Sludge generated in wastewater treatment plants need to be transferred from one location to another and because of the nature of sludge which varies in thickness, selection of the right type of pumps can be tricky. There are times that the sludge need to be conveyed from one treatment process to another while there are conditions that the it might be required to be disposed off in nearby landfills and thus the role of pumps come into subject of discussion here.
Generally those that are most frequently employed for use in sludge pumping activities include progressive cavity, plunger and diaphragm pumps. Each type offers own advantages depending on the application or needs and that includes the concentration of sludge which we are dealing with as well. At times, selection criteria can be complicated due to the fact that certain sludge has variable thickness generated at different intervals depending on the wastewater plant process control.
Progressive Cavity is usually selected based on the requirements and needs on having a more easily controlled pumping flow rates and also in terms of ease of use and simple operations. Progressive cavity pump is considered a self-priming type due to the fact that it is made up of just a single threaded rotor operating in helix stator made up of rubber. The pump must not be operated dry or else the rubber might burn out and replacing a new unit means a heavy disruption to the wastewater treatment operation. Apart from that, the pump can also frequently breakdown and encounter leakages coming from wear and tear happening at the rotors side and replacing a new one will be quite expensive if there is no spare part from the manufacturer. Otherwise, with available capacity that stretches up to 75liters per second, this is usually more than sufficient for a normal sludge transferring process.
Plunger Pump (insert picture)
Due to the grittiness of incoming sludge, sometimes plant operators would rather opt for plunger pumps. There are many advantages associated with using this type of unit mainly is because the pulsating effect will lead to more concentrated sludge buildup in the hopper after the pumps. When operating under low velocities, it can also help to resuspend the solids in pipelines and with high discharge heads depending on model from manufacturers; it can create discharge head of up to 3 meters. Needs on having adjusted flow and speed control can also be enhanced by using a variable pitch drive belts put into it. Overall, similar like progressive cavity pumps, plunger types are also self-priming which means that it will avoid the hassle that usually comes about when it comes to sludge pumping applications. (Related subject: Sludge transfer for thickening process)
Diaphragm pumps offers flexibility and portability as long as there are pneumatic supplies. It uses a set of membrane that will constantly contract and enlarge to deliver flow through a check valve. Diaphragm pumps usually have lower capacities and discharge head giving only about 15 liters per second with 15 meter of head. The most common problem associated with using diaphragm pump is that it will frequently subject to normal wear and tear especially on the diaphragms whereby replacement set is needed to be placed on standby in case of breakdown. Somehow when it comes to sludge whereby grits are present, it will lead to more maintenance problems and thus, it is better to consider other types of pumps unless the subject of flexibility comes into consideration here.