Anaerobic co-digestion of swine manure with sweet potato or cassava in different C/N ratios

ABSTRACT: Anaerobic co-digestion (AcoD) of waste is a method of increasing methane (CH4) yield and improving biofertilizer quality. This study aimed to evaluate the best AcoD conditions for swine manure (SM) with sweet potato (SP) or cassava (C) in different amounts in semi-continuous biodigesters. Initially, using batch biodigesters, an AcoD test of the SM with SP or C was performed, adopting carbon/nitrogen (C/N) ratios of 10/1, 13/1, 17/1, and 22/1. Based on the results, a C/N ratio of 10/1 was chosen, which was the proportion that resulted in the highest reduction of volatile solids (VS) and specific biogas production. From these results, the experiment was carried out in semi-continuous biodigesters, consisting of three treatments (control (SM), SP 10/1, and C 10/1) with five replicates and a hydraulic retention time (HRT) of 30 days. Total solid (TS) and volatile solid (VS) reductions, biogas and CH4 yields, alkalinity, and volatile acidity were measured. The control treatment differed from the others and resulted in decreased biogas yield (752 LN.kgVSadded -1), CH4 (449 LN.kgVSadded -1), and CH4 content (59.7%). The AcoD treatments (SP and C) did not differ significantly for biogas yield (respectively, 901 and 883 LN.kgVSadded -1) and CH4 (respectively, 590 and 547 LN.kgVSadded -1); however, they differed in CH4 content (65.5% and 61.9% respectively). The treatments showed general reduction averages of 76.1% and 85.9% for TS and VS, respectively, with no statistical difference found between them. The AcoD of the SM with SP or C increased the production and quality of the biogas, increasing the concentration of CH4 therein.

摘要：厌氧共消化（Anaerobic co-digestion, AcoD）是提升甲烷（methane, CH₄）产率、优化生物肥料品质的废弃物资源化处理手段。本研究旨在评估猪粪（swine manure, SM）分别与甘薯（sweet potato, SP）、木薯（cassava, C）以不同配比进行厌氧共消化的最优工况，实验采用半连续式生物消化器（semi-continuous biodigesters）开展。
初始阶段，本研究借助批次式生物消化器（batch biodigesters）开展猪粪与甘薯、猪粪与木薯的厌氧共消化预试验，设置碳氮比（carbon/nitrogen, C/N）分别为10/1、13/1、17/1及22/1。基于预试验结果，最终选定碳氮比10/1作为正式实验的配比——该配比下挥发性固体（volatile solids, VS）削减率与比产沼气量均达到最高水平。
基于上述结论，正式实验采用半连续式生物消化器开展，共设置3组处理：对照组（仅添加猪粪，SM）、SP 10/1组、C 10/1组，每组设置5个重复，水力停留时间（hydraulic retention time, HRT）为30天。本实验测定的指标包括总固体（total solid, TS）与挥发性固体削减率、沼气及甲烷产率、碱度（alkalinity）及挥发性酸度（volatile acidity）。
结果显示，对照组与其余两组共消化处理组存在显著差异：对照组的沼气产率（752 LN·kgVSadded⁻¹）、甲烷产率（449 LN·kgVSadded⁻¹）及甲烷体积占比（59.7%）均低于共消化组。厌氧共消化处理组（SP及C组）的沼气产率（分别为901、883 LN·kgVSadded⁻¹）与甲烷产率（分别为590、547 LN·kgVSadded⁻¹）无显著统计学差异，但甲烷体积占比存在明显差异（分别为65.5%、61.9%）。
各组处理的总固体与挥发性固体平均削减率分别为76.1%与85.9%，组间未检测到统计学差异。综上，猪粪与甘薯或木薯的厌氧共消化可有效提升沼气产量与品质，显著提高沼气中甲烷的浓度。