Anaerobic digestion of wool scouring wastewater in a digester operated semi-continuously for biomass retention

An anaerobic digester, operated semi-continuously in order to retain high concentrations of biomass in the digester, was used to treat wool scouring wastewater. At a space load of 9·9 kg COD m⁻³ day ⁻¹ (hydraulic retention time, 2·8 days) >56% of the COD and >47% of the grease were removed. At these efficiencies, this rate was estimated to be at least 2·5·3· times greater than that which would be achieved in a continuously stirred digester. Preliminary studies of enzymatic pretreatment of the scouring effluent showed that significantly improved treatment rates and/or efficiencies could be achieved—i.e. >70% removal of both the COD and grease at a space load of 12 kg COD m⁻³ day⁻¹. It is unlikely that any substancial levels of flocculation would develop in this system and it is expected that the moderate use of polyelectrolytes would be required to help maintain the VSS concentration in the reactor.