نشریه علوم و مهندسی آب و فاضلاب
سال ششم شماره 1 (بهار 1400)

Scaling is known as one of the most important issues and limitation in aqueous systems, which involved several industries. Applying an efficient, economic and environment friendly solution to control scale formation is challenging. Scaling prevents efficient heat transfer by forming an insulated layer on the surface of heating elements. Moreover, scaling increases the pressure drop in the process and consequently it raises maintenance costs and even leads to system shut down. Using antiscalants is considered the most promising method to control scale formation. To this end, antiscalants are added to the process water. These compounds have received a lot of attention due to the fact that they can control the deposition by the low values and coverage of several mechanisms and can be used simultaneously with the process and do not have significant waste. Antiscalants disrupt the scaling process through a variety of mechanismsincluding threshold effect, crystal modification, dispersion or sequestration. In the current study, scale formation process and the role of antiscalants are discussed.

Due to the increased use of plastic materials in the daily lives of human all over the worlds and the concerns about the negative impacts of petroleum based plastics on aquatic and soil environments, the researchers have attempted to introduce biodegradable alternatives to such plastics. The non-biodegradability of petroleum based plastic is due to the large and long polymer molecules and the strong bonds between them, which ultimately makes it very difficult and even impossible for microorganisms to break down the molecules. The bioplastics are simply decomposed into their constituent units by the activity of living organisms and do not remain in the environment. Polyhydroxyalkonates (PHAs) are among the biodegradable polymers that have been received attention in the recent years. PHAs are polyester compounds that are produced by bacteria under special conditions. Feast/famine methodology is one of the methods for PHA production from bacteria. In this method, a sequencing batch recator (SBR) is used to supply feast and famine conditions, so that bacteria which are capable to produce PHA, compete with other microorganisms and obtain the maximum amount of PHA from the culture medium. In this review article, the method of feast/famine and the influential factors on producing PHA including feed type, feast/famine ratio, feed to microorganism (F/M) ratio, dissolved oxygen and nutrients concentration are investigated.

Over the last few years, our country has been facing to the water crisis. Therefore, this is important and necessary to creating a fair balance between available freshwater resources and the amount of demand and consumption in communities. That is why water resources proper management and advanced methods development has an essential role in the supply of freshwater. The purpose of present research is to evaluate the quality of the water in the Qanat of the Tabriz University and provide a suitable purification system for the exploitation of that water in the sports complex of the university to properly water resources management and reduce consumption. For that goal, in the first step, according to the results of qualitative experiments of Qanats water, 18 scenarios were proposed, for comparing and choosing the best candidate, it has been taken four main criteria and 13 sub-criteria. In this study, multi-criteria group decision making, TOPSIS method, and Simple Additive Weighting method (SAW) have been used. Which GFDM software has been used to analyze multi-criteria group decision making. Finally, according to the decision makers’ results, the value of each criterion was calculated and analyzed; and it was found that the H scenario was the best choice of the decision makers' point of view was reverse osmosis as a desalination method, sand filter, cartridge filter, and ultra-filter was the best choice for pre-treatment and chlorination.

Disadvantages of conventional techniques for removal of heavy metals from aquatic systems has led to the application of more efficient methods. Biosorption using microalgae is one of the appropriate methods to remove heavy metals. In this study which is performed on 2019, the efficiency of green algae, Scenedesmus obliquus which has a good potential for growing in wastewater, was investigated for the removal of nickel (Ni) as a toxic metal. The algae were first grown up in the BG-11 medium. The algae’s optimum growing condition in a medium consisted of Ni ions, were obtained by applying different temperatures in primitive condition: 10 ppm Ni, pH: 7±0.1. The optimum temperature was accordingly obtained as 30°C with OD = 0.81. Subsequently different Ni solutions (0, 0.5, 1, 2, 5, 10 and 20 ppm) at several contact times (1, 7, 14, and 21 day) were considered; while pH and temperature were 7±0.1 and 30±2 ºC, respectively. The results demonstrated that the algae have optimum Ni removal efficiency (91.07%) at the Ni concentration of 10 ppm. Equilibrium data for Nickel were fitted well by Langmuir adsorption model with maximum adsorption capacity of 25.76 mg/g at the 4th day contact time. The results showed that the microalgae S.obliquus, as a biosorbent, has appropriate capacity to remove heavy metals, especially Ni, from wastewater.

Saffron is a plant with high nutritional and commercial value, which has a good economic value when presented in high quality. This study was conducted in a randomized complete block design with two factors; type of irrigation water source (well water W1 and treated wastewater of municipal wastewater W2) and type of irrigation system (surface S1 and subsurface S2) with three replications. According to the results of chemical analysis of unconventional irrigation water source, treated wastewater in Torbat-e-Heydariyeh treatment plant met the standards of irrigation water for crops. The results of the mean squares in testing the irrigation system type and contrast of two factors showed that all quantitative traits of saffron were insignificant except two traits of dry weight of cream and stigma dry weight which were significant at the level of 1% probability. Also the results of the mean squares of saffron quality traits in the factor of type of irrigation source and the contrast of two factors showed that all quality traits, except moisture and total coliform which became significant at the level of 1% probability, became insignificant. Based on the results, the highest yield was obtained for quantitative traits of flower number, stigma dry weight and cream dry weight for W1S1 treatment and wastewater treatment. Treatments did not show significant differences. Also, for the quality traits of pyroxene, crocin, safranal and total coliform in W2S2 treatment, it was the highest value and wastewater treatments did not have a negative effect on product quality.

Corrosion is one of the major problems in utilizing sewage networks. In some points of wastewater networks, such as drop shafts, the corrosion intensity due to hydrogen sulfide gas accumulation is significant. In Arak main concrete wastewater collector line which transfers waste water from city to wastewater treatment plant the corrosion conditions of sewage pipe in the vicinity of the dropshaft were investigated with the help of sewer CCTV inspections. The occurrence of severe corrosion defects was monitored then intensity of hydrogen sulfide gas was measured. For reduce the intensity of hydrogen sulfide gas and the moisture content of the pipe atmosphere, stack ventilation and circulation pipes, were constructed then the values ​​of hydrogen sulfide gas were again measured. Maximum and minimum values of hydrogen sulfide were reduced 11.9 and 9.09 percent, respectively. The tensile strength test was performed on the last tie rod of ladder stairs. The yield stress of the last stair of ladder in dropshaft manhole was lower than the value of upstream and downstream manholes, that it indicates corrosion in dropshaft manhole was more severe. Due to the observation of the presence of hydrogen sulfide gas in the manholes and in order to investigate the effect of this gas on the metal of the manholes ladder, the tensile strength test of the last step of the manholes ladder and its upstream and downstream manholes was performed. Comparison of yield stress values showed the accumulation of hydrogen sulfide gas and the occurrence of Hydrogen Embrittlement in the ladder.