Journal of Environmental Engineering

Disinfection of municipal wastewater effluents is a critical component of water pollution control. To achieve this, novel alternative disinfection technologies have been getting attention recently such as pulsed ultraviolet (UV) light, which can be used to inactivate microorganisms in a short time. Therefore, the research reported in this paper was undertaken to determine the efficacy of pulsed UV light for inactivation of Escherichia coli and Bacillus subtilis spores, in synthetic and real municipal wastewater effluent. The results with synthetic municipal wastewater effluent demonstrated that complete inactivation was obtained with an 8-cm sample distance, 30-mL sample volume, and 15-s time combination for E. coli [$8.53{\log }_{10}$ colony-forming units $(\mathrm{CFUs})/\mathrm{mL}$ reduction], whereas a 15-mL sample volume (with the same sample distance and treatment time) was required for B. subtilis ($7.57{\log }_{10}\mathrm{CFU}/\mathrm{mL}$ reduction) at total energy dose of $10.9\mathrm{J}/{\mathrm{cm}}^2$. A response surface model was developed to predict the inactivation for E. coli and B. subtilis spores. Using sterilized real wastewater effluent with the same experimental conditions of an 8-cm distance and 30-mL volume for E. coli, and 8-cm distance and 15-mL volume for B. subtilis, complete inactivation required the same 15-s treatment for E. coli, but 20-s treatment for B. subtilis. In addition, a 2.5, 5, 10, 15, and 25% ($\mathrm{volume}/\mathrm{volume}$) E. coli or B. subtilis inoculum was added to the synthetic municipal wastewater effluent, and treated by pulsed UV-light for 5–45 s. Results showed that pulsed UV treatment at the optimum conditions increased suspended solids removal by 26.5 and 21.45%, for E. coli and B. subtilis, respectively. Overall, the results of the research reported in this paper clearly demonstrated the complete inactivation of vegetative cells or spores in municipal wastewater effluents, and further demonstrated the reduction of suspended solids, suggesting that pulsed UV light has the potential to be used for disinfection of municipal wastewater effluent.

Immiscible displacement processes are of key importance in remediation actions of light nonaqueous phase liquid (LNAPL) contaminated soil and groundwater. LNAPLs remain trapped in soil pores after a spill or flushing process due to the interplay of viscous, gravity, and capillary forces. In this research immiscible displacement tests were conducted in homogenous and heterogeneous sand samples. Also, the influence of fine content, mineralogy, and wettability was evaluated by testing mixtures of coarse sand with silt, zeolite, bentonite, and hydrophobic sand. Obtained results highlight the importance of pore-scale heterogeneities on the resulting displacement pattern in macroscopically homogeneous samples, and show the preferential accumulation of LNAPLs at the interfaces between different materials in heterogeneous samples. Fine particle content shows no important consequences on residual saturation but significantly changes relative permeability. In addition, the presence of hydrophobic particles also modifies hydraulic conductivity and residual LNAPL saturation. Finally, relative permeability models were fitted to experimental data in order to estimate relative permeability of tested samples.

The negative effects of urbanization on water quantity and quality and the performance of bioretention for treating runoff and reducing concentrations and loads of sediment, nutrients, pathogens, and selected trace metals have been well documented. This study evaluated the efficiency of a bioretention system installed in semiarid Daly City, California, for a large suite of pollutants, including some that have been rarely evaluated in such systems. Stormwater flow and pollutant concentrations were measured before and after the construction of a bioretention system consisting of rain gardens and a bioswale. After installation, concentrations of most pollutants were reduced and met water quality guidelines. Water quality improvements (concentration or load reductions) were demonstrated for total Hg, polychlorinated biphenols (PCBs) and dioxins ranging between 18 and 100%, and a suite of more conventional pollutants [SSC, Cd, Cu, Ni, Pb, Zn, and polycyclic aromatic hydrocarbons (PAHs)] ranging between 20 and 90%. Results were less favorable for methylmercury. The balance of evidence suggests that such systems, when designed and functioning correctly, can be highly effective in treating pollutant concentrations and loads in stormwater runoff in semiarid environments.

This study presents interior microwave discharge electrodeless iodine lamps ($\mathrm{IMDEL}\text{-}{\mathrm{I}}_2$) that assist the photodegradation of ${\mathrm{CS}}_2$ at room temperature and atmospheric pressure. The investigation examined the photolysis efficiency of ${\mathrm{CS}}_2$, the absolute removal amount (ARA), and the energy yield (EY) under different gas residence times and input powers and also included an analysis of the photodegradation products of ${\mathrm{CS}}_2$. The experimental results indicated that the $\mathrm{IMDEL}\text{-}{\mathrm{I}}_2$ was capable of emitting ultraviolet (UV) radiation in bands of 206.2, 250–350, and 385–400 nm, and vacuum ultraviolet (VUV) light at 178.3, 180.1, 183, 184.4, and 187.6 nm. The photodegradation rate of ${\mathrm{CS}}_2$ in the $\mathrm{IMDEL}\text{-}{\mathrm{I}}_2$ system was 93.4%, with ARA of $18.1\mathrm{mg}/\mathrm{s}$ and EY of $82.5\mathrm{mg}/\mathrm{kWh}$ at the gas retention time of 1.98 s, an input power of 796 W, and an initial concentration of $85.6\mathrm{mg}/{\mathrm{m}}^3$. The final photolysis products of ${\mathrm{CS}}_2$ were identified to be ${\mathrm{SO}}_2$, ${\mathrm{CO}}_2$, CO, and COS in the gaseous phase, and $(\mathrm{CS}{)}_n$, ${\mathrm{SO}}_{4^{2-}}$, and sulfur in the solid phase.

Escherichia coli photorepair and dark recovery was investigated in two different water sources. Sterilized drinking water and wastewater effluent treated for reuse were spiked with either wild E. coli isolate or a laboratory-purchased E. coli strain and ultraviolet (UV)-irradiated at fluences from 40 to $120\mathrm{mJ}/{\mathrm{cm}}^2$. Although no threshold UV fluence was established after which E. coli photo and dark repair did not proceed, the extent of repair was generally low, not exceeding 0.5 log. Contrary to the repair results, the 48-h regrowth of E. coli disinfection survivors reached up to 3 log, likely due to the remaining inactivated E. coli cells that served as a source of biodegradable carbon postdisinfection. Although it is proposed that concerns regarding bacterial repair under drinking and reuse water UV disinfection conditions are overestimated based on experiments at low UV fluences, the long-term postdisinfection safety of water may be underestimated for conditions of low or no disinfection residual, or where nutrients are present, and regrowth could occur.

Engineered injection and extraction (EIE) is a method of in situ remediation of contaminated groundwater in which a treatment chemical that reacts with the contaminant is injected into the contaminated aquifer, and a series of injections and extractions of clean water are performed in nearby wells to promote the spreading of the treatment chemical throughout the contaminated aquifer. Numerical simulations are used to investigate the use of EIE for sorbing groundwater contaminants. The aquifer is homogeneous and confined with negligible ambient groundwater flow. A range of sorption parameters are considered for both linear equilibrium sorption and linear kinetic sorption, and both instantaneous and rate-limited bimolecular reactions are discussed. An effective EIE sequence is developed for a sorbing contaminant and is compared with a sequence developed for aqueous, nonsorbing contaminants. The results show that for contaminants that exhibit fast sorption and fast reaction, the EIE sequence developed for sorbing contaminants can achieve nearly complete contaminant degradation. For contaminants with linear equilibrium sorption and rate-limited reaction, the sequence can achieve nearly complete degradation if the duration of the remediation process is scaled with the inverse of the reaction rate constant. For contaminants that exhibit slow sorption, the EIE sequence designed for aqueous, nonsorbing contaminants achieves higher overall contaminant degradation, but requires more energy and higher injection and extraction rates.

High-temperature wastewaters and process waters in many industries have been a concern, compromising the integrity of polymeric membranes in filtration processes or requiring the temperature to be lowered for further treatments. Filtration processes employing ceramic membranes, however, can treat high temperature water owing to the inherent thermal resistance of ceramic materials, and may benefit from increases in permeate flux attributable to decreases in water viscosity at higher temperatures. In this study, the performance of a ceramic ultrafiltration membrane was evaluated for the filtration of feed solutions containing colloidal silica at temperatures between 25 and 90°C, the range encountered in various industries. Results indicated the net benefit of increasing permeate production at elevated temperatures, with a nearly 90% increase in steady-state flux from 25 to 90°C. However, this increase was lower than that observed for pure water filtration, in which the flux increase with increasing temperature was entirely attributable to viscosity reduction. Resistance-in-series model analysis and cake property characterization suggested that total fouling resistance increased as temperature increased, with physically removable cake formation as the dominant fouling mechanism.

This paper reports a new approach to understanding membrane fouling in membrane bioreactors (MBR). The foulants were categorized into those inside the membrane (internal fouling) and those on the membrane forming the so-called external fouling layer (external fouling). The volumes of the internal and external foulants were determined with the aid of a confocal laser scanning microscope (CLSM) after staining the foulants. Thus, the porosities of both the membrane and the external fouling layer were calculated, which explained the contributions of internal and external fouling to transmembrane pressure (TMP) from the standpoint of fundamental filtration theory. The categorical method indicates that external fouling may dominate the long-term operation of MBR with the formation of the external fouling layer, whereas internal fouling, in the form of pore constriction, may cause both initial and final TMP jumps under the operating conditions in the current study. In addition, a mathematical model was developed to dynamically link TMP with the basic filtration parameters (e.g., porosities of the membrane and external fouling layer, thickness of the external fouling layer, pore size inside the membrane, and size of the particles forming the external fouling layer). The model quantitatively describes the contributions of both internal and external fouling and further supports the experimental results.

Hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$) is one of the main odorant gases emitted from anaerobic sludge blanket (UASB) sewage treatment plants (STPs) and other anaerobic environments. The present work is an attempt to quantify ${\mathrm{H}}_2\mathrm{S}$ formation in seven full-scale UASB reactors across India and suppression of sulfide formation using pilot-scale UASB reactors and adopting a liquid-phase odor and corrosion control method that enhances sulfate (${\mathrm{SO}}_4^{2-}$) concentration in raw sewage up to $100–120\mathrm{mg}/\mathrm{L}$. Results for full-scale UASBs reveal that ${\mathrm{H}}_2\mathrm{S}$ varies 0–20.3 ppm because of high influent sulfates that range $100–150\mathrm{mg}/\mathrm{L}$ as the result of ingress of industrial wastewater in domestic sewage. However, results for the pilot-scale UASBs reveal that ${\mathrm{SO}}_4^{2-}$ in the influent ($38–40\mathrm{mg}/\mathrm{L}$) converted to sulfide ($15–20\mathrm{mg}/\mathrm{L}$) at ORP and pH to the safe range ($\mathrm{ORP}=-75\mathrm{mV}$; $\mathrm{pH}=6.9–7.3$). After sulfate enhancement, sulfide was observed to be $30–40\mathrm{mg}/\mathrm{L}$; COD removal, 80–85%; and ORP ranging from $-65$ to $-103\mathrm{mV}$. Furthermore, iron salt (${\mathrm{FeCl}}_3$), which was added at $30\mathrm{mg}/\mathrm{L}$ (a $1:1$ ratio to sulfide concentration) minimized sulfide in the reactor up to 99%.