نشریه علوم و مهندسی آب و فاضلاب
سال ششم شماره 4 (زمستان 1400)

Designing and promoting innovative methods with up-to-date and localized technical solutions can be helpful in efficient management of the wastewater treatment industry and achievement of sustainable development. Despite this, prevailing laws and policies are sometimes ineffective or do not support the desired results. Therefore, the preparation of an upstream strategic document by taking into account the opportunities and challenges, particularly in the field of wastewater treatment technology development, can identify gaps and take measures to resolve them in order to refer the necessary measures to the relevant agencies. In this research, in addition to the future studies on the development of wastewater treatment technologies, vision and quantitative indicators for the next twenty years were determined. Accordingly, the opinions of 58 managers of the country's water and wastewater department, industry experts and university professors were used through the meetings of the technical and steering committee. The basis for formulating the actions and policies required in this research is the Technological Innovation System (TIS) based on components for the development, dissemination and exploitation of technology. In this research, while enumerating the challenges of the development of wastewater technology in the country, the relevant policies have been explained.

Conventional water treatment processes include screening, coagulation, flocculation, sedimentation, filtration and disinfection. Many coagulants are widely used in conventional water treatment processes. These materials can be classified into inorganic and organic coagulants. Many researches on natural coagulants were carried out in recent years. This study evaluates Tragacanth as natural coagulants aids with poly aluminum chloride (PAC) for the removal of turbidity and coliform bacteria from water Karoon River. Tragacanth is a gum that extracted from astragalus. According to results of this study, adding tragacanth as a coagulant aid improved performance of the process and experimental observations showed that by applying tragacanth as coagulant aid in optimal conditions, larger flocks are formed compared to PAC applications and the sedimentation rate was higher. In total, this study showed that dose of 0.06 mg/l of tragacanth as a coagulants aid with 15 mg/l of PAC coagulant in high turbidity (480-500 NTU) has the best performance in reducing turbidity and total coliform.

One of the important steps in the process of removing water turbidity is the use of coagulants. Amongst the most applied materials is poly aluminum chloride (PAC) which is used to precipitate colloidal particles. The use of this compound, which contains Aluminum, in the coagulation causes some residual aluminum in the water. Natural and synthetic coagulants aid can be used to reduce the effects of overuse of poly aluminum chloride. In this study, the effect of bentonite and polyelectrolyte coagulant aid in the turbidity removal process of Babasheikhali water treatment plant is investigated. The results showed that optimum pH for turbidity removal was 8 and the optimal concentration of poly aluminum chloride at the optimum pH was 10 mg/L. In the presence of bentonite, the optimal PAC concentration decreased to 4mg/L and the turbidity removal efficiency increased to 92%. The results also showed that the combination of PAC and polyelectrolyte together can be used to reduce the concentration of heavy metals in the incoming water. Therefore, bentonite and polyelectrolyte coagulants aid can be used as a suitable option along with poly aluminum chloride to remove turbidity from the water treatment plant.

Pressure management can reduce leakage and water loss in water distribution networks. Therefore, pressure management is considered as one of the most important ways to reduce costs related to the operation and maintenance of water distribution networks, especially in worn-out networks. Therefore, the pressure of water supplied to consumers should be as low as possible. This approach to reducing pressure in the distribution network by water and wastewater companies has led to an increase in the need for domestic water pressure boosting systems (using pumps and tanks), which in turn increases energy consumption. This discrepancy in the interests of water and wastewater companies and energy consumers highlights the perspective of the water-energy relationship. The aim of this study is to find a solution to optimize the pressure in water distribution networks through the use of domestic water pressure boosting systems while simultaneously minimize the total cost of leakage, pipe burst repairs and energy consumption. In this research, EPANET software is used for hydraulic analysis of the network as well as the use of pressure-based analysis to model as close as possible to the actual operating conditions. The research method has been implemented as a pilot for Baharestan city in Isfahan, and the results show that the optimal pressure is about 48 meters of water column and at a pressure of 41 meters, the costs of water and energy are equal.

Land subsidence, as one of the most dangerous environmental phenomena, can occur for a number of reasons, including the over-extraction of the aquifer and the decline of groundwater level. Subsidence begins with vertical displacements and often causes trough, sinkhole, or deep cracks in the ground surface. The occurrence of this phenomenon in most cases causes damages that are often irreversible and costly. Therefore, for the sustainable development of the region, it is very important to accurately predict the occurrence of subsidence and controll it prior to its occurance. In recent decades, the drought and excessive extraction of groundwater resources, and as a result, the water-level decline, especially in dry and low rainfall regions, has been the main cause of this phenomenon in the plains of Iran. The aim of this study was to calculate the amount of subsidence due to the water table decline in Kashan plain. For this purpose, by collecting the required data, the groundwater has been modeled using GMS software, and based on that, the amount of subsidence during the last years has been determined. The results of this study showed that the land subsidence in the study area is increasing both in terms of quantity (from a few millimeters to several centimeters) and in terms of extent. The maximum subsidence was obtained as 5.95 cm. Therefore, it is very necessary that in addition to planned management and exact control on the exploitation of groundwater of region, academic studies, and quick actions be applied to provide the drinking and agriculture water required by other methods such as the water transfer from other areas.

Urban drainage Systems are of the vital infrastructures, which are responsible for the safe transport of runoff. In recent decades, the increase in surface runoff has led to inadequate capacity in some parts of drainage network, which results in over-flowing. Land use and population density around these areas pose a high risk of loss of lives and injuries. Since in previous studies, vulnerability indicators were not considered in the assessment of bottleneck’s risk, in this study, hazards and vulnerability indicators are combined together for calculating the risk index which is used for the prioritization of bottlenecks. In order to prioritize the bottlenecks of urban drainage system in Tehran catchment using the Simple Additive Weighting (SAW) method, the hydraulic modeling and Analytic Hierarchy Process (AHP) has been used for calculating the weight of indicators. For this purpose, five indicators have been defined which are population density around the bottlenecks, density of properties and diversity of land uses at these areas, average percentage of canal/main channel river filling, degree of bottleneck submergence, channel or river rank and flow velocity in canal/river. The results showed that the major critical bottlenecks are located in the eastern sub-basin of Tehran: in Abuzar, Maghsoudbeig and Bakhtar canals.