基于LCA框架的深圳市典型污水处理系统的能值综合评估与不确定性分析

Nowadays, there are many kinds of wastewater treatment systems in China, and these systems require different resource inputs, energy consumption and economic costs, but present different production efficiencies and environmental impacts. Thus, a thorough ecological economic evaluation method is required to assess and guide resource and energy saving of wastewater treatment systems in China. Life cycle assessment is a great tool to evaluate resource and energy consumption in an industry, but it does not consider economic and social factors, or human labor,information and technology; meanwhile, it lacks a common denominator of measuring different materials and energy. However, emergy thoery and method, can serve as a potential great tool to comprehensively evaluate material and energy flows in ecological economic systems. In this project, we try to use LCA-based emergy analysis to evaluate four main wastewater treatment systems in Shenzhen, South China. Firstly, a special LCA-based emergy index system for wastewater treatment systems needs to be constructed to evaluate the production efficiency, environmental loading and sustainability. Secondly, emergy synthesis is used to analyze and compare the resource and energy consumption of these wastewater treatment systems and their production efficiencies and environmental impacts, to select and optimize those wastewater treatment systems with low resource cost and energy consumption. Finally,emergy analysis of the wastewater treatment systems with repeated measurement data should be accompanied by an uncertainty analysis, especially for transformity, in order to overcome the shortcoming of common emergy-based case studies without confidence interval.

目前我国污水处理的工艺杂多，其处理成本和效果不同，资源投入、能源消耗和对环境的影响迥异，亟需进行全面的生态经济综合评估。生命周期评估(LCA)是目前较常用的生态经济综合评估方法，但由于未考虑社会经济影响和劳务、信息、技术成本，且缺乏统一度量物质与能量流的评价标准，其应用常常受到限制。而能值理论方法，以能值为统一量化平台，为系统物质循环和能量流动的量化、整合分析与综合评价提供了思路和手段。本项目拟以深圳市典型污水处理系统为研究对象，采用能值与LCA相结合的办法，致力于建立一套基于LCA框架且适用于污水处理系统的能值综合评价指标体系；重点开展污水处理系统重复样本的能值综合评估、能值转换率计算与不确定性分析的研究，弥补常规能值分析缺少统计显著性的缺陷；通过能值评估和对比，综合考察不同污水处理方法的资源投入、能源消耗和废弃物排放对环境的影响，为筛选、优化和推广节能环保的污水处理方法提供参考依据。

我国污水处理工艺种类繁多，处理成本和效果各异，资源投入、能源消耗、温室气体排放和对环境的影响也不尽相同，亟需对其开展全面的生态经济综合评估。本文以深圳市三个典型污水处理系统为研究对象，采用能值分析方法，首先构建了一套基于LCA框架且适用于污水处理系统的能值综合评价指标体系，尤其是构建了能值匹配率指标和修正了环境负载率和能值可持续发展指标；其次，开展了污水处理系统的能值综合评估，结果发现这三个污水处理系统都具有较低的环境负载率（0.016~0.020）和较高的能值可持续发展程度（2470~3631），且污水处理厂A由于处理规模较大，具有相对最好的能值综合特性。但污染物去除对环境的正影响应该要纳入到环境负载率的评价，从而会大幅提高污水处理的能值可持续发展评价结果（22791~39755），且污水处理厂B由于其出水水质较好，而展现出了最好的能值综合特性。第三，通过相关分析和回归分析发现，污水处理系统的能值匹配率和可持续发展指标都与污水处理规模密切相关（P<0.01），且随着污水处理规模的增加而增加。第四，通过比较增加污水或者污泥深度处理环节前后的能值综合特性，发现它们能显著改善污水处理系统的能值综合特性。最后，本文估算了深圳市典型污水处理厂单位污水处理的能耗约为0.20度/吨，经济成本为0.71~0.89元/吨，其中，电力消耗和劳务工资福利是最主要的两大经济成本来源。若增加再生回用环节，则电力消耗需要增加0.023度/吨左右，经济成本需要增加0.388元/吨左右。