Energy Optimization at Municipal Wastewater Treatment Plants

北美的大多数污水处理厂都已接近其设计寿命，因此需要投入大量资金进行扩建和升级，以满足日益严格的污水质量标准，同时应对不断增加的能源成本以及对经济和环境可持续性的更高需求。根据美国环保署的数据，城市污水处理厂（MWWTP）每年消耗约750亿千瓦时，占美国发电量的3%。曝气能耗约占污水处理厂总能耗的60%。此外，生物固体的处理和处置费用占废水处理总费用的50%-60%。城市污水处理部门面临的主要技术挑战涉及营养物和生物固体管理，以及能源优化，需要向能源中性和资源回收转变模式。与第一代生物营养物（氮和磷）去除（BNR）工艺相反，BNR工艺通过氨和有机氮氧化为硝酸盐，然后反硝化为氮气，第二代BNR工艺通过亚硝酸盐进行硝化和反硝化，以及用亚硝酸盐厌氧氧化氨，不仅提供了高达40%的显著节能，但也减少了急需的外来有机碳的添加，以补充废水中用于反硝化的有机物，最多可减少90%。所有第二代BNR工艺都采用悬浮生长系统，与生物膜或固定膜工艺相比，需要更高的水力停留时间和更大的生物反应器体积。MWWTP的能量产生主要涉及厌氧消化。然而，在水力停留时间约为15-30天的传统蒸煮池中，挥发性固体还原（VSR）的效率通常在50%左右。虽然最近，厌氧沼气池通过与城市生物固体共消化食物垃圾来提高沼气产量，但协同作用的基本原理尚未得到很好的理解。拟议研究计划的总体长期目标是通过减少用于脱氮的曝气能量和增强厌氧消化中将城市生物固体转化为甲烷来最大限度地减少MWWTP的能源消耗。该项目有三个短期目标：(1)开发综合生物膜工艺，即在单个反应器中结合短程硝化和厌氧氨氧化的流化床生物反应器；(2)研制高速率生物膜厌氧流化床超声反应器；(3)研究食物垃圾与废水生物固体共消化协同效应的基本工艺参数。

Most wastewater treatment plants in North America, are approaching their design life necessitating significant capital investment for expansion and upgrade to meet increasingly stringent effluent quality criteria while addressing increased energy costs and heightened needs for economic and environmental sustainability. According to the US EPA, municipal wastewater treatment plants (MWWTP) consume about 75 billion KWH annually, or 3% of the US electricity generated. Aeration energy accounts for about 60% of the overall energy consumption at MWWTP. Furthermore, biosolids processing and disposal costs account for 50%-60% of overall wastewater treatment costs. The main technical challenges facing the municipal wastewater sector relate to nutrients and biosolids management, as well as optimization of energy, necessitating a paradigm shift towards energy neutrality and resource recovery. In contrast to the first generation of biological nutrient (nitrogen and phosphorous) removal (BNR) processes, which remove N by oxidation of ammonia and organic nitrogen to nitrates and then denitrifying to nitrogen gas, second generation BNR processes which nitrify and denitrify through nitrite as well as anaerobically oxidizing ammonia with nitrites, not only offer significant energy savings of up to 40%, but also reduce the addition of much-needed extraneous organic carbon to supplement the wastewater organics for denitrification by as much as 90%. All the second-generation BNR processes employ suspended growth systems that require much higher hydraulic retention times and much larger bioreactor volumes compared to biofilm or fixed-film processes. Energy generation at MWWTP primarily involves anaerobic digestion. However, the efficiency of volatile solids reduction (VSR) in conventional digesters with hydraulic retention times of around 15-30 days, is typically around 50%. While recently, the biogas production from anaerobic digesters has been enhanced through co-digestion of food wastes with municipal biosolids, the fundamentals of synergism are not well understood. The overall long-term objective of the proposed research program is to minimize energy consumption at MWWTP through reduction of aeration energy for nitrogen removal and enhanced conversion of municipal biosolids to methane in anaerobic digestion. The project has three short-term objectives: (1) development of an integrated biofilm process i.e. a fluidized bed bioreactor that combines short-cut nitrification with anaerobic ammonia oxidation in a single reactor; (2) development of a high-rate biofilm anaerobic fluidized bed digester with ultrasonication, and (3) investigation of the fundamental process parameters contributing to the observed synergistic effects of co-digestion of food wastes and wastewater biosolids.