Journal of Environmental Engineering

Previous studies have revealed that the application of zero-valent iron (ZVI) in reducing nitrate is limited by ammonium production and the requirement for adequate pH control. The current study focused on developing a new material potentially applicable in permeable reactive barriers, which can reduce nitrate without ammonium release under unbuffered pH. The new material, referred to as ZanF, is derived from zeolite modified by Fe(II), followed by borohydride reduction. The pseudo-first-order rate constant $\left(k_{\mathrm{obs}}\right)$ of ZanF in the early period of nitrate reduction was 10 times higher than that of the ZVI used in this study. However, the $k_{\mathrm{obs}}$ of ZanF decreased in the reaction period that followed. Even though both ZVI and ZanF produced ammonium as a product of nitrate reduction, ZanF removed it to below detection limits via adsorption, whereas ZVI did not remove it to any significant extent. ZanF maintained its high reactivity even under an initial pH of 6.2 without buffer. The higher ZanF/solution ratio increased the removal rate of ZanF as well as the removal efficiency.

To meet the increasing need for reduction of exhaust emissions from stationary sources, many technologies have been developed to remove ${\mathrm{SO}}_2$ from flue gas. In this study the anodic oxidation of sulfur dioxide in aqueous solutions of sulfuric acid with a unique reactor design and electrode configuration has been investigated. An electrochemical absorption column larger than laboratory scale was employed. A titanium rod cathode and platinum expanded mesh anode separated by a cation exchange membrane were used as electrodes in the cylindrical electrochemical reactor. The effects of current densities of 10, 1, and $0.1{\mathrm{Am}}^{-2}$ , initial ${\mathrm{SO}}_2$ concentrations of 500, 2,500, and $\mathrm{5,000}\mathrm{ppm}$ , gas flow rates of 0.75, 1.5, and $5{\mathrm{L\; min}}^{-1}$ , sulfuric acid concentrations of 1, 5, and $10\%\left(\mathrm{w}\right)$ , gas composition, and electrolysis time on removal efficiency, current efficiency, energy consumption, and mass transfer coefficient were reported. Removal efficiency of 94% was obtained with a high current efficiency of 94%, energy consumption of $2.22\times {10}^{-2}\mathrm{kW}{\mathrm{hm}}^{-3}$ , and mass transfer coefficient of $5.9\times {10}^{-5}{\mathrm{ms}}^{-1}$ without additives or pretreatment. At the current densities of 0.1, 1, and $10{\mathrm{Am}}^{-2}$ , the removal efficiencies were 10, 94, and 98%, respectively. Removal efficiency was observed to decrease as inlet ${\mathrm{SO}}_2$ concentration, gas flow rate, and electrolyte concentration increased. The presence of ${\mathrm{CO}}_2$ in the gas mixture led to a decrease in the ${\mathrm{SO}}_2$ removal efficiency. During electrochemical absorption of ${\mathrm{SO}}_2$ into the ${\mathrm{H}}_2{\mathrm{SO}}_4$ solution, the concentration of acid is increased from 5 to 10%. At the end of the studies, electrochemical desulfurization succeeded in meeting the regulation requirement, and the absorbing liquid remained in a reusable form.

A continuous flow flat sheet hybrid membrane aerated biofilm reactor (MABR) was used to treat a synthetic wastewater containing perchloroethylene (PCE); $1.25–2.5\mathrm{g}$ chemical oxygen demand (COD)/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade $70\mathrm{mg}{\mathrm{L}}^{-1}$ of PCE in $9\mathrm{h}$ without the accumulation of any intermediate compounds, resulting in a removal rate of $247\mathrm{mmol}$ of $\mathrm{PCE}{\mathrm{h}}^{-1}{\mathrm{m}}^{-3}$ in a reactor with a specific membrane area of $4.048{\mathrm{m}}^2{\mathrm{m}}^{-3}$ . MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72–81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.

This paper investigates the effect of chelating agents on the bioavailability of Fe and Cu during anaerobic digestion. The results on metal speciation and methane production in anaerobic serum bottles showed that biomass was able to grow in the presence of citrate $1\mathrm{mM}$ and nitrilotriacetic acid (NTA) $1\mathrm{mM}$ , suggesting that the binding sites at the cell surface competed efficiently for the metals with the chelating agents added. The presence of free ethylenediaminetetraacetic acid $1\mathrm{mM}$ inhibited methanogenesis, and this seemed to be related to a loss in metal uptake capacity. Although the addition of soluble microbial products (SMP) did not change metal distribution in anaerobic systems, it caused an increase in the rate of methane production, and it is believed that direct uptake of Cu-SMP complexes was responsible for this increase. The best protection against Cu toxicity occurred when stoichiometric amounts of NTA, which should complex and solubilize most of the Cu, was added, and it is likely that NTA prevented lethal concentrations of Cu from being adsorbed onto the cell and hence internalized.

The accumulation of soluble microbial products (SMP) in a membrane bioreactor (MBR) was investigated both experimentally and theoretically. The sieving mechanism of the microfiltration membrane was experimentally demonstrated as inadequate to explain the salient accumulation of SMP in an MBR. The retarded transport of SMP through porous membranes was postulated as a new mechanism for the elevated SMP concentration in the MBR. Owing to the higher affinity of SMP to the membrane matrix, the convection velocity of SMP across the membrane can be much slower than that of water. The ratio of SMP concentration in the effluent to that in the MBR can be determined with a rigorous solution of the convection-dispersion equation developed based on the retarded transport. In addition, a mass balance model considering SMP generation in the MBR and SMP transport through the membrane was developed to describe the SMP concentrations in the MBR and in the effluent. The simulation results were in good agreement with the experimental data, indicating that the accumulation of SMP in the MBR could be attributed to the retarded transport of SMP through the membrane. The proposed model provides a new conceptual framework for evaluating the fate of SMP and the performance of MBR.

This paper proposes an algorithm for a robust optimal design of the biological reactor and secondary settling facilities in suspended growth nitrogen and phosphorus removal systems. Robust optimization includes uncertainty in the decision-making procedure and seeks a solution that remains “close” to optimal for all potential operation scenarios. It thus differs fundamentally from the deterministic and stochastic approaches, where uncertainty is ignored or a solution based on either the most likely scenario or the average performance over all potential scenarios is produced. The robust optimization of a suspended growth system is a multiobjective optimization problem concerned with minimization of the global costs and variability of the system’s performance around the optimal. The proposed robust optimization approach uses the ASM3 model, making use of its performance prediction capabilities to produce a powerful tool for designing activated sludge systems. The algorithm was applied to the design of the biological reactor and secondary settling facilities for the Vila Real municipal wastewater treatment plant (Portugal).

Information Collection Rule (ICR) water quality and treatment data were screened from an end-user’s perspective and data distributions were developed based on the screened data set. Questionable data were flagged and missing categorical variables were replaced where possible. Sparseness of flagged data indicated a high level of ICR data quality while recovery of missing descriptors substantially amplified the data set. Data patterns demonstrated anticipated relationships between disinfection practices and water quality: plants with high concentrations of organic precursors preferentially employed chloramines and avoided prechlorination; plants with high bromide levels also tended to employ chloramines although bromide did not impact prechlorination practice. Though plants employing chloramination used significantly higher chlorine doses than plants using only free chlorine, when normalized to total organic carbon (TOC) this difference largely disappeared. The median ICR chlorine to TOC ratio was $1.54\mathrm{mg}$ ${\mathrm{Cl}}_2∕\mathrm{mg}\mathrm{C}$ . Applied chlorine to ammonia-nitrogen ratios at chloramine plants varied widely but the median value was near the theoretical $1:1\text{molar}$ ratio. Significantly higher bromide to TOC ratios at ground water plants, compared to surface water plants, resulted from the typically lower TOC and higher bromide levels in ground waters.

Estimation of settlement for municipal solid waste (MSW) landfills is critical to the successful site operation and maintenance as well as to the future development of the sites. In this paper, the six existing settlement prediction models are analyzed according to the three landfill types. 15 MSW landfill sites are classified into three categories, Types I, II, and III depending on their settlement activity levels and fill age. Measured settlement data of each landfill site are plotted as a strain curve on a logarithmic time scale, and the slope of the curve is used to determine a settlement activity level. First, the parameters of each prediction model are evaluated to determine their typical values for each type of the landfills. The results will serve as a basis for engineers to determine if their calculated model parameters are within the typical ranges. Second, each model’s performance of predicting settlement for the landfill sites is analyzed against the measured settlement data to compare the model’s applicability according to the landfill types. The results recommend specific prediction models to be used in a certain landfill type(s).

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of $460\mathrm{mg}{\mathrm{L}}^{-1}$ , with one reactor run as a control, one with $1.7\mathrm{g}{\mathrm{L}}^{-1}$ of powdered activated carbon (PAC), and the third with $1.7\mathrm{g}{\mathrm{L}}^{-1}$ of granular activated carbon (GAC). While COD removal was high in all reactors $(>90\%)$ , in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low $(<18\mathrm{mg}{\mathrm{L}}^{-1})$ , even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage.

Parts of New England have naturally high arsenic concentrations in groundwater. High arsenic correlates broadly with bedrock type, but levels are patchy, so other conditions must affect arsenic mobilization. Microorganisms capable of arsenate $\left(\mathrm{As}\right(\mathrm{V}\left)\right)$ respiration, if present, could affect arsenic speciation and mobility in groundwater. An arsenate-reducing bacterium, designated NP4, was isolated from groundwater obtained from a well in Northport, Me., with extremely high $(>\mathrm{1,400}\mathrm{\mu }\mathrm{g}{\mathrm{L}}^{-1})$ arsenic. Sequencing of the 16S rDNA showed that NP4 groups with the Sulfurospirillum genus. It can grow using arsenate, nitrate, iron(III), selenate, manganese(IV), sulfite, sulfur or thiosulfate as terminal electron acceptors and lactate, formate and pyruvate as electron donors. It can also grow on fumarate or lactate alone. This Sulfurospirillum isolate is distinct from other members of the genus in its carbon and electron acceptor usage. The activity of this type of microorganism could negatively affect groundwater quality by converting $\mathrm{As}\left(\mathrm{V}\right)$ to the more toxic and difficult to remove $\mathrm{As}\left(\mathrm{III}\right)$ form.

The preoxidation of a highly polluted waste pharmaceutical fermentation broth using wet air oxidation (WAO) has been studied as a possible method for the effective removal of organics. The applied (pre)treatment method should enhance the biotreatability of the pharmaceutical fermentation broth in terms of reduced initial toxicity and higher biodegradability. Preliminary experiments in the pilot biological treatment plant were successful only at low organic loads, whereas the system collapses at higher ones. The characterization of the fermentation broth was started by common physicochemical analysis, whereas several bioassays were used to determine its impact on biological treatment plants and the environment. Toxicity prior to and after WAO was determined using the acute Vibrio fischeri test, measurement of inhibition of ${\mathrm{O}}_2$ consumption, and the Daphnia magna acute test. Ready biodegradability of the treated and untreated broth has also been assessed. WAO experiments were accomplished in the $2\mathrm{L}$ batch reactor at different temperatures $(240∕280°\mathrm{C})$ and operating pressures. WAO experiments confirmed reduction of the toxicity toward microorganisms, whereas oxidized wastewater was more toxic to daphnids. Biodegradability of the oxidized broth has also been enhanced. Further work has been focused on designing appropriate combination of WAO and biological processes.

A bench-scale study was conducted to determine the inactivation of adenovirus (Ad) types 2, 5, and 41 by ultraviolet (UV) light, chlorine, and monochloramine. The motivation for this study was to determine whether UV disinfection followed by chlorine or monochloramine for a very short contact time (e.g., a minute) could satisfy regulatory requirements for four-log virus inactivation. In order to overcome the difficulty Ad 41 presents for enumeration of the virus in cell culture, a technique was used that combined immunofluorescent staining of viral antigen with traditional scoring of cytopathic effect. A UV dose of $40\mathrm{mJ}∕{\mathrm{cm}}^2$ (millijoules per square centimeter) (applied using a collimated beam apparatus) achieved approximately one-log inactivation of adenovirus types 2, 5 and 41, confirming previous research. Ad 41 was found to be more UV resistant to UV light than Ad 2 or Ad 5 at UV doses $>70\mathrm{mJ}∕{\mathrm{cm}}^2$ to a statistically significant degree (95% confidence); however, at lower UV doses there were no statistically significant differences. Experiments with Ad 5 and Ad 41 at $5°\mathrm{C}$ and pH 8.5 showed that chlorine was very effective against Ad 5 and Ad 41, with a product of disinfectant concentration and contact time (CT) of $0.22\mathrm{mg\; min}∕\mathrm{L}$ providing four-log inactivation. Monochloramine was less effective against these adenoviruses, with a CT of $350\mathrm{mg\; min}∕\mathrm{L}$ required to achieve 2.5-log inactivation of Ad 5 and 41 at $5°\mathrm{C}$ and pH 8.5.

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume hydrolysis is the rate-limiting step, but none consider the role that the kinetics of biological flocculation and the sludge settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetic of biological flocculation, and have analyzed its role on the removal of particulate COD in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. This paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge settling properties with the aeration tank behavior, and is a reasonable first approximation that can be used for activated sludge system design and operation.

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes: rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume that hydrolysis is the rate-limiting step, but none considers the role that the kinetics of biological flocculation and the sludge-settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetics of biological flocculation, and have analyzed its role on the removal of particulate chemical oxygen demand in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. The first paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge-settling properties with the aeration tank behavior, and the second paper presents experimental evidence that the proposed model is a reasonable first approximation that can be used for activated sludge system design and operation.

The results of an investigation of the effect of antimicrobial coatings on inactivating microbes on and within the media used in cloth media disk filtration systems are presented herein. Four filter fabrics were evaluated using a modified form of the American Association of Textile Chemists and Colorists Test Method 100 in 1996. The fabrics had been treated with two antimicrobial agents by two coating vendors. Treated fabrics were subjected to backwash cycles to examine whether the antimicrobial properties were retained during normal filter operation. Initially, the fabrics treated with Zoonocide exhibited significant microbial reduction whereas fabrics treated with AlphaSan exhibited little microbial reduction. Once the fabrics treated with Zoonocide were subjected to a backwash cycle, the biocidal properties of the fabrics were depleted. Lack of durability of the coating was either because it washed off easily or the antimicrobial properties were chemically depleted, rendering the treatment ineffective.

Iron oxide impregnated onto an activated carbon $\left(\mathrm{FeAC}\right)$ has a high arsenic (As) removal capacity with the potential to be used in existing activated carbon column systems. Objectives of this research were to investigate $\mathrm{As}\left(\mathrm{V}\right)$ removal from aqueous-phase systems using fixed-beds packed with $\mathrm{FeAC}$ and to determine if the triple layer model (TLM) with the homogeneous surface diffusion model (HSDM) could describe $\mathrm{As}\left(\mathrm{V}\right)$ removal in the columns. Rapid small-scale column tests (RSSCT) were conducted at various empty bed contact times (EBCT). Effluent $\mathrm{As}\left(\mathrm{V}\right)$ breakthrough $(10\mathrm{\mu }\mathrm{g}∕\mathrm{L})$ was incipient for the 0.20-min EBCT experiment, whereas $\sim 2300$ bed volumes of water at 1-mg/L inlet concentration of $\mathrm{As}\left(\mathrm{V}\right)$ was treated at an EBCT of $2.1\min$ before breakthrough occurred. The TLM with three $\mathrm{As}\left(\mathrm{V}\right)\text{-}\mathrm{FeAC}$ surface reactions coupled with the HSDM provided accurate prediction of $\mathrm{As}\left(\mathrm{V}\right)$ removal in the RSSCT.