Modelling of chlorine effect on floc forming and filamentous micro-organisms of activated sludges

CARAVELLI A.; CONTRERAS E.; GIANNUZZI L.; ZARITZKY N.

WATER RESEARCH

Elsevier

Año: 2003 vol. 37 p. 2097 - 2105

0043-1354

Chlorination is the most economical, non-specific method to control the excessive growth of filamentous microorganismscausing bulking in activated sludge systems in the treatment of food industrial wastewaters; it was one of thefirst methods used to control filamentous bulking and is still widely employed. Considering that chlorination affectsboth floc-forming and filamentous micro-organisms and leaves undesirable disinfection by-products, it is necessary todefine the adequate doses to control bulking, minimizing the effect on floc-forming bacteria.In the present work the effect of biomass concentration and type of micro-organism on chlorine decay kinetics wasevaluated; the inactivation of either a filamentous (Sphaerotilus natans) or a floc-forming (Acinetobacter anitratus)micro-organism due to chlorination was also analyzed.For chlorine decay assays, the samples were treated in a batch system with sodium hypochlorite ranging between 9.8and 56.6mg Cl2 (gVSS)1. Respirometric assays were used to evaluate the effect of chlorine on micro-organismsrespiratory activity; in these cases, sodium hypochlorite doses ranged between 2.5 and 18 mgCl2 (gVSS)1.A model that allowed to predict simultaneously chlorine consumption and respiratory activity decay for both microorganismsas a function of time was proposed. The model includes three coupled differential equations correspondingto respiratory inhibition, readily organic matter oxidation by chlorine and chlorine decay. The rate of chlorine decaydepended on both, type and concentration of the micro-organisms in the system. Chlorine consumption rate due to S.natans was 2–4 times faster than A. anitratus. Using the proposed model initial critical chlorine doses (the lowest initialdose that leads to a total inhibition of the respiratory activity) were calculated for both micro-organisms and values of11.9 mgCl2 (gVSS)1 for S. natans and 4.5 mgCl2 (gVSS)1 for A. anitratus were obtained. These critical doses indicatedthat in non flocculated pure cultures, floc-former bacteria A. anitratus was more susceptible to chlorine action than S.natans.