چكيده به لاتين
Antibiotics are considered as emerging contaminants which due to continuous discharge into aquatic environments can lead to long-term adverse effects on aquatic life and human health; therefore, it is very important to remove them from aquatic environments. In addition to effective removal of antibiotics, it is important to manage the sludge produced by their removal processes. Therefore, main purposes of this study were to investigate performance of electrocoagulation (EC) process for removal of rifampin (RIF) antibiotic from aquatic environments and to improve floated sludge (FS) dewaterability by coagulation and flocculation process. The EC process in a batch system on synthetic wastewater was investigated. For this purpose, in pre-tests of EC process by one-factor-at-a-time (OFAT) method, effects of parameters including initial pH, spacing between electrodes, voltage, stirring speed, initial RIF concentration, reaction time, shapes of aluminum electrodes and their arrangement inside reactor were evaluated on RIF removal efficiency and operating costs of the process. Then, based on the pre-tests, important parameters were selected for study, process modeling and optimization in main tests by Response surface methodology (RSM). To evaluate the effect of coagulation and flocculation process on improving dewaterability of FS, ferric chloride (FeCl3) and ferric chloride sludge (FCS) were studied as coagulants. To have a more precise evaluation in this regard, scanning electron microscopy (SEM), SEM images processing and energy dispersive X-ray spectroscopy (EDX) were also performed. Based on the pre-tests, parameters of initial pH, voltage, initial RIF concentration and reaction time were selected as important parameters for evaluation by RSM. Under optimal conditions by RSM, RIF removal (%) of 90.41%, TOC removal (%) of 67.53%, operating costs of 62.38 US$/(kg RIF removal), TSS of FS of 5766 mg/l, final pH of 8.45, final temperature of 30.8 ℃ and FSproduced (%) of 3.69% were obtained at reaction time of 10.96 min, initial RIF concentration of 5 mg/l, voltage of 19.83 volt and initial pH of 9. It was observed, in optimal FS dewaterability conditions by FCS (pH=7, FCS dose=100 mg/g DS) and FeCl3 (pH=11, FeCl3 dose= 20 mg/g DS), CST was reduced from 40.36 s to 28.08 s and 16.08 s, respectively. In addition, SEM images and their analysis by ImageJ software showed that porous structures as a result of use of FCS and FeCl3, have improved dewaterability of FS. According to result of EDX analysis, it was observed that most of the elements present in optimal FS dewaterability conditions by FeCl3 and FCS were also present after filtering; therefore, there were most of the elements in the structure of flocs.
