How Does Chitosan Affect Methane Production in Anaerobic Digestion?

Abstract

The expanding use of chitosan in sewage and sludge treatment processes raises concerns about its potential environmental impacts. However, investigations of the impacts of chitosan on sewage sludge anaerobic digestion where chitosan is present at substantial levels are sparse. This study therefore aims to fill this knowledge gap through both long-term and batch tests. The results showed that 4 g/kg total suspended solid (TSS) chitosan had no acute effects on methane production, but chitosan at 8–32 g/kg TSS inhibited methane production by 7.2–30.3%. Mass balance and metabolism of organic analyses indicated that chitosan restrained the transfer of organic substrates from solid phase to liquid phase, macromolecules to micromolecules, and finally to methane. Further exploration revealed that chitosan suppressed the secretion of extracellular polymeric substances of anaerobes by occupying the connection sites of indigenous carbohydrates and increased the mass transfer resistance between anaerobes and substrates, which thereby lowered the metabolic activities of anaerobes. Although chitosan could be partly degraded by anaerobes, it is much more persistent to be degraded compared with indigenous organics in sludge. Microbial community and key enzyme encoding gene analyses further revealed that the inhibition of chitosan to CO2-dependent methanogenesis was much severer than that to acetate-dependent methanogenesis.

Hormesis-Like Effects of Tetrabromobisphenol A on Anaerobic Digestion: Responses of Metabolic Activity and Microbial Community

“…Obviously, all of these reactors were dominated by Firmicutes, Bacteroidetes, Chlorof lexi, and Euryarchaeota, which are consistent with previous publications in mesophilic anaerobic digesters. 12,14 However, there are no obvious variations of the bacterial and archaeal species at the phyla level in the presence and absence of TBBPA. Thus, further explorations at genus level were conducted, with the results being shown in Figure 4.…”

“…Organics metabolism directly depends on the key enzyme activity in anaerobic digestion (Figure 5). 12 Figure 5a−d shows the activities of AK, CODH, ACDS, and F420, which are respectively related to the processes of acetogenesis, homoacetogenesis, acetoclastic methanogenesis, and hydrogenotrophic methanogens, in the control and TBBPA-present reactors (i.e., 0.1 and 2.0 mg/L). 15 It can be found that 0.1 mg TBBPA/L remarkably stimulated the AK activity but significantly lowered the CODH activity (p < 0.05 in the two cases, Table S5).…”

“…This result shows some difference from that of chitosan at 16 mg/kg TSS, which inhibited hydrogenotrophic methanogens more severely than acetoclastic methanogens (the quantity of [EC: 6.2.1.1] decreased from 6.31 × 10 5 to 3.98 × 10 4 copies/g VSS, while that of [EC: 2.8.4.1] decreased from 1.58 × 10 10 to 7.94 × 10 6 copies/g VSS), and the reason might be ascribed to the different effect mechanisms of TBBPA and chitosan on methanogens, with the former mainly being acetate-derived electron competition and the latter being mass transfer resistance. 12 Environmental Relevance. The extensive use of TBBPA unavoidably results in its release into the environment; huge endeavors have therefore been made to evaluate its potential toxicity.…”

“…Anaerobic digestion is a complex ecosystem in which various microbial species (e.g., acidogens, acetogens, and methanogens) interact with each other to form a complicated network. , Through such network interactions, anaerobic digestion transforms organic matter into methane, which cannot be accomplished by an individual population. , Regardless of engineered and natural environments like anaerobic digesters and sediments, anaerobic digestion is a vital process closely related with carbon cycles, and generally co-exists with TBBPA. It is expected that the presence of TBBPA might alter the functional microbial species involved in such network and thereby affects the anaerobic digestion process and corresponding carbon cycles.…”

Calcium Hypochlorite Promotes Dark Fermentative Hydrogen Production from Waste Activated Sludge

“…Under the background of growing energy demand and fossil fuel shortage, it is urgent to exploit some renewable resources, such as biomass energy. WAS contains plentiful biodegradable organics that make it possible to be adopted as the substrate for recycling various biofuels, such as diesel, alcohol, methane, and hydrogen . Among these substances, hydrogen is considered as a clean energy source, with no carbon dioxide generated in the burning process, and water is the only combustion product.…”