Characteristics and Anaerobic Co-Digestion of Press Water from Wood Fuel Preparation and Digested Sewage Sludge

Abstract

Technical drying of harvested wood fuels is heat and energy consuming, while natural pre-drying in the forest, e.g., in stacks or storage piles, is accompanied by energy losses through natural degradation processes. Dewatering of energy wood by mechanical pressing is an innovative method to reduce the moisture content prior to thermal drying while producing press waters (PW, also referred to as wood juice) as a by-product. To date, the characteristics and utilization potentials of PW are largely unknown. In this study, three different spruce- and poplar-based PW were analyzed for their characteristics such as dry matter (DM), organic dry matter (oDM) concentration, pH-value, element concentration or chemical compounds. Additionally, they were used for anaerobic digestion (AD) experiments with digested sewage sludge (DSS) serving as inoculum. The fresh matter-based DM concentrations of the PW were between 0.4 and 3.2%, while oDM concentrations were between 87 and 89%DM. The spruce-based PW were characterized by lower pH-values of approx. 4.4, while the poplar-based PW was measured at pH 8. In the AD experiments, DSS alone (blank variant) achieved a specific methane yield of 95 ± 26 mL/goDM, while the mixture of spruce-based PW and DSS achieved up to 160 ± 12 mL/goDM, respectively. With further research, PW from wood fuel preparation offer the potential to be a suitable co-substrate or supplement for AD processes.

Hydrothermal Treatment of Residual Forest Wood (Softwood) and Digestate from Anaerobic Digestion—Influence of Temperature and Holding Time on the Characteristics of the Solid and Liquid Products

“…The results of all analyses were evaluated based on mean values ± standard deviations. A similar procedure was executed in other studies [48,49].…”

Optimizing Anaerobic Digestion at Ambient Temperatures: Energy Efficiency and Cost Reduction Potential in Panama

“…The anaerobic biomass present in the digested sludge makes it suitable for use as inoculum [25]. There are several studies where it has been used as an inoculum in the co-digestion of substrates such as grease traps [26], wood chips [27], and organic waste [28].…”