Moving-bed biofilm reactor combined with three-dimensional electrochemical pretreatment (MBBR-3DE) for 2,4-D herbicide treatment: application for real wastewater, improvement of biodegradability.

2,4-Dichlorophenoxyacetic acid (2,4-D) is a herbicide that is considered as a carcinogenic and highly toxic contaminant, and due to its biological and chemical stability, its degradation is very difficult. Therefore, this study aimed to investigate a hybrid system's efficiency of three-dimensional electrochemical (3DE) process and a moving bed biofilm reactor (MBBR) in removing 2,4-D herbicides from aqueous solutions. In this experimental study, the electrochemical degradation of 2,4-D herbicide in a 3DE process with a G/ß-PbO2 anode was first investigated as a pretreatment process. Then, in the post-treatment stage, MBBR with continuous flow was used. The amount of aeration in the MBBR reactor was 4 L min-1, and the amount of dissolved oxygen (DO) was in the range of 3-5 mg L-1. The effect of various parameters such as hydraulic retention time (HRT) and filling ratio were investigated. The amount of sewage injection was set between 0.001-0.004 L min-1. Routine microbiological biochemical tests were used to detect bacteria. BOD5/COD, COD/TOC, AOS, and COS ratio parameters were used to determine the biodegradability of 2.4-D due to the effluent of the 3DE process. The results showed that with increasing current density, decreasing pH, decreasing herbicide concentration and increasing electrolysis time, the herbicide degradation efficiency increased by 3DE pretreatment process. Based on the results of MBBR post-treatment process efficiency, with increasing HRT and filling ratio, the herbicide removal efficiency increased. According to the results, the highest removal efficiencies of 2,4-D and COD herbicides were obtained during HRT of 24 h, and the filling ratio of 70% were 97.33% and 88.95%, respectively. The consortium of 2,4-D degrading bacteria identified in this study included E. coli, Enterobacter spp., Bacillus spp., Alcaligenes spp., Proteus spp., Acinetobacter spp., Pseudomonas spp., Arthrobacter, and Brevundimonas vesicularis. In the MBBR biological process, the reaction kinetics followed the Grau second-order model (R 2 = 0.98). In general, the results showed that the combined process of 3DE with G/ß-PbO2 anode and MBBR biological process has relatively high efficiency in 2,4-D herbicide degradation and can be used as a suitable complementary treatment method in wastewater containing non-degradable compounds such as phenoxy herbicides, e.g., 2,4-D should be used.

Sonophotocatalytic treatment of AB113 dye and real textile wastewater using ZnO/persulfate: Modeling by response surface methodology and artificial neural network.

The present study investigates the synergistic performance of the sonophotolytic-activated ZnO/persulfate (US/UV/ZnO/PS) process in the decolorization of acid blue 113 (AB113) dye from aqueous solution and its feasibility for the treatment of real textile wastewater. Decolorization of AB113 solution was modeled by central composite design-response surface methodology (CCD-RSM) and artificial neural network (ANN) approaches and optimized by CCD-RSM and genetic algorithm (GA) approaches. Statistical metrics indicated that both CCD-RSM and ANN approaches seemed satisfactory. However, the results of statistical fit measures indicated a relative superiority of CCD-RSM as compared to the ANN approach. The results of optimization of the process parameters by CCD-RSM and GA approaches appeared to be similar as follows: pH = 6.1, reaction time = 25 min, US power density = 300 W/L, ZnO = 0.88 g/L and PS = 2.43 mmol/L. The synergistic effect of the hybrid US/UV/ZnO/PS process in comparison with its individual processes (US, UV, ZnO, and PS) was found to be 54.3%. Quenching experiments discovered that and HO are the main oxidizing radicals in a mildly acidic condition of the reaction solution. The removal efficiency of AB113 in the presence of some anions decreased in the order of bicarbonate > sulfate > phosphate > nitrate > chloride. Further, the reusability feasibility of ZnO showed that the ZnO material retained its photocatalytic property after five successive cycles of reusability test, while Zn2+ ion concentration in the reaction solution was measured to be 2.81 mg/L. The findings also indicated that the integrated process application suppresses extremely chemical and electrical costs. The study of the feasibility of the US/UV/ZnO/PS process in the treatment of real textile wastewater was done by determining COD, TOC and BOD5/COD ratio. Results demonstrated that the 96.6 and 97.1% reduction of COD and TOC was achieved after 5 and 7 h reaction time, respectively. The obtained BOD5/COD ratio changed from about 0.15 (for non-treated wastewater) to about 0.61 with increasing reaction time from zero to 90 min. In conclusion, the hybrid US/UV/ZnO/PS system can be proposed as a novel and promising approach to be utilized as a pretreatment technique before a biological treatment process to facilitate the biological treatment of recalcitrant textile wastewater.

The Assessment of Trihalomethanes Concentrations in Drinking Water of Hamadan and Tuyserkan Cities, Western Iran and Its Health Risk on the Exposed Population.

BACKGROUND: The aim of the present study was to calculate and to assess the potential lifetime cancer risks for trihalomethanes from consuming chlorinated drinking water in Hamadan and Tuyserkan cities, western Iran in 2016-2017. STUDY DESIGN: A cross-sectional study. METHODS: Seventy-two water samples were collected from the distribution systems and from the outlet of water treatment plants (WTPs) and the experiments were carried out to determine the desired parameters. All the sampling and measurement methods were according to Standard Methods. The obtained data were analyzed using SPSS software. RESULTS: The mean concentration of total THMs in the summer and winter was 42.75 and 17.75 µg/L, respectively, below the WHO and Iranian standard. The positive correlation was observed between temperature and THMs levels. Moreover, THMs concentration in Shahid Beheshti's WTP was several times lower than in Ekbatan's WTP. Chloroform, the dominant species of THMs, was identified at different sampling points. The highest cancer risk in Hamadan was 1.4×10-5 and 4.8×10-5 for male and female, respectively; and the cancer risk was obtained to be 5.6×10-7-2.26×10-6 in Tuyserkan. CONCLUSION: The drinking water obtained from the studied area is safe in terms of THMs concentration. Nevertheless, the highest cancer risk was higher than the EPA's acceptable level of 10-6.

Kinetic and isotherm of hexavalent chromium adsorption onto nano hydroxyapatite.

BACKGROUND: Hexavalent chromium (Cr (VI)) is an important contaminant in surface and groundwater and its removal from contaminated water and wastewater has received interest in recent years. This study aimed to explain the removal process of Cr (VI) from aqueous solution using nano hydroxyapatite (n-HAp) as an adsorbent material. METHODS: Cr (VI) removal experiments with the prepared n-HAp were carried out as the batch test in 100 ml flask while agitating on the shaker. The influence of pH (3 toll), contact time (3-60 min), Cr (VI) concentration (1 to 2 mg/L) and adsorbent dosage (0.025 to 1 g/L) were explored. Three isotherms models and eight kinetics models were used to evaluate the experimental data, respectively. For validation of kinetic and isotherm data, correlation coefficient, sum of square errors (SSE) and normalized deviation were used. RESULTS: The removal efficiency of Cr (VI) was improved an increase in Cr (VI) and n-HAp concentration. The results best fitted with Langmuir model and the pseudo-second-order rate reaction. Analysis of data with Dubinin Radushkevich isotherm showed that the adsorption of Cr (VI) onto synthetic n-HAp is a chemisorption process. CONCLUSION: The n-HAp as an ecofriendly compound is effective adsorbent for the removal of Cr (VI) from aqueous solution. Accordingly, n-HAp is feasible and promise adsorbent for treating polluted Cr (VI) groundwater.