Application Note

Low-Pressure Blowers In Wastewater Treatment Applications

By Gatlin Gold, Atlas Copco Compressors

blowers

Oil-free blowers are an essential element of municipal and industrial wastewater treatment facilities, where they are utilized to power a variety of applications. Eight of the most common processes/applications fueled by blowers include:

  1. Diffused Aeration. Bacteria require oxygen to survive. In this process, compressed air is pumped through and released below the wastewater’s surface in order to ensure that the bacteria receive a continual supply of air — and that the wastewater treatment process remains consistent.
     
  2. The Activated Sludge Process. Utilized in medium- to large-scale industrial plants, the activated sludge process separates the flocculants (i.e., suspended solids) from the wastewater through sedimentation. Effluent (or the outflowing of water to a natural body of water from the wastewater treatment facility) enters the aeration tank or lane, and low-pressure air is introduced through a grid of diffusers. Water usually passes through the process in a few hours, while the sludge retention rates vary from a few days in warmer climates, to a few weeks in colder weather.
     
  3. Lagoon Aeration. Similar to the activated sludge process, lagoon aeration is typically used in rural areas with small- to large-sized plants. A series of shallow earthen basins (lagoons) act as the aeration basins and holding tanks — it’s in this treatment pond that biological oxidation of wastewaters occur. Although lagoons are often equipped with surface aerators, there are several diffuser systems available specifically for these applications. A well-designed diffused air system uses approximately half as much energy as surface aeration.
     
  4. Membrane Bioreactor (MBR). The MBR process uses additional filtration to produce a higher quality effluent and is a variation of the activated sludge process. Common in medium- to large-scale plants, the MBR features an ultrafine membrane filter installed at the discharge end of a standard aeration basin. Pumps installed on the membrane filters create a slight vacuum and pull the effluent through the membrane. The ultrafine holes in the membrane do not allow the biological microbes to pass through the membrane, keeping the microbes in the aeration basin. The membrane becomes clogged or fouled in this process and requires more frequent cleaning.
     
  5. Moving Bed Biofilm Reactor (MBBR). The MBBR is a much more compact method of wastewater treatment that can be scaled to fit any size plant, and is a version of the traditional activated sludge system. In this method, the reactor is filled with thousands of biofilm carriers (plastic balls) that protect the bacteria used to breakdown pollutants in the wastewater. A diffuser grid produces the air required to effectively disperse the biofilm carriers throughout the basin, while also providing the necessary aeration for biofilm growth.
     
  6. Sequencing Batch Reactor (SBR). The sequencing batch reactor (SBR) is also a very compact process typically used in small- to medium-sized plants. A small SBR consists of two equal-sized tanks that alternate between treatment stages. The process begins with the filling of one of the tanks. As soon as the first tank is filled, wastewater is diverted to the second tank and the process begins again. The multiple tank (reactor) design allows the plant to operate continuously and larger plants use more reactors to accommodate higher loads.
     
  7. Anaerobic Digestion. Anaerobic digestion is used to treat the sludge created by the wastewater treatment process, as well as other biological waste. By definition, anaerobic digestion does not use air; instead, a series of microorganisms break down solid waste into methane and carbon dioxide gas, in addition to nitrogen, ammonia, and hydrogen sulfide in smaller quantities. This biogas is extracted from the reactor and either flared to reduce greenhouse gas emissions or treated in a series of filters before being injected into a generator. Once injected into a generator, the biogas can be used for onsite electricity and heat generation, also known as a cogeneration system. Depending on the composition and amount of waste in the digester, this process can produce a substantial amount of energy that can be used for plant operations.
     
  8. Filter Backwashing. This is a form of preventative maintenance where water is pumped backwards through to filter in order to prevent the filter media from becoming too dirty — or even unusable.