MLSS and MLVSS are both used as measures of the microorganism
concentration in the activated sludge system. MLSS
includes both the volatile and inert solids in the mixed liquor.
MLVSS more closely approximates the biologically active portion
of the solids in the mixed liquor, as microbial cellular material
is organic and volatilizes or burns at 550 C. The volatile fraction,
i.e. the ratio of MLVSS: MLSS observed in this experiment concurs
with the typical values given by Metcalf and Eddy (2003) (0.85) and
Woodside and Kocurek (1997) (0.80). In the present study, MLSS is
measured more frequently than MLVSS, as the analytical test for
suspended solids is quicker than the test for volatile suspended
solids. Hence, the MLVSS was approximated by using the ratio of
MLVSS: MLSS.