Characterization of efficient xylanases from industrial-scale pulp and paper wastewater treatment microbiota

Xylanases are widely used enzymes in the food, textile, and paper industries. Most efficient xylanases have been identified from lignocellulose-degrading microbiota, such as the microbiota of the cow rumen and the termite hindgut. Xylanase genes from efficient pulp and paper wastewater treatment (PPWT) microbiota have been previously recovered by metagenomics, assigning most of the xylanase genes to the GH10 family. In this study, a total of 40 GH10 family xylanase genes derived from a certain PPWT microbiota were cloned and expressed in Escherichia coli BL21 (DE3). Among these xylanase genes, 14 showed xylanase activity on beechwood substrate. Two of these, PW-xyl9 and PW-xyl37, showed high activities, and were purified to evaluate their xylanase properties. Values of optimal pH and temperature for PW-xyl9 were pH 7 and 60 ℃, respectively, while those for PW-xyl37 were pH 7 and 55 ℃, respectively; their specific xylanase activities under optimal conditions were 470.1 U/mg protein and 113.7 U/mg protein, respectively. Furthermore, the Km values of PW-xyl9 and PW-xyl37 were determined as 8.02 and 18.8 g/L, respectively. The characterization of these two xylanases paves the way for potential application in future pulp and paper production and other industries, indicating that PPWT microbiota has been an undiscovered reservoir of efficient lignocellulase genes. This study demonstrates that a metagenomic approach has the potential to screen efficient xylanases of uncultured microorganisms from lignocellulose-degrading microbiota. In a similar way, other efficient lignocellulase genes might be identified from PPWT treatment microbiota in the future.

Treatment of Wastewater from Pulp and Paper Mill using Coagulation and Flocculation

In this work, an effluent sample from a local medium-scale paper mill has been treated using alum as a coagulant and chitosan (natural polymer) as a flocculant. Initially, the dose of alum has been optimized by adjusting the zeta potential to near zero for best coagulation results. The dose of 0.04 g/L was able to merely coagulate and unable to cause sweep flocculation of impurities. Then, at the optimised dose of 0.04 g/L various concentrations of chitosan in the range of 0.1-0.5 g/L were investigated for obtaining maximum flocculation of the suspended impurities. The physico-chemical parameters like pH, total suspended solids (TSS), chemical oxygen demand (COD), absorbance, and zeta potential were studied for comprehending the flocculation behavior. The observed results exhibited that the maximum flocculation was achieved at the chitosan concentration of 0.3 g/L. At the flocculant concentration of 0.3 g/L, 81% TSS removal and maximum 78% COD were reduced. Moreover, zeta potential value of the collected supernatant was close to zero (–1.49 mV) which showed larger floc formation and easy settleability of the impurities. In all, it can be said that the utilization of chitosan along with alum may be a better option for the treatment of pulp and paper wastewater as well as other similar types of wastewater.

Treatment of UASB-treated recycled paper wastewater using SBR and SBBR: A comparison

Anaerobic-oxic (AO) systems have been extensively adopted for the biological treatment of wastewater from recycled paper mills, which is characterized by high chemical oxygen demand (COD) concentrations and contains hundreds of organic compounds. In this study, an up-flow anaerobic sludge blanket (UASB) served as the anaerobic treatment of recycled paper mill wastewater. Then, either a sequential batch reactor (SBR) or a sequential batch biofilm reactor (SBBR) were adopted as aerobic treatment to treat the UASB effluent respectively. Parameters such as COD, BOD5, and TSS were measured to compare the treatment performance of SBR and the SBBR. After 80 days’ operation, COD removal efficiency of SBR and SBBR were 21.79 ± 3.4% and 38.38 ± 2.69% respectively; TSS removal efficiencies were 20.84 ± 5.15% and 47.02 ± 5.84% respectively. The results indicated that SBR was effective for removing residual organic matter in UASB effluent. However, SBBR showed significant advantages for the removal of COD and total suspended solids (TSS), which are ascribed to the effective biomass retention and biofiltration of SBBR.