Journal of Environmental Engineering

With the exception of some strict kinetic formalism, biofilm thickness constitutes a basic parameter for analyzing the mechanisms of mass transfer as a result of microbiological growth. A research gap exists, however, related to a constant (in time) biofilm thickness, a biofilm age and the system efficiency, namely the study of a biological fixed-film reactor operated with a constant biofilm age and thickness. The present work examined the influence of the biofilm age and thickness in the biodegradation process of an organic substrate. Biofilm thickness was related and measured indirectly by introducing the concept of biofilm age. This concept is commonly used in suspended biomass but is usually disregarded in fixed systems (solids retention time). In some recent studies, solids retention time is referred to only as a result of operation conditions and not a design parameter. By contrast, this work studied biofilms in a range of ages from 0.5–1 day to 5–6 days, allowing behavior comparisons of reactors operated at constant film thickness, contrary to usual procedures in continuous fixed biomass systems. A clear differentiation of microbial profiles (performed using the fluorescence in situ hybridization technique) was found for the different biofilm ages. The results showed that biofilm age can significantly influence substrate removal and those ages 0.5–1 day, 4–5 days, and 5–6 days had the most favorable results with higher substrate removal rates, indicating that operating the biomass systems with a controlled age may be advantageous. In addition to the potential benefits of efficiency, such an operation would also significantly reduce the suspended matter in the final stage of sedimentation because at those ages is not likely to experience significant biofilm detachment.

Increasing demand for food and irrigation motivates reuse of wastewater. In this study, the effective role of water hyacinth (Eichhornia crassipes) for remediation of nutrients and metals/metalloids present in kitchen wastewater (KWW) has been evaluated. This study is an initiative to turn zero-value kitchen wastewater into a valuable wastewater resource. KWW samples were collected from the hostel mess of an educational institution in India. The physical and chemical parameters were monitored for 4 weeks. In the initial sample, concentration of electrical conductivity (EC), total dissolved solids (TDS), nitrate-nitrogen (${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$), ammonium-nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$), phosphate-phosphorous (${\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}$), and potassium (${\mathrm{K}}^{+}$) were found to exceed the standard limit for irrigation water quality, whereas the concentration of these parameters reduced to 63.71%, 63.71%, 99.01%, 94.36%, 98.05%, and 83.30%, respectively, when fresh KWW plus water hyacinth (WH) was kept for 28 days. However, an increase of 51.73% and 117.34% biomass (fresh weight) was observed for fresh $\mathrm{KWW}+\mathrm{WH}$ and decomposed $\mathrm{KWW}+\mathrm{WH}$, respectively. A higher value of bioconcentration factor (BCF) was found for iron (8,363.40) in fresh $\mathrm{KWW}+\mathrm{WH}$, whereas a higher BCF value for iron (1,481.33), nickel (1,497.3), zinc (5,225.4), and mercury (1,286.9) was observed in decomposed $\mathrm{KWW}+\mathrm{WH}$. It was also observed that calcium, copper, magnesium, sodium, lead, and potassium showed a translocation factor (TF) $>1$ in fresh $\mathrm{KWW}+\mathrm{WH}$, whereas calcium, magnesium, sodium, and mercury showed $\mathrm{TF}>1$ for decomposed $\mathrm{KWW}+\mathrm{WH}$. This study shows one approach for reducing the wastewater handling problem and paves the way for solving demand for freshwater.

A cyanobacterial strain, Leptolyngbya sp., was used for ${\mathrm{CO}}_2$ biomitigation due to its effectiveness for bioconversion of ${\mathrm{CO}}_2$ and higher yield of biomass. In the present research study, ${\mathrm{CO}}_2$ biomitigation was done using cyanobacteria cultivated in scrubbed water containing sodium carbonate in equilibrium with various concentrations of ${\mathrm{CO}}_2$ (5%–30%), at different pH conditions (7–11), with different inoculum sizes (5%–12.5%) and at various temperatures (20°C–35°C). The biomass obtained after ${\mathrm{CO}}_2$ biomitigation was analyzed for its carbohydrate, protein, and lipid contents. The maximum biomitigation of ${\mathrm{CO}}_2$ was found to be in the range of 74.44±0.89% to 22.98±0.56% for ${\mathrm{CO}}_2$ concentration of 5% to 30%. The maximum productivities were found as follows: biomass, $27.71\pm 0.12\mathrm{mg}/\mathrm{L}/\mathrm{day}$; lipid, $6.62\pm 0.06\mathrm{mg}/\mathrm{L}/\mathrm{day}$; carbohydrate, $10\pm 0.21\mathrm{mg}/\mathrm{L}/\mathrm{day}$; and protein, $7.92\pm 0.15\mathrm{mg}/\mathrm{L}/\mathrm{day}$ at pH 9, 15% ${\mathrm{CO}}_2$, inoculum size of 12.5%, and a temperature of 25°C. As the flue gas contains ${\mathrm{CO}}_2$ in the range of 10% to 15%, the present cyanobacterial strain could be viewed as a valuable aid for ${\mathrm{CO}}_2$ mitigation in the future.

Nitrogen removal performance was investigated in a sequencing batch reactor (SBR) and two moving bed sequencing batch reactors (MBSBRs) containing a given proportion (20% v/v) of various carrier materials. The maximum total nitrogen (TN) removal efficiency (78%) was achieved using an MBSBR packed with luffa sponge (LS) substrate; polyurethane (PU) foam cube-packed MBSBR and SBR systems followed at 71% and 62%, respectively. Suspended-growth biomass played a role in the conversion of ammonium-N to nitrite-N and nitrate-N. Simultaneous nitrification and denitrification (SND) processes enhanced TN removal in the MBSBRs. In addition, LS facilitated denitrification by serving as a carbon source. Pyrosequencing analysis showed that the enhanced nitrate removal rates in Reactor B (RB; MBSBR-PU) and Reactor C (RC; MBSBR-LS) systems may be attributed to Clostridia enrichment; the higher relative abundance of Clostridia in RC may have caused the superior nitrate removal rate therein. Pseudomonas was the dominant genus in denitrification processes in RB and RC. This work demonstrates that MBSBRs are capable of outperforming traditional SBRs and that the choice of carrier material is essential to MBSBR wastewater treatment performance.

Compacted sand-bentonite mixtures have been treated as a good substitute for the barrier material at the landfill. At low stress, desiccation-induced moisture variations may cause a reduction in the plastic deformability of bentonite and shrinkage cracking, which can increase the uncontrolled migration of leachates. In addition, if the strength of the base material is not good enough, then the effective operation of the liner system may be threatened. Waste tire fiber continues to be a major environmental concern for all around the world; hence, it is quite essential to reuse waste tire fiber in order to reduce environmental and health hazard problems. Consistent with this fact, the potential benefit of using the waste tire fiber for landfill application has arisen to enhance the material function. Therefore, the objective of this study was to examine the possibility of adding tire fiber as a reinforcement material to sand-bentonite mixtures to improve the stability of the liner without significantly increasing its hydraulic conductivity. Tests were performed on sand and bentonite mixtures mixed in a proportion of $90:10$ and $80:10$ and with 5%, 10%, and 15% of tire fiber. Test results suggested that the inclusion of 15% tire fiber made a sand-bentonite mixture less prone to swelling. The compression index and swelling indexes are affected by the presence of the tire fiber in the mixture. With the inclusion of the tire fiber, a greater increase in hydraulic conductivity was observed for the mixture containing a higher amount of bentonite. The addition of tire fiber enhanced the effective strength parameter of the mixture. The energy absorption capacity (EAC) of the mixture sharply increased with tire fiber content and confining pressure; however, it decreased with an increase in the bentonite content in the mixture.

Environmental risks associated with child growth are complex, and intervention effectiveness has been consistently poor. To improve effectiveness, proper intervention points inside the complex system must be identified. Integrating site-specific knowledge, machine learning, and statistical modeling offers a powerful approach to addressing this problem. In this study, a novel four-step method is employed to identify the key environmental factors to low child height-for-age in Guatemala. The four steps included (1) the development of a region-specific, ranked list of contributing factors to low child height-for-age via informal interviews and literature; (2) the application of a clustering method to a large regional data set; (3) the identification of the top six ranked variables shared between Step 1 and 2; and (4) the analysis of the clustered, regional data set in a multigroup path analysis incorporating the top six ranked variables, diarrheal prevalence, and child height-for-age. Results suggested that an increase in diarrheal prevalence was not consistently associated with a decrease in child height-for-age. Having soap for handwashing was significantly correlated with lower diarrhea and higher height-for-age. The effect was larger in the poorer population. Finally, disease in maize was significantly correlated with lower diarrhea. This method provided an approach to reducing, modeling, and ranking large numbers of environmental risk factors to child growth, identifying potential regional intervention points.

A novel modified attapulgite has been developed. The method is based on the modification of attapulgite with humic acid, and its application is for the removal of Cr(III) in different conditions. It is characterized using Fourier-transformed infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). Then, the adsorption behaviors of as-prepared product are evaluated by static adsorption of Cr(III) from wastewater. The effect of pH, contact time, temperature, concentration, and adsorbent dosage on adsorption of Cr(III) is discussed. The results indicate that adsorption amount of Cr(III) on modified attapulgite is better than that of natural attapulgite. The temperature of the Cr(III) solution is found to have a significant influence on the adsorption amount. The Langmuir isotherm is used to describe well the equilibrium adsorption data, and the enthalpy change is evaluated by the Van’t Hoff equation. The thermodynamic analysis indicates that the adsorption is an exothermic and spontaneous process. Finally, the adsorption kinetic conformed to the quasi-first-order and quasi-second-order ratio equations.

The impacts of temperature on the characteristics of hydrochars from pig manure (PM) following hydrothermal carbonization (HTC) at 140°C–220°C for 1 h were investigated. The total organic carbon (TOC) content was 35.7%–39.1% and the total contents of nitrogen (N), phosphorus (P), and potassium (K) were 7.9%–8.1% in the hydrochars with yields of 97.4%–53.5%. The hydrochars had high nutrient recovery rates, and the contents of TOC, N, P, ash, and fixed carbon increased whereas those of K and volatiles decreased with increasing temperature. Fourier transform infrared (FTIR) spectroscopy and mass ratio of hydrogen to carbon (H/C) showed continuing aromatization of the hydrochars with increasing temperature. The characteristics of the hydrochars and the derivative thermogravimetry curves confirm that the composition of the hydrochars changed dramatically at 160°C–180°C, which was found to be a suitable temperature for low-temperature hydrothermal carbonation for fresh PM. However, the hydrochars were weakly acidic and the concentrations of Cu and Zn exceeded the standard limits for organic fertilizers.

While titanium dioxide (${\mathrm{TiO}}_2$) is highly regarded as one of the most promising catalysts for air-pollution mitigation, its practical use has been challenging due to structural complexity, process scalability, and high cost of existing fabrication methods. In this study, a facile spray-coating method is employed for fabrication of a ${\mathrm{TiO}}_2$-coated filter, with fibrous structure allowing for satisfactory airflow, sufficient pollutant–catalyst interactions, and reusability. Scanning electron microscopy (SEM) analysis shows that ${\mathrm{TiO}}_2$ nanoparticles were immobilized firmly on the surface of the membrane’s fibers. Energy dispersive X-ray (EDX) analysis reveals a homogeneous layer of ${\mathrm{TiO}}_2$ nanoparticles on the pleated washable synthetic (PWS) fibers. The photocatalytic oxidations of volatile organic compounds (VOCs) and carbon monoxide (CO) are analyzed in both the laboratory and field tests. ${\mathrm{TiO}}_2$-coated PWS filter membrane ($60\times 60\times 5\mathrm{cm}$) shows higher benzene and toluene removal efficiency (approximately 80%–86%) under UV radiation than that in the dark (less than 10%). This result indicates that photocatalytic oxidation on the surface of ${\mathrm{TiO}}_2$-coated PWS filter membrane contributes greatly to benzene and toluene degradation. The corresponding pilot-scale photocatalytic air filtration unit shows ethylene reduction rate of $1.59\pm 0.52{\mathrm{ppm}\min }^{-1}$ in a $45{\mathrm{m}}^3$ postharvest storage room. In a demonstrative elimination of automotive exhaust gases, the ${\mathrm{TiO}}_2$ coated PWS filter membrane shows a 16% decrease in CO generated from a motorcycle. This study shows the potential use of the cost-effective ${\mathrm{TiO}}_2$-coated filter membrane for indoor air quality improvement.

Mesoporous nitrogen-doped carbon quantum dot (NCQD)/BiOCl composites are fabricated via a facile solvothermal method, which exhibits outstanding photocatalysis for removing organic pollutants under visible and near-infrared light. The modification effect of NCQDs on the surface of BiOCl molecules not only extends the visible and near-infrared light response ranges but also improves the efficiency with which charge carriers are separated, which is beneficial to enhancing photocatalytic performance. Investigations of the photocatalytic reaction mechanism indicate that holes and ${{\mathrm{O}}_2^{-}}^{}$ are the main active species in the degradation process of levofloxacin over mesoporous $\mathrm{NCQD}/\mathrm{BiOCl}$ composites, where the holes play the dominant role.

Modeling is an important aspect of water quality management because it saves material and labor costs. The nonlinearity of water quality variables due to the complex chemical and physical processes in a body of water makes the modeling process difficult. This study used an artificial neural network (ANN) approach, a powerful computational tool for nonlinear relationships, to develop a model that estimates the summer concentration of total nitrogen (TN) and total phosphorus (TP) in US lakes using interrelated and easily measurable water quality parameters. Two ANN models, using regional and national data sets, and one linear regression model were trained, tested, and validated using three inputs (pH, conductivity, and turbidity) that were statistically correlated with the outputs. The prediction accuracy of the ANN models consistently outperformed the linear regression model. The statistical accuracy of the ANN models for regional data sets was superior to that of the national data set. A sensitivity analysis showed that pH was the most predictive parameter for nutrients. These results indicate that the ANN modeling technique can be a screening tool for an overall estimation of nutrient concentrations in regional lakes.

The purpose of this study was to investigate thermal stratification and eutrophication in the Zayandeh Roud Dam reservoir located in the central part of Iran using the CE-QUAL-W2 two-dimensional model. The model was used to simulate the temperature and water quality parameters of the reservoir from 2013 to 2015. The selected water quality parameters, which are effective in eutrophication, included nitrate (${\mathrm{NO}}_3$), phosphate (${\mathrm{PO}}_4$), dissolved oxygen (DO), and total phosphorus (TP). Model calibration and validation were done from October 2013 to January 2015, and the results showed an appropriate convergence between the simulated and observed data. Based on the simulated data, summer stratification in the Zayandeh Roud reservoir caused changes in water quality and anaerobic conditions of the hypolimnion. The reservoir eutrophication condition was investigated based on Carlson’s index, which indicated that the reservoir was in the eutrophic condition in most months of the year. In addition, two management scenarios, reduction of nutrients loads and reaeration of the hypolimnion, were evaluated to mitigate the eutrophication. The former can produce a mesotrophic condition while the latter needs excessive reaeration in order to decrease trophic levels and phosphorus concentration in the hypolimnion.