A review of combined advanced oxidation technologies for the removal of organic pollutants from water

Water pollution through natural and anthropogenic activities has become a global problem causing short-and long-term impact on human and ecosystems. Substantial quantity of individual or mixtures of organic pollutants enter the surface water via point and nonpoint sources and thus affect the quality of freshwater. These pollutants are known to be toxic and difficult to remove by mere biological treatment. To date, most researches on the removal of organic pollutants from wastewater were based on the exploitation of individual treatment process. This single-treatment technology has inherent challenges and shortcomings with respect to efficiency and economics. Thus, application of two advanced treatment technologies characterized with high efficiency with respect to removal of primary and disinfection by-products in wastewater is desirable. This review article focuses on the application of integrated technologies such as electrohydraulic discharge with heterogeneous photocatalysts or sonophotocatalysis to remove target pollutants. The information gathered from more than 100 published articles, mostly laboratories studies, shows that process integration effectively remove and degrade recalcitrant toxic contaminants in wastewater better than single-technology processing. This review recommends an improvement on this technology (integrated electrohydraulic discharge with heterogeneous photocatalysts) viz-a-vis cost reduction in order to make it accessible and available in the rural and semi-urban settlement. Further recommendation includes development of an economic model to establish the cost implications of the combined technology. Proper monitoring, enforcement of the existing environmental regulations, and upgrading of current wastewater treatment plants with additional treatment steps such as photocatalysis and ozonation will greatly assist in the removal of environmental toxicants

Investigating Effectiveness of Multi-walled Carbon Nano Tubes in Acid Black1 Dye Removal from Aqueous Solution

Abstract Introduction: Dye effluents of some industries contain many toxic, carcinogenic, and mutagenic compounds therefore, wastewater colored contaminants of such industries should be meticulously refined using an appropriate method before discharging waste-water to the environment. Therefore, this study aimed to evaluate the effectiveness of Multi-Walled Carbon Nanotubes (MWCNTS) in dye removal of Acid Black 1 (AB1) from colored wastewater. Methods: This laboratory study was conducted in the batch system and MWCNTS were used as absorbents to remove AB1 dye. In fact, this study investigated the effect of various factors influencing dye removal, such as adsorbent dose, initial dye concentration, contact time, and pH. Results: The study results showed that pH=3 is regarded the best pH for the dye removal. The equilibrium time for AB1 dye absorption on MWCNTS was 60 minutes. As dye concentration increased, dye removal rate decreased. Besides, increasing the amount of adsorbent increased the dye removal efficiency and at the absorbent dose of 600 mg/L, dye removal efficiency was reported 98.86% and 94.62% for 30 and 50 mg/L dye concentrations respectively. AB1 dye removal followed Langmuir isotherm and Pseudo-second-order kinetic models. Conclusion: The results of absorption studies revealed that increasing the contact time and the absorbent dose as well as reducing the pH lead to an increase in dye removal efficiency. Overall, the study findings demonstrated that MWCNTS could be used as an efficient absorbent in regard with decolorization of azo dyes from wastewater

nvestigation of Acid Black1 removal using multi wall Nano tubes Carbon in Aqueous Solution

Introduction: Dye effluents of some industries include many toxic, carcinogenic, and mutagenic compounds; therefore, colored contaminants of such industries should be carefully treated using an appropriate method before discharging wastewater to the environment. This study aimed to evaluate the performance of Multi-Walled Carbon Nanotubes (MWCNTS) as an effective adsorbent in removing Acid Black 1 (AB1) from colored wastewater. Methods: This laboratory study was conducted in the batch system and MWCNTS was used as an adsorbent to remove AB1 dye. The effect of various factors influencing dye removal, such as adsorbent dose, initial dye concentration, contact time, and pH investigated in this study. Results: The results showed that pH=3 was the best pH for dye removal and the equilibrium time for AB1 dye adsorption on MWCNTS was 60 minutes. As dye concentration increased, dye removal rate decreased. Besides, increasing the amount of adsorbent increased the dye removal efficiency and at the adsorbent dose of 600 mg/L, dye removal efficiency was 98.86% and 94.62% for 30 and 50 mg/L dye concentrations, respectively. Also, AB1 dye removal followed Langmuir isotherm and Pseudo-second-order kinetic models. Conclusion: The results of adsorption studies showed that by increasing the contact time and the adsorbent dose and reducing the pH, dye removal efficiency was also increased. In addition, MWCNTS could be used as an efficient adsorbent for decolorization of azo dyes from wastewater

Total Coliforms and Turbidity Removal of Water in the Continuous Sand Filter

The continuous filter is a kind of sand filter, which will operate without any interruptions for backwashing and also it accepts high-suspended solid levels in feed stream. Fouled sand is continuously removed from the filter bed, washed and recycled back without interruption with filtration process. Various samples of water with certain amounts of turbidity enter through a feed pipe and being distributed to the filter. A central column runs from top to bottom of the filter. The water is led through an outer tube in the column by a set of radial, distributor arms. The polluted water flows up ward through the sand bed. The water emerges; clean, in the top section of the tank, and eventually spills over a weir, and then inters into a discharge pipe. In this research, the continuous sand filter was studied to determine its disinfection efficiency in addition to turbidity removal. The results showed that the filtered water had a high quality and the turbidity reduction was 95.5 %. Inspecting the work of the filter had revealed that the removal rates of coliforms and microbial colonies were 99.67 % and 98.99 % respectively. On the other hand, by the use of direct filtration, turbidity reduction was over 97 %. In direct filtration, drinking water with less than 1 NTU turbidity was provided. This continuous sand filter has the advantage of stable operation and more energy saving as compared to the conventional ones

Application of Acoustical Processor Reactors for Degradation of Diazinon from Surface Water

Background: Since organophosphorus pesticides are widely used for industry and insect control in agricultural crops, their fate in the environment is very important. Pesticide contamination of surface water has been recog­nized as a major contaminant in world because of their potential toxicity towards human and animals. The objec­tive of this research was to investigate the influence of various parameters including the influence of time, power, and initial concentration on degradation of diazinon pesticide. Methods: The sonochemical degradation of diazinon was investigated using acoustical processor reactor. Acous­tical processor reactor with 130 kHz was used to study the degradation of pesticide solution. Samples were ana­lyzed using HPLC at different time intervals. Effectiveness of APR at different times (20, 40, 60, 80, 100, and 120 min), concentrations (2, 4 and 8 mg/L) and powers (300W, 400W, 500W) were compared. Results: The degradation of the diazinon at lower concentrations was greater in comparison to higher concentra­tions. There was also direct correlation between power and diazinon degradation. In addition, when the power increased, the ability to degraded diazinon increased. Conclusion: The sonodegradation of diazinon pesticide at different concentrations and powers was successfully provided. It has been shown that APR can be used to reduce the concentration of dissolved pesticide using high frequency

Study of Cadmium Removal from Environmental Water by Biofilm Covered Granular Activated Carbon

The contamination of water by toxic heavy metals is a world-wide environmental problem. Discharges containing cadmium, in particular, are strictly controlled due to the highly toxic nature of this element and its tendency to accumulate in the tissues of living organisms. Low concentration (below 5 mg`/L) of cadmium is difficult to treat economically using chemical precipitation methodologies. Ion exchange and reverse Osmosis which can guarantee the metal concentration limits required by regulatory standards, have high operation and maintenance costs. The goal of this research was to determination of efficacy of using GAC, Biofilm and BAC columns to treat low concentration cadmium bearing water streams and was to determination of the effects of temperature and pH on the adsorption isotherms. Studies were conducted to delineate the effect of pH, temperature, initial Cd and adsorbent concentration on adsorption of Cd2+ by GAC, BAC and Biofilm. Breakthrough curves for removal of 0.5 mg/L Cd2+ by GAC, Biofilm and BAC columns at two contact times were plotted. Batch adsorption and column data are compared, pH is shown to be the decisive parameter in Cd removal for GAC but not for BAC or biofilter. Lagergren plots confirm applicability of first-order rate expression for adsorption of Cd by GAC, BAC and Biofilm. The adsorption coefficient (Kad) for BAC was 2-3 times greater than those with plain GAC. Bed Volumes of water containing 0.5 mg/L Cd2+ treated at breakthrough for GAC, Biofilm and BAC columns were 45, 85 and 180 BV respectively. BAC is more efficient than GAC in the removing of Cd from water environment