DYNAMICS OF NON-O1 VIBRIO-CHOLERAE AND FECAL-COLIFORMS IN EXPERIMENTAL STABILIZATION PONDS IN THE ARID REGION OF MARRAKESH, MOROCCO, AND THE EFFECT OF PH, TEMPERATURE, AND SUNLIGHT ON THEIR EXPERIMENTAL SURVIVAL

We studied the spatial-temporal dynamics of non-O1 Vibrio cholerae num bers at a stabilization pond treatment plant. This bacterium's seasona l dynamics were the inverse of those of fecal coliforms, with high lev els in hot periods and low levels in cold periods. Stabilization pond treatment did not significantly reduce non-O1 V. cholerae numbers betw een the system's inflow and outflow points. In contrast, fecal colifor ms were reduced by 98.95% in hot periods and by 94.91% in cold periods . Significant rho coefficient values for the Spearman correlation betw een numbers of non-O1 V. cholerae and temperature and pH of 0.91 and 0 .76, respectively, were found at the system's outflow point. An experi mental study of the effects of pH, temperature, and sunlight on the su rvival of non-O1 V. cholerae and fecal coliforms confirmed the inverse behaviour of the two bacterial groups noted in the stabilization pond s. Alkaline pH values of 8 and 8.8 promoted the survival of non-O1 V. cholerae and inhibited that of Escherichia coli. Low temperatures (8 d egrees C) prolonged E. coli survival (k = 0.002/h), while a temperatur e of 23 degrees C reduced it markedly (k = 0.022/h). Non-O1 V. cholera e did not survive as well as E. coli at 8 degrees C (k = 0.009/h). The effect of temperature on non-O1 V. cholerae appeared to be closely li nked to nutrient levels. Non-O1 V. cholerae appeared to be less sensit ive to sunlight than E. coli whose survival was markedly reduced, part icularly during summer periods. Non-O1 V. cholerae and E. coli did not behave in the same way in water subjected to stabilization pond treat ment. The use of fecal coliforms as an indicator of the potential heal th hazard of the effluent may not be adequate for this treatment proce dure.