Motor-driven agitators for circulating liquid media, namely, agitators for mixing, stirring and homogenizing liquid manure and waste water for agricultural purposes and/or for producing biogas through circulation; motor-driven pumps as part of agitators for circulating liquid media, namely, motor-driven pumps as part of agitators for mixing, stirring, and homogenizing liquid manure and waste water for agricultural purposes and/or producing biogas through circulation