In order to meet the Quality protocol PAS 110 for use of digestate as a fertiliser the plastics content must be reduced. How the plastics are removed will depend on the upstream process however Huber Technology have successfully trialled and installed their Strainpress for plastics removal at a number of sites.
At Andigestion in Devon, Huber initially supplied a Strainpress with a 5mm screen immediately after the digester and this met the original PAS 110 however more plastics were required to be removed by the local farmers and a second Strainpress with a 3mm mesh has now been installed after the first storage tank.
The Strainpress® is totally enclosed and the liquid phase is under pressure allowing the first unit to be installed between the digester and the first digestate storage tank. In this instance we used the constant head in the digester to pressurise the Strainpress.
The second unit was installed between the first digestate storage tank and the second and was pump fed.
The oversize plastics falls out of the Strainpress into a skip mounted below the Strainpress.
Cleaning of the Strainpress is by mechanical means and no additional water, chemicals or flocculants are required.
The resultant screenings from the 5mm mesh showed a good capture ratio, with the screenings at about 50% dry solids.
With over 316 Strainpress’s installed in the UK alone, many for the same client, this is a well proven and reliable piece of equipment.