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Abstract
Melanoidins are dark-coloured recalcitrant pollutants found in many industrial wastewaters including coffee-manufacturing effluent, molasses distillery wastewater (MDWW) and other wastewater with molasses as the raw material. The wastewaters are mostly treated with anaerobic digestion after some dilution to minimize the inhibition effect. However, the dark colour and recalcitrant dissolved organic carbon (DOC) mainly caused by melanoidin are not effectively removed. The aim of this study was to investigate the removal of colour and remnant DOC by different coagulants from anaerobically digested MDWW. From the six coagulants tested, ferric chloride had the highest melanoidin (48%), colour (92.7%) and DOC (63.3%) removal at pH 5 and a dosage of 1.6 g/l. Both polymer and inorganic salt coagulants tested had optimal colour, melanoidin and DOC removal at acidic pH. The molecular size distribution of synthetic melanoidins by liquid chromatography-organic carbon detection indicated a preferential removal of high-molecular-weight melanoidins over low weight melanoidins by the coagulation. Further studies should focus on how to improve biodegradability of the treated effluent for it to be reused as dilution water for anaerobic digestion.
ORCID
Yongjun Zhang http://orcid.org/0000-0001-5562-9090
Acknowledgements
We appreciate the help of Dr. Anke Putschew for the analysis with LC-OCD. The support and assistance of Cristina Senge and Kapitzk Liane are also highly appreciated. We also thank Alaina Mack for proof-reading and editing the manuscript. Milton M'Arimi is financially supported by Deutscher Akademischer Austausch Dienst and National Commission of Science, Technology and Innovation, Kenya.
Disclosure statement
No potential conflict of interest was reported by the authors.