Buchun Si

Conversion efficiency and oil quality of low-lipid high-protein and high-lipid low-protein microalgae via hydrothermal liquefaction.

Hydrothermal liquefaction (HTL) is a promising technology for converting algae into biocrude oil. Here, HTL of a low-lipid high-protein microalgae (Nannochloropsis sp.) and a high-lipid low-protein microalgae (Chlorella sp.) was studied. An orthogonal design was applied to investigate the effects of reaction temperature (220-300°C), retention time (30-90 min), and total solid content (TS, 15-25%wt) of the feedstock. The highest biocrude yield for Nannochloropsis sp. was 55% at 260°C, 60 min and 25%wt, and for Chlorella sp. was 82.9% at 220°C, 90 min and 25%wt. The maximum higher heating values (HHV) of biocrude oil from both algae were ∼ 37 MJ/kg. GC-MS revealed a various distribution of chemical compounds in biocrude. In particular, the highest hydrocarbons content was 29.8% and 17.9% for Nannochloropsis and Chlorella sp., respectively. This study suggests that algae composition greatly influences oil yield and quality, but may not be in similar effects.

Recovery of reducing sugars and volatile fatty acids from cornstalk at different hydrothermal treatment severity

This study focused on the degradation of cornstalk and recovery of reducing sugars and volatile fatty acids (VFAs) at different hydrothermal treatment severity (HTS) (4.17-8.28, 190-320°C). The highest recovery of reducing sugars and VFAs reached 92.39% of aqueous products, equal to 34.79% based on dry biomass (HTS, 6.31). GC-MS and HPLC identified that the aqueous contained furfural (0.35-2.88 g/L) and 5-hydroxymethyl furfural (0-0.85 g/L) besides reducing sugars and VFAs. Hemicellulose and cellulose were completely degraded at a HTS of 5.70 and 7.60, respectively. SEM analysis showed that cornstalk was gradually changed from rigid and highly ordered fibrils to molten and grainy structure as HTS increased. FT-IR and TGA revealed the significant changes of organic groups for cornstalk before and after hydrothermal treatment at different HTS. Hydrothermal treatment might be promising for providing feedstocks suitable for biohythane production.

Elemental migration and characterization of products during hydrothermal liquefaction of cornstalk

Biofuel production from lignocellulosic biomass through hydrothermal liquefaction (HTL) is a promising direction. This study characterized the products and investigated the elemental migration during the HTL of cornstalk at seven different operation temperatures (210-375°C). The biocrude oil yield significantly increased from 7.04% (210°C) to 23.32% (290°C) as the temperature increased, and decreased to 21.07% when further increased to 375°C. A carbon recovery of 11.03-38.69%, and a hydrogen recovery of 7.77-25.61% were achieved in the biocrude oil. Hydrogen (27.87-70.94%) and nitrogen (74.56-81.76%) were effectively recovered in the aqueous phase. GC-MS, HPLC, TGA and FT-IR analysis indicated that major organic compounds in the biocrude oil were interestingly similar between 210°C and 270°C. The identified compounds included hydrocarbons, esters and carboxylic acid. The calculative yields of biocrude, hydrogen, methane and biochar reached 7.04-23.32, 0.07-0.29, 7.12-12.08 and 3.01-22.42t/100t cornstalks, respectively.

Bioprocess engineering for biohythane production from low-grade waste biomass: technical challenges towards scale up

A concept of biohythane production by combining biohydrogen and biomethane together via two-stage anaerobic fermentation (TSAF) has been recently proposed and considered as a promising approach for sustainable hythane generation from waste biomass. The advantage of biohythane over traditional biogas are more environmentally benign, higher energy recovery and shorter fermentation time. However, many of current efforts to convert waste biomass into biohythane are still at the bench scale. The system bioprocess study and scale up for industrial application are indispensable. This paper outlines the general approach of biohythane by comparing with other biological processes. The technical challenges are highlighted towards scale up of biohythane system, including functionalization of biohydrogen-producing reactor, energy efficiency, and bioprocess engineering of TSAF.

Improve the biodegradability of post-hydrothermal liquefaction wastewater with ozone: conversion of phenols and N-heterocyclic compounds

Hydrothermal liquefaction is a promising technology to convert wet biomass into bio-oil. However, post-hydrothermal liquefaction wastewater (PHWW) is also produced during the process. This wastewater contains a high concentration of organic compounds, including phenols and N-heterocyclic compounds which are two main inhibitors for biological treatment. Thus, proper treatment is required. In this work, ozone was used to convert phenols and N-heterocyclic compounds with a dosage range of 0-4.64 mg O3/mL PHWW. After ozone treatment, the phenols were fully converted, and acids were produced. However, N-heterocyclic compounds were found to have a low conversion rate (21.7%). The kinetic analysis for the degradation of phenols and N-heterocyclic compounds showed that the substitute played an important role in determining the priority of ozone reactions. The OH moiety in the ring compounds (phenols and pyridinol) may form hydroxyl radical, which lead to an efficient reaction. A substantial improved biodegradability of PHWW was observed after ozone treatment. The ratio of BOD5/COD was increased by about 32.36%, and reached a maximum of 0.41. The improved biodegradability of PHWW was justified by the conversion of phenols and N-heterocyclic compounds.

Inhibitors degradation and microbial response during continuous anaerobic conversion of hydrothermal liquefaction wastewater

One critical challenge of hydrothermal liquefaction (HTL) is its complex aqueous product, which has a high concentration of organic pollutants (up to 100gCOD/L) and diverse fermentation inhibitors, such as furfural, phenolics and N-heterocyclic compounds. Here we report continuous anaerobic digestion of HTL wastewater via an up-flow anaerobic sludge bed reactor (UASB) and packed bed reactor (PBR). Specifically, we investigated the transformation of fermentation inhibitors and microbial response. GC-MS identified the complete degradation of furfural and 5-hydroxymethylfurfural (5-HMF), and partial degradation (54.0-74.6%) of organic nitrogen and phenolic compounds, including 3-hydroxypyridine, phenol and 4-ethyl-phenol. Illumina MiSeq sequencing revealed that the bacteria families related to detoxification increased in response to the HTL aqueous phase. In addition, the increase of acetate-oxidizing bacteria in UASB and acetogens in PBR showed a strengthened acetogenesis. As for the archaeal communities, an increase in hydrogenotrophic methanogens was observed. Based on GC-MS/HPLC and microbial analysis, we speculate that dominant fermentation inhibitors were transformed into intermediates (Acetyl-CoA and acetate), further contributing to biomethane formation.

Integrated anaerobic digestion and algae cultivation for energy recovery and nutrient supply from post-hydrothermal liquefaction wastewater

Post-hydrothermal liquefaction wastewater (PHWW), which contains approximately 80% of original feedstock resources, shows great potential to achieve sustainable development of an environment-enhancing energy system. A combination of anaerobic digestion and algae cultivation was proposed for methane recovery and nutrient supply from PHWW. Granular activated carbon (GAC) and ozone were used to enhance energy recovery from the PHWW. The results indicated that with GAC addition, the maximum methane yield increased by 67.7%-228 mL/g CODremoval. In addition, Chlorella vulgaris displayed optimal growth in a 5-fold diluted digestate with a 2.32 g/L maximum biomass content and 180 mg/(L·d) biomass production rate. The total energy yield was 565 kJ/g COD, which was 27.4 times higher than that without GAC. Integration of anaerobic digestion and algae cultivation, particularly with GAC addition during fermentation, is a feasible and advantageous process for energy recovery from PHWW.