Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
May, 2003

Monitoring of Specific Gravity of Wastewater

Q. I have a simple question to ask. In wastewater or plating processes, is there any reason to have to do a continuous monitoring of the density (specific gravity) of the liquid during the process.

A. In waste water treatment I have not seen anyone use density (specific gravity) monitoring. Most waste water flows do not have very large variations in density. Those few that do probably do not have useful correlations between the density differences and the control parameters of interest (such as BOD, COD, Oil & Grease, and metals concentrations).

I have seen it used in plating and cleaning chemistry bath maintenance with grab samples processed manually, but not in a continuous (automated) process mode. Some very large plating and cleaning operations could conceivably make use of an automated system (and it is possible that some are already using an automated system) to test or control the specific gravity of the process bath. A simple continuous flow, constant volume (constant liquid height), liquid level flow through cell with a force gauge in the bottom could be used to measure the density continuously. This could be used to automate chemical additions and bath maintenance.