Removal of sulphite-reducing clostridia spores by full-scale water treatment processes as a surrogate for protozoan (oo)cysts removal

At eight full-scale water treatment plants in the Netherlands the removal o f spores of sulphite-reducing clostridia (SSRC) was determined. By sampling and processing large volumes of water (1 up to 500 litres) SSRC were detec ted after each stage of the treatment. This enabled the assessment of the r emoval efficiency of the full-scale unit processes for persistent micro-org anisms. A comparison with literature data on the removal of Cryptosporidium and Giardia by the same type of processes revealed that SSRC can be consid ered as a potential surrogate. The average Decimal Elimination Capacity (DE C) of the overall treatment plants ranged from 1.3-4.3 log. The observed ac tual log removal of SSRC by the unit processes and the overall treatment at one of the studied locations showed that the level of variation in removal efficiency was approximately 2 log. Moreover, from the actual log removal values it was observed that a low SSRC removal by one unit process is partl y compensated by a higher removal by Subsequent unit processes at this loca tion. SSRC can be used for identification of the process conditions that ca use variation in micro-organism removal which may lead to process optimizat ion. further research is necessary to determine the optimal use of SSRC:in water quality monitoring for the production of microbiologically safe drink ing water.