Escherichia coli Regrowth in Disinfected Sewage Effluent: Effect of DOC and Nutrients on Regrowth in Laboratory Incubations and Urban Streams
2013
McCrary, K Jordan | Harclerode Case, Cara L. | Gentry, Terry J. | Aitkenhead-Peterson, Jacqueline A.
This study examined the potential for regrowth of Escherichia coli in laboratory-incubated microcosms spiked with ultraviolet (UV)-disinfected sewage effluent and extracts derived from turfgrass or leaf litter. A second part of the study examined the potential of nutrients for predicting E. coli in two urban streams with point source effluent. Microcosms containing effluent and vegetation extracts were incubated for 72 h, samples were withdrawn over six time periods for measurement of E. coli. Streams were sampled every 2 weeks and E. coli and nutrients measured. E. coli counts in the microcosms exceeded the Texas state secondary contact recreation standard for surface water quality within 12 h for the turfgrass and within 18 h for leaf litter extracts. Univariate analysis of variance found that the interaction between vegetation extract source and concentration was more important than source of vegetation or concentration of extract alone. In the two streams sampled downstream of a point source effluent discharge, between 82 and 92 % of the variance in annual E. coli during high stream flow and between 55 and 57 % of the variance in annual E. coli during low stream flow was described by stream water-dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), NH₄-N, NO₃-N, or PO₄-P. Once effluent is discharged to surface water, particularly during high flow conditions, DOC and DON derived from the landscape and nitrogen and PO₄-P derived from the effluent will provide ideal conditions for E. coli regrowth in surface waters downstream of the point source discharge.
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