Iranian Journal of Chemical Engineering (IJChE)

Abstract Constructed wetlands have been increasingly used as an effective method for removing heavy metals from wastewater. This study aimed to investigate the combined effect of sawdust and Hydraulic Retention Time (HRT) on the performance of vertical-flow constructed wetlands cultivated with Phragmites Australis to remove Pb and Co from oily wastewater. To this end, nine barrels were used to construct the wetlands, which were filled with coarse gravel, polluted soil, and varying percentages of sawdust (0%, 20%, and 40%). Phragmites Australis cuttings were then cultured inside the barrels and irrigated with heavy metal-contaminated oily wastewater for three different hydraulic retention times (5, 10, and 15 days). After the vegetation period, plant, soil, and wastewater samples were collected and analyzed for Co and Pb concentrations, from which transfer factor (TF), bioconcentration factor (BCF), and removal efficiency (%) were derived. Results showed that while both Pb and Co removal efficiencies were affected by HRT and sawdust, the removal efficiency of Pb (36.66%) was higher than that of Co (30.83%). TF was less than one and was not affected by HRT and sawdust, but the effect of HRT and sawdust on increasing BCF was significant. However, Phragmites Australis demonstrated suboptimal performance in the uptake and transfer of metals from the root to stem.

Abstract Many communities in the world use groundwater as a source of potable water. The high nitrate concentration is a serious problem in groundwater usage. This study utilizes a biological denitrification method to investigate a moving bed biofilm reactor (MBBR) for the case of Tehran's groundwater. One pilot-scale MBBR with a 3 liter volume was designed and used in this research. The denitrification reactor operates under anoxic conditions. Methanol was used as a carbon source in the reactor throughout the study, and fifty percent of the reactor volume was occupied with KMT packing (k₁). To determine the optimum nitrate loading rate, the concentration of nitrate changed from 100 to 400 mg N/l. It was concluded that heterotrophic denitrifying bacteria converted nitrate to nitrogen. According to obtained results, the removal efficiency and optimum loading rate were estimated during the experiments in different concentrations and different HRTs for this type of reactor. Sodium nitrate was in the feed source in the anoxic reactor. The maximum removal rate of nitrate was measured to be 2.8 g of NO₃-N m^-2 carrier d^-1. Therefore, it was shown that the optimum loading rate of nitrate and the optimum COD/N were equal to 3.2 g of NO₃-N m^-2 carrier d^-1 and 6 g of COD/g N respectively.

Abstract The membrane bioreactor (MBR) is a  treatment bioreactor of urban and industrial wastewaters. The advantages of the MBR technology encompass high-quality effluents, less space requirements, and high-speed startups. This study aims to investigate the fouling phenomenon in the flour industry sewage treatment. The pilot has been designed and constructed in line with the research concerning the industrial wastewater treatment. After the adaptation of microorganisms, physical and chemical tests such as chemical oxygen demands (COD), turbidity and total suspended solids (TSS), extracellular polymeric substances (EPS), and soluble microbial products (SMP) were conducted during the process. The concentration of mixed liquor suspended solids (MLSS) in the membrane bioreactor ranged between 5000 and 8500 mg/L. Hydraulic retention times (HRTs) were fixed at 4, 8, and 16 h. Three types of resistance were considered via measuring the leakage current and transmembrane pressure (TMP). Accordingly, the total resistance rates for HRTs of 4, 8, and 16h were 22.5×10¹⁰, 21.3×10¹⁰, and 20.4×10¹⁰ m^-1 respectively. Considering the average organic loading rate (OLR) in three HRTs of 4, 8, and 16 h (8.84, 5.13, and 2.84 kg the COD/m³×day respectively), the daily feed was provided to the bioreactor, and the removal efficiency of COD was assessed. An average removal of 95 % was achieved in the whole process. In this method, the input turbidity of the effluent has been increased to 187 NTU and, then, reduced to less than 3 NTU. It was also observed that EPS, SMP, and the extracted carbohydrates played more vital roles in the membrane biofouling than the extracted proteins.

Abstract Different methods of urban sewage sludge energy recovery such as burning, gasification, pyrolysis and digestion based on the net energy production efficiency, advantages and disadvantages and complexity of these processes have been investigated in this article. The best method for energy production from sludge was selected among different methods according to energy and the amount of the greenhouse gas production. The capacity of the constructed power plant was calculated and investigated economically for each scenario. Quantitative and qualitative information on sludge was required to carry out this research so Ekbatan wastewater treatment sludge was analyzed. The results showed that the sludge of this treatment plant has 5.7% solids, containing 65.7% volatiles and the dry heat value is about 15100 kJ/kg. It was found that the best scenario for sludge energy production in this treatment plant is a digestion process with pure net energy production of 73.2 × 107 kJ/d. The energy recovery in an anaerobic digester can prevent the emission of 16,680 tons of CO2 annually and release about 1,460 tons of CO2 per year. The chemical analysis shows that the selected sludge has a potential production of 25m3 of CH4 for each m3 of sludge. The annual amount of biogas that can be recovered from municipal treatment plant is 836543 m3. On the other hand, the biogas can be used to generate electricity. The power of the plant is about 216.8 kW that with the construction of this power plant, an annual saving of 1.5 million dollars will occur.