猪场粪污分步加热沼气发酵方法及其动力学基础

Biogas fermentation (anaerobic digestion) could be considered one of the most promising treatment alternatives for swine wastewater. However,the quantity of swine wastewater is so tremendous that enhance of temperture is very difficult, resulting in a low efficiency in biogas production in winter. Aiming at this problem, a scientific hypothesis that anaerobic digestion process with several-step heating could improve the efficiency of biogas production under the same heating energy is put forward. In order to prove this hypothesis, the kinetics of temperature effect on biogas fermenntation of swine wastewater will be investigated to get kinetics model and temperature activity coefficient. Based on the kinetics model and temperature activity coefficient,the promotion of efficiency of biogas production and requirement of heating energy of anaerobic digestion with one-step and two-step heating will be comparely analyzed, to prove the possibility that anaerobic digestion process with two-step heating could improve the efficiency of biogas production.A simulant experiment of anaerobic digestion of swine wastewater will be carried out to compare the efficiency of biogas production of digestion process with one-step and two-step heating,in order to validate the correctness of hypothesis and the reliability of theory analysis. Ground on the validation results from experiment, theory analysis of the promotion of efficiency of the biogas fermentation wtih several-step heating will be carried out, to determine the maximum of the promotion of efficiency in biogas production and energy saving and the optimum heating steps. Finally, the theory and method of biogas fermentation with several-heating will established, which will lay the theoretical foundation for the development of new process of swine wastewater treatment.

沼气发酵(厌氧消化)是猪场粪污颇具前景的处理方法，但是猪场粪污水量大、升温困难，冬季处理效率低、产沼气少甚至不产气。针对这一难题，提出“在相同加热能量条件下，通过分步加热可以提高沼气发酵产气效率”的科学假设。为了证实这一假设，本项目拟通过猪场粪污沼气发酵温度影响动力学的研究，获取动力学模型及温度活性系数；依据动力学模型和温度活性系数，对比解析一步加热与两步加热沼气发酵的效能提升率以及需要的加热能量，从理论上求证两步加热沼气发酵提高产气效率的可能性；然后通过模拟沼气发酵试验对比研究一步加热与两步加热沼气发酵的产气效率，检验假设的正确性及理论推导的可靠性；进一步进行多步加热沼气发酵效能提升作用的理论解析，确定分步加热沼气发酵效能提升最大值和能量节约最大值以及最适加热步数。最后，建立分步加热沼气发酵方法，为猪场粪污处理新工艺的开发奠定理论基础。

本项目从理论推导和试验验证两方面验证了分步加热策略提升猪场粪污沼气发酵效率的可行性，并探讨了影响效率提升的因素。.（1）建立了定量描述容积产气率和有机负荷之间关系的动力学模型，基于模型适应性统计指标判断，新模型比以往模型更能准确地描述有机负荷对容积产气率的影响。采用其它研究者公开报道的沼气发酵实验数据验证了新模型的通用性和适用性。获得了表征温度对沼气发酵效率定量影响的温度活性系数（θ），这些系数表明猪场粪污沼气发酵对15~20 ℃范围的温度变化比20~35 ℃范围温度变化更敏感。.（2）理论计算表明，分步加热可以提高沼气发酵温度，第一部分废水比例（p）越低，能量废水比（h）越高，分步加热提升温度的幅度越大。利用产气动力学模型和温度活性系数，模拟推导了分步加热沼气发酵相比一步加热沼气发酵产气性能提升效率计算模型。模型计算表明，第一部分废水比例（p）越低，环境温度（T0）越低，负荷越高，加热步数越多，分步加热产气效率提升幅度越大。在环境温度为10 ℃、容积负荷2.0~5.0 gCOD L-1 d-1条件下，两步加热沼气发酵产气效率比一步加热可以提高104~261%，三步加热比一步加热可以提高116~343%。.（3）以清水为介质的温度验证试验证明了分步加热提高原料沼气发酵温度的可行性。以猪场废水为原料，采用完全混合式厌氧反应器（CSTR）的沼气发酵试验显示，在环境温度为10℃、负荷3.0 gCOD L-1 d-1条件下，两步加热策略可以提升沼气产量4.06~20.1%。采用厌氧序批式反应器（ASBR）的沼气发酵试验表明，在负荷2.0~5.0 gCOD L-1 d-1条件下，两步加热比一步加热容积沼气产气率平均提高66.7~87.5%，三步加热比一步加热平均提高100~125%，三步加热比两步加热平均提高20.0%。分步加热的沼气产量提升效率试验值显著低于理论分析值，主要是因为试验验证时，存在污泥流失的问题（特别是CSTR反应器），温度较高的反应器没有接近最大容积产气率。. （4）相比一步加热沼气发酵，两步加热沼气发酵系统的酸碱缓冲性能好, 并且污泥最大比产甲烷活性高于一步加热沼气发酵污泥。