不同来源生物质废弃物热解炭化农业应用潜力分析:生物质炭产率、性质及促生效应

Potential of pyrolysis for agricultural application of different biowastes:Biochar yield,properties and their crop growth effects

【目的】中国农业生物质废弃物种类多、数量大,且存在病原菌、农药和抗生素残留等潜在生态和环境风险。热解炭化作为一种废弃物的安全处理方法,其生物质炭的循环得率、性质及其土壤改良和促进作物生长的效应还需系统的比较研究。【方法】本研究选取作物生产来源的原生生物质、养殖业来源的次生生物质、食品加工处理的残余生物质等共26种生物质废弃物原料,在同一条件下炭化,分析不同来源原料热解后生物质炭产出率与性质。以小白菜(Brassica campestris L.ssp.)为试材进行盆栽试验,研究生物质炭对作物生长及土壤改良效应,进而评估这些废弃物炭化农业循环的应用潜力。【结果】供试26种废弃物炭化后的生物质炭产出率介于22%~71%,有机碳循环回收率介于22%~81%,氮素循环回收率介于21%~67%。26种废弃物生物质炭的pH和阳离子交换量差异较小(变异系数10%左右),总有机碳、氮、水分、灰分含量等差异较大,变异系数在60%~70%;而不同原料生物质炭的电导率和溶解性有机碳含量变化极大,变异系数大于90%。生物质炭盆栽试验中,生物炭添加1%,小白菜生物量提升效应介于-34%~314%,变异系数大于100%;小白菜品质提升效应介于-14%~228%,变异系数为59%;土壤肥力提升效应介于20%~360%,特别是土壤有效磷含量提升幅度在0~24倍,均值为359%。同时,生物质炭产出率与生物质炭中灰分呈显著正相关,生物质炭的碳氮回收率与原料中碳氮含量呈显著正相关;不同原料热解炭化的质量回收率、碳氮回收率与小白菜产量及品质等指标间变化差异较大,在小白菜产量效应和品质效应间,部分生物质炭存在抵消作用,而另一部分生物质炭表现为协同作用。【结论】综合考虑热解炭化的生物质炭化循环率及碳氮回收循环率和土壤质量-植物生长协同提升效应,供试26种原料中,蚕砂、稻壳牛粪、骨粉、双孢菇渣、兔粪、羊粪和玉米渣的炭化循环率和土壤质量-植物生长协同提升幅度较高(>50%),为优先炭化农业利用的生物质废弃物;而木糖渣、稻壳粉、椰渣、高粱酒渣、核桃皮、蚓粪和红茶渣等废弃物热解炭化,因炭化循环率较低,或者土壤质量-植物生长提升的不一致效应,认为不宜炭化农业利用;而其余废弃物热解炭化后的效应介于上述两类之间,具有较高的炭化循环率和一定程度的土壤质量-植物生长协同提升效应,属于可炭化农业利用的生物质废弃物。

【Objectives】Biowastes from agricultural production exist in various forms.These wastes are produced in large quantities,having consequent environmental risks due to antibiotics,plant pathogens,and pesticide residues in them.Producing biochar by pyrolysis is an environmentally friendly way of dealing with biowastes.This study assessed the efficacy of different biowastes for biochar production and their effects on crop yield and quality.【Methods】A pot experiment was conducted using pakchoi as test crop materials.A total of 26 types of agro-biowastes were collected from primary biowastes(e.g.straws),secondary biowastes(e.g.livestock dung)and by-products from food processing.All the feedstocks were pyrolyzed under the same condition to make biochar.We analyzed the biochar yield of different feedstocks and their physicochemical properties.The feasibility of pyrolysis and the effect of biochar on crop production were assessed.【Results】The yield of biochar from the tested biowastes ranged in 22%-71%.The biochar recovery of carbon and nitrogen ranged in 22%-81% and in 21%-67%,respectively.The coefficient of variation(CV)of the pH and cation exchange capacity of the biochars was 10%;that for total organic carbon,total nitrogen,moisture,and ash contents were 60%-70%;and that for electrical conductivity,dissolved organic carbon and total P contents were>90%.In the pot experiment,biochar was amended to 1%.The pakchoi biomass increase ranged from-34%to 314%compared to the no biochar control,with a CV of 100%.However,the quality index increase of pakchoi ranged in -14%-228%,with a CV of 59%.Meanwhile,soil fertility improvement ranged in 20%-360%,significantly increased by 0-24 folds(359% on average).Moreover,changes in biochar yield and carbon and nitrogen recovery were found inconsistent with the improvements in biomass and quality of pakchoi across the biochars from different feedstocks.Some biochars showed tradeoffs between biomass production and pakchoi quality,while a few showed synergism,in the pot experiment.Significant positive correlations were found between biochar yield and ash content and between biochar recovery of organic carbon and nitrogen and their content in the feedstock.【Conclusions】The biochar yield,recovery of organic carbon and nitrogen,and the synergistic improvement of the soil-plant system were synthesized.Of the 26 biowastes tested,silkworm residue,rice husk dung,bone powder,agaricus bisporus residue,rabbit manure,sheep manure and corn residue had higher yield for biochar recovery and had a high synergistic improvement of the soil-plant system(>50%).These biowastes should be prioritized for pyrolysis and biochar application in agriculture.On the other hand,xlose residue,rice husk powder,coconut residue,brewery sorghum residue,walnut residue,wormcast,and black tea residue were not recommended for pyrolysis and biochar use in agriculture due to either low biochar yield and element recovery or inconsistent improvement of the soil-plant system.The others could be considered conditionally potential for biochar production and application in agriculture due to acceptable resource recovery and soil-plant improvement of their pyrolyzed biochar.