[jhcoleman53]

In terms of the “order” of rate equations, are chemical kinetics and biodegradation kinetics the same?  I’m asking because there seems to be some inconsistency in explanations when I’m trying to look up definitions.  For example, when researching biodegradation, I’ve seen “first order” defined as a reaction rate that is dependent on the concentration of only one component; “second” order as a rate that is dependent on two components; “pseudo first order” as a 2nd order reaction in which one component is present in such excess that any change in its concentration would not contribute to the rate.  On the other hand, in definitions of chemical kinetics, I see “first order” defined as one in which the rate id directly proportional to concentration of a component, i.e. if you double the concentration, the rate doubles; “second order” is a reaction in which the rate increases exponentially, i.e., if you double the concentration, the rate quadruples.  Are these two types of definitions saying the same thing and I’m just not getting it?  Or are chemistry reaction kinetics and biodegradation kinetics two different animals?  I'm confused. 
Thanks.

[Babcock_Hall]

I don't think that there is a difference in definitions.  This is a bit of a guess as to what might be confusing you, but there are two kinds of second order reactions.  One is of the form A+D product(s).  Some (but not all) reactions of this type follow rate = k[A][D].  This reaction is first order in A, first order in B, and second order overall.  On the other hand some reactions in which A is a reactant follow rate = k[A]^2.  This reaction is second order in A and second order overall.  A reaction such as 2A  product(s) might follow this rate law.

[Babcock_Hall]

first order in B,

There was a typo above.  Make that "first order in D"