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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.

This study describes the bactericidal and sporicidal effects of four disinfectants on a geosmin-producing strain of Streptomyces griseus. The disinfectants investigated were chlorine, chloramine, chlorine dioxide and ozone. Chlorine and chlorine dioxide at concentrations around 1 mg/l were effective inactivators of both spore and mycelial propagules. Decimation times of less than 1 min were determined in each case. Both growth forms exhibited a high ozone demand, but decimation times resulting from an initial dose of around 2.5 mg/l were approximately 1.5 min. Monochloramine was comparatively less effective: at a concentration of approximately 1 mg/l the decimation times for spores and mycelia were 13.8 and 22.7 min, respectively.

Standard colorimetric methods based on the initial reduction of formate to formaldehyde were found to yield erratic results when applied to the analysis of millimolar concentrations of formate in a microbial culture medium. The source of interference was identified as inorganic orthophosphate inhibition of the magnesium/hydrochloric acid reduction stage. Passivation of magnesium by millimolar concentrations of phosphate is known to occur at low pH and it is proposed that this phenomenon is responsible for the inhibition of the reduction process. The presence of orthophosphate in biological extracts is almost universal and would lead to acceptance of spuriously low values for formate concentration if the previously unreported inhibitory effect is not recognized. The colorimetric method of Barker and Somers in which formate is reacted directly with 2-thiobarbituric acid to form the chromophore was evaluated and proved to be entirely free from interference by orthophosphate and other medium components. This method although less sensitive than the formate reduction methods is therefore suggested as the method of choice for the determination of formate in biological or other solutions containing phosphate.