Why are sewage pumps more susceptible to corrosion?

Nowadays, the reason why the water pump is corroded is still an extremely serious problem faced by our country and even the world, involving all departments of the national economy, we must strengthen efforts to study and solve this problem.
At present, most sewage pump products are made of metal materials. The mechanism of metal corrosion is an electrochemical phenomenon. Experimental research shows that the corrosion of metals in sand water slurry is much more serious than that in clean water. The internal corrosion of the sewage pump is caused by the slurry. The solid particles in the slurry will accelerate the corrosion rate of the flow passage parts of the pump, and also aggravate the wear.
In clean water, iron oxidizes, releasing electrons and forming anodes
Fe= Fe2+ +2e ¯
At the same time, oxygen in clean water produces oxidation-reduction reaction and forms cathode
Oz +4e- +2H2o =40H¯
If the water contains hydrogen ions, which is an acidic solution, it will produce the reduction reaction of oxygen and form a cathode
2H+ +2e¯=H
The interaction between the products of anode and cathode produces corrosion products, which are iron hydroxide, ferric oxide or ferric oxide. In clean water, the products of the reaction form a protective layer that prevents the diffusion of oxygen to the cathode, thereby reducing the corrosion rate. However, in the solid water mixture, this protective layer will be damaged by the solid particles in the water, as well as the oxide and sulfide particles in the water, which is the main reason why the corrosion of sewage pump is more serious than that of centrifugal pump.

What effect does the blockage of the cooler of the vacuum unit have on the turbine?