城市污泥好氧堆肥过程空气阻流区特征及尾气排放响应机制

Aerobic composting is one of the typical technologies for the treatment of sewage sludge, and the emission of off-gas including odors and greenhouse gas is an increasing problem for the development of the composting industry. The emission of off-gas is corresponding to the anaerobic region in matrix particles, of which the distribution is intensively affected by the obstructed gas region in matrix. However, few researchers pay attention to the distribution of the obstructed gas region and its effects on the off-gas emission without the effectively measurement method for the obstructed gas region in compost matrix. So, this proposal is applied for the aim of obtaining that information during aerobic composting process of sewage sludge and includes three parts as follows: (1) developing a new analysis method through measuring the obstructed gas region by estimating parameters from pulse gas tracer experiments based on the two-region model; (2) identifying the key environmental factors which affect the distribution characteristics of obstructed gas region in matrix; (3) elucidating the response mechanism of the off-gas emission to the obstructed gas region on the basis of the coupling relationship between the obstructed gas region and anaerobic region in the particle, and then exploring the optimal operation for the reduction of hazardous off-gas emission. The expected achievements can be used to promote the technology of pollution control for odors and greenhouse gas during aerobic composting of sewage sludge.

好氧堆肥是处理城市污泥的主要技术途径之一，但堆肥过程中堆体排出大量臭气和温室气体等有害尾气，正日益成为制约行业发展的重要问题。这些气体的产生和释放均与堆体颗粒厌氧区的存在有关，而堆体空气阻流区是影响颗粒厌氧区分布的关键因素之一。由于缺乏有效的堆体空气阻流区分析方法，目前关于堆肥过程空气阻流区特征及尾气排放响应机制的研究还较少。因此，本项目拟以城市污泥好氧堆肥过程为研究对象，分三步开展以下研究：(1)基于两区模型，构建气体脉冲示踪反演堆体物料空气阻流区特征参数的方法；(2)识别影响堆体内空气阻流区特征的关键堆体环境因素；(3)在分析空气阻流区与颗粒厌氧区分布间耦合关系的基础上，阐明堆体尾气排放对空气阻流区特征的响应机制，探索减少堆肥过程臭气排放和温室气体的工艺策略。本研究可为城市污泥好氧堆肥过程中有害尾气排放消减技术开发和优化提供理论依据。

了解堆体内空气阻流区特征及尾气排放对其响应机制，是开发有机固废好氧堆肥有害尾气污染原位控制新技术的关键。本项目在优化气体示踪实验条件（示踪气体种类、输入脉冲量、柱型）的基础上，建立了一种新的基于气体示踪-反演的堆体空气阻流区特征参数分析方法；基于该方法，首次报道了堆肥升温期、高温期堆体的空气阻流区特征参数，并可模拟不同高度堆体空隙和尾气中O2浓度时态变化。进行翻堆、不同膨松剂添加、不同通风强度等处理下城市污泥好氧堆肥过程，通过上述示踪-反演方法，得到城市污泥堆肥过程中堆体内空气阻流区比例系数（φ）和两区间一级传质系数（α）的范围，分别为0.38~0.54、0~0.019 min-1；通过相关性分析，识别出影响这些参数的关键因素为挥发性固体含量、含水率和通风强度。利用溶解氧（DO）微电极，测定不同表面氧浓度下的污泥堆肥颗粒内部DO径向分布曲线，拟合得到颗粒表面氧浓度-内部好氧/厌氧区分布方程；与两区流模型结合，建立了基于多孔结构内气体传质特征的堆体氧分布耦合模型，可模拟不同流场特征下堆肥过程中堆体空隙、颗粒内部及尾气中氧分布。研究了不同通风量、供氧浓度和调理剂添加下污泥好氧堆肥过程中空气阻流区特征和温室气体（CH4、N2O）排放规律；基于上述氧分布耦合模型，计算各工艺条件下堆肥不同阶段颗粒厌氧区分布；分析颗粒厌氧区与温室气体排放的相互关系，阐明温室气体排放对堆体空气阻流区特征的响应机制。本项目的研究成果，能够为有机固废好氧堆肥有害尾气原位减排技术开发提供科学依据，具有重要的理论及实际意义。