Journal of Environmental Engineering

Reverse osmosis (RO) has long been recognized as an efficient separation method for treating and removing harmful pollutants such as dimethylphenol in wastewater treatment. This paper studies the effects of a RO network configuration of three modules of a wastewater treatment system using a spiral-wound RO membrane for the removal of dimethylphenol from its aqueous solution at different feed concentrations. The methodologies used for this research are based on simulation and optimization studies carried out using a new simplified model which takes into account the solution-diffusion model and film theory to express the transport phenomena of both solvent and solute through the membrane and to estimate the concentration polarization impact, respectively. This model is validated by direct comparison with experimental data derived from the literature and which includes a dimethylphenol rejection method performed on a small-scale commercial single spiral-wound RO membrane system at different operating conditions. The new model is implemented to identify the optimal module configuration and operating conditions that achieve higher rejection after testing the impact of RO configuration. The optimization model is formulated to maximize the rejection parameters under optimal operating conditions of inlet feed flow rate, pressure, and temperature for a given set of inlet feed concentration. In addition, the optimization model is subjected to a number of upper and lower limits of decision variables, including the inlet pressure, flow rate, and temperature. The model also takes into account the pressure loss constraint along the membrane length commensurate with the manufacturer’s specifications. The research clearly shows that the parallel configuration yields optimal dimethylphenol rejection with lower pressure loss.

In an effort to further understand the fourfold higher fluoride removal capacity of chemically activated cow bone (CAB) previously reported compared to bone char, fundamental properties of CAB were evaluated in this study. The CAB media contained bassanite ($\mathrm{Ca}{\mathrm{SO}}_4·0.5{\mathrm{H}}_2\mathrm{O}$) and monetite (${\mathrm{CaHPO}}_4$) minerals that were not present in bone char. In this study, the effectiveness of these minerals for fluoride adsorption was evaluated. High-purity (99.6%) monetite was prepared in the laboratory and showed a threefold higher fluoride adsorption capacity than CAB (20.0 and $6.4\mathrm{mg}/\mathrm{g}$, respectively). The ethylene glycol monoethyl ether (EGME) specific surface area (SSA) of monetite was twice that of the CAB media (260 versus $134{\mathrm{m}}^2/\mathrm{g}$) and thus may account for a portion of the threefold higher capacity of monetite versus CAB. The increased capacity of monetite can also be partly attributed to the high surface charge (zeta potential) on the monetite compared to CAB (27.1 and 7.5 mV, respectively, measured at pH 7). The high zeta potential suggests electrostatic adsorption as the fluoride removal mechanism. In contrast to monetite, the bassanite also present in CAB had negligible fluoride removal capacity. Therefore, monetite is found to be promising for fluoride removal to mitigate the negative health impacts of excess fluoride concentrations in drinking water.

Dissolved organic matter (DOM) is the major regulated pollutant of landfill leachate in solid waste management industries. Recently, aged-refuse bioreactor (ARB) has received increasing attention for reduction of DOM from mature leachate due to low energy consumption, easy operation, simple maintenance, low cost, and high treatment efficiency. However, the information regarding alternation of the DOM nature during ARB treatment is highly limited. To figure out appropriate posttreatment for effluent of ARB and meet elevated discharge standards, especially in developing countries, this study investigates the characterization of mature leachate DOM during ammonia stripping and two-stage ARB treatment by means of synchronous scanning fluorescence spectra, excitation-emission matrices spectra, and molecular size distribution. The analytical results indicated that ammonia stripping could not significantly remove DOM, though the process was effective in ammonia nitrogen reduction. In contrast, ARB could remove substantial DOM. The first stage ARB preferentially attacked both fulivc-acid-like and humic-acid-like organic molecules and the second stage ARB played a polishing treatment role with a similar treatment fashion. The final effluent after ammonia stripping and two-stage ARB treatment still contained fulvic-acid-like DOM with low molecular weight (<5 kDa) that should be further removed by appropriate posttreatment.

In this study, the characteristics of sediment deposition with three levels of wastewater, different shear stress, and initial sediment concentration were investigated in an annular flume. Sediment used for experiments was taken from the Pirbalut small dam reservoir, located in southwest Iran. The velocity and the shear stress profiles were measured, using an acoustic Doppler velocimeter (ADV). The results showed that the concentration of cohesive sediment decreased with time, and finally it reached an equilibrium concentration of sediment. The ratio of equilibrium concentration to initial concentration ($C_{eq}:C$) with a constant shear stress, for different initial sediment concentrations and different levels of wastewater were almost the same. The equilibrium concentration depends on the initial concentration sediment. Adding wastewater to the mixture caused the increasing of threshold and full deposition shear stress. The critical shear stresses for full deposition for three wastewater levels of 0, 30, and 60% are obtained as 0.050, 0.081, and $0.084\mathrm{N}/{\mathrm{m}}^2$, respectively.

This study used 16S rRNA gene-based terminal-restriction fragment length polymorphism (T-RFLP) analysis to investigate full-scale membrane bioreactors (MBRs), which mainly treat domestic wastewater, with specific examination of the microbial communities on membrane biofilms. Using cluster analysis and principal component analysis based on T-RF profiles, the microbial community structures of biofilms on moderately fouled membranes were distinguished from those on slightly fouled membranes and from activated sludge in the MBRs. Furthermore, biofilms on the severely fouled membranes hosted characteristic microbial communities under high-flux operation. The microbial community structures showed correlation with transmembrane pressure and the humus and iron biofilm contents. The microbial communities in membrane biofilms can indicate the fouling state.

Efficient anaerobic digestion (AD) of sludge is crucial for the overall energy balance, minimization of carbon footprint, and the economy for most wastewater-treatment plants (WWTPs). In recent years, intermittent feeding (IF) has become increasingly interesting because it has been shown to better condition the digester microbiology for overloading events. Additionally, IF is required when AD facilities move toward being active players in grid balancing via on-demand delivery and storage of green energy (i.e., power-to-gas). In this study, six laboratory-scale IF digesters were operated at 34, 37, and 40°C in a 300-day experiment to determine the impact of temperature on methane yield and long-term stability at typical conditions for conventional WWTP sludge digestion. The results show that IF led to no significant differences in methane yield observed among tested temperatures at an organic loading rate of $3\mathrm{kg}\mathrm{VS}{\mathrm{m}}^{-3}{\mathrm{days}}^{\mathrm{-1}}$ and a hydraulic retention time of 16 days. However, in an on-demand energy-delivery scenario, increased temperature could be interesting because of significantly increased methane production in the first hours following feeding.

Earthworms have been in existence for approximately 600 million years and have adapted to toxicity. They may help cleaning wastewater by devouring micro-organisms. Although the performance of earthworm-based wastewater-treatment technology is still under investigation, this study contributes some performance data to the investigation process. This study observes the performance in terms of removal efficiency of water quality constituents and energy requirements of an earthworm-based wastewater-treatment plant to treat the effluent from a dairy farm located at the California State University Fresno Agricultural Laboratory. Results show that the nitrogen-based water quality constituents, ammonium nitrogen (NH4), nitrate nitrogen (NO3-N), and total kjeldahl nitrogen (TKN), can be removed at higher removal efficiencies (above 90%). The removal efficiencies for biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) are found to be promising, but the removal efficiencies for other water quality constituents [e.g., calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), phosphorus (P), etc.] are found to be poor. In terms of energy consumption, 55% of total energy requirement data show better performance than a baseline study. This study was conducted with a pilot treatment plant. Study findings recommend that additional caution and protocols should be maintained during water quality sampling and other types of data-collection processes.

This study investigated treatment of dairy wastewater in one-stage anaerobic moving biofilm reactors (AMBRs) at ambient temperature. To support biological treatment with abiotic processes (iron corrosion), metallic iron was included in the porous structure of supports. The AMBRs were operated at a hydraulic retention time of 5.5 days and organic loading rate (OLR) of 3.9 and 7.5 kgCOD (chemical oxygen demand)/(${\mathrm{m}}^3\times \mathrm{day}$). At OLR 3.9 kg$\mathrm{COD}/({\mathrm{m}}^3\times \mathrm{day})$, COD removal was significantly higher with 2% iron in the support structure than without iron ($86.6\pm 7.8\%$ versus $81.3\pm 9.0\%$). Adding Fe to the supports did not influence biogas productivity or the biogas production rate. Fe addition significantly increased phosphorus removal from about 50% in AMBRs without added Fe to $72.1\pm 8.4\%$ with 2% iron. Further increasing Fe content to 3% did not increase COD or P removal. In all reactors, acetoclastic methanogens predominated over hydrogenotrophic methanogens; however, Fe promoted growth of Methanobacteriaceae.

The dewaterability of sludge from two conventional activated sludge (CAS) and three membrane bioreactor (MBR)–based wastewater treatment plants is investigated prior to and after anaerobic digestion. The concentration and composition of extracellular polymeric substances (EPS) mostly affect the dewaterability of all raw sludge samples. Better sludge dewaterability is observed when the concentration of proteins, carbohydrates, uronic acids, and humic acids is below approximately 400, 250, 200, and $40\mathrm{mg}/\mathrm{L}$, respectively. In contrast, the specific resistance to filtration (SRF) increases in the sludge samples with a higher EPS concentration. The MBR results in a lower EPS production and a uronic acid–dominating EPS composition. This especially affects the dewaterability of one MBR sludge, also characterized by high salinity and a smaller particle size. Anaerobic digestion results in a higher SRF for both CAS and MBR sludge, with the particle-size distribution having the preponderant effect on the digested sludge dewaterability.

Biofilm formation and manganese oxidizing bacteria (MOBs) in water transmission and distribution systems can lead to a wide array of water quality issues, operational problems, and negative hydraulic impacts. To investigate possible methods to control biofilm formation, a study using chlorine dioxide (${\mathrm{ClO}}_2$) and sodium hypochlorite (NaOCl) was performed with rotating annular reactors (ARs). Results showed that low ($0.5\mathrm{mg}/\mathrm{L}$ as ${\mathrm{ClO}}_2$) and high ($1.0\mathrm{mg}/\mathrm{L}$ as ${\mathrm{ClO}}_2$) doses of ${\mathrm{ClO}}_2$, and $2.0\mathrm{mg}/\mathrm{L}$ as ${\mathrm{Cl}}_2$ of NaOCl, were effective at mitigating biofilm to different extents by oxidizing readily available dissolved manganese (Mn) and iron (Fe) and/or inactivating biofilm populations. The most effective biofilm control strategy tested was a $2.0\mathrm{mg}/\mathrm{L}$ dose of NaOCl, which provided significant reductions of suspended bacteria (2.1 log reduction), established biofilm (2.5 log reduction), and new biofilm growth (3.2 log reduction). Results from this study suggest that the implementation of treatment strategies for the control of existing and future biofilms should consider both (1) the removal of readily available metals by oxidation, and (2) the direct inactivation of attached bacteria.

This paper describes field testing of a small-scale, continuous-flow electrodisinfection reactor assembled with four ${\mathrm{IrO}}_2$-coated titanium plates and operated in bipolar mode using direct current, installed at the Marrero wastewater treatment plant in Marrero, Louisiana. The objective of this testing was to demonstrate the technical feasibility of replacing the current wastewater-effluent hypochlorination process with this new disinfection technology. Bacterial inactivation and chlorine production were the main parameters recorded. The experiments reported in this study demonstrate that the electrodisinfection process can meet and exceed 5-log coliform removal in a short contact time, thereby proving to be efficient enough to be considered as an alternative to chlorination in wastewater treatment facilities. Optimum operational conditions for fluid retention time, and volumetric current density and rate, were stablished from the experimental results. The following design recommendations summarize these findings: retention time of $5\pm 0.3\min$, minimum volumetric current density of $\mathrm{1,000}\mathrm{A}/{\mathrm{m}}^3$, and minimum volumetric current rate of $80\mathrm{A}·\mathrm{h}/{\mathrm{m}}^3$. Implementation of these operational conditions in the field yielded excellent disinfection efficiencies and low chlorine residual production.

Field installations of two iron-enhanced sand filters (IESFs), designed to remove phosphate and particulates from stormwater runoff, were monitored and maintained for 1–3 years. One application, a traditional IESF in an agricultural watershed, retained over 64% of the influent phosphate load, whereas the second, a pond perimeter IESF in a developing suburban watershed, retained 26%. The measured average effluent event mean concentration (EMC) for the traditional IESF was $56.1\mathrm{\mu g}/\mathrm{L}$. All events exhibited positive removal of phosphate (i.e., effluent $\mathrm{loads}<\mathrm{influent}$ loads). In contrast, the measured percent phosphate retained for the pond perimeter IESF in 2013, 2014, and 2015 was 18, 25, and 45%, respectively. In addition, the average effluent EMC for the 3 years was 64.1, 54.2, and $19.9\mathrm{\mu g}/\mathrm{L}$, respectively. Half of the events (14 of 28) were found to have negative removal (i.e., effluent $\mathrm{loads}>\mathrm{influent}$ loads). Events with negative removal tended to be smaller events with low influent phosphate concentrations ($3.7–39.4\mathrm{\mu g}/\mathrm{L}$). Nonroutine maintenance improved the hydraulic performance of the pond perimeter IESF and, after a rinsing event, also improved phosphate retention rates to an average of 45%. There are believed to be at least two reasons for this difference in performance between the two IESFs: First, the traditional IESF was treating agricultural tile drainage with a low particulate phosphorus concentration, while the pond-perimeter IESF had a degrading mat of filamentous algae transported onto the surface, creating a source of phosphate that was not quantified. Second, the pond-perimeter IESF had treated a relatively large volume of water for its size, resulting in substantial flow-through in the filter within 5 years of operation. This is greater than anticipated for an IESF, and may have partially caused the reduction in performance.