ABSTRACT
Biochemical operations only alter and destroy materials that microorganisms act upon, i.e., those that are subject to biodegradation or biotransformation. If soluble pollutants are resistant to microbial attack, they are discharged from a biochemical operation in the same concentration that they enter it, unless they are acted on by chemical or physical mechanisms such as sorption or volatilization (see Chapter 22). Insoluble pollutants entering a suspended growth biochemical operation become intermixed with the biomass and, for all practical purposes, are inseparable from it. Consequently, engineers consider this mixture of biomass and insoluble pollutants as an entity, calling it mixed liquor suspended solids (MLSS). If insoluble pollutants are biodegradable, their mass is reduced. On the other hand, if they are nonbiodegradable, their only means of escape from the system is through MLSS wastage and their mass discharge rate in the wasted MLSS must equal their mass input rate to the system. Attached growth processes usually have little impact on nonbiodegradable insoluble pollutants, although in some cases those pollutants are flocculated and settled along with the biomass discharged from the operation.
