The removal of the dried sludge is provided for by dividing the sludge beds into rows of three terraces each, there being three such rows. At the foot of the lower terrace of each group will be an industrial track of narrow gauge for operating hopper cars. A wooden chute at the end of each second bed will discharge the sludge to the cars on the industrial tracks. These tracks are connected to an incline operated by a small motor with cables for hauling the cars to the top of the bank, where the sludge will be transferred into cars on a spur track of the Gorge Route Railroadthe spur track it is proposed to use in conjunction with the city transit lines in conveying chemicals to the treatment site and for removing the dried sludge to some point of disposal.

Consideration was given to the proposition of pumping the wet sludge by compressed air to drying beds more suitably located from a construction standpoint. The only available sites were found to be distant 2 to 3 miles from the treatment works. The long pipe line necessary to convey the sludge to the beds, with the attending line losses for pumping to considerable distances, caused the abandonment of this scheme.

NORTH END PLANT.

The general works as planned are similar to those for the South End plant, with individual characteristics as noted.

The grit chamber consists of three channels provided with inclined screens of the bar type, similar to those designed for the Brighton plant at Rochester, N. Y. The screens will be cleaned by means of hand rakes. The detritus may be removed by flushing through valve-controlled cast-iron pipes below the floor and discharging on the slope below.

The sedimentation plant, consisting of one tank, corresponds in type to that for the main plant, but will be 84 feet long, with two flow-through chambers 8.5 feet wide, having a flow capacity of 1.7 cubic feet per second, which is 120 per cent of the average rate expected in 1930.

For conveying materials to the plant an elevator is provided on the face of the cliff. A small travel hoist, operating on a structural frame, will deliver chemicals from the elevator shaft to the disinfecting plant, while the dried sludge will be conveyed in cars on an inclined railway as at the major works.

The operation of this plant will require labor on the average of a few hours daily, and it is supposed that this will be supplied from the main plant.

SEDIMENTATION PLANT COSTS.

Estimates of cost of construction and operating have been prepared for both plants. The former are

Water supply. Inclined railway. Spur track.. Walks and steps.. Venturi meter.. Land..

Total

0.000

2,20 25,000

237.100

FINE SCREENING.

The studies relating to fine screens have been confined to those of the Riensch-Wurl disk type, though without intention of excluding others from consideration. The sizes have been selected upon the Sanitary Corporation ratings in such proportion that with all units in operation the maximum diversion planned will be accepted with an overload on the screens of about 70 per cent. During periods of average dryweather flow, with one screen out of commission, the balance of the plant will be overloaded to the extent of 10 per cent. Provision is also made in the screen house for one extra screen.

The long lines of rough-tunnel sewers and the frequent drops in the lines of the surface sewers at Niagara Falls causes the suspended solids to be considerably comminuted. Because of the resulting attrited condition of the raw sewage as it will reach the treatment plant, it is believed that a much smaller percentage of the suspended solids will be retained on the screens than is usual in other localities. Ratings have therefore been based on-inch slots in the screen plates.

As in the case of sedimentation, the screen effluent will be treated with commercial bleach as a disinfectant, although the dose required will be somewhat larger than in the case of the tank effluent. It has been assumed that seven parts of available chlorine per million parts of sewage will suffice. To provide for the time needed for the action of the disinfectant, tanks or channels must be installed to allow of a 30-minute detention before discharging into the river waters, this period being based upon flows equivalent to 120 per cent of the average, which gives capacity sufficient to retain 1950 maximum flows for about 18 minutes. To further compensate for the attenuated character of the sewage and attending inefficiency of the fine screens, it is proposed to secure contact with the chemical in tanks of the two-story type, thus providing for additional reduction of the suspended solids.

An outline of the general plan for fine-screen treatment is shown on plate 57, together with a cross section detail of the detention tank. The plant consists of a combination grit and coarse screen chamber; fine screen house, disinfection plant, detention tanks, and sludge beds. No change has been made in the plans for treatment at the subsidiary plant.

GRIT AND COARSE SCREEN CHAMBER.

This chamber consists of three channels providing a reduction in velocity for the settlement of heavy inorganic matter. At the outlet end of the channels on a raised portion of the floor are set the coarse

screen racks. The grit may be flushed through gatecontrolled pipes discharging onto the slope below.

FINE SCREENS.

The screen house contains four 14-inch screens of the Riensch-Wurl revolving disk type, mounted in pits with structural frames, platforms, and operating equipment. An extra pit is provided for one future unit. The sewage enters and discharges from the screen pits through channels, the openings being controlled by gate valves. The retained solids are swept from the screen plates by brushes carried on a revolving spider frame, and are removed into containers which are taken from the house at intervals by means of a trolley hoist. It is proposed to burn the screenings in an incinerator.

DISINFECTION PLANT.

The disinfection plant will be similar to that described under tank treatment, though additional storage capacity will be required in the fine screen installation.

DETENTION TANKS.

A cross-section detail of the tank proposed for detention is shown on plate 57. This tank is to be 50 feet long with two sludge compartments. The detention period is to be 30 minutes, based on 120 per cent of the average flow as of 1930. Each tank has a capacity in the flow chambers of 14,000 cubic feet, equivalent to 7.8 cubic feet per second, thus rendering a total of six tanks necessary. The method of distribution to these tanks will be similar to that described under sedimentation. It is not possible to determine the percentage of reduction of suspended solids accomplished by fine screens combined with 30minute sedimentation, except by experiment. It is thought, however, that this will be somewhat less than that obtainable by 2-hour sedimentation, and is offered as the minimum needed to accomplish the disinfection required, and at the same time secure a removal of organic matter comparable with that suggested for other riparian towns.

SLUDGE BEDS.

The sludge beds have been laid out on a basis of six persons per square foot, this amounting to onehalf that required for Imhoff tank treatment. It is probable that this allowance is more than ample, but any reduction is not considered wise in view of the lack of data on the subject. Removal of the dried sludge is provided for in like manner to that described under the sedimentation process.

POWER DEVELOPMENT FROM SEWAGE
EFFLUENT.

The subject of sewage treatment can not be left without pointing out the possibilites of utilizing the effluent for the purpose of power development.

There is at present an average rate of sewage flow of 20 cubic feet per second available for this purpose. On the ground plan (plate 57) of the fine screen treatment project a small power house unit has been shown, though not included in the estimate, whereby a head of 110 feet can be obtained. Operating under a head of 110 feet, with a supply of 20 cubic feet per second, four units of Pelton impulse wheels would develop approximately 200 horsepower and would cost in the vicinity of $12,000 for complete installation, including supply line, Pelton wheels, automatic governors, and generators.

The operation of the disposal plant would require as a maximum but 20 horsepower, leaving the balance available for other purposes.

REFUSE DISPOSAL.

At the present time the mixed refuse of Niagara Falls is carted to a shaft over the Bath Avenue sewer and there flushed to the river at a point below Suspension Bridge.

The refuse thus disposed of consists of garbage, rubbish, and street sweepings. Some ashes are found in the mixed refuse, but the larger portion of ashes is disposed of separately. Brush, weeds, lawn rak ings, etc., are dumped on a vacant lot near the plant and burned. All other forms of refuse are dumped indiscriminately into the river with the possible exception of bed springs and the like, too large to pass through the shaft.

Irrespective of the applicability of existing United States Federal Statutes,1 there is no question but what other means of disposal of the city's refuse should be found and the present practice abolished. To this end, and in extension of the study of remedies for river pollution, there have been made rough estimates of the cost of an incinerator as the most satisfactory method of disposal and as further offering a means for the destruction of refuse from the sewage treatment works.

No

Records are kept of the number of loads delivered, the time of arrival, and the name of the driver. record has been kept of volume or of weight of the refuse, but from personal observation combined with the data available, it is estimated that the average daily collections is about 75 to 80 cubic yards. This estimate does not include the ashes, which are disposed of separately.

An approximate classification of mixed refuse has been made from weighted averages of the per capita

1 Revised Statutes of United States, Fifty-fifth Congress, third session, volume 2, chapter 425, section 13.