USE OF BACILLUS-SUBTILIS SPORES TO EVALUATE THE EFFICIENCY OF SODIUM-HYPOCHLORITE AT DIFFERENT CONCENTRATION AND PH VALUES

The sporicidal action of NaOCl at 50, 75, 105, 150 and 200 mg/l of fre e available chlorine (FAC) at pH 9.8 and 105 mg/l at pH 7.0, 8.0 and 9 .0, was studied using lots of spores of Bacillus subtilis ATCC 19659 s uspended in water with 15% v/v glicerol at 30-degrees-C. The contact t imes were chosen from a death range in preliminary studies. The decima l reduction (DR) in the number of spores subjected to contact with the hypochlorite solutions was determined by difference between the decim al logarithm (log) of the initial number spores (not submitted to the solution) and the surviving spores after each time contact. Simple lin ear regression models were fitted to the DR values as function of spor e contact time in each solution. These equations were used to estimate the spore initial death time (SIDT) and D value of each solution. A l inear relation was found between the log of SIDT (Y1), in minutes, the log of D values (Y2), in minutes and the log of hypochlorous acid con centration (G), in mg/l. The equations G= mg/l FAC/1 + 10pH - 750, Y1 = -1.0945G + 1.5106 (r2 = 0.99) and Y2 = -0.8869G + 1.1401 (r2 = 0.99) were rearranged and transformed by software ''DERIVE'' for algebric s implification originating a fourth equation to estimate the NaOCl solu tion contact time (T) required to produce a given DR at a given concen tration of FAC an pH value: T = 32.4026 e-2.52014G + 13.8065 DR e-2.04 213G, where e = neperian base; 50mg/l <FAC<200mg/l, at 30-degrees-C; 7 .0<pH<9.8.