Research On The Coupling Effect Of Potassium Hydroxide And Steam Explosion Pretreatment On Anaerobic Digestion Of Corn Stover For Biogas Production

Biogas, as a clean energy, can be produced from lignocellulosic biomass via anaerobic digestion (AD). However, lignocellulosic materials have complex structure, which leads to some problems in AD, such as the longer lag phase time and lower gas production rate. Getting over recalcitrance of lignocelllose is effective way to fuel production from lignocellulosic biomass. In current work, different pretreatments were applied to enhance the digestibility of corn stover (CS).The influence of steam explosion (SE) pretreatment at following pressure 1.2,1.5,1.8, and 2.1 MPa and residence time 5,10,15,20, and 25 min on AD of CS was studied. It was found that SE was a pretreatment method of high efficiency. Considering energy consumption and efficiency, SE pretreatment of CS at 1.2 MPa for 10 min was considered as an optimal choice to improve AD and the cumulative methane production reached 223.2 mL/gvs, which was 55.2% more than untreated.The influences of 0.5%,1.0%,1.5%, and 2.0% KOH pretreatment at 20℃ and sequent pretreatment of potassium hydroxide and steam explosion (SPPE) on AD of CS were studied. The results showed that KOH pretreatment was a good method to improve the cumulative methane yield.1.5% KOH was an appropriate pretreatment to improve the efficiency of AD and the cumulative methane yield reached 208.6 mL/gvs, which was 45.1% more than untreated. The cumulative methane yield of CS from 1.5% KOH-1.2 MPa,10 min (SPPE15%) was 258.8 mL/gvs, representing a very significant (α<0.01) improvement of 80.0%, compared with untreated. The biodegradability (BD) of CS after SPPE1.5% was 62.5%.The influences of 0.5%,1.0%,1.5%, and 2.0% KOH pretreatment at 60℃ and sequent pretreatment of thermal potassium hydroxide and steam explosion (SPTPE) on AD of CS were investigated. The results showed that thermal KOH pretreatment had higher efficiency than KOH.1.5% thermal KOH was an appropriate pretreatment to improve the efficiency of AD and the cumulative methane yield reached 243.1 mL/gvs, which was 56.4% more than untreated and 16.5% higher than 1.5% KOH treated at 20℃. The cumulative methane yield of CS from 1.5% thermal KOH-1.2 MPa,10 min (SPTPE15%) was 292.9 mL/gvs, causing a very significant (α<0.01) improvement of 88.5%with respect to untreated. The BD of CS after SPTPE1.5% reached 70.7%.The influence of water consumption in preimpregnation on SE with AD of CS was studied. It was found that preimpregnation was essential for SE performance. Solid-liquid ratio of 1:4 (80% of moisture content) had no significant difference from solid-liquid ratio of 1:9 (90% of moisture content) about SE.1:4 preimpregnation saved a lot of water in SE pretreatment and was a more economical and practical method.In order to reduce the cost of KOH pretreatment, spent KOH solution, which was named as black liquor (BL), was reused circularly to pretreat CS for many times. The influence of BL pretreatment on AD of CS was studied. The results showed that after ten times recycling of BL, the cumulative methane yield was effectively increased up to 211.1 mL/gvs, which was 56.1% more than untreated. No significant difference in overall methane yields of 1.5% KOH and BL treated CS was observed. In addition, BL pretreatment significantly saved water and KOH consumption at 56% and 57% respectively compared to KOH pretreatment.SPPE/SPTPE and BL pretreatment might be promising methods of practical application to pretreat CS in the future AD industry.