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

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 (TiO 2 ) 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.

Experimental design and modeling of removal of organic matter and nutrients in the OMW by calcium bentonite

“…Total suspended solids are determined by filtration method AFNOR T90-105 [24]. The chemical oxygen demand analysis was carried out using closed reflux colorimetric method with potassium dichromate solution as oxidant and nano colour colorimeter [25]. Total polyphenols were measured using the method developed by Macheix et al (1990) [26].…”

Study of the catalytic activity of multilayer graphene (MLG), molybdenum oxide (MoO2), and manganese ferrite (MnFe2O4) on the melanoidin removal by ozonation process

“…Some dyes, such as melanoidins, are resistant to conventional methods of biological treatment, whether aerobic or anaerobic, resulting in an incomplete color removal from wastewater (Li et al 2017;Kaushik et al 2018). During these processes, an increase in color may even occur due to the repolymerization of melanoidins (Peña et al 2003;Mabuza et al 2017). That said, the development of alternative technologies for the removal of melanoidins from urban wastewater is indispensable.…”

Anaerobic treatment of post-hydrothermal liquefaction wastewater from >i<Spirulina>/i< associated with microaeration and photocatalysis

“…after 4 hours of irradiation, for initial values of COD between 1.05 and 7.37 g/L. Mabuza et al (2017) studied the integration of anaerobic digestion under thermophilic conditions and photocatalytic degradation using a TiO2-ZnO hybrid catalyst for the treatment of molasses wastewater. The initial concentrations of COD and TOC were 6.6 g/L and 3.2 g/L, respectively.…”