This article is the last in a series of six parts. Read the other parts of the series here. The previous articles in this series (Pumps & Systems, November 2015, December 2015, January 2016, March 2016 and May 2016; read them here) discussed some of the main challenges that modern wastewater composition places on sewer systems. The articles presented ways to minimize the associated risk. As mentioned in this series, the production of so-called “non-woven products” has grown tremendously in recent years, and the problem is likely to remain. Not all of these non-woven products end up in the world’s wastewater transport systems. The most dangerous items are “disposable” wipes. Because these products’ labels imply that they are harmless to sewer systems, most users dispose of them by flushing them down the toilet. This habit is particularly problematic for nurseries, retirement homes and other similar facilities where dischargers are connected to the municipality sewerage. In certain ranges and fields, measures are in place to minimize the risk of improper disposal into the sewerage. Unfortunately, many of these measures are not yet fully effective. Various fields are working on improvements to this worldwide infrastructure challenge.
Shifting trends in water use and changing sewage composition cause complex problems for the world’s sewer systems.
KSB
09/22/2016
Image 1. A bar screen is loaded with “flushable” products. (Images and graphics courtesy of KSB Inc.)
Figure 1. This graph shows the sequences for de-ragging speed over time.
Image 2. This impeller’s asymmetrical blade arrangement offers wide free passages, ensuring that even larger, rigid solids pass easily and are reliably handled by the pump.
A further focus for the engineers when designing this impeller’s blades was their ability to create a swirl in the hub area. This swirling effect shifts fibers away from the impeller hub and transports them to the outside.
When they rotate, free-flow impellers develop a strong swirl that keeps the solids in the pump casing suspended and, in combination with the inclined suction area, generates an additional flushing action. This significantly reduces the risk of clogging in the impeller’s center caused by long fibers, particularly wet wipes.
To read other articles in this series, click here.