Huajun Huang

The comparison of the migration and transformation behavior of heavy metals during pyrolysis and liquefaction of municipal sewage sludge, paper mill sludge, and slaughterhouse sludge

Municipal sewage sludge, paper mill sludge, and slaughterhouse sludge were pyrolyzed and liquefied for the production of bio-char. The migration and transformation behavior of Cu, Cr, and Zn during pyrolysis and liquefaction of these sludges were studied. Pyrolysis and liquefaction promoted mobile fraction (F1 and F2) to stable fraction (F3 and F4). The results showed that pyrolysis and liquefaction largely affected the redistribution of Cu and Zn in raw materials. The environmental risk assessment results indicated that the environmental risk levels of Cu and Zn were significantly reduced in bio-char, and risk level of Cr was slightly decreased after pyrolysis or liquefaction. Both pyrolysis and liquefaction were promising detoxification technologies for the three sludges in terms of the mitigation of heavy metals toxicity. It was suggested that dewatered sludge could be reduced toxicity/risk before utilization by pyrolysis or liquefaction technology, especially for Cu and Zn in slaughterhouse sludge.

Study on demetalization of sewage sludge by sequential extraction before liquefaction for the production of cleaner bio-oil and bio-char.

Demetalization of sewage sludge (SS) by sequential extraction before liquefaction was implemented to produce cleaner bio-char and bio-oil. Demetalization steps 1 and 2 did not cause much organic matter loss on SS, and thus the bio-oil and bio-char yields and the compositions of bio-oils were also not affected significantly. However, the demetalization procedures resulted in the production of cleaner bio-chars and bio-oils. The total concentrations and the acid soluble/exchangeable fraction (F1 fraction, the most toxic heavy metal fraction) of heavy metals (Cu, Cr, Pb, Zn, and Cd) in these products were significantly reduced and the environmental risks of these products were also relived considerably compared with those produced from raw SS, respectively. Additionally, these bio-oils had less heavy fractions. Demetalization processes with removal of F1 and F2 fractions of heavy metals would benefit the production of cleaner bio-char and bio-oil by liquefaction of heavy metal abundant biomass like SS.

Biochar stability assessment methods: A review

Biochar is being developed as a candidate with great potential for climate change mitigation. Sequestering biochar carbon in soil contributes greatly to the reduction of greenhouse gases emissions, and biochar stability is the most decisive factor that determines its carbon sequestration potential. However, methods that can be used universally for direct or indirect assessment of biochar stability are still under investigation. This present review aims to give comprehensive and detailed up-to-date information on the development of biochar stability assessment methods. The method details, advantages and disadvantages, along with the correlations between different methods were reviewed and discussed. Three stability assessment method categories were identified: I) biochar C structure analysis, II) biochar oxidation resistance determination, and III) biochar persistence evaluation by biochar incubation and mineralization rate modelling. Biochar persistence value (e.g., mean residence time, MRT) obtained from incubation and modelling and biochar elemental ratios such as H/Corg and O/Corg are the current most commonly used biochar stability indicators. Incubation and modelling method is too time-consuming while H/Corg and O/Corg ratios are qualitative and conservative, although the effectiveness of these two methods can be further improved. On the other hand, biochar C structures such as aromaticity and degree of aromatic condensation obtained from nuclear magnetic resonance (NMR) analysis and benzene polycarboxylic acids (BPCA) molecular markers and biochar oxidation/degradation recalcitrance obtained from proximate analysis (volatile matter and fixed carbon yields), thermal recalcitrance index (R50), and H2O2- and heat-assisted oxidation (Edinburgh stability tool) are being developed as promising proxies to indicate biochar stability.

An overview of the effect of pyrolysis process parameters on biochar stability

Biochar produced from biomass pyrolysis is becoming a powerful tool for carbon sequestration and greenhouse gas (GHG) emission reduction. Biochar C recalcitrance or biochar stability is the decisive property determining its carbon sequestration potential. The effect of pyrolysis process parameters on biochar stability is becoming a frontier of biochar study. This review discussed comprehensively how and why biomass compositions and physicochemical properties and biomass processing conditions such as pyrolysis temperature and reaction residence time affect the stability of biochar. The review found that relative high temperature (400-700 °C), long reaction residence time, slow heating rate, high pressure, the presence of some minerals and biomass feedstock of high-lignin content with large particle size are preferable to biochar stability. However, challenges exist to mediate the trade-offs between biochar stability and other potential wins. Strategies were then proposed to promote the utilization of biochar as a climate change mitigation tool.

Liquefaction of Biomass for Bio-oil Products

Biomass is considered to be one of the most important renewable energy sources and will become an important part of future sustainable energy system. Liquefaction is a promising thermochemical conversion process that is applied to convert biomass into bio-oil (target product), biochar, and gases. The process is usually carried out in water or another suitable solvent at 250–400 °C under pressures of 5–25 MPa. This chapter firstly collects and sorts out the available review literatures on the liquefaction of biomass. Next, the effects of processing parameters on the liquefaction of biomass are briefly summarized. Then, the characterization and application studies of biochar (solid-phase product) are discussed. Finally, the main upgradation methods of bio-oil (liquid-phase product) are introduced. The ultimate aim of this chapter is to offer some reference for the study of biomass liquefaction.