E. Coli cb390 as an indicator of total coliphages for microbiological assessment of lime and drying bed treated sludge

The use of a single host strain that allows for an evaluation of the levels of total coliphages in any type of environmental sample would facilitate the detection of and reduction in complexity and costs, favoring countries or areas with technical and economic limitations. The CB390 strain is a candidate for this type of simultaneous determinations, mainly in water samples. The objective of the study was to establish the recovery capacity of the CB390 strain in solid and semi‐solid samples and to evaluate the microbiological quality of the sludge generated and stabilized by lime and drying beds in two WWTPs in Colombia. The results of both matrices indicated that CB390 recovered similar numbers of total coliphages (p > 0.05) against the two host strains when evaluated sepa-rately. Only the drying bed treatment was able to reduce between 2.0 and 2.9 Log10 units for some microorganisms, while the addition of lime achieved a maximum reduction of 1.3 Log10 units for E. coli. In conclusion, the CB390 strain can be used in solid and semi‐solid samples, and the treatment in a drying bed provided a product of microbiological quality. However, the results are influenced by the infrastructure of the WWTP, the treatment conditions, and the monitoring of the stabilization processes.