In approaching a subject upon which so much has already been written, it may be desirable to point out that the improvements which have taken place in recent years in connection with sewage disposal are so extensive and varied, and have developed at such a comparatively rapid rate, that most treatises now in existence are in many respects more or less out of date. It is true that further developments may be anticipated in the future, but these will probably be concerned more with additions and improvements in matters of detail than of principles, which are now to a great extent agreed upon. The time would thus appear to have arrived when it is desirable to describe in detail the various methods of construction now generally adopted in the design, of present-day sewage disposal works.

In order to avoid a repetition of the usual preliminary details to be found in all the existing literature devoted to this subject, it is assumed that readers are acquainted with the nature of the problem to be solved in the design of sewage disposal works, with the varying characteristics of the different liquids included under the term “sewage,” and with the engineering formulÆ and requirements involved in the design of tanks, filters, and similar constructional works. The present volume will thus consist exclusively of descriptions, illustrated with drawings and photographs, of the various tanks, chambers, filters, beds, and other details of sewage works, including the numerous types of appliances required in connection therewith.

In other works dealing with this subject it has been customary to use as illustrations, drawings of works actually carried out by their authors or other engineers. While these are interesting and valuable to a certain extent, their application under other conditions is limited, and their usefulness is thus much reduced. In the present volume the illustrations of the various details of construction do not, as a rule, represent actual working drawings adapted to any particular set of conditions, but are shown in diagrammatic form for the purpose of serving as suggestions to engineers in search of ideas which they can adapt to meet the requirements of any particular scheme upon which they may be engaged. It will follow that the engineer must in all cases rely upon his own practical experience and judgment in deciding to adopt any of the various methods of design and construction illustrated and described in the following pages; and it may be found that a combination of several types, or even a combination of several details of different types, combined with practical experience and mature judgment, will frequently produce the most suitable and efficient scheme.