Membrane Filtration And Fouling Behavior For Domestic Wastewater Effluent Organic Matters

As the major pollutants to be removed for wastewater reuse, effluent organic matters(EfOM) have its own properties, including complex components and vaied extent of humification. Recently, membrane filtration, especially pressure-driven ultrafiltration(UF) and nanofiltration(NF), obtained increasingly concerns due to advantages beyond conventional wastewater reclamation technologies, such as stable effectiveness in pollutants removal, small footprint and easy-manipulation. However, continuous flux decline with filtration constrains membrane filtration application significantly. In the present work, comprehensive comparative analysis of EfOM and its components and properties, were carried out to unveil correlation with flux decline of UF and NF. After indentification of major components and properties of EfOM controlling membrane flux decline, a fouling indicator, names as florescence-size index(FSI), was proposed to imply the fouling propensity of EfOM, and to give direct guideline for pre-treatment selection and optimization. The results obtained herein would be very useful for understanding of EfOM initiated flux decline and to instruct membrane filtration application.Comparative analysis on EfOM components and properties were carried out to evaluate their correlation with membrane flux decline in UF and NF. The experiments indicated that the applied secondary bio-chemical processes had insignificant impact onto EfOM content and compositions, which mainly comprised of humic-like substances, followed by soluble organism metabolites and fulvic-like substances. From the molecular weights distribution determination, EfOM contained two major components with MWD larger than 100 k Da and smaller than 5 k Da, while majority of components are small molecule organic matters(<1 k Da) with humic-like properties. The abundance of hydrophobic components in EfOM that mainly comprised of humic-like and fulvic-like substances were consistently higher compared with those of hydrophilic components, which were mixture of soluble organism metabolites and aromatic hydrocarbon protein. Notwithstanding, sludge retention time(SRT) in wastewater treatment process displayed eventually effect onto EfOM content and composition, as that an increased SRT resulted in a graduate elevation trend of soluble organism metabolites content within EfOM.Constant-pressure mode filtration tests were conducted to reveal the real components or properties of EfOM controlling membrane flux decline in UF and NF. The results suggested that during NF separation of EfOM combine with FSI factor anaysis, the pollutants which represented by soluble organism metabolites and humic-like substances were closely related to the flux deline. Macromolecular organic matters of hydrophilic components took major responsible for the quick flux decline in early-stage, the major reasons for these results were that NF flux decline mainly resulted from deposition of hydrophilic soluble organism metabolites on non-porous NF surface. For the whole flux decline, small molecular humic-like of hydrophobic substances affect flux profile throughout the filtration. During UF separation of EfOM, macromolecular organic matters acted as the main factors governing UF flux decline, and its hydrophobic components preferentially led to UF flux decline, while hydrophobic substances would narrow or clog UF membrane pore. The analysis results from colony and PCR-DGGE displayed that biofouling caused by EfOM on UF membrane surface was severe compared with those of NF, and continuous permeate production in UF accompanied with an increasing of biomass density and bacterial community diversity of biofouling layer.On the basis of correlation of EfOM with flux decline and biofouling behavior, the major components characterizing indicator for fouling propensity of EfOM on NF were determined, named as fluorescence-size-index(FSI). After stepwise multi-variables regression, the FSI comprised mainly of small MW hydrophobic substances and related closely with EfOM fouling propensity could be obtained. This FSI number not only provide an indicator to evaluate the EfOM fouling propensity, but also guide the selection and optimization of NF pre-treatment method.