A combined anaerobic digestion system for energetic brewery spent grain application in co-digestion with a sewage sludge

Life-cycle assessment as a prospection stage for the biochemical methane potential of pretreated lignocellulosic biomass

The goal of neutrality in greenhouse gas emissions has intensified the search for renewable fuels. However, it is crucial to ensure sustainability of new technologies before proposing their implementation. This study proposes the use of life-cycle assessment (LCA) as an intermediary tool to identify critical hotspots in the exploration of hydrothermal pretreatment of lignocellulosic biomass, followed by biochemical methane potential assessment. Brewer s spent grain (BSG) was investigated, and laboratory-scale results were applied in an attributional assessment model with business-as-usual serving as the baseline. The LCA revealed that assumptions made in the lab could pose limitations. In Brazil, the two-stage co-digestion of pretreated hydrothermal BSG showed promising prospects, with a reduction to a new value of -54 kg CO2-eq Ton-1 BSG compared to 90 kg CO2-eq Ton-1 BSG in the business-as-usual scenario. Within the top ten global beer producing countries, only Brazil and Spain demonstrated potential for exploring this proposal.

Effects of various rotational speeds of hydrodynamic disintegrator on carbon, nutrient, and energy recovery from sewage sludge

Until recently, sewage sludge produced in wastewater treatment processes was considered problematic waste. It currently constitutes a valuable substrate for raw materials and energy recovery. One of the methods of intensifying resource recovery from sludge is its pretreatment by means of disintegration methods. This study presents the CFD modelling and experimentally investigates the use of a hydrodynamic cavitation rotor operated with various rotational speeds (1500, 2500, and 300 rpm) for the recovery of organic compounds, nutrients, and energy. Rheological properties of raw sludge, a non-Newtonian fluid, were determined and used in the modelling calculations. Cavitation zones were observed for 2500 rpm and 3000 rpm, although a stronger cavitation effect occurred for a rotational speed of 3000 rpm. A rotational speed of 1500 rpm was too low to generate a pressure drop below 1705 Pa, and no cavitation was recorded. An increase in rotational speed from 1500 rpm to 3000 rpm for each analysed energy density caused an increase in SCOD and nitrogen concentration. Moreover, it was determined that at low energy densities (<105 kJ/L), mechanical tearing was the dominant factor responsible for carbon recovery, and at its higher values (≥105 kJ/L), the cavitation phenomenon became increasingly important. Rotation speed also had a significant effect on methane yield (YCH4). An increase in YCH4 by 6.2% was recorded only for disintegrated sludge at a rotational speed of 1500 rpm in reference to untreated sludge. Disintegration conducted at higher rotational speeds led to a decrease in YCH4 (-0.7% for 2500 rpm and -7.9% for 3000 rpm).

Subcritical water pretreatment enhanced methane-rich biogas production from the anaerobic digestion of brewer's spent grains

ABSTRACTThis study evaluated the effectiveness of a semi-continuous flow-through subcritical water hydrolysis (SWH) pretreatment of brewer's spent grains (BSG) for subsequent application in the anaerobic digestion (AD) process. BSG pretreatment was conducted at 160 °C and 15 MPa with a flow rate of 10 mL water min-1 and 15 g water g-1 BSG. The results revealed that SWH attacked the hemicellulose structure, releasing arabinose (46.54 mg g-1) and xylose (39.90 mg g-1) sugars, and proteins (34.89 mg g-1). The start-up of anaerobic reactors using pretreated BSG (747.71 L CH4 kg-1 TVS) increased the methane yield compared with the reactor without pretreatment (53.21 L CH4 kg-1 TVS). For the process with pretreatment, the generation of electricity (134 kWh t-1 BSG) and heat (604 MJ t-1) are responsible for the mitigation of 43.90 kg CO2 eq t-1 BSG. The adoption of SWH as an eco-friendly pretreatment of biomass for AD could be a technological route to increase methane-rich biogas and bioenergy production, supporting the circular economy transition by reducing the carbon footprint of the beer industry.

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

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.