Per-Anders Hansson’s research while affiliated with Swedish University of Agricultural Sciences and other places

CONTEXT: There is a growing interest in investments in technology that can help farms to become fossil-free, without compromising their economic incentives, and while significantly reducing greenhouse gas (GHG) emissions. Biogas is an interesting technology in this respect, however, the possible farm-level economic impacts from investing in a biogas-based system are not well understood, yet they are decisive to understand farmers’ incentives for adoption. OBJECTIVE: The objectives are to i) develop a scenario which allows the farms to become fossil-free in their input use, ii) assess the farm-level economic consequences of adoption and iii) quantify change in global warming potential in a 100-year period (GWP100) from the biogas-scenario. METHODS: We use a stochastic partial budgeting approach to simulate farm-level economic benefits and costs associated with changes and uncertainty related to economic effects. We also use life cycle assessment for the quantification of the climate effects, which enable us to examine the potential climate impact in reduction of fossil-based inputs in baseline scenario by transitioning to the biogas scenario. The study is based on simulation for a hypothetical dairy farm with 300 milking cow and a corresponding 325 ha of arable land that produces 75 % mixed grass and 25 % clover.

Agri-food systems constitute around one-third of global greenhouse gas (GHG) emissions, with roughly half consisting of non-CO 2 GHGs, mainly methane (CH 4 ) and nitrous oxide (N 2 O). Methods and technologies to mitigate non-CO 2 GHGs are currently limited, which is a reason for agriculture being categorised as a hard-to-abate sector. This study examines mitigation of GHG emissions from manure storage headspace through oxidisation of CH 4 emissions at low concentrations using a thermal catalytic process with and without subsequent CO 2 capture and storage (CCS). The technology is studied using a combination of process modelling and life cycle assessment at four CH 4 concentrations: 300, 1000, 3000 and 10000 ppmv. The primary energy demand and net climate effect were evaluated, reaching a net climate effect of + 0.10, -0.77, -0.91 and − 0.97 g CO 2 -eq emitted/g CO 2 mitigated, respectively. The wide range of results is mainly influenced by the process energy demand being strongly correlated to the CH 4 concentration. The sensitivity analysis shows that a net negative climate effect can also be achieved at 300 ppmv with access to low emission energy sources. Coupling CCS worsens the net climate effect of the system at all studied CH 4 concentrations, mainly due to the additional energy demand for CO 2 separation.

Climate change mitigation by increased paper recycling can alleviate the two-sided pressure on the Swedish forest sector: supplying growing demands for wood-based products and increasing the forest carbon sink. This study assesses two scenarios for making use of a reduced demand for primary pulp resulting from an increased paper recycling rate in Sweden, from the present 72% to 78%. A Conservation scenario uses the saved primary pulp to reduce pulplog harvests so as to increase the forest carbon sink concomitant with constant overall wood product supply. In contrast, a Substitution scenario uses the saved primary pulp to produce man-made cellulosic fibers (MMCF) from dissolving pulp replacing cotton fiber, implying increased overall wood product supply. Our results suggest that utilizing efficiency gains in paper recycling to reduce pulplog harvests is better from a climate change mitigation perspective than producing additional MMCF to substitute cotton fiber. This conclusion holds even when assuming the use of by-products from dissolving pulp making and an indirect increase in MMCF availability. Hence, unless joint improvements across the value chain materialize, the best climate change mitigation option from increased paper recycling in Sweden would seemingly be to reduce fellings rather than producing additional MMCF.

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. Supplementary Information The online version contains supplementary material available at 10.1186/s13068-023-02412-1.