INACTIVATION OF ENTEROCOCCI AND FECAL-COLIFORMS FROM SEWAGE AND MEATWORKS EFFLUENTS IN SEAWATER CHAMBERS

Inactivation in sunlight of fecal coliforms (FC) and enterococci (Ent) from sewage and meatworks effluents was measured in 300-liter effluen t-seawater mixtures (2% vol/vol) held in open-topped chambers. Dark in activation rates (k(D)s) were measured (from log-linear survival curve s) in enclosed chambers and 6-liter pots. The k(D) for FC was 2 to 4 t imes that for Ent, and inactivation was generally slower at lower temp eratures. Sunlight inactivation was described in terms of shoulder siz e (n) and the slope (k) of the log-linear portion of the survival curv e as a function of global solar insolation and UV-B fluence. The n val ues tended to be larger for Ent than for FC, and the k values for FC w ere around twice those for Ent in both effluent-seawater mixtures. The combined sunlight data showed a general inactivation rate (k) ranking in effluent-seawater mixtures of meatworks FC > sewage FC > meatworks Ent > sewage Ent. Describing 90% inactivation in terms of insolation (S-90) gave far less seasonal variation than T-90 (time-dependent) val ues. However, there were significant differences in inactivation rates between experiments, indicating the contribution to inactivation of f actors other than insolation. Inactivation rates under different long- pass optical filters decreased with the increase in the spectral cutof f wavelength (lambda(50)) of the filters and indicated little contribu tion by UV-B to total inactivation. Most inactivation appeared to be c aused by two main regions of the solar spectrum-between 318 and 340 nm in the UV region and >400 nm in the visible region.