REMOVAL OF MELANOIDINS FROM AN INDUSTRIAL WASTEWATER T.Nguyen 1 , L. Fan 1 , F.A. Roddick 1,2 1. School of Civil, Environmental and Chemical Engineering, RMIT University, Melbourne, VIC 3001 2. Corresponding author: Tel: +613 9925 2080, fax: +613 9925 3746. (E-mail: felicity.roddick@rmit.edu.au ) ABSTRACT Melanoidins are high molecular weight polymers that contribute a dark brown colour and high organic load to some industrial effluents and result from reactions between sugars and amino acids, peptides or proteins (Maillard reaction). The objectives of this laboratory scale study were to investigate the feasibility of a range of processes, separately, or in combination as appropriate, for the removal of colour from a melanoidin-containing wastewater. The effectiveness of coagulation with a range of organic and inorganic coagulants, membrane filtration, ozonation and UVC/H 2 O 2 treatment for colour removal was investigated. INTRODUCTION Melanoidin-containing wastewaters are produced by industrial fermentation processes which employ molasses, such as alcohol and baker’s yeast production. Melanoidins are high molecular weight polymers that contribute a dark brown colour and high organic load to effluents (González et al., 1999). The formation of melanoidins is via a series of consecutive and parallel chemical reactions between amino compounds and carbohydrates during the Maillard reaction (Kim et al., 1985; Cämmerer and Kroh, 1995). The chemical properties of melanoidin are similar to those of humic substances, being acidic, polymeric and highly dispersed colloids which are negatively charged due to the dissociation of carboxylic and phenolic groups (Migo et al., 1993). The colour, nitrogen content and carbon content are determined by the degree of polymerisation (Motai, 1974), aromaticity and saturation (Cämmerer and Kroh, 1995) that occurs as a result of the reaction conditions (ie. temperature and formation time). Melanoidins are resistant to biodegradation (Zhou et al., 2008) thus the brown colour is not readily removed by conventional biological treatment and can even increase due to re-polymerisation (Peña et al., 2003). The structure and characteristics of the melanoidins are still not fully understood and this has consequently hindered the development of an appropriate process for their removal (Satyawali and Balkrishnan, 2008). Methods which have been used to remove and/or decolourise humic-like matter and melanoidins include biological treatment with specific microorganisms, or consortia of microorganisms, and physico-chemical treatment. Biological treatment comprises both aerobic and anaerobic processes (Nandy et al., 2002; Jiménez et al., 2004). Physico-chemical treatment includes activated carbon adsorption (Mall and Kumar, 1997; Bernardo et al., 1997); coagulation and flocculation (Migo et al., 1993; Zhou et al., 2008); oxidation using ozone (Kim et al., 1985; Peña et al., 2003), UV/H 2 O 2 or UV/H 2 O 2 /Fe (II) (Çatalkaya and Sengul, 2006) and membrane treatment (Mutlu et al., 2002). The original concentration of colour and the molecular size, and the net charge of the coloured molecules, plus the characteristics and concentration of the other species present, will greatly influence the effectiveness of the colour removal process. There has been very little consistency in the types of samples investigated and the methods used for measurement of colour concentration, and frequently the degree of colour removal is given in percentage terms with no initial values given. Consequently, no consistently effective method for melanoidin removal is apparent from examination of the literature. The objectives of this laboratory scale study were to investigate the feasibility of and to compare coagulation, membrane filtration, ozonation and UV/H 2 O 2 oxidation separately or in combination as appropriate, for the removal of colour from an industrial wastewater stream containing melanoidins. This wastewater had very high colour and COD levels which have not been previously reported in the literature. MATERIALS AND METHODS Wastewater samples Melanoidin-containing industrial wastewater samples were stored at 4°C on receipt. The samples were filtered (0.45 m membrane) prior to the measurement of absorbance, DOC, true colour and fluorescence. Chemicals Alum (Al 2 (SO 4 ) 3 .16H 2 O, AR), lime (CaO, LR) and FeCl 3 were supplied by BDH. ACH (aluminium