A novel strategy for efficient anaerobic co-digestion based on the pretreatment of corn stover with fresh vinegar residue

Biogas from lignocellulosic feedstock: current status and challenges

The organic wastes and residues generated from agricultural, industrial, and domestic activities have the potential to be converted to bioenergy. One such energy is biogas, which has already been included in rural areas as an alternative cooking energy source and agricultural activities. It is produced via anaerobic digestion of a wide range of organic nutrient sources and is an essential renewable energy source. The factors influencing biogas yield, i.e., the various substrate, their characteristics, pretreatment methods involved, different microbial types, sources, and inoculum properties, are analyzed. Furthermore, the optimization of these parameters, along with fermentation media optimization, such as optimum pH, temperature, and anaerobic digestion strategies, is discussed. Novel approaches of bioaugmentation, co-digestion, phase separation, co-supplementation, nanotechnology, and biorefinery approach have also been explored for biogas production. Finally, the current challenges and prospects of the process are discussed in the review.

A Review of the Current State and Future Prospects in Resource Recovery of Chinese Cereal Vinegar Residue

Vinegar residue (VR) is a typical organic solid waste in Chinese cereal vinegar production. It is characterized by high yield, high moisture and low pH and is rich in lignocellulose and other organic matter. To avoid the environmental pollution caused by VR, it should be properly treated. The industry’s existing treatment processes, landfills and incineration, cause secondary pollution and waste of resources. Therefore, there is an urgent demand for environmentally friendly and cost-effective resource recovery technologies for VR. To date, a considerable amount of research has been performed in the area of resource recovery technologies for VR. This review summarizes the reported resource recovery technologies, mainly anaerobic digestion, feed production, fertilizer production, high-value product production and soil/water remediation. The principles, advantages and challenges of these technologies are highlighted. Finally, as a future perspective, a cascade and full utilization model for VR is proposed by considering the inherent drawbacks and economic-environmental feasibility of these technologies.

Effects of combined ultrasonic and grinding pre-treatments on anaerobic digestion of vinegar residue: organic solubilization, hydrolysis, and CH4 production

ABSTRACTThe high lignocellulose content of vinegar residues (VR) limits their biochemical methane potential (BMP) in anaerobic digestion (AD). However, unlike reported high cellulosic materials such as straw and grass, single pre-treatment with ultrasonication or grinding only slightly improved VR AD, due to the high protein and carbohydrate contents of VR. This study used statistical analysis to show that the methane yield, protein and polysaccharide release, and hydrolysis performance during VR AD were significantly enhanced with a combined grinding-ultrasound pre-treatment. Specifically, at 60 min of ultrasonic, the group with the combined pre-treatment (60 min + RS) showed the highest VR BMP (∼307.1 mLCH₄/gVS), 68.7% greater than that in the control group. This group also exhibited optimal conditions for dissolution of polysaccharide and protein, with accumulated amounts of ∼500 and 1600 mg/L, respectively. The highest volatile fatty acid (VFA) concentration in the 60 min + RS group was 61.5% higher than that in the control group. Both dissolution and hydrolysis experiments suggested that ultrasound accelerated protein release from VR, particularly after the particle size was reduced, and that the grinding pre-treatment had a positive effect on polysaccharide release.

Novel application of pyrolytic carbon generated from waste tires: Hydrolytic and methanogenic performance promotion in vinegar residue anaerobic digestion

Random disposal of waste tires and vinegar residues is deleterious to the environment; these materials can be sufficiently treated using pyrolysis and anaerobic digestion, respectively. In this study, pyrolytic carbon was used to enhance the performance of the anaerobic digestion of vinegar residues, which is a much more economic method comparing with dosing commercial-level carbon based materials. The conductivity of pyrolytic carbon at 1000 °C is much higher than that of commercial activated carbon. At a dosage of 10 g per 29 g of vinegar residues, the maximum volatile fatty acid production was 4225.4 mg COD/L in the reactor (effective volume of 400 mL) with inoculum to substrate ratio (ISR) of 1:1, representing an increase of 50.3% from that of the control reactor. A sufficient dosage is necessary to improve methane yield. The maximum methane yield was obtained at a pyrolytic carbon dosage, obtained at 1000 °C, of 12 g per 29 g of vinegar residues. The results indicated that the differences in the microbial communities of the control and experimental reactors correlated with the performance; however, the deep microbial mechanism of pyrolytic carbon boosting anaerobic digestion performance must be explored in further studies.

Removal performance and mechanisms of toxic hexavalent chromium (Cr(VI)) with ZnCl2 enhanced acidic vinegar residue biochar

Acidic vinegar residue (VR) and toxic hexavalent chromium (Cr(VI)) are unfavorable substances due to their toxicity against the environment. In this study, modified biochar was prepared to investigate the removal mechanisms of Cr(VI). The results showed that ZnCl₂ could yield highly aromatic products with improved pore structures. The adsorption capacity of modified biochar reached the highest efficiency (236.81 mg g^-1) when the mass ratio of ZnCl₂/VR was 1, which is higher than the control (9.96 mg g^-1). In addition, Cr(VI) adsorption coexisted with physical and chemical adsorption. The mechanisms of modified biochar to Cr(VI) removal included electrostatic attraction, pore filing, reduction and surface complexation. Notably, as a fermented product, VR biochar was a nitrogen-rich product; the formation of the amino group could provide a direct solid site for Cr(VI) adsorption. Subsequently, amorphous silica could be converted into silanol to provide additional adsorption sites. This work establishes the theoretical basis for efficient Cr(VI) removal and VR reuse.

The effect of microwave pretreatment on anaerobic co-digestion of sludge and food waste: Performance, kinetics and energy recovery

This paper studied the effect of microwave (MW) pretreatment on anaerobic co-digestion of sludge (SS) and food waste (FW). Using SS and FW as digestive substrates, the MW pretreatment method was used to determine the changes in the substrate matrix by means of batch anaerobic digestion at 37 °C. The kinetics of methane production were calculated, and the changes in organic matter during anaerobic co-digestion, the properties of the anaerobic-digested effluent, and the net energy output of the co-digestion system were determinated. The results showed that MW pretreatment was beneficial to the dissolution of organic matter, conversion of protein to NH₄⁺-N, cumulative methane production, unit biomethane yield, and reaction rate of methane production in the SS and FW anaerobic co-digestion system. The highest cumulative methane production in the co-digestion system reached 3446.3 ± 172.3 mL (35 days), which was 19.93% higher than that of the control. Furthermore, MW pretreatment significantly increased the accumulation of VFAs and the content of butyric acid in the anaerobic-digested effluent, which was beneficial to the methanogenesis process. The MW pretreatment of all co-digested substrates produced a greater net energy output than the control, and the MW-SS + MW-FW group yielded the highest net energy output, which was 76.25 kJ/g Fed VS. The results indicated that MW pretreatment prior to SS and FW anaerobic co-digestion is an effective way to improve the anaerobic digestion efficiency and energy recovery rate.