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Removal of plastics from digested food waste using Huber Technology Strainpress units

In order to meet the quality protocol PAS 110 for use of digestate as a fertiliser, Andigestion needed to remove additional plastic particles from the digestate. After bench and full scale trials Huber Technology installed a permanent Strainpress between the digester and storage tank.

Figure 1. Strainpress on Gantry

Installing the Strainpress on a gantry allows for gravity discharge of the cake straight into a skip under the platform. The gantry comes fully wired, complete with access stairs and room for maintenance on the platform.

The Strainpress is totally enclosed and uses the head available between the Digester which is constant and the storage tank which is variable therefore no pumping is involved. This has the disadvantage that the flow rate varies between 15 and 32m³/hour based on the level in the storage tank and flow control may be installed to regulate the flow to approximately 20m³/hour which is the flow HUBER Technology recommend for 5mm mesh on this application.

Cleaning of the Strainpress is by mechanical means and no additional water or flocculants are required.

The Strainpress is fitted with a 5mm perforated mesh basket as standard and future trial work will study the operation of the unit with a 3mm perforated mesh basket. This 3mm perforated mesh basket will reduce flow and increase pressure across the mesh.

The screenings from the 5mm perforated mesh basket showed a good capture ratio at approximately 50% dry solids. The amount of shredded plastic removed can clearly be seen in Figure 2.

Figure 2. Pressed screenings from the Strainpress

HUBER Technology and Andigestion believe that the 5mm perforated mesh basket will be sufficient. However trial work will be undertaken to observe if there are any benefits to the screenings.

Figure 3. Combined Pneumatic and Electrical Control Panel

The Strainpress has proven to be very popular with the Water Authorities.Therefore Huber have optimised their control system for the Strainpress unit. The new combined panel supplied as standard in stainless steel, has a clear layout and indication as can be seen in Figure 3. The left side of the panel contains the compressor and air regulation equipment to control the discharge cone pressure. The right hand side contains the electrical controls.

Figure 4. Site Installation

The gantry and Strainpress is assembled in the factory and the legs and bracing fitted on site onto a concrete slab on 7 mounting points. The 2 pipe connections and power supply only is required on site for the installation.

Andigestion have been successful in being the first company in the UK to achieve PAS110 standard. HUBER Technology are pleased to have assisted in helping Andigestion in achieving this standard and look forward to a long successful working relationship.

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