基于外加碳源调控氨同化作用的污泥堆肥系统氮素损失控制机理与技术研究

Large ammount of sewage sludge need to be treated due to the increase of the sewage water flow in China. The treatment and disposal of sewage sludge have been of great concern. Aerobic fermentation, also called composting, is a major technology for sewage sludge treatment based on its many advantages, such as low investment and operational cost. However, nitrogen loss during composting process resulted in the decrease of nitrogen content in products, which seriously affected the quality of the products. The ammonia released and deteriorated the surrounding air condition because of nitrogen loss. At present, the problem of nitrogen loss during composting process has not been effectively solved in practice. It has been found that extra carbon sources added in composting system could reduce the nitrogen loss, while the mechanism was unclear. Little is reported about the relationship between extra carbon sources and ammonia bio-assimilation. In the project, the optimal carbon source material will be adopted to reduce nitrogen loss. The effects of the extra carbon source material in nitrogen transforming process will be studied by enzyme and molecular biology analysis. The relationship of the biodegradability of the extra carbon source and ammonia volatile rate will be caculated. The effects of the extra carbon source on microbial community of ammonia assimilation will be analyzed. The purpose of this project is to investigate the dynamics of key enzymes and substrates duiring ammonia assimilation process, to reveal the mechanisms of nitrogen loss reduced by adding the extra carbon source to improve ammonia assimilation, to provide technological parameters for reducing nitrogen loss in the composting process, and to offer the theoretical references for regulating nitrogen loss.

随着我国污水处理能力的不断提高，城镇污水厂污泥处理问题得到了各方面的极大关注。污泥堆肥（好氧发酵）投资少、运行费用低，是国内外污泥处理普遍采用的主流技术。污泥堆肥过程中大量的氮素损失严重影响堆肥产品肥效及环境空气质量，而目前该问题尚未得到有效解决。已有研究表明，外加碳源可减少污泥堆肥过程中的氮素损失，但其作用机理尚不清楚，另外堆肥工艺中关于碳源特性与生物氨同化相互作用关系的研究亦属空白。本项目通过优选保氮效果显著的外加碳源，利用酶学、分子生物学等多种技术手段，研究污泥堆肥系统中外加碳源对氮素转化过程的影响，明确外加碳源生物利用率与氨气挥发速率的响应关系，考察外加碳源对氨同化功能微生物种群结构的影响，探讨氨同化过程中关键底物及关键酶活性的变化规律，揭示外加碳源调控生物氨同化作用以降低氮素损失的作用机理，进而提出外加碳源调控的优化工艺控制条件，为污泥堆肥系统氮素损失控制提供理论依据及技术支撑。

污泥好氧堆肥技术由于其经济性、操作简单，目前是污泥处理的主要技术之一。但在污泥好氧堆肥过程中，氨气挥发问题严重，造成空气污染和污泥氮素含量较低。本研究针对城市污水厂污泥低碳氮比的特征，筛选出了能够有效控制氮素损失的蔗糖作为外加碳源，通过响应曲面法实验确定了其使用方法，最佳投加量为2%，投加时间点为58.28小时，蔗糖浓度为100%（即固体投加）。在使用该碳源的基础上，研究了碳源对氮素形态转化的影响，发现了氮素形态主要在氨态氮和有机氮之间转化，投加碳源可明显增加有机氮的含量。利用氮同位素和污泥的体外培养，确定了碳源可使氮素同化率增加26.35%，在升温期和高温期较为明显。利用氧气、二氧化碳的在线监测结果和污泥浸提液BOD5含量的变化，发现碳源可生化性是影响氮素损失的主要因素之一，并建立了描述微生物呼吸速率与氨气挥发之间相互关系的非线性回归方程。研究了外加碳源对氨同化微生物种群的影响，发现外加碳源增加了氨同化微生物的数量，加快了堆肥系统碳源的代谢速度，提高了代谢中间产物α-酮戊二酸的浓度，酶学分析结果显示，添加外加碳源提高了氨同化关键酶的活性，包括：谷氨酸脱氢酶（GDH）、谷氨酰胺合成酶（GS）和谷氨酸合成酶（GOGAT）。在高温期当氨浓度高于1.5mg/kg干污泥时，GDH路径在氨同化过程中发挥主要作用，在降温期当氨浓度低于1.1mg/kg干污泥时，GS/GOGAT循环发挥主要作用。以氨气挥发速率为评价指标，对污泥堆肥工艺参数进行优化，发现较高的含水率有利于控制氨气的挥发，污泥pH值较高时，OH-浓度上升会促进氨根离子向氨气转化，通风速率与氨气挥发量呈正相关，结合有机质降解效率，最佳通风量为0.2L/min，翻堆不利于控制高温期的氨气挥发，但有利于氧气的传质，减少堆肥的氨气挥发总量。根据堆肥过程中有机质含量、工艺参数，利用MATLAB神经网络工具箱建立了描述外加碳源与氨气挥发速率之间的数学模型。本项目的研究成果对污泥堆肥技术的应用基础研究、新技术开发和工程化应用都具有重要的理论意义和实用价值。

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