Characterisation of the impact of coagulation and anaerobic bio-treatment on the removal of chromophores from molasses wastewater

The performance of a coagulation sequence using aluminium chlorohydrate (ACH) and a low MW 34 polydiallyldimethylammonium chloride (polyDADMAC), and ferric chloride, for decolourising a high35 strength industrial molasses wastewater was compared at bench scale. At their optimum dosages, 36 ACH/polyDADMAC gave higher colour removal than FeCl3 (45% cf. 28%), whereas COD reduction 37 was similar (~30%), indicating preferential removal of melanoidins (a major contributor to the 38 colour) by ACH/polyDADMAC. Size exclusion chromatography and fluorescence excitation39 emission matrix spectrometry suggested that chromophoric Fe-organic complexes were formed 40 during FeCl3 treatment of the molasses wastewater, which appeared to compromise 41 decolourisation efficiency. Anaerobic bio-treatment of the wastewater enhanced the coagulation 42 efficiency markedly, with FeCl3 achieving 94% colour and 96% COD removal, while 43 ACH/polyDADMAC gave 70% and 56% removal, respectively. The improved decolourisation was 44 attributed to the decrease in low MW organics (< 500 Da) and biopolymers by the biological 45 treatment, leading to reduced competition with melanoidins for interaction with coagulant/flocculant. 46 For both the wastewater and biologically treated wastewater, ACH/polyDADMAC treatment gave 47 flocs with markedly better settling properties compared with FeCl3.