Treatment and resource recovery options for first and second generation bioethanol spentwash - A review.

A decline in the availability of fossil fuel resources coupled with deleterious environmental concerns has prompted further research into biofuels. Conventional bioethanol production via a first-generation approach may soon become superseded through integration with lignocellulosic feedstocks. However, the underlying concerns pertaining to the disposal of high-strength liquid waste (i.e. spentwash) remain both unchanged and constitute a substantial cost to bioethanol manufacturers. Therefore this review details current efforts in the literature to elucidate various approaches for spentwash treatment and investigate the potential for resource recovery. Insight into the composition of distillery wastewater is given in the lead-up to a thorough discussion encompassing the origin, transformation and characterisation of the highly problematic melanoidin compounds entrained within this effluent. Close examination of advanced organic characterisation methods used by researches yields further insight into the nature of spentwash dissolved organic matter (DOM). Employment of both biological and physio-chemical treatment schemes to alleviate the environmental footprint of such high-strength wastewater are also reviewed. Opportunities to dramatically improve the economic viability of biofuel production by exploiting the potential for resource recovery in the form of energy, organic/inorganic constituents and effluent reuse are discussed. Overall, the review culminates by highlighting recommendations for future work to accelerate the onset of an environmentally benign bio-refinery.

Characterisation of dissolved organic matter in fermentation industry effluents and comparison with model compounds.

Advanced organic characterisation methods were used to investigate the suitability of lab-based model compounds as surrogates to mimic the dissolved organic matter (DOM) of both first and second generation fermentation industry effluents. Comparisons to both humic acid and synthetic melanoidin revealed the limitations of using these model organic compounds in treatment studies of biorefinery effluent. Rapid resin fractionation (RRF) of effluent from yeast cultivated on molasses suggests that 64% of the dissolved organic matter is present in the form of very hydrophobic acid (VHPhoA) compounds. Molecular weight distribution by size exclusion chromatography (LC-OCND) and fluorophore specific intensity by fluorescence excitation and emission matrix (FEEM) of the yeast effluent was comparable to signatures from humic acid. This indicates that humic acid would be a suitable model compound for oxidation, adsorption and filtration studies. Differences among the fermentation industry effluents were found to be inherently dependent on both the biochemistry of yeast and processes used. RRF and FEEM spectra of effluent from bioethanol production on cellulosic feed highlighted a preponderance of neutral compounds with fluorophore specific intensity characteristic of non-humic compounds with a higher fraction of neutral compounds (41%) relative to VHPhoA (38%), SHPhoA (16%) and HPhi (5%) moieties. Findings were not consistent with commercial humics, synthetic melanoidins or other cellulosic and lignocellulosic based effluents from Kraft and Thermomechanical pulp mills since the actual pollutants are heavily dependent on the pre-treatment process. This suggests further work is required to develop a model compound for treatment studies of effluent from second generation bio-refineries.