Dry co-digestion of sewage sludge and rice straw under mesophilic and thermophilic anaerobic conditions

Effects of different fermentation assisted enzyme treatments on the composition, microstructure and physicochemical properties of wheat straw used as a substitute for peat in nursery substrates

To solve the central problems caused by traditional composting treatments, such as long-time consumption and poor regulation effects, this study used three fermentation methods and four enzymes to develop rapid and directional regulation methods to convert wheat straw into a suitable substrate. The results showed that the mixed anaerobic method led to better pH (4.39-5.75) and EC values (1.27-1.89 mS/cm) in the straw substrates, while the aerobic method retained more nutrients and increased lignin and cellulose contents by 5.07-8.04% and 1.52-3.32%. The cellulase mixed with hemicellulase or laccase treatments all increased the crystallinity by 0.45-7.23%. The TG/DTG results showed that all treatments decreased the initial straw glass transition temperature, particularly when using the mixed anaerobic method, with decreases of 10.63-25.48 °C. Overall, mixed anaerobic fermentation and multiple enzymes, including cellulase, have been suggested as alternative biological modification methods for straw substrates.

Steam explosion pretreatment of rice straw to improve structural carbohydrates anaerobic digestibility for biomethanation

Effectiveness of steam explosion (SE) pretreatment for deconstructing the complex structural carbohydrates (SC) and lignin recalcitrance properties of rice straw (RS) for conjunctive improvement of biofuel yield and waste valorization was evaluated. This work exhibited successful pretreatment of RS at a different pressure (1.2, 1.5, and 1.8 MPa) and retention (3, 6, 9, and 12 min) for enhancement of SC contribution to biomethane production. Regression analysis demonstrated that SE pretreatment efficiency improved at high-temperature and short-retention time for biodegradation of RS. Maximum cumulative methane yield (EMY) achieved 254.8 mL/gvs at 1.2 MPa (3 min) of SE-treated RS with 62.7% of very significant improvement compared with untreated RS (156.6 mL/gvs). Furthermore, solid fraction of xylose, arabinose, cellobiose, glucose, and acid-soluble lignin in SE-treated RS of 1.2 MPa (3 min) were biodegraded by 27.4%, 46.4%, 100%, 48.8%, and 14.1%, respectively, after anaerobic digestion. Therefore, SE pretreatment was an encouraging approach for enhancing SC conversion to biomethane and waste resource to circular economy.

Anaerobic digestion of soft drink beverage waste and sewage sludge

Soft drink beverage waste (BW) was evaluated as a potential substrate for anaerobic co-digestion with sewage sludge to increase biogas production. Results from this study show that the increase in biogas production is proportional to the increase in organic loading rate (OLR) rate due to BW addition. The OLR increase of 86 and 171% corresponding to 10 and 20% BW by volume in the feed resulted in 89 and 191% increase in biogas production, respectively. Under a stable condition, anaerobic co-digestion with BW did not lead to any significant impact on digestate quality (in terms of COD removal and biosolids odour) and biogas composition. The results suggest that existing nutrients in sewage sludge can support an increase in OLR by about 2 kg COD/m³/d from a carbon rich substrate such as soft drink BW without inhibition or excessive impact on subsequent handling of the digestate.