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.

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