Energy saving at waste water treatment plants by integreted optimization of treatment and use of energy
The project used a combination of energy audit, process audit, on-line measurements and electrical submetering techniques to identify methods of improving energy efficiency without deteriorating purification process. Bioreactors were main consuming sites.
The Action Plan for the Aquatic Environment has caused the implementation of both nitrogen and phosphorus removal at Danish wastewater treatment plants. The energy consumption within wastewater treatment plants in Denmark is estimated to approximately 210 GWh. This is approx. 1% of the total Danish electricity consumption. The main part of the energy (app. 70%) is used during aeration, stirring and sludge recirculation. Early projects on practical energy optimization at wastewater treatment plants were conducted by VKI in 1978 and 84, resulting in savings by control of aeration equipment using oxygen sensors. Due to implementation of new complex processes, further energy saving at the wastewater treatment plants will be more complex and require an integration of process expertise, measurements, data handling (IT technology) and knowledge on plant equipment. Generally about the project: Following will be developed and tested: 1) Methods for evaluation of energy efficiency of plant and a model for integrated reduction of nitrogen emission from wastewater discharge and energy savings. 2) Methods for controlled, automatic optimisation of aeration via variable oxygen set points, based on actual microbial demand in the activated sludge process. 3) Methods for energy optimization by controlling energy consumption for aeration, stirring and sludge recirculation. 4) Process rearrangement for energy optimization. 5) Presentation of results and arranging courses. The methods are developed by integrating process know-how and energy requirement of the equipment with the optimization of the energy consumption. Energy conservation should not cause reduction in discharhe quality
Plants having pre-treatment prior to the bioreactors were having a lower consumption than plants without this treatment because of higher energy consumption of aerators. Oxygen set point, sludge concentration, stirring during denitrification, speed and submersion of surface aerators and oxygen demanding load are the main factors to investigate and control to achieve energy savings. High saving potential is the maximum saving estimated during the project. Medium and low are graduation of the maximum saving potential. The estimate of 10-40% savings indicates that it is possible to achieve the project objectives of 15-30% savings. Plants without pre-treatment have a higher electricity use in the bioreactors. Small plants are often without pre-treatment and are therefore having a higher consumption. Key figures for energy consumption varied between 28 and 73 kWh per PE year (an average of 35 kWh is a reasonable average figure), 0.34 and 0.70 kWh per m3. Recent Danish legislation (2000) claims energy conservation in public owned institutions and industries if the corresponding economic savings are reasonable. Therefore, it seems probable that results of this project can be implemented
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| GRONTMIJ A/S | ||
| Holstebro kommune | ||
| Affald Varme Århus |
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