What is the difference in pump selection for wastewater treatment plants versus water treatment plants?
asked 25 November 2016 asked by Joanna (450 points)
The same pump can,t be use for both application mainly because wastewater contain solids. You can have information about pumps type and their applications at the following link: http://www.pumpscout.com/articles-scout-guide/pump-types-guide-aid100.html
Selecting the pump starts out in the same way. You need to know your desired flow range, your pumping head, and the characteristics of your fluid you are pumping (solids size, %solids, temperature, etc). Most clean water pumps are centrifugal pumps and can produce some large heads and large flows if required. Non-clog sewage pumps are centrifugal, but because of the impeller opening size to pass solids, cannot always hit the same discharge head. Positive displacement type pumps (progressive cavity, rotary lobe) can be used for pumping sludge from the waste processes at either type of plant.
An important difference lies in the type of fluid, sludge or effluent and whether it contains solid or greasy particles or if it has good settling properties vs. water that is relatively low in suspended matter (river, underground source, or drinking water). Submersible pumps are generally preferred for wastewater, and surface pumps are more common for discharging treated drinking water. The type of pump is usually determined by the suction height, which cannot exceed ten meters.
Key differences: Type of fluid: sludge, wastewater, potential for fibrous material, etc. Head loss: this usually is not significant in a WWTP because of limited linear distances. Static head, however, is the criterion to consider in selecting a pump (it remains quite limited—max 10 m). Flow rates: often larger pumps, recirculation, plant inlet (i.e., primary facility) Willingness to use variable speed drives to lessen hydraulic shocks.
The choice of pump in these instances is driven by the nature of the fluid being treated, the type of facility, and the degree of treatment performed. (1) Pump impellers: The type of impeller determines the kind of pump. Vortex impeller pumps are better suited for wastewater, while single or multi-channel pumps are better for drinking water and grey water. Pump manufacturers can provide accessories and specialized pumps like grinders in the case of wastewater that contains solid or fibrous matter in order to prevent fouling and clogging. This type of device is usually installed upstream of the facility. (2) Material: The pump should be resistant to corrosion and abrasion from grit-filled wastewater. Usually this means stainless steel or Abrasit-coated cast iron parts. Some manufacturers specially treat pumps with a ceramic coating to increase hydraulic performance. (3) Installation: Pumps placed upstream of treatment plants are often used in lift stations and enable collected water to be fed through a constant or intermittent flow into the treatment facility. So, in the case of wastewater, submersible pumps are placed directly in the wet well (controlled according to water levels—the engine must remain in contact with the fluid to allow for cooling, although some specialized engines allow for internal cooling). In these cases, total dynamic head is mainly determined by static head. Surface pumps can be used if the suction height is not greater than just under 10 m (better suited to drinking water). Specially adapted surface pumps can be used to empty sludge from decanter centrifuges. Downstream of the treatment plant, depending on the kind of effluent, standard pumps for clear/drinking water can be used for distribution or discharge of treated water (the dynamic head can be high in relation to the discharge point). (4) Whether or not to add a variable speed drive? This is a complex calculation that requires consultation with engineers, feasibility studies, algorithms specific to the type of wastewater and other considerations that will ensure both the cost effectiveness and the reliability of the pumps.