Journal of Environmental Engineering

Azo dyes are a water-pollution problem causing damage to ecosystems and human health. Soybean peroxidase–catalyzed reactions of azo dyes, Acid blue 113 (AB113) and Direct black 38 (DB38), were optimized for color removal using response surface methodology on a Box–Behnken design (BBD). Parameters optimized were ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration (mM), pH, and enzyme concentration ($\mathrm{U}/\mathrm{mL}$; U is a standard unit of catalytic activity). Optimum conditions for AB113 were pH 4.49, 2.57 mM ${\mathrm{H}}_2{\mathrm{O}}_2$, and $1.52\mathrm{U}/\mathrm{mL}$ of enzyme for a predicted 5.6% color remaining (experimental value of 8.1%) and $R^2$ value of 99.68%; and for DB38 the conditions were pH 3.68, 2.92 mM ${\mathrm{H}}_2{\mathrm{O}}_2$, and $2.84\mathrm{U}/\mathrm{mL}$ of enzyme for a predicted 3.6% color remaining (experimental value of 5.1%) and $R^2$ value of 99.07%. In addition, the agreement with the one-factor-at-a-time approach was checked. The BBD is a less time-consuming approach that allows identification of interactions between parameters. Kinetic studies (Michaelis–Menten model) quantitatively confirmed the efficiency and effectiveness of enzymatic dye treatment.

The electrocatalytic degradation of phenol has been investigated by combining two processes, namely electrocoagulation (EC) and electrooxidation (EO), as a hybrid process. Ti/Pt-Fe and Ti/Pt-Al pairs of electrodes have been used in the study. The effects of various operating parameters such as electrode material, initial pH (${\mathrm{pH}}_i$), applied current, and temperature have been evaluated based on phenol removal rate. Experimental results showed that the Ti/Pt-Fe electrode system provided more than 98% phenol removal for 3 h of process time at ${\mathrm{pH}}_i$ 7.56 and applied current of 2 A. Kinetic studies were also conducted to understand the mechanism of the phenol removal by the hybrid process. The reaction kinetics for the EO part were fitted to a pseudo-first-order rate law, and the increase in $k_{\mathrm{obs}}$ values was observed with the increase of applied current at ${\mathrm{pH}}_i$ 7.56. For the adsorption part, diffusion was mostly the rate-controlling step for phenol uptake onto hydroxide flocs. The transformation by-products have been identified for the hybrid process, and it was seen that hydroquinone, benzoquinone, and pyrocatechol occurred at initial stages, and then benzoquinone and hydroquinone were subsequently converted to pyrocatechol. Through the final stages, the quinones converted to carboxylic acids, such as maleic acid and oxalic acid, because the phenol degradation and coagulation took place concurrently.

The generation of electricity in a membraneless microbial fuel cell (ML-MFC) was studied using dewatered sludge containing a mixed culture of electrogenic bacteria (EB). The EB acted as a biocatalyst to enhance the degradation of chemical oxygen demand (COD). Scanning electron microscope (SEM) observations revealed the formation of a biofilm at the anode surface. Phylogenetic analysis proved the presence of Pseudomonas species and Bacillus subtilis, which actively boosted the electron transfer, in the biofilm. Moreover, three unstructured kinetic models for EB growth, namely the logistic, Kono and Asai (KA), and combined continuous logistic and Fermi (CCLF) models, were proposed and validated. The logistic and KA growth models had high $R^2$ ($>0.91$) and low root-mean-square error (RMSE) ($<1.082$) values, while the CCLF model showed low values for both $R^2$ (0.48) and RMSE (5.431). The experimental data showed that the logistic model could best describe the growth of EB in the ML-MFC.

The need for stormwater quality control, especially the control of nutrients, has been recognized due to the widespread problem of water eutrophication. The bioretention system, as a green infrastructure, can remove the nutrients in stormwater runoff through the adoption of an internal water storage zone (IWSZ) and ground plants. However, the design of bioretention has to be guided by a holistic sustainability assessment to avoid problem shifting. Thus, this study aims to evaluate the environmental and economic impacts of alternative bioretention system configurations relative to their flood control and nutrient management capabilities using life cycle assessment (LCA) and life cycle cost analysis (LCCA). Seven scenarios with different configurations were generated to investigate the influence of design parameters (i.e., depth of IWSZ, ground plant species) on the life cycle cost and the environmental impact categories of eutrophication, ecotoxicity, fossil fuel depletion, and global warming potential. The trade-off was observed between the nutrient removal performance, some environmental impacts, and cost. This study suggested a proper depth of 45 cm for IWSZ and the insignificance of selecting ground plant species.

In this study, water samples from 123 households were collected from the point of collection (POC) to the point of use (POU) in Dar es Salaam, Tanzania. The objectives were to assess water collection and storage practices at the household level and to determine how water becomes contaminated. Household interviews revealed three main mixing combinations used in households: (1) city water with well water (CW); (2) water purchased from vendors with city water (VC); and (3) city, vendor, and well water (WVC). The quality of city water at the POC was deemed excellent (low water quality index), whereas it diminished at the POU for all water sources. Statistical analysis showed that the main reason for mixing well water with city water was to dilute the well water’s salty taste ($p<0.05$). It was found that the practice of mixing all three water sources was due insufficient storage containers ($p<0.05$). These impairments to water quality require an integrated response that combines hygiene education and improvements to water storage, water treatment, and regulation of vendors.

An anaerobic continuously stirred tank reactor (CSTR) integrated with an external tubular nanofiltration membrane module was operated for 466 days. Studies were conducted to compare the efficiencies in flux and operational permeability recovery of two different chemical cleaning processes. Chemically enhanced backwashes (CEBs) were applied for approximately 176 days of the study and their influence on chemical cleaning performance and membrane fouling rate following chemical cleanings were also investigated. The anaerobic nanofiltration membrane bioreactor used in the study was fed a high-strength, potato starch–based synthetic wastewater (average chemical oxygen demand of $83.4\mathrm{g}/\mathrm{L}$ and average total suspended solids of $5.8\mathrm{g}/\mathrm{L}$). Important findings were that a static, one-phase cleaning process using caustic cleaning chemicals outperformed a dynamic, three-phase cleaning process that also incorporated acidic cleaning chemicals; the acidic phase of the three-phase cleaning had a detrimental effect on the overall cleaning procedure’s performance; CEBs enhanced the performance of cleaning processes; and, finally, caustic cleaning solutions provided benefits to both membrane cleaning effectiveness and rate of fouling in the short term but may lead to an increased rate of membrane fouling in the long term.

Excessive discharge of phosphates in municipal and industrial effluents into water bodies continues to amplify the rate and extent of eutrophication that is impairing aquatic ecosystems throughout the world. Consequently, research into technologies to combat the problem of eutrophication continues unabated. This study aimed to develop a protocol to encapsulate dewatered lime-iron sludge in calcium alginate beads and assess and optimize its phosphate adsorption performance. Response surface methodology (RSM) and artificial neural network (ANN) were used to optimize the encapsulation process through parameter variation. RSM was superior in capturing the nonlinear behavior of the process. Numerical optimization in RSM revealed that maximum adsorption could be obtained from beads prepared using 0.25 g sodium alginate and 0.5 g lime-iron sludge in 25 mL of distilled water to produce a homogeneous mixture and added dropwise into a solution of 0.31 g ${\mathrm{CaCl}}_2$ in 25 mL of distilled water. The accuracy of the RSM prediction was subsequently validated by laboratory experiments that revealed a residual error of 2.9% and thus highlights the applicability of the model. Batch experiments were conducted and modeled to expound the mechanisms of adsorption. Kinetic data were best simulated using the pseudo-second order model while equilibrium data followed the Langmuir isotherm at room temperature and the Sips isotherm at higher temperatures. Physisorption, hydrogen bonding, dipole interaction, and ligand exchange were the dominant attachment mechanisms while film and intraparticle diffusion were the pertinent transport mechanisms. The beads exhibited a maximum monolayer adsorption capacity of $8.3\mathrm{mg}/\mathrm{g}$ that compared well to other phosphate-targeting adsorbents reported in the literature.

Microbial fuel cells are bioelectrochemical devices that use exoelectrogenic biofilms to convert organic matter into electric energy. Recent research of microbial fuel cells has occurred because of their potential to perform energy net-positive degradation and transformation of wastewater constituents. However, most studies have focused on small-scale ($<1\mathrm{L}$) batch systems with simple and homogenous feedstocks such as acetate. These studies are useful for identification of isolated variables in a controlled environment, but the system architectures are not scaleable to wastewater treatment applications and the feedstocks do not reflect the heterogeneity of real domestic wastewater. The emerging research evaluating scaled-up microbial fuel cells operating with domestic wastewater substrate has described new and different biofilm characteristics and associated transformations other than those seen in bench studies. Scale-up of wastewater microbial fuel cells presents challenges including feedstock variability, changing environmental conditions, and biofouling. To advise the design of pilot-scale systems, this review discusses process stream selection and system architecture with the aim to maximize net energy benefit, defined as the sum of treatment energy savings and direct energy recovery.

The removal of Reactive Black 5 (RB5) dye and chemical oxygen demand (COD) was investigated using a three-dimensional (3D) electrochemical (3DE) reactor with multiwalled carbon nanotubes (MWCNTs). The experiments were performed according to a Taguchi design model, with the variables being the solution pH (2–9), current density ($10–25\mathrm{mA}/{\mathrm{cm}}^2$), reaction time (15–60 min), MWCNT concentration ($25–200\mathrm{mg}/\mathrm{L}$), and RB5 concentration ($25–100\mathrm{mg}/\mathrm{L}$). The best conditions for optimum removal of RB5 and COD were pH 3, MWCNT concentration $200\mathrm{mg}/\mathrm{L}$, current density $15\mathrm{mA}/{\mathrm{cm}}^2$, RB5 concentration $100\mathrm{mg}/\mathrm{L}$, and reaction time 60 min. Among the main factors, the solution pH for removal of COD and RB5 and the current density for energy consumption had the highest impact. The 3D system generated more ${\mathrm{H}}_2{\mathrm{O}}_2$ and OH radicals compared with a two-dimensional (2D) system because the MWCNTs act as microelectrodes in the optimal conditions. In the 3D process, the production of high levels of reactive species led to an increase in the degradation of RB5 into aromatic compounds and various acids.

The modification of anodes to improve the startup and biodegradation is an effective way to advance the development of microbial fuel cells (MFCs) as a promising technology for wastewater treatment. This paper studied tourmaline material loaded on a carbon cloth anode to improve the performance of MFCs. The effects of different tourmaline contents on the performance of MFCs were investigated, and the tourmaline physical effect was analyzed by X-ray diffraction (XRD), infrared spectra, scanning electron microscopy (SEM), and biomass on the anode. In the MFC with a 0.1-g tourmaline-modified anode, the time required for one cycle was reduced to 24 h in the process of acclimation, and the startup time was reduced from 247 to 96 h. In addition, the degradation time of a batch was reduced to 25 h, chemical oxygen demand (COD) removal reached 91.5%, and the maximum power density was $546\mathrm{mW}/{\mathrm{m}}^2$. The biomass was $5.263\pm 0.05\mathrm{nmol}\mathrm{P}/{\mathrm{cm}}^2$ (the phosphorus content of microorganisms per square centimeter of carbon cloth). Therefore, a modified anode with proper tourmaline loading has a positive effect on the attachment of microorganisms and the startup period of MFCs.

This preliminary study investigates how the removal of human adenovirus in a membrane bioreactor (MBR) depends on the MBR configuration. Results from a sidestream MBR (ssMBR) are compared with data from an immersed MBR (iMBR) and literature data for another iMBR with 0.45-μm pore size hollow-fiber membranes used in all three reactors. The central premise of the study is that different fouling mitigation approaches in the ssMBR and iMBR lead to differences in membrane fouling and human adenovirus 40 (HAdV 40) removals. The hypothesis tested is that the fouling layer acts as an additional separation barrier and is largely responsible for virus removal in MBRs. Higher HAdV 40 rejection observed in the ssMBR is attributed to a higher density fouling layer formed in the ssMBR under conditions of cross-flow shear. The interpretation is supported by the measured differences in the dissolved organic carbon (DOC) removal and in the specific UV254 absorbance (SUVA254) reduction as well as in the transmembrane pressure response to periodic cleaning in the two MBRs (average decreases in HAdV 40 log removal value of 0.30 and 0.85 in ssMBR and iMBR, respectively). Although the additional energy required to create cross-flow in the ssMBR does not result in permeate flux enhancement over the iMBR baseline, the denser fouling layer in the ssMBR is a more effective barrier for viruses. This trade-off should be considered when weighing the priorities of energy savings and effluent quality.