Waste water treatment by a combination of bioreactor and nanofiltration

Abstract

A new hybrid process has been developed and tested for the treatment of dumpsite leachate, a highly contaminated multicomponent waste water. The process consists of an activated sludge bioreactor, a nanofiltration stage and chemical oxidation or adsorption. The essential feature of the process is the recycling of the nanofiltration concentrate into the bioreactor. Due to the selectivity of nanofiltration membranes, the concentrations especially of recalcitrants in the loop are significantly increased, which in turn results in a higher rate of biodegradation without increasing the hydraulic residence time. Non-biodegradable components are removed from the system via nanofiltration permeate, excess sludge or chemical oxidation or adsorption on activated carbon. Compared to a straightforward process bioreactor/ chemical oxidation or bioreactor/adsorption, the specific consumption of oxidant or activated carbon of the new process is significantly lower. Pilot plant tests on four dumpsites, each over a period of several months, demonstrated the reliability of the process and confirmed our expectations with respect to specific consumptions. Observation of the nitrification, which is very sensitive to toxic components, confirmed that the biology was not affected by the substantially increased levels of rejected components of the nanofiltration. Compared to the straightforward process, the elimination rate of the bioreactor — ζ= 1 -( COD permeate)/ COD leachate) — was increased between 9% and 17%. We are convinced that this new process is not confined to the treatment of leachate but is applicable for a variety of industrial waste waters.