Formerly it was attempted to use the same kind of contact bed for continuous treatment as is used for intermittent treatment, but, as was to be expected, the results obtained were so unsatisfactory that the experiments had to be discontinued. Now somewhat different forms are utilised, which are mostly protected by patent rights, and the mode of distribution has also been altered by the introduction of patent distributors or sprinklers, which cause the sewage to fall in very thin streams upon the filling material.
In the Manchester experiments, the proprietary continuous contact bed does not appear to have given satisfactory results. Better effluents were obtained at Leeds, and at York the results obtained are said to have been very good.
On the whole, however, it is but right to say that the experience gained so far is not sufficient to entitle us to form definite opinions, and for this reason it will be better to await further results.
VI. MANAGEMENT OF PLANTS FOR THE ARTIFICIAL SELF-PURIFICATION OF SEWAGE.
[Sidenote: Plants for the artificial self-purification of sewage require very careful handling.]
It was formerly frequently concluded that neither septic tank nor contact beds required careful superintendence, but that they could be worked by automatic machinery and left to themselves. It was therefore maintained that the working expenses of plants of this nature would be next to nil. This was, however, not Mr. Dibdin’s view, who, after years of careful study, came to the conclusion that they were delicate pieces of mechanism which required careful watching.
Since, Mr. Dibdin’s conclusions have been amply confirmed by all careful experimenters.
For instance, Mr. Fowler, the chemist in charge of the Manchester experiments, observed before the Royal Commission on Sewage Disposal as follows: “It is a delicate operation (the management of septic tank and contact beds), which requires careful watching! There is no doubt whatever about that!” (Question 5651.)
Again, the conditions of successful working of contact beds, laid down by the same gentleman on page 64 of the Manchester report for the year ending March 27, 1901, are ample proof of this, and they show very clearly how extremely careful the supervision of such a plant ought to be, and that in the hands of inexperienced men it will soon come to grief.