Immobilized enzymatic membrane surfaces for biocatalytic organics removal and fouling resistance.

This research reported on the immobilization of environmentally friendly enzymes, such as horseradish peroxidase (HRP) and laccase (L), along with the hydrophilic zwitterionic compound l-DOPA on nano-filtration (NF) membranes. This approach introduced biocatalytic membranes, leveraging combined effects between membranes and enzymes. The aim was to systematically assess the efficacy of the enzymatic modified membrane (HRP-NF) in degrading colors in the wastewater, as well as enhancing the membrane resistance toward organic fouling. The enzymatic immobilized membrane demonstrated 96.3 ± 1.8% to 96.6 ± 1.9% removal of colors, and 65.2 ± 1.3% to 67.2 ± 1.3% removal of TOC. This result was underpinned by the insights obtained from the radical scavenger coumarin, which was employed to trap and confirm the formation of PRs through the reaction of enzymes and H2O2. Furthermore, membranes modified with enzymes exhibited significantly improved antifouling properties. The HRP-NF membrane experienced an 8% decline in flux, while the co-immobilized HRP-L-NF membrane demonstrated as low as 6% flux decline, contributed by the synergistic effect of increased hydrophilicity and biocatalytic effects. These findings confirmed that the immobilized enzymatic surface has added function of degrading contaminants in addition to separation function of nanofiltration membrane. These l-DOPA-immobilized enzymatic membranes offered a promising hybrid biocatalytic membrane to eliminate dyes and mitigate membrane fouling, which can be applied in many industrial and domestic water and wastewater treatment.

Low-temperature anaerobic digestion of chicken manure at high organic and nitrogen loads - strategies for controlling short chain fatty acids.

Objective of this work was to investigate the technical feasibility of low-temperature, closed-loop two-stage (liquid-solid) anaerobic digesters to treat chicken-manure (TS:68%; NH3:8 g/L) as a sole-feedstock. Effect of pH, temperature, treatment-duration, organic loading rate (OLR) and inoculum-recirculation ratio on short chain fatty acids (SCFA) production was studied. Digesters were operated at 20 ± 1 °C for 282-d over 4 batch-runs (∼70-d/batch) at an OLR of 8.78-4.3 gVS/L/d. Results showed that specific methane yield above 0.6 LCH4/gVS was feasible with a methane concentration > 60%. SCFA speciation of the entire system was monitored through the liquid-digester. Among SCFA indicators, the ratios of propionic-to-acetic acids, (butyric + valeric)-to-acetic acids, and total SCFA-to-alkalinity were observed within the limit, i.e., below 1.4, 0.3 and 0.8, respectively, indicating high-digester stability. This strategy allowed early detection, diagnosis of process failures in high-solids digester in fed-batch mode, and re-evaluation of operating protocol to enrich performance with economic-benefits.

Processing High-Solid and High-Ammonia Rich Manures in a Two-Stage (Liquid-Solid) Low-Temperature Anaerobic Digestion Process: Start-Up and Operating Strategies.

Globally, livestock and poultry production leads to total emissions of 7.1 Gigatonnes of CO2-equiv per year, representing 14.5% of all anthropogenic greenhouse gas emissions. Anaerobic digestion (AD) is one of the sustainable approaches to generate methane (CH4) from manure, but the risk of ammonia inhibition in high-solids AD can limit the process. Our objective was to develop a two-stage (liquid-solid) AD biotechnology, treating chicken (CM) + dairy cow (DM) manure mixtures at 20 °C using adapted liquid inoculum that could make livestock farming more sustainable. The effect of organic loading rates (OLR), cycle length, and the mode of operation (particularly liquid inoculum recirculation-percolation mode) was evaluated in a two-stage closed-loop system. After the inoculum adaptation phase, aforementioned two-stage batch-mode AD operation was conducted for the co-digestion of CM + DM (Total Solids (TS): 48-51% and Total Kjeldahl Nitrogen (TKN): 13.5 g/L) at an OLR of 3.7-4.7 gVS/L.d. Two cycles of different cycle lengths (112-d and 78-d for cycles 1 and 2, respectively) were operated with a CM:DM mix ratio of 1:1 (w/w) based on a fresh weight basis. Specific methane yield (SMY) of 0.35 ± 0.11 L CH4g/VSfed was obtained with a CH4 concentration of above 60% for both the cycles and Soluble Chemical Oxygen Demand (CODs) and volatile solid (VS) reductions up to 85% and 60%, respectively. For a comparison purpose, a similar batch-mode operation was conducted for mono-digestion of CM (TS: 65-73% and TKN: 21-23 g/L), which resulted in a SMY of 0.52 ± 0.13 L CH4g/VSfed. In terms of efficiency towards methane-rich biogas production and ammonia inhibitions, CM + DM co-digestion showed comparatively better quality methane and generated lower free ammonia than CM mono-digestion. Further study is underway to optimize the operating parameters for the co-digestion process and to overcome inhibitions and high energy demand, especially for cold countries.