CFD simulation of a novel mixing and aeration system for wastewater treatment

水和废水系统是耗能大户，估计占美国总用电量的3%-4%。利用活性污泥法处理废水一般依靠曝气，为有机物的降解提供所需的氧气。目前的曝气系统占污水处理厂运行预算的50%至80%。随着能源成本的上涨以及人们对节能和减少碳足迹的日益关注，对节能曝气技术的需求越来越大。Ekologix地球友好解决方案公司(Ekologix)目前正在试验性地测试其新发明--Plunge-ASpiroTM Mix(PAM)，该产品可以减少高达60%的能源消耗。利用液体泵和从曝气反应器顶部引入的多个垂直射流，PAM在提供微小气泡的同时进行混合和曝气，从而提高了反应器的性能和能源效率。虽然目前设计的PAM的性能正在进行全面的测试，但为了进一步提高效率，应该在不牺牲工艺效率(即有机物破坏和硝化效率)的情况下，通过模拟交替的水力搅拌水平来进行水力和工艺优化。这可以通过计算流体动力学(CFD)来实现。本项目的目标是建立一个装有PAM基本设计的曝气池的CFD模拟模型，以确定池中的混合模式，并识别短路、死区和回流区。经过验证的CFD模型将与动力学模型相结合，以预测不同的水和空气流量、悬浮固体和溶解有机物浓度下的有机物去除。经过验证的CFD模型和生物动力学模型将为类似的活性污泥曝气池的设计提供有用的工具。

Water and wastewater systems are significant energy consumers with an estimated 3%-4% of total U.S. electricity consumption. Wastewater treatment using activated sludge process is generally aided by aeration, supplying the required oxygen for degradation of organic materials. Current aeration systems account for 50% to 80% of wastewater treatment plant operating budgets. With rising energy costs and a growing focus on energy conservation and carbon footprint reduction, there is increasing demand for energy-efficient aeration technologies. Ekologix Earth-Friendly Solutions Inc. (Ekologix) is currently experimentally testing its new invention, Plunge-AspiroTM Mix (PAM) that can reduce energy use by up to 60%. Using a liquid pump and multiple vertical jet streams introduced from the top of the aeration reactor, PAM concurrently mixes and aerates while supplying tiny bubbles, resulting in improved performance and energy efficiency of the reactor. Although, performance of current design of PAM is being tested in full-scale, both hydraulic and process optimizations should be conducted for further improvement in the efficiency by simulating alternating hydraulic mixing levels without sacrificing process efficiency (i.e. organics destruction and nitrification efficiency). This can be achieved by computational fluid dynamics (CFD). The objective of this project is to establish a CFD simulation model for an aeration basin fitted with a basic design of PAM to determine the mixing pattern in the tank and to identify short-circuiting, dead and recirculation zones. The validated CFD model will be coupled with kinetic models to predict the organics removal for variable water and air flow rates, suspended solids, and dissolved organics concentration. The validated CFD model along with the bio-kinetic model will be a useful tool for the design of similar activated sludge aeration basins.