Sludge Dewatering

X-RA and X-RAD are machines used for the thickening and dewatering of sludge. They represent a viable alternative to machines currently in use and have been designed to achieve high levels of thickening and dewatering, combined with a reduction in energy costs and maintenance. The machines both consist of a drum, with wedge wire spacing, inside which, by means of a geared motor with a low power and low RPM, rotates a screw with a variable pitch shaft. The two versions have the same dimensional footprint, what differs is mainly the screw pitch, the pneumatic counter pressure system (only present in Model X-RAD) and further technical measures needed for the different applications of the machine.

Both versions are equipped with a cleaning system necessary for the drum cleaning, which can be motorised or fixed. Additionally, it is possible to have the dehydrator/thickener, complete with all the ancillary equipment (X-POLI, X-AF, pumps, control panel, etc.), needed for correct operation installed on a stainless steel mobile skid.

In both models the incoming sludge should be first conditioned by a polyelectrolyte treatment to optimise the operation of the machines and obtain a proper flocculation of the sludge itself. X-RA and X-RAD can be provided with a static or dynamic flocculation system.

The flocculated sludge, once it enters the thickener or dehydrator is transported by a screw. The screw, depending on the type of machine, changes in pitch along its length, thus allowing the thickening or dewatering of the sludge.

During the rotation of the screw at low RPM, the separated water passes through the drum to then be channelled towards the discharge area of the eluate. After reaching the discharge zone, the sludge is conveyed towards the outlet, situated on the bottom of the machine which in the case of the X-RA model can be connected to a pump which transfers the product to a possible subsequent dewatering system, whilst in the X-RAD model, once passed the pneumatic counter pressure system, the sludge is discharged to a skip or similar; or drops into a suitable conveying system such as a screw or belt conveyor, or a cake pump.

To obtain the best performance in terms of sludge dewatering, the two machines can be installed one after the other: first the X-RA to give a thickened sludge of, depending on the model, from 4 to 8% of DS, followed by the X-RAD for dewatering, to a cake of up 25% DS.

A new concept for an electro-assisted dewatering machine. The X-ERAD is a development of a conventional X-RAD. The X-ERAD utilises a specific configuration of electrodes inside the body of the machine, these electrodes exert an electro-osmotic action that increases the dry solids content in the dewatered sludge produced by the machine, compared to a conventional X-RAD.

The mechanism acting inside the X-ERAD for sludge dewatering is a combination of; mechanical compression, that forces the sludge through the screw and to give a counter-pressure at the exit of the machine, and an electro-osmotic action, which works in a second stage and simultaneously with the mechanical part. The electro-osmotic factor of the X-ERAD system enables an extra amount of water to be removed from the sludge not normally possible with only a mechanical action. In this system, it is possible to produce a final sludge of approx. 25% DS.

The idea behind the X-ERAD is to give a solution able to satisfy the requirement to reach a high dry solid content, more than 20%, with a low increase in power consumption. Energy costs, relative to final increase in solid content for X-ERAD dewatering system, are less than conventional dewatering techniques operating under similar process conditions.

As in the conventional X-RAD version, the X-ERAD consists of a drum, with wedge wire spacing, inside which a screw with variable pitch turns at low RPM mounted on a shaft. The same counter-pressure and drum washing systems present in the X-RAD are installed in the X-ERAD.

The rotation of the screw allows sludge entering the machine to pass through the first section, where mechanical transport and compaction is responsible for drainage of most water, through the wedge wire. In the next section of the machine, the presence of special electrodes allows separation of an extra amount of water, before discharge of the finished material.

The electrodes, which start electro-osmotic separation, are powered by one or more electric generators. With the use of the control panel, it is possible to set several electric parameters (i.e. a maximum of three different sections inside machine); different working cycles of electric field and temperature control inside the machine drum; flexibility, in order, to optimise conditions for the sludge dewatering.

Modular systems for dewatering and thickening of sludge