ENZYMATIC HYDROLYSIS OF DAIRY COW EFFLUENT: HEMICELLULASE AND LACCASE EFFECTS

Short introductive summary Dairy sector increased by 8 % in 10 countries belonging to the Member States of Europe, from 2013 to 2016 (EUROSTAT 2016) contributing to methane emissions. However, the negative aspect related to the dairy activity can be converted in benefits regarding the energetic/economic potential hold in the cattle effluent if the recalcitrant effect of some components in the conversion process will be reduced. Enzymatic pre-treatment can play a key role in making available organic matter of this sort of effluent/waste and, consequently, will contribute to increase biomass digestibility and will enhance the biogas production. Taking into account the chemical composition of a dairy cow effluent, containing polysaccharides - cellulose and hemicellulose - and lignin, a complex aromatic alcohol polymer, it is predictable that it might be degraded by glycosyl hydrolases (such as cellulases and hemicellulases) and laccase enzymes. Thereafter, the resulting biomolecules (including sugars and oligosaccharides) can be converted into value-added biobased compounds or biofuels, like biogas/biomethane. Purpose of the work This work aims to study the effect of enzymatic hydrolysis in the recalcitrant dairy cow effluent, in order to make organic matter content suitable for further anaerobic digestion process. Approach The hydrolysis was performed by using commercial enzyme formulations NS-51003 exhibiting laccase activity and NS-22201 containing hemicellulase activity (both from Novozymes A/S, Denmark). Hemicellulase (H) and laccase (L) efficiencies were tested at different concentrations: 3.0-12 mL hemicellulase/g biomass (H3.0-H12) and 0.5-3.0 g laccase/100 g cellulose (L0.5-L3.0). A combination of both enzymes was tested at concentrations of 6 mL hemicellulase/g biomass plus 1.5 g laccase/100 g cellulose (H6+L1.5). Saccharification process was done under aerobic conditions at 50 °C, 180 rpm for 3 days. Sampling was done every 24 h and sugar composition was analyzed by HPLC. Temperature stability of laccase preparation was evaluated at pH 5. The total phenolic content was analyzed by the Folin-Ciocalteu assay (Singleton and Rossi, 1965). Scientific innovation and relevance According our previous work (Eusebio et al., 2017), enzymatic process enhances the subsequent biological conversion of the recalcitrant components present in the dairy cow effluent. Consequently, it was relevant that the enzymatic process was further optimised to maximise this desired effect. On the other hand, it was intended to evaluate the benefit of using a mixture of both commercial enzyme formulations, having as baseline the previous results. To the best of our knowledge, this is the first study reporting pre-treatment of dairy cow effluent using laccase. Results The pre-treatment with laccase provided a better glucose release than the application of hemicellulose, with the highest yield (44%) achieved when applying the highest laccase dosage (L3.0). Concerning the hemicellulase activity, a correspondent value of 17 % was obtained as the highest yield, using H3.0. Comparing with laccase effect, the mixture of enzymes activities (H6+L1.5) did not improve the saccharification process as only 28 % of sugar yield was achieved. Taking in account the attained results for laccase preparations, the stability of this enzyme activity was confirmed at pH 5. In addition, it was observed that samples treated with laccase provided the highest phenols concentration removal. Conclusions Waste enzymatic treatment had shown a good efficiency in transforming organic residues in more useful compounds, making them available for further anaerobic digestion process. Laccase (L3.0) provided the highest sugar released yield (44%) and show the capacity of decrease phenolic compounds content, compared to hemicellulase and the mixture of both enzymes. Laccase stability assays are in progress to assess the best pretreatment conditions that allow to reach the higher sugar release amount.