Effect of pretreatment and biomass blending on bio-oil and biochar quality from two-step slow pyrolysis of rice straw.

This study investigated biomass blending and water washing to improve product quality from two-step pyrolysis of rice straw. Rice straw (RS) was mixed with groundnut shells (GNS) and wheat straw (WS) in different weight ratios. Blending RS with GNS/WS in a 1:1 ratio increased the total bio-oil yields by 7-9% and reduced the pyrolysis gas and char yields by 5-7% and < 2%, respectively. RS was washed with water separately to examine the effect of removing water-soluble ash elements. The optimum washing duration was 60 min; the ash removal efficiency was then 26%. The bio-oil yields from washed straw increased by 4% over unwashed straw, and pyrolysis gas yields decreased. Combining the washing and blending processes increased the levoglucosan yield by 1.6-2.1 times compared to unwashed RS, and the water content in bio-oil was reduced by âˆ¼ 10%. Moreover, the biochar samples obtained after pyrolysis of washed biomass blends had potential fuel applications owing to low fouling or slagging propensity. They also had possible use in the soil for adsorption of soil contaminants and increasing acidic soil pH, with likely stability of âˆ¼ 1000 years in the ground. These results provide a promising alternative for efficiently converting rice straw to multiple value-added products.

Potential of stepwise pyrolysis for on-site treatment of agro-residues and enrichment of value-added chemicals.

This paper compares the yield and composition of bio-oil derived through stepwise and continuous pyrolysis of agro-residues. The temperature steps were selected using thermogravimetric analysis. Groundnut shell, empty fruit bunch pellets, and rice straw were pyrolyzed at 305 °C in the first step and 600 °C in the second step and pinewood chips were pyrolyzed at 340 °C and 600 °C. The cumulated yields of bio-oil were lower in both continuous and stepwise pyrolysis for agro-residues in comparison with woody biomass, with a corresponding increase in biochar and pyrolysis gas yields. Approximately 50% of the pinewood and 31-40% of the agro-residues were converted to bio-oil through both methods. This trend is explained by the differing biochemical composition of biomasses, and concentrations of inorganic components. Bio-oil fractions were separated into water-soluble and water-insoluble compounds before characterization. Bio-oil obtained in the first step was richer in organic acids, anhydrosugars, and carbonyl compounds, while the later fraction of bio-oil was richer in unbranched phenolic compounds. Thus, compounds known to promote bio-oil aging were separated into different fractions. Further, stepwise pyrolysis proved to be most effective for groundnut shells in isolating chemicals with a minimum loss of yield compared to continuous pyrolysis. A preliminary economic assessment of bio-oil showed that the value of bio-oil for crop residues was improved by 2-2.5 times during stepwise heating while for pinewood it reduced by half. This study provides a good starting point for further research in optimizing the temperature steps for pyrolysis and separation of chemicals from bio-oil.

Anaerobic treatment of LCFA-containing synthetic dairy wastewater at 20 °C: Process performance and microbial community dynamics.

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assessed at 20 °C. The effects of the LCFA concentration (33-45% of COD) and organic loading rates (2-3 gCOD/L·d) were determined using three parallel expanded granular sludge bed reactors. For the first time, long term anaerobic treatment of LCFA-containing feed at 20 °C was shown to be feasible and was linked to the microbial community dynamics in high-rate reactors. During a two-month operation, a soluble COD removal of 84-91% and COD to methane conversion of 44-51% was obtained. However, granular sludge flotation and washout occurred after two months in all reactors without volatile fatty acids (VFA) accumulation, emphasizing the need for sludge retention for long-term granular sludge reactor operation with LCFA-containing feed at low ambient temperatures. The temporal shifts in microbial community structure were studied in the high-rate treatment of SDW, and the process disturbances (elevated LCFA loading, LCFA accumulation, and batch operation) were found to decrease the microbial community diversity. The relative abundance of Methanosaeta increased with higher LCFA accumulation in the settled and flotation layer granules in the three reactors, therefore, acetoclastic methanogenesis was found to be crucial for the high-rate treatment of SDW at 20 °C. This study provides an initial understanding of the continuous anaerobic treatment of LCFA-containing industrial wastewaters at low ambient temperatures.

Anaerobic batch conversion of pine wood torrefaction condensate.

Organic compound rich torrefaction condensate, owing to their high water content and acidic nature, have yet to be exploited for practical application. In this study, microbial conversion of torrefaction condensate from pine wood through anaerobic batch digestion (AD) to produce methane was evaluated. Torrefaction condensate exhibited high methane potentials in the range of 430-492mL/g volatile solids (VS) and 430-460mL/gVS under mesophilic and thermophilic conditions, respectively. Owing to the changes in the composition, the methane yields differed with the torrefaction condensates produced at different temperatures (225, 275 and 300°C), with a maximum of 492±18mL/gVS with the condensate produced at 300°C under mesophilic condition. The cyclic batch AD experiments showed that 0.1VSsubstrate:VSinoculum is optimum, whereas the higher substrate loading (0.2-0.5) resulted in a reversible inhibition of the methane production. The results suggest that torrefaction condensate could be practically valorized through AD.