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Enteromorpha prolifera (Ep), a dominant low-lipid marine macroalgae with about 30% ash content, is seasonally bloomed along the coast of eastern China, whereas crude glycerol is a main byproduct of biodiesel industry. This study focused on the biocrude production from Ep with crude glycerol, in comparison to those from Ep alone, and Ep with glycerol at different reaction temperatures (240 °C −360 °C). The highest biocrude yield of 38.71% was obtained at 320 °C using Ep with crude glycerol (mass ratio: 1:6), which was much higher than those using Ep alone (13.35%) and Ep with glycerol (16.14%) at the same ratios. After the optimization of the mass ratio of Ep to crude glycerol and retention time, the highest biocrude yield further reached 47.28% at a mass ratio (Ep to crude glycerol) of 1:5 and a retention time of 50 min. The addition of crude glycerol significantly improved biocrude production as well as reduced the oil nitrogen content. Elemental analysis indicated the nitrogen contents of biocrude oil from Ep with crude glycerol were nearly less than 1%, much lower than those under other conditions and similar to that of petroleum. This study suggested that the addition of crude glycerol could improve the yield and quality of the biocrude oil from eutrophic low-lipid high-protein algae.

s Chlorella sp., as a kind of microalgae with high proteins content and rigid cell walls, is a potential material for proteins recovery as poultry feed supplement source. This study proposed an algal biorefinery paradigm for sequent production of proteins and biogas from microalgae Chlorella sp. via CO2 assisted hydrothermal treatment and anaerobic digestion. The CO2 could be sustainably refilled as being a bioproduct of biogas. As a widely-used environmentally benign hydrothermal catalyst, the addition of CO2 could reduce treatment temperature and CO2 is easily removed by depressurizing. Microalgal cells were more disrupted with rising temperature from 70 °C to 150 °C, which facilitated the recovery of proteins. The recovery of proteins increased from 6.32% to 69.81%. After proteins recovery, the C/N ratio of microalgal residues was significantly higher than the untreated Chlorella sp. The process of proteins recovery could relieve the hydrolysis limitation of cell walls but reduce organics remained in microalgal residues. Biomethane production from microalgal residues exhibited a similar rising trend to proteins recovery. The highest cumulative biomethane production of 194.63 mL/gVS was achieved for the group at 130 °C, and the lowest value of 104.42 mL/gVS was obtained for the group at 70 °C. Excess microalgal cells disruption and side reactions led to the poor biomethane performance for the group at 150 °C, consistent with the decreased proteins recovery. During anaerobic digestion, the concentration of acetic acid distributed in a range of 0.05–0.44 g/L, which was dominant among total volatile fatty acids. The proteins as poultry feed supplement would be preferable to be considered as the main product, and the biomethane was considered as the side product. Carbon balance analysis revealed that most groups could basically meet the CO2 demand for HTT except the group at 150 °C. 130 °C was considered as the favorable treatment temperature level, leading to a proteins yield of 0.41 g/gVS and biomethane yield of 91.47 mL/gVS by Chlorella sp.

Human waste (HW) poses environmental and public health risk, thereby its sustainable management is becoming a serious growing challenge. Anaerobic digestion (AD) has long been introduced as an environmental-friendly and sustainable waste management technology with bio-methane as final product. Energy production via AD of HW would significantly contribute to low-carbon energy production systems and circular bio-economy. In this study, optimal conditions, inhibiting factors, and microbial community changes in continuously fed biogas reactors during anaerobic digestion of HW at elevated influent feedstock concentration (IFC) were investigated. The highest methane yield (327 ± 21 mL g VS−1) was obtained at IFC of 3% TS. Increased IFC deteriorated the process and affected the microbiome dynamicity. Specifically, methane production was reduced by 50% with a concomitant increment of ammonia, Na+, and K+ concentration. Two archaeal species (Methanosaeta and WSA2) were dominating the microbial community at stable period. Two uncharacterized microbial groups (WWE1 and WSA2) were present and a potential syntrophic interaction between these two members was hypothesized to play a crucial role in achieving a well-performing process. AD process treating HW showed promising results for valorization of HW to clean energy-biomethane both in environmental and economic aspects. Specifically, 1 t of HW VS could obtain a greenhouse gases (GHG) mitigation of −54 to −272 kg CO2,eq via the AD process. The LCA results demonstrated that such a bioenergy system would also bring about environmental savings in ecosystem quality and resource damage categories. Although ammonia inhibition at elevated IFC found as a potential inhibitory factor, it can be easily overcome using co-digestion strategies or nitrogen recovery at upstream.