Journal of Environmental Engineering

Abstract

Being classified as a suspected carcinogen, 1,4-dioxane (1,4-D) has been one of the most frequently detected organic contaminants in groundwater sites. Due to the common co-occurrence of 1,4-D with chlorinated compounds and a lack of comprehensive health advisory guideline standards established for potable water and other uses on a global scale, a new research emphasis to reflect more realistic situations needs to be placed onto the effects of common co-existing chemicals such as 1,1-dichloroethene, trichloroethylene, cis-1,2-dichloroethylene, and 1,1,1-trichloroethane on the environmental fate of 1,4-D. Additives (e.g., ions, nutrients, enzymes) are also introduced to enhance 1,4-D treatment efficiencies. To the best of our knowledge, however, there is no review article dealing with the removal of 1,4-D in the presence of chlorinated solvents and other interfering substances. Understanding its concurrent removal with the main chlorinated co-contaminants is necessary for more insightful and proper design of effective remediation strategies for 1,4-D. This review article will focus on the behavior, transport, and persistence of 1,4-D in the presence of other pervasive groundwater contaminants and substrates under diverse environmental conditions and treatment technologies. This review will also provide detailed information on currently available remediation technologies for 1,4-D (either individually or co-occurring) and potential key points to be considered for future technologies development.

Practical Applications

1,4-dioxane (1,4-D) is an emerging toxic pollutant that is found as a contaminant in soil and groundwater. Despite its harmful nature, there are not many global standards regulating its levels in water. Therefore, finding effective ways to remove harmful pollutants is crucial for safer waters, requiring extended research and time. 1,4-D often exists together with other contaminants such as chlorinated solvents, making water treatment more difficult, costly, and less efficient. This review explains the physical and chemical behaviors of other co-contaminants when combined with 1,4-D as well as the current removal technologies as categorized based on physical, chemical, biological, or combination (hybrid) methods. It is found that each removal technique has its strengths and weaknesses but some failing to eliminate the co-solvents although they successfully removed 1,4-D. Thus, future research is warranted to further elucidate key reaction mechanisms between 1,4-D and other co-contaminants and to test real scale applications.

Drainage-based gas control methods will cause mine gas to be discharged into the atmosphere, causing environmental pollution and aggravating the greenhouse effect. Methane in mine gas can be oxidatively decomposed by using microbial technology, to reduce mine gas emissions and the threat of gas to mine safety. However, coal mines’ methane and oxygen concentrations change in real time. To explore the effects of different methane and oxygen concentrations on the methane-oxidizing bacteria mixed community, a methane-oxidizing bacteria mixed community was enriched and cultured from mine soil samples in this study, and its community structure, cell morphology, and methane degradation ability were analyzed. The results showed that the methane-oxidizing bacteria Methylomicrobium accounted for 55.6% of the total, Cloacibacterium accounted for 19.39%, and Methylophilus accounted for 10.3%. The methane degradation rate of the mixed community can reach $29.98\mathrm{\mu mol}{\mathrm{mL}}^{-1}{\mathrm{d}}^{-1}$. Using the Michaelis–Menten kinetic equation analysis, it was found that the methane degradation effect was the highest when the methane concentration was 1%–20%, and the maximum methane oxidation rate could reach $57.078\mathrm{\mu mol}{\mathrm{mL}}^{-1}{\mathrm{d}}^{-1}$. When the oxygen concentration ranged from 1% to 50%, the methane degradation ability of methanotrophs gradually increased with the increase of oxygen concentration.

New energy vehicles and solid-state batteries (SSBs) will help to reduce the carbon footprint by up to 103% if fully commercialized and installed by 2035. This research collected market data on China’s E-car power batteries in the production phase from the past five years to the next 25 years in order to calculate the carbon emission reduction ratio achieved by new electric vehicles’ (EVs) power batteries. Using SimaPro software, analysis results reveal that among seven types of batteries, lithium iron phosphate (LFP), cobalt manganese oxide (NCM-811) batteries, and SSBs have the lowest production carbon footprint values of 44, 51.1, and 43.7 ${\mathrm{kgCO}}_2\mathrm{e}$, respectively. When compared to LFP and NCM batteries, SSBs have the potential to reduce the carbon footprint of EV batteries by up to 39%. So, SSBs will have a higher market value and installed capacity, accounting for 65% of all batteries by 2040, which can prove the significance of new energy vehicles in reducing carbon emissions in the transportation field. Finally, the five technical and economic characteristics (cost competitiveness, cycle life, C-rate, energy density, and safety) of LFP-based lithium-ion battery (LIB), NMC-811, and lithium lanthanum zirconium oxide (LLZO) based on SSBs batteries are summarized. The promise of the SSBs’ energy density and safety has prompted several automakers to invest in NCM-811 and LFP technologies. The cost of SSBs per kWh will eventually be lower than that of its counterparts once supply chains are established. This is because the material cost is reduced when using solid-state electrolytes with higher energy density. After all, less raw material is required per kWh.

Groundwater flowing through a nonaqueous-phase liquid (NAPL) source zone may generate large NAPL-contaminated saturated soils and act as a long-term source of soils and groundwater contamination. Remediation efficiency and cost are greatly influenced by an accurate prediction of the thermal conductivity of NAPL-contaminated saturated soils. In this work, a series of thermal conductivity tests were carried out using a thermal probe method to investigate the influencing factors together with the prediction model. The results show that the thermal conductivity of contaminated saturated soil versus NAPL content can be divided into three stages. The variation of the thermal conductivity with NAPL content shows a slow decrease in the first stage, a significant decrease in the second stage, and a more moderate decrease in the third stage. Based on the 53 complete mineral data of soils collected from the literature, the thermal conductivity of the solid particle equation was modified. It is confirmed that quartz content is a crucial factor influencing $k_s$ and cannot be replaced by sand content. Subsequently, a new model is proposed for the prediction of the thermal conductivity of contaminated saturated soil. To improve the prediction accuracy of the model, a new normalized thermal conductivity equation ($k_e$) and a relationship of $\theta$ and $k_s/k_l$ were proposed to modify the new model. After modification, the new model can provide a well-performing prediction for the thermal conductivity of NAPL-contaminated saturated soils.

Methane oxidation mediated by methanotrophs is limited, under anoxic condition, by electron acceptors availability, such as oxygen, and ineffective enrichment of microbes. Methylocystis sp., as a typical type II methanotroph, uses nitrite as a terminal electron acceptor and flexibly couples with methane oxidation. This special electron transfer process potentially accelerates methane anoxic oxidation. In this study, two lab-scaled bioreactors were inoculated with reservoir sediment. Both control and treatment groups were fed with ${\mathrm{CH}}_4$, and the treatment group was also supplemented with nitrite as an electron acceptor to enrich effective methanotrophs. The result indicated that Methylocystis sp. performs a major role in methane oxidation and denitrification; 33 key proteins critical for methane metabolism and denitrification were significantly upregulated. The Methylocystis sp.–initialized methane oxidation encoded by particulate methane monooxygenase (pmoABC) then metabolized the product to ${\mathrm{CO}}_2$ in the formaldehyde oxidation VI pathway (${\mathrm{H}}_4\mathrm{MPT}$) and reduced nitrite to nitrogen. Subsequently, ${\mathrm{CO}}_2$ and nitrogen were further transformed into bicarbonate and ammonia in enzymes encoded by cynT and nifK, respectively, both of which were reused by Bacillus sp., Caenimonas sp., Methylocella sp., and other coexisting microorganisms. The strain, Methylocystis sp. L03, was isolated and found to independently reduce nitrite and oxidize methane in an anoxic environment. This study revealed that the unexpectedly flexible methane metabolism by aerobic methanotrophs under nitrite-rich anoxic environments may act as an important and overlooked methane sink, constituting a unique link between the two global nutrient cycles of carbon and nitrogen.

Abstract

Membrane aerated biofilm reactor (MABR) technology is currently garnering wide acceptance as a wastewater treatment technology due to process and operational advantages that have accrued during many years of investigation, but despite these achievements, the challenge of biofilm thickness control still persists. This work was therefore designed to expand the current knowledge of MABR operations, particularly with respect to biofilm thickness management and reactor performance stability. Biofilm thickness was controlled with intermittent washing of the membrane bundle based on a bulk dissolved oxygen (DO) concentration set-point of $0.2\mathrm{mg}/\mathrm{L}$. This nonaggressive membrane cleaning mechanism subdued biofilm sloughing, but maintained biofilm erosion, which supported the development of a multifunctional biofilm with the thickness and microbial activity adequate to stabilize reactor performance over 185 days. Applied in the treatment of municipal wastewater, the MABR demonstrated average organic carbon and ammonia nitrogen (${\mathrm{NH}}_4^{+}─\mathrm{N}$) removal efficiencies of $92\%\pm 2\%$ and $100\%\pm 7.8\%$, respectively. The total inorganic nitrogen removal reached $84\%\pm 5\%$ at mean surface loading rates of $10\%\pm 0.7\mathrm{g}\mathrm{COD}/{\mathrm{m}}^2/\mathrm{d}$ and $0.93\pm 0.07\mathrm{g}\mathrm{N}/{\mathrm{m}}^2/\mathrm{d}$ within a hydraulic retention time of 2.5 h and with minimal reactor down time. The average biofilm density determined at the end of the study was $17.6\mathrm{g}/\mathrm{L}$, while the biofilm thickness determined to be 0.49 mm. A 16S rRNA analysis of the MABR microbial population at each stage indicated that a microbial community with sufficient biodiversity and relative abundance for stable reactor performance was sustained. Demonstrating that intermittent membrane cleaning with water effectively stabilized the MABR biofilm thickness, reduced process upsets, and maintained high performance at high substrate loading.

Practical Applications

The current drive for energy neutrality, drastic reduction in energy costs, and increasingly stringent wastewater discharge rules has led to the quest for the development of energy efficient and effective wastewater treatment technologies. MABR is one of these developing technologies. Compared to traditional biological wastewater treatment methods, MABRs offer improved performance with regards to the removal of pollutants from wastewater and energy efficiency. MABR is a biofilm-based technology, whose success depends on the biofilm thickness. Moreover, a biofilm with adequate thickness is required to maintain the diversity and abundance of the microbial community required for high and stable performance over extended operational periods. But, the effective control of biofilm thickness remains a lingering challenge in the application of MABR technology. In practice, biofilm thickness control is commonly accomplished by promoting biofilm detachment using air bubbles. However, several studies have reported performance upsets and performance lag that can sometimes last up to several months following each biofilm detachment episode due to substantial biofilm loss. This study recommends a biofilm thickness management protocol that involves gentle detachment of loosely bound biofilms through nonaggressive cleaning and cleaning episodes initiated when a set operating condition is attained.

Multispecies water quality modeling is critical for simulating complex chemical reactions in drinking water distribution systems. An updated EPANET 2.2–compatible version of EPANET multi-species eXtension (EPANET-MSX) was used, which included dispersion and improved mass balance reporting, to simulate an experimental study. The use of EPANET-MSX was supplemented by an automated Python script to process experimental data, handle model execution, and analyze results. Nicotine-associated chlorine loss in drinking water—initially investigated from a drinking water security perspective—modeled with EPANET-MSX was compared with bottle test and test injection data. Two reaction models were tested (with and without a reactive intermediate), and the model that included a reactive intermediate nicotine species using dispersion was found to produce the best model agreement with experimental data. These results provide a demonstration of the new features within EPANET-MSX in the context of the nicotine-chlorine reaction.

Abstract

This study develops an optimal design of a municipal water resource recovery facility (WRRF) to treat a high-nitrate industrial waste. The study demonstrated two basic results: first, that a numerical optimization scheme has the potential to significantly reduce construction and operating costs for wastewater treatment. Second, it demonstrated the potential for high-nitrate industrial waste to partially satisfy the electron acceptor requirement for treating municipal wastewater, whereas the wastewater reduces the demand for supplemental carbon for treating the nitrate. The optimization scheme sought to minimize an objective function, which included annualized construction costs, operating costs, and penalties for environmental performance. The optimization algorithm used was the Nelder–Mead method. This was coupled with a commercial activated sludge simulation program in an iterative calculation to predict the performance of successive process designs. The optimized process had a predicted 89% removal of total nitrogen from the combined municipal and industrial wastewater. The optimization reduced the objective function by 53% in comparison to initial designs that were manually optimized without the algorithm. The supplemental carbon requirement was reduced by 15.5% over literature values. The unique aspect of this research is the coupling of an external biological simulation model with a numerical optimization algorithm that could significantly improve the cost-effectiveness of process design along with operating costs and effluent quality. Furthermore, it demonstrates the feasibility of treating these types of wastes in a municipal facility.

Practical Applications

The results of this study indicate that coupling a numerical optimization scheme with commercial activated sludge (or other) process simulation models has the potential to make the construction and operation of treatment facilities significantly more cost effective. This study also shows that high-nitrate industrial wastewater has the potential to be treated in combination with municipal wastewater, reducing the cost of supplemental carbon for the nitrate reduction while simultaneously reducing the cost of aeration for the wastewater treatment. We began by developing a daily cost of treatment (the objective function) based on the annualized cost for design parameters such as aeration tank and clarifier size plus operating costs for aeration and pumping energy, methanol dosage, and solids disposal. Added to this were cost penalties for effluent discharge of biochemical oxygen demand (BOD), total suspended solids (TSS), and nitrogen species. The optimization scheme iteratively makes adjustments to the design parameters to seek to minimize the total costs in the objective function. The development of an objective function that includes capital and operating costs and environmental performance factors is unique to this study.

The degradation of typical dye wastewater has always been a continuous concern in wastewater treatment. Microelectrolysis is a technology that offers the advantages of being green and highly efficient in treating wastewater. However, traditional binary microelectrolysis has problems, such as low applicability and high dependence on acidic environments. This study prepared ternary microelectrolytic materials, optimized the key conditions of material preparation and wastewater treatment, explored the removal mechanism of ternary microelectrolytic materials for dye wastewater, and quantitatively analyzed the contribution of different removal paths in the removal process of dye. For chemical oxygen demand (COD), the removal contributions of adsorption, flocculation, ${·\mathrm{O}}_2^{-}$, $·\mathrm{OH}$, and reduction were 22.23%, 20.35%, 15.43%, 6.62%, and 0.71%, respectively. For the chorma removal of vital red, the removal contributions of adsorption, flocculation, $·{\mathrm{O}}_2^{-}$, $·\mathrm{OH}$, and reduction were 21.07%, 55.97%, 14.57%, 4.62%, and 0.91%, respectively. For the chorma removal of disperse blue, the removal contributions of adsorption, flocculation, $·{\mathrm{O}}_2^{-}$, $·\mathrm{OH}$, and reduction were 7.81%, 72.36%, 11.52%, 6.10%, and 0.70%, respectively. Ternary microelectrolysis can achieve an ideal removal effect in a neutral treatment environment. The material structure, $·{\mathrm{O}}_2^{-}$ produced in the system, and pH regulation of effluent are crucial in the removal process of dye wastewater. Ternary microelectrolysis materials are superior to traditional binary microelectrolysis materials due to their double cathode characteristics, strong applicability, and ability to operate in a neutral treatment environment. This study can serve as guide for ternary microelectrolysis technology in the treatment of typical dye wastewater.

Because coagulation and flocculation do not remove suspended particles but condition particles for removal downstream, performance of these processes is assessed by relative removal of particles and organic matter in downstream processes. Predictive models of coagulation and flocculation performance do not include information about downstream processes, but they could be more generally applied if they did. In this paper, the AguaClara hydraulic flocculation model is modified so that a fitting parameter, $k$, becomes a function of sedimentation capture velocity. Experimentally, tap water with 90 NTU of kaolinite clay was treated with six PACl doses of $0–2.79\mathrm{mg}/\mathrm{L}$ as Al, a hydraulic flocculation residence time of 6.5 min with a dimensionless flocculation product of 62,200, and six tube settler detention times of 8.4–1.4 min for capture velocities of 0.1 to $0.6\mathrm{mm}/\mathrm{s}$, achieving settled turbidities of 0.21–82.5 NTU. The analysis revealed an exponential relationship between $k$ and the sedimentation capture velocity, which appears related to the shape of typical particle size distributions. An addition to the model that incorporates capture velocity lowered the normalized root mean square error of the data from 0.414 to 0.113 logarithmic performance ratio units. The updated model is more readily applied to water treatment plant design and analysis and allows for design trade-offs to be made when considering hydraulic flocculation and sedimentation process parameters.

Drinking water distribution systems (DWDS) are some of the critical components of a drinking water system, providing water supply services to our growing populations. To maintain the safety of the drinking water supply, the water distributed through these systems needs to be regularly disinfected to ensure that it remains free of pathogens and to minimize the risk of contamination during distribution. In DWDS, balancing the risks of excessive chlorine and microbial contamination is crucial for public health due to chlorine additions in the storage tanks of these systems. Proposing effective risk-mitigation strategies requires simulations of plausible contamination scenarios and input from local experts, given the challenge of maintaining an appropriate residual chlorine level that is effective but not excessive. In addition, excessive discharge of chlorine into the environment can result in increased water pollution levels and the production of harmful disinfection byproducts, such as trihalomethanes, posing a threat to the health of waterbodies and having implications for total maximum daily loads (TMDLs). Here, we presented a framework that couples the analytical hierarchy process (AHP) with water quality simulations for decision making related to mitigating the risk of contamination to DWDS for extreme chlorine levels. We demonstrated this framework on a section of a DWDS in a highly populated city, where an accidental overapplication of chlorine resulted in the chlorine level in the tank being excessively high. Various local experts provided input about important decision criteria, their relative importance, and potential risk-mitigation strategies. Using the input in our framework, we determined important decision criteria and identified geographic zones of the DWDS at risk of chlorine contamination. The presented framework can be used in preventing chlorine contamination risks in DWDS located in other population centers. It was found that the areas closest to the tank, in terms of distance or time of travel, are more vulnerable due to the potential for rapid dispersion of contaminants. The results demonstrated the importance of incorporating expert opinions into the decision-making process and highlighted the capability of AHP in risk assessments. Future research can explore other decision-making methods, consider demographic characteristics of affected populations, and apply our presented framework to entire drinking water systems to further improve risk-mitigation strategies for preventing chlorine contamination risks in DWDS located in other population centers.