Wastewater treatment comprises a mixture of treating domestic sewage, industrial effluent and occasional water run-off into the sewers. The aerator provides air input and oxygen transfer to promote the growth of micro-organisms which breaks down dissolved and suspended organic solids. The mixture of wastewater and micro-organisms passes from aeration tank to a clarifier/sedimentation tank where the biomass settles and concentrated as sludge. Some of the sludge is recycled into another aeration process to maintain the biomass (activated sludge), and the rest is pumped to anaerobic digesters. In industrial wastewater, large volumes of wastewater continuously flowing through various treatment processes for re-use or before disposal. Not unlike water treatment, the top mounted mechanical mixers, submersible mixers, inline mixers, pumps and submersible pumps among others are used in process tanks, chemical dosing and mixing or liquid transfer. The process can be continuous, periodic or in batches.