nbVSS - nonbiodegradable Volatile Suspended Solids

In the nomenclature of wasterwater engineering the nbVSS, stands for nonbiodegradable Volatile Suspended Solids (nbVSS). The nbVSS referes to the concentrations of nonbiodegradable organic material, among wich the cell debris from endogenous respiration. (pages 581)
The nbVSS concentration is of great significance in proces design. The effect of nbVSS concentration in the influent will be significant in proces sludge production and aeration volume requirements. (page 704)
The nbVSS concentration resulting from cell debris is typically arelativly small fraction of the VSS in a bioreactor used to treat municipal and some industrial wastewaters. For typical untreated municipal wastewaters the nbVSS concentration may be in the range from 60 to 100 mg/L, and following primary treatment may range from 10 to 40 mg/L. (page 586)
The wastewater nonbiodegradable volatile suspended solids concentratie can be estimeted from analyses for COD, sCOD, BOD, sBOD, and VSS concentration, and by assuming a constant COD/VSS ratio for both biodegradable and nonbiodegradable VSS:

Where:

nbVSS =	nonbiodegradable Volatile Suspended Solids	[g/m³] or [mg/l]
BOD =	Biological Oxygen Demand	[g/m³] or [mg/l]
COD =	Biological Oxygen Demand	[g/m³] or [mg/l]
bpCOD =	concentration of biodegradable particulate COD	[g/m³] or [mg/l]
pCOD =	concentration of particulate COD	[g/m³] or [mg/l]
sCOD =	concentration of soluble COD in activated-sludge effluent	[g/m³] or [mg/l]

source: Metcalf and Eddy