Journal of Environmental Engineering

One of the main purposes of a landfill cover system is to minimize the migration of water into waste, known as percolation, and thereby reduce excessive leachate production. One possible way to achieve this goal is to use a two-layer cover with capillary barrier effects (CCBEs) for arid and semi-arid regions. For a humid climate or prolonged rainfall, the two-layer system with CCBEs is expected to lose its effectiveness for minimizing water percolation. A new three-layer landfill cover system is proposed and investigated for humid climates. This new system adds a fine-grained soil (i.e., clay) underneath a two-layer barrier with CCBE (i.e., a silt layer overlying a gravelly sand layer). The study is conducted by carrying out a one-dimensional (1D) water infiltration test in a soil column. The soil column was instrumented with tensiometers, heat dissipation matric potential sensors, and moisture probes to monitor the variations of pore-water pressure and water content with depth. The amount of water volume infiltrated into the soil during ponding was also monitored. In addition, transient seepage simulations were carried out to back-analyze the soil column test and to investigate the influence of saturated permeability of clay on the effectiveness of the three-layer system. Based on the 1D experiment and numerical analysis, no percolation was observed after 48 h of constant water ponding, which is equivalent to a rainfall return period of greater than 1,000 years. This is consistent with the results from the numerical back analysis. However, the upper two-layer capillary barrier is only effective for a rainfall return period of approximately 35 years. This indicates that the proposed bottom clay layer is necessary for a humid climate. Numerical parametric simulations reveal that with an increase of saturated clay permeability by three orders of magnitude (i.e., from $5.7\times {10}^{-9}\mathrm{m}/\mathrm{s}$ to $5.7\times {10}^{-6}\mathrm{m}/\mathrm{s}$), the amount of percolation is approximately 0.1 mm after 12 h of constant water ponding, which is equivalent to a rainfall return period of greater than 1,000 years.

The present study investigates the electrocoagulation-electroreduction (EC-ER) and ozonation process (ECRO process) for the treatment of grey wastewater (GWW) loaded with organic and inorganic matter, oil and greases (O&G), and total suspensions solids (TSS). Several factors, such as electrode materials, current density, electrolysis time, initial pH, wastewater conductivity, and ozone dosage were investigated. High treatment efficiency of GWW was recorded while applying the EC-ER technique followed by the ozonation process. The best performance for GWW treatment by the EC-ER process was obtained using aluminum and graphite electrodes operated at current density of $0.9\mathrm{A}/{\mathrm{dm}}^2$, during 90 min of electrolysis time and at pH around 10 whereas the ozonation treatment of GWW was found to be more effective at pH 8 and at $9.2\mathrm{g}/\mathrm{h}$ of ozone dosage. Under these optimal conditions, combining the electrochemical (EC-ER) and ozonation processes enhanced the removal of organic and inorganic contaminants from GWW. The ECRO process reduced total chemical oxygen demand (${\mathrm{COD}}_{\mathrm{T}}$) by $91.31\pm 1.09\%$, total organic carbon (TOC) by $84.59\pm 1.71\%$, soluble chemical oxygen demand (${\mathrm{COD}}_{\mathrm{s}}$) by $90.17\pm 0.26\%$, and dissolved organic carbon (DOC) by $82.11\pm 2.19\%$. Besides, the removal efficiency of biological organic demand (BOD), O&G, and total phosphorous (${\mathrm{P}}_{\mathrm{T}}$) reached $92.61\pm 0.24\%$, $90.40\pm 0.31\%$, and $86.66\pm 0.00\%$, respectively.

In this study, a two-stage fractional programming (TSFP) method is developed for supporting municipal solid waste (MSW) management under uncertainty. The model can not only balance two conflicting objectives through converting a multiobjective problem into a ratio one, but also can analyze multistage decision effects when promised policy targets are violated. Moreover, the TSFP model can facilitate dynamic analysis of capacity expansions for waste management facilities. The developed method is applied to a case study of long-term MSW management planning. The solutions obtained from TSFP can provide desired waste-allocation schemes and capacity-expansion plans under different policy scenarios. The results allow in-depth analyses in terms of conflicting objectives, policy scenarios, and capacity expansions.

Iron and manganese are commonly found in natural waters, particularly in groundwater. Because of the importance of particle size distribution (PSD) on the performance of removal processes, this research focuses on understanding the PSD and $\zeta$-potentials of oxidized iron/manganese in water, as a function of pH, ionic strength, and hardness. After rapid oxidation of dissolved iron/manganese, laser diffraction (LD), dynamic light scattering (DLS), and fractionation through serial membrane filtration techniques were used to define the PSD. For manganese dioxide, the $\zeta$-potential was found to decrease as the pH decreased and as the ionic strength and hardness increased, resulting in a higher aggregate size. The aggregation rate of manganese dioxide strongly increased with hardness. On the other hand, ferric hydroxide PSD was not significantly altered by ionic strength or hardness at pH values relevant to typical natural waters. A combination of several techniques was found to be essential for providing a complete picture of the PSD. The DLS and LD techniques were generally well adapted for nano-scale and micron-scale particles, respectively. The serial membrane filtration technique was suggested for water practitioners working toward the selection of an appropriate process for iron/manganese control in drinking waters.

This study investigated the electrochemical oxidation of chlortetracycline in aqueous solution using a ${\mathrm{Ti}/\mathrm{PbO}}_2$ anode under ultrasound irradiations. The influence of various parameters such as electric current applied, power of ultrasound, and treatment time were evaluated and optimization process was investigated by using factorial design and central composite design methodology. The results indicated that the chlortetracycline degradation rate was greatly influenced by the current and the treatment time. A current intensity of 3.92 A under ultrasound irradiation of 20 W (at 500 kHz) for a period of treatment of 95 min were found to be the best conditions for chlortetracycline oxidation in term of cost-effectiveness. The initial concentration ($10\mathrm{mg}/\mathrm{L}$) could be optimally diminished up to 73.3% while using a ${\mathrm{Ti}/\mathrm{PbO}}_2$ anode. Under these conditions, a relatively high mineralization of chlortetracycline (61.4% of total organic carbon removal) was recorded. Then, the optimal conditions were applied on a municipal wastewater effluent (sampled after secondary treatment) and artificially contaminated with $10\mathrm{\mu g}/\mathrm{L}$, $100\mathrm{\mu g}/\mathrm{L}$, and $10\mathrm{mg}/\mathrm{L}$, respectively. The treatment was more effective with the municipal effluent (chlortetracycline could be oxidized up to 98%) because of the presence of chloride ions that could easily be transformed into active chlorine. Chlortetracycline could be oxidized by both direct anodic electrochemical oxidation (by means of hydroxyl radicals) and indirect electrochemical oxidation via mediators, such as hypochlorous acid generated by chloride oxidation.

The present study brings insight to the antimicrobial activity of isolated bacterial species in a vermifilter (VF) during the combined treatment of domestic wastewater and organic fraction of municipal solid waste (OFMSW). The study showed that vermifilter resulted in an effluent with biochemical oxygen demand (BOD) $<20\mathrm{mg}/\mathrm{L}$ and $\mathrm{coliforms}<{10}^3\mathrm{MPN}/100\mathrm{mL}$, signifying higher treatment and pathogen removal efficacy. A total of 41 colony forming units (CFU) were isolated, out of which 12 strains were selected, which exhibited higher antimicrobial activity against pathogenic bacteria and fungi. This observation indicated the existence of a mechanism responsible for removal of pathogens, and based on comparative sequence analysis of 16S rRNA genes, the characterized bacterial strains could be subdivided into two phylogenetic clusters: Firmicutes and $\gamma$-Proteobacteria. These findings suggested that identified strains contribute to the search for new sources of antimicrobial substances and enhancing the disinfection efficiency during wastewater treatment by vermifiltration.

In this study, an inexact inventory-theory-based waste management planning (IIWMP) model was developed and applied to support long-term planning of the municipal solid waste (MSW) management system in the City of Xiamen, the special economic zone of Fujian, China. In the IIWMP model, the techniques of inventory model, inexact chance-constrained programming, interval-valued fuzzy linear-programming, and mixed-integer linear programming were integrated. The waste inventory problem that existed in Xiamen’s MSW management systems are addressed in association with the complexities of multiple uncertainties. Decision alternatives for waste allocation and capacity expansion with minimized system cost under different risk levels were provided for MSW management in the City of Xiamen. The results indicate that the developed model was useful for identifying desired waste management policies under various uncertainties.

This study investigated the treatment of drainage water containing mono ethylene glycol (MEG) using duckweed (Lemna gibba). Six identical continuous flow duckweed-based treatment systems (DBS) were used at different initial MEG concentrations and hydraulic retention times (HRTs). The MEG removal efficiency decreased from $85.9\pm 1.3$ to $79.3\pm 2.1\%$ by increasing the initial concentration from 200 to $400\mathrm{mgMEG}/\mathrm{L}$, respectively. However, the efficiency of DBS deteriorated significantly at higher MEG concentrations; i.e., the removal efficiencies decreased to $36.4\pm 1.2\%$ and $7.1\pm 0.9\%$ at concentrations of 800 and $\mathrm{1,200}\mathrm{mgMEG}/\mathrm{L}$, respectively. The performance of DBS was completely inhibited at MEG concentrations exceeding $\mathrm{1,200}\mathrm{mg}/\mathrm{L}$. The removal efficiency of MEG significantly increased from $37.2\pm 1.3$ to $79.3\pm 2.1\%$ when HRT was increased from 6 to 18 days. Nevertheless, the removal efficiencies of MEG remained unaffected when HRT was increased up to 21 days. The uptake process of MEG by duckweed typically followed first-order exponential decay relationships. These results support the recommendation that a duckweed pond system be operated at an HRT of 18 days, and with a MEG concentration below $400\mathrm{mg}/\mathrm{L}$.

The movement and degradation of drugs in soil and water environments are related to surface interactions with oxide nanoparticles. These nanoparticles could be stationary substrates or suspended in aqueous solution. In this study, different pH solutions of the common antibiotic ampicillin (AMP) were mixed with $\le 50\text{-}\mathrm{nm}{\mathrm{Fe}}_2{\mathrm{O}}_3$ (maghemite) particles. Both sorption and breakdown of AMP were observed. For initial drug concentrations from $\sim 3\mathrm{\mu M}$ to 2.9 mM, the overall AMP removal from solution can be described by linear isotherms with removal coefficients ($K_r$) of 394 ($\pm 43$) $\mathrm{L}{\mathrm{kg}}^{-1}$ at pH 2, 551 ($\pm 37$) $\mathrm{L}{\mathrm{kg}}^{-1}$ at pH 6, and 256 ($\pm 37$) $\mathrm{L}{\mathrm{kg}}^{-1}$ at pH 8. At pH 4, AMP removal can be described by a Freundlich isotherm of $\log K_f=3.27$ ($\pm 0.19$) and $n=0.57$ ($\pm 0.15$). AMP solutions were separated from maghemite nanoparticles after mixing and analyzed by liquid chromatography/mass spectroscopy (LC/MS) techniques, resulting in the detection of penicilloic and penilloic acid breakdown products.

In separate sewer systems, there is a risk that wastewater from illicit connections may enter a stormwater sewer and ultimately outfall into receiving waters, adversely affecting receiving water quality and increasing risks to public health. A common approach in using methods for the detection of wastewater pollution in stormwater systems for some municipalities is to take grab samples at the outlet of a stormwater sewer, some distance away from the point(s) of ingress of the pollution. However, once pollution enters a stormwater network, the concentration or detectability of indicator parameters may change. The aim of this study was to evaluate the variation in detectability of various wastewater quality parameters depending upon the distance from the point of ingress of the wastewater into a stormwater sewer. This includes E. coli, total coliform, Enterococci, conductivity, turbidity, total suspended solids, and ammonium. This study introduces a maximum detection distance—the maximum distance at which the detection of individual quality parameters would no longer be reliable. Recommendations on planning a wastewater detection program and selecting appropriate indicator parameters are given.

The role of environmental forcings on the fecal contamination dynamics in small coastal streams was investigated, using the Aljezur coastal stream (Portugal) as a test case. An integrated modeling approach, combining hydrological and coupled hydrodynamic-fecal indicator bacteria models, was applied to selected scenarios of relevant forcings, on the basis of previously calibrated and validated model applications. The forcings investigated included: tides, winds, waves, atmospheric pressure, bathymetry, river flow, and upstream fecal bacteria concentrations; this study targeted the characterization of the relative importance of these factors on the fecal contamination dynamics, to enhance our understanding of small coastal streams water quality dynamics. Results highlight distinct patterns for dry and wet periods. Fecal bacteria transport is mainly forced by tidal propagation, in dry periods; and by freshwater flows, during wet periods. The analysis reveals a complex hydraulic and water quality dynamic resulting from the interactions between the environmental forcings and strongly dependent on their relative strength. This analysis can be extrapolated for systems with a similar balance between the environmental factors.