高含固污泥厌氧消化过程中含固率对污泥有机质降解效率的影响机制

Anaerobic digestion of high-solids sludge deals with sludge with solids content ranged from 10% to 20%. The process uses higher concentration of organic substrates than conventional anaerobic digestion,and this change leads to higher volumetric biogas yield and less heating energy. However, the efficency of sludge organic degradation probably decreases due to the negative impact of high solid concentration. Thus, in this study, a mechanism hypothesis on the effect of solid concentration on organic degradation during anaerobic digestion of high-solids sludge is proposed.Based on the hypothesis, mass transfer performance and rheological properties of high-solids sludge are first analyzed, and then their relevance with sludge stirring and their influence on sludge organic degradation are discussed. Next, during anaerobic digestion of high-solids sludge, the intermediate products, mainly including volatile fatty acids and ammonia are monitored, and then the influence of their accumulation on sludge organic degradation is concluded. Subsequently, the effect of sludge organic content and composition on organic degradation is evaluated, and the change of sludge characteristics due to co-digestion and pretreatment and its impact on organic degradation are analyzed. Finally, the hypothesis will be verified or amended so as to describe the influence mechanism of solid concentration on organic degradation. Based on the mechanism, a series of measures will be proposed systematically for the improvement of organic degradation during anaerobic digestion of high-solids sludge.

高含固污泥厌氧消化进泥含固率为10%-20%，相对于传统污泥厌氧消化提高了有机底物浓度，可以减少反应器加热能耗，提高单位容积产气量,但受制于高固体浓度带来的负面影响，污泥有机质降解效率反而有可能下降，成为削弱高含固污泥厌氧消化优势的关键因素。本项目针对这一问题，提出了固体浓度影响厌氧消化过程中有机质降解效率的机制模型.围绕该假设，首先分析高含固污泥的传质性能和流变学性质，寻求这些特性与污泥搅拌之间的相互影响，进而分析其与污泥有机质降解效率的内在联系；监测不同含固率污泥厌氧消化过程的中间产物，如氨与挥发性脂肪酸的累积、转化规律，分析污泥含固率经中间产物间接影响有机质降解效率的内在机制；研究有机质含量、组分对高含固污泥厌氧消化的影响，分析共消化、预处理对高含固污泥特性的改变乃至影响有机质降解效率的内在机制；最终验证或修正前述机制模型，并据此建立强化高含固污泥厌氧消化有机质降解效率的调控方法。

厌氧消化是实现污泥减量化和能源化的重要处理方式，但传统工艺进泥含固率仅2~6%，处理效率较低；而进泥含固率为10~15%的高固体厌氧消化可以提高反应器处理效率并增加容积产气量。然而，高固体浓度也可能成为制约污泥有机质转化效率的关键因素。针对这一问题，本课题首次系统研究了高含固污泥的传递性质，发现高含固污泥为假塑性非触变流体，粘度随含固率呈指数增加，而当污泥含固率小于15%时，其热常数基本与水一致；相对于水中的扩散系数，在含固率15%的污泥及其消化污泥中，碘离子扩散系数分别下降了8到90倍。在无搅拌高固体消化系统中，微生物活性普遍下降40~50%，甲烷菌仍以乙酸型产甲烷菌为主，但优势菌从鬃毛产甲烷菌转变为甲烷八叠球菌，同时氢营养型和甲基营养型产甲烷菌比例显著增加。此外，进泥有机质含量低是导致高固体厌氧消化性能下降的另一关键因素。连续性实验表明，高固体浓度条件下，传质受阻且搅拌困难，同时较高的底物浓度引起较高的中间产物浓度；传质受阻除直接影响生化反应效率外，还可导致中间产物特别是氨的积累，造成功能微生物活性抑制，从而恶化消化性能。传质效率、水解效率及有机质含量为影响高含固污泥消化性能的三种关键因素。据此本项目建立了强化污泥高固体厌氧消化性能的低温热水解预处理、与餐厨垃圾共消化方法。经70℃、30 min的低温热水解处理后，污泥粘度下降30%以上，消化周期从30~35天缩短至15~22天，处理能力提高30~50%。通过与餐厨垃圾共消化，污泥高固体厌氧消化产气量明显提高，两种底物的最佳混合比例为1:1（基于VS）。而且，高固体条件更能发挥共消化的协同效应，并对盐分、油脂具有更好的耐受能力。通过对系统的综合评估，低温热水解预处理联合高固体厌氧消化具有最佳的环境收益、较低的处理成本和较高的能效水平。基于上述成果，共发表期刊论文15篇，会议论文 3篇，其中SCI 检索13 篇，授权国家发明专利1项，培养研究生7名，上述成果已用于昆明主城区污泥处理处置工程的设计和调试。