Treatment of Saline Organic Wastewater by a Submerged Anaerobic Membrane Bioreactor (SAMBR)

Abstract

The aim of this thesis was to assess the potential of a Submerged Anaerobic Membrane Bioreactor (SAMBR) for the treatment of saline organic wastewater.. Firstly, it was found that anaerobic biomass can be acclimatised to salinities up to 20 g NaCl/L over a period of about 35 days during three batch feedings. Experiments were also carried out to evaluate the performance of anaerobic biomass during a sudden reduction and re-exposure to salinity; anaerobic biomass showed high performance during fluctuations in salinity. Then, SAMBRs were used for saline sewage treatment and it was found that 99% Dissolve Organic Carbon (DOC) removal could be obtained at 8 hours hydraulic retention time (HRT). Different start-up strategies and inoculation of halotolerant species into a SAMBR were investigated. In addition, the reduction of biogas sparging time caused an increase in TMP by 0.025 bar, but also an increase in effluent DOC removal and inside the SAMBR by 10% and 20%, respectively. Powdered Activated Carbon (PAC) addition resulted in a TMP decrease of 0.070 bar, and a 30% and 5% increase in DOC removal inside the SAMBR and effluent, respectively.The mechanisms of anaerobic biomass under high salinity were studied by investigating the role of compatible solutes, extracellular polysaccharides (EPS), and Archaeal microbial evolution. Glycine betaine was found to have the most positive effect on anaerobic biomass when added to medium with high salinity. This was found not only in batch experiments, but also in continuous ones using a SAMBR. The effluent composition from the SAMBR treating saline wastewater was analysed, and post treatment strategies using mainly PAC were analysed. The treatment of this effluent with 1.7 g PAC/L can lead to greater than 80% DOC removal. The treatment of wastewater with high salinity and Cr (III) in a system consisting of a SAMBR, an aerobic Memebrane Bioreactor (MBR) and a PAC column was examined. The system obtained 95% and 70% removal of Cr (III) and Chemical Oxygen Demand (COD), respectively. Using molecular techniques inside the SAMBR, species were identified that were capable of surviving in high salinity and Cr (III). In a short-period experiment, relaxation, liquid backwash and gas backwash techniques were compared and showed the superiority of gas backwashing to reduce fouling of the membrane. The specific resistances of a membrane operated for 100 days in the SAMBR showed that more than 90% of the total resistance was attributed to the biofilm cake layer, about 5-7% to the compounds attached on the membrane surface and about 3% to the membrane resistance and to the compounds in the inner pores of the membrane.