Reducing Clogging in Wastewater Pumps: Introducing the AmaDS3 Pump Station
Solid materials suspended in domestic sewage or industrial wastewater can cause serious problems for pumps in wastewater management facilities. Solid chunks such as pieces of wood, metal or plastic can become lodged in a pump’s throat, reducing the flow and even jamming the impeller. (Figure 1) More insidious, fibrous wastes (including cloth, pieces of string, plastic, even hair from people and their pets) can collect in large rope-like tangles that can block pipes and valves or jam pumps. Fibrous solid wastes are a growing problem, due to the increasing popularity of products such as cleaning wipes, disposable diapers and mop pads. While these products are intended to be disposed of as solid waste, consumers often find it convenient to simply flush them down a toilet and into the wastewater stream. Modern toilets and appliances are designed to use less fresh water, resulting in a higher percentage of solids in the wastewater, further exacerbating the problem.
A variety of tactics have been attempted to help wastewater pumps to deal effectively with solid materials in the waste stream. Pumps may be fitted with impellers that have a large ‘free passage clearance’ (defined as the size of a sphere that could pass through the pump without getting stuck). This helps reduce a pump’s vulnerability to chunks of solid waste, but the advantage comes with a cost: impellers with large free passage clearance may have lower hydraulic efficiency than multi-vane impellers with narrower passages. Special ‘cutter’ or ‘grinder’ impellers can help break up solid materials, but are not entirely effective when confronted with the tougher components of fibrous waste. These impellers typically have lower hydraulic efficiency than conventional impellers. Operators of wastewater treatment facilities still find that the messy and time-consuming task of clearing blocked or clogged pumps needs to be done far too often.
KSB’s new AmaDS3 pump station takes a different approach to the solids in the waste-stream problem. This device is intended for use in geographically dispersed wastewater collection systems where water from a remote site needs some help from pumps to reach a central treatment facility. In order to minimize blockages and the resulting down-time, the AmaDS3 is designed so that solids in the water have as little direct contact with the pumps as possible. This is achieved through an ingenious flushing cycle. Wastewater entering the pump station first passes through a pair of solids separation chambers which screen out most solid chunks and fibrous material. The relatively solids-free water then continues to a holding tank. When the control system senses that the tank is nearly full, it turns on pumps that reverse the flow back though the solids separation chamber. Check valves prevent flow back through the inlet pipe, so that the water – once again carrying the solid materials in suspension – is forced through the outlet piping, downstream to the next stage in the wastewater processing cycle. Since the pumps only have to handle pre-screened water, there is much less risk that these vital components will become jammed with solid materials. In practice, each unit has two separation chambers and pumps that act in parallel as redundant systems. In the event that one of these systems requires attention, the appropriate side of the system can be isolated with manual valves and taken apart for clearing or service. The other side of the unit remains operational.
AmaDS3 pump stations are built as a sealed unit and designed to be installed in a dry well. The exterior of the unit remains dry and clean, so that maintenance operations are less dirty and difficult. Because the solids separation system is largely self-cleaning (due to the reverse flow cycle), these units require relatively little maintenance. When work is required, the separation chamber and booster pumps are conveniently located on the exterior of the unit where they can be easily accessed. In addition, since the pumps and impellers can be optimized for hydraulic performance, these units can deliver significantly lower energy costs compared to conventional submerged pumps with efficiency-robbing anti-clogging features.
These pump stations are ideal for wastewater management systems that serve large geographical areas since they provide operators with a reliable, low-maintenance and efficient way of collecting sewage and industrial wastewater from distant corners of their territory. AmaDS3 pump stations are especially valuable in situations where flow volumes are low, head requirements high and the likelihood of encountering significant amounts of solid and fibrous wastes also high. When small submersible pumps are used under these conditions, clogging can occur relatively frequently because of the relatively small free passage of these pumps. The pumps used in an AmaDS3 never come into direct contact with the solids and deliver much more reliable service.