مجله آب و فاضلاب
پیاپی 152 (امرداد و شهریور 1403)

Accurate and precise measurement of arsenic concentration in water is one of the challenges in areas with the natural potential to create this pollutant. The purpose of this study is to determine the inorganic arsenic concentration by colorimetric and naked eye detection methods. In this regard, the BF2-Curcumin reagent was synthesized and applied. In the first step, this reagent was optimized with consideration of four concentrations: 15, 20, 25 and 30 µM (in 60% ethanol). Then, the three parameters of detection time (1 to 15 min), arsenic concentration (5 to 10000 µg/L) and arsenic pH solution (3 to 10) were investigated in detecting processes. In the second part of the study, the solid phase of reagent was designed and synthesized. For simplicity the arsenic measurement, solid phase consisting of a paper sheet coated with BF2-Curcumin and nano silica was used. The synthesized materials were characterized by FESEM/EDX, XRD, FTIR, VSM, TEM and N2 sorption-desorption analysis. According to the results, during the arsenic detection process, the reagent color changed from orange to blue, and the absorbance intensity decreased at 509 nm, while increasing at 602 nm; 602 nm was selected for detection. The results indicated that the best BF2-Curcumin reagent concentration is 20 µM, with R2=0.97. Under optimum conditions (pH=8 and 3 min), the relationship between absorbance intensity at 602 nm wave length and arsenic ion concentration is between 0.06 and 130 µM, with 0.21 µM as the limit of detection. Investigating the effect of ions interference showed that the concentration (mg/L), cations, and anions that exist in water interfered with arsenic detection. The magnetic adsorbence of Fe3+-TMSPT-MNPs was used to transfer the target analyte and eliminate the interference. On the other hand, the optimum time to produce nano silica sheets was 4 hours. Moreover, there is a good correlation between absorbance intensities at 520 nm and arsenic ion concentration at the 0.06 to 100 µM limitation, with 1.94 µM as the limit of detection in the solid phase. Finally, real samples were collected from the Sirvan River branches in Kurdistan province; then, more than 90 percent were recovered by spiked sample method in the 60 to 80 µM concentration in the both phases. So, this reagent can be employed as a testing kit to detect arsenic in the field.

In this paper, various issues related to the design and construction of a pump station under high-level underground water conditions in Dorood City using different approaches are investigated. These methods include deep wells, sheet pile walls, and secant walls. By evaluating the deficiencies of these methods in dealing with high-level underground water conditions, a new approach called the Top-Down method is studied and introduced; it was previously presented for the construction of caissons and buildings. In comparison to other methods, the advantages and disadvantages of the Top-Down method are evaluated, leading to its selection; Subsequently, the problems, including the waterstop placement system and construction details were addressed and modified. Architectural and structural details for the construction of such structures applying the Top-Down method were then presented in the research. Finally, the efficiency and robustness of the proposed approach in the design and construction of concrete sewage structures exposed to high-level underground water, are demonstrated from the technical and economic perspectives, construction time, costs and safety level.

Biosustainability, toxicity, and the potential for disruption of aquatic ecosystems and human health have made azo dyes into a serious environmental issue in industrial wastewater. In this context, a group of bacteria isolated from dye-contaminated wastewater was used in a moving bed bioreactor with polyurethane foam biocarriers for the biodegradation of Congo red azo dye. According to the EzBioCloud database (eztaxon), the dominant bacterium identified through DNA extraction, PCR, and 16S-rRNA sequencing showed the highest similarity to Lysinibacillus Capsici PB300(T). The efficiency of dye and chemical oxygen demand (COD) removal in the MBBR was examined in relation to process time, filling ratio, and dye concentration. Dye removal in this system was optimized, maintaining the pH at 7 ± 0.2, the temperature at 35 ± 1.0 °C, and COD at 980 mg/L. The highest removal efficiencies for dye and COD were 92% and 85.1%, respectively, after 72 hours at a dye concentration of 50 mg/L and a filling ratio of 40%. Kinetic modeling was employed to study biodegradation. The R² value for the first-order model was 0.9457, while for the second-order model it was 0.9791. The second-order kinetic model (Grau's equation) provided a more accurate prediction of dye degradation in the MBBR system. This study confirms the successful degradation of Congo red azo dye using immobilized bacteria on Polyurethane foam (PUF) biocarriers in the MBBR bioreactor.

Photocatalytic technology offers novel solutions for wastewater treatment using visible light. Graphitic carbon nitride, as a polymeric semiconductor, has attracted significant attention in this field. However, overcoming the limitations of this material remains a major challenge for researchers. In this study, a graphitic carbon nitride photocatalyst was synthesized using a thermal polymerization method with melamine as a precursor in a new gaseous atmosphere of CO2. For comparison, similar samples were synthesized in common atmospheres such as N2 and air. The structure, morphology, and properties of the samples were characterized using various analyses. Additionally, considering the importance of E.Coli bacteria, their antibacterial activity against this bacterium was evaluated under both light and dark conditions. The sample synthesized in the CO2 atmosphere had a surface area approximately 3 and 2 times higher than those synthesized in air and nitrogen atmospheres, respectively. Also, the luminescence intensity of this sample was significantly lower, indicating an improvement in photocatalytic performance. The results of microbiological tests showed that the CN-CO2 sample completely inactivated E.Coli bacteria with an initial concentration of 107 CFU/mL when exposed to an effective dose of 0.2 g/L within 180 minutes under visible light irradiation. In contrast, the CN-air and CN-N2 samples inhibited 62.7% and 29.5% of the bacteria, respectively. The results also indicated that CN-CO2 had a high ability to inhibit bacterial growth in the dark. The results of the disk diffusion assay and bacterial viability tests in solid media also confirmed these findings. Given the significant advantages of this nanomaterial (CN-CO2), including high photocatalytic activity, strong antibacterial properties, and a simple and one-step synthesis method, it can be used as an efficient photocatalyst for water and wastewater treatment industries.

The volume of produced sludge and its characteristics depend on the quantitative and qualitative characteristics of wastewater, the treatment process, and the operating conditions. Relatively high production of excess biological sludge is considered one of the main drawbacks of aerobic processes used in biological wastewater treatment. This research was conducted in the existing industrial treatment plant of Pars Shiraz sugar factory with a capacity of 5 cubic meters per day. In this research, the effects of temperature changes in the anoxic tank and return line were investigated to increase the biological removal of sludge, reduce the excess biological sludge; also, the effects of temperature changes on the biokinetics parameters in the activated sludge system were analyzed. The average values of the biomass production coefficient (Y) or growth efficiency in the 100-days study period, after the biological reactor reaches a stable state, varied from 0.75 to 0.54 at the return sludge temperature of 40 °C, decreasing to 0.38 at 50 °C and 0.30 at 60 °C in terms of (gMLSS/gCOD). This research demonstrated that while the biomass production coefficient decreases with the increasing return sludge temperature, it also has a negative impact on the quality of the effluent with respect to both quality and biokinetics parameters. The results indicated that the existing conventional bioreactor, with the return sludge temperature of 40 °C, achieves a significantly higher efficiency in removing pollutants, maintainingconventional range of biokinetics parameters, reducing the amount of sludge production coefficient and excess sludge disposal.

Water quality control in terms of solutes, color, taste, odors and existing bacteria is of vital importance from a health point of view. Water quality problems in storage facilities can be classified as microbiological, chemical and physical. Water stagnation in many storage facilities is probably the most important factor associated with declining water quality. Accumulation of sediment in cisterns leads to potential water quality problems and increased demand for disinfectants, microbial growth, water turbidity and chlorine depletion. To investigate the safety of the stored water, further research is needed. Requirements outlined in Issue Sixteen of the Iranian National Building Code emphasize specifications related to water storage tanks. In this research, the field observation method was employed to investigate the requirements of the national building regulations for 105 cisterns of apartments in Kermanshah city in two types of polyethylene and galvanized steel. Additionally, the factors affecting the problems that have been created inside the cisterns of the apartments have been evaluated. The results showed that in 8% of the apartments, the subscribers used direct pumping, which contravenes the established requirements. Furthermore, in 26% of the cisterns, the amount of residual free chlorine is lower than the recommended amount specified in Publication 1053 of the National Standard of Iran. In 7% of the cisterns, the water temperature is higher than the value suggested in the English standard (BS 8558:2015). All cisterns are not equipped with warning pipes, overflow pipes, drain pipes, or vent pipes. Rust was clearly seen inside the galvanized steel cisterns. There is accumulated sediment at the bottom of all cisterns. In 86% of cisterns with a volume of more than 1000 liters, water stagnation occurs due to the inlet and outlet being located on the same side. Therefore, legal follow-ups and periodic visits to the cisterns of buildings are essential.