نشریه علوم و مهندسی آب و فاضلاب
سال سوم شماره 2 (تابستان 1397)

Recognizing, calculating and planning for reducing Non-Revenue Water (NRW) has been one of the aims and plans in Iranian water and wastewater companies for more than two decades. In the meantime, Real Loss-es (RL), which constitute a major part of non-revenue water, are mainly due to leakage in various parts of the water supply systems and a large part of the NRW reduction activities is put to prevent and reduce RL. However, like other projects and activities, it should be implemented to the extent with economic justifica-tion. Since it is difficult to achieve a quick and practi-cal method for calculating the economic leakage rate, the companies often use a reduction in the percentage of non-revenue water in their targeting. However ac-cording to the IWA, the use of percentage of NRW as a technical indicator is never been recommended. In this paper, followed by a quick review of the performance indicators of non-revenue water, the method of bench-marking of non-revenue water, targeting actions, and calculating the economic leakage level (ELL) are pre-sented for a city in Isfahan province. In this city, the real loss was 7 times the economic level of leakage. There-fore, the real loss reduction measures were proposed and planned among which the active leak detection in 10-month interval was the priority due to high ILI.

The main objective of this paper is to determine the cost structure of the companies in charge of water production and distribution and to estimate the marginal cost of production of drinking water in Tehran. For this purpose, the Translog cost function is used to estimate the cost of production, transmission and distribution of water in Tehran Water and Wastewater Company. Analysis framework is based on a seemingly unrelated regression system. Time series data for the period of 1997-2012 has been used in this study. The results indicated that the labor, raw materials and other services inputs are substitute sand labor and capital inputs are complements. Results also showed that product cost elasticity is greater than unit and a diminishing returns to scale exists in Tehran Water and Wastewater Company. Finally, by using the calculated parameters and objective of minimizing the total cost of production, transmission and distribution of drinking water, the optimal production capacity in drinking water is calculated for Tehran. The results showed that, the optimal production capacity in Tehran drinking water is 376.15 MCM per year.

Considering the importance of sufficient pressure in supplying demand in water distribution networks, it is necessary to study the factors affecting pressure variation, that the roughness of pipes directly affects the pressure of nodes. Therefore, the study of factors affecting the change in roughness coefficient (Hasen-Williams) in water distribution networks is important. Pipes diameter, age and corrosion are among factors affecting the change in the roughness coefficient of pipes that are evaluated in this paper. The roughness coefficients were plotted against each of the above mentioned factors, and the approximate relations of the roughness coefficient was obtained by fitting to the obtained graphs. Finally, by combining the relations obtained, a general relation is obtained for the roughness coefficient. Also, in this paper, the cast iron pipes, for which laboratory data is available, were used to obtain a mathematical relationship.Then again, instead of using the roughness coefficient of new pipes in analysis and design, the roughness coefficient for the end of the design period was used, taking into account the effective factors mentioned.To evaluate the results of the proposed method, a two-loop network was investigated in two common and real situations. The results showed that if the roughness coefficient of new pipes at the end of design period is used for designing, there will be a save of about 50% in cost of pipes, but then the network pressure at the end of design period will be reduced by more than 25%. Therefore, in order to ensure that there is sufficient pressure and demand satisfaction throughout the design period, it is necessary to accept an increase in the cost of network implementation at the beginning of the project.

Human societies nowadays undergo huge expenses to meet the water requirements aiming at maximizing the benefits and minimizing the costs. The goal of reduced costs can substantially be met by reduction in the cost of network pipes while satisfying the minimum pressure at nodes; i.e. 14 meters. This study is a multi-objective optimization function that will be constructed in a part of the water distribution network of the Homashahr city in Kerman province. In optimization of water distribution network, in addition to financial problems, other aspects should also be noted such as pressure and velocity of water in pipes which play key role in network design. In this study, the pressure was considered as a second objective function and the velocity was set as a boundary condition. When the objective function is defined only on the basis of cost, the network can face inadequate pressure in consumers’ connections. In this study “WaterGems” software is used for hydraulic simulation and also optimization process based on genetic algorithm. Based on the two objective functions defined in terms of cost reduction and improved network pressure, a scenario with suitable condition was derived. This scenario caused 15% reduction in total costs of the project.

Water contamination is one of the most important challenges involved in the human health and environment. In particular and due to the high growth of industry, the contamination by heavy metals is very worrying and of much concern. Heavy metals can provide the incidence of many dangerous diseases especially different types of cancers. During the recent years, chitosan and chitosan nanoparticles and their derivations have attracted many researches on adsorption of contaminants especially heavy metals, due to their content of OH and NH2 groups, non-toxicity, low cost and availability. In this review paper, preparation of chitosan, chitosan nanoparticles and kinds of modified chitosan have been investigated and their applications in heavy metals adsorption process from aqueous solutions have been briefly outlined. The effect of significant parameters on the adsorption process such as chitosan crystallization, the concentration of adsorbent, the initial concentration of heavy metals, process time, solution pH, and temperature as well as isotherm and adsorption kinetics have been investigated. Then the response surface methodology (RSM) has been explained and common methods for optimizing the adsorption process parameters for heavy metals have been examined. Finally, recycling and reuse of chitosan-based adsorbents in the absorption process have been evaluated.

The reuse of urban wastewater treatment needs to be further explored due to some extent of potential hazards raised from the spread of various contagious diseases and the presence of toxic elements. At the same time and due to the presence of carbon and nitrogen, the treated wastewater can have beneficial effects on physical and chemical properties of agricultural soil. To assess the impacts of such irrigations, research has been made as farm pilots for depths of 0-40 cm in soil, in a completely randomized design with three replications of five treatments of irrigation. The study treatments were the well water T1, wastewater T2, combining 50% water and 50% wastewater T3, alternate irrigation water and wastewater T4, and the combination of 33% water and 66% wastewater (used by farmers) T5. The well water treatment were considered as control sample. Chemical analysis showed permissible changes in cations and anions in soil irrigated by treated urban wastewater in accordance to irrigation standards. Average amounts of Calcium, Potassium, Phosphorus, Nitrogen, Sulfate, Magnesium, Sodium and Chloride were measured as 22.80, 494.4, 7.87, 1.028, 9.34, 8.34, 39.2 and 25.7 mg/l, respectively. The amounts of average EC and pH were respectively equal to 3387 μm/m and 8.7. In general, the results showed that using treated urban wastewater had no destructive effect on soil.