Comprehensive assessment of chlorination disinfection on microplastic-associated biofilms.

Chlorination on microplastic (MP) biofilms was comprehensively investigated with respect to disinfection efficiency, morphology, and core microbiome. The experiments were performed under various conditions: i) MP particles; polypropylene (PP) and polystyrene (PS), ii) MP biofilms; Escherichia coli for single-species and river water microorganisms for multiple-species, iii) different chlorine concentrations, and iv) different chlorine exposure periods. As a result, chlorination effectively inactivated the MP biofilm microorganisms. The disinfection efficiency increased with increasing the free chlorination concentration and exposure periods for both single- and multiple-species MP biofilms. The multiple-species MP biofilms were inactivated 1.3-6.0 times less than single-species MP biofilms. In addition, the PP-MP biofilms were more vulnerable to chlorination than the PS-MP biofilms. Morphology analysis verified that chlorination detached most MP biofilms, while a small part still remained. Interestingly, chlorination strongly changed the biofilm microbiome on MPs; the relative abundance of some microbes increased after the chlorination, suggesting they could be regarded as chlorine-resistant bacteria. Some potential pathogens were also remained on the MP particles after the chlorination. Notably, chlorination was effective in inactivating the MP biofilms. Further research should be performed to evaluate the impacts of residual MP biofilms on the environment.

Microplastic removal in conventional drinking water treatment processes: Performance, mechanism, and potential risk.

The effectiveness of traditional drinking water treatment plants for the removal of Microplastics (MPs) in the size range of tens of micrometers is currently uncertain. This study investigated the behavior and removal efficiency of four different sized polystyrene MPs (10-90 µm in diameter) in a simulated cascade of coagulation/sedimentation, sand filtration, and UV-based oxidation over technically relevant time frames. In the coagulation and sand filtration steps, the larger the MP size, the better it was removed. The coagulant type and water characteristics (i.e., pH and the presence of natural organic matter) influenced the coagulation efficiency for MPs. X-ray microcomputed tomography technique and two-site kinetic modeling were used to identify the mechanisms involved in sand filtration. The MPs > 20 µm could be completely retained in sand by straining, while the attachment to the sand surface was likely responsible for the retention of MPs < 20 µm. However, approximately 16% of 10 µm MPs injected passed through the sand, which were further fragmented by UV oxidation. UV/H2O2 treatment promoted the MP fragmentation and chemical leaching more significantly than UV treatment, resulting in a higher toxicity for UV/H2O2-treated water. Our findings pave the way for deeper understanding of how MPs behave and transform in a sequential drinking water treatment process.

Soil microbial communities-mediated bioattenuation in simulated aquifer storage and recovery (ASR) condition: Long-term study.

This study evaluated the long-term organic removal performance and microbial community shift in simulated aquifer storage and recovery (ASR) conditions. For this purpose, anoxic soil box systems were operated at 15 °C for one year. The results showed that the assimilable organic carbon (AOC) concentration in the anoxic soil box systems was successfully decreased by 79.1%. The dissolved organic carbon (DOC) concentration increased during the initial operational periods; however, it subsequently decreased during long-term operation. Readily biodegradable organic fractions (i.e., low-molecular weight (LMW) neutrals and LMW acids) decreased along with time elapsed, whereas non-biodegradable fraction (i.e., humic substances) increased. Proteobacteria and Acidobacteriota were predominant in the anoxic box systems throughout the operational periods. Firmicutes and Bacteroidota suddenly increased during the initial operational period while Gemmatimonadota slightly increased during prolonged long-term operation. Interestingly, the microbial community structures were significantly shifted with respect to the operational periods while the effects of AOC/NO3- addition were negligible. Various bacterial species preferring low temperature or anoxic conditions were detected as predominant bacteria. Some denitrifying (i.e., Noviherbaspirillum denitrificans) and iron reducing bacteria (i.e., Geobacter spp.) appeared during the long-term operation; these bacterial communities also acted as organic degraders in the simulated ASR systems. The findings of this study suggest that the application of natural bioattenuation using indigenous soil microbial communities can be a promising option as an organic carbon management strategy in ASR systems.

Feasibility of membrane distillation process for potable water reuse: A barrier for dissolved organic matters and pharmaceuticals.

In this study, the feasibility of the membrane distillation (MD) process as a wastewater reclamation system for portable reuse was investigated. The flux was stably maintained at about 20 L/m2h (LMH) at ΔT 30 °C, compared to higher flux at ΔT 50 °C, which showed a rapid decrease in the flux due to severe fouling. MD produced excellent quality of potable water satisfied the drinking water standards of Korea from effluent of sewage treatment plant (ESTP). The fractions of the hydrophobic OC (HOC) and chromatographic DOC (CDOC) from LC-OCD analysis was firstly suggested to understand different organic transport during the MD process. The transport of organic matters across the MD membrane mitigated at low operation temperature and the transported organics in all the tested waters were mostly volatile low molecular weight organics, aromatic amino acids. All of thirteen selected pharmaceuticals were completely removed by MD, regardless of their properties. In order to retard the membrane fouling of the MD process, coagulation and filtration pre-treatments were applied. The pre-treatment process coupled MD process could successfully remove impurities including NH4-N without severe membrane fouling. Moreover, coagulation pretreatment reduced transport of ammonia due to decrease in pH.

Assimilable organic carbon removal strategy for aquifer storage and recovery applications.

Aquifer storage and recovery (ASR) technology has been adopted as a strategic water management tool. However, during the injection of oxic and organic carbon-containing water to the underground aquifers, severe phenomena such as clogging and groundwater deterioration have been reported. To prevent these severe phenomena, assimilable organic carbon (AOC) concentration has been controlled in the ASR applications by supporting bacteria growth potential. In this study, the AOC removal strategy was investigated in a simulated ASR system using an indigenous bacterium, Pseudomonas jinjuensis. AOC removal was evaluated under three different experimental conditions: (i) 30 °C and aerobic, (ii) 15 °C and aerobic, and (iii) 15 °C and anoxic. The effects of contact media such as sand and granular activated carbon on AOC removal efficiency were also investigated. Results show that under the 30 °C aerobic condition, P. jinjuensis could remove 99.8% (13 µg L-1) of AOC with soil. The variations in the organic fractions determined by liquid chromatography with organic carbon detector analysis were observed and showed trends similar to those of AOC determined by the flow cytometry method. The indirect injection method in ASR application was recommended due to the AOC removal benefit by soil indigenous bacterium.

Retardation of wetting for membrane distillation by adjusting major components of seawater.

Wetting by fouling is phenomenon specific to membrane distillation (MD) and are regarded as challenges to the seawater membrane distillation (SWMD) process. To understand fouling and wetting, the influence of Mg and Sr crystals, which can potentially cause scaling, as well as Ca crystals deposited on the membrane surface were investigated. Mg(OH)2 and CaSO4 had significant impact on fouling and wetting. Even if CaCO3 and SrSO4 had no effects on fouling and wetting as single salts, CaCO3 and CaSO4 were dominant in synthetic seawater without Mg(OH)2. However, the occurrence of Mg(OH)2 scales became a cause for concern if Ca ion was removed from seawater for the prevention of fouling and wetting. Therefore, Mg as well as Ca should be removed for proper fouling and wetting control. NaOH/Na2CO3 softening was used for the removal of Ca and Mg ions. In addition, based on the inhibition effects of Mg ions on Ca scales, a new pretreatment method involving the injection of MgCl2 to increase the Mg /Ca ratio was examined.

Phosphorous recovery from sewage sludge using calcium silicate hydrates.

Phosphorous is an essential limiting nutrient for which there is no substitute. Its efficient recovery from sewage treatment plants is important to mitigate both dependence on limited reserves of exploitable phosphate rock and eutrophication of surface waters. Here, we evaluate the use of calcium silicate hydrates (CSH) to recover phosphorous eluted from sewage sludge. Phosphorous elution experiments were conducted with acid and base leaching solutions. The phosphorous recovery efficiency with CSH was compared to that with other calcium compounds, and the final product was analyzed to assess its potential value as fertilizer. Dried sewage sludge from the West Lake Ecological Water Resource Center, South Korea, having 123 g-P kg-1, was used for these tests. About 55% of the phosphorus in the sludge was released with an elution solution of 0.1 M H2SO4. A dose of 15 g L-1 of CSH recovered 89.6% of the eluted phosphorous without the need for additional pre-treatment, and the resulting calcium phosphate product (in brushite form, based on XRD analysis) exhibited superior settleability than that resulting from Ca(OH)2- and CaCl2-induced precipitation. XRD peaks of the calcium sulfate hydrate (in gypsum form) and residual CSH were also observed. The final product contained a relatively high content of the total P2O5 eluted in a 2% citric acid solution (43.1%), which suggests that it might be readily used to fertilize crops.

Oxidation of bisphenol A by UV/S2O8(2-): comparison with UV/H2O2.

The UV/S2O8(2-) process was applied to decompose bisphenol A (BPA), which is a representative endocrine-disrupting chemical (EDC), and was comared with the UV/H2O2 process. The BPA degradation efficiency by UV/S2O8(2-) was increased by increasing S2O8(2-) concentration or decreasing BPA concentration. The presence of humic acid caused an inhibitory effect. The BPA oxidation rate by UV/S2O8(2-) was increased in the following order: neutral pH (pH(i) = 7) < acidic pH (pH(i) = 4) < basic pH (pH(i) = 10). The main oxidizing species in the UV/S2O8(2-) system was sulphate radical (SO4(-*)), whereas the main oxidizing species in the UV/H2O2 system was OH radical (OH*). Compared with UV/H2O2, the UV/S2O8(2-) process showed higher performance for not only BPA degradation but also its mineralization, which means that SO4(-*) is a more effective oxidant for BPA than the OH*. The results shown in this study imply that the SO4(-*) -based UV/S2O8(2-) process can be an excellent alternative process for the widely used UV/H2O2 process, with higher remediation performance.