Microwave-Hydrogen Peroxide Assisted Anaerobic Treatment as an Effective Method for Short-Chain Fatty Acids Production from Tannery Sludge

Abstract

Tannery sludge is disposed of in landfills as it is considered a special residue by the Italian legislation, creating pollution and waste. This paper aims at evaluating the performance of the anaerobic fermentation process to obtain short-chain fatty acids (SCFAs) from this waste. The assessment of the most appropriate conditions, in terms of pH, temperature, initial total solids (TSs) content, and application of oxidizing-thermal pretreatment has been developed. The batch test trials revealed that the combined microwave and hydrogen peroxide (MW-H2O2) pretreatment followed by thermophilic conditions gave the best results, in terms of the acidification yield (0.31 gCODSCFA/gVS0) and maximal SCFA concentration (above 26 g CODSCFA/L). In the tests conducted without pretreatment, the mesophilic temperature should be preferred since the acidification performances were comparable to or even better than their thermophilic counterparts. The SCFA composition analysis showed that in mesophilic fermentation, tannery sludge can generate up to 50% acetic acid (CODAc/CODSCFA), if previously pretreated (MW-H2O2). This research acts as a forerunner for the appropriate handling of this resource, to employ it for the development of a new tannery industry focused on a circular approach, rather than to simply dispose of it in landfills.

Microwave pretreatment of wastewater sludge technology—a scientometric-based review

“…This also improved the stability of the digester by increasing the buffering capacity of the digester, AS: FVW (25:75) had the highest nutrient dissolution and 10% methane yield with microwave pretreatment at 300 W Co-digestion and microwave pretreatment make hydrolysis no longer the limiting step in AD, but methane production the new limiting step, and how to improve the final methane yield and reduce energy efficiency costs becomes a new challenge (Agrawal et al 2023 ) CaO 2 -assisted microwave pretreatment Maize straw CaO 2 -assisted microwave pretreatment effectively reduced the crystallinity of maize straw and increased the initial water-soluble carbon (WSC) content and lignocellulose degradation. Degradation of lignin, cellulose, and hemicellulose reached 25.48%, 43.38%, and 66.29%, respectively The addition of CaO 2 , although it increases the degradation of lignin by microwave pretreatment, creates residues in the maize straw sludge that can be a burden on subsequent residual sludge treatment (Lu et al 2023 ) Combined microwave and hydrogen peroxide pretreatment Tannery sludge Due to the high content of macromolecular organic matter in tannery sludge, microwave pretreatment can be used to break it down and recover not only bio-based chemicals (e.g., short-chain fatty acids), but also biofuels from the sludge Although microwave pretreatment can recover most of the polluting waste from tannery sludge, this treatment method is only at the laboratory stage and the industrialization and continuity of the treatment system still requires a lot of research (Tuci et al 2022 ) Microwave and CaO co-pyrolysis Sewage sludge and water hyacinth Microwave pretreatment facilitates the reduction of activation energy and promotes pyrolysis reactions. The addition of CaO reduced the yields of acids and sugars by 10.52% and 5.08%, respectively.…”