Advances in modifying lignin structures for largely enhancing high-lignin biomass saccharification

Enhanced denitrification of dispersed swine wastewater using Ca(OH)2-pretreated rice straw as a solid carbon source

In a pilot-scale packed bed reactor, the denitrification performance and microbial community structure of the dispersed swine wastewater treatment using calcium hydroxide (Ca(OH)₂) pretreated rice straw as a carbon source were investigated. In a Ca(OH)₂-pretreated rice straw supported denitrification system (Ca(OH)₂-RS), the removal efficiency of NO₃^--N was 96.39% at an influent NO₃^--N load of 0.04 kg/(m³•d). Meanwhile, there was no obvious accumulation of NO₂^--N or chemical oxygen demand (COD) in the effluent of Ca(OH)₂-RS. The contents of soluble microbial byproduct-like substances and tryptophan-like substances in the effluent of Ca(OH)₂-RS were reduced by 46.2% and 43.4%, respectively, compared with the influent. Overall, the Ca(OH)₂-pretreated rice straw system had a strong resistance to fluctuations in water quality conditions, such as influent NO₃^--N and COD concentrations. According to the microbial assay results, the Ca(OH)₂ pretreatment enriched more denitrifying bacteria. Among them, Proteobacteria (42.33%) and Bacteroidetes (35.28%) were the dominant bacteria. Moreover, the main denitrifying functional bacteria, generanorank_f_Saprospiraceae (13.32%), norank_f_Porphyromonadaceae (4.22%), and Flavobacterium (3.25%), were enriched in Ca(OH)₂-RS. This suggested that using Ca(OH)₂-pretreated rice straw as a carbon source was a stable and efficient technology to enhance the denitrification performance of dispersed swine wastewater.

Biogas and Volatile Fatty Acid Production During Anaerobic Digestion of Straw, Cellulose, and Hemicellulose with Analysis of Microbial Communities and Functions

The anaerobic digestion efficiency and methane production of straw was limited by its complex composition and structure. In this study, rice straw (RS), cellulose, and hemicellulose were used as raw materials to study biogas production performance and changes in the volatile fatty acids (VFAs). Further, microbial communities and genetic functions were analyzed separately for each material. The biogas production potential of RS, cellulose, and hemicellulose was different, with cumulative biogas production of 283.75, 412.50, and 620.64 mL/(g·VS), respectively. The methane content of the biogas produced from cellulose and hemicellulose was approximately 10% higher than that produced from RS after the methane content stabilized. The accumulation of VFAs occurred in the early stage of anaerobic digestion in all materials, and the cumulative amount of VFAs in both cellulose and hemicellulose was relatively higher than that in RS, and the accumulation time was 12 and 14 days longer, respectively. When anaerobic digestion progressed to a stable stage, Clostridium was the dominant bacterial genus in all three anaerobic digestion systems, and the abundance of Ruminofilibacter was higher during anaerobic digestion of RS. Genetically, anaerobic digestion of all raw materials proceeded mainly via aceticlastic methanogenesis, with similar functional components. The different performance of anaerobic digestion of RS, cellulose, and hemicellulose mainly comes from the difference of composition of raw materials. Increasing the accessibility of cellulose and hemicellulose in RS feedstock by pretreatment is an effective way to improve the efficiency of anaerobic digestion. Since the similar microbial community structure will be acclimated during anaerobic digestion, there is no need to adjust the initial inoculum when the accessibility of cellulose and hemicellulose changes.

Feasibility of anaerobic digestion on the release of biogas and heavy metals from rice straw pretreated with sodium hydroxide

The feasibility of anaerobic digestion on the release of biogas and heavy metals from contaminated rice straw pretreated with NaOH solution was studied. The results show that NaOH pretreatment can significantly boost the release of biogas and heavy metals from rice straw using anaerobic digestion. Under the optimal conditions for biomass pretreated 6% (w/w) NaOH with a solid-to-solution ratio of 1:20, total biogas and methane yields of 446.3 mL/g and 263.5 mL/g volatile solids were achieved, which were 22.18% and 41.59% higher than those of the control without NaOH pretreatment, respectively, and the release percentages of Cd, Pb, Cu, and Zn from rice straw reached 86.95-97.69%. The release of heavy metals from rice straw can contribute to both the degradation of lignin by NaOH pretreatment and the utilization/transformation of lignocellulose via anaerobic digestion. The acidification levels and total volatile fatty acid contents significantly influence on the release of heavy metals. Based on the Illumina HiSeq sequencing analysis, the dominant phyla in the biogas residues were proteolytic (Bacteroidetes) and hydrogen-producing (Firmicutes) bacteria, while the growth of Methanospirillum and Methanosaeta in anaerobically digested effluent was promoted. The results revealed that anaerobic digestion combined with NaOH pretreatment is suitable for the disposal of heavy metal-contaminated biomass.

Lignin - An underutilized, renewable and valuable material for food industry

Lignin is the second most abundant biorenewable polymers only next to cellulose and is ubiquitous in various plant foods. In food industry, lignin often presented as a major component of by-products from plant foods. In the last decade, the food and nutritional interests of lignin attracted more and more attentions and great progresses have been accomplished. In the present review, the structure, physicochemical properties, dietary occurrence and preparation methods of lignin from food resources were summarized. Then, the versatile activities of food lignin were introduced under the subtitles of antioxidant, antimicrobial, antiviral, antidiabetic and other activities. Finally, the potential applications of food lignin were proposed as a food bioactive ingredient, an improver of food package films and a novel material in fabricating drug delivery vehicles and contaminant passivators. Hopefully, this review could bring new insights in exploiting lignin from nutrition- and food-directed views.

Flocculation performance of lignin-based flocculant during reactive blue dye removal: comparison with commercial flocculants

A novel lignin-based flocculant (LBF) with superior flocculation performance was prepared from paper mill sludge in this work. The functional groups of LBF and alkaline lignin (AL) were determined by Fourier transform infrared spectroscopy (FTIR). The flocculation performance of LBF integrated with polyaluminum chloride (PAC) was tested in reactive dye wastewater treatment. Floc properties and color removals in multiple flocculation systems were discussed. Results indicated that the dye removal (93%) was greatly facilitated as the LBF was integrated with PAC (PAC + LBF). In addition, floc properties and color removals were significantly improved in the presence of Ca²⁺ and Mg²⁺. In contrary, flocculation performance was greatly restricted in the presence of SO₄^2-. LBF was less pH sensitive and shear sensitive than polyacrylamide (PAM) due to the enhanced charge neutralization and bridging action. On the basis of that, LBF could be used as a promising flocculant in dye wastewater treatment.