Statistical Optimization of Operational Parameters for Enhanced Naphthalene Degradation by Photocatalyst

The optimization of operational parameters for enhanced naphthalene degradation by TiO2/Fe3O4-SiO2 (TFS) photocatalyst was conducted using statistical experimental design and analysis. Central composite design method of response surface methodology (RSM) was adopted to investigate the optimum value of the selected factors for achieving maximum naphthalene degradation. Experimental results showed that irradiation time, pH, and TFS photocatalyst loading had significant influence on naphthalene degradation and the maximum degradation rate of 97.39% was predicted when the operational parameters were irradiation time 97.1 min, pH 2.1, and catalyst loading 0.962 g/L, respectively. The results were further verified by repeated experiments under optimal conditions. The excellent correlation between predicted and measured values further confirmed the validity and practicability of this statistical optimum strategy

Permanganate/Bisulfite Pre-Oxidation of Natural Organic Matter Enhances Nitrogenous Disinfection By-Products Formation during Subsequent Chlorination

The permanganate/bisulfite (PM/BS) process is a novel oxidation process, which can degrade micropollutants within several seconds. As natural organic matter (NOM) ubiquitously exists in an aquatic environment, the PM/BS process will inevitably react with NOM, which may impact the disinfection-by-products (DBPs) formation during subsequent chlorination. This study investigated the effect of PM/BS pre-oxidation of NOM on DBP formation. It was found that TOC removal reached a plateau when the molar ratio of PM to BS was 1:5. Increasing ratios of PM to BS decreased the intensity and area of fluorescence spectroscopy. PM and BS doses, pre-oxidation time, pH of solutions and concentration of Br− impacted the formation potential of various DBPs. PM/BS pre-oxidation decreased the formation of TCM while increasing the yields of N-DBPs, thus increasing the risk of water quality. Calculated toxicity analysis showed that a general increase in CTI was observed with PM/BS pre-oxidation, indicating that PM/BS pre-oxidation had a negative effect on risk control of overall cytotoxicity. Although the PM/BS process could accelerate the degradation of micropollutants, the elevated DBPs formation, especially highly toxic N-DBPs, needs enough attention to control water-quality risk

Characterizing Water Pollution Potential in Life Cycle Impact Assessment Based on Bacterial Growth and Water Quality Models

For the life cycle assessment (LCA) of wastewater management, eutrophication is considered the most relevant factor. However, eutrophication is not the only pathway through which wastewater influences the environment, and merely characterizing eutrophication potential is not sufficient for the LCA framework to reflect the influence of wastewater. This study defines the Bacterial Depletion of Oxygen (BDO)—a new impact category that represents the oxygen depleting potential caused by the growth of microorganisms—and characterization models and characterization factors are developed for the application of BDO. Water quality models (both one- and two-dimensional) are incorporated into the BDO characterization models so that the LCA framework includes some spatially differentiated factors, and can be used to estimate the direct impact of wastewater on receiving environment (IBDO value). Based on three case studies, this study demonstrates how the BDO category can be applied for the evaluation of wastewater management. Results show that increases in the downstream distance and self-purification coefficients reduce the IBDO value, whereas the increase in water velocity raises the IBDO value. Future integration of the BDO category with water quality models must link the dilution effect of water bodies, the environmental carrying capacity of receiving water, and the distribution of water pollutants in eutrophication and bacterial oxygen depletion

Identify stakeholders' understandings of life cycle assessment results on wastewater related issues

To facilitate decision-making processes in waste management, it is important to not only evaluate environmental impacts, but also to measure how stakeholders form opinions and make choices based one valuation results. Life cycle assessments (LCAs) have been widely used to evaluate environmental impacts; however, LCAs cannot be used to measure how people make judgments based on evaluation results. As such, in this study, we combined LCA with conjoint analysis, an economic method that allows individuals to consider all factors and demonstrate their preferences simultaneously. We used this combined method in a case study on wastewater treatment, and obtained two major types of estimation results: (1) the relative importance of each impact category of LCA, and (2) the overall preferences of respondents for each alternative. This study also highlighted some issues regarding the combination of methodologies, such as the selection of impact categories in LCA, the conversion of impact categories into understandable attributes for conjoint analysis, and weaknesses in conjoint analysis that need to be addressed and corrected in future studies

Selective activation of peroxymonosulfate to singlet oxygen by engineering oxygen vacancy defects in Ti3CNTx MXene for effective removal of micropollutants in water

Defect engineering is an effective strategy to boost the catalytic activity of MXene towards heterogeneous peroxymonosulfate (PMS) activation for water decontamination. Herein, we developed a facile approach to fine-tune the generation of oxygen vacancies (OVs) on Ti3CNTx crystals by Ce-doping (Ce-Ti3CNTx) with the aim of mediating PMS activation for the degradation of micropollutants in water. By varying the dopant content, the OV concentrations of Ti3CNTx could be varied to enable the activation of PMS to almost 100% singlet oxygen (1O2), and hence the effective degradation of sulfamethoxazole (SMX, a model micropollutant). Various advanced characterization techniques were employed to obtain detailed information on the microstructure, morphology, and defect states of the catalysts. The experimental results showed that SMX removal was proportional to the OVs level. Density functional theory (DFT) models demonstrated that, in contrast to pristine Ti3CNTx, the OVs on 10%Ce-Ti3CNTx could adsorb the terminal O of PMS, which facilitated the formation of SO5•− as well as the generation of 1O2. We further loaded the optimized catalysts onto a polytetrafluoroethylene microfiltration membrane and also demonstrated the efficient removal of SMX from water using a convection-enhanced mass transport flow-through configuration. This study provides new insights into the effective removal of micropollutants from water by integrating state-of-the-art defect engineering, advanced oxidation, and microfiltration techniques

Genetic Diversity of Hydrogen-Producing Bacteria in an Acidophilic Ethanol-H2-Coproducing System, Analyzed Using the [Fe]-Hydrogenase Gene▿ †

Hydrogen gas (H2) produced by bacterial fermentation of biomass can be a sustainable energy source. The ability to produce H2 gas during anaerobic fermentation was previously thought to be restricted to a few species within the genera Clostridium and Enterobacter. This work reports genomic evidence for the presence of novel H2-producing bacteria (HPB) in acidophilic ethanol-H2-coproducing communities that were enriched using molasses wastewater. The majority of the enriched dominant populations in the acidophilic ethanol-H2-coproducing system were affiliated with low-G+C-content gram-positive bacteria, Bacteroidetes, and Actinobacteria, based on the 16S rRNA gene. However, PCR primers designed to specifically target bacterial hydA yielded 17 unique hydA sequences whose amino acid sequences differed from those of known HPB. The putative ethanol-H2-coproducing bacteria comprised 11 novel phylotypes closely related to Ethanoligenens harbinense, Clostridium thermocellum, and Clostridium saccharoperbutylacetonicum. Furthermore, analysis of the alcohol dehydrogenase isoenzyme also pointed to an E. harbinense-like organism, which is known to have a high conversion rate of carbohydrate to H2 and ethanol. We also found six novel HPB that were associated with lactate-, propionate-, and butyrate-oxidizing bacteria in the acidophilic H2-producing sludge. Thus, the microbial ecology of mesophilic and acidophilic H2 fermentation involves many other bacteria in addition to Clostridium and Enterobacter