WHY TO SELECT WASTEWATER PUMPS IN WASTEWATER TREATMENT PLANTS?

Wastewater is by definition a medium which describes used water, not referring if it is caused by private homes, industries or communes. In its raw condition it is pumped or transported by gravity to the next wastewater treatment plant (WWTP). The wastewater treatment process is basically divided into a mechanical, biological and optional also into a chemical treatment stage. The transportation of the media inside of WWTPs is done by different pump types. Most common are wastewater pumps with special impellers and positive displacement pumps, which are mainly used in the sludge line of the treatment process. Compared with other industries, e.g. the desalination or pulp and paper industry where each process step is defined by a certain pump type, there is no clear strategy available for the pump selection in the wastewater treatment process. The selection of the pumps is done by experience of planning offices as well as by the experience of the sewage plant operators. There is no standard available, which recommends a certain pump type for a certain application or process step. Taking this into consideration, pumps are selected, which may not be the best choice for a certain pumping position based on efficiency, wear or reliability. Based on this, three wastewater treatment plants are analyzed according to the process, different pump positions and the related pumped media. The analysis shows that different pump types are used for the same media. Some of them have a higher or lower failure potential as well as a different efficiency level. In some pumping positions where the media is already precleaned also the question of selecting wastewater hydraulics can be critically scrutinized. For one WWTP also a power and energy saving analysis is done. Installed hydraulics are changed theoretically with hydraulics at a higher efficiency level. An energy saving potential of about 2 % compared to the whole power consumption of the installed pumps is calculated. By doing this analysis the requirement of having a standard available for the right pump selection in wastewater treatment plants is figured out. Wastewater hydraulics are in some positions not the best choice related to the energy saving potential.