Factors affecting the biotransformation of quaternary ammonium compounds

Quaternary ammonium compounds (QACs) are cationic surfactants, which are extensively used in various domestic, industrial and medical applications, primarily as disinfectants. QACs are predominant micropollutants found in both engineered and natural systems. QACs are not only toxic to organisms but also have recently been implicated in the proliferation (co-selection) of antibiotic resistance, which is now recognized as one of the most pressing problems for both human and environmental health. Biodegradation/biotransformation is the major process that may contribute to the elimination of the risk associated with these compounds in the environment. Although the pathways and kinetics of QAC biotransformation has been well studied in biological systems, optimum conditions for an efficient QAC biotransformation are not known.

In this project, biological, chemical and physical factors affecting the biotransformation of QACs such as presence of QAC degrading microorganisms, QAC concentration and structure, oxygen concentration, temperature, adsorption to organic/inorganic surfaces, and concentration and type of readily biodegradable organics will be evaluated and optimum conditions for QAC biotransformation in biological systems will be identified. The outcomes of this project will improve the understanding on the biotransformation of QACs in the biological systems and supply systematic information for designing treatment systems for complete QAC removal, thus contribute to the protection and welfare of both environmental and human health.

Synopsis

Progress & Outcomes

1. Isolation of BAC degrading Pseudomonas spp. strains: Four Pseudomonas spp. were isolated from activated sludge of Pasakoy Wastewater treatment plant and confirmed for BAC biotransformation.

2. MIC testing: BAC minimum inhibitory concentration of each isolates was determined using CSLI’s macro-dilution assay. 

Fig. SOD system

3. Kinetic Assays: BAC biotransformation kinetics of strain AS20 were tested at various cell densities, temperature, BAC concentration for three BAC homologues. We found very interesting things; BAC degradation can not be completed and BADMA accumulates at 40 celcius.  

4. BAC biotransformation pathway: BAC biotransformation pathway has not been completely elucidated due to short life time of the intermediates. We developed a strategy - stoichiometric oxygen dosing (SOD)- to identify each intermediate in the pathway.    

BAC

BDMA