Application of Biochar to Water and Wastewater Treatment for Removal of Emerging Micropollutant

Abstract

Micropollutants often refer to endocrine disrupting compounds (EDC) and/or pharmaceuticals and personal care products (PPCPs). Those chemicals such as bisphenol A, 17β-estradiol, atenolol, benzophenone, and benzotriazole have been linked to serious human health and ecological impacts. However further understanding of their toxicity and epidemiology has been hindered by the lack of advanced analysis techniques for those micropollutants at trace amount. Recent development of advanced analysis techniques (GC/MS/MS or LC/MS/MS) enabled us to detect the micropollutants in water at very low concentrations (ng/L - μg/L). Therefore it is possible to understand the impact of micropollutants at trace amount as well as the removal of micropollutants from the water. Traditionally water treatment process based on the coagulation does not effectively remove the micropollutants due to the small molecular size and the polarity of target. The micropollutants can be removed by the adsorption with the adsorbent such as powder activated carbon. Adsorption with activated carbon having a high-binding affinity has been widely used to eliminate various pollutants in the aqueous environment. Activated carbon is known as a superior material for water treatment process. However the activated carbons are mainly generated from wood resources, even though the recent studies indicate the under-representative materials (e.g., coconut shell) were started to being used for the activated carbon synthesis. On the contrary, biochar is generated from the pyrolysis of the wasted biomass (e.g., livestock manure). It becomes a cost effective and environmental sustainable option compared to activated carbons. As a result, the treatment of EDCs and PPCPs with biochar has been considered, as a cost effective and environmental sustainable strategy, by water related stakeholders. The objective of this study is to determine the removal efficiencies of target EDCs/PPCPs having different physicochemical properties by biochar in comparison to powdered activated carbon (PAC). The adsorption pattern of each chemicals was determined by isotherm experiments and the effect of various water quality conditions were examined. Additionally the effect of co-existing kaolinite to the adsorption of target EDCs/PPCPs was observed. The removal efficiency by biochar was approximately 5-30% higher than that by PAC depending on experimental conditions, presumably due to the higher polarity, higher surface area, and bigger micro pore volume of biochar. The removal of compounds followed the order: E2 > BZP > BPA > BZT, which is indicated by the decrease of Freundlich affinity coefficients for both biochar and PAC. A pH increase from 3.5 to 10.5 decreased the removal by adsorption of BZP, BZT, BPA, and E2 by 11.5, 11.4, 10.7, and 4.7% using biochar, respectively. Overall, biochar had a higher adsorption capacity for all tested chemicals compared to PAC. The removal efficiency of biochar in the presence of kaolinite was higher than that of PAC with kaolinite, presumably because the relatively high surface area and pore volume of biochar resulted in a higher adsorption capacity for the target compounds. Removal of the compounds in the absence of kaolinite followed the order: BZP > ATN > BZT by Langmuir maximum adsorption capacities. An increase in the pH from 3.5 to 10.5 decreased the adsorption of ATN, BZP, and BZT by 14.5, 2.1, and 14.4%, respectively, by biochar-kaolinite. Overall, biochar as adsorbent for micropollutant removal has shown the better adsorption capacity for all tested chemicals compared to PAC, suggesting that biochar derived from wasted biomass may be a promising sorbent for water/wastewater treatment in near future.;분석기술의 발달로 전세계의 수자원에서 ng/L~μg/L으로 존재하는 미량오염물질이 검출되고 있다. 극히 낮은 농도로 검출됨에도 불구하고 생태계와 인간에 영향을 미칠 수 있는 가능성이 있다. 전통적인 정수/폐수 처리 시스템에서는 미량오염물질을 완전히 제거하기 어렵다. 그러나 활성탄을 이용한 흡착기술로 이러한 미량오염물질을 상당량 제거 가능하다. 기존에 토양개량 목적으로 사용되던 바이오차가 최근 수처리 분야에서 주목 받고 있다. 바이오차는 바이오매스를 열 분해시키는 과정에서, 즉 가스와 가열처리 시에 바이오 연료가 생성될 때 얻어지는 부산물이다. 바이오차는 작용기의 표면밀도와 고도로 응축된 구조 등의 특성을 가지고 있어 미량오염물질을 제거하기 위한 최적의 흡착제로서 잠재성을 가지고 있다. 대표적인 미량오염물질인 아테놀올, 벤조페논, 벤조트리아졸, 비스페놀 A, 17-베타에스트라디올의 제거를 위해 바이오차를 흡착제로 사용하였고 상업용 분말 활성탄을 대조군으로 사용하였다. pH, 바탕이온, 이온강도, 천연유기물, 캐올리나이트를 이용해 자연 생태계와 유사한 조건을 조성하여 흡착에 미치는 영향을 살펴보았다. 바이오차는 분말활성탄에 비해 5~30% 높은 흡착 효율을 보였다. Freundlich 등온모델에 따르면 제거대상물질의 제거율은 다음과 같다: E2 > BZP > BPA > BZT. 또한, pH가 증가할수록 흡착효율이 감소하는 경향을 보였다. 캐올리나이트의 존재가 바이오차의 흡착효율 상승에 영향을 미칠 것이라는 가정과는 달리, 눈에 띄는 영향을 보이지 않았다. 분말 활성탄과 비교하여 바이오차가 상기의 오염물질에 대해 높은 흡착 제거율을 보임으로써 정수/폐수처리와 환경에서 촉망되는 흡착제가 될 것임을 시사했다.