Characterization of the DOC in nanofiltration permeates of a tertiary effluent

In order to develop a feasible technology for a safe ground water recharge with treated waste water, quality and characteristics of four different nanofiltration (NF) permeates were investigated for separation of organic constituents in the treated tertiary effluent. To avoid high fouling and scaling potentials during the membrane process, we also used NF membranes with larger pore size, and with a molecular weight cut-off (MWCO) in the range of several thousands g•mol−1. Adsorption behavior on powdered activated carbon (PAC) of the dissolved organic carbon (DOC) permeating through these membranes was significantly better than that of the feed waters (tertiary effluent and microfiltered tertiary effluent). A numerical analysis of the adsorption isotherm data according to the Ideal Adsorbed Solution Theory (IAST) confirmed these results. Size exclusion chromatography (SEC) prooved that the reduction rate for adsorptive removal of DOC from NF permeates increases with decreasing molecular weight. In the feed water DOC adsorption on PAC is negatively influenced by humic substances (HS). As well as the adsorptive removal of DOC by PAC, soil aquifer treatment (SAT) showed similar DOC removal rates in the low molecular range and therefore offers a promising option by combining “large pore” NF-membrane filtration with conventional SAT for more effective DOC removal with the aim of an artificial ground water recharge.