A review of quality and biological treatment of landfill leachate is presented. Conventional ex-situ treatment normally demands multistage process treatment schemes, which may encompass both aerobic and anaerobic technologies alongside chemical precipitation and/or oxidation. This is to be contrasted with the more recent membrane bioreactor technology, which generally demands much reduced preand post-treatment and has a much reduced footprint compared with conventional biotreatment. Results are summarised in terms of the key determinant of COD removal for waters characterised in terms of BOD/COD ratio and age. Process operation is characterised with respect to COD strength and loading rate, hydraulic retention time and number of individual unit operations.

As with all membrane processes, turbulence, as promoted by aeration in submerged membrane bioreactors (MBRs) or pumping in sidestream (SS) systems to produce somewhat higher effective cross-flow velocities, increases mass transfer and reduces fouling. This is manifested in an elevated critical flux, the flux at which the membrane permeability is sustained. However, the non-Newtonian nature of the sludge makes precise rheological characterisation difficult. In this study, a calculation of the appropriate hydrodynamics parameters for a SS MBR configuration is presented. Optimisation of the aeration in a submerged MBR system has been attained by defining the minimum air velocity required for Taylor bubble formation.

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The effect of extracellular polymeric substances and soluble microbial products developed from wastewater and mature landfill leachate biomass was assessed using a pilot-scale membrane bioreactor operating polymeric and ceramic air-lift sidestream multichannel membranes. The plant was operated under identical conditions of sludge retention time, system hydrodynamics ,and parity of food-to-microorganism ratios. Biomass samples were extracted and fractionated (fixed and bound material, carbohydrate and protein extracts) and chemically and physically analyzed with the feedwaters. Both ceramic and polymeric membranes were tested and the critical flux (J C ) determined according to the classical flux-step analysis. Although permeability (K) of both materials reduced with increasing flux (J), the ceramic material had a higher resistance to fouling, demonstrating a higher K (by a factor of 1.2 and 3.2 for wastewater and leachate, respectively, at J of 30 L Á m 22 Á h 21 ) and lower fouling rate (dP/dt) (by more than an order of magnitude at the same J) than the polymeric membrane. Evidence suggests that deterioration of membrane permeability resulting from leachate biomass arises from the feedwater itself, rather than the products derived from the biomass, and that colloidal and/or soluble total organic carbon is primarily responsible for it. Water Environ. Res., 80, 2193Res., 80, (2008.

The fouling potential of membrane bioreactor biomass developed from sewage and mature landfill leachate feedwaters was assessed using a pilot scale Membrane Bioreactor (MBR) operating polymeric and ceramic air-lift sidestream multi-channel membranes. The plant was operated under identical conditions of sludge retention time, system hydrodynamics and parity of F/M ratios. Biomass samples were extracted and fractionated (fixed and bound material; carbohydrate and protein extracts) and chemically and physically analyzed, along with the feedewaters. Both ceramic and polymeric membranes were tested and the critical flux determined according to the classical flux-step analysis. Although permeability (K) of both materials reduced with increasing flux (J) the ceramic material had a higher resistance to fouling, demonstrating a higher K (by a factor of 1.2 and 3.2 for sewage and leachate respectively at J of 30 L.m -2 .h -1 ) and lower dP/dt (by more than an order of magnitude at the same J) than the polymeric membrane. Evidence suggests that the high fouling propensity of the leachate biomass arises from the feedwater itself, rather than the products derived from the biomass, and that colloidal and/or soluble TOC represents the principal foulant.