling should be controlled to extend its application. In this study, modulation of diffusible signal factor (DSF) system, the quorum sensing (QS) system that regulates EPS formation by microorganisms, was considered as a promising option to manage biofouling. Among many DSF compounds, cis -2-Decenoic acids (CDA) was selected. The experimental results showed that, as the CDA concentration increased, the density and number of stained cells decreased. The lowest density was observed when the CDA concentration of 300 nM was applied. The EPS on membrane surface decreased with increasing concentration of CDA. The CDA dosing also affected the EPS composition. At the 300 nM CDA dose, the total EPS reduced by up to 57% and the protein fraction by 35%. This study revealed the biofilm reduction effect of CDA under various conditions for MBR sludge. The application of CDA can be adapted to control biofouling in the MBR process.

Numerous chemical modifications on activated carbon such as acidic conditioning, thermal treatment and metal impregnation have been investigated to enhance adsorption capacities of micropollutants in water treatment plants. In this study, chemical modification including acidic, alkaline treatment, and iron-impregnation was evaluated for adsorption of 2,4-dichlorophenol (2,4-DCP). For Fe-impregnation, three concentrations of ferric chloride solutions, i.e., 0.2 M, 0.4 M, and 0.8 M, were used and ion-exchange (MIX) of iron and subsequent thermal treatment (MTH) were also applied. Surface properties of the modified carbons were analyzed by active surface area, pore volume, three-dimensional images, and chemical characteristics. The acidic and alkaline treatment changed the pore structures but yielded little improvement of adsorption capacities. As Fe concentrations were increased during impregnation, the active adsorption areas were decreased and the compositional ratios of Fe were increased. Adsorption capacities of modified ACs were evaluated using Langmuir isotherm. The MIX modification was not efficient to enhance 2,4-DCP adsorption and the MES treatment showed increases in adsorption capacities of 2,4-DCP, compared to the original activated carbon. These results implied a possibility of chemical impregnation modification for improvement of adsorption of 2,4-DCP, if a proper modification procedure is sought.

근래 해수담수화나 하수재이용에서 정삼투와 역삼투 공정을 결합한 FO-RO 공정에 대한 연구가 많이 이루어지고 있다. 역삼투 공정은 기본적으로 까다로운 전처리를 거쳐야하는 경우가 많은데 이를 정삼투 공정으로 대체하는 것이 기본적인 개념이다. 정삼투 공정은 멤브레인은 사이에 두고 염도차가 있는 두 용액을 순환시켜주면 두 용액 사이의 삼투압 차이에 의해 염도가 높은 쪽으로 물이 이동하는 현상을 이용한다. 정삼투 공정의 장점은 역삼투 공정과는 다르게 자연적인 삼투압을 이용하기 때문에 가압이 할 필요가 없다. 그렇기에 역삼투 공정의 운전비용의 많은 부분을 차지하는 전력비를 감소시킬 수 있다. 또한 후단의 역삼투 공정의 부하를 감소시켜주는 효과도 있다. 하지만 역삼투 공정과 마찬가지로 정삼투 공정에서도 농축수가 발생하게 되고, 하수가 농축되기 때문에 적절한 처리 없이 배출하지 못하는 단점이 있다. 본 연구는 실험실 규모의 정삼투 장치를 이용하여 회수율 50%를 기준으로 하수 농축수를 생산하고 수질 분석과 유기물 특성분석을 통해 농축수의 생물학적 처리가 가능한지 알아보았다. COD 22.1 mg/L, BOD 9.7 mg/L 수준의 K시 WWTP 2차 침전지 유출수를 원수로 사용하였고, 농축된 후에는 COD 38.6 mg/L, BOD 7.9 mg/L 의 값을 보였다. 이는 2차 침전지 방류수가 농축되면서 난분해성 유기물이 증가하였다는 것을 보여준다. 또한 FEEM을 이용하여 유기물의 intensity를 측정한 결과 aromatic protein-like, fulvic 과 humic acid-like의 intensity가 크게 증가하였다. 이상의 결과로 정삼투 농축수의 생물학적 처리를 위해서는 난분해성 유기물의 분해가 필요할 것이라고 생각된다.