Quanti tray sealer

The Most Probable Number (MPN) of TC and E. coli was determined by the quanti-tray/2000 Colilert-18^® test (9223 B-2004 Colilert-18^®)⁶⁰ in 100 mL (MPN 100 mL⁻¹) samples taken from the P-FBR influent and effluent as well as from the anolyte of the electrochemical cell. An IDEXX Quanti-tray sealer (IDEXX Laboratories Inc., Maine, USA) was used to seal the trays that were subsequently incubated for 22 h at 35 °C. For all dilutions required, filtered sterilized distilled water was used.

The Colilert-18 (ISO 9308-2:2012, IDEXX Laboratories, Inc., Westbrook, ME, USA) and Enterolert-E (ISO 7899-1, IDEXX Laboratories, Inc., Westbrook, USA) MPN method procedures were executed according to the company instructions (IDEXX Laboratories, Inc., Westbrook, ME, USA) for the enumeration of Escherichia coli and intestinal enterococci, respectively. Three dilutions were performed (1:10; 50:50; 9:10) due to the suspicion of the high microbiological load. Briefly, 100 mL of each diluted sample and one vial of Colilert-18 and Enterolert-E were added to sterile vessels, capped and shaken to dissolve the reagent, the content was transferred to a 97-well Quanti-Tray (IDEXX Laboratories, Inc., Westbrook, USA), heat-sealed in the Quanti-Tray Sealer (IDEXX Laboratories, Inc., Westbrook, ME, USA), and incubated at 35 ± 0.5 °C for 18 hours (Colilert-18) or 41 ± 0.5 °C for 24 hours (Enterolert-E). After incubation, Quanti-Trays were observed under ultra-violet (UV) light (365 nm) and the fluorescent cells were counted and referred to the MPN table provided by IDEXX for the enumeration of E. coli and intestinal enterococci. Microbiological counts were reported as MPN/100 mL.