Activated carbon (AC), used for removal of organic micropollutants in European wastewater treatment plants (WWTPs), is usually produced from non-renewable resources that need to be transported over long distances. Utilising local residual biomass as a raw material may be advantageous in terms of sustainability. This study investigated the environmental and energy balances of using biowaste and biomass from landscape management for micropollutant removal at a commercial scale WWTP. Both residual biomasses were processed using the integrated generation of solid fuel and biogas from biomass (IFBB) technique to obtain a press cake that was used as feedstock for AC production. The results showed a lower global warming potential (GWP) and cumulative energy demand in comparison to a fossil-based conventional AC Differences in GWP between residual and fossil ACs were enhanced when the end-of-life incineration step was considered, and residual AC had a lower social risk associated with its production. Energy efficiency of AC production was substantially increased by utilising waste heat generated in the pyrolysis process of biochar production and by using electricity generated in a combined heat and power plant using biogas from the methanation of IFBB press fluids. Converting residual biomass into activated carbon using IFBB and a state-of-the-art pyrolysis and activation unit along with energy recovery would improve WWTP sustainability and self-sufficiency in terms of the raw materials required.

Biomass-based energy accounts for a notable share of renewable heat and electricity generation in Germany. Due to limited alternative uses, biomass obtained from management of semi-natural grasslands is a potential feedstock. Technical and environmental limitations exist in using this biomass for combustion, due to the presence of harmful elements. Converting biomass using integrated generation of solid fuel and biogas from biomass system (IFBB) produces a solid fuel with lower concentrations of harmful elements and a press liquid usable for biogas generation. In this study, solid fuel generation with a commercial scale IFBB unit was investigated. The concentration of harmful elements such as N, S, Cl, and K in the solid fuel was significantly reduced compared to the original biomass silage. Emissions during combustion of the solid fuel briquettes were below German legal thresholds. Elemental concentration of solid fuel obtained from commercial scale process had a significant improvement in removal rate of harmful elements than the prototype. Hence, the limitations of using semi-natural grassland biomass as an energy source were overcome. The commercial scale IFBB plant could be used in practice to handle large volumes of green residual biomass by converting it into a solid fuel with favorable fuel properties.

Life cycle assessment (LCA) of waste treatment processes is often associated with considerable uncertainties. The aim of this study is to estimate the total uncertainty in the modelled composting system and the influence of material and process parameters on the uncertainty. Four composting combinations with fresh (FC) and mature substrate compost (MSC) from partially enclosed (PEC) and open composting (OC) were investigated. Perturbation analysis was used to determine the effect of parameters on the result and Monte Carlo simulation was used to estimate the total uncertainty. This study showed that the production of MSC using PEC had the lowest overall impacts across all impact categories except ozone depletion. Results of the Monte Carlo simulation showed that comparing composting options was challenging. The sensitivity ratios obtained from the perturbation analysis showed that the process parameter percentage of carbon fraction degraded was the most influential for FC. In MSC, the moisture content in the input material and the substitution factor used for peat were the most influential. Monte Carlo simulations demonstrated the overall uncertainty of the model and its relevance when comparing results between combinations. The perturbation analysis identified the parameters that required more accurate data to reduce the uncertainty in the model. Graphical abstract

Interest in biochar as an additive to enhance anaerobic digestion (AD) has grown in the context of biomass cascading use and the 2050 net-zero goal. However, few studies have investigated the effects of biochar on AD from a biochar production perspective, including biomass feedstocks and pyrolysis temperatures. To valorise biomass and better understand the mechanisms and environmental implications of using biochar in AD, this study investigated the effects of distinct biochar types on AD under acid stress-induced process inhibition using batch tests. The results demonstrated that biochar can mitigate acid stress and enhance the methane production rate. The kinetic rate constant of methane production is positively related to the buffer capacity of the tested biochars (R ² = 0.88). The choice of feedstocks is a crucial factor (P = 0.003), particularly the best-performing biochars derived from raw grass silage. In contrast, the pyrolysis temperature effect was less significant (P = 0.18). Furthermore, the analysis of biochar indicates that the alkali (K) and alkaline earth (Ca, Mg) metals contained in biochar may be one of the important factors contributing to buffer capacity (R ² = 0.82 to 0.86). Hence, buffer capacity is a crucial quality criteria when evaluating biochar for AD applications. Raw grass silage biochars are promising for acid stress mitigation due to their high buffer capacity, while carbon-rich woody biochars have high CO₂ sequestration potential. A compromise between mitigating acid stress and sequestering carbon is the use of pre-treated grass biochar. Overall, the use of biochar-enriched digestate offers a potential way to close material loops and complete the biomass-to-biochar value chain.

Composting is a waste management practice that converts organic waste into a product that can be used safely and beneficially as a bio-fertiliser and soil amendment. Non-methane volatile organic compounds (NMVOCs) from composting are known to cause damage to human health and the environment. The impact of waste management on the environment and workers is recognised as a growing environmental and public health concern. Measurements of NMVOCs emitted during composting have been carried out only in a few studies. NMVOC emissions are typically reported as a group rather than as species or speciation profiles. Recognising the need to investigate the issues associated with NMVOCs, the objective of this study is to estimate variation in life cycle assessment (LCA) results when NMVOCs are considered individual emissions compared to grouped emissions and to compare midpoint and endpoint life cycle impact assessment (LCIA) methods. In general, the ReCiPe 2016 LCIA method estimated the highest impact from the composting process in comparison to IMPACT World+ and EF 3.0 for the impact categories of ozone formation, stratospheric ozone depletion, and particulate matter formation. For ReCiPe 2016 and IMPACT World+, the NMVOC emissions were not linked to human toxicity characterisation factors, meaning that the contribution from NMVOC towards human health risks in and around composting facilities could be underestimated. Using individual NMVOCs helps to additionally estimate the impacts of composting on freshwater ecotoxicity and human carcinogenic and non-carcinogenic toxicity potential. If ecotoxicity or toxicity issues are indicated, then LCA should be accompanied by suitable risk assessment measures for the respective life cycle stage.

Newly developed and innovative RUN technology aims to recover nutrients from urban wastewater (blackwater) and biowaste (kitchen waste). The development of RUN technology has been supported by the life cycle assessment (LCA) in order to identify hotspots and trade-offs. While the performance of the process at a laboratory scale did not show any environmental benefits from P recovery, the LCA results have helped to improve the environmental performance at the following scale-up step. The recovery of P on a technical scale was environmentally beneficial, especially in terms of the global warming potential (GWP). However, there were still some trade-offs, e.g., freshwater and marine eutrophication were slightly higher compared to conventional P fertilizer production. Given that P is considered a critical raw material and that climate change is probably the most pressing environmental issue, RUN technology has the potential to deliver on both domains.