생물학적 하수처리공정 내 나노입자의 독성영향 및 메커니즘

학위논문(박사) - 한국과학기술원 : 건설및환경공학과, 2012.8, [ viii, 98 p. ]Silver nanoparticles (Ag NPs) are the most widely used in the consumer products and have a great potential for a broad range of future applications. Studies have demonstrated the release of Ag NPs from different consumer products, suggesting that released Ag NPs would enter municipal wastewater treatment plants (WWTPs) via sewage. As WWTPs provide potential pollutant pathways into aquatic ecosystem, WWTPs are considered to be key intermediate stations in a recent risk assessment for Ag NPs. Therefore, this study was conducted to evaluate the impact of Ag NPs particularly on biological wastewater treatment processes. Conventional activated sludge system (CAS), biological nitrogen removal (BNR), and anaerobic digestion (AD) processes were selected as three model biological treatment processes. In BNR process, nitrification efficiency of activated sludge was decreased by 7 and 26% with 1 and 10 mg/L Ag NPs, respectively, in batch test. However, no significant inhibition was observed in denitrification up to 10 mg/L Ag NPs. This result suggests that Ag NPs have a different inhibitory effect on activated sludge depending on the growth environments. About 70-90% of Ag NPs were removed by adsorption onto sludge and/or sedimentation, and 10-30% of Ag NPs remained in the supernatant. In continuous operation of a sequencing batch reactor (SBR) for 3 months, bigger Ag NPs (i.e., dh = 82.4 ± 61.2 nm) had little impact on nitrification, while nitrification efficiency dramatically decreased after adding smaller Ag NPs (i.e., dh = 28.0 ± 15.2 nm). This is because small particles have higher reactivity due to the larger surface area and number of particles than those of big ones at the same concentration. In CAS system, Ag NPs did not show any adverse effect on organic removal under the conditions of this study. However, it was found that long-term exposure of Ag NPs and their accumulation onto sludge could cause operational problems (i.e., equipment malfunction leading to ...한국과학기술원 : 건설및환경공학과

산발효 최적화와 혐기성 막결합생물반응조를 이용한 유기성 폐기물의 이상 혼합 소화

학위논문(석사) - 한국과학기술원 : 건설및환경공학과, 2008.2, [ ix, 73 p. ]Anaerobic digestion using various organic wastes could be promising environmental technology because it can provide not only waste treatment also bioenergy production. Due to low efficiency and effluent quality of conventional anaerobic digestion, several new or modified systems for improving performance have been developed, and post treatment is inevitably applied for water reuse. Good performance using phase-separation technology has been reported because of providing optimal environments for each major group of microorganisms and their associated biological reactions. In a two-phase process, overall process efficiency is determined by acidogenic phase since it includes hydrolysis, referred to the overall rate-limiting step, so optimization of acidogenic phase is necessary. Having all merits of anaerobic digestion, anaerobic membrane bioreactors (AnMBRs) can offer high quality effluent, but the major obstacle for wide application of AnMBRs is fouling problem which is directly related to the operational cost. In contrast to aerobic MBRs, fouling characteristics of AnMBRs has not been studied a lot. Therefore, this study was performed to improve the methane production rate and effluent quality by modified two-phase anaerobic digestion system consisted of optimized acidogenic fermentation and AnMBRs. Additionally, characteristics of membrane fouling in submerged AnMBRs were evaluated though ultrafiltration of sludge in AnMBR at various HRTs. Firstly, anaerobic batch tests were conducted to find out optimum co-substrate condition for maximum acidification. Three kinds of substrates, livestock wastewater, sewage sludge and food waste leachate, were used and an optimized substrate condition was determined by maximum VFA increase and SCOD increase simultaneously using statistical analysis. Suggested optimum mixing ratio of livestock wastewater, sewage sludge and food waste leachate was 0.4 : 1.0 : 1.1, respectively on COD basis. Secondly, response surface me...한국과학기술원 : 건설및환경공학과