spp. cysts andspp. oocysts in drinking water treatment residues: comparison of recovery methods for quantity assessment.

Abstract

Water treatment plant (WTP) residues, e.g. sludge and filter backwash water (FBW), may contain pathogenic microorganisms, asspp. andspp. However, recovering protozoa from such matrices lacks a formal and precise protocol, which is imperative to improve research in their detection, removal and inactivation. The latter includes a deeper challenge as some recovery methods may compromise viability. This study applied different recovery methods forcysts andoocysts spiked into settled sludge and FBW obtained from a bench treatment. Procedures in sludge involved direct centrifugation, alkaline and acid flocculation, including purification by immunomagnetic separation (IMS). FBW samples were tested for membrane filtration (MF) and heated Tweenscrapings followed or not by IMS. Propidium iodide (PI) inclusion was used for oocyst viability evaluation prior and after recovery. Results with purified suspensions lead to higher recovery efficiencies (RE) for, which was assumed to relate to poorfluorescence. Analytical quality assessments were carried out with ColorSeedfor the methods that stood out for each matrix and the results indicated lower RE than when organisms from purified suspensions were recovered. Ferric sulphate flocculation and MF, both followed by IMS reached 32.25% and 11.00% RE forspp. and 19.61% and 2.00% forspp., respectively. All of the tested methods affected oocyst viability. These results encourage further research to overcome the matrices complexity explained in this paper and increase RE, taking effects in protozoa viability into consideration.