Tertiary Waste Water Treatment with Flotation Filters

Tertiary waste water treatment has been usually carried out by adding filtration after an activated sludge process, which can be fitted with pre- or simultaneous precipitation for removal of phosphorus. Filtration is operated either as a mechanical unit operation for upgrading the removal of suspended solids only, or as contact filtration where the precipitation of phosphorus is boosted with a minute dose of trivalent iron or aluminium. Instead of using conventional downflow filters, tertiary treatment can also be carried out with flotation filters where flotation is accomplished in the head above the filter, necessary for filtration in any case. The possibility of using flotation between secondary clarification (sedimentation) and filtration, when it is needed, results in a very good load bearing capacity and in a high degree of removal of solids. This means that excellent operational results can be achieved with an almost complete reliability in all operational circumstances at a very reasonable cost. Long experience in Finland from a medium size (30 000 pe) activated sludge plant with simultaneous precipitation fitted with flotation filter tertiary treatment in 1984, shows that values of BOD7 ≤ 5 mg/l, Ptot ≤ 0.3 mg/l NH4-N ≤ 1 mg/l and of suspended solids ≤ 5 mg/l can be continuously achieved, in the treatment of municipal waste water where total nitrification is applied.

Necrobacillosis and immunity in mice

SUMMARYThe study arose from the recent finding that sub-lethal numbers of certain bacterial species greatly enhanced the infectivity of Fusobacterium necrophorum.A severe F. necrophorum infection in mice, cured with metronidazole, produced significant though slight resistance, which was demonstrable by challenge with a minute dose of F. necrophorum (< 20 organisms) suspended in a sub-lethal dose of Escherichia coli (300 × 10 organisms) to enhance fusobacterial infectivity. In an earlier comparable experiment, challenge with F. necrophorum alone, in necessarily large doses (≥3 × lO organisms), failed to demonstrate that a single cured fusobacterial infection gave rise to resistance; such an infection neither protected against the fatal necrobacillosis produced by challenge nor prolonged survival.A sub-lethal E. coli infection was also shown by challenge with a minute dose of F. necrophorum (< 10 organisms), suspended in a sub-lethal dose of E. coli (152 × 10 organisms), to produce significant though slight protection against necrobacillosis.The degrees of resistance demonstrated were too slight to give any encouragement to the prospect of an effective necrobacillosis vaccine.

ADRENAL CORTICAL HORMONES AND RESISTANCE TO HISTAMINE STRESS IN THE INFANT RAT

ABSTRACT The adrenal gland corticosterone concentration in the infant rat is similar to that found in the intact unstressed normal adult. 1–2 day old rats did not respond to histamine administration with an increase in adrenal cortical hormone content while adults exhibited the expected increase. The 90 minute dose-mortality relationship for histamine was determined on these stress-non-responsive infant rats. Prior treatment with cortisone, cortisol, corticosterone or ACTH did not significantly influence the number of deaths occurring at a given dose of histamine. These results are compatible with the hypothesis that, in the otherwise normal animal, the abrupt secretion of ACTH and the adrenal cortical hormones in response to acute stress may not contribute stress resistance to contemporaneous insults, at least to those allied to histamine administration.