Investigating the synergy of integrated anaerobic digestion and photodegradation using hybrid photocatalyst for molasses wastewater treatment

Journal article

Authors / Editors

Ochieng, Aoyi

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Publication Details

Author list: Mabuza J, Otieno B, Apollo S, Matshediso B, Ochieng A

Publisher: Springer

Place: HEIDELBERG

Publication year: 2017

Journal: EURO-MEDITERRANEAN JOURNAL FOR ENVIRONMENTAL INTEGRATION (2365-6433)

Journal acronym: EURO-MEDITERR J ENVI

Volume number: 2

Issue number: 1

Number of pages: 10

ISSN: 2365-6433

eISSN: 2365-7448

Languages: English-Great Britain (EN-GB)

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Abstract

Anaerobic digestion (AD) can remove the high organic load of molasses wastewater (MWW), but is ineffective in removing the characteristic dark brown colour caused by biorecalcitrant melanoidin. Ultraviolet (UV) photodegradation, can mineralise the biorecalcitrants leading to complete colour removal, but with a high-energy input and low organic load removal. This study investigated the plausibility of integrating the two processes for organic load and colour reductions. Desk scale AD and photodegradation processes were carried out in batch reactors. A hybrid photocatalyst consisting of titanium dioxide (TiO2) and zinc oxide (ZnO) was used for photocatalytic degradation. Biodegradation at thermophilic conditions in the bioreactor achieved high total organic carbon (TOC) and chemical oxygen demand (COD) reductions of 80 and 90%, respectively, but with an increased colour intensity. Contrastingly, UV photodegradation achieved a high colour reduction of 92% with an insignificant 6% TOC reduction, after 30 min of irradiation. During photodegradation, the mineralisation of the biorecalcitrant organic compounds led to the colour disappearance. The energy required for the TOC reduction was 40-fold higher than that required for the colour reduction in the same irradiation period, suggesting that the UV process was only suitable for colour reduction. Therefore, there is a possible synergy when the two processes are integrated, with AD preceding UV, where AD removes the high COD/TOC while UV removes the recalcitrant colour at a reduced cost.

Keywords

Anaerobic digestion, Energy demand, Molasses wastewater, photodegradation, Synergy

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