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

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

Salinity effects on biodegradation of Reactive Black 5 for one stage and two stages sequential anaerobic aerobic biological processes employing different anaerobic sludge

In this study the effect of NaCl, normally found in dye bath wastewaters employing reactive azo dyes, on the performance of sequential anaerobic-aerobic processes for treatment of Reactive Black 5 (RB5) containing media, with concentration in the range 100-500mgL-1, was investigated. Three possible scenarios of the sequential anaerobic-aerobic process, namely two stage process and one stage processes employing either anaerobic or activated sludge, were considered. The results showed a statistically significant enhancement of the anaerobic decolourisation efficiency as a result of the addition of 30gL-1 NaCl to the RB5 containing media for two stage processes and one stage processes employing anaerobic sludge. NaCl at 30gL-1 concentration also inhibited aerobic colour formation during two stage processes whereas it prevented aerobic decolourisation during one stage processes. HPLC and UV Vis analysis indicated that during anaerobic phase/stage the majority of azo bonds in RB5 molecules cleave whereas the hydrophobicity/MW of the resulting dye reduction metabolites decreases. The same analysis revealed partial mineralisation of RB5 reduction metabolites under aerobic conditions. The results of the present work also showed that the effect of salt on anaerobic decolourisation efficiency, TVFA and methane production was dependent on the exposure history of anaerobic sludge

Wastewater valorization by pure bacterial cultures to Extracellular Polymeric Substances (EPS) with high emulsifying potential and flocculation activities

Nowadays much effort has been devoted for the development of cost-effective and environmentally friendly processes to obtain extracellular polymeric substances (EPS) with high emulsifying and flocculation activities. The aim of this study was to evaluate the capacity of bacterial strains previously isolated from oil-contaminated areas to produce EPS with high emulsification and bioflocculant properties during cultivation in domestic and bilge wastewater and in industrial crude glycerol. A total of seven bacterial strains were screened for EPS production, from which two strains, Pseudomonas aeruginosa LVD-10 and Enterobacter sp. SW, were selected as potential EPS producers. EPS with high emulsifying capacity in olive oil (a maximum of 96.6 and 89.8% for strain SW and LVD-10, respectively) was produced using bilge wastewater as substrate. EPS with a slightly lower emulsifying capacity was obtained using crude glycerol. In addition, the flocculation activity of the EPS extracted from strains LVD-10 and SW grown on crude glycerol was considerably higher (81.6 and 73.3%, respectively) than that obtained with other substrates. This is the first study that points out that EPS with emulsifying and flocculation potential activity can be produced from bilge wastewater and crude glycerol. The production of biopolymers with broad biotechnological applications using low-cost substrates can be a means to valorise waste streams.info:eu-repo/semantics/publishedVersio

Adaptation of anaerobic biomass to saline conditions: Role of compatible solutes and extracellular polysaccharides

This study investigated the role of compatible solutes, extracellular polysaccharides (EPS), and nutrients on anaerobic biomass when stressed with salinity. When 1 mM of osmoregulants glycine betaine, α-glutamate and β-glutamate were added separately to serum bottles containing biomass not adapted to sodium, and fed with glucose and 35 g NaCl/L, all the compatible solutes were found to alleviate sodium inhibition, although glycine betaine was found to be the most effective. The effect of glycine betaine on different anaerobic bacterial groups under salinity stress was monitored using VFAs, and showed that methanogens were more protected than propionate utilisers. Moreover, the addition of 1 mM of glycine betaine to anaerobic biomass not adapted to salinity resulted in significantly higher methane production rates compared with anaerobic biomass that was exposed for 4 weeks to 35 g NaCl/L. Interestingly, under saline batch conditions when the medium was replaced totally the culture produced less methane than when only new substrate was added due to compatible solutes cycling between the media and the cell. The elimination of macronutrients from the medium was found to have a more pronounced negative effect on biomass under saline compared with nonsaline conditions, and because of the synthesis of N-compatible solutes sufficient nutrients should always be present. On the other hand, the absence from the medium of micronutrients did not further reduce biomass activity under salinity. Finally, a higher production of EPS was obtained from biomass exposed to higher salt concentrations, and its composition was found to change under different saline conditions and time. As a result, biomass under saline conditions had a slightly higher mean flock size compared with the biomass that was not subjected to salt. © 2008 Elsevier Inc. All rights reserved

Chromium removal mechanisms and bacterial community in an integrated membrane bioreactor system

A wastewater with high salinity (35 g NaCl/L) and chromium (0-200 mg Cr/L) was treated with an integrated system of a submerged anaerobic membrane bioreactor (MBR), followed by an aerobic MBR and a powdered activated carbon (PAC) column. The final effluent from the system was generally below 10 mg Cr/L (95% removal), although the chemical oxygen demand removal was not high (70%), possibly because of the inhibition of anaerobic and aerobic biomass by Cr and high salinity. This is the first study that investigated the performance of an integrated system with a synthetic tannery wastewater under variations in both chromium and salinity over 100 days. Molecular techniques detected the presence of certain bacteria in the submerged anaerobic MBR that could survive under both high salinity and chromium concentrations; these findings could be valuable as these bacteria could be isolated and then bioaugmented into an MBR for the treatment of tannery wastewater. The study also examined the distribution of chromium in anaerobic biomass and determined the main chromium removal mechanisms under high salinity. After 24 h of addition, the largest quantity of chromium was removed as a precipitate and the second largest was found in the residual ash of the biomass. High salinity positively affected chromium adsorption by the biomass, but only during the first 5 min. This work is important because it has implications not only for treatment plant design but also for studies on chromium removal by biomass

In situ biogas upgrading and enhancement of anaerobic digestion of cheese whey by addition of scrap or powder zero-valent iron (ZVI)

Cheese whey is an easily biodegradable substrate with high organic matter that can be anaerobically digested to biogas; however, the process is often inhibited by excess acidification due to the presence of undissociated volatile fatty acids and requires considerable concentration of alkaline buffer. The current study investigates a new approach for biogas upgrading, and increase of total CH4 in conjunction with buffering acidification by using zero-valent iron (powder and scrap metals at concentrations 25, 50, and 100 g/L) in anaerobic granular sludge and cheese whey under mesophilic batch conditions. During the first 2 cycles (total 34 days), a high performance was found in anaerobic bottles with 25 g/L powder zero valent iron (PZVI) and 50 g/L scrap zero valent iron (SZVI) since they had a higher total CH4 production compared to anaerobic bottles free of ZVI, as well as 97% CH4 composition in produced biogas compared to 74% CH4 for anaerobic bottles free of ZVI. Under these conditions, no additional NaOH was added to anaerobic bottles with 25 g/L PZVI and 50 g/L SZVI to increase the pH and at the end of 2nd cycle the concentration of VFAs was substantially lower compared to the anaerobic bottles free of ZVI. However, no positive effects of ZVI in terms of alkaline buffer were found at the 3rd and 4th cycle probably due to ZVI inactivation outer surface layer. Based on the experimental findings (anaerobic bottles: (a) 25 g/L PZVI, (b) 50 g/L SZVI and (c) free of ZVI) an economic comparison for anaerobic digestion of cheese whey by large scale was contacted and pointed out that the best scenario was the anaerobic digestion by addition of 50 g/L SZVI, followed by anaerobic digestion free of ZVI and last was the anaerobic digestion by addition of 25 g/L PZVI. This study highlights a new proof of concept for in-situ biogas upgrading and alleviation of acidification by addition of 50 g/L SZVI or 25 g/L PZVI during anaerobic digestion of cheese whey

A modified method for the determination of chemical oxygen demand (COD) for samples with high salinity and low organics

This study proposes a modification to the standard method for the determination of the chemical oxygen demand of samples with a salinity up to 40 g NaCl/L and low organic concentrations (20-230 mg COD/L). The masking of chloride by the use of a HgSO4:Cl ratio of 20:1 prior to digestion, and the use of 3 g K2Cr2O7/L in the digestion solution resulted in an error of less than 10% and 12% for samples containing 40 g NaCl/L at 20-190 mg COD/L and 230 mg COD/L, respectively. Comparison of the standard method with the new proposed method using a synthetic sewage highlights the large errors (50-85%) of the standard method in contrast to an error of less than 10% for the proposed modified method