waterTech - Projects
waterTech - Projects
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Waste Water Treatment Plants
WWTPs: An Optimisation of Processes and Systems
Energy and water are key resources to sustain a growing population and to ensure continued economic growth. In effect, the two are inextricably linked; energy is required to purify water and water is required to generate electrical power. Waste Water Treatment Plants (WWTP) account for approximately 1% of the world’s total energy consumption and 3% of the electrical load in the United States [US EPA]. Due to population growth and increasing environmental standards, this is expected to grow by over 20% by 2020. According to Tchobanoglous et al., 30% of the operating cost of a waste-water treatment plant is budgeted for energy use. Sludge treatment often represents more than 50% of the total waste-water treatment cost. Furthermore, the treatment of waste water also requires significant use of chemicals and consumables. To place it in an Irish context, waste water treatment accounts for approximately 50% of local authorities’ energy costs.
The key objective of this project is to demonstrate improved resource efficiency (e.g. water, chemical, energy) and process control improvements at Municipal Wastewater Treatment Plants.
This will be achieved through a number of steps;
- Benchmark the resource efficiency of the WWTP using two key methodologies – i.e. Exergy Analysis and Life-Cycle Analysis (LCA).
- Identify changes in energy/resource requirements for various plant loadings and seasonal changes.
- Identify key areas for resource efficiency improvements – potentially activated sludge/anaerobic digestion.
- Make recommendations to the system owners.
- Develop process control strategy.
- Model and demonstrate process control improvements according to loading and seasonal changes.
Flow Processes and Technologies
Aeration
The injection of air bubbles into water can induce significant and desirable convective mixing. This may be used for local enhancement of heat and mass transfer from surfaces but also to entrain chemical compounds, biological agents or particles in suspension in the wake of rising air bubbles where shed vortices play an important role in the convective mixing. Different regimes of bubble injection may be sought depending on the application. Uniform distribution of small bubbles may be used to achieve large mass transfer areas, for example for the aeration of sewage water. Air injection can also be used to create slug flows of rising Taylor bubbles and liquid plugs for example to increase permeate flux through filtration membranes in ultra-filtration applications. In general, the bubbles' sizes and their dynamic characteristics are determined by a range of complex processes which are particularly challenging to study by experimental means and equally difficult to model accurately. Research on the dynamics of air bubbles in liquids has been conducted by Dr Yan Delaure in collaboration with the Fluids and Heat Transfer Laboratory at Trinity College Dublin since 2004 with the financial support in particular of Science Foundation Ireland. One of the main research achievements has been the development and validation of advanced and efficient computational solvers capable of accurate modelling of all processes found in an dispersed multiphase (air/water) flow application including bubble injection, free rise, bounce and slide. Two sample animations of three dimensional flow are shown below.
| Bubble detachement and bounce following injection through a nozzle | Sliding bubble ploughing through a thermal boundary layer |
Efficient Turbomachines for Pumping and Energy Extraction or Conservation
Computational Fluid Dynamics has become an effective modelling tool which is extensively used for the study and design of a broad range of turbomachines. A number of research projects are currently underway to study a range of applications. One study is concerned with the optimisation of a single impeller pump for sewage application. Clogging conditions are being investigated with a view to improving pump operation. Another study is considering the integration of optimisation models with efficient 2D and 3D CFD models to assess the sensitivity of numerical optimisation to modelling errors. The models in this case are applied to vertical axis wind turbines. Another project is considering the potential of energy recovery in hydraulic systems using micro-hydroturbines.
Sample microturbine structured surface mesh