WATER AND WASTEWATER
Year:2020 | Volume:31 | Issue:2 (126) |Papers Count:11

Nitrate contamination in water resources has become an important issue because of the environmental issue and potential risk to human health. The aim of this study is investigating the stabilization of modified bentonite nanoparticles by cationic surfactant on pumice aggregates to remove nitrate from aqueous environments. Bentonite nanoparticles were investigated by XRD, EDAX, and SEM techniques after modification by CTAB surfactant with the thermal method on the substrate of Pumice aggregate stabilization and physical and structural characteristics of the adsorbent. In this research, response surface method based on the Box-Behnken model was used for evaluation of the effects of independent variables such as pH, temperature and the amount of adsorbent on the response function and prediction of the best response value. Langmuir and Freundlich isotherm models were used for calculating the equilibrium constants and pseudo-first and second order constants. According to the results, the optimum nitrate removal efficiency was determined 63. 49% based on the Box-Behnken model in pH = 5, the adsorbent concentration of 15 g/L, and temperature 35° C. As well, the nitrate removal rate was increased by increasing the amount of adsorbent and contact time unless the removal efficiency was decreased with an increase in pH and initial nitrate concentration. Isotherm surveying showed that the laboratory data had better agreement with Langmuir isotherm and the best kinetic model of adsorption was determined by the pseudo-second-order kinetic model. Also, the recovery efficiency in 5 cycles of absorption and desorption was observed more than 85%. This study showed that modified Pumice aggregates could be used as an effective and economical adsorbent for pollutants elimination.

During the last decades, removal of wastewaters using visible active photocatalytic systems has attracted great attention which led to development of various nanostructured photocatalysts toward purification. Among such contaminants, products including those used in agricultural applications like insecticides and pesticides are of great importance. In this project, the unique Ag/AgBr nanospheres were prepared by a facile single-step co-precipitation method in the presence of 1-Butyl-3-methylimidazolium bromide ([BMIM]Br) ionic liquid (IL) and CTAB as the halide source and surfactant, respectively. The products were well characterized by X-ray diffraction powder (XRD), Scanning Electron Microscopy (SEM), Diffuse Reflectance Spectroscopy (DRS), and nitrogen adsorption-desorption isotherms (BET). The XRD pattern confirmed the presence of both AgO and AgBr crystalline phases in the structure well. In addition, the SEM micrographs indicated that the sample has the spherical morphology and the particles size is below 100 nm. According to the photocatalytic experiments, the product was very efficient for the degradation of acetamipirid insecticide solutions under visible light. Also, the results implied that the photoreaction obeyed first order kinetic and the rate constant was evaluated to be 0. 145 h-1.

The textile industry wastewater causes serious environmental problems due to its high toxicity and color. Therefore, it is necessary to find an effective treatment technology for removing organic dyes from wastewater. Cavitation is one such modern technique which has been considered for the treatment of complex pollutants because of its ability to generate highly reactive free radicals. Up to now, researchers have mostly focused on qualitative interpretations and related scientific techniques, and there has been no quantitative cost analysis for pollutant control in textile industries for decision making purposes. Future studies need to focus on the cost analysis of more processes in textile wastewater treatment, such as advanced oxidation and combined and biological processes. Thus, this research was conducted with the aim of investigating and comparing various single and combined processes using the hydrodynamic cavitation (in a single system and with a specific contaminant) to remove reactive black 5 dye. Hydrodynamic cavitation (HC) was applied by using an orifice plate with a 7 mm hole diameter at the inlet pressure of 4 bars. Single processes, photocatalysis, photolysis, adsorption and combined processes, cavitation + photolysis, cavitation + photocatalyst and cavitation + photocatalysis were investigated in dye elimination and each of them was optimized by changing the various parameters (pH, TiO2 nanophotocatalyst concentration, irradiation power and dye concentration) and their best efficiency was obtained. In addition, considering the cost of energy and the nanophotocatalyst consumed by the processes, along with the process efficiency, processes were ranked by defining the index of efficiency to cost ratio. In the studied processes, efficiency increased as pH reduced, however, in the case of the photolysis process, efficiency increase at the highest level of the basic pH was significantly higher than acidic pH. Increasing the nanophotocatalyst concentration up to an optimum level resulted in efficiency increase. The decolorization rate increased as the irradiation power increased. The processes efficiency decreased with an increase in the initial concentration of the dye. In terms of efficiency, cavitation + photocatalysis, photocatalysis, cavitation + photolysis, photolysis, cavitation + photocatalyst, cavitation and adsorption processes, with the dye removal efficiencies of 83, 60, 52, 49, 43, 38 and 13% were placed first to seventh. This is while, considering both efficiency and cost consumption, photolysis process and then processes of cavitation + photolysis, cavitation and photocatalysis were ranked first to fourth, respectively with the best ratios. Hydrodynamic cavitation is a promising approach for dealing with industrial pollutants and the combination of this process with other advanced oxidation processes yields desirable results. Considering the parameters of energy and the cost of consumed nanophotocatalyst in the comparison of processes is very important and the output efficiency of the process should not be the only criterion. Paying attention to the substantial costs of nanophotocatalysts such as nanotitanium dioxide, combined techniques (e. g., the combination of cavitation with other advanced oxidation processes) lead to less consumption of nanomaterial and lower operational costs and are therefore cost-effective.

In order to ensure drinking water meets the standards, utilization of novel treatment technology with low cost and minimum effects on environment is inevitable. Zero-valent-iron in micro and nano scale is extensively used to remove wide range of contaminants from water. Besides the ZVI, granular activated carbon is used in household water purification systems as a low-price, porous medium that adsorbs different contaminants (e. g. organic species and chlorine) and modifies the odor and turbidity of water. The aim of this study is investigation of the efficiency of ZVI and GAC in the treatment of tap water. In this study, the efficiency of zero-valent-iron in scales of nano (NZVI, d50=50 nm) and micro (MZVI, d50=50 µ m) and granular activated carbon (GAC, d50=1 mm) in purification of tap water is evaluated. For this purpose, five experimental columns (length=50 cm and inner diameter=2 cm) filled by nano and micro ZVI, and GAC in different mass percentages are prepared, whereas continuous tap water flow of Tehran at the rate of 4. 4 ml/min during 28 days (totally 177 liters) is injected through each reactive column. Temporal variations of calcium, magnesium, sodium, potassium, nitrate, and total iron, as well electrical conductivity, pH in the influent waters to and effluent waters from the five reactive columns are sampled and analyzed three times over experimental time at the end of 1st, 7th, and 28th day (totally 18 samples). Simultaneously with the water sampling, the variations of pore water pressure along the columns are measured through pressure gauges. The results indicated that the reactive column containing NZVI (individually or combined with GAC) are proficient in reduction of ions concentration from the influent water in comparison to those containing MZVI and GAC. Decreasing the permeability of reactive materials, reduction of reactivity over time, release of iron into effluent water, and increase of water alkalinity are challenges accompanied by the columns containing NZVI. Results of this study reveal that combinational use of GAC and MZVI in household purification system provides a potentially promising reactive medium with acceptable pollutant removal efficacy and life-time, as well less side effects.

Mercury (Hg) is one of the water pollutants and its removal from the aqueous environment is important. The major goal of this study was to remove the Hg (II) from aqueous solution by synthesizing a modified nanochitosan with carbon disulfide functional groups. Nanochitosan was synthesized using citric acid as an environmentally friendly crosslinking agent, and then it was modified with a carbon disulfide functional group. The characteristics of synthesized nanocomposite were studied by using proton nuclear magnetic resonance (1HNMR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Batch adsorption experiments of Hg (II) in metal ion solution were conducted under different conditions such as pH, temperature, contact time, initial concentration of metal ion and adsorbent dosage. The adsorption process was conducted to investigate the compatibility of data with isotherms models (Freundlich and Langmuir), kinetics (pseudo-first-and second-order rate equations) and adsorption thermodynamics in a batch system. Reusability of adsorbent using 0. 5 mol/L HCl and also effect of ion interferences were investigated for selectivity of adsorbent. Obtained results from this study confirmed the successful synthesis and functionalizing process of the nano-adsorbent. The optimal values were reported as pH=7, adsorbent dosage of 0. 2 g/L, initial concentration of 30 mg/g Hg (II) and contact time of 120 min. Sorption of mercury agreed well with the Langmuir isotherm model, confirming a monolayer adsorption. The maximum equilibrium adsorption capacity for mercury ions was 303. 03 mg/g. The results of kinetic studies showed that the sorption process followed the second order model. The results of thermodynamics showed that the adsorption process was exothermic and spontaneous. Possibility of recovery of adsorbent was investigated up to five cycles and desorption percentage of mercury ions was more than 95%. Also, the results of ion interferences effect in mixed solution showed that the percentage of mercury removal with the functionalization of nanochitosan by carbon disulfide increased up to 88% and the synthesized adsorbent has a high selectivity for mercury ions. Based on the high adsorption efficiency obtained for mercury ions in the mixed solution, the synthesized adsorbent can be at promising approach in treatment of real wastewaters with low concentrations of mercury ions and other interfering ions in order to obtain an admissible effluent standard. The results showed that the synthesized nanoadsorbent is an efficient low cost adsorbent for mercury removal from wastewater due to its high adsorption capacity, as well as its reusability and selectivity for mercury.

Estrogen-like compounds are very important for causing negative effects in humans and animals. These compounds at low concentrations cause negative effects and can be transported through the food chain. Therefore, there is concern about the presence of these pollutants in Caspian coastal waters. In order to determine the concentration of 4-nonylphenol and octylphenol compounds, surface sediment samples from 25 rivers leading to the Caspian Sea were collected in Mazandaran province. After the preparation steps (drying, extraction and column chromatography), the specimens were injected into a mass spectrometer (GC-MS) gas chromatography apparatus. The mean concentration of 4-nonylphenol and octylphenol compounds was determined in the range of 114. 43-4681. 31 ng/gdw for 4-nonylphenol and 7. 26-1281. 52 ng/gdw for octylphenol, respectively. Based on the results of this research, stations located in densely populated and urban areas showed higher concentrations than stations located in low-population and rural areas. No significant relationship was found between these compounds and TOC. Therefore, the changes in the concentration of these compounds are not a function of changes in the concentration of TOC in sediments. Therefore, it is expected that the arrival of untreated sewage will control the distribution of these compounds in river water. In general, the results of this study point to the necessity of continuous improvement of sewage treatment systems in Mazandaran province.

The petrochemical industry, including petrochemical processing, oil refining, and natural gas production, generates large amounts of wastewater. Thus, the petrochemical industry produces a large amount of wastewater containing a variety of pollutants. Therefore, the main objective of this study is to evaluate the treatment and simultaneous production of methane from petrochemical wastewater by different cathode materials in single membrane-less microbial electrolysis cells. Three single membrane-less microbial electrolysis cells were made of polymethyl methacrylate. The systems were 15 cm long, 15 cm wide and 10 cm deep with a total volume of 2. 25 L. Anaerobic sludge was obtained from an anaerobic digester of Isfahan municipal wastewater treatment plant (Isfahan, Iran). The anodes and cathodes were held together by plastic screws with electrodes spaced 2 cm apart. The MECs performance was described by using several main parameters, electricity generation, gas production, COD removal, and pH levels. According to the results, the removal rate of COD in microbial electrolysis cells with the SS316 cathode was higher compared to the other two systems. So that the maximum removal efficiency of COD with SS316 cathode under a voltage of 1V at HRT of 48h was 85%. Also, the results indicate that the production rate of methane and the content of methane with the system containing the SS316 was higher compared to the other two systems. The maximum methane production rate of 56 ml was with a content of 85% under a voltage of 1V at HRT of 48h. Based on the results, the microbial electrolysis cell containing the SS316 cathode was introduced as a promising system to treat and produce methane from petrochemical wastewater.

Pressure management (PM) is one of the most effective methods of leakage management in water distribution networks (WDNs). In addition to reducing leakage, it provides many benefits for water utilities. The purpose of this paper is an economic analysis of the PM through a comprehensive cost-benefit analysis, taking into account the various aspects of the implementation of PM in WDNs. For this purpose, a mathematical model was developed for evaluating the benefits arising from implementing PM on the reduction of leakage, pipe breaks, active leakage control, water consumption, energy consumption, building damages and the increase of customer satisfaction and the costs of purchase, installation, operation and maintenance, and revenue reduction due to the reduction of water consumption. Using the developed model, the net benefit and benefit/cost ratio can be calculated for each PM scheme. As a case study, the advanced PM system was implemented through the installation of time modulated (TM) and flow modulated (FM) pressure reducing valves (PRVs) in a district metered area (DMA) located in Mashhad city. The net benefit and benefit/cost ration was then estimated by the developed mathematical model. The results showed that the net benefit of PM system through FM is greater than TM and the benefit/cost ratio was obtained 3. 7 and 3. 2 respectively. The developed mathematical model will assist water managers and practitioners in comprehensive understanding of the benefits and economic justification for implementing PM schemes.

The prediction of the intrusion of saline water into coastal aquifers as a result of changing the amount of groundwater extractions is a prerequisite for managing groundwater. This study investigates the capability of different types of Support Vector Regression (SVR) models to predict salinity concentrations at the selected well in the small coastal aquifer under different groundwater abstraction conditions. SVR models were trained and tested using input (random transient pumping from the production wells) derived from Latin Hypercube Sampling and output (salinity concentration at the selected well) datasets. The trained and tested models were then used to predict salinity concentrations at the selected well for new pumping datasets. The models ability for predicting and generalizing compared with commonly used artificial neural network (ANN) model was evaluated using different performance criteria. The results of the performance evaluation of the models showed that the predictive capability of the polynomial SVR model is superior to other models. Also, comparing different performance criteria for all SVR models, except for linear SVR model, proved their acceptable predictive performance. The prediction and generalisation ability of polynomial SVR, recommends using these models to connect to the optimization algorithm for a surrogate model based simulation-optimization approach in sustainable management of coastal aquifers.

Access to freshwater resources is today one of the crucial issues in most countries including the Middle East and Iran. Owing to a small population in the past, water crisis was not as tangible as in the present time. Today, however, the crisis is more obvious than the past along with the growing rise of global population, global warming, excessive utilization of environmental resources, and human need for more food as well as dropping rainfall compared to previous years in many parts of the globe. Passive defense involves various dimensions, one of which is to protect and preserve such facilities as urban drinking water. This paper has tried to investigate water supply facilities in Yasouj City with an analytical viewpoint based on library and documentary studies to provide solutions from the perspective of passive defense. Thereby, both internal and external factors and quadruple strategies in urban water supply facilities can be determined with an approach that identifies and allows the application of current and future criteria and considerations of passive defense. The selected strategies were prioritized by QSPM method. Also, the distribution pattern was examined with GIS, and the necessary analyses was performed by the SWOT evaluation model. Our results suggest that it seems necessary to prioritize the development of a strategy for the reconstruction and modernization of Yasouj drinking water supply system with an emphasis on passive defense. The subsequent priorities go to strategies of joint channel construction for all installations because of inadequate layout of the facilities, while using camouflage techniques. In addition, construction of diversion reservoirs is needed in order to deceive enemies, increase security cameras. The telemetry systems (remote control) for wells and reservoirs should be upgraded throughout the city with exact localization using GIS to fully cover the water supply facilities.