SUMMARY: Sterilized raw sewage sludge enriched with sulphate and inoculated with pure strains of Desulphovibrio desulphuricans produced negligible sulphide. Unsterilized sludge supplemented with 7% (w/v) CaSO4.2H2O and inoculated with crude cultures of sulphate‐reducing bacteria obtained from sewage yielded 1·0% S2‐ (wt S2‐ produced as H2S/vol. of raw sludge) in 6 months at 30°. By repeated subculture more active cultures developed which produced 1% S2‐ in 7 days and 1·2–1·9% in 28 days. Digested sludge yielded only 0·1% S2‐. In semicontinuous fermentations at 30°, raw sludge without added sulphate produced 20 times its own volume of gas containing 70% CH4 and 30% CO2. When 5% CaSO4.2H2O and an active crude culture of sulphate reducers were added, gas production decreased steadily to zero. There were no differences in pH, temperature and redox potential in sludges producing methane or sulphide. The chief cause of inhibition appeared to be the action of sulphide: 0·02% soluble sulphide (S2‐) totally inhibited methane formation; 0·01% S2‐ initially decreased gas production by one‐quarter but there was a slow recovery to normal, suggesting acclimatization of the methane‐producing organisms to sulphide.
Linked fermentations, in which gas from a methane fermentation swept H2S from a sulphide fermentation, gave a final gas mixture of about 60% CH4, 30% CO2 and 5–10% H2S. The yield of sulphide depended on the rate of sweeping.
Toxoplasmosis is common among all warm-blooded animals in most parts of the world. Food is a neglected source of infection but seems to have been responsible for the small outbreak described here. Case histories The three people concerned were men in their mid-twenties who shared a house in south London. The most severely affected man (case 1) developed a constant frontal headache eight days after moving into the house. The
SUMMARY
A laboratory process for the microbial production of sulphide from sewage sludge enriched with sulphate has been further developed. Semicontinuous fermentations yielded 0·9–1·0% S2‐ using a 10‐day replacement time (RT) and 0·8% S2‐ with a 5‐day RT. Yields at 37° were slightly higher than at 30°; at 43° and above yields were much lower. A mixture of 70% N2 and 30% CO2 was successfully used as sweeping gas to remove H2S; other proportions of these gases were less efficient. Stripping H2S from the sludge in an external column was as efficient as passing the stripping gas through the bulk of the fermenting sludge.
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