Biogas plant management decision support – a temperature and time-dependent dynamic methane emission model for digestate storages

The aim was to develop a temperature and time-dependent model that can calculate the methane production in an anaerobic digester and its subsequent digestate storage tank under realistic and variable conditions. With a daily resolution, the model was applied to a Swedish dairy farm under two different climatic conditions. The most influential parameters were hydraulic retention time and the substrate specific first order reaction rates in the digester, which have a big influence on the residual biogas potential, and hence the potential methane production in the digestate storage. The management of the storage can have a large impact on the emissions from the storage due to its temperature dependence. The model can be used to support plant design and operation of anaerobic digesters and storages, but further research is needed to determine first-order reaction rates and the relationship between the ambient and digestate temperatures at different times of the year

Waste Heat Driven Integrated Membrane Distillation for Concentrating Nutrients and Process Water Recovery at a Thermophilic Biogas Plant

To efficiently utilize low-concentrate digestate nutrients, further treatment is needed to decrease their volume, recover process water, and increase nutrient concentrations. Membrane distillation (MD) is a thermally driven process that is advantageous due to its ability to harness low-grade waste heat to treat highly complex wastewater streams. This study assessed the techno-economic performance of integrating MD for two-fold concentrations of nutrients and the recovery of process water from digestate at a thermophilic biogas plant. Thermal assessment showed that the recovered waste heat from flue gas and digestate fully met the thermal energy demand of MD and saved 20% of boiler energy by heating incoming slurry. The permeate flux from MD was 3.5 L/(m(2)h) and 3.1 L/(m(2)h) at 66 degrees C and 61 degrees C digestate inlet temperatures during winter and summer, respectively. With internal heat recovery, the specific heat demand for MD was 80 kWh/m(3) and 100 kWh/m(3) in winter and summer, respectively. The unit cost of MD permeate was estimated to be 3.6 euro/m(3) and 4.1 euro/m(3) at a digestate feed temperature of 66 degrees C and 61 degrees C (with heat recovery), and 7.6 euro/m(3) and 9.1 euro/m(3) (without heat recovery) in winter and summer, respectively. However, cost sensitivity analyses showed that waste heat recovery and thermal energy cost variations had a significant impact on the MD permeate production cost. Nevertheless, the economic assessment indicated that the thermal integration of a biogas plant with industrial-scale MD digestate treatment capacity could be economically feasible, with winter being more economically favorable due to higher waste heat recovery

Microbial community development during syngas methanation in a trickle bed reactor with various nutrient sources

Microbial community development within an anaerobic trickle bed reactor (TBR) during methanation of syngas (56% H-2, 30% CO, 14% CO2) was investigated using three different nutrient media: defined nutrient medium (241 days), diluted digestate from a thermophilic co-digestion plant operating with food waste (200 days) and reject water from dewatered digested sewage sludge at a wastewater treatment plant (220 days). Different TBR operating periods showed slightly different performance that was not clearly linked to the nutrient medium, as all proved suitable for the methanation process. During operation, maximum syngas load was 5.33 L per L packed bed volume (pbv) & day and methane (CH4) production was 1.26 L CH4/L-pbv/d. Microbial community analysis with Illumina Miseq targeting 16S rDNA revealed high relative abundance (20-40%) of several potential syngas and acetate consumers within the genera Sporomusa, Spirochaetaceae, Rikenellaceae and Acetobacterium during the process. These were the dominant taxa except in a period with high flow rate of digestate from the food waste plant. The dominant methanogen in all periods was a member of the genus Methanobacterium, while Methanosarcina was also observed in the carrier community. As in reactor effluent, the dominant bacterial genus in the carrier was Sporomusa. These results show that syngas methanation in TBR can proceed well with different nutrient sources, including undefined medium of different origins. Moreover, the dominant syngas community remained the same over time even when non-sterilised digestates were used as nutrient medium

Future climate impacts of sodium-ion batteries

Sodium-ion batteries (SIBs) have emerged as an alternative to lithium-ion batteries (LIBs) due to their promising performance in terms of battery cycle lifetime, safety, operating in wider temperature range, as well as the abundant and low-cost of sodium resources. This study evaluated the climate impacts of three SIBs, and compared to two LIBs under four scenarios with considering potential changes in battery performance and background productions between 2020 and 2050. To ensure a fair comparison, all batteries were modeled in the 21,700 form, and a battery dimensioning model was developed to calculate the required amount of components for each battery. We found that equal to lower GHG emissions result from the use of SIBs compared to LIBs under optimal performance scenarios. From 2020 to 2050, the climate impacts of SIBs decreased by 43-57 %. The relative contribution of the battery manufacturing process decreases from 18-32 % to 2-4 % due to the increasingly share of clean energy in the electricity grid, while the relative contribution of key battery component materials increases over time, especially for cathode active materials. These results emphasize the significance of decarbonizing the electric grid, and suggest that future investment in SIBs is promising from an environmental point of view

Life cycle assessment of an all-organic battery: Hotspots and opportunities for improvement

Organic batteries are emerging as a potential sustainable power source for future flexible devices. Using life cycle assessment, this study analyzed the environmental impacts from the synthesis process for an all-organic battery with conducting redox polymers as active materials for electrodes. Synthesis steps were modeled and analyzed in detail, based on actual laboratory processes data for electrodes, and industrial data for other battery components. Complete and transparent inventory data are presented and can be used in future environmental assessments. The organic battery studied is still at an early development stage, so environmental hotspots and potential improvements in the synthesis processes were examined. For selected environmental impact categories, the life cycle assessment results showed that synthesis of cathode backbone was the major contributor (47-63%) to the environmental impacts of the all-organic battery cell among different synthesis stages, because of a long synthesis route associated with high solvent usage. Solvents (e.g., dichloromethane), catalysts (e.g., copper oxide, Pd (PPh3)4), zinc, and waste treatment processes were important single contributors to the total impacts. The results reveal significant potential for improvement by optimizing the amount of solvents needed to synthesize battery electrodes. Changing treatment methods for laboratory waste solvents can also strongly influence the results

Climate impact and energy efficiency from electricity generation through anaerobic digestion or direct combustion of short rotation coppice willow

Short rotation coppice willow is an energy crop used in Sweden to produce electricity and heat in combined heat and power plants. Recent laboratory-scale experiments have shown that SRC willow can also be used for biogas production in anaerobic digestion processes. Here, life cycle assessment is used to compare the climate impact and energy efficiency of electricity and heat generated by these measures. All energy inputs and greenhouse gas emissions, including soil organic carbon fluxes were included in the life cycle assessment. The climate impact was determined using time-dependent life cycle assessment methodology. Both systems showed a positive net energy balance, but the direct combustion system delivered ninefold more energy than the biogas system. Both systems had a cooling effect on the global mean surface temperature change. The cooling impact per hectare from the biogas system was ninefold higher due to the carbon returned to soil with the digestate. Compensating the lower energy production of the biogas system with external energy sources had a large impact on the result, effectively determining whether the biogas scenario had a net warming or cooling contribution to the global mean temperature change per kWh of electricity. In all cases, the contribution to global warming was lowered by the inclusion of willow in the energy system. The use of time-dependent climate impact methodology shows that extended use of short rotation coppice willow can contribute to counteract global warming

Optimizing power-to-H2 participation in the Nord Pool electricity market: effects of different bidding strategies on plant operation

The operation of power-to-X systems requires measures to control the cost and sustainability of electricity purchased from spot markets. This study investigated different bidding strategies for the dayahead market with a special focus on Sweden. A price independent order (PIO) strategy was developed assisted by forecasting electricity prices with an artificial neural network. For comparison, a price dependent order (PDO) with fixed bid price was used. The bidding strategies were used to simulate H2 production with both alkaline and proton exchange membrane electrolysers in different years and technological scenarios. Results showed that using PIO to control H2 production helped to avoid the purchase of expensive and carbon intense electricity during peak loads, but it also reduced the total number of operating hours compared to PDO. For this reason, under optimal conditions for both bidding strategies, PDO resulted in an average of 10.9% lower levelised cost of H2, and more attractive cash flows and net present values than PIO. Nevertheless, PIO showed to be a useful strategy to control costs in years with unexpected hourly price behaviour such as 2018. Furthermore, PIO could be successfully demonstrated in a practical case study to fulfil the on-demand requirement of an industrial captive customer

Energy performance of compressed biomethane gas production from co-digestion of Salix and dairy manure: factoring differences between Salix varieties

Biogas from anaerobic digestion is a versatile energy carrier that can be upgraded to compressed biomethane gas (CBG) as a renewable and sustainable alternative to natural gas. Organic residues and energy crops are predicted to be major sources of bioenergy production in the future. Pre-treatment can reduce the recalcitrance of lignocellulosic energy crops such as Salix to anaerobic digestion, making it a potential biogas feedstock. This lignocellulosic material can be co-digested with animal manure, which has the complementary effect of increasing volumetric biogas yield. Salix varieties exhibit variations in yield, composition and biomethane potential values, which can have a significant effect on the overall biogas production system. This study assessed the impact of Salix varietal differences on the overall mass and energy balance of a co-digestion system using steam pre-treated Salix biomass and dairy manure (DaM) to produce CBG as the final product. Six commercial Salix varieties cultivated under unfertilised and fertilised conditions were compared. Energy and mass flows along this total process chain, comprising Salix cultivation, steam pre-treatment, biogas production and biogas upgrading to CBG, were evaluated. Two scenarios were considered: a base scenario without heat recovery and a scenario with heat recovery. The results showed that Salix variety had a significant effect on energy output-input ratio (R), with R values in the base scenario of 1.57-1.88 and in the heat recovery scenario of 2.36-2.94. In both scenarios, unfertilised var. Tordis was the best energy performer, while the fertilised var. Jorr was the worst. Based on this energy performance, Salix could be a feasible feedstock for co-digestion with DaM, although its R value was at the lower end of the range reported previously for energy crops

Prospective life cycle assessment of a flexible all-organic battery

Strong interest from researchers and industry is accelerating development of flexible energy storage technologies for future flexible devices. It is critical to consider the environmental perspective in early development of new emerging technologies. In this study, cradle-to-factory gate prospective life cycle assessment (LCA) was performed on production of an all-organic battery with conductive redox polymers as electrode material. To gain a better understanding of the environmental performance of the all-organic battery, a flexible lithium-ion (Li-ion) battery with lithium titanate oxide and lithium cobalt oxide as electrode active materials was modeled as reference. Main environmental impacts of the all-organic battery were attributable to anode and cathode production, with electrode backbones being the main contributors. Solvents, catalysts, waste treatment, energy, and bromine were key individual contributors. Comparison with the flexible Li-ion battery indicated inferior environmental performance of the all-organic battery due to its relatively low specific energy (Wh/kg) and large amount of materials needed for production of its electrode backbones. Sensitivity analysis showed that changing scaling-up parameters and the production route of 3,4-ethylenedioxythiophene (a precursor of electrode backbones) strongly influenced the results. In order to lower the environmental impacts of the all-organic battery, future research should focus on designing a short production chain with lower material inputs of electrode backbones, increasing battery cycle life, and improving the specific energy of the battery. In addition, relevant recommendations were provided for prospective LCAs of upscaled systems