High-value organic acid recovery from first-generation bioethanol dunder using nanofiltration

Nanofiltration (NF) was investigated for the recovery of platform chemicals, specifically, succinic acid, from high-strength bioethanol waste (dunder). Conventional methods focusing on chemical precipitation entail poor selectivity in complex matrices and are inherently expensive owing to the consumption of large volumes of chemicals and the generation of excess by-product sludge. For these reasons, three commercially available NF membranes with varying molecular weight cut-off were screened in a dead-end configuration to benchmark transmission behavior at different solution chemistries including pH, feed pressure, concentration, and ionic strength prior to filtration with the industrial effluent. Examination of behavior with model solutions only reveals that both NF270 and NTR-7450 membranes exhibit a succinic acid permeation above 80% irrespective of pH and solute concentration, while the addition of inorganic salts, in particular, divalent species, lowered the transmission of succinic acid with all membranes, in particular, NF90. Measurements of the surface charge (zeta potential) before and after filtration of the industrial effluent indicate a shift toward more positive values for the polyamide membranes (NF90 and NF270) within the pH range of 2-10. This change in surface charge was attributed to the formation of complexes between humic compounds and divalent cations present in elevated concentrations. Considerable fouling was observed for all membranes with the mean permeate flux around 2 L/m(2)h at 5 bar for the NF270 and NTR-7450 membranes; however, findings from deionized water rinsing suggest that the majority of foulants reside within the reversible fouling layer. Finally, size exclusion chromatography (liquid chromatography-organic carbon detection) findings highlight substantial (>70%) rejection of biopolymers, humics, building blocks, and low-molecular-weight neutral species following filtration with all membranes. Overall, this work demonstrates the merits and potential of nanofiltration in the recovery of high-value organic acids from concentrated bioethanol waste

High-value organic acid recovery for the valorisation of bioethanol dunder using two-stage membrane processing

Despite rapid proliferation of biofuels to secure long-term energy demands, the generation of high-strength liquid waste remains a substantial challenge to both research and industry. Notwithstanding this, opportunities for valorisation, specifically the recovery of selected platform organic acids embedded within this waste, may considerably alter the economics of commercial production facilities. The use of membrane filtration offers substantial merit for this purpose and is therefore extended to the present study. A comprehensive characterisation study was first completed to discern waste streams most suited for organic acid recovery from a commercial bioethanol distillery. Size exclusion chromatography (LC-OCD) complemented findings from sorption characteristics (resin fractionation), ICP-OES and FEEM spectroscopy. Importantly, HPLC analyses revealed elevated concentrations of succinic acid constituting a high-value commodity (chemical precursor) within bioethanol dunder, coupled with lower quantities of oxalic acid.Ultrafiltration pre-treatment was then assessed for the removal of polysaccharides, humic and building block matter. Implications of MWCO and effluent dilution upon filtration performance (fouling propensity, organic acid transmission and rejection of undesired moieties) were scrutinised in a dead-end stirred-cell configuration. Comparatively, transverse vibration of submerged hollow fibres served as a novel strategy demonstrating marked improvement in critical flux and the rejection of biopolymers and humics, even with highly concentrated feed. Additional work for optimisation extended operational conditions to a supra-critical regime whilst providing extensive insight into fouling layer reversibility, in addition to methods for minimising TMP such as periodical relaxation and mixed-mode vibration.Commercially available nanofiltration membranes were employed for the second stage polishing of UF permeate, and assessed for intrinsic properties including electrokinetic potential, organic acid transmission at varying pH and mono/divalent salts addition. EDX spectroscopy and SEM imaging of membranes following filtration with Biodunder corroborated the notion of humic acid macromolecular fouling due to bridging of free functional groups by divalent inorganics.Finally, the last section of this work investigated the suitability of lab-based model compounds as surrogates to mimic the DOM of biofuel and other fermentation industry effluents

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