Journal of Environmental Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This review seeks to summarize the current literature regarding the removal of viruses from wastewater using membrane bioreactors (MBRs). Membrane bioreactors are an effective technology for the removal of viruses from wastewater and do so with greater efficiency than conventional activated sludge treatment plants. However, much is unclear about the capabilities and mechanisms of this process. Membrane pore size is commonly thought to be an important factor impacting virus removal, but this effect is primarily observed when the pore size is smaller than the virus diameter, and the effects vary by virus. A variety of factors can impact the effectiveness of MBRs in virus removal, with the presence of a biofilm foremost among them. Balancing the presence of a biofilm with regular membrane backwashing and cleaning to maintain consistent flux remains a critical consideration in MBR operation. Differences in reported removal efficiencies of human viruses compared to model viruses (such as bacteriophages) call into question the reliability of these model viruses in assessing the effectiveness of virus removal in MBRs. More investigation, particularly with full-scale MBR systems, must be performed to further understand the potential of MBRs in virus removal.

This study investigated the possibility of using granules of crushed concrete demolition waste (CCDW) as a reactive medium in a permeable reactive barrier (PRB) to remediate groundwater contaminated with heavy metals. Factors influencing the process of sorption, such as the contact time, initial metal concentration, agitation speed, and sorbent dosage, were studied. The sorption data were described using four isotherm models (Langmuir, Freundlich, Redlich–Peterson, and Radke–Prausnitz), whereas the continuous experimental results were fitted with three breakthrough curve models (Thomas, Bohart–Adams, and Yan). The performance of the reactive barrier in the set of continuous column experiments was monitored using different effluent contaminant concentrations of groundwater, hydraulic conductivity, and solution pH.

Polyhydroxyalkanoate (PHA) accumulating microbial enrichment was established on volatile fatty acids (VFAs) containing leachate derived from the organic fraction of municipal solid waste (OFMSW). The enrichment was based on a 12-h feast-famine batch cycle and an exchange ratio of 50% in which VFAs were completely consumed in less than 50 min during stable periods of operation. No pH control was applied in the system, and the pH went as high as 9 due to the presence of amongst others, ammonia [$500\mathrm{mg}·{\mathrm{L}}^{-1}$ total ammonia nitrogen (TAN) on average]. The degree of enrichment was evaluated with fluorescence in situ hybridization (FISH), and a yet unknown genus of large (3–5 μm diameter) beta-proteobacteria appeared dominant in the culture. A method for estimating the fraction of PHA accumulating active biomass in the total volatile suspended solids was established, and the results indicated an increase of this fraction from 25% to 56% after implementing two modifications in the operational protocol: (1) a pretreatment of the substrate removing virtually all settleable solids; and (2) a settling phase in the enrichment reactor after the feast phase, selectively removing nonsettleable solids and slowly degradable substrates. The PHA accumulation potential of the culture was $77\pm 18\mathrm{wt}\%$ PHA ($\mathrm{n}=3$) after 3 h in batch accumulation experiments. The results suggest the potential feasibility of PHA production under conditions that were previously considered economically favorable but technically difficult.

A microbial fuel cell (MFC) was constructed to remediate cadmium (Cd) contaminated soil, and the effects of Cd concentration (0, 5, 20, and $100\mathrm{mg}/\mathrm{kg}$) and electrode spacing (3, 6, and 9 cm) on reactors were studied. The results showed that different Cd concentrations had no significant effect on the output voltage and internal resistance. However, the electrode spacing was inversely proportional to the MFC power generation and proportional to the charge transfer internal resistance (${\mathrm{R}}_{\mathrm{ct}}$) by the electrochemical impedance spectroscopy (EIS) test. The maximum power density was $22.93{\mathrm{mW}/\mathrm{m}}^2$ (in $\mathrm{MFC}\text{-}0\mathrm{mg}/\mathrm{kg}$) and $22.71{\mathrm{mW}/\mathrm{m}}^2$ (in MFC-3 cm), which was the best among the MFCs of different Cd concentrations and electrode spacing, respectively. After 50 days of operation, the maximum accumulation rate of Cd at the cathode was observed in $\mathrm{MFC}\text{-}5\mathrm{mg}/\mathrm{kg}$ and MFC-3 cm, which were 130.00% and 107.70%, respectively. The kinetic analysis showed that high Cd concentrations and large electrode spacing could reduce the accumulation of Cd (${\zeta }_{\mathrm{Cd}}$) at the cathode as a result of the influence of soil respiration and cation migration, respectively. The results revealed that a MFC is a feasible option for remediating Cd contaminated soil, and the electrode spacing was the main determinant of the MFC performance and Cd accumulation rate, while the impact of the Cd concentration was minimal.

Release of lead (Pb) in drinking water from lead service lines has been extensively studied in single pipes, and the importance of water chemistry has been reported. However, the impact of variations in water chemistry parameters during water supply from the treatment plant to the downstream distribution network is crucial to understand toward minimizing lead release rates and has not yet been researched. This study proposes a comprehensive framework for investigating the changes in dissolved lead concentrations resulting from variations in the concentration of water chemistry parameters (such as pH, orthophosphate, free chlorine disinfectant residual, dissolved inorganic carbon and natural organic matter). The framework accounts for changes in the chemistry as water flows in a typical, full-scale water distribution network from the treatment plant to the homes through iron distribution mains and lead service lines under dynamic hydraulic conditions. The approach comprises the development of a multispecies reactive transport model for simulating important water chemistry reactions in distribution mains using EPANET-MSX. This water chemistry model is coupled in the framework with a mass transfer-based model for lead release from service lines. The resulting trends of water chemistry parameters variations with water age are qualitatively verified with general trends from experimental and field studies. The influence of complex water chemistry on the spatial and temporal profile of lead levels are analyzed by generating holistic simulations for a full-scale water distribution network case study. Three relevant treatment scenarios of pH adjustment, disinfectant dosage, and orthophosphate addition are presented to reflect the importance of the causal relationship between water chemistry variations in distribution mains and dissolved lead release from service lines. A strong correlation is observed between % change in dissolved lead levels and variations in pH, free chlorine residual, and orthophosphate residual in distribution mains. Further, practical implications for the use of the proposed framework to identify lead release hotspots, suggest potential sampling locations, and optimize remedial treatment measures to control lead dissolution for safe water supply are discussed.

A kind of porous carbon spherical material with high specific surface ($S_{\mathrm{BET}}=\mathrm{1,292}{\mathrm{m}}^2/\mathrm{g}$) was synthesized from deactivated methyl tert butyl ether (MTBE) resins with KOH as the activator (KAC). This synthesized material was characterized by Brunner Emmet Teller (BET) measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and X-ray fluorescence (XRF). Additionally, the mechanism of adsorbing methylene blue (MB) on this porous carbon sphere was studied and interpreted from kinetics, adsorption equilibrium and thermodynamic properties. Results showed that the kinetics data fitted the pseudo-second-order model well; the adsorption equilibrium data followed Langmuir model with a maximum adsorption capacity of $478.5\mathrm{mg}/\mathrm{g}$; and the thermodynamic parameters displayed an endothermic and spontaneous adsorption process of MB on carbon spheres.

Effluent from textile mills is considered one of the most polluted among all industrial effluents because it contains a large amount of toxic dyes that are released during the dyeing processes. Conventional methods have been found to be inefficient in removing those toxic synthetic dyes from the effluent. Entrapped photocatalytic membrane (EPM) is one of the recently established technologies that has very good potential in treating textile effluent. EPM combines photocatalysis, an advanced oxidation process, and membrane separation in a single unit to treat the effluent. In this paper, fabrication and characterization of an ultrafiltration EPM composed of polyvinylidene fluoride (PVDF) and titanium dioxide (${\mathrm{TiO}}_2$) was conducted. Different concentrations of ${\mathrm{TiO}}_2$ (0%, 1%, 2%, and 3% by weight) were used to fabricate EPMs. The increase in the concentration of ${\mathrm{TiO}}_2$ changed the morphological behavior of the membrane, which was evaluated using the results obtained from scanning electron microscopy (SEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM), contact angle, and tensile stress studies. EPM was employed in a photocatalytic reactor to remove Remazol Turquoise Blue dye from synthetic textile effluent. The incorporation of ${\mathrm{TiO}}_2$ enhanced the performance of the membrane by providing high photocatalytic activity under ultraviolet (UV) illumination. After 4.5 h of operation of the EPM containing 3% ${\mathrm{TiO}}_2$, the removal of total organic carbon (TOC) and color were 91% and 93%, respectively.

Advances in sensor technology have increased our ability to monitor a wide range of environments. However, even as the cost of sensors decline, only a limited number of sensors can be installed at any given site. The physical placement of sensors, along with the sensor technology and operating conditions, can have a large impact on our ability to adequately monitor environmental change. This paper introduces a new open-source Python package, called Chama, that determines optimal sensor placement and technology to improve a sensor network’s detection capabilities. The methods are demonstrated using site-specific methane emission scenarios that capture uncertainty in wind conditions and emission characteristics. Mixed-integer linear programming formulations are used to determine sensor locations and detection thresholds that maximize detection of the emission scenarios. The optimized sensor networks consistently increase the ability to detect leaks, as compared to sensors placed near each potential emission source or along the perimeter of the site.

Biological treatment for volatile organic compound (VOC)–contaminated wastewater with conventional aeration methods causes significant stripping loss of pollutants due to its high volatility. To overcome this problem, the membrane-aerated biofilm reactor (MABR) was developed. The aim of this study was to reduce acetonitrile (ACN) stripping loss during the aeration process and to evaluate MABR performance under different hydraulic retention times (HRTs) and ACN surface loading rates. The MABR was operated with an inlet ACN concentration of $300\mathrm{mg}/\mathrm{L}$ at four HRT conditions—4, 6, 9, and 12 h. Experimental results indicated that nearly 49% of ACN was stripped due to mechanical aeration, whereas stripping loss due to MABR was approximately 0.1%. A HRT of 6 h was found to be the optimum condition with removal efficiencies of ACN, total organic carbon (TOC), chemical oxygen demand (COD), and total nitrogen (TN) at 98%, 87%, 84%, and 69%, respectively. This MABR could achieve removal of ACN with a maximum surface loading rate and removal capacity of 3.75 and $3.63\mathrm{g}/{\mathrm{m}}^2·\mathrm{d}\text{ay}$, respectively. This study therefore established improved MABR efficiency with shorter HRT requirements.

${\mathrm{Fe}}_3{\mathrm{O}}_4$-coated pretreated biochars (${\mathrm{Fe}}_3{\mathrm{O}}_4$@PBC) were prepared for the first time by a Fe(III)-ethanol solution impregnation-calcination method. When photo-Fenton catalysts were used, their effectiveness in removing metronidazole (MNZ) from aqueous media was evaluated. ${\mathrm{Fe}}_3{\mathrm{O}}_4$@PBC samples were characterized by X-ray diffraction, scanning electron microscope, vibrating sample magnetometer, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller methods. The results showed that ${\mathrm{Fe}}_3{\mathrm{O}}_4$ coating was successfully formed on the surface of ${\mathrm{HNO}}_{3\text{-}}$ pretreated biochar, and ${\mathrm{Fe}}_3{\mathrm{O}}_4$@PBC can be separated by applying an external magnetic field. The coating of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ did not change the pore structure and maintained a high surface area of the biochar. Fe loading significantly affected the photo-Fenton degradation and adsorption ability of MNZ. The highest MNZ removal rate and the greatest catalytic ability were found in the PBC-6.6Fe sample containing 6.6% Fe by mass. Various operating parameters, such as solution pH, ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration, and MNZ concentration, were tested during MNZ’s photo-Fenton catalytic degradation. The results indicate that the highest MNZ degradation efficiency can be derived from a moderate acidic solution, and the optimal pH is 3. Using PBC-6.6Fe, the increase of ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration from 30 to $60\mathrm{mmol}·{\mathrm{L}}^{-1}$ promotes the degradation of photo-Fenton, and both an excessive ${\mathrm{H}}_2{\mathrm{O}}_2$ and an increase in MNZ concentration suppressed the process. Under the conditions of $0.4\mathrm{g}·{\mathrm{L}}^{-1}$ PBC-6.6Fe, $300\mathrm{mg}·{\mathrm{L}}^{-1}\mathrm{MNZ}$, $60\mathrm{mmol}·{\mathrm{L}}^{-1}{\mathrm{H}}_2{\mathrm{O}}_2$, and initial pH of 3, 95.1% of MNZ was degraded. The PBC-6.6Fe had good stability, and its removal efficiency was still over 92% after five repeated uses. This study confirmed that •OH played a dominant role, while ${\mathrm{O}}_2^{•-}$ and ${\mathrm{h}}^{+}$ played a weaker role in the photo-Fenton system. The results indicated that ${\mathrm{Fe}}_3{\mathrm{O}}_4$@PBC served as a prospective visible-light-driven catalyst similar to Fenton for the treatment of wastewater containing MNZ.

This study evaluated nitrogen removal characteristics in a biofilm system for recirculating aquaculture wastewater treatment with different carriers and aeration modes under salinity conditions ($35\mathrm{g}\mathrm{NaCl}{\mathrm{L}}^{-1}$) and oligotrophic stress (total organic $\text{carbon}<5.0\mathrm{mg}{\mathrm{L}}^{-1}$). The results demonstrated that the nitrification process was inhibited at a high salinity concentration of $35\mathrm{g}\mathrm{NaCl}{\mathrm{L}}^{-1}$, and an ammonia oxidation efficiency greater than 80% required 45 days but resulted in high nitrite accumulation. No significant differences in ammonia oxidation and denitrification efficiencies were found between the polypropylene and polyurethane foam carriers, whereas compared with the polyurethane foam carrier, the polypropylene carrier with a higher aeration duration of 6 h in Phase 2 needed less time (99 days) for the acclimatization of complete nitrification. However, no denitrification efficiency was found with full-time aeration, and the highest denitrification efficiency was $34.11\%\pm 6.05\%$ with no aeration. Poor denitrification performance was mainly due to oligotrophic stress from carbon source deficiency, and an efficient denitrification efficiency of $62.7\%\pm 8.2\%$ was achieved with the addition of biodegradable polycaprolactone (PCL).

The objective of this study is to compare the hydrology of prescriptive and water balance cover designs for Larimer County Landfill in Colorado via hydrologic models parameterized from laboratory-measured testing of undisturbed and remolded landfill soils. A prescriptive cover is designed to limit percolation into underlying waste via a low-permeability layer, whereas a water balance cover is designed to limit percolation via storing infiltrated precipitation and subsequently releasing the water through evaporation and transpiration. Soil characteristics and engineering properties were determined for an existing prescriptive closure cover and two borrow areas. Hydrologic modeling was completed using commercially available software to predict percolation through the prescriptive and water balance covers. The wettest 10 consecutive years on record with a complete meteorological data set (1992–2001) were selected for the analysis. Predicted percolation through a prescriptive cover was $<0.1\mathrm{mm}/\text{year}$, and evaporation was the main mechanism for removing water from the cover profile. Predicted percolation in the water balance cover models ranged from 4.9 to $13.2\mathrm{mm}/\mathrm{year}$ depending on borrow area soil, cover thickness, and vegetation parameters. Transpiration was the main mechanism for removing water from the water balance cover models.

Compost leachate is one of the most strongly polluting wastewaters, which is found in significantly large amounts. The major objective of this research was to study the biological treatment of compost leachate in an upflow–downflow hybrid anaerobic reactor, located in a compost production plant designed to process $200\mathrm{t}/\mathrm{day}$ of urban solid waste. A range of models based on different kinetics have been tested using the experimental data from measurements taken from the hybrid anaerobic reactor. The substrate removal using the second-order rate ($k_{2(s)}$) was found to be 22.3 day^–1. The rate constant ($U_{\max }$) for maximum removal and the constant ($K_B$) for the saturation value for the Stover–Kincannon model was determined to be 90.9 and $97.3\mathrm{g}/\mathrm{L}·\mathrm{day}$, respectively, which resulted in the best fitting of this model to the actual compost leachate plant data.

The harmful effects of cadmium (Cd) to human health associated to its structure and chemical form. Cd(II) pollution is classified as causing economic and environmental damages due to being a probable human carcinogen and its severe effects to ecosystems. This work asserted a facile synthesis and easy-to-collect adsorbent to remove Cd(II). The magnetic-graphene oxide-based nanocomposite was synthesized via a two-step process of coprecipitation and polymerization. The batch adsorption results indicated that the highest adsorption capacity could be reached over the wide pH range of 4.0–6.0. The adsorption isotherms and kinetic studies suggested that the Cd(II) adsorption followed a pseudo second-order model and the Langmuir model, took place in monolayer coverage, and was strongly controlled by chemisorption. The formation of ternary surface complexes through cross-linked nitrile groups under cadmium-promoted bridging type improved Cd(II) adsorption capacity. The thermodynamic studies are an indicator of endothermic reaction, which describes the feasible and spontaneous nature of Cd(II) adsorption behavior in the view of temperature from 20°C to 40°C. The maximum adsorption capacity of adsorbent for Cd(II) ($270.27\mathrm{mg}{\mathrm{g}}^{-1}$) was higher than those of most of previous researches. The magnetic graphene oxide (GO)-based nanocomposite was synthesized via a two-step process of co-precipitation and polymerization by polyacrylonitrile (PAN).

The water sector is facing emerging challenges, as cyber-physical threats target Supervisory Control and Data Acquisition (SCADA) systems of water utilities. A cyber-physical stress-testing platform is presented in this work, named RISKNOUGHT, which is able to model water distribution networks as cyber-physical systems, simulating the information flow of the cyber layer and the feedback interactions with the physical processes under control. RISKNOUGHT utilizes an EPANET-based solver for the physical process and a customizable network model for the SCADA system, capable of implementing complex control logic schemes within a simulation. The platform enables the development of composite cyber-physical attacks on various elements of the SCADA, including sensors, actuators, and PLCs, assessing the impact they have on the hydraulic response of the distribution network and the level of service. The platform is tested on a proof-of-concept benchmark network with promising results that demonstrate that the platform can form an innovative cyber-physical tool to support strategic planning and risk management.

This investigation focused on phycoremediation of pollutants from synthetic coke-oven wastewater using a cyanobacterial consortium of Leptolyngbya sp. and Planktothrix sp., and biomass production. Lethal dose analysis was performed for test strains with varying concentrations of pollutants, and maximum biomass obtained were $322.7\pm 22.54$, $322.3\pm 12.06$, and $352\pm 12.53\mathrm{mg}{\mathrm{L}}^{-1}$ at $2\mathrm{mg}{\mathrm{L}}^{-1}$ phenol, $175\mathrm{mg}{\mathrm{L}}^{-1}$ ammoniacal-N, and $30\mathrm{mg}{\mathrm{L}}^{-1}$ nitrate, respectively. A one-factor-at-a-time (OFAT) approach was followed to determine suitable operating conditions for maximum removal by varying pH (8–10); inoculum size (IS) (5%–10%); and initial concentrations (ICs) of phenol ($2–3\mathrm{mg}{\mathrm{L}}^{-1}$), ammoniacal-N ($150–200\mathrm{mg}{\mathrm{L}}^{-1}$), and nitrate ($30–40\mathrm{mg}{\mathrm{L}}^{-1}$). The most preferred condition as analyzed by OFAT was $\mathrm{pH}=8$; $\mathrm{IS}=10\%$; and initial concentrations of $\mathrm{phenol}=2.5\mathrm{mg}{\mathrm{L}}^{-1}$, a $\mathrm{mmoniacal}\text{-}\mathrm{N}=175\mathrm{mg}{\mathrm{L}}^{-1}$, and $\mathrm{nitrate}=30\mathrm{mg}{\mathrm{L}}^{-1}$. Response surface methodology (RSM) was used to obtain the optimum condition for removal of the pollutants and biomass production. Further experiments were performed at the optimum conditions as analyzed by OFAT and RSM with synthetic treated coke-oven wastewater (STCW) containing mixed pollutants, and the results were compared. Both OFAT and RSM analysis results were effective for real wastewater treatment, but from an economic point of view, OFAT analysis results were more suitable. Biomolecules, namely carbohydrate, protein, and lipid molecules, were extracted from treated cyanobacterial biomass to assess the prospect of value-added product formation. Mechanistic pathways for metabolism of pollutants were discussed.

In water treatment plants, the design of contact tanks is of critical importance for effective disinfection of potable water. The most important design problem in these flow-through systems is the formation of recirculation and flow jet zones, which reduce mixing efficiency of the contact system. To this end, in this study, a porous baffle design is proposed as an alternative to the slot baffle design, which may provide an alternative solution to these problems. Experimental and numerical studies were conducted on a 1:10-scale laboratory model of a prototype water treatment contact tank located in the province of Eskisehir in Turkey. To understand the effectiveness of the proposed porous baffle design, before the use of alternative porous baffle designs, heterogeneous soil-gravel mixtures with specified porosities were prepared and placed inside the baffles such that the porosity of the baffle could alternatively be changed in the flow direction. The purpose here is to investigate the efficiencies of several baffle configurations without using elaborate solid baffle structures that will mimic the performance of the porous baffle. The porous designs were thoroughly investigated, relying on the efficiency indexes obtained from dye tracer experiments. Experimental studies conducted for different porosity distributions indicate that the baffle porosity should increase in the flow direction along the chamber length so that the flow jet entering to the chamber with high momentum should be allowed to pass to the neighboring chamber relatively higher than the flow jet emerging from the chamber. This important observation led to the design of the porous baffle with variable porosity in the flow direction for a controllable fluid transfer between neighboring chambers. The proposed design successfully improves the hydraulic efficiency from poor to average based on the baffling factor measure, and the Morrill ($M_o$) index approaches 2, which is recommended by regulations. To further ascertain the contribution of the proposed baffle design, a computational fluid dynamics (CFD) model was developed for the simulation of turbulent flow through the porous baffle, and it was validated by the experimental studies conducted in this study. The simulated mean velocity profiles and tracer results were in good agreement with the experimental results. Visualization of internal structure of the flow through the tank and the baffles revealed that the momentum of the entering flow jet to the chamber could effectively turn dead zones into active mixing zones in the neighboring chamber. The authors emphasize that in the final design, porous baffle solid structures will be used that will mimic the pore structure characteristics of the design alternatives determined in this study instead of the use of the soil-gravel mixtures in this experimental study.

Overexploitation of nonrenewable energy resources and the problems associated with their unfair utilization have demanded for alternative sources of renewable energy. Lignocellulosic wastes including cereal straws, sugarcane bagasse, and banana stem, etc., have the potential for conversion into future fuel sources. Banana stem juice (BSJ) was extracted and explored for its potential in biogas production. The study found that BSJ can be fermented within 5–7 days using an anaerobic digestion process and is suitable for biogas production. The present study also focused on enhancing biogas production by adding microbial cultures with the substrate (BSJ) during the anaerobic digestion process. Five bacterial species, namely Streptomyces sp., Bacillus subtilis, Pseudomonas aeruginosa, Lactobacillus plantarum, and Desulfovibrio desulfuricans (separately, in combinations and a mixed culture) were investigated to find the efficiency for boosting biogas production. The optimal conditions as microbial dose, pH, retention time, and temperature for getting the highest yield of biogas through the anaerobic degradation process were analyzed. The best results were observed at 5% microbial dose at pH 8. The P. aeruginosa demonstrated the best results among the cultures studied. On adding a 5% dose of P. aeruginosa, at 8 pH and 30°C temperature for a retention time of 5 days, 3,350 mL of biogas containing 75% of methane share was produced from 1L of BSJ. Under the same conditions, chemical oxygen demand (COD) and total organic carbon (TOC) were reduced by 29% and 38%, respectively, in comparison to unfermented BSJ. It was found that the addition of microbial consortia during biogas production significantly improved the methane production and reduced the COD and TOC content.

California has consistently altered natural water resources to provide water for its growing population and to support the fifth largest economy in the world. However, the old ways of coping with the California’s urban water needs—overdraft of groundwater, stream depletion, and greater imports—will no longer meet the demands of the 21st century. We examine California’s water history and present several promising solutions to the challenge of urban water security: a combination of conservation and efficiency, desalination, stormwater capture, water reuse, and water banking. These options for urban water, including direct potable reuse, will help dry cities in California and elsewhere achieve more sustainable and diversified water supply portfolios. Pilot and demonstration-scale projects, along with innovations in systems management and new regulations, point the way toward more resilient water supplies for dry cities. Movement toward regional collaboration, implementation of new technologies, and new regulatory regimes are helping to realize a one-water vision. Different cities will develop their own water supply portfolio options appropriate for their geography, values, and urban form on a path toward meeting the urban water challenges of this century.

In this study, a comprehensive assessment of doped ceramic water filters (doping with hydroxyapatite and alumina) was conducted for potential application in household water treatment. The efficiency/reliability was assessed via statistical data analysis and normal distributions. It was found that the doped ceramic water filters had high porosity ($63.25\%\pm 0.31\%$ by volume) and a substantial flow rate ($14.76\pm 1.43\mathrm{L}·{\mathrm{h}}^{-1}$). The removal of bacterial contaminants [i.e., log reduction value (LRV)] was also found to be associated with the percentage of porosity. Hence, the doped filters were both efficient and reliable in removing bacterial contaminants (LRV of $4.69\pm 0.19$). The removal of chemical/viral contaminants was related to the doping with hydroxyapatite and alumina. Due to kinetics, the removal of viral contaminants also depended on the flow rate of the doped ceramic water filters. This resulted in high efficiency in the removal of viral contaminants (LRV of $3.47\pm 0.35$) and high reliability in the removal of chemical contaminants (LRV of $2.26\pm 0.07$). The current results suggest that the doped filters are suitable materials for application in household water treatment.

The widespread use of Ag and ZnO nanoparticles (NPs) in commercial products has raised concern of their potential adverse impact on humans and the environment. These NPs most commonly enter the environment from the effluents of wastewater treatment plants (WWTPs). To understand the impact of these NPs on microbial communities, this study focused on adding environment-relevant concentrations of Ag ($1\mu \mathrm{g}/\mathrm{L}$), ZnO ($0.1\mu \mathrm{g}/\mathrm{L}$), and Ag+ZnO ($1\mu \mathrm{g}/\mathrm{L}+0.1\mu \mathrm{g}/\mathrm{L}$) to water collected from where the Carbondale Southeast WWTP effluent mixes with Crab Orchard Creek in IL, USA. Nanoparticles-spiked samples were withdrawn immediately and after 72 h for dynamic light scattering analysis. Optical density analysis by ultraviolet–visible spectroscopy, quantitative PCR analysis, and deoxyribonucleic acid sequencing were also conducted after 72 h. The results showed that ZnO NPs, at the studied concentration, were toxic, as a decrease in microbial biomass at Day 3 compared to the Control was reached, with an increase in mass fraction of nanoscale particles over time. However, when ZnO NPs were added in combination with Ag NPs, the adverse impact of ZnO NPs was mitigated, as an increase in microbial biomass was reached compared to the Control at Day 3, with a decrease in mass fraction of nanoscale particles over time. Ag NPs alone, at the studied concentration, did not bring significant impact on the microbial biomass. The relative abundance of the bacterial population affected the most by the addition of NPs was Firmicutes, with an increase in 13.74% compared to the Control when Ag+ZnO NPs were added. This study demonstrated the response of microbial communities to increased environment-relevant concentrations of NPs in a short period of time. The result will provide information that may aid in the preparation of guidance or regulations related to discharge of mixtures of NPs to surface water.

Production wastewater of pymetrozine leads to producing a lot of highly concentrated saline organic wastewater so that the related environmental aspects must be studied. In this study, a response surface methodology (RSM) was employed to investigate the effects of different operating conditions on the removal organic nitrogen compounds in pymetrozine production wastewater by a complex extraction with a mixed extractant containing di(2-ethylhexyl) phosphate and benzene. The Box-Behnken design (BBD) was used to optimize the extraction process and to evaluate the individual and interactions effects of the pH, diluent volume fraction, water to organic phase (W/O), temperature, and extraction time on organic nitrogen compounds removal. An optimized extraction efficiency of 78.91% from the RSM was obtained at a pH of 12.7, diluent volume fraction of 54.8%, W/O of 0.8, temperature of 24°C, extraction time of 35 min. Also, $2.94\mathrm{mol}/\mathrm{L}$ of HCl solution was used as stripping agent in the back extraction process. The back extraction efficiency of organic nitrogen compounds reached 88.9% when the W/O was $1:1$ and the extraction time was 15 min. An extractant after stripping can be repeatedly used by test verification.

This research concentrated on the isolation and preparation of biosurfactant-producing bacterial strains for the degradation of aromatic amine compound 2,4-diaminotoluene (2,4-DAT). Three strains, designated as Isolates 1, 2, and 3 (${\mathrm{I}}_1$, ${\mathrm{I}}_2$, and ${\mathrm{I}}_3$), were isolated from soil and used in the degradation studies. Among the three isolates, ${\mathrm{I}}_1$ showed the highest growth rate and degradation capacity, approximately $30\mathrm{mg}{\mathrm{L}}^{-1}$. The highest degrading capability was found in ${\mathrm{I}}_1$ followed by ${\mathrm{I}}_2$ and ${\mathrm{I}}_3$. The three strains were tested for biosurfactant screening, and the lipopeptide nature of the biosurfactant was identified through characterization studies. The stability of the biosurfactants was also tested at different temperatures and in various pH ranges. The investigation of biosurfactant-mediated remediation was further carried out using the three strains and lipopeptide biosurfactants. Intermediates formed after degradation were analyzed using high-performance liquid chromatography (HPLC), which showed that the compounds were eluted within 3 min. The results showed that biosurfactants raised the degrading capability of these strains for 2,4-DAT by 14.54, 27.15, and $35.79\mathrm{mg}{\mathrm{L}}^{-1}$.

In this study, three solid-phase iron sources—FeS, ${\mathrm{FeCO}}_3$, and sponge iron—were used to investigate the autotrophic denitrification efficiency in low-carbon-to-nitrogen ($\mathrm{C}/\mathrm{N}$) wastewater. Among these iron sources, FeS obtained the best efficiency, with a nitrate removal of 96% at 120 h under $\mathrm{C}/\mathrm{N}=1$ and ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}=40\mathrm{mg}·{\mathrm{L}}^{-1}$. Then, batch experiments with FeS as an electron donor were conducted to evaluate the effect of different influent $\mathrm{C}/\mathrm{N}$ ratios and ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ concentrations. According to the results of the experiments, the nitrate removal efficiency of the mixotrophic system was greater than that of the pure autotrophic system under low-$\mathrm{C}/\mathrm{N}$ ratios, and the TN (total nitrogen) removal efficiency was also enhanced. In the mixotrophic system, the nitrate removal reached 98% in 48 h under a $\mathrm{C}/\mathrm{N}$ ratio of 1, and ${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$ was in the range of $20\mathrm{mg}·{\mathrm{L}}^{-1}$ to $40\mathrm{mg}·{\mathrm{L}}^{-1}$. Additionally, some accumulation of ammonia was observed in the nitrogen conversion process. According to microbial analysis, the synergistic action of heterotrophic and autotrophic denitrifiers improved nitrate removal.

In this study, a new technology was proposed for removing ${\mathrm{SO}}_2$ and NO from industrial flue gas via wet catalytic oxidation technology that uses a mud-phosphorus emulsion as the absorption liquid. In this study, the optimal reaction temperature, gas rate, oxygen content, and mud-phosphorus emulsion solid-to-liquid ratio were determined. At a reaction temperature of 60°C, the gas flow rate was $300\mathrm{mL}·{\min }^{-1}$, the oxygen content was 20%, and the solid-to-liquid ratio in the mud-phosphorus emulsion was $0.125\mathrm{g}·{\mathrm{mL}}^{-1}$. When the system was operated for 880 min, the desulfurization rate was 99%; when the system was operated for 860 min, the denitrification rate was still 99%, and the desulfurization and denitrification effects were ideal. The proposed technology opens new avenues for the purification and resource utilization of sulfur-containing flue gas.

Concrete crack healing by microbial calcium carbonate producers has been intensively studied for the last 10 years. To overcome the harsh environments of concrete, various carriers have been tested for their ability to protect the healing bacteria. Using expanded clay (EC) as a carrier is attractive because it provides adequate bond strength to the cement composites as well as protection to the bacteria from harsh environments. In this study, self-healing performance by EC was examined using styrene-acrylic emulsion coatings. First, the presence of bacteria (Lysinibacillus boronitolerans YS11) within EC was verified using electron microscopy after the bacteria were immobilized. Although coating has a negative effect on the preservation of bacterial density under normal conditions, the bacterial density was higher for coated EC [$5.0\times {10}^4$ colony forming unit $(\mathrm{CFU})/\mathrm{g}$ of EC] than for uncoated EC ($2.4\times {10}^3\mathrm{CFU}/\mathrm{g}$ of EC) when exposed to a harsh environment (60°C and pH 12) for 48 h. This suggests that coating the surface of EC was successful in protecting bacteria from the environmental stressors. Even though bacteria were within the EC, the bacterial survival rate quickly declined with time inside the mortar. However, the bacterial density was much higher for coated than for uncoated EC at day 28, suggesting that the coating provides the bacteria with excellent protection from the harsh environment within the mortar. The concrete healing rates were 70% for uncoated EC and 75% for coated EC, compared to the healing rate of 50% and 42% for plain mortar and mortar with empty EC, respectively. These results suggest that the healing rate has increased with EC containing bacteria.

Portions of the marsh sediments at the LCP Chemicals Georgia Site (Site) were dredged and removed in 1999. However, sediment samples obtained four years later showed 0.54 $\mathrm{mg}/\mathrm{kg}$ average mercury concentrations within the remediated portion of the marsh. Groundwater was investigated as a potential contributor to recontamination. A mass discharge study on a transect running along the marsh/upland boundary was used to calculate mass discharges from upland groundwater to sediment and surface water for mercury and lead. Using conservative assumptions, the groundwater loading analysis showed that the maximum spatially averaged groundwater contribution of mercury to the sediments was $0.02\mathrm{mg}/\mathrm{kg}$, less than the measured sediment concentration ($0.54\mathrm{mg}/\mathrm{kg}$) by an order of magnitude. The discharge analysis also showed that low marsh sediment porewater concentrations result in an infinitesimal change in the water quality in the stream when diluted by mixing with surface water. The magnitude of the mass discharge, in accordance with an established classification system, indicated that both mercury and lead plumes were classified as Mag 5 plumes at the Site. That is, a stream flowing at 0.028 ${\mathrm{m}}^3/\mathrm{s}$ [1 cubic foot per second (cfs)] would not be threatened by the discharge from this Site, and flow at this Site is significantly higher than $0.028{\mathrm{m}}^3/\mathrm{s}$ (1 cfs). This work demonstrated that the groundwater pathway for lead and mercury does not contribute significantly to the degradation of sediments or water quality in this marsh. This paper demonstrates the use of relatively straightforward mass balance calculations using data collected from strategically positioned monitoring wells to evaluate the potential offshore flux of groundwater contaminants and their potential impact on surface sediment and surface water.

As communities throughout the world work to reduce the impacts of urban stormwater on receiving streams, new stormwater controls have been a welcome addition to the established suite of green infrastructure practices. One such innovative control is the regenerative stormwater conveyance (RSC), which has shown mixed performance based on a limited number of studies to date. In this study, an RSC was constructed in Knoxville, Tennessee, and monitored for water quality and hydrologic performance over a 16-month period. Although modest cumulative volume reductions (6% overall) were realized, performance was found to substantially vary by season. Specifically, during the growing season when vegetation is active and water tables are low, performance increased to a cumulative volume reduction of 29%. Although effluent pollutant concentrations (total suspended solids, ammonium, nitrate, phosphate, sulfate, copper, and zinc) were consistent with those reported in the literature, concentration reductions were limited, and performance only slightly improved when load reductions were considered (load reductions for all parameters ranged from $-342\%$ to 38%). This is predominately attributed to low inlet concentrations, and emphasizes the need to evaluate stormwater control effectiveness based on multiple criteria. The frequent export of total suspended solids at the site ($-60\%$ load reduction) also suggests that the pools were too shallow, and that optimization of this design feature is needed to minimize internal scour. This work emphasizes the influence of seasonal processes such as evapotranspiration, and antecedent site conditions such as water table elevation and soil saturation on RSC function. Specifically, the data indicate that performance of these systems is likely to be highest when the RSC’s sandy media can drain between storms, allowing recuperation of storage volume. Additional research is needed to fully quantify RSC function and develop design criteria for RSCs under various site conditions.

Approximately 80% of US centralized Small Water Resource Recovery Facilities (WRRFs) serve populations less than 10,000 and can be significantly less energy efficient (E2) relative to larger systems. This study’s purpose was to provide case studies of E2 in small WRRFs through documentation of unit process energy use (within four small WRRFs), E2 changes reported by operators following a project that provided E2 recommendations to 83 WRRFs, and investigate barriers to E2 through surveying of operators (including comparisons between systems of different size and E2 implementation). Aeration was the largest energy component (66%–73%) of total energy use and space heating can be significant (4%–35%). E2 changes were reported by 19 operators, and facilities with available bills exhibited energy reductions of 4%–35%. Variable frequency drive (VFD) installation and improved operations exhibited the largest savings. Application of an E2 benchmarking model for small WRRFs was effective for measuring E2 improvements in systems with varying flowrates. Responses from 66 operators expressed financial barriers and lack of time or other priorities as the largest barriers in making E2 improvements.

Volatile organic compound (VOC) source profiles of Chengdu were established based on stack and fugitive emission source samples by field measurements. A total of 54 VOC samples collected from the petrochemical industry, printing, wood-based panel manufacturing, wood furniture coating, and shoemaking industry were measured. A total of 80 VOC species were classified into five categories, including aromatic hydrocarbons, halocarbons, and oxygenated VOCs (OVOCs). Combined with the results of measurement and literature surveys, the sector-specific emission factors conducted from the solvent-using consumption varied range from 0.35 to 1.45 Kg VOCs per Kg of solvent-use consumption ($\mathrm{Kg}·{\mathrm{Kg}}^{-1}$). Ethanol and m-xylene were predominant species of solvent used in the printing industries. Urea-formaldehyde resin was widely used as an adhesive in more than 80% of wood-based panels in Chengdu; a lot of formaldehyde and other harmful substances were directly discharged into the environment without any treatment. The evaluation of the source reactivity for various VOC emission sources were conducted. Aromatic hydrocarbon was found to be the most abundant component in the wood furniture coating and shoemaking industries. The ozone formation potential (OFP) for the unit mass of VOCs emissions was the highest for m/p-xylene (25.12%). The secondary organic aerosol (SOA) formation was also calculated, and the aromatic contributed 82.16% for almost all of the SOA formation. Furthermore, several proposals were made to reduce or regulate VOC emissions in Chengdu.