Description of the Digestion Plant

This description is based on information supplied by Mr. Hicks: “The anaerobic digester was maintained at 80° F. and fed daily with meat waste. The appearance of the raw meat waste was greenish-brown, opalescent, with much settleable solids and fat in small lumps. It had a typical meaty odour, like stale soup, and the pH was 7·5 to 12. After two days' digestion at 80° F. the waste was light to deep amber in colour, clear and bright initially, becoming turbid on standing and depositing solids with colloidal sulphur. It had a peculiar amine smell and some sulphides were present. The pH was 7.1 to 7.7. After ten days retention in the oxidation pond the liquor was deep green, somewhat opalescent, with few stringy solids but some colloids. There was free ammonia at times but never any sulphides. The pH was 8·0 to 9·5. The Biochemical Oxygen Demand, in five days at 65° F., fell during digestion from 1553 in the raw waste, to 134 in the digester, to 53.2 in the oxidation pond. During this digestion, gas was evolved at the rate of 219,000 cubic feet per million gallons treated and at 37.17 cubic feet per pound of dry matter destroyed. The most important chemical transformations are, first. the conversion of organic sulphur bodies to sulphides and the oxidation of sulphides in the oxidation pond with complete removal in

less than half an hour, and, secondly, the conversion of protein nitrogen to ammoniacal nitrogen with the release of ammonia in the oxidation pond following the rise of pH.

“Biologically the raw wastes were virtually inactive, a few flagellates appearing occasionally. In the digester there were many active ciliates and flagellates, and chains of Cyanophyaceae were formed on the surface of the liquor after shaking. Some vibrios and Chlamydomonas were identified. In the oxidation pond there was a dense population of Chlorella and many Chlamydomonas. In sunny weather particularly, Paramecium occurred in very great numbers”.

In Material forwarded to Cambridge (England), Dr. Pringsheim was able to identify Chlorella saccharophila, Tetraedron sp., Polytoma uvella, and Sphaerotilus natans in the digester fluid and Chlorella, Chlamydomonas, Nitzschia and Monas sp. in the oxidation pond fluid. Clostridium was also present in the oxidation pond sample which arrived in England in an anaerobic condition.