نشریه علوم و مهندسی آب و فاضلاب
سال هفتم شماره 2 (تابستان 1401)

Hydrological cycle is directed into thermodynamic non-equilibrium state and maximum entropy production through thermodynamic processes. Therefore, it is possible to understand and describe hydrological cycle through computation of entropy production rate and the maximum entropy production principle (MEP). Based on MEP, if there are sufficient degrees of freedom within a system, it will adopt a steady state at which entropy production is maximized under existing restrictions. This principle can help to estimate the hydrological components and parameters without need for detailed understanding of watershed characteristics. Due to the importance of this issue in the science of hydrological modeling and the lack of Persian resources in this field, the present study examines the hydrological cycle from a thermodynamic point of view using valid scientific sources. In this study, the hydrological cycle is considered as a thermodynamic system and the method of calculating entropy production rate by components of water balance is presented. Also, how to estimate hydrological components using the MEP principle is explained in a simple example. Overall, the MEP principle holds great promise for equipping us with a better understanding of the organization of hydrological processes within the Earth system and development of the models based on non-equilibrium thermodynamic.

The most problems in the field of municipal waste management are related to the organic fraction of municipal solid waste (OFMSW). In this experimental study, the effect of hydrochars produced at 150, 190, and 230 °C on AD process was analyzed with a sample of the OFMSW of Tehran. Due to the hydrothermal carbonization process, with increasing temperature, the hydrochar yield decreased and due to the increase in thermal value, the energy yield in hydrochar-190 was maximum. The effect of hydrochars on biogas production was variable and in hydrochars-150 and 190, 23.25 and 41.3% increase in biogas production was observed, respectively. This phenomenon was due to the destruction of the hard structure of the OFMSW. On the other hand, in hydrochar-230, there was a 30.63% reduction in biogas production, which was due to the production of inhibitor products such as phenol and furfural in the hydrothermal carbonation process. According to the results, the best conditions for the maximum production of biogas in the produced hydrochar at temperature of 190 °C and a retention time of 40 minutes. Also, the percentage of methane production in this condition was 63.25%.

The textile industry is one of the largest consumers of water and chemicals, so that each kilogram of textile product requires 100-200 liters of water.Therefore, due to the limited water resources available, having the most pollution among industrial activities and the need to comply with wastewater disposal standards in the environment necessitates wastewater treatment. This study was conducted by review-descriptive method using existing studies. In this article, a review of floating treatment wetland and its application in the wastewater treatment of the textile industry, the key factors affecting the treatment and the combined role of plants and bacteria for maximum purification of contaminated water are presented. Plant tissue in water, roots and rhizomes in sediments play a major role in pollutant treatment. Examining the results of the advantages and disadvantages of different methods in wastewater treatment of the textile industry shows that floating wetland technology is an alternative to traditional and expensive wastewater treatment methods. According to the researches, Phragmites australis is widely used in this technology. Phragmites australis, along with Acinetobacter, Pseudomonas and Rhodococcus, can reduce COD by 92%, BOD by 91%, dye by 86% and heavy metals by 87%.

Sludge treatment and disposal processes in wastewater treatment plants account for a significant portion of the total treatment costs. One of the most expensive parts of sludge treatment is chemical conditioning. Study of the effect of process chain on the conditioning and dewaterability can effectively optimize and reduce operating costs and increase the quality of effluent sludge. This paper investigates the impact of aerobic digestion of waste sludge in Yazd wastewater treatment plant by SBR method on its dewaterability. For this purpose, the waste sludge sample of the plant was aerated in the laboratory at different residence times from 1.5 to 7 days. Then the dewaterability of the sludge was measured by two methods of Specific Resistance to Filtration (SRF) and Tests of Time of Filtration (TTF) in two cases with and without chemical conditioning with cationic polyacrylamide. The results showed that sludge aeration for up to 3 days without conditioning led to the best sludge dewaterability. The best results were obtained at 1.5 days aeration for the conditioning mode with polymer, which improved the dewaterability up to 4.5 times in the optimum polymer dosage. In this case, the polymer dosage decreased by 30% compared to the non-aerated conditioned sludge. It indicates the effect of digestion retention time on dewaterability. At the beginning of the process, the decomposition of cellular material improves the release of water from solid particles. Still, its continuation reduces the dewatering capability due to reduced particle size and conversion to colloidal materials.

Land subsidence is defined as equal to the vertical displacement of the ground over a specified time.  Declining water table elevation is one of the main causes of subsidence that can cause irreparable damage to surface and subsurface structures, especially in urban areas. In this research, the magnitude of subsidence due to water withdrawal from the pumping well has been estimated, and the factors affecting it have been determined. For this purpose, by collecting data from two water wells located in Kashan city, the subsidence analysis was performed based on the finite element numerical method using PLAXIS2D software. The results show that the water pumping during one year causes a decrease in the water table elevation and, as a result, the land subsidence by a few centimeters, but under a constant flow rate of water withdrawal from the well, the magnitude of subsidence in the studied wells is heterogeneous. Also, increasing the water withdrawal flow rate from wells up to 700 m3/day and the depth of wells up to 500 meters has increased subsidence, but after that, the amount of subsidence remains constant. Therefore, it can be concluded that the flow rate and depth of water withdrawal from the well are effective on the land subsidence and must be managed.

Phytoremediation is one of the innovative, economical as well as eco-friendly desalination methods. The current study was aimed at investigating the amount of uptake and removal of some contaminants and nutrients from saline waters by vetiver grass (Chrysopogon zizanioides L. Roberty). This research was performed as multi-factorial in a completely randomized design including three different levels of saline effluent (1, 10 and 14 dS/m) and two planting densities (10 and 20 vetiver plants) with three replications.  The vetiver grass was cultivated in 220-liter tanks with a cross-section of 0.23 square meters located in the educational farm at Isfahan University of Technology (IUT), Isfahan, Iran. Moreover, parameters changes including electrical conductivity (EC), cations (Ca, Mg and Na) as well as nutrients (N, P, and K) were measured with a residence time of 3, 7, and 14 days. The obtained results indicate that the vetiver grass can reduce EC (14-15.88%), cations (Ca (32.94-41.67%), Mg (29.51-57.14%), and Na (5.59-14.36%) as well as nutrients N (31-44.03%), P (44.15-51.54%), and K (24.37-56.32%)) from different salinity levels during 14 days. Furthermore, there is no significant difference between 10 and 20 vetiver plants in terms of uptake of contaminants due to high plant growth.