Influence of step increases in hydraulic retention time on (RS)-MCPP degradation using an anaerobic membrane bioreactor

Mechanism of cell proliferation during starvation in a continuous stirred tank anaerobic reactor treating food waste

Anaerobic digestion is a mature technology; however, the mechanism of cell proliferation during starvation has not yet been clarified. In this study, a continuous stirred tank reactor (CSTR) treating food waste was exposed to deliberate starvation for 12 days. The cell density and the variability of digestate characteristics during starvation were monitored. Starvation increased cell density from 2.8 × 10¹⁰ to 7.9 × 10¹⁰ cells mL^-1 within 2 days and reduced the residual substrate. This increase in cell density was suggested owing to a switch of the anaerobic digester microorganisms' substrate preference to the complex fractions because the easily digestible fractions were exhausted. The prolonged starvation of more than approximately 3-6 days induced an increase in the free ammonia concentration to an inhibitive level of more than 0.10 g-N L^-1 for anaerobic digestion microorganisms due to the excessive ammonification of residual nitrogen, thereby resulting in a drastic decrease in cell density. Our results demonstrated that a deliberate starvation operation in an appropriate timeframe applied to a CSTR treating food waste is beneficial to proliferate cells and, at the same time, reduce residual substrate.

Anaerobic membrane bioreactor (AnMBR) for bamboo industry wastewater treatment

Bamboo industry wastewater (BIWW) poses severe environmental problems because of its high organic matter content. In this study, anaerobic membrane bioreactor (AnMBR) was applied for BIWW treatment. During the start-up stage, the system presented an effective degradation with a final COD removal of 91%. Compared to the intermittent mode, a higher membrane rejection (45% COD, 60% NH3-N) was obtained when the system was operated continuously. N2 flushing was applied for membrane cleaning, and the cleaning efficiency was significantly influenced by the hydraulic retention time (HRT). While operated under HRT ≥ 5 d, membrane fouling could be effectively controlled. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis indicated the membrane top area suffered the most serious fouling. Gel permeation chromatography (GPC) and gas chromatography-mass spectrometry (GC-MS) analyses revealed most organic matter in BIWW was eliminated by AnMBR. However, benzene and fluoro derivatives were detected in the permeate as the by-products.

Effect of Mecoprop (RS)-MCPP on the biological treatment of synthetic wastewater in an anaerobic membrane bioreactor

The effects of Mecoprop (RS)-MCPP were investigated in an anaerobic membrane bioreactor (AnMBr) fed with synthetic wastewater containing stepwise increases in Mecoprop concentration, 5-200 mg L(-1) over 240 days. Effects were observed in terms of soluble chemical oxygen demand (COD) removal efficiency, volatile fatty acid (VFA) production, and methane yield. Soluble COD removal efficiency was stable at Mecoprop concentrations below 200 (±3) mg L(-1), with an average of 98 (±0.7)% removal. However, at 200 (±3) mg L(-1) Mecoprop, the COD removal efficiency decreased gradually to 94 (±1.5)%. At 5 mg L(-1) Mecoprop, acetic and propionic acid concentrations increased by 60% and 160%, respectively. In contrast, when Mecoprop was increased to 200 (±3) mg L(-1), the formation and degradation of acetate was unaffected by the higher Mecoprop concentration, acetate remaining below 35 mg L(-1). Increases in the Mecoprop specific utilization rate were observed as Mecoprop was increased stepwise between 5 and 200 mg L(-1).

Effect of organic loading rate on organic matter and foulant characteristics in membrane bio-reactor

In this study, the influence of organic loading rate (OLR) on the performance of a membrane bio-reactor (MBR) was investigated. The MBR was operated with 6 different OLRs between 0.5 and 3.0 kg COD/m(3)d. The hydrodynamic parameters of the MBR were kept constant. The hydraulic retention time and sludge retention time were kept at 8h and 40 d respectively. From the experimental investigation, it was found that the removal efficiency of DOC, COD and NH(4)-N decreased when OLRs were increased from 0.5 to 3.0 kg COD/m(3)d. Higher OLRs of 2.75-3.0 kg COD/m(3)d resulted in a higher transmembrane pressure development. The fractionation of organic matters showed more hydrophilic substances with higher OLRs. A detailed organic matter characterization of membrane foulant, soluble microbial product and extracellular polymeric substances showed that bio-polymers type substances together with humic acid and lower molecular neutral and acids were responsible for membrane fouling.

Impact of the herbicide (RS)-MCPP on an anaerobic membrane bioreactor performance under different COD/nitrate ratios

The degradation of (RS)-MCPP was investigated in an anaerobic membrane bioreactor (AnMBR) using nitrate as an available electron acceptor under different COD/NO(3)(-)-N ratios. Results showed high soluble COD removal efficiency (80-93%) when the reactor was operated at high COD/NO(3)(-)-N ratios. However, the COD removal started to decline (average 15%) at high nitrate concentrations coinciding with a drop in nitrate removal efficiency to 37%, suggesting that the denitrification activity dropped and affected the AnMBR performance when nitrate was the predominant electron acceptor. Additionally, the removal efficiency of (RS)-MCPP increased from 2% to 47% with reducing COD/NO(3)(-)-N ratios, whilst the (RS)-MCPP specific utilisation rate (SUR) was inversely proportional to the COD/NO(3)(-)-N ratio, suggesting that a lower COD/NO(3)(-)-N ratios had a positive influence on the (RS)-MCPP SUR. Although nitrate had a major impact on methane production rates, the methane composition was stable (approximately 80%) for COD/NO(3)(-)-N ratios of 23 or more.