Brown juice assisted ensiling of straw and press cake for enhanced biogas production and nutrient availability in digestates

Abstract

The study investigated the effects of ensiling and brown juice-assisted ensiling of wheat straw and press cake from a green biorefinery plant prior to anaerobic co-digestion (Aco-D) with cattle manure on methane yield and nutrient availability in the digestates. Straw was ensiled with and without brown juice at field-scale and lab-scale levels, followed by Aco-D with manure using continuous stirred-tank reactors (CSTR) and batch tests. The digestates from CSTR were incorporated into the soil to study nitrogen and sulphur dynamics and availability over 80 days. Results show that ensiling of straw increased net inorganic nitrogen release in soil and reduced net inorganic sulphur immobilisation compared to the non-ensiled straw. Brown juice-assisted ensiling of straw at the lab-scale level significantly increased methane production by 14 % and increased hydrolysis and methane production rates compared to non-ensiled straw. These results demonstrate that ensiling of straw has the potential as a pre-treatment technique for enhanced biogas production and higher nutrient availability in digestates for crop production and provides an opportunity to valorise brown juice as an ensiling additive.