Abstract
This study aimed to evaluate the impact of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) in municipal wastewater treatment. The results showed that organic removal efficiencies were above 94% at all C/N conditions. Nutrient removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and accumulation of extracellular polymeric substances (EPS) in the mixed liquor and sludge cake as a result of deteriorated granular quality. Foulant analysis suggested significant difference existed in the foulant organic compositions under different C/N ratios, and humic substances were dominant when the fastest fouling rate was observed. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5.
Highlights
Granular anaerobic membrane bioreactors (G-AnMBRs) offer a promising opportunity to transform conventional municipal wastewater plants into net producers of renewable energy with significantly reduced sludge handling costs and energy demand while occupying a small footprint (Chen et al, 2017a)
The results suggested that decreasing C/N ratio from 100/5 to 100/10 did not adversely influence the organic removal since complete retention of all particulate chemical oxygen demand (COD) and macromolecular COD components was achieved by the membrane and most of the readily biodegradable COD was removed by aerobic and anaerobic biodegradation (Martinez-Sosa et al, 2011)
Stable NH4-N removal (Table 1) over 92.5% was observed in spite of varying C/N ratios in influent, because the population of autotrophic nitrifying bacteria was not impacted by the change of C/N ratios (Lin et al, 2016)
Summary
Granular anaerobic membrane bioreactors (G-AnMBRs) offer a promising opportunity to transform conventional municipal wastewater plants into net producers of renewable energy with significantly reduced sludge handling costs and energy demand while occupying a small footprint (Chen et al, 2017a). Martin-Garcia et al (2011) successfully applied a G-AnMBR, and reported that the G-AnMBR had much slower fouling than the C-AnMBR because the G-AnMBR sludge had a lower mixed liquor suspended solids (MLSS) and 50% less of soluble microbial products (SMP) than those of the C-AnMBR. Sponge media could positively affect the concentration and properties of microbial products (e.g. SMP and extracellular polymeric substances (EPS)) in granular sludge, cake layer as well as settling zone mixed liquor, and reduce fouling resistance by 50.7%, thereby alleviating membrane fouling
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