Municipal wastewater is one of the largest volumes of wastewater which contains various organic compounds from proteins and fats to carbohydrates and nucleic acids. Municipal wastewater of Behshahr city (Mazandaran, Iran) was evaluated using aluminum sulfate and iron chloride as chemical coagulants and pectin and sodium alginate as natural ones. Biological oxygen demand was investigated at different temperatures and coagulant concentrations. The fraction of full factorial statistical method and Qualitek-4 software were applied for designing experiments and analyzing the results to determine the optimal conditions for achieving the highest reduction in wastewater organic load and biological oxygen demand. In the case of biological oxygen demand, the optimal condition was achieved at 25°C, using 1, 0.02, 1.5 and 1 g/L of aluminum sulfate, sodium alginate, iron chloride and pectin, respectively. Under the optimal condition, the percentage of biological oxygen demand reduction was equal to 34.5%. Maximum BOD removal of 40.9% was obtained at 25°C using aluminum sulfate, sodium alginate, iron chloride, and pectin at concentrations of 0.6, 0.02, 1.5, and 6 g/L, respectively. The contribution of aluminum sulfate, sodium alginate, iron chloride, and pectin concentration in biological oxygen demand removal of the studied wastewater was 3.8%, 22.4%, 16.3%, and 14.4%, respectively. Coagulation temperature and aluminum sulfate concentration with approximately 42.7% and 3.8% contribution values were determined as the most and the least effective factors in biological oxygen demand reduction.

Reducing fresh water resources and the quality of water in the agricultural has led to importance of the finding new sources of water for irrigation. In this regard, the use of non-conventional waters is one of the options. Using of drainage water as a non-conventional water source is one of the solutions to solve the water deficiency problem in agriculture. The present study was carried out to evaluate and simulate the quality of the drainage water of the rice fields in the city of Soumatserra, located in the F4 unit of Sefidrud Irrigation and Drainage Network for reuse in irrigation and evacuated to the environment. In order to investigate the quality of drainage water for discharge to surface water resources and reuse in irrigation, the concentration of the nitrate, orthophosphate, ammonium, biological oxygen demand, dissolved oxygen, total dissolved solids and acidity was measured in nine points in May-July 2017 and was compared with the standards of the Environmental Protection Agency, the Environmental Protection Agency of Iran, Institute of Standards and Industrial Research of Iran. The highest concentration of nitrate, orthophosphate, ammonium, and biological oxygen demand were 1.25, 0.184, 2.91 and 89 mg/ l in May and the lowest concentration of dissolved oxygen and the highest concentration of total dissolved solids were 3.6 and 289 mg/l in July. Also, the highest and lowest value of pH was 8.23 in May and 7.26 in June. Drainage water in terms of nitrate, orthophosphate, total dissolved solids and acidity, according to the mentioned standards was allowed in reuse in irrigation and discharge to surface water resources. But in terms of dissolved oxygen, biological oxygen demand and ammonium was diagnosed over the limit for reuse in irrigation and discharge to surface water resources. According to estimation of the pollution load of the drain to the Anzali wetland, it was found that the highest amount of pollution during the sampling period was occurred in May.

In order to evaluate the quality of effluent pollutants from the rainbow trout breeding farms in the selected farms of Kohgiluyeh and Boyer Ahmad Province, water samples were taken from five individual farms during the years 2021-2022. The physical and chemical indicators of water including acidity, biological oxygen demand, dissolved oxygen, electrical conductivity, nitrite, nitrate, phosphate, total suspended solids, total dissolved solids, total hardness, alkalinity, iron, oxygen saturation were measured once in each season from the inlet and outlet water (each treatment with 3 replicates). Based on the results, the range of pH changes (5.93-7.29), biological oxygen demand (6.41-7.56 mg/l), ammonium (0-0.319 mg/l), nitrite (0-0.181 mg/l), nitrate (2.19-19.2 mg/l), phosphate (0. 1-0.18 mg/l), total alkalinity (132-238), dissolved oxygen (3.35-8.11 mg/l), electrical conductivity (311-899 microsiemens/cm), TDS (203.7-607.9), and total hardness (312-157.77 mg/l) were obtained. The results showed that the concentrations of ammonium, nitrite, nitrate, phosphate, EC, and total dissolved solids parameters in the effluent compared to the input from the different farms has increased due to the increase of metabolism, fish density, concentration of nutrients, drugs and disinfectants, intensity and speed of water and the oxygen concentration in the effluent of the farms has decreased due to more metabolic activities than the input from the rearing ponds. Also, the amount of biochemical oxygen demand (BOD) and environmental chemical oxygen demand (COD) were increased and the dissolved oxygen was consumed and its amount decreased due to the increase of organic substances, nitrate, and the provision of oxidation conditions.

This research evaluated the efficiency of combined anaerobic-aerobic processes for the treatment of slaughterhouse wastewater. The anaerobic reactor consists of a 3.95 L Plexiglas column with 60 mm diameter and 140 cm height. The cylindrical particles of polyvinyl chloride with 2 mm diameter and 1250 kg m-3 density packed to 60 cm of column were used as biomass saving material. The designed aerobic reactor also has a Plexiglas column with 10 cm internal diameter, 90 cm height and 60 cm useful height. Anaerobic fluid bed and aerobic mobile bed reactors were exploited for retention times of 18, 24, 32, 40 and 48 h. The efficiency of total suspended solids, biological oxygen demand and chemical oxygen demand removing were evaluated in different stages. Under the applied condition, chemical oxygen demand, biological oxygen demand and suspended solids were removed by 85.94, 92 and 66%, respectively. Maximum methane production of 3765 mL per day was obtained after 31 h at the residence time of 18 h. The anaerobic reactor plays very important role in reduction of the chemical oxygen demand, and the aerobic reactor is necessary to clear the anaerobic treated wastewater and ensure the quality of the final waste.

Whey is one of the major dairy wastes which is rich in organic compounds. These compounds reduce oxygen dissolved in water, inactivating the active water ecosystem and cause the loss of aquatics. An optimized composite formula of coagulator concentrations including Pectin, Sodium alginate, Aluminum sulfate and Iron chloride and coagulation temperature was determined to reduce biological oxygen demands in whey. Experiments designing was done using fraction of full factorial statistical method and Qualitek-4 software and Taguchi approach was applied for results analysis. Optimal conditions was obtained in Aluminum sulfate, Sodium alginate, Iron chloride and Pectin concentrations equal to 2, 0.02, 1.5 and 1 g L-1, respectively and temperature as 25 degree centigrade. The expected reduced percentage in biological oxygen demands in optimal conditions was estimated as 33.722. Coagulating temperature was recognized as the most effective factor to reduce organic load of whey with a contribution share equal to 63%. Aluminum sulfate concentration changes showed less effectiveness (1.7%) and Iron chloride concentration changes had a negligible impact as 7%. The changes of Sodium alginate and Pectin concentrations were effective as 18 and 10%, respectively in reducing the biological oxygen that is needed.

Biological indicators play a pivotal role in enhancing our comprehension of the ecological status and health of wetland ecosystems. This study investigated the ecological status of Chaghakhor International Wetland utilizing the biological value index Z at 10 water and sediment sampling sites. The Z index results revealed a Beta-mesosaproby status (Z = 2.30 ± 0.03) with moderate pollution. The findings from the artificial neural network model, displaying a determination coefficient of 0.943, indicated that elevated levels of parameters such as sediment electrical conductivity (553.97 ± 18.43), chemical oxygen demand (15.18 ± 0.44), biological oxygen demand (8.23 ± 0.52), and total dissolved solids (173.66 ± 7.63) in water significantly influenced changes in the biodiversity index Z. Human activities surrounding the wetland, particularly the expansion of agricultural lands, appear to have exerted a substantial impact on the present conditions. Consequently, improving agricultural land management, specifically through agricultural system reform, and preventing agricultural runoff from infiltrating the wetland environment are indispensable strategies for ecosystem preservation. Additionally, continuous monitoring of benthic communities in Chaghakhor Wetland and assessment of seasonal variations are crucial for formulating necessary conservation programs.

The utilization of non-conventional water sources, such as saline water, drainage, and sewage, has proven to be highly effective in managing droughts given the limitations of the country's water resources. The primary advantage of utilizing effluent from urban wastewater treatment plants is the stability of these sources, their accessibility, and their low cost for irrigating agricultural lands, which ultimately addresses the issue of water scarcity. In this study, the quality of Shiraz urban sewage treatment plant effluent was evaluated for agricultural purposes by calculating the National Sanitation Foundation of America water quality index (NSFWQI) and the Oregon water quality index (OWQI) using daily data from 2018 to 2019. Nine parameters were selected to calculate the NSFWQI index for the Shiraz treatment plant, including turbidity, temperature, phosphate, nitrate, coliform, biological oxygen demand (BOD), total dissolved solids (TDS), dissolved oxygen (DO), and pH. The OWQI quality index is similar to the NSFWQI index but includes eight parameters: temperature, dissolved oxygen, biological oxygen demand, pH, nitrogen, total phosphorus, total dissolved solids, and fecal coliform. The results showed that the average NSFWQI values varied between 28.73 and 31.54 in different months, indicating poor quality. The monthly OWQI values ranged from 4.38 to 7.95, indicating very poor quality. Therefore, given the low quality of the effluent, it is recommended for use only in irrigating non-productive plants, forest parks around Shiraz, and a limited part of urban green space.

Textile wastewater contains substantial pollution loads in terms of Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Suspended Solids (TSS), Total Dissolved Solids (TDS) and heavy metals. Phytoremediation used for removing heavy metals and other pollutants by aquatic macrophytes treatment systems (AMATS) is well established environmental protective technique. A lab scale study was conducted to test the feasibility of water hyacinth for treating textile wastewater. The pH was reduced from alkaline to nearly neutral in all cases studied with the introduction of water hyacinth. The maximum reduction in the conductivity was 55.71% while the BOD and COD reduction ranged from 40 to 70%. A great deal of reduction in the total solids was noted in all the waste samples with a maximum reduction of 50.64%. Water hyacinth has tremendous potential to absorb heavy metals from the textile wastewater as it resulted in 94.78% reduction of chromium, 96.88 % in zinc and 94.44 % reduction in copper. ANOVA showed a significant (p<0.05) reduction in all the pollutants with the passage of time. Thus water hyacinth can be an efficient biological agent in reducing the pollution loads in textile industry wastewater.

The impact of rainbow trout farm effluents on water physico-chemical parameters of Ryjab River was investigated. Five stations were considered at different parts of the river. Station 1 located at the headwaters of the river, station 2 after nearly 30 percent of fish farms, station 3 after 60 percent of fish farms, station 4 after the last fish farm and station 5 located one kilometer after the last fish farm. Water physico-chemical parameters including temperature, oxygen, pH, carbon dioxide, electrical conductivity, ammonia, nitrate, nitrite, phosphate, total dissolved solids, biological oxygen demand and chemical oxygen demand were measured every 15 days at different stations from March to February, 2012. The results showed that there was no difference between the study stations in terms of nitrate rate (P>0.05). The fish farm effluent had significant impact on Ryjab water parameters including pH, CO2, oxygen, alkalinity, the total hardness, the electrical conductivity, ammonia, phosphate, TDS, BOD5 and COD (P 0.05). In conclusion, the effluents of rainbow trout farms have caused the pollution of the Ryjab River and the water physico-chemical parameters have changed.

Rivers can be contaminated with different pollutants such as trout farms. Evaluation of the effect of trout farm on water quality is important to give new permission for trout farm construction. In current work, the effect of constructed trout farms near the Deinachal River on some physicochemical properties namely chemical oxygen demand (COD), biological oxygen demand (BOD5), dissolved oxygen (DO), pH, temperature, turbidity, nitrate, nitrite, phosphate, heavy metals, total hardness, total alkalinity, calcium, magnesium, electrical conductivity, fecal coliform and ammonium were studied and the water quality was classified using Iran Water Quality Index (IRQWI). Results showed that except nitrite, ammonium, chromium, nickel, lead, cadmium and mercury, other parameters affected by both trout farms and domestic wastewater. However, assimilative capacity of Deinachal River due to entrance the branches into the river can improve the water quality.