Journal of Environmental Engineering

With growing environmental concern over the pollutants being disposed of and the consequent pollution of surface water/ground water, the stringent environmental regulation called zero-liquid-discharge effluent treatment has gained popularity. Zero-liquid-discharge effluent treatment technologies avoid the liquid effluent being released outside the plant and can reuse water, which is an important commodity for any process plant. However, such technologies incur significant capital costs and recurring costs in terms of energy consumption. With the growth in industries in different sectors, such as chemicals, pharmaceuticals, textile, dyes and dye intermediates, dairy, food, and pulp, it is of paramount importance for the government and environmental regulating authorities to impose zero-liquid-discharge as the norm for the certain plants producing a certain amount of effluents. Thus, industries should develop sustainable and cost-effective zero-liquid-discharge technologies. Conventional zero-liquid-discharge technology comprises pretreatment, brine concentrator, and brine crystallizer to solidify all the impurities by thermal evaporation; such plants often have very high-energy consumption per cubic meter of effluent treated. Membrane-based technologies prior to brine concentrators can decrease the load of thermal evaporators by concentrating the effluent to a significant extent. However, the membrane used in zero-liquid-discharge technologies should have certain specific characteristics. They should be able to withstand the high organic load and high total dissolved solids concentration and consequently high pressure. The organic, inorganic, and biofouling on the membrane surface should not be so high so that the membranes can last longer. The present paper reviews different membranes used in zero-liquid-discharge technologies, their characteristics, and their performances and shows the perspectives and scope for future research in the area. Osmotically assisted reverse osmosis and low-salt-rejection reverse osmosis are relatively newer developments in zero and minimal discharge applications. The present paper shows new insight into this domain and provides directions for developing zero-liquid-discharge processes.

Abstract

This study aims to evaluate the effect of factors influencing the performance of a small-scale operating wastewater treatment plant (WWTP) integrating anaerobic baffled reactor (ABR) and biofilters with temperature fluctuations in the psychrophilic–mesophilic range. Over nine months of monitoring, the overall removal efficiencies for total chemical oxygen demand (TCOD), soluble chemical oxygen demand, particulate chemical oxygen demand, total suspended solids, ammonia nitrogen (${\mathrm{NH}}_3–\mathrm{N}$), and phosphorus (P) were 92%, 82%, 98%, 98%, 49%, and 31%, respectively, on average. The ABR’s TCOD removal efficiency (57%) was about 20% lower than the simulated efficiency using the Bremen Overseas Research and Development Association (BORDA)’s ABR design model, implying that temperature fluctuation and intermittent wastewater flow are possibly the factors that most affect performance. Although it was lower than the expected efficiency, the global performance of the system is supported by the significant contribution of horizontal and vertical gravel biofilters. The effluent quality complies with the local standard for wastewater discharge, except for the high content of nitrogen and phosphorus concentrations, which can be used for crop irrigation. To improve the WWTP performance, we recommend using a primary settler considering the use of a chemically enhanced solid separation process to avoid overloading organic solids in the ABR operation.

Practical Applications

This study evaluates the efficiency of a domestic WWTP composed of an ABR and horizontal and vertical flow hybrid gravel filters without vegetation located in a small city in Bolivia where temperature conditions are highly variable ($8–24°\mathrm{C}$). The WWTP treats wastewater from a population of 500 families. The WWTP performance under typical OLR, superficial loading rate, and hydraulic retention time (HRT) showed high removal efficiencies of 92% and 98% for COD and total suspended solids (TSS) respectively, obtaining high-quality effluent suitable for crop irrigation. This configuration is adequate for treating high-strength wastewater at low-moderate temperatures that can be replicated as a decentralized water treatment system in small cities with similar climatic conditions. It is recommended to avoid intermittent flow in ABRs to avoid the washout of organic solids. It is also advisable to complement the configuration with the installation of a primary settler that contemplates an enhanced chemical stage to effectively separate organic and inorganic solids before the ABR. In this way, the treatment capacity of these systems could be increased.

The sludge-water mixture in anaerobic reactors with confined sludge, such as the upflow anaerobic sludge blanket (UASB) with anaerobic sludge confined in a sludge bed and the internal reflux packed-bed anaerobic reactor with anaerobic sludge attached to a filler, can be mixed according to the designed hydraulic dynamic process. In this study, sludge-water mixing models of an UASB and an internal reflux packed-bed anaerobic reactor were established and validated using test models reported in the literature. The sludge-water mixing in the UASB consists of an advective diffusion unit and a water complete mixing output unit connected in series. The sludge-water mixing and reaction of the internal reflux packed-bed anaerobic reactor achieved that of a continuous stirred tank reactor (CSTR) in large-scale reflux transport mode with cycle time as the mixing time scale. The internal mixing pattern, complete mixing time, and the volume participating in complete mixing were obtained for the UASB test with hydraulic retention time $(\mathrm{HRT})=5$, 6, 8, and 10 h by model calculation to analyze the sludge-water mixing process. Its mixing achieved that of a CSTR under higher hydraulic load, and that of a series connected two-stage CSTR in advective diffusion mode under lower hydraulic load. The model analysis for the reported internal reflux packed-bed anaerobic reactor with $\mathrm{HRT}=72$, 48, 24, 12, 6, and 0.25 days showed that there existed mixing time scales shorter than the minimum reflux cycle time adopted in the test, in which the transport of the reflux alone made the sludge-water mixing and reaction stably equivalent to that of a CSTR. Both test reactors achieved CSTR at a lower mixing intensity with a velocity of $0.40–0.80\mathrm{m}/\mathrm{h}$ and complete mixing time scale of 1.0–1.9 h for the UASB and an available velocity of $5.0\mathrm{m}/\mathrm{h}$ and complete mixing time scale of 0.15 h for the internal reflux packed-bed anaerobic reactor.

The biological treatment process in high-altitude areas faces the problems of low biological activities, high aeration energy consumption, and low treatment efficiency due to the low atmosphere pressure and consequently low oxygen content. As a new type of simultaneous nitrogen and phosphorus removal process, simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) has the advantages of high efficiency, low operation cost, and low aeration energy. Compared with the traditional sewage biological treatment process, SNDPR needs less dissolved oxygen (DO) and can save carbon source, so it may be suitable for solving the problems in high-altitude areas caused by low pressure and low oxygen. In this study, SNDPR system reactors were operated under different atmosphere pressures, one at 100 kPa and three at 72 kPa, with different anaerobic/aeration time. The chemical oxygen demand (COD) and total phosphate (TP) removal performance remained the same efficiency, while the nitrogen-removal rate increased slightly at 72 kPa. The low atmosphere pressure enhanced the phosphorus-accumulating organisms but inhibited ammonia-oxidizing bacteria based on the cycle study results. Studies on the activities of enzymes related to nitrogen removal showed that the processes of ${\mathrm{NH}}_4^{+}\to {\mathrm{NH}}_2\mathrm{OH}\to {\mathrm{NO}}_2^{-}$ and ${\mathrm{NO}}_3^{-}\to {\mathrm{NO}}_2^{-}$ were enhanced, while the processes of ${\mathrm{NO}}_2^{-}\to {\mathrm{NO}}_3^{-}$ and ${\mathrm{NO}}_2^{-}\to \mathrm{NO}$ were restrained as the atmosphere pressure declined. Under the condition of 72 kPa, the SNDPR systems were optimized by prolonging the anaerobic time and reducing the aeration time. The residual ammonium concentration increased predictably ($<5\mathrm{mg}/\mathrm{L}$) as the aeration time decreased, while the nitrogen-removal efficiency improved. The aeration energy consumption at 72 kPa by a shorter aeration time was 89% of that at 100 kPa. The further study on the microbial community analysis showed that the abundance of Dechloromonas [identified as denitrifying phosphorus-accumulating organisms (DPAOs)] increased from 0.126% at 100 kPa to 5.499% at 72 kPa, which explained the nitrogen removal and phosphate uptake under the low atmosphere pressure.

Abstract

Antibiotic resistance has become a complicated environmental problem. Controlling the emission of antibiotics, antibiotic-resistant bacteria (ARB), and their antibiotic-resistance genes (ARGs) at hotspots is important for reducing environmental antibiotic resistance. Here, a ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{-}\mathrm{polydopamine}$ (PDA)-Ag nanocomposite was successfully fabricated via hydrothermal synthesis, polydopamine coating, and in situ Ag reduction. The nanocomposite exhibited a core-shell structure with a nanosized magnetic ${\mathrm{Fe}}_3{\mathrm{O}}_4$ core ($\sim 200\mathrm{nm}$) coated with one layer of nanosilver Ag nanoparticles (Ag NPs) decorated polydopamine. Its application potential as a bifunctional material for the removal of multidrug-resistant (MDR) bacteria, ARGs, and antibiotics was investigated. The ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{-}\mathrm{PDA}\text{-}\mathrm{Ag}$ showed a good performance on inhibiting the MDR bacteria and effectively reduced the abundance of ARGs. The removal of ciprofloxacin (CIP) via catalytic reduction with this composite was evaluated. The optimized results showed that nearly 82.3% of CIP ($C_0=10\mathrm{mg}/\mathrm{L}$) was removed within 30 min with the amount of ${\mathrm{Fe}}_3{\mathrm{O}}_4\text{-}\mathrm{PDA}\text{-}\mathrm{Ag}$ of $0.5\mathrm{g}/\mathrm{L}$ and the concentration of ${\mathrm{NaBH}}_4$ of 10 mM. Furthermore, the catalytic activity of the composite did not decrease even after five cycles, indicating its good reusability as the catalyst. This study provided a preliminary two birds with one stone strategy for solving the environmental problem of antibiotic-resistance pollution.

Practical Applications

Antibiotic resistance has become a comprehensive and complicated environmental pollution problem. The selective pressure exerted by antibiotics and the proliferation of ARB and ARGs can promote the bloom of environmental antibiotic resistance. Single control of the emission of a certain kind of pollutant (antibiotics, ARB, or ARGs) at hotspots will not effectively solve the environmental pollution problem of antibiotic resistance. Here, we provided a one stone, two birds strategy for solving this problem of environmental antibiotic resistance in virtue of the dual function of a magnetic nanosilver composite in inhibiting multidrug-resistant bacteria and catalyzing antibiotic degradation.

Abstract

The efficacy of microbially mediated stabilization of soil mass depends on soil aggregation and further depends on the complex interplay of environmental parameters, microbial extracellular metabolic products, and surface characteristics of soil particles. Failures of flood control dikes or similar structures often culminate from minor erosion of soil particles initiated by groundwater seepage. Although the introduction of microbial metabolic products in controlling soil erosion has been studied by researchers, the influence of slow fluvial activities on the composition, characteristics, and their impacts on attachment mechanisms of extracellular polymeric substances (EPS) on soil surfaces have remained unexplored. Impacts of slow fluvial activities on the amount and chemical composition of EPS produced by Lysinibacillus sp. DRG3, a nonpathogenic soil bacterium, and the attachment mechanisms of the EPS produced under noncalcifying, nonureolytic, and ureolytic calcifying bioprocesses on the sand surfaces were investigated. DRG3-inoculated specimens were incubated in the presence of steady circulation of aqueous media containing minimal concentrations of minerals and carbon and nitrogen sources to simulate groundwater movements through soil. Quantity, compactness, continuity, and viscosity of EPS and the amounts of carbohydrate, protein, lipid, DNA, and RNA found in EPS increased with circulation velocity and incubation duration. EPS were found to attach to sand through electrostatic interaction and hydrogen bonding. Internally, EPS components interacted with each other through electrostatic interaction, hydrogen bonding, and hydrophobic interaction. Electrostatic interaction appeared to weaken with increasing media circulation intensity and alkalinity. In contrast, EPS production and hydrogen bonding intensified under increased media circulation. Results of this investigation suggest microbe-mediated soil aggregation becomes stronger and more efficient under slow media circulation and are expected to have implications on microbially mediated soil stabilization, particularly in addressing soil erosion. This study provides useful insights for successful field implementation of biomediated soil stabilization. Work presented herein also demonstrates a role for microbial activities found in subterranean environments in strengthening an existing sand deposit.

Practical Applications

In recent years, civil engineers have shown an interest in biomediated soil improvement for a variety of applications mainly to address the limitations of traditional ground improvement techniques such as higher cost and non environment friendliness. The microbes used in this study are soil residing, nonpathogenic, and respond positively in all three metabolic pathways. They can grow and produce EPS and calcite consuming nutrients from the minerals available in the groundwater. Therefore, this process is relatively less expensive. In the present study, neither high doses of nutrients were introduced that might have harmful effects on the surrounding ecosystem nor any harmful chemical generated as a byproduct of the precipitation reaction. Additionally, the process for imparting interparticle aggregation used in this study did not require the provision of nutritional supplements to implement the process in the field and was therefore self-sustaining. However, the efficacy of microbe-mediated soil improvement depends on microbially mediated soil particle aggregation. The understanding of the nature and mechanism of the EPS-sand interaction developed from this study will further contribute to the successful implementation of this technique in the field.

Abstract

Plunging jet aerators are considered energetically attractive devices for oxygenation because of their good mixing characteristics and ease of construction and operation. In this mechanism of plunging jet aeration, the air-water interfacial area is increased by a free-falling jet impinging on the surface of a water pool. In this study, experimental data from various configurations of plunging hollow jet aerators are explored in formulating the correlations for predicting the values of volumetric oxygen transfer coefficient ($K_{L}a$) with the jet variables (discharge, jet thickness, jet velocity, jet length, depth of water pool, pipe outlet diameter, number of jets). Nonlinear regression modeling equations derived from dimensional and nondimensional data sets are compared with the neuro-fuzzy (ANFIS), support vector regression (SVM), artificial neural network (ANN), M5 tree (M5), and random forests (RF) methods. SVM models calibrated with both types of data sets provided better results when tested on the unseen data sets. Regression equations are also useful and give acceptable results. The SVM models and regression equations are further checked for effectiveness on the data set of past study on plunging hollow jets. The nondimensional form of the regression equation derived in the current study fits reasonably well when tested on the oxygenation data from previous work as compared to the other regression models. The sensitivity of the jet variables is also tested, which showed jet velocity and jet thickness as major contributing factors in oxygenating the aeration pools.

Practical Applications

An aeration device adds oxygen to water and wastewater during treatment to ensure that microorganisms have enough oxygen to oxidize organic pollutants. Aeration requirements for aeration tanks vary greatly depending on the organic load, and one or more hollow jet aerators can be fitted to accommodate the fluctuating load. Hollow jet aerators are well suited to use in packaged wastewater treatment plants. The annular opening of these aerators can be adjusted accordingly based on the varying load. High-velocity thinner jets are better for quickly renewing air-water films and generating shear and turbulence in the receiving pool, but wastewater should be well screened before aeration to avoid clogging of the small annular opening. The results of this study on the capacity of plunging hollow jet aerators of different configurations/arrangements at varying operating conditions were reflected by the dimensional as well as nondimensional relationships between oxygen transfer rate and jet equipment parameters. Implementing these relationships on previous jet aeration data indicates that the equations are accurate enough to be used to situations similar to those in this investigation. Without any prior experimental effort, these equations can be used to estimate the oxygen transfer expected in practical applications.

Particulate matter (PM) accumulates on urban interfaces, including pavement, as source areas. This PM can be recovered with street sweeping (SS) before transport by stormwater. Without SS recovery, PM is transported/deposited in a series of drainage components from a stormwater inlet/catch basin without a sump (CB), a conveyance system, a best management practice (BMP), and to receiving waters. PM separated in a CB and BMP can be recovered by maintenance. This study quantifies PM recovered from SS, CB, and BMP maintenance across Florida. Moisture content (MC) and particle size distribution (PSD) were measured for all samples. PM dry bulk density (${\rho }_{\mathrm{b}}$) as a function of MC was only examined for SS. With a cumulative gamma model, shape factor ($\gamma$, an index of size heterodispersivity), scale factor (k, an index of size central tendency) and gravimetric size (diameter) indices are generated from PSD data. Study results indicate a statistically significant increase in the MC of PM in BMPs as compared to SS. The median MC values are 34%, 27%, and 6% for BMPs, CB, and SS. The median dry ${\rho }_{\mathrm{b}}$ of the heterodisperse PM recovered by SS is $1.36\mathrm{g}/{\mathrm{cm}}^3$, approximately log-normally distributed and a non-linear function of MC. In this study, SS is less effective in recovering finer PM. Coarse PM is deposited during conveyance/treatment, therefore PSDs recovered from BMPs are relatively monodisperse compared to SS. Results inform the design of maintenance for PM load recovery. Extensibility to nutrient/metal load credits can be based on PM-partitioned data. Such extensibility can target PM recovery and used in a basin management action plan for a total maximum daily load.

Using high amounts of chlorine to disinfect contaminated natural waters for drinking purposes can produce an unpleasant taste and odor and contribute to the formation of toxic byproducts. These challenges can be addressed through the combined use of lower amounts of chlorine and silver. Several studies in well water or solutions inoculated with bacteria or viruses have demonstrated that this combination produces a synergistic effect in the inactivation of pathogens. This study investigated the synergistic inactivation of bacteria in natural waters (from a pond with 4.82 NTU and upstream with 11.9 NTU in Virginia) using low doses of silver (added as silver nitrate) and free chlorine (from Aquatabs). There was a significant synergistic effect at 3-h contact time, and the ${\log }_{10}$ reductions of E. coli and total coliform bacteria (TCB) were $\ge 1.44$ and $\ge 2.73$, respectively, with the lower-turbidity water, and 0.87 and 1.29, respectively, with the higher-turbidity water. Chlorine effectiveness was significantly reduced by higher turbidity, whereas silver effectiveness was not. Thus, for waters with higher turbidity, silver alone or a combination of low doses of silver and chlorine may produce a higher bacteria inactivation than chlorine alone. In addition, bacteria inactivation by the MadiDrop+ (MD, a commercial silver-ceramic tablet that releases silver ions for point-of-use water disinfection), with low doses of free chlorine in water from a stream in South Africa, was tested. The MD alone at 8-h contact time obtained $\sim 1\text{-}{\log }_{10}$ reduction for E. coli and $\sim 2\text{-}{\log }_{10}$ reduction for TCB. However, some of the MD-free chlorine combinations achieved a similar bacteria reduction with a substantial reduction of contact time (between 6 and 7 h less). Overall, these results show that the silver–chlorine synergistic effect demonstrated in previous studies with solutions inoculated with pathogens is also present in the more realistic scenario of natural waters that contain more complex matrices.

Abstract

Perfluoro-2-propoxypropanoic acid (PFPrOPrA), a free acid form of GenX, is a problematic perfluorinated alkyl substance (PFAS). Standard and advanced wastewater treatment methods are unable to effectively degrade PFAS due to its strong and unreactive C-F bonds. ${\mathrm{TiO}}_2$ photocatalytic, radiolytic, and ultrasonic irradiation (USI) methods were applied in an attempt to degrade PFPrOPrA. A bimolecular rate constant for the reaction of ${\mathrm{e}}_{\mathrm{aq}}^{-}$ and GenX of $(3.09\pm 0.03)\times {10}^7{\mathrm{M}}^{-1}·{\mathrm{s}}^{-1}$ was measured in a buffered aqueous solution by monitoring the transient signal of the hydrated electron as a function of GenX concentration. Corroborating this relatively slow rate constant, less than 2% GenX degradation was observed after 8 h of continuous ${}^{60}\mathrm{Co}$ gamma radiolysis under a variety of conditions. ${\mathrm{TiO}}_2$ photocatalysis at 350 nm under alkali conditions showed minimal destruction of GenX without detectable levels of defluorination as measured by the production of fluoride ions. However, upon ultrasonic irradiation at 640 kHz and 396 W in an argon-saturated aqueous solution, greater than 80% of GenX was degraded within 60 min, yielding fluoride ions as the major product. We propose that the ultrasonic-induced degradation of GenX occurs primarily by pyrolysis. Computational methods were used to probe the energetics of the completing degradation pathways and possible pyrolytic products. The results demonstrate ultrasonic-induced pyrolysis is a promising process to mineralize GenX. The process can be accurately monitored and likely extended to mineralize a variety of perfluorinated and polyfluorinated substances.

Practical Applications

This study probed the application of radiolysis, ${\mathrm{TiO}}_2$ photocatalysis, and USI to degrade an emerging problematic perfluorinated compound, GenX. Under the experimental conditions employed, the degradation of GenX was slow by ${\mathrm{TiO}}_2$ photocatalysis, and radiolysis. Although reductive transformation of PFAS by hydrated electrons generated during radiolysis has been demonstrated, the reaction did not lead to rapid mineralization and is highly dependent upon reaction conditions. USI, however, resulted in the rapid degradation of GenX significant mineralization as measured by the formation of fluoride ions. Complementary computational studies of the pyrolytic pathways provide insight about mineralization, which may be extrapolated to different classes of PFAS and thermal-induced degradation. The results of this research illustrate that USI is a powerful method to mineralize GenX and suggest it may be applicable for treatment of an array of PFAS-contaminated waters and wastewaters. Although the energy demand for USI-based water treatments can be high and thus costly, USI is a promising alternative for mineralization of PFAS in preconcentrated or concentrated waste streams.

In this paper, the ability of resource treatment of black smelly river sediment to reduce life-cycle greenhouse gas (GHG) emissions and its environmental benefits were calculated using the US EPA life-cycle assessment (LCA) model. Different from previous studies, this paper used the willingness-to-pay method to determine the weight factors of various environmental impact types in this study and proposed a calculation model of carbon emissions and environmental benefits in the whole process of resource utilization of sediment, rather than a new method to treat black smelly river sediment. Take the Qingxi River sediment treatment and recycling project in Dongguan, China, as an example: the carbon reduction, environmental impact, and environmental benefit of different stages of sediment treatment are calculated. The results show that 93.419 kg of carbon dioxide, 0.202 kg of methane, and 0.001 kg of nitrous oxide are produced for 1 t of river sediment, in which the preparation process of unburned brick contributes 99% of carbon dioxide, 82.67% of methane, and 100% of nitrous oxide emissions and is the stage that produces the most greenhouse gases. The 1 t of sediment resource treatment can reduce the generation of 29.066 kg carbon dioxide and 0.855 kg of methane. The comprehensive net environmental benefit of processing 1 t of river sediment is 1.492 yuan, and the environmental benefit is 1.684 times the environmental cost. This study identified that the treatment and recycling of river sediment has better environmental benefits. The preparation process of unburned brick can be optimized to further reduce carbon emissions and produce better environmental benefits.

Increasing water demand due to socio-economic development often requires structure-level interventions, e.g., infrastructure expansion of water supply systems to bridge the gap between demand and water supply. Evaluating different expansion options is critical to making informed decisions. This study focuses on evaluating infrastructure investment options from the reliability perspectives of a water supply system. The evaluation framework is comprised of probabilistic demand projections, stochastic streamflow generation, a mixed-integer programming, and system performance evaluation. Different “industry understood” performance metrics, e.g., annual reliability, maximum delivery capacity, the probability of unsuccessful status, and the magnitude of potential water shortage, can be employed to evaluate the performance of water supply systems. This framework has been applied to Tampa Bay Water, a regional supply agency on the west coast of Florida, United States. The probabilistic demand projections for the future (2021–2040) consider socio-economic projections and climate conditions based on the statistics of historical observations. The Latin Hypercube Sampling algorithm is used to capture the bivariate distribution of supply and demand. This mixed-integer programming is a daily system optimization that minimizes operational cost and considers operational constraints and preferences, e.g., water withdrawal permits, facility production capacity, and water production preferences. Current infrastructure capacity and operational conditions are defined as the baseline scenario. Two additional planning scenarios of expanding the treatment capacity of a surface water treatment plant by ${\mathrm{75,708}\mathrm{m}}^3/\mathrm{day}$ [20 million gallons per day (mgd)] and ${\mathrm{113,562}\mathrm{m}}^3/\mathrm{day}$ (30 mgd) in the year 2028 are investigated. Results reveal that annual reliability would increase with the expansion of surface water treatment plant capacity. The spatio-temporal supply and demand variability determines that the firm yield from the surface water treatment is less than its expanded production capacity. Except for low demand realizations in the future, the duration and magnitude of potential water shortage could be reduced in both scenarios with engineering intervention. Although this framework is demonstrated for a regional water utility in Florida, it can be applied to other water supply systems around the world.

In the US Virgin Islands, $>90\%$ of households have rain catchment systems that utilize large cisterns; however, these systems are at high risk of microbial contamination. Available water treatment technologies provide varying levels of protection from microbial contamination and can be expensive. Therefore, we evaluated a low-cost water treatment train that included a passive chlorinator, carbon filter, and membrane filter to provide whole-house treatment for microbial contamination in a mock, pressurized, intermittent-use water system. Two types of locally available passive pool chlorinators were modified and tested for free chlorine residual (FCR) levels across a set of different water use scenarios. Additionally, tracer dye tests were conducted to evaluate chlorine contact time in the system, a carbon filter was evaluated for chlorine removal efficiencies, and a 1-micron nominal filter was evaluated for its effect on system pressure and microbial removal efficiencies. Results suggested the modified passive chlorinators provided relatively consistent chlorine dosing (offline: standard deviation range 0.54 to 0.79 ppm FCR, 3 trials, $\mathrm{n}=43$; inline: standard deviation 0.53 ppm FCR, 1 trial, $\mathrm{n}=16$) and tracer dye tests identified a minimum contact time for high flow rates (18.9 LPM, 5 GPM) of $>45\mathrm{s}$. The carbon filter reduced FCR levels from as high as 18.5 ppm to $<0.13\mathrm{ppm}$ ($\mathrm{n}=9$), while the 1-micron nominal filter had negligible effects on system pressure and provided $0.7\log 10\mathrm{MPN}/100\mathrm{mL}$ removal of total coliforms ($\mathrm{n}=9$). The data suggest that passive chlorination can potentially be a low-cost option for whole-house water treatment for microbial contamination, but further research is needed to demonstrate system stability in a wider range of use cases over a longer period of time along with simplified practitioner protocols for field use.

The World Health Organization (WHO) and US Centers for Disease Control and Prevention (CDC) recommend cleaning soiled surfaces with soap and water, followed by use of approved disinfectant. However, data are lacking on the potential efficacy of soapy water alone as a disinfectant for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is relevant to low-resource settings where soapy water is prevalent for handwashing. To our knowledge, no appropriate biosafety level 1 (BSL-1) surrogate has been identified and confirmed for use in studies with soapy water and the highly infectious SARS-CoV-2. Therefore, our objectives were to determine the efficacy of soapy water alone as a disinfectant against SARS-CoV-2 and if commonly used BSL-1 bacteriophage surrogates could serve as a surrogate model for testing soapy water as a disinfectant. Overall, results indicate that SARS-CoV-2 can be reduced $>4{\log }_{10}$ in suspension but only $0.50{\log }_{10}$ on a nonporous surface with 10 min of exposure to 0.5% soapy water. This difference is potentially attributed to less area of exposure on surfaces than in suspension. Phi6 (a verified SARS-CoV-2 surrogate for other disinfectants) was not appropriate for SARS-CoV-2 disinfection with soapy water. Further research is needed to determine an appropriate surrogate for SARS-CoV-2 disinfection with soapy water as disinfection of MS2 was similar to SARS-CoV-2 on surfaces only. Our work highlights the importance of confirming surrogates for each disinfectant used. Based on our results, we do not recommend a change to the current WHO and CDC surface disinfection protocols that recommend using soapy water to preclean a surface before applying disinfectant.

Plastic litter in the urban environment has been identified as a source of microplastics and stormwater a pathway for its transportation to freshwater and marine environments. However, few studies exist on the potential for litter to contribute to microplastics in a land-based system. This laboratory-based study involves simulation of the weathering of four polymers [low-density polyethylene (PE-LD), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET)] in a land-based environment using accelerated photodegradation with three exposure times. Microplastics generated were quantified with Fourier transform infrared spectroscopy and identified using a spectra reference library. The results showed differences in release patterns and number of particles produced. For LD-PE, no clear pattern of UV-degradation was demonstrated, because the number of particles released from exposed and unexposed (control) samples was in the same order of magnitude. PS and PET showed similar patterns, where the number of particles released increased with exposure duration. The numbers of particles detected were, on average, 1, 8, and $31\mathrm{particles}/{\mathrm{cm}}^2$ for PS and 3, 3, and $16\mathrm{particles}/{\mathrm{cm}}^2$ for PET for exposures of seven, 28, and 56 days, respectively. PP produced the largest number of particles after 28 days exposure (ca. $58\mathrm{particles}/{\mathrm{cm}}^2$) which then decreased after 56 days (ca. $21\mathrm{particles}/{\mathrm{cm}}^2$). It was hypothesized that the number of particles increased with exposure time and that the generated particles then further fragmented into pieces of undetectable particle size ($<10\mathrm{\mu m}$).

A mobile treatment system equipped with a custom-built sonolysis reactor was deployed at a site in California to treat groundwater impacted with per- and polyfluoroalkyl substances (PFAS). Extracted groundwater was treated in a 700-kHz sonolysis reactor for batch treatment under different power densities (122, 203, and $305\mathrm{W}/\mathrm{L}$) and operating temperatures (15°C and 25°C). Sonolytic treatment resulted in 93%–100% removal of the 15 PFAS identified in the groundwater, and PFAS degradation rates increased proportionally with increasing power density and temperature at operating conditions of 25°C. For all experimental conditions evaluated, greater removal was observed for perfluorinated carboxylic acids (PFCAs) [e.g., 95.1% to 100% for perfluorohexanoic acid (PFHxA)] than perfluorinated sulfonic acids (PFSAs) [68.3% to 95.2% for perfluorohexane sulfonate (PFHxS)] for similar carbon chain lengths. Similarly, greater removal was observed for longer-chain PFAS [e.g., 95.4% to 99.5% for perfluorooctanoic acid (PFOA)] compared with short-chain PFAS [56.9% to 90.4% for perfluorobutanoic acid (PFBA)]. Substantial removal of total oxidizable precursors (TOP) and specific precursors [65.5% to 99.1% for 4:2 fluorotelomer sulfonate (FTS), 6:2 FTS, 8:2 FTS, and perfluorooctane sulfonamide (FOSA)] was also observed under all conditions tested. Additionally, formation of nitrate was observed, with concentrations below maximum contaminant levels (MCLs). Overall, the results demonstrate that sonolysis treatment of PFAS-contaminated groundwater can effectively degrade PFAS without the formation of short-chain PFAS and the oxidation byproducts chlorate and perchlorate.