Influence Of Biomass Feedstocks And Production Temperatures On The Structure-activities Of Biochar

Due to its high potential application in improving soilphysico-chemical properties and fertility、 reducing greenhouse gasemission and retaining contaminants, biochar has attracted widespreadattention in recent years. However, limited work has been done on thesystematic investigation on biochar properties from the large variety ofbiomasses and their influences on the applications. The relationship ofstructure–activity of biomasses and the derived biochar is still unclear. Inthis thesis, three plant-based biomasses （corn stalk, wheat straw, and grass）and three municipal waste-based biomasses （pig manure, eggshell andsewage sludge） were selected and converted into biochars at350oC and500oC under limited O₂condition. Differences of element composition,physico-chemical properties, functional groups, and mineral componentsbetween the two types of biochars were compared. Mineraliztion ofbiochars based on the microbial activity was conducted. Using statisticanalsis of PCA and cluster, we grouped biochars for agriculturalapplication. The main results are as follows:（1）The pH and PZC of plant-based and municipal waste-based biochars were similar, within the range of8–10. Carbon content of allthree plant biochars was56.8–60%, higher than that of all the municipalwaste biochars （13.4–39.1%）, while the latter had higher yield and ashcontents （44.0–55.7%and45.1–90.4%, respectively）, compared to lowercontent in the plant biochars （22.3–6.3%and21.8–22.3%, respectively）.The CEC of municipal waste biochars (49–334cmol·kg^-1) wassignificantly higher than that of the plant biochars (46.3–50.1cmol·kg^-1),while the AEC of municipal waste biochar (12.0–16.0cmol·kg^-1) is lowerthan that in the plant biochars (33.5–63.2cmol·kg^-1). XRD analysisshowed that plant-based biochars had high contents of KCl, while moreCaCO₃existed in municipal waste biochars. FTIR results show that theintensity of plant biological carbon in-OH,-COOH and-CH2was higherthan that of municipal biochar, the latter containing higher intensity of-CO₃and P-O peak.（2） TC、metal content、pH、 PZC、CEC, and AEC of biochar weremore dependant on the production temperature. When the temperatureincreased from350oC to500oC, TC、metal content、pH、 PZC、and CECincreased by33%，30%,18%,16%, and90%, respectively. However, AECwas reduced by30%. A strong correlation between biochar CEC andmetal concentration （350oC, R²=0.87;500oC, R²=0.922） was foudn, so didthe soluble anion and AEC （350oC, R²=0.92;500oC, R²=0.70）. Theproduction temperature has little effect on molecular structure and phase composition of biochar.（3） Stability of biochar is a prerequisite for the carbon sequestration,Our test showed the mineralizzation potential of biochars resulted inincomplete conversion of cellulose and hemicellulose components inbiochars. It showed that there was a high mineralization rate of biochar inthe first week, about0.895–3.025mg·g^-1·day-1, In the first15days, themineralization rate of saw dust biochar was significantly higher than ofbiochar made from straw, after15days, sawdust mineralization ratebecame lower than the mineralization rate of straw.In training for the50days, the mineralization rate of two biochar decreased to lower level andin the steady state. The initial higher mineralization rate is mainly becausesome dissolved organic carbon （DOC） contribution, the content of DOCwas4.44mg g^-1in sawdust which was significantly higher than that ofrice straw DOC content (1.77mg g^-1).（4） This work classified three biochar groups from20waste biomassfeedstocks which would guide appropriate application of biochar into field.The results showed that all20biochars can be classified into three clusters.Cluster1was comprised of bone dregs and eggs hull biochars. Biocharsderived from waterweeds and waste paper is nearby biochar producedfrom shrimp hull and chlorella, which can be classified as Cluster2.Cluster3included biochars derived from wood and crop wastes as well asbiochars from wastewater sludge and pig manure. The results can be aguidance when adding biochar into farmland.Given the amendment of biochar to soil at50t·ha^-1, It will introducerich nutrients and trace metals, whereas toxic metals were much less andnegligible lower than0.35mg·kg^-1, compared to the Class I of ChinaEnvironmental Quality Standards for Soil. Results indicated turning wastebiomasses into biochar can be a potential way to supply soil nutrients andtrace metals and different group biochars can be applied appropriately intosoils with different properties to avoid the excessive or deficient use.