Water treatment is amid a profound transformation and its importance is growing worldwide. Water is an increasingly scarce commodity, especially in poorer nations where it is not available in adequate quantities.
As a result of the growing demand for water due to agriculture, industry, and energy generation, bottlenecks are becoming increasingly severe. A responsible, resource-saving approach to water is necessary for the future.
Water treatment serves a critical function in the subject of water availability. Approximately 80 percent of global wastewater is untreated, despite treatment being technically possible in many cases.
There is considerable potential to significantly reduce the level of water consumption by industry in the long term.
Exploiting the Potential of the Water Treatment of the Future
Energy efficiency is an important aspect, particularly in industrialized countries. Wastewater treatment plants consume a significant amount of energy because of the energy-intensive processes in aeration tanks.
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Due to ambitious climate protection goals and increasing energy costs, energy efficiency in water treatment will become a vital issue in the future.
In the field of energy technology for wastewater treatment tanks, reliable technologies sustainably reduce energy consumption. These are highly attractive from the operator’s perspective.
Investing in modern ventilation technology makes a quick return and enhances plant efficiency without excessive expense, particularly with older water treatment plants.
The water treatment of the future has great potential for mitigating water scarcity, reducing energy consumption, and promoting responsible management of raw materials. For instance, the generation of energy from wastewater holds considerable potential.
Generating Electricity and Heat from Wastewater
In water treatment, one of the most critical issues for the future is generating energy from wastewater.
Each cubic meter of wastewater holds four times the energy utilized to purify that water; theoretically, a wastewater treatment plant can produce more energy than it consumes.
The underlying principle is straightforward: In general, the solids present in wastewater, such as toilet paper and excrement, may be used in biogas plants to generate electrical energy and heat.
The technology required for this process has already successfully been applied, but there is still much room for growth. As a result, there is ongoing research on novel technologies aimed at increasing sludge incineration. These technologies are being tested as prototypes and display promising results.
However, there are still many obstacles that must be overcome before the full potential of energy generation from wastewater can be realized.
One of these obstacles is that the percentage of solids that may be extracted from wastewater before the purification process must be significantly increased. The addition of polymers that cause the sludge to clump together could be employed to overcome this.
Saving Energy at Wastewater Treatment Plants
Energy efficiency is the most significant problem for the water treatment of the future. Operators of wastewater treatment plants continuously face increasingly strict environmental regulations. However, efficiency measures must be introduced to counteract increasing electricity prices.
To understand the importance of energy efficiency in wastewater treatment tanks, the energy balance of a treatment plant must be considered.
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There are approximately 10,200 wastewater treatment plants in Germany and these use a total of around 4,400 gigawatt hours (GWh) of electrical energy each year. This corresponds to a consumption of 35 kWh/population equivalent per year.
Wastewater treatment plants are currently responsible for approximately 0.7% of Germany’s power consumption.
Aeration is the main consumer of energy for almost all wastewater treatment plants with sludge processes. The percentage of power consumed by plants that employ aerobic sludge stabilization ranges from 60% to 80%, while this figure is around 50% for plants that carry out sludge digestion.
There are other energy consumers that are not as substantial as the sludge process. The primary energy consumers include the following:
- Pre-dewatering
- Post-dewatering
- Internal recirculation DN
- RLS handling
- Intermediate lifting mechanism
- Grit trap aeration
- Denitrification circulation (DN)
- Spatial filter
- Aeration tank ventilation
- Digester circulation
- Inlet lifting mechanism
It can be seen from the average power consumption of these plants that the aeration of aeration tanks holds the most potential for energy consumption reduction, as well as the constantly running pumping stations, such as the inlet, internal recirculation, and the intermediate lifting mechanism.
Additional Measures for Increasing Efficiency
Enhancing the energy efficiency of aeration tanks and utilizing sludge or digester gas to generate energy and heat are not the only potential measures for the water treatment of the future. Potential also lies in the integration of renewable energies into the energy systems of wastewater treatment plants.
For example, the installation of wind turbines or solar cells on the grounds of wastewater treatment plants could be used to further improve the ratio of generated energy to total energy consumption.
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However, these measures are subject to the same constraints as other sites and the profitability of the investment is dependent on the typical conditions, such as local wind and sunshine conditions.
Although the utilization of solar collectors for heat generation is also of particular interest for plants without sludge digestion, this method will likely serve only a minor role in the future.
For plants with aerobic sludge stabilization, there is already typically an excess of heat available during the summertime, which leads to the measure being redundant for this type of wastewater treatment plant.
Alternative measures for providing energy-efficient water treatment include the plan to utilize hydroelectric power in both the inlets and outlets of the wastewater treatment plant.
However, this only offers limited potential due to the available fall height being low, and the amount of generated energy does not justify the effort and expense involved.
In the case of larger plants with sludge incineration, it is advised to utilize bar screen debris as an extra fuel source to further increase energy efficiency. However, the potential of this technology is limited by the use of bar screen debris washers, which reduce the amount of debris that accumulates.
Demand-Driven Aeration Technology: High-Efficiency Measures
Depending on the wastewater treatment plant, the aeration process is responsible for 60-80% of the total energy requirement. This is why aeration is particularly important for the water treatment of the future.
What Happens in an Aeration Tank?
To understand why aeration tanks consume so much energy, consider the processes in a biological cleaning system.
The aeration tanks eliminate organic substances, such as nitrogen compounds and phosphates, from the mechanically pre-clarified wastewater. This decomposition is affected by microorganisms such as bacteria.
Firstly, to biologically remove phosphates from wastewater, the first part of the tank has low levels of oxygen. Subsequently, a significant volume of oxygen is introduced into the wastewater via compressed air.
Because of the increase in oxygen, the bacteria rapidly multiply and this causes the phosphates to bind with the biological sludge when mixed with a dissolved precipitant. Following this, the sludge decomposes in secondary treatment tanks and can be fed back into the aeration tanks or conveyed to the sludge treatment system.
This process utilizes a substantial amount of energy because of the introduction of large amounts of compressed air.
Challenges and Potential for Optimization in Aeration Technology
The challenge of aeration technology mainly involves the delivery of a demand-driven air supply that can handle severe fluctuations in load profiles and changing contamination levels.
Older wastewater treatment plants typically utilize blower technologies that always deliver the same amount of oxygen regardless of the supply situation, but this is not always required.
As a result, the challenge is the implementation of demand-driven aeration whilst also supplying the partial-load ranges of the load profile as efficiently as possible.
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AERZEN efficiently supplies energy to aeration tanks via a product portfolio that utilizes one or more blower technologies. These are implemented according to the individual needs of each wastewater treatment plant.
This approach means that it is possible for maximum efficiency to be achieved and for the potential savings to be fully exploited.
The portfolio includes positive displacement blowers, turbo blowers, and rotary lobe compressors. Each of these technologies comes with specific advantages and strengths, and these can be tailored to the individual needs of the treatment plant.
For example, turbo blowers are highly energy efficient by design and rotary piston machines have excellent adjustability and almost consistent efficiency in the partial load range.
The rotary lobe compressor is a hybrid, and it combines the advantages of blower and compressor technology into one system. Depending on the application, it is recommended to select either a combination of different technologies or the most efficient technology for the considered case.
Different technologies may be installed as well as different sizes, and further potential for savings can be accomplished if this approach is used in conjunction with an intelligent global control system.
Experience has demonstrated that considerable energy savings may be achieved via optimized aeration. For instance, the installation of an AERZEN turbo blower and a Delta hybrid enabled the Rheda-Wiedenbrück wastewater treatment plant to save 40,000 euros per year in energy costs.
This information has been sourced, reviewed and adapted from materials provided by Aerzener Maschinenfabrik GmbH.
For more information on this source, please visit Aerzener Maschinenfabrik GmbH.