مجله آب و فاضلاب
پیاپی 146 (امرداد و شهریور 1402)

Lack of water is considered the most important threat to the survival of human beings and natural ecosystems. Food and energy security, health and industrial progress, which are the main components of the sustainable development of societies, depend on water more than anything else. Water consumption in Loshan power plant is 2600 L/MWh raw water, which is very high compared to the production capacity and is due to having a tower in its cooling system. Considering the high volume of water consumed in this power plant compared to the production efficiency and on the other hand, reducing the amount of rainfall and droughts that have occurred, it is necessary to provide a solution to modify the consumption pattern for this power plant. Considering the special position of this power plant, solutions to modify the water consumption pattern by recycling clean drains (blow down of boilers, back wash of sand filters and water sampling), purification and recycling the blow down of cooling towers into the water cycle and optimization of cooling towers (replacing drippers, replacing nozzles and optimizing water distribution to increase efficiency, using a rotating nozzle to increase the time and speed of the water droplets hitting the air in order to transfer more heat) are suggested. According to the experimental data, the conductivity of boiler blowdown is about 10 μs/cm and the expenses of recycling the blowdown of boiler by using heat exchanger is estimated about 324.425.000 Rials.

In the goals of the United Nations for the sustainable development of societies in the third millennium, the approach of water and food nexus is considered one of the important interdisciplinary perspectives in the direction of the dynamic balance of production and consumption of resources. Due to the consumption of more than 90% of the country's water resources in the agricultural sector, access to accurate statistics of this field is vitally important in creating a balance between water production and consumption in the water-food nexus approach. In such a way, the presentation of incorrect statistics or statistics with many errors, especially by official authorities, by entering into different models developed by researchers, will lead to distorted results, wrong decisions and ultimately economic and environmental damages and social tensions. In this research, with the approach of using the connections of ecosystems, water-food nexus was investigated; Thus, the correlation between the presented statistics of the production sector and the water consumption sector was analyzed by using water-food nexus with the method of uncomplicated calculations. Based on the information, the inconsisitency of the statistics provided by different departments is evident. According to the statistics of crop production in 2014-2015 and 2019-2020, the undercultivated area in the agricultural sector in 2019-2020 has grown by about 1% compared to 2014-2015, and in 13 provinces the undercultivated area has increased and in other provinces the undercultivated area in the agricultural sector has decreased. Water consumption in the agricultural sector has grown by about 10%, so that in 23 provinces, water consumption in the agricultural sector has increased and in 8 provinces, water consumption in the agricultural sector has decreased. This difference is due to the change in the cultivation pattern and the crop selected by farmers in the country. Also, according to the amount of programmable water that has been announced by the Ministry of Energy, in 12 provinces, the amount of programmable water is not enough to meet the Pure water consumption for crops, and even in some provinces, the amount of programmable water is only enough to supply garden products. This important and basic finding implies and emphasizes the need to solve the problems of statistics of different authorities of the country.

In this study, first, the water purification process was modeled by the hybrid of direct osmosis membrane and ultrafiltration, then the current system was compared with experimental results in terms of quality control and costs. In the direct osmosis process, a highly concentrated sodium polyacrylate solution was used as the draw solution. When the FO side of the hybrid membrane met wastewater, seawater, or saltwater, clean water was drawn through the FO membrane into the SPA solution. Then, the clean water was removed from the SPA solution through the UF membrane by applying pressure, which can be hydraulic or mechanical, less than 1 bar. Modeling was done to prove the validity of the design concept. Some model equations were extracted to simulate the performance of the hybrid membrane, and the experimental data were analyzed based on the model equations. It is believed that this method allows the production of RO quality water at a UF pressure much lower than the RO pressure and thus leads to a significant reduction in energy consumption for water production. It was noticed that more water (than the calculated value) could be drawn to the SPA solution when the CSPA,0 was<15.75 wt% while less water was drawn when CSPA,0 was>15.75 wt%.

Cutting oils are used in machining operations to reduce friction, provide lubrication and cooling properties, and prevent corrosion. Biological methods for treating wastewater from these oils have low efficiency. Therefore, other methods should be considered to treat this type of wastewater. The purpose of this study was to investigate the use of electrocoagulation for treatment of wastewater containing cutting oil. In this regard, an electrochemical reactor equipped with two aluminum electrodes and a direct power source was used. The efficiency of the electrocoagulation process was evaluated by measuring the removal percentage of chemical oxygen demand in a certain time range. The effect of various operating parameters such as oil concentration, applied voltage, stirring speed, initial pH, distance, and surface of electrodes on the efficiency of the electrocoagulation process was investigated. The results of the experiments showed that reducing the oil concentration from 3% by volume to 0.5% by volume led to an increase in the efficiency of the purification process up to 97.3%. Increasing the voltage from 40V to 60V reduced the time required for wastewater treatment with the same efficiency from 50 min to 20 min. Decreasing the distance between the electrodes from 6 cm to 2 cm and increasing the effective area of the electrodes from 60 cm2 to 180 cm2 reduced the time required for purification to 20 min. Also, the results of the tests showed that the time required for the purification process at medium stirring speeds (150 rpm) is low. The obtained results showed that the removal percentage of chemical oxygen demand in the neutral environment was high (95.9%). Therefore, due to the simplicity of the method, low operating cost, and the ability to design on an industrial scale, the electrocoagulation method can be used for the treatment of wastewater containing cutting oil.

Nowadays, the importance of ensuring the effluent standards of wastewater treatment plants is obvious. It is necessary to pay attention to the selection of the biological wastewater treatment process by considering different and diverse criteria. Because, the incorrect choice of the process increases costs and does not achieve the desired result. In this research, the technique of analytical hierarchy process and its combination with Taguchi method was used. By weighting and prioritizing the criteria and options by two groups of experts, including the scientific group and the executive group, the weight of each criterion and option was calculated. In the present study, options (in two cases including 7 conventional options and 7 advanced options), criteria (4 items) and comprehensive and complete sub-criteria (13 items) for selecting biological wastewater treatment processes in rural areas under various conditions have been considered. Finally, it was concluded that in both perspectives, the sub-criteria of providing disposal criteria and standards and the ability to reuse wastewater and climatic conditions were placed in the first and second priority. These sub-criteria received weights of 0.113 and 0.108 from the scientific point of view and 0.122 and 0.106 from the executive point of view. Also, the present study showed that the model of combining AHP and Taguchi method is a successful model for determining the method of biological wastewater treatment for various conditions. Finally, according to the results of this study, the prioritization of biological wastewater treatment options for wastewater treatment in Ahar village was done as a case study and the output results showed that the first priority of all experts is the artificial wetland method and MBBR, from a scientific point of view, Extended Aeration and ABR-Wetland, and in the executive point of view, artificial wetland and A2O methods were prioritized (conventional and advanced methods, respectively).

Supplying safe drinking water is one of the necessary actions of today's human societies because of the lack of water resources and successive droughts. Arsenic is a toxic element that can cause serious problems such as cancer if its amount was higher than the allowed limit, and it is used for the long term. In this study, the removal of arsenic by monolithic nylon 6 and hybrid nylon 6/zirconia nanomembrane was investigated. The monolithic nylon 6 and hybrid nylon 6/zirconia NMs were synthesized using a novel electrospinning method. The microstructure and presence of zirconia nanoparticles were evaluated by means of scanning electron microscope, X-ray energy dissipation spectrometer and Fourier transform infrared spectrometer. The mechanical properties of NMs were investigated. The value of zeta potential (ξ) was measured as an important factor in arsenic absorption. The filtration process was performed with a constant pressure of 0.82 bar and with an initial concentration of arsenic equal to 0.05 mg/L. Characterization of monolithic nylon 6 and hybrid nylon 6/zirconia nanomembrane (NMs) showed that the average fiber diameter was 163 ± 15 nm and 180 ± 38 nm, respectively. Also, the presence of zirconia nanoparticles within the hybrid NMs was confirmed by infrared spectroscopy analysis. The zeta potential of zirconia NPs was measured as a key factor to create the driving force for arsenic adsorption. The value of zeta potential was calculated as -14 mV at the neutral pH. The results of the stress-strain test showed that the tensile strength of monolithic nylon 6 and hybrid nylon 6/zirconia NMs is equal to 6.9 and 3.1 MPa, respectively. The filtration performance of both membranes was evaluated and it was found that the efficiency coefficient of monolithic nylon 6 and hybrid nylon 6/zirconia NMs is 25.01% and 31.61%., respectively. The fitting of blockage models on the experimental data showed that the intermediate blockage model was the dominant model. According to the 31.61% performance of arsenic removal, and also due to the findings of this research it is confirmed that the incorporation of zirconia NPs into the nylon 6 NFs can enhance the filtration ability to remove arsenic from the water sources.

Undoubtedly, the activated sludge process is one of the most common methods of biological wastewater treatment. Among the most common problems of activated sludge process systems is bulking of sludge (bulking). More than 50% of activated sludge wastewater treatment plants worldwide constantly or occasionally face this problem. In this case, the relative density of the flocs is low. It causes inappropriate sedimentation in secondary ponds and causes problems such as reducing treatment efficiency and imposing additional costs in the treatment and disposal of excess activated sludge. The current study, which was carried out on a laboratory scale (pilot) in the refinery unit of Shahid Tondgoyan Petrochemical Company, to investigate the factors affecting the creation of bulking. Factors include process parameters such as adjusting the ratio of input feed to microorganism (F/M), microorganism concentration, supply of nitrogen and phosphorus nutrients, dissolved oxygen, temperature, pH, and the use of cationic polyelectrolyte coagulant to improve the sedimentation rate of activated sludge. The optimal parameters in the amount of sedimentation are F/M equal to 0.35, MLSS in the range of ppm 2500 to 3000 ppm, nitrogen, and phosphorus nutrients relative to the amount of pollution (COD/N/P) in the range of 100/4/1 until 100/5/1, dissolved oxygen 2 to 3 mg/L, temperature 25-35 °C, pH range 8.5 and in the dose of 4.8 mg/gr TSS/L of cationic polyelectrolyte coagulant in 180 min. In general, by adjusting the process parameters in the indicated range, the amount of SVI can be controlled in the desired range of close to 150 mg/L.

Froth flotation is an effective method for separating fine solid particles from aqueous solutions based on surface properties. The most important phenomenon in this issue is the formation of solid-gas bubble accumulation. Appropriate selection of operating conditions such as size, shape, charge and hydrophobicity of nanoparticles, concentration, pH solution, flow rate and gas velocity, bubble size and flotation reagents such as surfactants for hydrophobicizing particles is essential to increase absorption by gas bubbles and collect them in the froth. In this article, an attempt has been made to examine the potential and limitations of the process of flotation of nanoparticles and their separation from solutions, or the use of nanoparticles as collectors, reinforcements and stabilizers of the froth, and the existing challenges and solutions to overcome them should be explained. According to the progress made in the field of equipment and reagents used, the flotation method could be a promising method to remove, separate, recover and purify nanoparticles from the solution.