Nitrification Inhibition by Quatenary Ammonium Compounds in Wastewater from Small Communities and Schools

Quaternary ammonium compounds (QAC) are used extensively in many different types of products. They are rated as nontoxic but are inhibitory, if not toxic at very low levels to nitrifying bacteria. Examples of typical QAC products and their use are discussed in the paper. The best approach to prevent inhibition of nitrification where nitrogen is a prime concern in wastewater discharges is to prevent or remove the QAC before it gets into the wastewater. However, this is frequently not practical. The complications of removing QAC in a treatment system are magnified because it is very slow to biodegrade and very little is known of its degradation rate. Several approaches to treating QAC are presented with examples given. It is concluded that treatment is possible with the methods outlined and detailed designs are difficult because of the lack of degradation rates.