Screen-washing creates savings

A combined inlet system is being used as part of the Tipperary Group DBO Project to boost efficiency and cut energy costs.

Earth Tech Ireland is using Eimco Water Technologies' J+A Combined Inlet System (CIS) for eight sites included in the Tipperary Group DBO Project. The Combined Inlet System is a complete packaged inlet works which includes fine screening, screenings washing and de-watering together with high-efficiency grit removal, all in a single compact unit.

The order was worth in the region of £750,000.
For this project the CIS units included the J+A Wash-Flow screen, based on the very successful Hi-Flow band screen, and includes the addition of integral screenings washing. With the Hi-Flow/Wash-Flow screen all the solids are retained inside the screen band, and there is no carry-over of solids which can be a problem with other screen designs.
Independent tests carried out by UKWIR confirmed the system's high efficiency - with 6mm apertures, the Hi-Flow screen achieved a screenings capture ratio of 81%. This is the highest screenings capture ratio to have been achieved by any 6mm aperture screen to date, improving the performance of the downstream process and giving additional savings in operating and maintenance costs throughout the life of the plant.

The Hi-flow screen is an 'in to out' flow band screen and the washing is carried out in the flow inside the screen band before the screenings are removed. The washing system is based on the J+A Washpactor, where the washing energy is provided by an impeller, which only runs when the screen is operating, reducing energy costs.
The high-energy turbulence provided by the impeller completely liquefies the faecal matter in the sewage. This material then passes through the screen perforations with the outlet flow from the screen. The washed rag, together with other non-biodegradable material, is then removed by the screen-lifting mechanism in the normal way.
For flows up to 250l/s the Wash-Flow screen can be supplied with an integral screw compactor for de-watering the washed screenings.

This option provides high-efficiency screening - 3mm or 6mm apertures - together with screenings washing and de-watering, all in a single compact machine.
When used in the CIS system the Wash-Flow screen is installed on the inlet to the grit settlement tank.

Following screening and screenings washing, the sewage flow then passes forward for grit removal. The grit removal process is based on the velocity and retention time in the tank.

Flow capacity
As the flow passes through the tank, grit particles greater than 0.2mm diameter fall to the bottom of the hopper. The collected grit particles are then removed from the tank by a grit pump, which transfers the material to a grit-classifier for de-watering.
The CIS can be designed to suit any application. Dependent on the flow capacity required, it can be supplied as a full- or part-steel fabrication.

The CIS provides a cost-effective alternative solution to a conventional sewage treatment inlet works, and with a much smaller footprint.

The inclusion of the Wash-Flow screen enhances the system and offers further cost benefits.
Effective screenings washing not only produces screenings that are clean, free of faecal solids and odour-free, but also further reduces the volume of material which has to be taken off-site for final disposal.

The combination of high-efficiency screening and screenings washing provided by the Wash-Flow screen will help the plant achieve the lowest possible whole life costs.

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