Remediation of micropollutants in water sources by microalgae technologies

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Micropollutants (MPs) in wastewater stem from municipal, hospital, industrial wastewaters and agricultural runoff. MPs originate from the use of pharmaceutical and personal care products such as drugs, cosmetics, shampoos and chemicals, etc. MPs can be classified as pharmaceuticals, personal care products, pesticides and industrial chemicals. MPs has posed raising concern recently. They are discharged increasingly in wastewater at worryingly high levels and being treated ineffectively in water and wastewater treatment system. They enter the food chain and drinking water, subsequently exposing people and creating an epidemiological problem. Despite chemical treatment of MPs proved to be useful for MPs removal, biological treatment is still preferable because of its low-cost and biomass recovery. However, several MPs are poorly biodegradable. This study aims to improve the performance of a microalgae treatment system towards MPs remediation. The screening of microalgae species is performed at first. The growth dynamics of a freshwater (𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 𝘷𝘢𝘭𝘨𝘒𝘳π˜ͺ𝘴) and marine microalgae (𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 sp. and 𝘚𝘡π˜ͺ𝘀𝘩𝘰𝘀𝘰𝘀𝘀𝘢𝘴 sp.) in various salinities were investigated. Maximal biomass yields were 400–500 mg/L at 0.1–1% salinity while the TOC, NO3 ⁻-N, PO₄³⁻-P were eliminated 39.5–92.1%, 23–97.4% and 7–30.6%, respectively. Through the scanning electron microscope, the cells of freshwater 𝘊. 𝘷𝘢𝘭𝘨𝘒𝘳π˜ͺ𝘴 were broken due to high salinity but not the 𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 sp.. Thus, the 𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 sp. was selected for the next stage. In the next step, the extracellular polymeric substance (EPS) and enzyme extrusion of 𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 sp. using seven carbon sources and two salinities were investigated. EPS and enzyme are the key factors involving in the micropollutant cometabolism of microalgae. Results indicated that EPS and enzymes of microalgae cultured with glucose and saccharose outcompeted other carbon sources. The EPS reached 30 mg/L, having doubled the amount of protein than carbohydrate. For superoxide dismutase and peroxidase enzymes, the highest concentrations were beyond 60 U/ml and 6 nmol/, respectively. This amount could be potentially used for degrading 40% ciprofloxacin of concentration 2000 ΞΌg/L. These results highlighted that certain carbon sources and salinities could induce 𝘊𝘩𝘭𝘰𝘳𝘦𝘭𝘭𝘒 sp. to produce EPS and enzymes for pollutant co-metabolism and also for revenue-raising potential. In the same experiment but using MPs additionally, EPS and enzyme concentrations increased from 2 to 100-fold in comparison with only sole carbon sources. This confirmed that MPs cometabolism had occurred. The removal efficiencies of tetracycline, sulfamethoxazole, and bisphenol A ranged from 16-99%, 32-92%, and 58-99%, respectively. By increasing EPS and enzyme activity, the MPs concentrations accumulated in microalgae cells also fell 400-fold. The cometabolism process resulted in several degradation products of MPs. Based on the results, proper carbon sources for microalgae can be selected for practical applications to remediate MPs in wastewater while simultaneously recovering biomass for several industries and gaining revenue. To enhance the MPs cometabolism efficacy, microalgae were pretreated with CaOβ‚‚ prior to using for sulfonamide remediation. The optimal dose of CaOβ‚‚ was 0.05 – 0.1 gCaOβ‚‚/g biomass. Thanks to CaOβ‚‚, EPS level has increased 2 – 3 times to enhance MPs cometabolism. In the batch condition, the overall MPs removal efficiencies of the pretreated microalgae did not differ significantly from the non-pretreated one but several degradation products of sulfanomide compounds were detected. It highlighted that CaOβ‚‚-pretreated microalgae have cometabolized MPs to the degradation products in a greater extent. In the continuous mode, after 60d operation, the MPs removal efficiency of the pretreated microalgae was higher than the non-pretreated 10-20%.
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