مجله آب و فاضلاب
پیاپی 147 (مهر و آبان 1402)

Organic pollutants soluble in water such as chlorine compounds, biphenyls and aldrins caused by dyes, detergents, herbicides and toxins cannot be removed in conventional purification processes such as filtration. Carbon nanotubes have a high ability to separate organic pollutants, but its slurry application is not desirable due to the need to remove them at the end of purification. In the present study, upgraded carbon nanotubes attached to particles of sand filters (CNTsand) were synthesized and used to remove organic pollutants. The capacity and efficiency of these nanotubes and the variables affecting it including pH, temperature, contact time and concentration were investigated. Also, reaction kinetics and adsorption isotherms were analyzed. The results showed that CNTsand has a high capacity to remove organic compounds. The data processing showed the pseudo-second order kinetic model for the elimination reaction and the Langmuir isotherm was the most consistent. The reaction enthalpy change equal to ΔH=11.02 kJ/mol and the free energy change from ΔG=-7.32 to -9.20 kJ/mol both indicate an endothermic and thermodynamically spontaneous reaction. Therefore, the adequacy and efficiency of the upgraded nanotube coating on sand grains in removing organic pollutants was confirmed.

Considering the necessity of access to fresh water for sustainable growth and development, the use of various technologies for desalination of salt water is one of the solutions to increase access to fresh water. Various problems of conventional water desalination methods have led to the emergence of new methods such as capacitive deionization technology. CDI technology is an emerging electrochemical adsorption technology to remove water-soluble ions. In recent years, the development of this technology has attracted the attention of many researchers from the functional and economic point of view. Recent research results show that to overcome the challenges of CDI technology, focusing on two areas of effective porous electrodes and applied architectures can be more effective than other solutions. Therefore, this article provides a brief overview of CDI technology and investigates its emergence, progress, and challenges. Furthermore, various types of structures with capacitive electrodes have been introduced along with their unique features, drawbacks, and advantages. Also, this article describes in detail the quantitative and qualitative performance comparison of different geometries of CDI technology, such as flow-by CDI, flow-through CDI, MCDI, FCDI and i-CDI. The results show that, currently, CDI technology using nanostructured carbon electrodes is economical for the deionization of low and medium salinity waters (3 g/L). Despite numerous challenges, capacitive deionization technology has the potential to provide a sustainable source of fresh water in the future. This technology offers a clean and environmentally friendly solution, with low energy consumption and economical operation.

To optimize the use of coagulants and coagulant aids, it is important to understand the structure of the sludge and its effect on parameters such as turbidity and color. In this study, the levels of total solids, fixed solids, and volatile solids were measured in the return sludge from a water treatment plants coagulation unit. The impact of these parameters on the consumption of ferric chloride and polyelectrolyte, as well as on the reduction of turbidity and color, was investigated. Thirty samples were taken from the inlet water, outlet water, and return sludge to measure each parameter. The highest levels of TS, FS and VS were found to be 8.4%, 96.2%, and 15.4%, respectively. In this case, the consumption of ferric chloride and polyelectrolyte was lowest, at 3 and 0.03 mg/L, respectively. The highest levels of turbidity and color in the return sludge were found to come from the inlet water, at 55 NTU and 19 TCU, respectively. The Kolmogorov-Smirnov test showed that an increase in TS, FS and VS in the return sludge reduced the consumption of ferric chloride and polyelectrolyte by p < 0.05. Additionally, an increase in return sludge solids led to a higher removal rate of turbidity and color, with a confidence level of p < 0.05. Overall, this study highlights the importance of understanding the structure of chemical sludge and its impact on the effectiveness of coagulants and coagulant aids in water treatment plants. By optimizing the use of these chemicals, water treatment plants can operate more efficiently and effectively, resulting in cleaner and safer drinking water for communities.

Sludge is a by-product of urban wastewater treatment plants using a biological method, which needs to be properly processed and managed in order to avoid environmental pollution and maintain the health of society. The main goal of the current research is to analyze the amounts of sludge disposal and energy recovery in the wastewater treatment plant in south of Tehran, emphasizing the nexus between carbon and energy footprints. Biogas and electricity produced in the wastewater treatment plant were carefully examined. Their impact on reducing direct and indirect emissions and carbon footprint was calculated using relevant international coefficients based on the amount of methane gas and electricity produced. Also, the amount of waste sludge was analyzed during the period of eight years (2014 to 2021). During the investigated period, at least 2414 tons, maximum 22850 tons and an average of 7265.4 tons of sewage sludge were produced per month. The amount of waste sludge produced per million cubic meters of treated wastewater is 24.4, 99.8 and 57.1 tons, respectively. On average, 9.5 million m3 of methane are produced every year, which is equivalent to 146347.54 tons of CO2/ year. On average, 1.1 MW/hr is produced in the power plant of the treatment plant, which is equivalent to preventing the emission of 3612 to 6472 tons of CO2/ year. The total direct and indirect emissions prevented are equal to 149,960 to 152,820 tons of CO2 equivalent. The production of biogas and its consumption to produce electricity in the investigated wastewater treatment plant has a significant effect on reducing greenhouse gas emissions.

There is a great importance in investigating and measuring microbial corrosion in the cooling tower of thermal power plants, especially in the case of open cycles. Moreover, this issue becomes more important in the situation where the source of water supply for cooling tower is river or sea water. In this research, the cooling tower water for Ramin Power Plant, which is supplied from the Karun River, is examined as a point of of microbial growth. For this purpose, microbial tests including TBC (general test) and specific bacteria tests such as APB, FP, IRB, NRB, Aero, SRB and TRB, physicochemical tests (conductivity, salinity, pH, turbidity) and the amount anions and cations, are carried out in the water sample of the cooling tower. In the TBC test, the approximate number of bacterial colonies is 107 cfu/ml, which is in a very heavy range. The results of APB and IRB test indicate the value is much higher than the permissible limit and the presence of Aero bacteria. On the other hand, in the analysis of anion and cation, sulfate and chlorine species have a very high concentration of more than 1000 ppm. Therefore, to deal with microbial factors, and as a solution in the first priority, the method of chlorination with water shock is recommended. The second priority includes the general method based on oxidizers such as ozonation and bromination. Selective removal of sulfate and nitrate ions is suggested as the third priority solution due to the high concentration of these ions and the intense activities of SRB and NRB bacteria.

In this research, the ozonation process has been used as a supplementary stage of purification to reduce the amount of chemical oxygen demand and remove bacteria, especially E. Coli, from the effluent of the paper industry. Box-Behnken Design statistical method is used to optimize the treatment conditions. In this method, the effect of three variables governing the ozonation process, including the initial pH of the effluent, the amount of input ozone (mg/min) O3 and the duration of ozonation (min) t, was investigated. The results showed that the amount of input ozone and pH had the greatest impact on reducing COD (up to about 80%). Also, the maximum efficiency of the ozonation process for the complete removal of E. Coli was seen in acidic conditions with high amounts of ozone and increasing the duration of ozonation. According to the results, it was found that ozone in molecular form and by direct attack in acidic environments played a role in the destruction of pollutants. Design Expert software was used to determine the optimal conditions, minimize residual COD and maximize the efficiency of the ozonation process. The values of pH=5.2, ozone amount (131mg/min) and duration (23 min) are predicted to reach the lowest residual COD value (48 mg/L) and the highest efficiency (100% removal of E. Coli). According to the investigations carried out in this research, it can be concluded that the use of ozonation process to reduce COD and effectively remove E. Coli from the waste water of paper industry is a promising complementary method.