The pulp and paper (P&P) industry creates a significant amount of wastewater that may contain potentially harmful organic pollutants and solid wastes which must be treated and removed before the water can be safely discharged back into the environment. Numerous wastewater treatment technologies may be employed depending on the process stage, the desired level of treatment, the volume of wastewater being treated and the nature of the pollutants in the water. Aerzen, an international manufacturer of blowers and compressors, specializes in aeration technology for the treatment of wastewater in several industries. This article provides a brief overview of aeration technology and highlights how Aerzen blowers and compressors can be used to efficiently treat wastewater in the pulp and paper industry.

The aeration process

The aeration process brings air (oxygen) in close contact with the wastewater to promote the growth of microorganisms that allow for the biodegradation of organic matter. Aeration also removes dissolved gases (such as carbon dioxide) and oxidizes dissolved metals such as iron, hydrogen sulfide and volatile organic chemicals (VOCs). Once oxidized, these dissolved solids fall out of solution and become particles in the water that can be removed by filtration or floatation.

The efficiency of aeration depends on the amount of surface contact between air and water, which is controlled primarily by the size of the water droplets or air bubbles. Insufficient oxygen may cause inadequate biodegradation, resulting in anaerobic decomposition, which may lead to offensive odors and incomplete treatment of pollutants. It is therefore necessary to systematically inject oxygen at critical points along the P&P wastewater chain to solve these potential problems quickly and efficiently.

A wastewater aeration system is comprised of aeration blowers that push air through diffusers submerged in wastewater in an aeration tank. These blowers must operate continuously to ensure proper biodegradation of organic matter. The diffusers release air bubbles within the wastewater, thereby increasing the amount of dissolved oxygen within the water. The dissolved oxygen is consumed by microorganisms that are suspended in the water, allowing for microbial growth and biodegradation of organic matter. The aeration system blowers, including the systems used to control them, are key components that govern the effectiveness and efficiency of wastewater aeration systems. These blowers are typically classified into positive displacement (PD) or centrifugal blowers, each having certain advantages and disadvantages.

PD blowers, including lobe-type and screw-type blowers, provide a fixed volume of air with every revolution that is independent of operating pressure. It is therefore possible to control the air flow rate by controlling the blower rotational speed. PD blowers have a relatively low initial cost and require relatively simple controls; however, they may be less efficient and may have limited flow capacities.

Centrifugal blowers (also known as dynamic blowers) provide a constant pressure over a range of air volumes. They have a limited operating pressure range, however, and the flow rate can be reduced according to the back pressure within the aeration system, by use of guide vanes, or more recently by use of a variable frequency drive. If the flow rate falls below a minimum value, centrifugal blowers will experience unstable pulsating flow called “surge,” which can cause mechanical damage to the blower.

Because of these and other disadvantages, pressure-based control technology has become outdated. More modern aeration system blowers utilize robust variable frequency drives, flow meters and more intelligent control techniques that enable the blowers to control parameters that directly impact the aeration process.

Aerzen positive displacement blowers

Aerzen has spearheaded the innovation of a line of blowers that can be used in various process stages in the pulp and paper industry, including the wastewater process for aeration, equalization, belt pressure feed and sludge clarifier tanks.

Special technology allows the Aerzen blowers to be energy efficient while satisfying a broad range of rapidly changing aeration requirements. This is accomplished by implementing a combination of newer, properly sized blower technologies managed by advanced intelligent controls that optimally distribute airflows, including variable frequency drives and advanced control system technologies.

Variable frequency drives adjust the blower airflow in real time to meet instantaneous airflow demands of the system. This makes for a more efficient aeration process by only providing the amount of air needed to meet the treatment objectives of the system rather than over-aerating the system, which wastes energy and subsequently drives up the operating costs of the system.

Aerzen’s AERprocess control system oversees the distribution of air to the aeration basins with automated control valves and airflow meters. The control system provides a rapid response to changing conditions while distributing air in the most efficient way possible at the lowest header pressure. What makes this type of technology special is that it is self-tuning, so the system analyzes its own performance and adjusts accordingly.

Aerzen blower packages are designed and manufactured with components that have a minimum useful life of fifteen years and a minimum mean time between overhauls of five years of continuous operation, with many customers experiencing a significantly longer useful life. The Aerzen blower package also provides a highly reliable belt drive system with the induction motor installed on a pivoting base that uses the weight of the motor to constantly provide the correct tension on the belts, extending the life of the belts to as much as two years.

The design of the Aerzen blower package also puts special emphasis on ease of maintenance of the blower system. When an acoustical blower enclosure is included with the blower package, maintenance access points are provided on the front and rear of the enclosure and provide ample room for routine maintenance of the blowers such as v-belt replacement, air filter maintenance and replacement, and oil replacement. The numerous system improvements and technical innovations that Aerzen has incorporated into their blower packages can improve efficiency and lower operating costs for the treatment of pulp and paper wastewater.

Aerzen company overview

Aerzen is a global manufacturer of blowers, compressors, rotary lobe compressors and turbo blowers, with 2,500 employees and more than 50 subsidiary companies worldwide. Founded in 1864, they manufactured their first PD blower in 1868, and now annually produce over 14,000 PD blowers and vacuum pumps and over 10,000 screw compressors. Aerzen’s U.S. headquarters in Coatesville, Pennsylvania, provides a full range of capabilities, including engineering and project management, manufacturing, sales and customer service, equipment repair and refurbishment, and spare parts. More information about their products and capabilities can be found on the Aerzen website.