A study of the effect of isothiazolones on the performance and characteristics of a laboratory-scale rotating biological contactor.
OBJECTIVE
To study the effect of the isothiazolone biocide (Kathon WT) on the performance of laboratory-scale rotating biological contactors (RBCs) and their component biofilms.


RESULTS
Biofilms were established on the RBCs and then exposed to 0.7-15 p.p.m. isothiazolones. Young, 1-week-old, biofilms were found to attain treatment efficiency equal to that of mature, 2-month-old, biofilms. Isothiazolone concentrations at 3 p.p.m. and above caused a progressive decline in treatment efficiency and 15 p.p.m. isothiazolones inhibited all microbial activity and resulted in the death of the biofilms. Bio-oxidation and the biodegradation of isothiazolones within the biofilms ontinued unhindered at concentrations which caused the total inhibition of planktonic bacteria.


CONCLUSIONS
There was at least a 10-fold difference in susceptibility of planktonic and biofilm bacteria to isothiazolones. The chemical oxygen demand (COD) test was shown to be a reliable tool for investigating the efficiency of wastewater treatment units when the influent contains isothiazolones, while the biochemical oxygen demand (BOD) was unreliable due to the inhibition of bio-oxidation by the biocide.


CONCLUSIONS
The results show that RBCs can be used to treat effluents containing isothiazolones at concentrations up to 1.5 p.p.m.
Laopaiboon
L
L
Department of Biosciences, University of Hertfordshire, Hatfield, Herts AL10 9AB, UK.
Smith
R N
RN
Hall
S J
SJ
D000255:Adenosine Triphosphate / Q000032:analysis; D001419:Bacteria / Q000187:drug effects*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D004866:Equipment Contamination; D005452:Fluoresceins / Q000032:analysis; D006868:Hydrolysis; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D013844:Thiazoles / Q000494:pharmacology*
D005452:Fluoresceins; D013844:Thiazoles; C037057:Kathon 886; D000255:Adenosine Triphosphate; D010100:Oxygen; C018506:diacetylfluorescein