Effective reductions in colour456nm, and UV254 and 280nm, (?0 % ) were achieved by coagulation using alum (1860 ppm). However, during ASB treatment, colour456nm increased (>100 % ) in both simulations. HPSEC analysis showed that removal of HMW (>3000 Da) was achieved through coagulation with the simultaneous removal of LMW (<300 Da) in the ASB simulations. Subsequent to the removal of HMW and LMW, an increase of intermediate-range compounds (300?000 Da) occurred. Solid-state 13C NMR analysis indicated some selective removal of aromatic and alkyl groups during the coagulation process and additional removal of aromatic C during ASB treatment.
The slightly higher proportion of HMW (>1000 Da) in ¡®A?than ¡®B?and the slightly higher proportion of aromatic C and alkyl groups remaining in the effluent of ¡®A?might be the basis for differences in the colour development in the two ASB simulators. The low nutrient loading (external) in the pre-treated wastewaters has been shown to be sufficient to sustain microbiological growth of organisms that contribute to colour formation with ASB treatment. This occurred in both simulations and it was concluded that the manipulation of the BOD:N:P ratio to optimise BOD removal had little effect on colour removal. This paper provides insight on the nature of recalcitrant organic compounds causing colour formation.