Nonwoven Modification And Its Application In Membrane Bioreactor Process

Wastewater reclamation is an efficient way to reduce fresh water consumption and environment protection. Membrane bioreactor（MBR）, which is a wastewater treatment technology, has been developed potentially. However, high membrane cost, intensive energy consumption, and serious membrane fouling have limted its further development. Therefore, low-cost coarse nonwoven was used as filtration materials insteaded of traditional membranes. However,nonwoven had membrane fouling problems and that it is generally poor in solid retention capicaty. Therefore, it is necessary to modify it.In this study, to enhance its antifouling property and effluent water quality, dynamic membrane and hydrophilic modification are applied. Diatomite-polyvinyl alcohol（PVA）, diatomite-iron oxide and ferric chloride nonwoven are used to modify nonwoven. The properties of modified and original samples are characterized by contact angle, Fourier transform infra red spectroscopy（FTIR）, scanning electron microscope（SEM） and tensile strength,et al. Original and modified nonwoven were applied in MBR system, respectively. The main contents are included in the following four aspects:（1） Original nonwoven is used in MBR system. Three operation modes of internal pressure, external pressure and anaerobic/aerobic（A/O） are used, respectively. Results showed that “external pressure” diatomite-nonwoven MBR system had membrane fouling. “Internal pressure” operation system had stable states and almost had no water head loss. “A” unit of A/O nonwoven MBR system also had membrane fouling problem, which made it hard to be applied.（2） Nonwoven is modified by diatomite-PVA. Contact angle of the modified nonwoven decreased from 112.71? to 53.83?. The comprision results of MBR wastewater reclamation systems showed that when the flux was 6.2-16.5 L/m² h, the modified nonwoven MBR system had stable perfoemance and good antifouling properties. Average effluent COD and NH₄⁺-N concentrations could be reduced to less than 45 and 2.5 mg/L, respectively. However, this method is complex and modification reagent expense is relatively high, which made it diffcult for large-scale application.（3） Nonwoven is modified by coating diatomite/iron oxide. Its contact angle decreased from 122.66° to 39.33°. When the flux was 18 L/m² h, modified nonwoven MBR system had stable operation, whiles the original one had membrane fouling. The two systems had good performance in removal COD, NH₄⁺-N, chromaticity and turbidity, which could meet the standard for wastewater reclamation. However, this modification method can not change the properties of nonwoven fiber. Diatomite-iron oxide attached on nonwoven surface could be removed easily.（4） Nonwoven is modified by ferric chloride. Results revealed that nonwoven fiber had partially rupture phenomenon and contact angle reduced greatly. Modified nonwoven MBR system could be operated in three different fluxes(14.5 L/m² h,20.5 L/m² h and 41 L/m² h) for more than 3 months without water head loss. Average effluent COD, NH₄⁺-N, NO₃⁺-N and NO₂⁺-N concentrations were 27.38 mg/L, 1.02 mg/L, 10.19 mg/L and 0.015 mg/L,respectively,which showed that the system had perfect treatment efficiency. The effluent Fe and Mn ion concentrations are relatively low（0.04 mg/L and 0.02 mg/L）. They all could meet the standards of wastewater reclamation.