MLSS vs MLVSS - which is best for operating a wastewater treatment plant?

Short post - but I am often asked about MLSS vs MLVSS and which is required to operate a wastewater treatment plant. As with most things wastewater - consistency is actually more important that the individual test. Remember, for wastewater operations we are looking for trends so running the same test each time is important for data analysis and operational decisions. Now for MLSS vs MLVSS.

MLSS - is the biological and inorganic solids dried at 105 Deg C. So we just remove the water from the solids. 

MLVSS - we take the dried sample from MLSS testing and put in a high temperature furnace 550 Deg C. This removes the volatile portion of the MLSS, which is all of the biological portion - cells, EPS, insoluble organics, etc. Leaving the inorganic fraction. so MLSS - Residual after 550 Deg C = MLVSS.

In all cases MLSS >​ MLVSS.

For WW, I work with plants that use MLSS, MLVSS, or both. Just use the same test for operation decisions and don't get into data paralysis.