Improving Energy Efficiency in Wastewater Treatment Plants
1 July, 2022
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A wastewater treatment plant separates solids from the liquid and consists of two basic stages: primary treatment and secondary treatment.
In the primary treatment stage, larger solids are removed from wastewater by settling.
Secondary treatment is a biological process for further removal of the remaining suspended and dissolved solids through a biological process of adding microorganisms to the wastewater. This process is accomplished in an aeration basin.
The purpose of this white paper is to contribute to a better understanding of how to improve energy efficiency in wastewater facilities, it is known for a fact that one of the biggest expenses in wastewater treatment operations is the cost of energy to run the blowers and compressors that produce air for the aeration basins. Improvements in energy efficiency allow the same work to be done with less energy.
The figures most often cited are that 40 to 50 per cent of a wastewater plant’s total energy usage can be attributed to the aeration process. By measuring the system’s air flows with an accurate, repeatable Dissolved Oxygen sensor, the aeration process can be better controlled to optimize the process and minimise plant energy costs. Especially with the increasing costs of energy which is a major concern of plant operators. Typically, treatment plants have a high potential for energy savings.
Dissolved Oxygen Measurement is a means to improve energy efficiency
The organic wastes entering a wastewater treatment plant are broken-down using biomass. The biomass must be kept alive by maintaining the proper dissolved oxygen concentration throughout the treatment process.
The ability to maintain the proper concentration of Dissolved Oxygen in an aeration basin is necessary to keep microorganisms alive for a breakdown of the organic waste.
A precondition for effective measures is built around the knowledge about the process characteristics of the individual plant sections.
Sewage that flows into a treatment plant is sent to a Primary clarifier tank to remove the garbage and sludge. Thereafter, it is routed to an Aeration basin where biomass is added and oxygen is blown into the mixture to agitate it. The microorganisms in the biomass thrive on oxygen and cause the organic substances in the sludge to proliferate and the generated solids to be precipitated.
In the absence of enough dissolved oxygen, at least some of the biomass will die, and the organic wastes will not be properly treated. Contrarily, when there is too much-dissolved oxygen, usually from over aerating, the wastewater treatment plant is needlessly wasting costly energy.
Monitoring dissolved oxygen is an essential part of the activated sludge process. It assists in ensuring that there is sufficient dissolved oxygen in the process for the biological activity to take place, and helps to optimize energy usage through controlled air addition.
Maintaining a proper level of dissolved oxygen can only be accomplished by using an online instrument such as the Endress+Hauser On-line Dissolved Oxygen (DO) sensor that will accurately and continuously measure the dissolved oxygen concentration at various stages throughout the treatment process.
Equipping the aeration basin with online DO measurement automates the aeration system to maintain the correct amount of DO. With the presence of the Dissolved Oxygen sensor and the monitoring system in the Aeration tank:
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- Oxygen levels are controlled by comparing the measured oxygen concentration and the oxygen set-point
- Optimized blower usage for reduced energy consumption which leads to a significant reduction in energy costs for the wastewater treatment plant