Sodium hypochlorite (NaOCI) is the most widely used disinfectant in the food industry despite the increasing availability of other disinfectants.Sodium hypochlorite fulfills many requirements as the ideal disinfectant and furthermore it has an excellent cleaning action. The effectiveness of sodium hypochlorite in the cleaning and disinfection processes depends on the concentration of available chlorine and the pH of the solution. Hypochlorous acid (HOCI) is a weak acid and dissociates to the hypochlorite ion (-OCI) and proton (H+) depending on the solution pH. It is generally believed that HOCI is the active species in the germicidal action, whereas the concentration of -OCI is a key factor determining the cleaning efficiency. This implies that the optimal pH region of the germicidal activity of sodium hypochlorite differs from that of its cleaning activity. This paper describes the theory and practice of the cleaning and disinfecting operations based on the use of sodium hypochlorite solution.

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Inhibition of the fermentation of propionate to methane and carbon dioxide by hydrogen, acetate, and propionate was analyzed with a mesophilic propionate-acclimatized sludge that consisted of numerous flocs (size, 150 to 300 ,um). The acclimatized sludge could convert propionate to methane and carbon dioxide stoichiometrically without accumulating hydrogen and acetate in a propionate-minimal medium. Inhibition of propionate utilization by propionate could be analyzed by a second-order substrate inhibition model (shown below) given that the substrate saturation constant, K., was 15.9 ,uM; the substrate inhibition constant, Ki, was 0.79 mM; and the maximum specific rate of propionate utilization, q,, was 2.15 mmol/g of mixed-liquor volatile suspended solids (MLVSS) per day: q, = qmSI[Ks + S + (S2IKj)], where q., is the specific rate of propionate utilization and S is the initial concentration of undissociated propionic acid. For inhibition by hydrogen and acetate to propionate utilization, a noncompetitive product inhibition model was used: q, = qmI[l + (PIKp)-], where P is the initial concentration of hydrogen or undissociated acetic acid and Kp is the inhibition constant. Kinetic analysis gave, for hydrogen inhibition, KP(H2) = 0.11 atm (= 11.1 kPa, 71.5 ,iM), q,,, = 2.40 mmol/g of MLVSS per day, and n = 1.51 and, for acetate inhibition, KP(HAC) = 48.6 ,uM, qn = 1.85 mmol/g of MLVSS per day, and n = 0.96. It could be concluded that the increase in undissociated propionic acid concentration was a key factor in inhibition of propionate utilization and that hydrogen and acetate cooperatively inhibited propionate degradation, suggesting that hydrogenotrophic and acetoclastic methanogens might play an important role in enhancing propionate degradation to methane and carbon dioxide. Production of CH4 from propionate is an important intermediate step in the bioconversion of organic matter to CH4 and CO2. Propionate degradation requires obligate protonreducing acetogens that form acetate, H2, and CO2 from propionate and H2-and acetate-utilizing methanogens (2, 4, 13). The equations for the reactions of the respective bacterial groups are as follows:

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Inhibition of the fermentation of acetate to methane and carbon dioxide by acetate was analyzed with an acetate-acclimatized sludge and with Methanosarcina barkeyi Fusaro under mesophilic conditions. A secondorder substrate inhibition model, qcH4 = qnS/[Ks + S + (S2IK)], where S was the concentration of undissociated acetic acid, not ionized acetic acid, could be applicable in both cases. The analysis resulted in substrate saturation constants, Ks, of 4.0 ,uM for the acclimatized sludge and 104 ,uM for M. barkeri. The threshold concentrations of undissociated acetic acid when no further acetate utilization was observed were 0.078 ,uM (pH 7.50) for the acclimatized sludge and 4.43 ,uM (pH 7.45) for M. barkeri. These kinetic results