Q

'sulf

^Sulf +Csulf

sulf

and using for the inhibition terms:

Kt inh, nit inh, nit

where Cox and C^ are the concentrations of oxygen and nitrate, respectively, and and K^

are half-saturation constants. ox and Kmh, nit are inhibition constants that need to be much smaller than typical nitrate or oxygen concentrations under ambient conditions. The Monod-type inhibition term /mhi ox will then remain ~0 as long as oxygen is present in significant amounts but reaches its maximum value of «=1 as soon as oxygen is depleted. Growth of SRB remains inhibited after iinh ox becomes ~1, because I¡„h, nit is still ~0 as long as nitrate is present. Once nitrate concentrations become very low, Iin^ nit also approaches ~ 1 and growth of SRB can start to increase to rates that will affect the concentration of the organic substrate (no more growth inhibition). Mathematically, the form of the inhibition terms resembles that used in model approaches that do not explicitly consider bacterial growth and decay for the computation of the oxidation rates of the organic compounds (39). VanCappellenet al. (60) have used inhibition terms of this form for the simulation of the oxidation of organic matter in aquatic sediments. Most comprehensive biodegradation models incorporate multiple inhibition terms into the growth equation(s). Following equation 21 and assuming that microbial groups are distinguished by their capacity of using a particular electron acceptor, a generalized formulation for microbial growth is then ax dt

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