Several methods were compared to treat heat treatment liquor on a municipal wastewater treatment plant, to reduce loading and allow upgrading.
To ensure low suspended solids in the return flows, granular anaerobic filters were chosen in parallel with membrane treatment:
an upflow wood-based charcoal anaerobic filter
an upflow floating polystyrene anaerobic filter
an aerobic reactor (activated sludge) coupled with microfiltration.
Very similar loading rates and removal efficiency was obtained with the anaerobic filters; they allow to treat highly concentrated effluents in a detention time of 10 h but COD removal efficiency was limited to 60%.
The higher contact time of up to 7 days in aerobic treatment, coupled with microfiltration, achieves elimination of 85% of COD and 95% of BOD. Nevertheless, loading rates and biomass concentrations remained low and flux on the membranes was heavily restricted.