The effect of pH, temperature, and inoculum on the fermentation of pulp and paper biosludge: increasing the nutrient availability for rearing of black soldier fly larvae

Pulp and paper production is one of the largest global industries producing annually 400 million metric tons of pulp and paper products and 6 million tons of pulp and paper biosludge (PPBS). From a resource efficiency and sustainability perspective, there is a need for improving PPBS management. This study assessed fermentation of PPBS as pretreatment to improve PPBS feasibility as feed for black soldier fly larvae. The impact of temperature, pH, and inoculum on the concentration of soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFA) was assessed. An initial pH of 10 and the addition of inoculum from an anaerobic digester substantially increased the concentration of sCOD. The obtained concentration of VFA was low compared to the VFA concentration needed to improve the growth of Black Soldier Fly Larvae (BSFL). The PPBS is recalcitrant to fermentation because of the high content of lignocellulose. Fermentation as done in this study does not convert PPBS to a feasible feed for black soldier fly larvae; thus, further research on improved fermentation is needed. However, fermentation at alkaline pH and addition of inoculum do increase the final pH of PPBS which improves its feasibility as feed for BSFL. Future studies should explore pH > 10 and temperatures > 55 °C to increase sCOD and improving generation of VFA by removal of inhibiting substances, testing other types of inoculum (rumen microorganisms) and co-fermentation.