Inhibition to the Activated Sludge Process

An issue that surfaces periodically, particularly for those of us involved in treating industrial wastewater, is a concern about inhibition to the activated sludge process from one or another chemical compound. A typical question might be, for example: “How high an ammonia concentration can my biological treatment system handle before inhibition or toxicity to the microorganisms begins to occur?” Determining this can best be done through oxygen uptake rate testing but this is not always practical. So some basic guidelines can be helpful but, unfortunately, such guidelines are not readily available. One source of information I really like comes from Novozymes (, a company that makes a variety of bioaugmentation products.

Provided below are three tables that I have cut and pasted from a Novozymes document entitled “Inhibitory Chemicals: Biological Wastewater Treatment.” This document, and several other excellent documents can be found at the Novozymes website. The other documents from Novozymes that I think are worthwhile, all available as free downloads as PDF files, are as follows:

        “A Guide to Wastewater Microbiology” Understanding how to classify microorganisms, their growth requirements, and their limiting factors.

        “Reference Guide to Activated Sludge”

        “A Guide to Higher Life Forms in Biological Wastewater Treatment Systems”