A comparative study on membrane fouling alleviation mechanisms by using nanoscale Fe3O4 and poly dimethyldiallylammonium chloride

Membrane bioreactor (MBR) has become a promising technology for wastewater treatment. However, membrane fouling frequently occurred which greatly increased operational expense. Two different membrane fouling alleviation mechanisms were explored in this study. Addition of poly dimethyldiallylammonium chloride (PDMDAAC) facilitated formation of flocs-flocs aggregates, which were more adaptable to the changing environment, resulting in less soluble microbial products (SMP) secretion. However, PDMDAAC lose activity gradually, and had a less sustainable effect on membrane fouling alleviation. Nanoscale Fe₃O₄ was applied to alleviate membrane fouling, and membrane sustainable filtration cycle extended 2-fold compared to the control group. Results showed that dehydrogenase activity in the reactor with optimal addition of nanoscale Fe₃O₄ increased 2.86 ± 0.11 times compared to control group. SMP (especially tryptophan protein-like substances) decreased to 9.79 ± 1.34 mg L^-1 with the addition of nanoscale Fe₃O₄, which was lower than that in the control group (15.31 ± 0.53 mg L^-1). It's speculated that nanoscale Fe₃O₄ performed as conductive material, which intensified interspecies electron transfer. The sludge dehydrogenase activity was then enhanced, which facilitated the utilization and microbial degradation of SMP, suppressing membrane fouling consequently.

Impact of static biocarriers on the microbial community, nitrogen removal and membrane fouling in submerged membrane bioreactor at different COD:N ratios

The polyvinyl formal (PVFM) biocarrier addition in a membrane bioreactor (MBR) was evaluated at high and low carbon/nitrogen (C/N) ratio of 20.0 and 6.7. Results indicated that static biocarrier addition could enrich nitrification and denitrification bacteria, dominating by Tauera, Amaricoccus and Nitrosospira at the genus level and slightly improved the total nitrogen removal even at a low C/N ratio. The bulk sludge characteristics (such as bigger particle size, lower SMP, lower SMP P/C) were also significantly changed in the hybrid MBR (HMBR), leading to a more sustainable membrane operation. The biocarrier addition also reduced the relative abundance of Sphingobacterials_unclassified, Ohtaekwangia and Rhodocyclaceae_unclassified at the genus level, indicating less membrane fouling in the HMBR. Consequently, HMBR with static PVFM addition could partially overcome the drawback of low C/N ratio for total nitrogen removal and membrane fouling control, providing a more resilient MBR to the undesirable environment such as low C/N ratio.

Impact of poly dimethyldiallylammonium chloride on membrane fouling mitigation in a membrane bioreactor

Poly dimethyldiallylammonium chloride (PDMDAAC) was applied in a membrane bioreactor (MBR) to study its effects on mitigation of MBR membrane fouling. Floc size, zeta potential, soluble microbial substances (SMP) and extracellular polymeric substances (EPS) secretion were studied with respect to PDMMAAC-dosing operations. Results demonstrated that a sustainable filtration cycle extended 3.3 times with the optimal PDMDAAC dosage of 90 mg L^-1. The addition of PDMDAAC could increase zeta potential of sludge floc, which led to the decrease in repulsive electrostatic interactions between flocs, as well as the facilitation of flocs-to-flocs aggregation. With the optimal dosage of PDMDAAC, the mean size of sludge was 3.23 ± 0.55 times higher than the control group, resulting in higher impact resistance and better adaptive capacity to the changing environment, which led to less SMP secretion. Moreover, a high contaminants removal rate was achieved in the reactor that was dosed with PDMDAAC. The average effluent concentrations of chemical oxygen demand and total nitrogen were less than 45.6 ± 2.85 and 5.23 ± 0.61 mg L^-1, respectively, and the corresponding removal rates were 93.1 ± 5.81% and 89.1 ± 9.61%.

Degradation of chloramphenicol by potassium ferrate (VI) oxidation: kinetics and products

The oxidation of chloramphenicol (CAP) by potassium ferrate (VI) in test solution was studied in this paper. A series of jar tests were performed at bench scale with pH of 5-9 and molar ratio [VI/CAP] of 16.3:1-81.6:1. Results showed that raising VI dose could improve the treatment performance and the influence of solution pH was significant. VI is more reactive in neutral conditions, presenting the highest removal efficiency of CAP. The rate law for the oxidation of CAP by VI was first order with respect to each reactant, yielding an overall second-order reaction. Furthermore, five oxidation products were observed during CAP oxidation by VI. Results revealed that VI attacked the amide group of CAP, leading to the cleavage of the group, while benzene ring remained intact.