Specific membrane bioreactor systems for municipal wastewater treatment and reuse
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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- This study is to evaluate and investigate the ability of specific membrane bioreactor systems in municipal wastewater treatment and reuse. The performance of up-flow sponge bioreactor, fluidised bed bioreactor (FBBR) with and without aerobic sponge reactor, and membrane bioreactor was separately investigated in the first stage of this study. The second part includes the evaluation of submerge membrane bioreactor and membrane bioreactor hybrid system integrated sponge bioreactor and/or fluidised bed bioreactor as a pre-treatment for membrane bioreactor. The effects of polyurethane sponge size and type on the performance of an up-flow sponge bioreactor were studied. Three different sponge cube sizes ( 1 x 1 x 1 cm, 2 x 2 x 2 cm and 3 x 3 x 3 cm) and four types of sponge (S28-30/45R, S28_30/60R, S28-30/80R and S28_30/90R) were investigated. The results indicate that there was no significant difference in the organic and nutrient removal rates between sponge types while the medium size sponge performed the best in terms of both biomass growth and pollutant removal. Under anaerobic conditions, the COD, T-N and T-P removal efficiencies were up to 70%, 45% and 55%, respectively, and significantly improved under aerobic conditions (e.g. > 90% DOC, 95% COD, 65% T-N and 90% T-P). Another 1ype of sponge bioreactor was also introduced, namely an attached growth sponge tray bioreactor (STB).At short hydraulic retention time (HRT) of 40 minutes, the STB could remove up to 92% of DOC and 40-56% of T-N and T-P at an organic loading rate (OLR) of 2.4 kg COD/m3sponge.day. This OLR also appeared to be the best for the STB as compared to the OLRs of 0.6, 1.2 and 3.6 kg COD/m3sponge.day. At 28 mL/min of flow velocity, STB achieved the highest efficiencies with 92% of DOC, 87.4% ofT-P, and 54.8% ofT-N removal. The anaerobic - aerobic FBBR (AAFBBR) coupled with granular activated carbon (GAC) could remove almost 95% of DOC. The highest nutrient removal efficiencies (75.4% P04-P and 70.4 % NH4-N) were achieved at organic loading rate (OLR) of 43.2 kg COD /m3.d. This OLR operating condition also resulted in the highest specific oxygen uptake rate (SOUR) and the amount of biomass attached on aerobic and anaerobic GAC. From the critical flux and modified fouling index (MFI) experiments, it was found that at OLR of 43.2 kg COD /m3.d, the AAFBBR could reduce membrane fouling which was evident from the higher critical flux (20 L/m2.h) and lower MFI (3.7 x 104 s/L2) achieved. A novel GAC-sponge FBBR was also investigated. The results indicate that during 30 days of operation, the FBBR could remove more than 95% of DOC and COD. The highest nutrient removal efficiencies of 74% P04-P and 65 % NH4-N were also achieved at day 7. After 30 days, membrane fouling was investigated by conducting critical flux experiments. The critical flux value was higher in the new FBBR (30 and 35 L/m2.h) as compared to the anaerobic GAC-FBBR only (25 L/m2.h). MBR performance was tested with a new combined inorganic-organic flocculant (CIOF) of FeCh and membrane performance enhancer (MPE5o). This system could remove almost 100% total phosphate while eliminating over 90% NH4-N and DOC during an 80-day of operation. The respiration tests revealed that the SOUR was stable around 1.5-2.0 mg 0 2/g MLVSS.h. The sludge volume index (SVI) of less than 100 mL/g during the operation showed the importance of CIOF on the improvement of settling properties of the sludge. Soluble carbohydrate concentration was also well correlated with DOC of the supernatant. CIOF was successful in the reduction of fouling of membrane as the membrane was only chemically cleaned after 53 days of operation. When STB was combined with MBR as a pre-treatment, the system could remove 95% of DOC, 83.6% ofNH4-N and 75.5% of P04-P. The SVI ofless than 100 mL/g during the operation indicated the good settling property of the sludge. The pilot-scale MBR hybrid system was experimented at Sydney 0 lympic Park to treat a municipal wastewater. The results showed that the system could successfully remove 92% of organic carbon and 95% of NH4-N. The system can also control the trans-membrane pressure (TMP) development at a significant low rate of 0.65 kPa/day. This result indicated that using new FBBR with aerobic sponge reactor as a pre-treatment for MBR is a promising method for reducing membrane fouling.
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