(1549)

Fig. 17. Revolving Hori

zontal Arm to Scott-Moncrieff's Effluent Distributor

perforated pipes, which rest on a concrete floor, and are kept in position by a wall of pigeon-hole brickwork constructed in the form of an octagon. This is carried up to a height of some 7 or 8 feet above the concrete floor, the material from that point to the surface of the bed being given a slight batter towards the centre.

The distribution of the septicised open tank liquor is effected by three kinds of distributors; the finished effluent from each kind being about the same in character. All the effluents are well nitrated, are of a brownish tint, contain an unusually large quantity of flocculent solids in suspension, and need to have them removed before being discharged into any watercourse. A satisfactory feature, however, is the fact that finished effluents may be exposed to the air for as long a period as five days without undergoing any appreciable change.

by means of wheels fixed on, or connected to its axle. The sewage is fed with the tank effluent by a supply pipe, and from this the sewage falls into the buckets of the wheel, and then spreads itself along the bucket, and by its weight causing rotation of the wheel-drum. The sewage is sprinkled from the buckets while the Distributor is revolving. A " head," or fall of some 15 inches, is sufficient to actuate the apparatus.

Fig. 19 illustrates a Triple-Drum Rotary Distributor for circular filters, as in use at Leslie.

Travelling Distributors.

This class of distributor, or sprinkler, is not so frequently used as those of the revolving type.

Fig. 20 illustrates Single-drum Travelling and Reciprocating Distributors on the Fiddian principle (see Fig. 19), at

the installation of the Heaton Norris Urban District Council, employed on rectangular filters each 92 feet long, 14 feet wide, and 3 feet deep, distributing at an average rate of 500 gallons per square yard per day strong chemically precipitated sewage, the effluent passing direct to the river Mersey. The

effluent from the tank is drawn from the trough (shown in illustration) by means of the syphon, and flows along the feed tube and thence into the buckets. The apparatus is arranged to ensure a reversal when the distributor reaches the end of the filter, and the return is forthwith commenced. A working 66 head of some 27 inches actuates this Distributor.

Some Facts as to Cost of Maintaining Distributors.

The problem as to what expense is justified, especially in large schemes, in maintaining highly efficient distributors, as against less efficient ones involving less expenditure in first cost and perhaps in maintenance, is important, and has recently been discussed by the Institution of Civil Engineers in connection with Mr. Watson's paper on the Birmingham Outfall Works. There filters 6 feet deep and fixed spray jets give a purification of from 33 per cent. to 64 per cent., treating 85 gallons per cubic yard per 24 hours. The total cost of the distributing apparatus, however, was only 6 per cent. of the total cost of the filters, and the tests for uniform distribution gave very poor results. The filtering medium is often very costly, but the work it is capable of doing depends largely upon the distributor, and this should be capable of sprinkling any varying quantity from a rate of about 100 gallons per square yard per day to 500, with a variation from the mean not exceeding 25 per cent., the unit area measurement being 25 square yards (18 inches by 18 inches). Mr. Watson made some valuable experiments through a raised filter, showing that as the liquid was sprinkled on the surface so it passed through and emerged from the bottom, thus disposing of the popular error that the liquid tends to spread itse'f out as it passes down.

of

CHAPTER XXV.

Growths on Contact Beds and Filters.

These growths appear to be of various kinds, and are but little understood. At many works they are the cause of putrefaction, even if they do not prevent the proper conduct of the method of treatment. These growths vary in appearance and in the length of time they take to grow. Variations in colour are also features of these growths. It does not seem that the method employed in the settlement of the solids has anything to do with it.

According to present knowledge, it would appear that from tank effluent, passed over filters, growths take place with most kinds of sewage; whether the crude sewage has been precipitated by chemical or by septic action, and where the filtering medium is clinker. With precipitated effluent, at Dorking, for instance, a pinkish-yellow, filamentous growth appeared a fortnight after the filters were brought into use.

This lasted six months, and then died, having caused the effluent to be bad during that period. On the other hand, at the same installation, with the same kind of sewage, where septic effluent was dealt with, the growth, which lasted for a similar period, did not become so strong nor cause interruption in the process. The growth is described as a greybrown amorphous one.

At Kingston-on-Thames, the grey growth is an annual one, from November to March. The effluent becomes bad during wintry weather because the growth forms an almost impervious mat on the surface of the filtering material.

With regard to the use of media which cause least trouble from growths, it makes but little difference whether the medium is clinker, broken brick, granite, saggars (vitrified stoneware), or sand.

In some cases with sand, as at Chorley, the filters being washed every week, after eight years' use there was still an absence of growth. At Horfield, with coarse clinker, and at York, with broken brick, coke, and slag, the result was similar after four years. On the other hand, at Accrington, clinker beds showed slight signs of growths, but only on their