Characterization of the solid residue generated in the detoxification step of sugarcane bagasse hemicellulosic hydrolysate and behavior in agricultural soils

ABSTRACT Overliming is an effective way of neutralizing and reducing the toxicity of the hydrolysates generated from acidic pretreatment of lignocellulosic biomass for ethanol production and others biotechnological products. Overliming generates a solid residue whose inadequate disposal may represent an environmental problem. This work aimed at the chemical characterization of the solid residue generated during the detoxification of the sugarcane bagasse hemicellulosic hydrolysate and evaluation of its behavior in soil. The solid residue was submitted to physicochemical and granulometric analysis and determination of the contents of sugars, metals and toxic compounds (acetic acid, furfural, hydroxymethylfurfural and phenols). The potential of the residue as corrective of soil acidity was determined by analyzing the quality attributes of soil correctives (neutralizing power – NP, relative total neutralizing power – RTNP, Ca and Mg contents and granulometry). The residue was also evaluated for its influence on soil microbial communities and toxicity through bioassays with Lactuca sativa seeds. The residue contributed to the overall improvement of soil chemical attributes. The levels of Ca, Mg, C, OM and CEC were increased, nutrients such as Zn, Fe, Ni, Cr and Mn were detected, and microbial communities were stimulated. Besides, the residue showed no significant values of toxic compounds and no toxicity to L. sativa seeds. The residue was able to reduce the soil pH and to keep it stable throughout the study period. As a higher amount of the residue was necessary to reach pH 7 than limestone, it should be used as an auxiliary corrective of acidity.

摘要 过量石灰中和法（Overliming）是一种可有效中和并降低木质纤维素生物质经酸性预处理后生成的水解液毒性的手段，该类水解液可用于乙醇生产及其他生物技术产品的制备。过量石灰中和法会产生固体残渣，若处置不当可能引发环境问题。本研究旨在对甘蔗渣半纤维素水解液脱毒过程中产生的固体残渣开展化学表征，并评估其在土壤中的环境归趋。研究人员对该固体残渣进行了理化与粒度分析，测定了其中糖类、金属及有毒化合物（乙酸、糠醛、羟甲基糠醛与苯酚）的含量。通过分析土壤改良剂的核心品质指标（中和能力（NP）、相对总中和能力（RTNP）、钙与镁含量及粒度特性），明确了该残渣作为土壤酸度改良剂的应用潜力。此外，本研究还借助莴苣（Lactuca sativa）种子生物测定试验，评估了该残渣对土壤微生物群落的影响及其自身毒性。研究结果表明，该残渣可整体改善土壤化学性状：钙、镁、有机碳、有机质（OM）及阳离子交换量（CEC）水平均得到显著提升；同时检出锌（Zn）、铁（Fe）、镍（Ni）、铬（Cr）与锰（Mn）等营养元素；且可有效促进土壤微生物群落的生长与活性。此外，该残渣未检出显著含量的有毒化合物，对莴苣种子无毒性作用。该残渣可降低土壤pH值，并在整个研究周期内维持pH值稳定。但由于将土壤pH调至7所需的残渣用量高于石灰石，因此该残渣仅可作为辅助性土壤酸度改良剂使用。