The effect of common sewage sludge treatment processes on oocysts of the coccidian protozoan Cryptosporidium was evaluated in laboratory simulations. The ability of primary sewage sedimentation to remove Cryptosporidium oocysts was found to be poor. Thermophilic (55 degrees C) aerobic digestion and sludge pasteurization at the same temperature were found to be effective treatments to inactivate Cryptosporidium oocysts. Approximately 10% of the oocyst population were found to be viable after 18 d exposure to mesophilic (35 degrees C) anaerobically digesting sludge. The viability of Cryptosporidium oocysts decreased within the range 20-40% in sludge-treated soil mesocosms over 30 d. The survival results obtained, however, indicated that oocysts would survive well beyond this period.

Methods were evaluated for the recovery of Cryptosporidium oocysts from water. Various types of cartridge filter were tested but proved to be inferior to the standard Cuno Micro-Wynd filter. Laboratory scale sand columns were also evaluated. The retention within the column material was satisfactory at low flow rates. However, the system was judged inadequate for monitoring because of the poor retention of oocysts within the column matrix at realistic flow rates. The continuous flow centrifuges tested were shown not to be capable of yielding satisfactory recoveries, although it is considered more refined machines currently available may warrant investigation. The vortex-flow filtration technique using the Membrex Benchmark device gave fairly consistent recoveries of 30-40%. However, the comparatively long process times would militate against the use of this device for monitoring purposes. A cross-flow filtration module was evaluated and gave relatively good recoveries (approximately 40-80%) at moderately high flow rates (0.9-1.01/min) from clean water samples spiked with Cryptosporidium oocysts.

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Methanogens colonised on reticulated polyurethane foam BSP rapidly lost biomass raven exposed to hydrodynamic stress.The loss was independent of the porosity of the BSP matrix.These findings indicate the binding forces between methanogen and particle surface is weak and may impose a limit on the potential for process intensification in fixed or fluidised bed methane digesters.

With funding from the European Commission, a consortium of members of the European Water Research Institutes is carrying out a programme of work with the objective of optimising and standardising a method for determining the presence in water of (oo)cysts of Cryptosporidium and Giardia. Each of the stages of the conventional analysis procedure (initial concentration, recoveryand identification and enumeration) are being investigated and the relative merits of existing and new methods are being assessed. Newly developed filters (Envirochek and Filta-Max) have been shown to be more efficient for initial recovery of (oo)cysts from water than the previously used Cuno cartridge filters. In addition, for the analysis of raw waters, flocculationwith ferric sulphate has been shown to give recoveries similar to the Envirochek and Filta Max. Modern purification systems such as immunomagnetic separation have also been assessed and found to offer some advantages over flotation although optimisation of the latter has brought improved efficiency. Preliminary assessment of solid phase cytometry has indicated that this technique could offer significant time savings compared to conventional microscopic counting. The results of the study will be used to propose a revised standard method to CEN.