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Use of Biochar to Produce Reclaimed Water for Irrigation Reuse Purposes
AuthorYanala, Sandeep R.
Civil and Environmental Engineering
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Contaminants of emerging concern (CECs), especially, pharmaceutical and personal care products (PPCPs) are not removed well during conventional wastewater treatment and hence pose water quality risk to the environment and potentially to public health. The goal of this work was to remove CECs, with emphasis on PPCPs, from treated municipal wastewater using biochar, a low-cost adsorbent, by conducting fixed-bed sorption experiments. The reclaimed water after biochar treatment is intended for use in growing crops/grass for livestock production. If the PPCPs are present in the reclaimed water at high levels, there is greater potential for the PPCPs to enter into human food chain through the meat and its products. Native biochar from slash materials of Jeffrey pine forest was hand ground and sieved to enable its use in column set-up experiments. Chemical activation of native biochar using 1N KOH was performed to obtain KOH-biochar. Initially, total organic carbon (TOC) was used as a surrogate for CECs present in water, and native as well as KOH-biochar were used to remove TOC from treated wastewater. Prior to TOC removal experiments, DI water was pumped through native and KOH-biochar present in column to reduce carbon leaching from biochar. These leaching experiments showed that the TOC leached by native biochar was negligible when compared to KOH-biochar. From breakthrough curves that were plotted for native and KOH-biochar for TOC removal from treated wastewater, It was observed that, even though KOH-biochar removal efficiency for TOC was better at the beginning, both native and KOH-biochar reached their respective saturation capacities within 100 minutes of continuous pumping. Whereas granular activated carbon (GAC) containing column did not reach its saturation capacity during 46 hours of continuous pumping, and reached effluent to influent concentration ratio (Ce/Co) ratio of 0.15 only at the end. The saturation capacities obtained for native and KOH-biochar are 0.05 mg TOC/g and 0.13 mg TOC/g, respectively which were quite low when compared to the adsorption capacities mentioned in the literature. Surprisingly, the results obtained suggest that biochar may not be a potential adsorbent for PPCP removal contradicting the work that has been published till now. The opposing results might be due to interference of leached carbon from biochar itself. Also, it might suggest that TOC cannot be used as surrogate for CECs. Hence, a total of 12 CECs were analyzed using LC-MS/MS, after collecting the effluent samples from KOH-biochar and GAC. Adsorption behavior varied widely among different CECs when KOH-biochar was used as adsorbent. So, compounds were broadly divided into three categories based on their breakthrough behavior and Ce/Co ratios. Caffeine, carbamazepine, DEET and PFOA had a greater range of Ce/Co values with highest value >0.5 during continuous adsorption tests and were included in category I compounds. Breakthrough curve predictions revealed that these compounds follow non-linear Thomas model with adsorption capacities of 396 µg L-1, 391 µg L-1, 1160µg L-1 and 31 µg L-1, respectively for caffeine, carbamazepine, DEET and PFOA. Category II compounds were comprehensively removed throughout the continuous tests. Diphenhydramine, fluoxetine and trimethoprim fall under this category with a narrow range of Ce/Co values and highest of <0.15. Ibuprofen, ketoprofen, meprobamate, primidone and sulfamethoxazole fall under category III whose removal is minimal using KOH-biochar with highest Ce/Co value greater than 1. However, GAC comprehensively removed all the PPCP compounds except for ibuprofen and ketoprofen proving it to be a better adsorbent than biochar. For category I and II compounds, an analysis of compound’s structure, functional groups present and characteristics revealed that π-π electron donor–acceptor might be the most dominant adsorption mechanism. However, no conclusions could be made regarding the reasons for minimal removal of category III compounds. Further, calculations were done to assess if the biochar employed had the potential to remove CECs from reclaimed water used for irrigated animal feed crops when biochar is used as a soil amendment. It was determined that, based on the results from continuous tests, biochar amendment to soils can remove 7 out of 12 CEC compounds analyzed and could possibly reduce their uptake by plants.