Low energy treatment system for brewery wastewater reuse

A pilot plant consisting of UASB, SBR and microfiltration in series was operated for 15 months to study a low energy treatment option for brewery effluent. The UASB was loaded up to 18 kg/kL.d. However for trouble free operation the loading had to be limited to 14 kg/kL.d. More than 80% of the feed COD was removed in the anaerobic process and a further 60% COD removal was observed in the aerobic process. An air backwashable microfiltration unit was used to remove suspended solids so that the treated water could be reused. The membrane unit was optimised by operating under dead-end, controlled flux conditions (permeate pumping) and air backwashing at set transmembrane pressure (TMP) (in practice the membranes are backwashed at set time interval). Operating energy cost calculations for the membrane system showed that the unit needs to be operated at low flux (say 20 to 30 L/m².h) to have a low energy demand. However this necessitates a large membrane area. Optimisation for capital and energy cost indicates that the unit needs to be operated at more than 60 L/m².h depending on the maximum TMP specified. The system energy balance was also calculated. The energy needed for the operation of all units less the energy gained from methane gas generated indicates that the system could yield a net energy of 2.5 kWh/kL water treated. The treated effluent had a turbidity of less than 1.2 NTU and the BOD5 less than 20 mg/L.