چكيده به لاتين
Biocarriers are vital in anaerobic moving bed biofilm reactors (AnMBBR). Bacteria and archaea are active in anaerobic processes and make biofilms by attaching to biocarriers. In addition, different biocarriers strongly induce the dynamics of the dominant microbial population in each system. Due to the positive impact of biocarriers on the performance of anaerobic processes, the purpose of this study was the anaerobic treatment of synthetic petrochemical wastewater with emphasis on the removal of styrene as a volatile organic compound in the anaerobic moving bed biofilm reactors. Biocarriers used in this study are polyethylene (k3) (30% of reactor height), granular activated carbon (GAC) (10 g/l), cuttlebone (10 g/l), and pumice (10 g/l). This study was performed in three cycles under different concentrations of styrene (20, 50, and 100 mg/l styrene) in five reactors under mesophilic (35 ° C) and batch conditions. Ethanol was added to the anaerobic process as a co-substrate and co-solvent. During the experiment, styrene removal, chemical oxygen demand (COD) removal, and biogas production were periodically investigated, and the performance of different biocarriers was compared with a control reactor.
The results showed that the production of biogas in the control reactor in different concentrations of styrene was between 174.26 to 358.34 ml/gCOD. The addition of biocarriers of polyethylene, granular activated carbon, cuttlebone, and pumice increased biogas production by 25-40%, 108-148%, 99-104%, and 87-111%, compared to the control reactor, respectively. In all three cycles and in all reactors, the percentage of styrene volatility from liquid to gas phase was less than 2% and the highest amount of volatility was related to the third cycle. Also, the addition of biocarriers reduced the volatility of styrene from liquid to the gas phase by 31.17-67.19%. In addition, the lag phase of biogas production in reactors using biocarriers was reduced compared to the control reactor. Styrene removal and COD removal in the control reactor in all three cycles were between 72.27-79.24% and 82.28-85.63%, respectively, while by adding biocarriers to other reactors, it reached 76.80-91.37% and 86.26-95.6%, respectively. Overall, the best performance for styrene removal, COD removal, and biogas production was achieved in all reactors at a concentration of 50 mg/l styrene. The alkalinity concentration increased during the process on average from 1950 to 2370 mgCaCO3/L, which indicates the buffering property of the process. In addition, volatile fatty acids (VFAs) were reduced, indicating their conversion to biogas. In addition, the pH increased significantly.
SEM images showed the presence of a diverse population of bacteria, including cocci and rod-shaped bacteria. However, the predominant species in reactors that used biocarriers were rod-shaped bacteria. EDX analysis shows various elements in microbial sludge, including carbon, oxygen, magnesium, silicon, aluminum, and zinc, in the mixed culture. These elements are present in extracellular polymeric substances (EPS) secreted by microorganisms. Nevertheless, few metals visible in EDX spectra might also originate from the mineral salt medium (synthetic media) used to support microbial activity and growth.
