Journal of Environmental Engineering

Nonaqueous phase liquids (NAPL) tend to be trapped within aquifers. The review first covers conventional technologies that rely on pumping water, hot water, and/or air sparging with vapor extraction. The review then addresses polymer and foam delivery, which are intended to directly add solutions to low-permeability zones, where NAPL resides. Based on data from the literature, the removal of hydrocarbons by any of the flushing techniques, including polymer and foams apply well for porous media whose hydraulic conductivity is greater than ${10}^{-4}\mathrm{m}/\mathrm{s}$, excluding silt and clay materials. For those lower permeability soils, electrokinetics (EK) appears appropriate. EK relies on imposing a voltage of DC current across the soil, which would engender three types of flows: electromigration, which causes ions to move to the electrode of opposite sign; electrophoresis, which causes charged particles, such as negatively charged clay particles or bacteria (mostly negatively charged but also some positively charged) to the electrode of the opposite sign; and electroosmosis, which occurs only when a zeta potential exists in the soil (typical of clay and silt) that would cause the movement of water and potentially NAPL. EK could be used to deliver anionic surfactants through electromigration or nonionic surfactants through electroosmosis (in clay or silt). An emerging hydraulic technique is chaotic advection, and it maximizes the contact between the delivered solution and the soil region of interest. The main challenge of applying EK in field studies is the familiarity of operators and scalability, as the electrodes cannot be more than 15–20 m apart.

Due to the serious environmental pollution and waste of resources resulting from aquaculture solid waste, its treatment and disposal have attracted wide attention in recent years. Aquaculture solid waste mainly consists of aquaculture sludge (AS) and fish processing waste (FPW). This paper reviews the characteristic and environmental impact of AS and FPW, respectively. The conventional and novel technologies for aquaculture solid waste management are analyzed and summarized. Discharged, constructed wetland, aerobic composting, anaerobic treatment, enzymatic or chemical hydrolysis, and aquaponics are conventional and well-known technologies used in aquaculture waste reduction, valorization, and recycling. Novel technologies are mainly applied to recycle resources or produce valuable by-products, including biodiesel, fish silage, biosorbent, hydrochar, lactic acid, hydrogen, and Hermetia illucens larvae growth from FPW, as well as phytoremediation and biofloc technology for AS treatment. Finally, future directions of aquaculture solid waste management are proposed.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous micro-organic pollutants that originate primarily from natural and anthropogenic activities. Water pollution due to such micro-organic contaminants is a serious problem because of their acutely toxic, carcinogenic, and mutagenic nature. Therefore, a sustainable remediation technique is essential for the elimination of PAHs from contaminated sites. PAH biosorption is the most cost-effective and environmentally friendly cleanup strategy; however, it is limited due to the sparingly water-soluble nature of PAHs. This paper provides a scientific comparison of the literature for PAHs biosorption through different biosorbents under different conditions. This review presents a critical summarization of PAH biosorption using different biosorbents. The role of physical or chemical alteration of biosorbents for PAH removal is introduced. The use of different biosorbents in PAH biosorption from aqueous solutions is discussed. The kinetics, isotherms, and thermodynamic investigations of PAH biosorption using different biosorbents as well as biosorption mechanisms and desorption of PAHs are discussed. It is concluded that many biosorbents have shown a great potential for detoxification of PAHs from aqueous environments.

Source-diverted blackwater, especially concentrated blackwater collected from vacuum toilet systems, has been demonstrated to be an ideal source for struvite (${\mathrm{NH}}_4{\mathrm{MgPO}}_4·6{\mathrm{H}}_2\mathrm{O}$) production. However, the impacts of total suspended solids (TSS) in blackwater toward struvite quality are not well addressed. In this study, a fluidized bed reactor (FBR) was operated in a batch mode to examine the influences of TSS in raw concentrated blackwater on phosphorus recovery efficiency as well as the purity and size of the produced struvite. The produced struvite was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The metal contents of the struvite product were determined by inductively coupled plasma mass spectrometry (ICP-MS). The results revealed that at appropriate water quality (e.g., $\mathrm{pH}=8.9$) and operating conditions [e.g., magnesium to phosphorus (Mg/P) molar ratio = 1.5], neither blackwater TSS nor FBR upflow velocity significantly affected the phosphorus recovery efficiency. TSS had a significant impact on the purity and size of the struvite product. The struvite purity increased with the decrease of TSS concentration within the studied range of $120–\mathrm{1,600}\mathrm{mg}/\mathrm{L}$. At higher TSS levels ($520–\mathrm{1,600}\mathrm{mg}/\mathrm{L}$), the struvite crystal remained small ($<5\mathrm{\mu m}$) with the FBR upflow velocity ranging from 18 to $90\mathrm{m}/\mathrm{h}$. When the TSS concentration was lower than $220\mathrm{mg}/\mathrm{L}$, the struvite crystal was able to grow continuously (up to 100 μm), and its size was directly impacted by the FBR upflow velocity. A greater upflow velocity was unfavorable to the agglomeration of struvite crystals.

A coupled thermo-hydro-bio-mechanical (CTHBM) numerical model to simulate the long-term behavior of municipal solid waste in landfills is presented. Three numerical simulations—a conventional landfill simulation with no leachate injection (CONV) and two bioreactor landfill simulations involving leachate injection—were carried out by applying the CTHBM model to a typical two-dimensional (2D) landfill cell configuration to analyze the effect of temperature on the long-term performance characteristics of a landfill system. Of the two bioreactor landfill simulations, one (BIOR-T) incorporated temperature effects on the waste decomposition, while the other simulation (BIOR-NT) did not. For the waste conditions simulated, the CONV and BIOR-T had a maximum waste temperature of 54°C and 62°C, respectively. The temperatures at the bottom liner were determined to be in the range of 1°C–32°C and 1°C–39°C over the entire simulation time of the CONV case and BIOR-T case, respectively. The effect of waste temperatures on moisture distribution, methane gas production, and landfill surface settlement was also assessed. The surface settlement response for BIOR-T and BIOR-NT simulations suggests that incorporating the effect of waste temperatures on the waste decomposition is important for a realistic prediction of the waste settlement in landfills. The BIOR-T and BIOR-NT simulations had a similar interface shear response, suggesting that the changes in the stiffness and shear strength of waste, due to incorporating temperature effects on the biodegradation rate, have no noticeable impact on the interface shear response in the bottom liner system. Overall, the proposed CTHBM model can be used to predict long-term performance characteristics (e.g., moisture distribution, landfill gas production, settlement of waste, temperatures) relevant for effective design of bioreactor landfills.

A differential biotrickling filter (DBTF) was developed as a research tool to minimize radial and longitudinal gradients, which hinder analysis in integral (column) reactors. The main design modifications were a very high gas recycle rate and a low, uniform liquid addition rate via an aerosol generator. The elimination capacity (EC), uniformity of biofilm formation, and long-term reliability of the reactor were evaluated. The maximum toluene elimination capacity was approximately $430\mathrm{g}/{\mathrm{m}}^3\mathrm{h}$, which was higher than the EC in most previous reports. The high EC potentially was due to the thin liquid film over the biofilm generated by low liquid trickling rates. Moreover, the high gas recycle rate (2.5–100 times the feed flow rate) allowed uniform substrate and nutrients distribution throughout the bed hence promoting favorable growth and performance of the microbes. These findings can serve as a guide in improving performance of industrial biotrickling filters. Substrate inhibition was observed at loading rates (LRs) higher than $513\pm 27\mathrm{g}/{\mathrm{m}}^3\mathrm{h}$. Despite operational issues that affected its long-term reliability, such as (1) unwanted growth of microbes on the pipes and in the aerosol reservoir, (2) a decline in the performance of the aerosol generator, and (3) limited fan capacity, the DBTF is a promising tool that can improve biofiltration research.

Using the computational fluid dynamic numerical simulation method, the gas, liquid, and solid three-phase hydrodynamic behavior in a self-made aeration fluidized bed reactor was simulated numerically. The influence of gas inlet velocity and solid phase volume on gas holdup, solid holdup, and liquid circulation velocity in the reactor were studied. Treatment of ${\mathrm{Cd}}^{2+}$ wastewater by the self-made fluidized bed showed that when inlet velocity was $0.3\mathrm{m}/\mathrm{s}$ and adsorbent dosage was 9.5%, the adsorption effect was the best, and the adsorption rate was 63.5%. Simulation results verified the experimental conclusions and clarified the interaction of the three phases of gas, liquid, and solid in the fluidized bed treatment of wastewater. The higher the air inlet speed, the lower was the solid content rate and the greater was the liquid circulation speed; at the same air inlet speed, the larger the solid phase volume, the higher was the solid content rate, the smaller was the solid phase volume, the greater was the liquid circulation speed, the higher was the gas holdup rate, and the higher was the utilization rate.

The construction of a catalyst with high activity and stability is crucial for wastewater treatment. In this study, Fe-Zr-Al/pillared montmorillonite (Fe-Zr-Al/Mt) catalysts were successfully prepared by the conventional (C) ion exchange method and the microwave-assisted (MW-assisted) method with iron as an active component and montmorillonite as a carrier. X-ray diffraction, scanning electron microscope, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy results were used to analyze the micromorphology of the catalyst and the existing form of active components. After comparing the basic fuchsin degradation rate and chemical oxygen demand (COD) removal rate of two prepared catalysts, the MW-assisted method was selected for subsequent studies. The influence of operating parameters, including initial pH, catalyst dosage, and reaction temperature, was optimized in the catalytic wet peroxide oxidation (CWPO) process for degradation of basic fuchsin. The results showed that under the optimal experimental conditions, about 99.23% of basic fuchsin and 81.48% of COD were degraded within 180 min, respectively. In addition, Fe-Zr-Al/Mt(MW) catalyst exhibited good stability and reusability. The catalytic activity decreased slightly after five consecutive runs, and the active component Fe leaching was only $0.0547\mathrm{mg}/\mathrm{L}$. The CWPO reaction mechanism on basic fuchsin degradation was proposed.

Floods have the potential to resuspend polycyclic aromatic hydrocarbons (PAHs) laden sediments and potentially impact drinking water intakes. This work identifies optimal operating conditions for the PAH removal from water using a combined permanganate (Mn(VII))/bisulfite advanced oxidation process (AOP). PAHs in aqueous solutions containing humic acid (HA) were treated using a combination of permanganate and bisulfite at different molar ratios. Results showed that the Mn(VII)/bisulfite AOP was an effective method to remove priority PAHs, but the dosage needs to be carefully controlled to avoid excessive by-products and reduce treatment costs. The optimal reaction conditions [${\mathrm{C}}_{[16\mathrm{PAHs}]}:{\mathrm{C}}_{[{\mathrm{KMnO}}_4]}:{\mathrm{C}}_{[{\mathrm{NaHSO}}_3]}=1:30:60$ (${\mathrm{m}}_{[16\mathrm{PAHs}]}:{\mathrm{m}}_{[{\mathrm{KMnO}}_4]}:{\mathrm{m}}_{[{\mathrm{NaHSO}}_3]}=1:22:29$) and $10\min <=\mathrm{reaction}\mathrm{time}<30\min$] were identified within a wide pH range (5.0–8.0). High removal efficiencies (85%–100%) were achieved for typically refractory high molecular weight PAHs, including pyrene (PYR), chrysene (CHRY), benzo[a]anthracene (B[a]A), benzo[b]fluoranthene (B[b]F), benzo[k]fluoranthene (B[k]F), benzo[a]pyrene (B[a]P), and dibenzo[a,h]anthracene (D[ah]A). The concentration of B[a]P was reduced to below $0.2\mathrm{\mu g}/\mathrm{L}$ from an initial concentration of $0.8\mathrm{\mu g}/\mathrm{L}$ in less than 30 min, and a $2\mathrm{mg}\text{-}\mathrm{OC}/\mathrm{L}$ concentration of HA had minimal effect on the effectiveness of AOP. The maximum concentration level of B[a]P is specified as $0.2\mathrm{\mu g}/\mathrm{L}$, according to National Primary Drinking Water Regulations issued by the EPA. Overall, the Mn(VII)/bisulfite AOP represents a promising technology for PAH removal to below minimum EPA drinking water standards in emergency scenarios, although the control of the dosages of permanganate and bisulfite is required.

Unscientific application of fecal sludge (FS) on agricultural fields in India has led to fecal coliform and heavy metal accumulation in the food chain. The design of FS treatment depends on accurate knowledge of its characteristics, which is seldom available for nonurban India, where most of the agriculture sector is concentrated. In this study, nonurban FS from India has been systematically characterized for physicochemical properties, nutrient, and pathogenic content to assess its ability to be used as a fertilizer. It was found that the collected FS has nutrients ($\mathrm{nitrogen}=3.0\%\pm 0.4\%$, $\mathrm{phosphorus}=29.07\pm 4.48\mathrm{mg}/\mathrm{L}$, $\mathrm{potassium}=43.57\pm 0.74\mathrm{mg}/\mathrm{L}$), organic carbon ($33\%\pm 3.2\%$), and physicochemical properties that qualify the Indian specifications of organic fertilizers, whereas its pathogenic content (i.e., $6\log \mathrm{cfu}/\mathrm{g}$, and 6 to 13 viable helminth $\mathrm{ova}/\mathrm{g}$) is high as per US regulations. Thus, collected FS requires treatment by unplanted drying bed and co-composting to be used as fertilizer.

The performance of a column-type anaerobic sequencing batch reactor (ASBR) with a high height-to-diameter ($H/D$) ratio of 10 was evaluated while treating slaughterhouse wastewater. The reactor was operated without any external mixers, gas recirculation, or liquid recirculation. The chemical oxygen demand (COD) removal efficiency was about 70%–75% at different hydraulic retention times (HRTs) (48, 32, 24, and $12\mathrm{h}$). Biogas production was stable at $4.5–8\mathrm{L}/\mathrm{day}$ biogas, comprising about 60%–70% methane between 2 and $5.2\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3·\mathrm{day}$. A high $H/D$ ratio promoted good retention of denser sludge, and increased the production of biogas. The novel bioreactor without any external mixing and biogas/liquid recirculation is a promising technique, which can save considerable energy compared with conventional bioreactors if the biogas generated is maintained properly inside the ASBR. Additionally, microbial analysis targeting the 16S ribosomal RNA (16S rRNA) gene indicated the dominance of methanogens, which comprised Methanosaetaceae (23.07%), Methanobacteriaceae (2.05%), Methanomicrobiaceae (1.85%), Methanoregulaceae (0.82%), Methanocorpusculaceae (0.64%), and Methanospirillaceae (0.42%).

Modeling air flow movement in the headspace of sanitary sewers is important for municipalities for sewer corrosion control and odor mitigation. This paper presents the results of field-measured air pressure and ${\mathrm{H}}_2\mathrm{S}$ variations affected by the operation of pump stations in a prototype sanitary sewer system. A total of five locations near four pump stations were monitored along a $5\text{-}\mathrm{km}$ trunk sewer. It was found that the air pressure in the vicinity of the pump stations showed an oscillation pattern in response to the pumping cycles. This is mainly due to the change in the headspace air volume resulting in air pressure fluctuations. A simple model is proposed to estimate the magnitude of the pressure fluctuation. Pump operations also have a direct impact on the ${\mathrm{H}}_2\mathrm{S}$ level downstream of the discharge manhole with relatively long forcemains.