MICROBIOLOGICAL SURVEY OF OPEN RECIRCULATING COOLING WATER-SYSTEMS AND THEIR RAW WATER-SUPPLIES AT 12 FOSSIL-FIRED POWER-STATIONS

Raw water supplies utilised at 12 fossil-fired power stations, as well as the corresponding open recirculating cooling water systems were su rveyed. Visual inspections were carried out and total aerobic and anae robic bacteria, anaerobic acid-producing bacteria, Thiobacillus., Nitr obacter spp., sulphate-reducing bacteria (SRB) and algae were quantifi ed. All raw water supplies and recirculating cooling waters contained all of the above groups of micro-organisms, with the exception of the two potable raw water supplies. In 75% of the systems, the numbers of SRB in the recirculating cooling waters were higher than in the corres ponding raw water supplies in 92% of the systems, the numbers of total aerobic bacteria were higher in the recirculating cooling waters than in the raw water supplies. However, no relationship between the sulph ate levels in the recirculating cooling waters and the numbers of SRB could be distinguished, or between the percentage increase in the numb ers of total aerobic bacteria and the cycles of concentration at which the system was operated. The frequency polygons of the occurrences of total aerobic and anaerobic bacteria in the raw water supplies and re circulating cooling waters did not follow normal distribution patterns . Visible biofouling deposits were observe at six of the power station s surveyed and the predominant algal group was the blue-green algae. H owever, in the raw water supplies, the predominant algal groups were g reen algae and diatoms. Microbiologically influenced corrosion was ide ntified in all five of the condensers inspected. Each system was found to be unique and no generalisations in terms of presence or activity of micro-organisms could be made.