Full-scale anaerobic treatment during more than 2
years confirmedthe results obtainedin the laboratory,
being possible to operate at moderate OLR (around 5–
6 kg COD/m3
d), maintaining COD removal efficiencies
higher than 90%. The suitability of AF reactors to treat
these effluents is clear, since no sludge flotation was
observed as could be expected. This indicates that the
biomass might be able to colonise the packing medium
andthat fat containedin raw milk was successfully
degraded, even during long-term operation. Inhibition
problems were only detected when temperature could
not be maintained(due to mechanical failures) or when
the alkalinity supplementation was interrupted. In both
cases, the VFA accumulation couldbe successfully
overcome after a short periodof operation. No purges
of biomass from the anaerobic reactor were necessary
during all operational periods, with the hydrodynamic
conditions imposed on the AF reactor being sufficient to
maintain the solids content of the liquid circulating
through the packing medium stable.
The anaerobic biomass washout was fedto the SBR
reactor andtherefore mixedwith the biomass present in
this unit. The total amount of waste sludges generated in
the whole plant was around2–3 kg VSS/d. The COD
andnitrogen obtainedfor the final effluent of the whole
plant was most of the time below 200 and10 mg/l,
respectively, which was adequate for discharge.