고농도 황산염을 함유한 COD/sulfate 비가 낮은 석유화학폐수의 생물학적 처리 = Biological treatment of petrochemical wastewater containing high strength sulfate with low COD/sulfate ratio

다국어 초록 (Multilingual Abstract)

Sulfate-rich wastewater treatment using anaerobic process has been gaining much attention in recent years. Treatment efficiency and methane recovery rate of anaerobic treatment for high strength sulfate wastewater are dependent on COD/sulfate ratio. It was reported that low COD/sulfate ratio (<1) in wastewater could lead to a failure of anaerobic process. In order to solve the problem, pretreatment study to remove sulfate from wastewater using SRB(sulfate-reducing bacteria) is required.
Along-term, lab-scale treatment study for Acrylonitrile wastewater produced from ’T’ Company in Ulsan containing high strength sulfate and not readily biodegradable organics was performed. The purpose of the study is to improve the existing biotreatment system and to find a possibility of high-efficiency ammonia removal by retrofitting of the existing system to BNR process. Treatment processes used in this study consisted of UV/TiO₂, UAHR(upflow anaerobic hybrid reactor), and AFBR(aerobic fixed biofilm reactor). Artificial wastewater was applied only for UAHR, and Acrylonitrile wastewater was treated using UV/TiO₂,, UAHR, and AFBR.
Acrylonitrile wastewater had very low biodegradability (BOD_(5)/TCODcr) of 0.113. Biological treatability study with applying anaerobic serum vial technique indicated that anaerobic process was capable of removing both organics and sulfate from Acrylonitrile wastewater with high sulfate concentration and low COD/sulfate ratio (<1). It was suggested that the activity of SRB(sulfate-reducing bacteria) played a major part in removal of both organics and sulfate from the wastewater.
Treatment of artificial wastewater with low COD/sulfate ratio (<2) using UAHR to remove sulfate and organics was investigated. The feasibility study was designed to find the removal characteristics of organics and sulfate for different HRTs, the distribution of biomass in UAHR, the relative fraction of SRB among anaerobic bacteria along with the reactor height, and the production and components of biogas from UAHR. The removal efficiency of organics ranged from 60.4 to 80.2% during the whole test period. Sulfate removal efficiency, however, was maintained above 90.4% during the period with HRT varying from 60hr to 24hr. Sulfate removal efficiency was found to sustain above 90% up to at a loading rate of 1.5 kg SO₄^(2-)/m³/day.
As the HRT decreased from 60hr to 12hr in UAHR treating artificial wastewater, CH₄ production rate of the biogas increased from 49.6 mL/day to 105.6 mL/day; however, the fraction of CH₄ in the biogas significantly decreased from 43.0% to 26.4%. It was confirmed that the production rate and fraction of CH₄ in the biogas was insignificant when treating high strength sulfate wastewater with low COD/sulfate ratio (<2). H₂S concentration in the biogas was stabilized at approximately 7.0ppm after the HRT reached 24hr. During the test period an inhibition by sulfide against the activity of SRB and other anaerobes in UAHR was not observed.
1/3 of biomass was found in the media packing layer and the remaining biomass was formed in the sludge blanket layer at the lower part of UAHR. SRB was distributed uniformly and well balanced with other anaerobes along with the reactor height. Organics and sulfate in the artificial wastewater were removed at the rate of 64.7% and 55.7%, respectively in the sludge blanket layer, where 50% of the layer was composed of SRB. Considering sulfate removal and SRB fraction along with the reactor height, it was determined that SRB dominated in UAHR
In order to increase biodegradability of Acrylonitrile wastewater, the pretreatment study with UV/TiO₂ was performed. After photocatalytic pretreatment of 8 hours, the biodegradability of the wastewater increased from 0.113 to 0.256, but pH decreased to below 3 due to dissociated Cl^(-) from organic compounds in the wastewater. As a result, the photocatalytic pretreatment was considered as infeasible due to long reaction time and pH neutralization cost.
Organics removal efficiency of photocatalytically pretreated Acrylonitrile wastewater in UAHR was below 50% during the operating period. Higher than 90% in the sulfate removal efficiency was achieved during Phase I through Phase Ⅲ(A), whereas it greatly dropped to below 45.6% at Phase Ⅲ(C) when the sulfate concentration in the influent increased over 800 mg SO₄^(2-)/L. The sulfate removal efficiency was not recovered for almost 2 months even after the sulfate concentration was lowered by dilution. Consequently, it was determined that the influent wastewater with low COD/sulfate ratio (< 1) to UAHR be remained below 800 mg SO₄^(2-)/L in concentration and within 1.0 kg SO₄^(2-)/m³/day in loading rate to attain a high removal efficiency of over 90% for sulfate and a short HRT.
It was found that SRB activity was not adversely affected by increased sulfate concentration of 1,500 mg SO₄^(2-)/L during Phase Ⅲ(C) based on low sulfide concentration (below 100 mg/L) in the effluent from UAHR despite a dramatic increase of sulfate concentration in the effluent. The amount of biogas generated was not significant, and the H₂S concentration in the biogas was as high as 10 ppm in spite of low sulfate loading rate and the fraction of H₂S was low and 6.7%.
After the pretreatment of Acrylonitrile wastewater using UV/TiO₂ and UAHR(Phase Ⅲ, HRT=48 hr), AFBR (HRT=20hr) was applied to remove the residual organic matter and NH₄^(+)-N at the same time. As the sulfate removal efficiency in UAHR was maintained at higher than 90%, the organics and NH₄^(+)-N in the wastewater were removed in AFBR at a high removal efficiency of over 93% and 85%, respectively. The removal efficiency of remaining organics and the nitrification rate of NH₄^(+)-N in AFBR were directly influenced by the removal efficiency of sulfate in UAHR. Therefore, it was suggested that the simultaneous removal efficiency of residual organic matter and NH₄^(+)-N from the wastewater in AFBR could be achieved at over 80% as long as the sulfate removal efficiency in UAHR was maintained over 90%.
It was concluded based on this research that UAHR was applicable for treatment of Acrylonitrile wastewater with high sulfate concentration and low COD/sulfate ratio (<1), and AFBR was capable of removing the residual organics and ammonia from UAHR.

목차 (Table of Contents)

• 목차
• Ⅰ. 서론 = 1
• Ⅱ. 문헌연구 = 3
• 2.1 난분해성 폐수의 생분해도 증가를 위한 전처리 = 3
• 2.1.1 광촉매 산화(UV/TiO₂)공정 = 5
• 2.1.2 무기이온이 TiO₂산화반응에 미치는 영향 = 10
• 2.2 자연계에서의 황의 순환 = 12
• 2.3. 황화합물을 함유한 산업폐수 = 15
• 2.3.1 황산염 함유 산업폐수 = 15
• 2.3.2 황화합물(H₂S, HS^(-), S^(0), 등)을 함유한 폐수 = 17
• 2.3.3 Acrylonitrile 폐수 = 19
• 2.4. 황산염을 함유한 폐수 처리 = 21
• 2.4.1 물리·화학적 처리 = 21
• 2.4.2 혐기성 소화공정을 이용한 생물학적 처리 = 22
• 2.4.3 황산염 환원 박테리아(Sulfate-reducing Bacteria, SRB) = 37
• Ⅲ. 실험장치 및 방법 = 42
• 3.1 Acrylonitrile 폐수의 생물학적 처리 가능성 평가 = 42
• 3.1.1 폐수내 유기기질 종류에 따른 미생물 성장가능성 평가 = 42
• 3.1.2 Acrylonitrile 폐수의 회분식 혐기성 처리 = 45
• 3.2 혐기/호기성 반응기를 이용한 황산염 함유 폐수처리 = 51
• 3.2.1 생분해도 증가를 위한 광촉매(TiO₂)전처리 = 51
• 3.2.2 혐기/호기성 반응기를 이용한 황산염 함유 폐수 처리 = 53
• 3.2.3 UAHR내 SRB 및 다른 혐기성 박테리아의 분포 = 58
• 3.2.4 UAHR에서의 Biogas 발생량 및 조성변화 = 61
• 3.3 분석항목 및 방법 = 62
• Ⅳ. 결과 및 고찰 = 65
• 4.1 Acrylonitrile 폐수의 생물학적 처리 가능성 = 65
• 4.1.1 폐수내 유기기질 종류에 따른 미생물 성장 = 65
• 4.1.2 Acrylonitrile 폐수의 혐기성 분해도 평가 = 69
• 4.1.3 Acrylonitrile 폐수의 독성도 평가 = 72
• 4.1.4 COD/Sulfate 비에 따른 SRB 활성도 평가 = 74
• 4.2. TiO₂를 이용한 Acrylonitrile 폐수 전처리 = 78
• 4.3 UAHR을 이용한 COD/Sulfate 비가 낮은 합성폐수 처리 = 82
• 4.3.1 UAHR에서의 유기물 제거 = 83
• 4.3.2 UAHR에서의 SS 거동 = 87
• 4.3.3 UAHR에서의 황산염 제거 = 89
• 4.3.4 UAHR에서의 황산염 제거가 유기물 제거에 미치는 영향 = 95
• 4.3.5 COD/Sulfate 비가 낮은 폐수 처리시 Biogas 발생특성 = 101
• 4.3.6 COD/Sulfate 비가 낮은 폐수 처리시 UAHR내 SRB 분포와 황산염제거 = 112
• 4.4 UAHR을 이용한 고농도 황산염 함유 석유화학폐수 처리 = 120
• 4.4.1 UAHR을 이용한 석유화학 폐수내 유기물 제거 = 122
• 4.4.2 UAHR에서의 석유화학 폐수내 황산염 제거 = 129
• 4.4.3 UAHR을 이용한 석유화학 폐수 처리시 유출 Sulfide 농도변화 = 134
• 4.4.4 UAHR을 이용한 석유화학 폐수 처리시 희석수비에 따른 황산염과 유기물 제거율의 변화 = 138
• 4.4.5 UAHR을 이용한 석유화학 폐수 처리시 유출 BA/VA 농도변화 = 140
• 4.5. AFBR에서의 석유화학 폐수의 잔존 유기물 및 질소제거 = 143
• 4.5.1 석유화학폐수의 UAHR/AFBR에 의한 생분해도 변화 = 144
• 4.5.2 AFBR에서의 잔존 유기물 제거 및 황산염 거동 = 147
• 4.5.3 AFBR에서의 잔존 NH₄^(+)-N 제거 = 150
• Ⅴ. 결론 = 156
• Ⅵ. 참고문헌 = 159
• Abstract = 181