Journal of Environmental Engineering

Singapore is a highly water-stressed country, and securing an adequate water supply has always been an important task for the government. Water reclamation and reuse attempted in 1966 were not a success because of the costly and unreliable technology. Fortunately, in 2003, advances in membrane technology enabled water reclamation and reuse to become both technically and economically feasible. Currently, reclaimed water accounts for 40% of the water supply in Singapore and is projected by the government to account for a larger proportion in the future. Some of the lessons learned and issues with the development of water reclamation and reuse in Singapore are briefly discussed.

This paper presents a modified mathematical model for substrate degradation and nutrient removal by aerobic microorganisms. The modified model is based on Activated Sludge Model No.1 (ASM1) for bacterial growth incorporated with substrate diffusion into flocs and biofilms. Monod kinetics are modified to consider the proton translocation theory for substrate dissociation in ASM1. Microbial growth rate coupled with mass transport rate was studied for heterotrophs and autotrophs in bulk solution and the boundary layer of biofilms to reveal the extra degree of freedom of this dynamic model. Moreover, the sensitivity analysis of the modified model was discussed at steady state using the Newton–Raphson technique. A decrement in the removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen (${\mathrm{NH}}_4\text{-}\mathrm{N}$) was obtained under the influence of the diffusion principle compared with modified Monod substrate conversion. However, the decline in biofilm thickness to 50 μm at heterotrophic and autotrophic biomass concentration of $15\mathrm{kg}/{\mathrm{m}}^3$ and $1\mathrm{kg}/{\mathrm{m}}^3$, respectively, enhanced the removal of both influent COD of $200\mathrm{mg}/\mathrm{L}$ and influent ${\mathrm{NH}}_4\text{-}\mathrm{N}$ of $30\mathrm{mg}/\mathrm{L}$ in an Integrated Fixed Film Activated Sludge (IFAS) pilot plant experiment established at Zenein wastewater treatment plant (WWTP), Giza, Egypt.

Carbon nano-onions/titanium dioxide (${\mathrm{CNOs}/\mathrm{TiO}}_2$) photocatalyst was synthesized by a simple sol-gel method and characterized by the methods of X-ray diffraction (XRD), scanning electronic microscope (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area (BET method), Fourier transform infrared (FTIR), thermogravimetric analysis (TG), differential scanning calorimeter (DSC), UV-Vis diffuse reflectance spectra (UV-Vis DRS), and high-performance liquid chromatography (HPLC). The photocatalytic activity of ${\mathrm{CNOs}/\mathrm{TiO}}_2$ photocatalyst was assessed by testing the degradation rate of Rhodamine B (RhB) under visible light irradiation. The results showed that the optimum photocatalytic activity was achieved when the mass ratio of CNOs to ${\mathrm{TiO}}_2$ was 10%. The aforementioned specific ${\mathrm{CNOs}/\mathrm{TiO}}_2$ photocatalyst resulted in a maximum RhB degradation efficiency of 78% ($10\mathrm{mg}/\mathrm{L}$ of RhB in 220 min). CNOs enhance the photocatalytic efficiency of ${\mathrm{TiO}}_2$ and improve the separation quantity of ${\mathrm{CNOs}/\mathrm{TiO}}_2$ catalyst from aqueous media. CNOs can be used as a modification agent to develop high-performance photocatalysts for the removal of organic pollutants.

Variations in groundwater flow regimes due to direct draining/pumping and surrounding climatic variabilities may significantly affect the spatial and temporal distribution of hydrocarbon compounds in the subsurface. The fate and transport of these contaminants have been studied quite adequately; however, the behavior of these pollutants under varying groundwater flow regimes has not been investigated in the past. Therefore, an extensive experimental investigation was made to study the effect of changes in groundwater flow velocity on the fate and transport of light nonaqueous phase liquids (LNAPLs) using a three-dimensional (3D) sand tank setup. The tank setup of size $60\mathrm{cm}\mathrm{long}\times 30\mathrm{cm}\text{wide}\times 60\mathrm{cm}$ deep embedded with sampling ports was packed with homogeneous sand having grain size in the range 0.5–1.0 mm. Pure phase toluene, a representative LNAPL, was released from the top port of the tank setup to create a pure phase pool of the LNAPL around the groundwater table. A constant water flux was allowed to flow first to maintain a base groundwater flow velocity in the horizontal direction. The flow velocity was then increased or decreased by changing the water flux passing through the saturated zone by keeping the water table location at the same height. Groundwater samples were collected routinely and were analyzed using gas chromatography–mass spectrometry (GC-MS). A series of batch experiments were also performed using the same groundwater and porous media used in the tank setup to estimate the biodegradation rate at different dissolved LNAPL concentrations. It was observed that the biodegradation rate increases up to 50 ppm concentration and remains almost the same until 100 ppm and then decreases with increasing concentration of LNAPL. The biodegradation rates corresponding to the observed concentration of LNAPLs in the tank setup were then used to conduct the simulation experiments. Results show that the dissolution rate of LNAPL increases linearly with groundwater velocity and was estimated for the three different groundwater flow regimes varying from 0.083 to $0.129\mathrm{cm}/\mathrm{h}$. The observed high rate of degradation of LNAPL for faster flow velocities shows the dependency of the degradation kinetics on dissolved LNAPL concentration. The observed breakthrough curves at different ports showed that horizontal and transverse transport of LNAPL was more prominent compared to its vertical movement. The observed concentration of dissolved toluene compared well with the simulated curves for the considered cases of groundwater flow velocities. The results of this study are of direct use in applying bioremediation techniques for field problems subjected to dynamic groundwater flow conditions.

Nanoscale zero-valent iron/copper supported on chelating resin ($\mathrm{D}\text{-}\mathrm{Fe}/\mathrm{Cu}$) was prepared for removing nitrate from water. Batch experiments were carried out to investigate the effect of solution chemistry, including the initial pH of the solution, initial dissolved oxygen (DO), coexisting anions, and humic acid on the removal of nitrate. Results showed that the initial pH and DO had a significant effect on the removal of nitrate. Coexisting anions, including ${\mathrm{Cl}}^{-}$, ${\mathrm{SO}}_4^{2-}$, ${\mathrm{PO}}_4^{3-}$, and ${\mathrm{HCO}}_3^{-}$, inhibited nitrate reduction. The removal efficiency of nitrate was 95.51%, and the selectivity of ${\mathrm{N}}_2$ was 52.49% at the end of the reaction. The results of X-ray photoelectron spectroscopy (XPS) analysis before and after the reduction showed that Fe(0) was directly involved in the nitrate reduction reactions. After the reaction with nitrate, Fe(0) was oxidized to Fe(II) or Fe(III), the content of Fe(II) increased, and the amount of Fe(III) decreased. The Fe(II)/Fe(III) cycle existed on the surface of Fe(0) during the reduction process with nitrate. Cu only provided active sites to adsorb hydrogen, without direct participation. The results demonstrated that $\mathrm{D}\text{-}\mathrm{Fe}/\mathrm{Cu}$ can be reused, and the removal efficiency of nitrate was 97.41% in the fifth recycle.

Fresh cow dung and iron scraps were added to municipal sewage sludge under laboratory-simulated anaerobic landfill conditions. Simulated anaerobic and semiaerobic landfilling of sludge without any additives were conducted in parallel. Differently treated sludge in landfill columns and leachates from these columns were collected regularly during a 360-day period and analyzed to assess the sludge stabilization rate. The results showed that throughout the study period the water content of anaerobic sludge + iron scraps treatment decreased the most quickly, followed by the semiaerobic sludge treatment. In contrast, the addition of cow dung under anaerobic conditions conspicuously increased the water content of this sludge mixture, with no effects on reducing water content. The final water content of anaerobic sludge + cow dung treatment was approximately 1.1 times higher than that of anaerobic sludge treatment. After 360 days, the total organic carbon (TOC) content of anaerobic sludge + iron scraps treatment and semiaerobic sludge treatment was reduced by about 28%, and the volatile matter (VM) content of these two treatments was reduced by about 25%, while the TOC and VM contents of anaerobic sludge treatment was reduced by only 4.3% and 6.3%, respectively. The total nitrogen (TN) content of anaerobic sludge + iron scraps treatment and semiaerobic sludge treatment was reduced by about 20% at the end of the study period, while the final TN content of anaerobic sludge treatment and anaerobic sludge + cow dung treatment was reduced by 11% and 13%, respectively. In addition, anaerobic landfilling with iron scraps and semiaerobic landfilling approaches increased cumulative leachate production (CLP) and facilitated the discharge of heavy metals (e.g., Zn and Cu) in the sludge compared with the anaerobic sludge treatment. The largest CLP and highest contents of heavy metals in leachate were observed in the anaerobic sludge + iron scraps treatment. In general, the ${\mathrm{NH}}_4^{+}-\mathrm{N}$ and TN contents in leachates from the four landfill columns exhibited an increasing trend with landfill time, while the TOC content in these leachates was decreased with landfill time. After 360 days, compared with the leachate from anaerobic sludge treatment, the ${\mathrm{NH}}_4^{+}-\mathrm{N}$, TN, and TOC contents in the leachate from anerobic sludge + iron scraps treatment were reduced by 38.6%, 32.8%, and 23.7%, respectively. The contents of these three properties in the leachate from semiaerobic sludge treatment were reduced by 40.4%, 20.7%, and 51.8%, respectively. The addition of iron scraps under anaerobic conditions and utilization of semiaerobic conditions were effective for improving the digestion performance of sludge. However, the addition of fresh cow dung did not accelerate sludge stabilization.

This research defines the utilization of the artificial neural network (ANN) for demonstrating the sorption percentage of cobalt from an aqueous solution using modified maghemite nanoparticles. The effect of operating conditions such as temperature (°C), initial cobalt concentration, initial pH, contact time (min), and sorbent mass (g) are focused on the best conditions for maximum cobalt ions removal. Prepared nanoparticles were described using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR) measurements. The Langmuir model had been adequately matched with the experimental equilibrium data. Kinetic data demonstrate that the pseudo-second-order and intraparticle diffusion models regulate the kinetic processes of sorption. An ANN model was developed using 25 data sets for training, five data sets for validation, and 10 data sets for testing by a single-layer feedforward back-propagation network with 20 neurons to get a minimum mean square error (MSE). A tanh-sigmoid was used as the activation function for input and purelin for output layers. The high correlation coefficient $(R^2)=1$ for trained data; $R^2=0.998$ for tested data; $\mathrm{MSE}=3.78\times {10}^{-28}$ of the trained data; and $\mathrm{MSE}=6.0513\times {10}^{-9}$ for tested data between the model, and the experimental data revealed that the model could forecast the release of cobalt from an aqueous solution using modified maghemite nanoparticles efficiently.

In this work, we adopted the impregnating-baking method to prepare ${\mathrm{CuO}}_{\mathrm{x}}$/granular activated carbon (GAC), ${\mathrm{CuO}}_{\mathrm{x}}$/activated carbon fiber (ACF), and ${\mathrm{CuO}}_{\mathrm{x}}$/powdery activated carbon (PAC) catalysts whose physicochemical properties were then investigated. The catalytic activities of the synthesized catalysts for degrading biologically treated coking wastewater (BTCW) were studied during the microwave-catalytic wet peroxide oxidation (MW-CWPO) process. The results showed that the catalytic activities were in the order of ${\mathrm{CuO}}_{\mathrm{x}}/{\mathrm{PAC}>\mathrm{CuO}}_{\mathrm{x}}/{\mathrm{ACF}>\mathrm{CuO}}_{\mathrm{x}}/\mathrm{GAC}$. When the catalyst and hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) dosage is ($2\mathrm{g}/\mathrm{L}$, $0.9\mathrm{mL}/\mathrm{L}$), ($3\mathrm{g}/\mathrm{L}$, $4\mathrm{mL}/\mathrm{L}$), and ($15\mathrm{g}/\mathrm{L}$, $10\mathrm{mL}/\mathrm{L}$), the degradation efficiency is approximately 86.4%, 80.9%, and 78.8% for ${\mathrm{CuO}}_{\mathrm{x}}/\mathrm{PAC}$, ${\mathrm{CuO}}_{\mathrm{x}}/\mathrm{ACF}$, and ${\mathrm{CuO}}_{\mathrm{x}}/\mathrm{GAC}$, respectively. The enhanced catalytic activity of ${\mathrm{CuO}}_{\mathrm{x}}/\mathrm{PAC}$ can be attributed to greater adsorption and “hot spot” generation as well as sufficient contact among the catalyst, ${\mathrm{H}}_2{\mathrm{O}}_2$, and organics in aqueous solution resulting from its large specific surface area and small particle size. The hydroxyl radical (•OH) is proved to be the main active free radical based on free radical scavenging. The catalysts showed limited stability due to the leaching of Cu and catalyst crumble down, which poses an important challenge.

Point-of-use water treatment (PoUWT) technologies have been shown to reduce incidences of waterborne diseases. However, their effectiveness is limited against the most harmful pathogens, such as protozoa and viruses, due to the inability to deliver effective and safe levels of disinfectant. This paper studies disinfection mechanisms and efficiency of silver and copper against Cryptosporidium parvum, Giardia lamblia, and MS2 bacteriophage through a novel PoUWT method, a ceramic tablet embedded with metallic ions. Results demonstrate that the PoUWT method can deliver safe and effective levels of silver and copper to inhibit sporozoite metabolic ability, and thus disinfect protozoa. Excystation reduced from 74% to 14% for Cryptosporidium parvum oocysts treated with silver-embedded ceramic tablets. Similar results were observed among Giardia lamblia oocysts and copper-treated oocysts. Fluorescence microscopy demonstrated two mechanisms for protozoa disinfection by metallic ions: (1) structural damage of oocyst walls, and (2) alteration of sporozoite structure. Also, MS2 bacteriophage viability reduced by 89% when treated with ceramic tablet treatment. Using the PoUWT method in this study, silver and copper show promise as disinfecting agents for protozoa.

Various protocols are used in the hydraulic design of sanitary sewers, with key differences related to the assurance of self-cleansing, and the selection of Manning’s $n$. Analyses reported in this paper show that (1) self-cleansing of sewer pipes should not generally be assessed based on a specified full-flow velocity, (2) the typical Manning’s $n$ values for specified pipe diameters recommended by ASCE are not generally appropriate, and (3) an exact analytic relationship between the minimum self-cleansing slope and the minimum flow rate can replace the empirical relations recommended by ASCE.

E. coli (EC) concentrations of the upstream boundary, tributaries, and stormwater in the lower Passaic River at Paterson, New Jersey, were modeled using multivariate polynomial regression (MPR). Baseflow indexes (BFIs) and river flows from upstream and downstream boundaries of the study area were used as predictors. The MPR models were developed by stepwise addition of the candidate terms. The candidate terms were selected based on their $t$-statistics and the final term was selected based on the Nash-Sutcliffe efficiency (NSE) of the overall model. The NSE values of the models ranged from 0.61 to 0.88. The boundary concentrations were earlier modeled using symbolic regression without BFI as a predictor, resulting in a set of highly complex models for the same data. This study demonstrates the suitability of BFI as a water quality predictor and the importance of identifying suitable predictors to develop defensible empirical water quality models. Further, the relation between EC concentrations and BFI could be used to infer whether the predominant pollutant source at a location is independent of rainfall or is rainfall driven.

The copper-based metal organic framework Cu-BTC (Copper Benzene-1,3,5-tricarboxylate) was synthesized by the solvothermal method, and AC/Cu-BTC composites were prepared by introducing different proportions of activated carbon (AC) into the reaction process by in situ synthesis. Various measures, including the use of an X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), and ${\mathrm{N}}_2$ adsorption apparatus were applied to characterize the structure, morphology, and surface area of Cu-BTC and AC/Cu-BTC. The adsorption properties and mechanism of methylene blue (MB) and methylene orange (MO) onto Cu-BTC and AC/Cu-BTC were studied. The results showed that Cu-BTC and AC/Cu-BTC have the same octahedral structure. The adsorption amount of MB onto AC/Cu-BTC composites was higher than that of Cu-BTC. The adsorption of MB onto Cu-BTC and AC/Cu-BTC was much higher than MO. The adsorption isotherms of MB and MO onto Cu-BTC and AC/Cu-BTC could be described by the Langmuir model, while the adsorption kinetics of the two adsorbents followed the pseudo second-order model. The negative values $\mathrm{\Delta }H$ and $\mathrm{\Delta }G$ illustrate the spontaneity and exothermicity of the process. The adsorption amount of MB on AC/Cu-BTC decreased from 49.39 to $32.45\mathrm{mg}/\mathrm{g}$ after 3 cycles of reuse.

The roles of ${\mathrm{H}}_2{\mathrm{O}}_2$ in supercritical water oxidation (SCWO) were investigated. The results showed that some of the ${\mathrm{H}}_2{\mathrm{O}}_2$ could persist for a short time in SCW, and organic pollutants were mainly oxidized by the ${\mathrm{O}}_2$ generated from the ${\mathrm{H}}_2{\mathrm{O}}_2$ in SCWO. However, the introduction of ${\mathrm{Fe}}^{2+}$ into the SCWO system with ${\mathrm{H}}_2{\mathrm{O}}_2$ formed a new Fenton oxidation environment, i.e., supercritical Fenton oxidation (SCFO), which showed the cooperative effect of Fenton oxidation and SCWO. Comparative experiments of phenol and $\mathrm{p}$-aminophenol (PAP) in SCWO and SCFO, respectively, were carried out. The results showed that, in the SCFO system, the ${\mathrm{CO}}_2$ yield from the oxidative degradation of phenol-simulated wastewater ($766.0\mathrm{mg}/\mathrm{L}$) in 45s could reach 73.3%, much higher than that in the SCWO (49.2%) under the same conditions. After 8 min, the ${\mathrm{CO}}_2$ yield in SCFO (97.4%) was also significantly higher than that in SCWO (89.4%). The degradation efficiency of PAP-simulated wastewater ($272.5\mathrm{mg}/\mathrm{L}$) in the SCFO system exceeded 94.3%, especially under acidic conditions, and the degradation efficiency reached 97.4%, much higher than that in the SCWO system (86.2%).

For immobilizing Anammox biomass, different materials have been studied such as sodium alginate (SA), polyvinyl alcohol (PVA), and so on. PVA-SA is one of the most popular materials because of various advantages of when compared with others. In this study, boric acid and sodium sulfate were applied to make PVA-SA gel beads, which is a new method of immobilization technology. This type of gel bead is less toxic, more stable in water, and more biologically active than gel beads made by other methods. First, two types of seed sludge were used to make gel beads that were introduced in two different continuous stirred tank reactors (CSTR). Only Reactor 1 used the seed sludge having Anammox biomass. By observing the difference in nitrogen performances, Reactor 2 was applied as evidence to detect the start-up of the Anammox process in Reactor 1. After 20 days, relying on the stoichiometric ratios, ${\mathrm{NO}}_2^{-}─\mathrm{N}$ and ${\mathrm{NH}}_4^{+}─\mathrm{N}$ removal efficiency and ${\mathrm{NO}}_3^{-}─\mathrm{N}$ concentration, the Anammox process was detected in Reactor 1 while the results of Reactor 2 revealed that aerobic oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were dominant in PVA-SA gel beads. Subsequently, after 180 days, the nitrogen removal performance reached nearly 70%, whereas the nitrogen loading rate (NLR) grew from 0.1 to $0.3\mathrm{kg}·\mathrm{N}/{\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y}$. Furthermore, fluorescence in situ hybridization (FISH) analysis also confirmed the presence of Anammox bacteria inside the PVA-SA gel beads. Based on these results, using Anammox bacteria immobilized in PVA-SA gel beads crosslinked with sodium sulfate is suitable for starting the Anammox process.

This paper represents an experimental and modeling study on the performance of a novel superwetting zirconium dioxide ultrafiltration membrane. The effects of different operating conditions were tested using an oily emulsion representing water produced from the Bakken oil reservoir (Canada). The Taguchi experimental methodology was used to predict the optimal operating conditions, and the results were validated experimentally. At optimal conditions, the ceramic membrane showed excellent performance for oil, total organic carbon (TOC), and turbidity rejections of 98%, 99%, and 99%, respectively. The highest flux achieved was $\mathrm{1,007}\mathrm{L}/\mathrm{h}·{\mathrm{m}}^2$ at a transmembrane pressure (TMP) of 0.12 MPa (1.2 bar). pH was found to have the greatest contribution to oil rejection. After chemical cleaning, a high flux recovery of more than 97% was obtained. Hermia’s cake formation model had the closest correlation to the experimental data. Finally, an artificial neural network (ANN) model was used to fit the experimental data. The best fit was reached using the Bayesian regularization training algorithm.