Journal of Environmental Engineering

Since the inocula for the start-up of the anaerobic reactors (ABs) is still limited in many places, the expansion of the source of feeding anaerobic granular sludge is critical for the application of anaerobic reactors. This paper describes the performance and the bacterial community change during the start-up period of a spiral symmetry stream anaerobic bioreactor (SSSAB) inoculated with four-year storage anaerobic granular sludge. The SSSAB could be successfully started within 58 days, indicating that long-term storage sludge could be an alternative seeding anaerobic reactor. The high-throughput 16S rRNA gene amplicon sequencing using the MiSeq platform was applied to reveal the microbial community change of the granular sludge. The first-time increase of influent chemical oxygen demand (COD) concentration was suggested to be carried out carefully, since the COD removal efficiency would fluctuate sharply if the increment of COD was not appropriate. After start-up, the influent COD concentration of SSSAB was $\mathrm{11,800}\pm 300\mathrm{mg}/\mathrm{L}$, while the hydraulic retention time was 12 h. The organic loading rate (OLR) reached up to $21.15\mathrm{kg}\mathrm{COD}/({\mathrm{m}}^3·\mathrm{d})$. The most dominant bacterial phyla in the anaerobic granular sludge during the start-up of the SSSAB were Actinobacteria, Bacteroidetes, Proteobacteria, Chloroflexi, and Firmicutes, which accounted for 77.60% of total bacteria on average. Actinobacteria, Chloroflexi, and Proteobacteria played an important role in sludge granulation and growth. Chloroflexi and Firmicutes were deduced to be the key bacteria for the recovery of sludge activity.

The soil remediation using Salix integra combined with oil-degraded microorganism Pseudomonas aeruginosa was conducted to investigate the effect on degradation of diesel ($\mathrm{10,000}\mathrm{mg}·{\mathrm{kg}}^{-1}$) in diesel-contaminated soil. The diesel contents in Salix integra tissue, and the activity of soil microorganisms and enzymes’ (dehydrogenase, catalase, and polyphenol oxidase) activities in rhizosphere soils were also assessed in different treatments. The results showed that the treatment of Salix integra combined with Pseudomonas aeruginosa displayed the highest removal efficiency (67.46%). Inoculating Pseudomonas aeruginosa could decrease the content of diesel in Salix integra’s tissues; however, there was no significant difference. Moreover, inoculating Pseudomonas aeruginosa significantly increased the rhizospheric microbial activity by 5.1–19.22% compared with the one only planting Salix integra. In addition, a close correlation between diesel removal ratios and the microbial activity was observed ($r=0.978$, $p<0.01$) in the Salix integra combined with Pseudomonas aeruginosa treatment. The activities of dehydrogenase were also significantly correlated with the microbial activity ($r=0.860$, $p<0.05$). All of the previous results confirmed that inoculating Pseudomonas aeruginosa could enhance the dissipation of diesel oil in soil. Thus, the composite system could be reasonably used to restore the ecological environment of organic contaminated soils.

The efficiency of a two-stage mesophilic anaerobic sludge digestion process was studied in comparison with a conventional process to treat urban sludge in relation to the hydraulic retention time (HRT) of the acid stage. This comparison, performed to optimize methane production in relation to the acid stage, was carried out in a pilot plant operating a two-stage process in parallel with conventional anaerobic digestion. The conditions of the conventional process were 22 days of HRT at 33.6°C; while the methanogenic stage was not changed (HRT 8.5 days at 33.5°C), the HRT of the acid stage ranged from $1.6\pm 0.3\mathrm{days}$ to $3.2\pm 0.6\mathrm{days}$ under a constant temperature of approximately 21.5°C. The results showed that the total anaerobic digestion process HRT can be reduced by at least 10.8 days using the two-stage technology without reducing the quality of the sludge effluent, operating at a HRT minimum of 1.6 days. Moreover, in the two-stage process, the optimum acid stage HRT to maximize methane production is 2.18 days.

Tanning factory is globally considered to be one of the most resource consuming and pollutants producing industries because it requires, for processing leather, large amounts of fresh water, chemical reagents, and energy, and in addition produces wastes, liquid as well solid, rich in organic matter and heavy metals (e.g., chromium). Such characteristics of tannery wastes make their biological treatment promising as well as challenging. This study deals with the effect of coagulation process as a pretreatment method on real tannery wastewater prior to anaerobic digestion (AD), with the aim of removing chromium and thus limiting its inhibitory effect on biological process. Different concentrations (100, 200, 400, 600, 800, and $\mathrm{1,000}\mathrm{mg}/\mathrm{L}$) of the coagulant ${\mathrm{FeCl}}_3$ were tested, at pH 7.5, with an initial total chromium concentration of $150\mathrm{mg}/\mathrm{L}$. The efficiency of metal removal was in the range of 0.44–29.38%. Simultaneously, the chemical oxygen demand was reduced by 0.86–28.80%, with the detrimental effect of lowering the total biogas production potential from tannery wastewater. Nevertheless, coagulation pretreatment enhanced the AD process of tannery wastewater, resulting in an increase of the cumulative biogas production by 10% and in a reduction of the digestion time by approximately 25%, in comparison with untreated wastewater. After 37 days of incubation, the maximum specific cumulated volume of biogas produced from the wastewater pretreated with $800\mathrm{mg}/\mathrm{L}$ of ${\mathrm{FeCl}}_3$ was $837\mathrm{mL}/\mathrm{g}$ total volatile solids added with approximately 84% of methane.

The day-to-day negative effect of contaminating substances on the ${\mathrm{NO}}_x$ removal effectiveness of photocatalytic surfaces and their recovery capacity after undergoing cleansing is of real academic and practical interest. This paper analyzes the ${\mathrm{NO}}_x$ removal effectiveness of two different types of photocatalytic concrete surface layers incorporating nano-${\mathrm{TiO}}_2$ particles. Both types of surfaces are examined before and after being subjected to dust accumulation and oil impregnation. The recovery of their ${\mathrm{NO}}_x$ removal capacity after undergoing various cleansing processes is also evaluated. The results are compared to those of their respective reference samples. The results show that the high ${\mathrm{NO}}_x$ removal capacity of the spray-coated samples is partially maintained even after a high concentration of dust accumulation. However, the water-cleansing process employed is sufficient to recover the lost ${\mathrm{NO}}_x$ removal capacity. It is also discovered that the nano-${\mathrm{TiO}}_2$ particles lose nearly all their photocatalytic capacity after being subjected to oil impregnation, and that the cleansing processes, either by an alkaline detergent or using an n-hexane solvent, fails to recover the initial ${\mathrm{NO}}_x$ removal capacity.

Bioretention cells (BRCs) are stormwater control measures that integrate water quantity and quality management. Previous research primarily focused on the performance of cells less than two years old, before potential clogging and sorption site saturation. To assess long-term effectiveness, this project evaluated the performance of a BRC after seven years to determine reductions in flow rate, flow volume, suspended solids, nitrogen, phosphorus, and fecal indicator bacteria (FIB). These observations were compared with analyses conducted immediately postconstruction. Inflow and outflow water samples were collected for sediment, nutrients, and FIB. Soil media samples were collected from multiple depths and analyzed for denitrifying bacteria. Results indicate the BRC remains effective at reducing storm flows, nutrients, and FIB. These reductions were correlated to outflow volume, rather than storm characteristics. The majority of denitrifying bacteria were present in the top media layers, despite the presence of an internal water storage layer for denitrification. This finding suggests denitrification primarily occurs at anoxic microsites in the upper layers and that a lack of carbon at deeper depths may limit significant microbial growth.

South African coal fly ash (CFA) has been used as a source of silicon and aluminum in the synthesis of faujasite zeolite and geopolymer. However, the synthesis of faujasite zeolite from CFA filtrate does not favor the industrialization of the process because of the small yield of the final product and the huge amount of waste generated. This study suggests a way of synthesizing a pure faujasite and geopolymer from the same batch of CFA. A pure faujasite, with a yield of 43.28%, was synthesized from alumina and silica that were sequentially extracted from CFA using ${\mathrm{H}}_2{\mathrm{SO}}_4$ (95–99%) and NaOH (8 M), while the remaining slurry was transformed into a geopolymer. This process shows that a waste material (CFA) can be transformed into two valuable products without major waste generated.

Mesoporous alumina (MA), synthesized at room temperature, is a high-performance adsorbent for removing arsenic [As(V)]. After adsorption for 1 h, the residual As(V) concentration in solution was found to be less than $0.007\mathrm{mg}/\mathrm{L}$ for an initial As(V) concentration of less than $2.235\mathrm{mg}/\mathrm{L}$. A marked increase in arsenic removal was observed for an increase in the dosage of MA from 0.05 to 0.15 g. However, a relatively smaller increase in As(V) removal was observed when the dosage of MA was increased from 0.15 to 0.30 g. Spent MA can effectively be regenerated with 0.05 M NaOH. Even after five adsorption-desorption cycles, MA retained most of its adsorption capability and was able to remove more than 82% of the initial arsenic. The adsorption capability of MA for arsenic species was found to be in the order of: ${\mathrm{H}}_2{\mathrm{AsO}}_4^{-}>{\mathrm{H}}_3{\mathrm{AsO}}_4>\mathrm{H}{\mathrm{AsO}}_4^{2-}>{\mathrm{AsO}}_4^{3-}$, which were removed by MA via hydrogen bond, electrostatic interactions, and ion exchange. It was found that the interactive effect of pH and initial concentration on As(V) removal percentage is of significance, while the interactive effect of adsorption temperature and adsorption time on As(V) removal is insignificant. The predicted maximum removal percentage of As(V) is 100%, and the corresponding optimized adsorption parameters were found to be as follows: adsorption time: 449 min; adsorption temperature: 45°C; initial pH: 3.97; initial concentration: $36.98\mathrm{mg}/\mathrm{L}$. The results showed that the adsorption equilibrium data were adequately represented by Langmuir model, and the maximum adsorption capacity $q_{\max }$ was $36.42\mathrm{mg}/\mathrm{g}$.

This paper investigates biodegradation of physically dispersed oil (WAF) and chemically dispersed oil (CEWAF). Two salinities are considered: low (6.5‰) and high salinity (29‰), and for each salinity two nutrient conditions are considered: low nutrient, using the background concentration ($0.05\mathrm{mg}\text{-}\mathrm{N}{\mathrm{L}}^{-1}$ and $0.10–0.20\mathrm{mg}\text{-}\mathrm{P}{\mathrm{L}}^{-1}$) and high nutrient, using concentrations of $100\mathrm{mg}\text{-}\mathrm{N}{\mathrm{L}}^{-1}$ and $10\mathrm{mg}\text{-}\mathrm{P}{\mathrm{L}}^{-1}$. Results show that the oil concentration for the WAF is $\sim 20\mathrm{times}$ less than that resulting from the CEWAF. In the WAF, the biodegradation of polycyclic aromatic hydrocarbons (PAHs) was not detected due to extremely low concentration. In contrast, the biodegradation of the alkanes and the methylated PAHs (mPAHs) is as high as 72% after 42 days and seem to be unaffected by the nutrient concentration. In the CEWAF, considerable biodegradation is noted for the alkanes, PAHs, and mPAHs. The enhanced oil biodegradation in the presence of dispersant suggests that chemical dispersion might be an effective approach in the treatment of spilled oil.

In this study, an improved interval two-stage programming (ITSP) model is applied for design and optimization of an activated-sludge process (ASP) wastewater-treatment system under uncertainty. Improved ITSP integrates full-infinite programming and two-stage programming into an interval linear programming framework. Improved ITSP is capable of addressing multiple uncertainties that exist in related costs, impact factors, and system objectives, which can be expressed as determinates and crisp interval values. The modeling approach allows uncertainties and decision makers’ aspirations to be directly communicated into the optimization process and resultant solutions. This is the first attempt to apply ITSP to an ASP wastewater-treatment system, in which pollutant discharge can be controlled in whole aspects. Results indicate that reasonable solutions would be generated. This model is applicable for a conventional ASP wastewater-treatment system without any nitrification because of the oxygen demand for ammonia oxidation. It can help decision makers to identify desired policies under various economic and system constraints by generating decision alternatives, which can also coordinate the conflicting interactions among economic cost, system efficiency, and pollutant mitigation.

Biochemical oxygen demand (BOD) is a variable that is missing or inaccurate in many water quality data sets because of difficulties in diluting highly polluted water samples. Machine learning algorithms, particularly support vector regression (SVR), are useful to build regression models to fill gaps in these data sets. The SVR can underpredict extreme-high values when they are few in number and underrepresented. This paper evaluates two methods, bootstrapping and data expansion, to mitigate the problem by increasing the proportion of extreme-high BOD in the data set before training the gap-filling model. Both methods were tested on the water quality data of Yuen Long Creek, Hong Kong, for the years 2000–2014. Both methods were effective in mitigating systematic underprediction and reducing their residual errors when the proportion of extreme-high values in the data set were increased from 3 to 30–40%. Both methods were useful for gap filling on BOD time series because extreme-high values are often the ones missing or inaccurate when highly polluted samples are diluted.

Long regeneration time and substantial water usage in desorption cycles impose potential barriers for practical applications of capacitive deionization (CDI). In this research, a single-pass continuous-flow CDI cell was used to explore the effect of desorption methods on electrode regeneration performance. The results demonstrated effective nature of polarity reversal during electrode regeneration compared to the conventional short-circuit method. A reversed polarity with optimized duration and magnitude of cell voltage while purging with a proper flow scheme exhibited substantial reductions on regeneration time and flush-water usage during the desorption processes of CDI. The beneficial aspects of preferred desorption methods were attributable to minimization of a readsorption effect by limiting the rate of ion transport to the oppositely charged electrode. The results of this research are beneficial for improving the operational efficiency and cost-effectiveness of CDI systems for engineering applications.

Cosolvents, such as short-chain alcohols used in oxygenated fuels, have the potential to increase the aqueous solubility of hydrophobic organic chemicals. Most of the attention has been focused on compound classes such as polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), with comparatively little attention directed to organochlorine pesticides, despite their environmental significance. The work reported here shows increases in the aqueous solubility of dieldrin and lindane of approximately 7.5 and 3.3 orders of magnitude, respectively, as the ethanol mass fraction, ${\omega }_c$, increases from 0.0 to 1.0. The relationship between the aqueous solubility of these compounds and the ethanol mass fraction differs from that of other hydrophobic compounds, requiring a two-part log-linear model, with the breakpoint occurring at ${\omega }_c\approx 0.35$ for the pesticides examined. The solubility relationship is heavily influenced by cosolvent–solvent interactions, with the breakpoint occurring due to a shift in these interactions, and consequently in the solubilization mechanism.

Leachate is a highly toxic wastewater produced in landfills that causes many environmental problems. One imperative action related to leachate management is the implementation of a leachate collection system and leachate treatment. Because leachate contains a wide range of contaminants, an interesting method that may be used in the future for the treatment of leachate is a photocatalytic treatment process using doped ${\mathrm{TiO}}_2$ nanoparticles. In this study, the performance of tungsten-doped ${\mathrm{TiO}}_2$ (W-doped ${\mathrm{TiO}}_2$) nanoparticles in the photocatalytic treatment of landfill leachate under the fluorescent light irradiation was examined. For this purpose, four influential parameters on the photocatalytic process using doped ${\mathrm{TiO}}_2$ nanoparticles (i.e., dopant content, calcination temperature, pH, and contact time of leachate with nanoparticles) were first experimentally investigated. Next, a quadratic regression equation using response surface methodology was used to predict the concentration of the leachate chemical oxygen demand (COD) in the aforementioned process. To ensure the validity of the model, eight basic assumptions of regression equations were investigated and attempted to be met. Using the model, the effect of each parameter on the photocatalytic treatment process was observed, and leachate COD concentration may be predicted with $R^2=0.92$. Finally, optimal conditions were determined using the model to achieve maximum COD removal efficiency. The confirmatory experiment results show that 46% COD removal efficiency is achievable at optimal conditions (i.e., pH of 6.63, tungsten content of 2.64% by weight, calcination temperature of 472°C, and contact time of 34 h).

A pilot-scale continuous-flow 915-MHz microwave enhanced advanced oxidation ($\mathrm{MW}/{\mathrm{H}}_2{\mathrm{O}}_2\text{-}\mathrm{AOP}$) treatment system was specifically designed and used for the treatment of sewage sludge. The focus of this study was to examine the interrelationship between chemical changes and physical transformation on the treated sewage sludge, and to perform energy analysis of the treatment system. A higher temperature and/or higher hydrogen peroxide dosage resulted in higher levels of solubilized total phosphate and total Kjeldahl nitrogen, an increase in chemical oxygen demand solubilization and volatile fatty acids production, reduced total suspended solids, and improved sludge dewaterability and settleability. The results demonstrated that this treatment system was well designed and could be used for the treatment of sewage sludge effectively. The scaled-up version of this $\mathrm{MW}/{\mathrm{H}}_2{\mathrm{O}}_2\text{-}\mathrm{AOP}$ treatment system could readily be implemented for real-time application in wastewater treatment plants.

Arsenic-containing groundwater is used normally as drinking water after treatment in rural areas of some developing countries. This study describes removing arsenate [As(V)] by contact filtration on a sand media using polyaluminum chloride (PACl) as a coagulant. Arsenic-contaminated water and PACl coagulant were introduced concurrently into a sand filter column. A PACl dose of $15\mathrm{mg}/\mathrm{L}$ reduced the arsenic (As) concentration in a synthetic groundwater ($\mathrm{pH}=8$) from $0.10\mathrm{mg}/\mathrm{L}$ to less than $0.01\mathrm{mg}/\mathrm{L}$. The 81-cm deep, 16-mm diameter single-sand column treated 38.4 pore volumes before it reached an assumed maximum allowable experimental head loss (4.50 m). Reducing the PACl dose resulted in an increased As concentration in the filter effluent. The PACl precipitate-As complex could be removed from the filter by flushing. Results suggest precipitated PACl is more efficient than aluminum oxide/hydroxide solid phases in As removal. Filter performance was shown to be independent of how the PACl was distributed in the filter column.

Waste activated sludge (WAS) is commonly treated by using anaerobic digestion (AD), which has the advantage of reducing sludge volumes and generating methane. However, the sludge structure limits the efficiency of these AD processes. In fact, most of the organic substance found in sludge is surrounded by cell walls or bound in complex structures [extracellular polymeric substance (EPS)] and can only be made ready for digestion after intense hydrolysis processes. This paper presents the preliminary results of tests carried out to compare the performances of pretreatments and intermediate treatments. They were both performed using a hybrid modality, that is, by combining an alkali agent and heat. Hybrid treatments at low doses [4–8% of the total soid (TS) matrix] of NaOH and $\mathrm{Ca}{(\mathrm{OH})}_2$ were carried out on WAS and on already digested sludge. Batch mesophilic digestion tests were used to assess the methane specific production of samples of WAS and digestate before and after lysis treatment. Digestibility tests revealed a specific methane yield of respectively 0.166 and $0.143{\mathrm{Nm}}^3/\mathrm{kg}{\mathrm{VS}}_{\text{added}}$ for raw WAS and digestate. The production of methane for the WAS sample increased by 40 and 66% when it was treated at 70 and 90°C, respectively, in combination with a NaOH dose of $4\mathrm{g}/100\mathrm{g}$ TS. Intermediate treatments carried out under the same operating conditions caused increases in the specific production of methane of 31% (70°C) and 54% (90°C), respectively, for the samples of already digested sludge. Using these results, it was calculated that if the digestion process was carried out in two steps, with a duration of 10 days each, the production of methane could increase by 27 and 17% (at 70 and 90°C), respectively, compared with the scenario that only used the pretreatment processes.

This paper aims to investigate the enhancement effect of tourmaline on anaerobic ammonium oxidation (ANAMMOX) process in two sequencing batch reactors (SBRs). SBR1 was operated in parallel with SBR2, but 2 g tourmaline was added to the reactor. The results showed that when the nitrogen loading rate (NLR) was gradually increased from 181.8 to $727.3\mathrm{mg}/(\mathrm{L}·\mathrm{d})$, the nitrogen removal rate (NRR) of SBR2 decreased to $99.0\mathrm{mg}/(\mathrm{L}·\mathrm{d})$ from $576.7\mathrm{mg}/(\mathrm{L}·\mathrm{d})$, corresponding to an increase of specific ANAMMOX activity (SAA) from 0.65 to $3.69\mathrm{mgN}/(\mathrm{gVSS}·\mathrm{h})$.Tourmaline could control pH value to provide a stable environment for enrichment of ANAMMOX bacteria. Tourmaline promoted the growth and metabolism of ANAMMOX bacteria and enhanced the activity of the ANAMMOX reaction but was not a benefit for the granulation of ANAMMOX sludge. At the end of the start-up period, the 16S rRNA genes of ANAMMOX bacteria in SBR1 ($8.21\pm 0.07\times {10}^9\mathrm{copies}/\mathrm{mL}$) were two orders of magnitude higher than that in SBR2 ($5.13\pm 0.08\times {10}^7\mathrm{copies}/\mathrm{mL}$). The ANAMMOX sludge of SBR1 possessed a higher extracellular polymer substances (EPS) content than the SBR2 reactor ($194–287\mathrm{mg}/\mathrm{g}$ VSS in SBR1 and $203–252\mathrm{mg}/\mathrm{g}$ VSS in SBR2). The level of heme $c$ and TTC-dehydrogenase in SBR1 were still higher than that in SBR2.

This paper presents an investigation into stabilization and solidification of a clay soil contaminated with methyl butyl ether (MTBE) using two different agents (cement and a mixture of bentonite and cement) through a program of laboratory experiments. The samples were prepared in two stages. In the first stage, they were prepared with 20 and 30% cement, but in the second stage they were prepared with 20 and 30% mixtures of bentonite and cement (with ratios of bentonite to cement equal to $1:1$ and $3:1$). Unconfined compression tests (UCT) and leaching tests using a gas chromatography (GC) apparatus were conducted on the samples prepared in the described two stages at different curing times. The results show that by using cement, the strength of the soil is increased. The results of the leaching tests on contaminated soil show a major reduction in the concentration of MTBE. Adding cement to contaminated soil causes a reduction in the concentration of MTBE, but by increasing the curing time, the concentration of MTBE is increased. It is also indicated that using a combination of bentonite and cement leads to reductions in MTBE concentration, and the amount of reduction is decreased by increasing the curing time. A bentonite to cement ratio of $3:1$ is more effective than $1:1$ in reducing the concentration of MTBE.

Recently, an efficient and promising process was developed to allow the removal of As, Cr, Cu, pentachlorophenol (PCP), and polychlorodibenzo-dioxins and furans (PCDDF) from soil using alkaline leaching. The present study evaluates the performance and the robustness of this decontamination process for the treatment of four different polluted soils by attrition and alkaline leaching at a pilot scale. The attrition process carried out on the coarse fraction ($>0.125\mathrm{mm}$) allowed the removal of 24–42% of As, 0–13% of Cr, 23–46% of Cu, 0–85% of PCP, and 17–64% of PCDDF from the different contaminated soils. Removal yields of 87–95% of As, 50–72% of Cr, 73–84% of Cu, 52–100% of PCP, and 27–73% of PCDDF were obtained after three leaching steps ($[\mathrm{NaOH}]=1\mathrm{M}$; $[\text{Cocamydopropylbetaine}—\mathrm{BW}]=3\%$ (w/w); $t=2\mathrm{h}$; pulp density $[\mathrm{PD}]=10\%$ [w/v]) conducted on the fine fraction ($<0.125\mathrm{mm}$). The performance of both attrition and alkaline leaching processes seemed to be influenced by the nature of the soil and the type and initial level of contaminants present in the soils. However, the entire leaching process seemed to be highly efficient, allowing the simultaneous reduction of concentrations of inorganic and organic contaminants. The cost, including direct and indirect costs, were estimated between US$214 and 454 per ton of treated soil, depending on the nature of the soil and the initial level of contamination.

Polychlorinated biphenyls (PCBs) are a family of synthetic chlorinated organic compounds that were manufactured in huge quantities and used worldwide in numerous commercial and industrial applications. They are often found in contaminated soil. This paper examines the regulatory guidance values used to control the health risks of direct contact with PCB-contaminated residential soil. A total of 2,471 PCB guidance values are identified, 57.2% from U.S.-related jurisdictions and 42.8% from 50 other United Nations member states. Values are identified for total PCBs, 70 individual PCB congeners, and 9 Aroclor PCB blends. The guidance values for total PCBs and most congeners vary by more than six orders of magnitude. Aroclor values are less variable because they are specified by fewer jurisdictions. Nearly half (49.5%) of PCB guidance values fall within uncertainty bounds computed from the U.S. Environmental Protection Agency cancer-risk guidance value model. For total PCBs, 30.0% of values fall within the uncertainty bounds of 0.11 to $0.78\mathrm{mg}/\mathrm{kg}$ (0.85 orders of magnitude), but expanding these bounds slightly to span from the results of Spain’s risk model to the value set by the U.S. Toxic Substances Control Act (0.08 to $1.0\mathrm{mg}/\mathrm{kg}$) captures 58.8% of the values. Nevertheless, extreme values at both ends of the value distributions emphasize that universal agreement on appropriate guidance values to control PCB health risks has yet to be attained.

Big Marsh is a large wetland site contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals, attributable to decades of illegal waste dumping. Compared to the conventional remediation technologies, phytoremediation has the potential to be a feasible and sustainable remedial option to remediate such a large extent of contaminated area. Three different experimental areas, representative of the three ecotypes present at the site, were chosen as a part of the field-scale phytoremediation project. A total of nine native and restoration species were planted at each area, and their potential to survive and remediate the soil was assessed. The ground was prepared at each area by tilling and homogenizing the soil, while compost was added to soil at one of the experimental areas. The experiment lasted for three growing seasons and the species planted were monitored during the first two seasons. At the end of the third season, the PAHs and heavy metal concentrations were analyzed in the roots and shoots of the surviving species and also in the soil samples collected in each growing season. The results showed a decrease in PAH concentrations in the compost-amended slag disposal area. Furthermore, uptake of PAHs only occurred in the roots of the surviving species in the unamended areas. No substantial changes were found in heavy metal concentrations in the soil in any of the three experimental areas. However, uptake of metals by the roots of all surviving species was observed.

Field and laboratory studies were conducted to evaluate the impact of biochar amendment on methane oxidation rates and microbial communities in landfill cover soils. Deoxyribonucleic acid (DNA) was isolated from soil and biochar-amended soil following incubation in laboratory soil columns and from samples collected from four test plots installed within the intermediate cover of an active landfill in northeastern Illinois. Next-generation sequencing of 16SrRNA gene amplicons following polymerase chain reaction (PCR) amplification was used to assess the community composition and relative abundance of methane-oxidizing bacteria among the samples. In field soil samples from both soil and biochar-amended soil covers, Type-I methanotrophs (primarily Methylomonas and Crenothrix species) were observed and prevailed over Type-II methanotrophs in terms of relative abundance, comprising 83 to $>99\%$ of the total methanotrophic community. Non–methane-oxidizing methylotrophs (e.g., Methylibium, Methyloversatilis, Hyphomicrobium, Bradyrhizobium) and facultative methanotrophs (e.g., Methylocella) were also detected along with obligate methanotrophs, reflecting a diverse bacterial community. Methane oxidation rates in batch assays were positively correlated with relative abundance of methanotrophs as well as methane concentration at depth in the soil at the time of sampling. These trends indicate a significant relationship between methane exposure history and methanotrophic community abundance and composition.

A significant amount of methane has been fugitively released into the atmosphere from landfill operating surfaces. Biologically active covers have been listed as crucial technologies and practices to mitigate fugitive emissions from landfills. The objectives of this work were to evaluate the performance of two biologically active covers, aged refuse (AR) and biochar-amended soil (BAS), on mitigating landfill methane emission and methane bio-oxidation and to identify the major factors influencing the bio-oxidation process. Soil cover was chosen as contrast. On the basis of a field experiment over 3 months, BAS or AR cover showed much better adaptability to methane influx and environmental factors than soil cover. Furthermore, the isotope results showed that the mean value of methane oxidation fraction ($f_{ox}$) was 61.5 or 56.1% in BAS or AR cover, respectively. The peak $f_{ox}$ was observed at the depth of 10 cm and decreased with increasing depth for both AR and BAS cover. Through the polymerase chain reaction—denaturing gradient gel electrophoresis (PCR-DGGE) analysis of methanotrophic diversity, Type I methanotrophs dominated in the BAS cell, while Type II methanotrophs predominated in AR cell. Both AR and BAS can be applied as temporary covers in the operating surface of landfills for enhancing the ${\mathrm{CH}}_4$ oxidation and mitigating ${\mathrm{CH}}_4$ emission from landfill operating surfaces.

This research investigated the treatment of landfill leachate using aerobic granular sludge (AGS). The AGS was cultivated from a lab-scale sequencing batch reactor (SBR). Leachate was gradually fed into the aerobic granular sludge SBR (GSBR) by mixing it with primary effluent at ratios varying from 10 to 90%. Regardless of the different mixing ratios or high free-ammonia (FA) and free-nitrous-acid (FNA) concentrations in the influent, the GSBR demonstrated high total ammoniacal nitrogen (TAN) removal efficiency, which ranged from 95 to 100%. The best results were obtained when the total nitrogen (TN) load was $0.3\pm 0.04\mathrm{kgN}/{\mathrm{m}}^3\mathrm{d}\mathrm{a}\mathrm{y}$ ($153\mathrm{mg}/\mathrm{L}$ of TAN in the influent), where the FA concentration was the lowest ($11\pm 1.4\mathrm{mg}/\mathrm{L}$). For a nitrogen load up to $0.68\pm 0.03\mathrm{kgN}/{\mathrm{m}}^3\mathrm{d}\mathrm{a}\mathrm{y}$ (i.e., TN $340\pm 13\mathrm{mg}/\mathrm{L}$ and FA $24.5\pm 1\mathrm{mg}/\mathrm{L}$), chemical oxygen demand (COD), TN, and phosphorus removal of GSBR were around 64, 42, and 84%, respectively. With the further increase in the nitrogen load, the TN, COD, and phosphorus removal rate of GSBR decreased significantly; however, the TAN removal efficiency remained constant at 90–100%. This study showed that the AGS is able to treat leachate with high concentrations of TAN ($912\mathrm{mg}/\mathrm{L}$), and simultaneous nitrification and denitrification play a significant role in nitrogen removal. From these promising results, the use of AGS for leachate treatment should be encouraged.

Determination of removal percentage (RP) of pollutants in a fixed-bed column system is time-consuming, difficult, and subject to errors. To overcome this problem, an artificial neural network (ANN) with different learning algorithms, activation functions, input variables, neurons in the hidden layers, and number of hidden layers was employed. For this purpose, the RP of Hg(II) ions by ostrich bone ash–nanoscale zero-valent iron composite (OBA/nZVI), as a novel adsorbent, was measured in a fixed-bed column experiment. Four effective variables, including inflow rate (F), initial pollutant concentration (C), bed height (Z), and pH were taken as input data and the RP of the composite was taken as output. Four ANN models, including different combinations of effective variables, were constructed to reveal the sensitivity analysis of the models. Normalized root mean square error (NRMSE), mean residual error (MRE), and linear regression ($R^2$) were used as criteria for comparison of estimated data by the models and the experimental data. Results indicated that the ANN4 model, comprising a trainlm learning algorithm and a log sigmoid activation function with all four input data, accomplished the best prediction of RP ($R^2=0.996$, $\mathrm{NRMSE}=0.028$, $\mathrm{MRE}=0.008$). The sensitivity analysis indicated that the predicted RP is more sensitive to pH, followed by F, Z, and C. This study demonstrated that the ANN model can be a more accurate and faster alternative to the laborious and time-consuming laboratory measurements for RP of Hg(II) ions in a fixed-bed column system.

A fluidized bed reactor (FBR) was employed to evaluate the removal and degradation of linear alkylbenzene sulfonate (LAS) from laundry wastewater without supplementary feeding. After immobilizing the biomass on the support material, the reactor was operated in two stages: Stage I, fed with a synthetic substrate, and Stage II, fed with laundry wastewater with a LAS concentration generally reported as being process disturbing in anaerobic systems to treat LAS ($21.7\pm 5.3\mathrm{mg}/\mathrm{L}$) and sodium bicarbonate as a buffering agent. Despite the low chemical oxygen demand (COD) in the influent during Stage II ($74\pm 26\mathrm{mg}/\mathrm{L}$), the observed proportions of LAS ($80\pm 11\%$) and COD ($91\pm 9\%$) removed were high. The microbiological analysis of samples collected from different regions of the FBR during Stages I and II suggests that the composition of the laundry wastewater may have also contributed to the biomass differentiation and that the environmental conditions in the different parts of the reactor affected the microbial composition. A remarkable proportion of genera capable of degrading aromatic compounds, including LAS, was observed in the upper compartments of the reactor, which was related to a facultative environment.

This work concerns the simultaneous effects of salinity and hydrocarbons on the biological activity and membrane fouling of a moving bed-membrane bioreactor (MB-MBR) fed with real high-salinity oily wastewater generated from the washing of oil tankers (slops). A biological treatment was possible with a proper biomass adaptation by means of a stepwise increase of slop concentration in six operational phases. The mechanism of microorganisms’ adaptation to salinity and total petroleum hydrocarbons (TPH) started in Phase IV, where the feeding was characterized by $7.4{\mathrm{gCl}}^{-}·{\mathrm{L}}^{-1}$ and $9\mathrm{mg}\mathrm{TPH}·{\mathrm{L}}^{-1}$, in which the removal efficiencies of chemical oxygen demand (COD) and total organic carbon (TOC) initially collapsed to 15 and 30%, respectively, and subsequently rose to 85 and 90%. Moreover, the TPH removal efficiency rose from 8 to 35% and then reached 70% at the end of the study. During Phase IV, the suspended biomass produced a great amount of extracellular polymeric substances (EPS) in bound polysaccharides form (${\mathrm{EPS}}_{\mathrm{bound},C}$) as storage of carbon to face the stressful conditions generated by salinity and hydrocarbons. However, a strong inhibitory effect of the pollutants toward the suspended biomass implied a collapse of ${\mathrm{EPS}}_{\mathrm{bound},C}$ in the last phase, during which the system was fed only with slop. Simultaneously observed was an increase in protein fraction of soluble microbial products (${\mathrm{SMP}}_P$), which was mainly because of the cell lysis of microorganisms. Therefore, the high biological removal efficiencies achieved in the last phase were mainly due to the biofilm growth on mobile carriers. Correlations between the irreversible cake resistance ($R_{C,\mathrm{irr}}$) and ${\mathrm{EPS}}_{\mathrm{bound},C}$, and between pore blocking resistance ($R_{\mathrm{PB}}$) and ${\mathrm{SMP}}_P$, highlighted that the hydrophilic ${\mathrm{EPS}}_{\mathrm{bound},C}$ favored the irreversible cake deposition on the membrane surface, whereas ${\mathrm{SMP}}_P$ mainly contributed to an increase in pore blocking.

Electropositive filtration (EPF) uses a macroporous filter media with a strong positive charge to achieve high separation factors for substances many times smaller than its nominal pore size; however, the variables that affect its performance are poorly understood. The objective of this work was to elucidate the significance of filter fouling and particle size in relation to electroadhesion in determining material removal by an electropositive filter. EPF performance was evaluated using humic acid (HA) and montmorillonite clay in adsorption and dead-end filtration experiments. Comparative analyses were done with a negatively charged microglass filter of similar nominal pore size. The electropositive filter had a higher selectivity for HA and clay because of favorable charge–charge interactions. HA and clay removal were governed by aggregate size and filter fouling. For the HA, accumulation of negatively charged material on the electropositive filter resulted in decreased removal as filtration progressed because of screening of the charge interactions. For the clay, rapid fouling resulted in high removal but plugging of the filter. Precoagulation resulted in optimum performance conditions—high selectivity and low headloss development.

This paper uses fuzzy logic–based models to predict and evaluate the performance of multimedia filters utilized in wastewater treatment. A fuzzy logic–based model is constructed and trained to predict the operating time (i.e., treated volume of water) of a multimedia filter. A preset acceptable turbidity value of 5 nephelometric turbidity units (NTU) is used as the breakthrough point. The model is based on a set of experimental data with variable flow rates and influent turbidity. The results from the fuzzy-based model indicate that the simulated treated volume at different inputs of turbidity and flow rate fits the experimental results with a coefficient of multiple determination ($R^2$) of 91.6%. To examine the efficiency of the developed model predicting treated volume, the results obtained from the model are compared with the results obtained from a multiple linear regression model. The accuracy of prediction of both models are examined using the mean absolute error (MSE), root-mean-square error (RMSE), and $R^2$. The MSE, RMSE, and $R^2$ for the fuzzy-based model are 5,318, 72.92, and 98%, respectively, whereas for the regression model they are 3,302, 57.46, and 99%, respectively. Although the regression model appears to be more accurate, the fuzzy-based model is deemed to be more advantageous because it can incorporate the uncertainties in inputs as a result of human judgments and can indicate the errors in the outputs.

Regenerative stormwater conveyance (RSC) is an open channel, sand-filtering system composed of a series of shallow aquatic pools, riffle weirs, native vegetation, and underlying media beds. Surface runoff entering an RSC is conveyed as nonerosive surface flow or subsurface seep through the media, and exits the system as surface flow, seep out, exfiltration into parent soil, or evapotranspiration (ET). Regenerative stormwater conveyances are expected to perform similar to other sand-media-based low-impact development (LID) stormwater control measures (SCMs), but the hydrological and water quality efficiencies of RSC have not been sufficiently validated in a variety of hydrogeological conditions to date. A RSC was installed in the coastal plain of North Carolina, receiving runoff from 5.2 ha. Surface flow was reduced substantially through the RSC, with 84% of inflow converted to a shallow interflow-like seep, referred to in this paper as seep out. High groundwater levels resulted in small overall exfiltration rates, but increased evaporation rates due to extended ponding. The conversion of surface runoff to seep out has significant implications for stormwater mitigation, releasing filtered water at slower rates than conventional conveyance channels, similar to undeveloped watersheds. The Brunswick RSC released similar fraction of seep out to that of shallow interflow observed in undeveloped watersheds.

Slurry trench cutoff walls with low-permeability backfill material, such as soil-bentonite and slag-cement-bentonite, are used widely for containment of subsurface pollution. In the design of slurry walls the potential service life for a given thickness or the wall thickness for a target service life are typically determined via analyses of one-dimensional contaminant transport. The difficulty of selecting appropriate inlet and outlet boundary conditions and the mathematical complexity of analytical solutions hinder engineers in undertaking a contaminant transport analysis–based design. Design charts for nondimensionalized effluent flux are presented by developing and using an analytical solution. The methodologies of using these charts in design are demonstrated.

In potable water treatment, the commonly used disinfectants are chlorine and ozone. Recently, the use of ozone has gained more acceptance due to its effective disinfectant properties. However, water treatment with ozone is more expensive because ozone production is an energy-intensive processes. Thus the mechanical mixing efficiency (passive mixing) of the contact system used in this process is critical to reduce the amount of disinfectant used to treat a fixed volume of water. Traditional contact tank designs suffer from poor mixing, short-circuiting, and high energy requirements to drive the flow through the contactor. This study introduces a patented novel baffle design to improve the efficiency of contact tanks. Computational fluid dynamics (CFD)–based analysis indicates that the proposed baffle design improves the mechanical mixing efficiency by 51% and reduces the energy required to drive the flow through the system and short-circuiting by 51 and 57%, respectively. Calculations indicate that the savings offered by this design will be on the order of several hundred thousand dollars per year for medium-sized water treatment plants. The proposed design is simple to implement without expensive infrastructure modifications, and can be used for both chlorine and ozone treatment.