DETERIORATION OF PH ELECTRODE RESPONSE DUE TO BIOFILM FORMATION ON THE GLASS MEMBRANE

Mixed-species freshwater biofilms have been grown in an aquarium-based fouling system. Glass pH electrodes and fouling coupons made from gla ss microscope slides are fouled simultaneously and in parallel with re spect to fouling water flow. The response of fouled pH electrodes to s tep changes in solution pH is determined by switching between two beak ers of solution. Biofilm formation on the coupons is examined under an optical microscope and quantified by optical absorbance and dry mass. The mass and optical absorbance of attached material are observed to increase over time and the r(2) correlation between them is 0.91. The 10-90% response time of the fouled pH electrodes is observed to increa se in a linear manner with increasing attached biomass and biofilm opt ical absorbance, though a degree of variation is observed, reflecting the highly variable nature of biofilms. Fouled responses are compared to a diffusion model previously used to describe the response of pH el ectrodes coated with stagnant layers. The model does not describe adeq uately the dynamic response of a fouled electrode and this has been at tributed to buffering effects of the biofilm and solutions entrained w ithin it.