Preparation/Characterization Of Highly Stable Biochar And Its Application

Crop straw is one of nature’s most abundant renewable lignocellulosic raw materials,and using straw as a raw material for preparing biochar not only maximises resources,but also has economic and environmental benefits.However,biochar can release large amounts of dissolved solids,which can affect the stability of its performance and thus limit its practical application.The saccharification residues（with lignin as the main component）from the bioethanol preparation process were used as a raw material for biochar.This multi-process combination not only saved the cost of collecting,handling and transporting the raw material for biochar（30.5%of the total cost）,but also its prepared biochar had very low release materials.The study used Acremonium cellulase enzymes to saccharify four crops of barley,wheat,corn and rice straw,and the straw saccharification residues were prepared into biochar at different temperatures.After characterisation of its properties,its performance as an adsorbent and soil conditioner was investigated respectively.The main findings are as follows:（1）The characteristics of biochar prepared from different raw materials and at different temperatures varied considerably:after saccharification by cellulase enzymes,the increase in lignin content of straw was 27～58%.The properties of biochar prepared from ordinary straw and saccharified straw（referred to as ordinary biochar and saccharified biochar respectively）differed considerably.Compared to ordinary biochar,the carbon content of the saccharified biochar was 0.06～16.13%higher,the specific surface area was increased by up to 2.74 times,the functional group types were more or less the same,the amounts of soluble release material decreased by 89.06%～96.12%,the thermal weight loss was 3.29～40.78%less（i.e.more thermally stable）and the particle strength varies depending on the material and the pyrolysis temperature.（2）Saccharified biochar with enhanced stability and adsorption properties as an adsorbent:500℃rice saccharified biochar and ordinary biochar were used for the adsorption of groundwater pollutant phenol.The content of lactone group,phenolic hydroxyl group,carbonyl group and the specific surface area of saccharified biochar was 55.56%,50.57%,311.56%and 167%higher than that of ordinary biochar,respectively.Both biochar had the maximum adsorption capacity for phenol at p H close to neutral,with the adsorption capacity of the saccharified biochar being 25.04%higher than that of the ordinary biochar.The kinetics of phenol adsorption on both biochar followed the Elovich model well.By fitting the isotherm model,the saccharified biochar tended to follow the Freundlich model,indicating that adsorption is a non-uniform multilayer phenomenon,whereas multiple adsorption modes may exist for the ordinary biochar.The equilibrium adsorption capacity of the saccharified biochar was increased by 41.63%compared to the ordinary biochar.The adsorption performance of the saccharified biochar was maintained at 84.86%after five cycles,and the weakening of its adsorption performance may be related to functional groups such as C=C,O=C-C and C-H bonds.（3）Saccharified biochar had a good synergistic effect as a soil amendment with chemoautotrophic microorganism:the four 700°C saccharified biochar were used for CO₂ adsorption with different adsorption capacities.The adsorption kinetic model showed that the four types of saccharified biochar were mainly physical adsorption.The CO₂ adsorption capacity of biochar was strongly influenced by temperature,with66～85%decrease from 30 to 70°C.As a one of the soil amendments,the CO₂adsorbed by biochar can be used as an inorganic carbon source for autotrophic microorganisms to promote their growth,thereby reducing soil CO₂ release and enhancing soil carbon sink.The synergistic effects of saccharified biochar and chemoautotrophic microorganisms in soil were investigated through their combination.The use of biochar changed the physicochemical properties of soil,so that p H and dissolved oxygen tended to increase,and total dissolved solids and conductivity decreased as a whole,which was related to the increase of microbial biomass in soil.The combination of the two increased the microbial amount by 273.87 pmol g^-1 soil（measured as ATP）,which was 124.25 pmol g^-1 soil（biochar only group）and 268.60pmol g^-1 soil（autotrophic bacteria only）higher than when the two were used alone.This paper provides a low cost,high performance,multi-process combined technology pathway for the resourceisation of lignocellulose.The saccharified biochar can be applied to groundwater and soil environments,providing an alternative solution for groundwater remediation,and increasing soil carbon sinks.