New solutions for digestate solid/liquid separation to apply on small alpine farm biogas plants
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The research aimed at implementing biogas-refinery from livestock effluents, by defining innovative/adapted technologies and processes for Nitrogen (N) control, which could be easy to apply in the alpine context and directly manageable by farmers. Both pilot and lab-scale experiments were carried out, in order to identify the best condition for the studied process line. An innovative system was tested: Solid-Liquid (S/L) separation by means of drainage bags, after induced flocculation with specific polyelectrolytes. The choice of materials concerned geotextile tissues in polypropylene for dehydration/dewatering applications. The polyelectrolytes used for the tests are emulsifiers, cationic polyacrylamide (CPAM). The optimal concentration of additives and the identification of the correct diameter of the pores were determined through preliminary lab tests of filtration, followed by field tests, by means of hanging drainage bags. The process achieved S/L separation efficiency from 60 to 70% in 13 days, respectively for slurry and for digestate; 60% of TKN and 85-90% of TS concentrated in 30-35% of the initial material. Norg concentrated into the SF (97%), which can be transported and used outside the farm, while 60% of N-NH4 concentrates in the LF, which can be further treated (i.e. with stripping or biological processes) or/and can be used for irrigation.