Wastewater

The objective of this article is to look at typical industrial wastewater agitation processes and share various energy saving compressed air/blower projects that have worked well over the years. These basic fundamentals are a good starting point to begin the evaluation of a project idea. There are three primary uses of compressed air in all wastewater treatment applications. This article will focus on agitation and movement of materials.

Supplying air to process equipment necessitates a system approach. Selecting the blowers is a critical design step, but far from the final one. The layout of the blower room and ancillary equipment is just as critical to project success as the blowers themselves.

Single-stage centrifugal blowers are a proven technology that have been around for many years and will probably be here for many years to come. A well maintained machine can last for decades and will likely outlast its original control system. Even if the control system is still in good working order the components might already be end of life and hard to replace if any of them fail. If you are thinking about modernizing the hardware (PLC / HMI / Instruments) this is also a great opportunity to make the system a little smarter and user friendly. 

One definition of “calibrate” is “to determine, rectify, or mark the graduations of something”. An ammeter is an instrument for measuring electric current. Therefore the simple definition of a calibrated ammeter is a current measuring device marked with units of measure, presumably amperes. In the blower industry, however, the term has developed a specific meaning. A calibrated ammeter is an instrument that measures a blower motor’s current draw and converts the measurement to a display of blower airflow rate. 
 

The plant recorded another win in its long list of accomplishments when it replaced aging multistage blowers with high-speed integrally geared blowers in 2020. The new blowers with Variable Frequency Drive (VFD) control are credited with a 40% reduction in energy consumption for aeration. This results in an annual savings of $35,000. The blower upgrade, which also helps protect the safety of employees, is expected to deliver a payback of less than five years.

Most control systems use Proportional-Integral-Derivative (PID) algorithms for controlling DO, basin air flow distribution, and blower pressure or flow. These algorithms are prone to hunting - the cyclic fluctuation of the controlled variable. Fluctuations that oscillate the DO several mg/L above and below the target DO concentration are common.

This article aims to discuss the various technologies of equipment that could be presented to a wastewater operator faced with a temporary need for blower air and to help the operator understand the impact (both monetarily through a “Total Cost of Rental” approach and environmentally) of their decisions.

A small site located within a floodplain, prone to erosion, and currently occupied by an existing in-service wastewater treatment facility is not at the top of any engineer’s list for a desirable site to expand a wastewater treatment plant or reclamation facility. However, these challenges created opportunity for specialized solutions during the design of the facility expansion; in particular, in designing the aeration and digester blower system.

Ever since it was commissioned in 1974, the Echallens wastewater treatment plant in the Swiss canton of Vaud has been generating power from the recovery of biogas. In May 2020, two old oil-lubricated piston compressors used to mix the sludge in the digester were replaced by one MINK claw compressor from Busch Vacuum Solutions. This enabled the amount of power required for this process to be reduced by up to 40 percent. For the director of the treatment plant, this means he needs less energy to produce energy.

Aerobic digestion is a common treatment technology used at small-to medium-sized wastewater treatment plants for the treatment of waste activated sludge (WAS). The objective of aerobic digestion is to treat the sludge for disposal, and for those trying to meet Class B biosolids, further reduce volatile solids (VS) and pathogens to ensure the sludge is suitable for land application.