Fungal fermentation on anaerobic digestate for lipid-based biofuel production

Abstract

BackgroundAnaerobic digestate is the effluent from anaerobic digestion of organic wastes. It contains a significant amount of nutrients and lignocellulosic materials, even though anaerobic digestion consumed a large portion of organic matters in the wastes. Utilizing the nutrients and lignocellulosic materials in the digestate is critical to significantly improve efficiency of anaerobic digestion technology and generate value-added chemical and fuel products from the organic wastes. Therefore, this study focused on developing an integrated process that uses biogas energy to power fungal fermentation and converts remaining carbon sources, nutrients, and water in the digestate into biofuel precursor-lipid.ResultsThe process contains two unit operations of anaerobic digestion and digestate utilization. The digestate utilization includes alkali treatment of the mixture feed of solid and liquid digestates, enzymatic hydrolysis for mono-sugar release, overliming detoxification, and fungal fermentation for lipid accumulation. The experimental results conclude that 5 h and 30 °C were the preferred conditions for the overliming detoxification regarding lipid accumulation of the following fungal cultivation. The repeated-batch fungal fermentation enhanced lipid accumulation, which led to a final lipid concentration of 3.16 g/L on the digestate with 10% dry matter. The mass and energy balance analysis further indicates that the digestate had enough water for the process uses and the biogas energy was able to balance the needs of individual unit operations.ConclusionsA fresh-water-free and energy-positive process of lipid production from anaerobic digestate was achieved by integrating anaerobic digestion and fungal fermentation. The integration addresses the issues that both biofuel industry and waste management encounter—high water and energy demand of biofuel precursor production and few digestate utilization approaches of organic waste treatment.

Fungal Pretreatments on Non-Sterile Solid Digestate to Enhance Methane Yield and the Sustainability of Anaerobic Digestion

“…The observed TS and VS contents (Table 1) were comparable to those reported by Zhong et al [19], who observed for the SFD from the co-digestion of animal manure and food wastes TS and VS contents of 30.60 ± 2.13% and 89.18 ± 0.29% on TS, respectively. However, lower VS contents were also found, as reported by Sambusiti [10] (83.8 ± 0.3% on TS) and Musatti et al [33] (80% on TS).…”

“…Unfortunately, the SFD from agrozootechnical residues has been widely recognized as a recalcitrant biomass, and its use in biogas production challenges the microbial community involved in AD [19]. Cellulose crystallinity and lignification degree decrease its digestibility and limit the theoretical biogas yields [20].…”

Chemical-free recovery of crude protein from livestock manure digestate solid by thermal hydrolysis

“…On the other hand, phosphorous mostly stayed in the leftover solid, while potassium dissolved in the solution after THP. As to the lignocellulosic compositions of MDS before THP, similar values have been reported (Tsapekos 2017;Zhong et al 2016). After THP, the content of each lignocellulosic component actually increased in the leftover solid almost proportionally from that in the original MDS sample, as a result of the dissolution of crude protein.…”

Chemical-Free Recovery of Crude Protein from Livestock Manure Digestate Solid by Thermal Hydrolysis

“…On the other hand, phosphorous mostly stayed in the leftover solid, while potassium dissolved in the solution after THP. As to the lignocellulosic compositions of MDS before THP, similar values have been reported (Tsapekos 2017;Zhong et al 2016).…”