Metal Concentrations in Soil Paste Extracts as Affected by Extraction Ratio

Saturated paste extracts are sometimes used to estimate metal levels in the soil solution. To assess the significance of heavy-metal concentrations measured in saturation extracts, soil paste extracts were prepared with distilled water in amounts ranging from 60–200% of the moisture content at saturation. Trace metals behaved as if a small pool consistently was dissolved independent of the extraction ratio applied. Metal concentrations in the solution hence were not buffered by the solid phase, but the observed behaviour would allow the estimation of metal concentrations in the soil solution as a function of moisture content. The behaviour of iron and manganese suggested that some microbial reduction occurred. The intensity increased with increasing extraction ratio but not to the extent of affecting dissolution of trace elements

Speciation of P in solid organic fertilisers from digestate and biowaste

Phosphorus (P) is a finite resource and its reuse in organic fertilisers made from biowaste and manure should therefore be encouraged. The composition of solid organic fertilisers (SOFs) depends on the type of feedstock and processing conditions, and this may affect P speciation and hence P availability. Phosphorus speciation was assessed in eighteen different SOFs produced from biowaste and digestate. Available P was determined in 10 mM CaCl2 extracts at a fixed pH of 5.5 and at a fixed total P concentration in the suspension. P was dominantly present as inorganic P (>80% of total P). There was a strong variation in the Fe content of the SOFs and hence in the fraction of P bound to reactive Fe/Al-oxides (PFe). The fraction of total P soluble at pH 5.5 correlated negatively with PFe pointing to fixation of P by metal salts added during processing, or by soil mineral particles in case garden waste was processed. Therefore, the use of iron salts in processing plants should be avoided. In addition, the presence of P in poorly soluble precipitates lowered the fraction of easily available P. Overall, this study shows that Pt alone is not a good indicator for the agronomic efficiency of SOFs due to large differences in P speciation among SOFs

Greenhouse gas emissions from a sandy loam soil amended with digestate-derived biobased fertilisers – A microcosm study

Nutrient recovery from anaerobic digestion systems provides several side streams that are useful as biobased fertilisers (BBFs). A microcosm approach was employed to assess the short-term greenhouse gas emissions from a sandy-loam soil enriched with 18 BBFs in comparison with mineral fertilisers (urea and calcium ammonium nitrate). In total, 20 different fertilisers were homogeneously incorporated into an arable sandy loam soil at a rate of 170 kg nitrogen (N) ha−1 and incubated at 80 % water-filled pore space. Over 18 days, the fluxes of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) released in the headspace of the microcosms were measured using a Gasera One Multi-gas analyser. Cumulative N2O emissions from the BBF treatments were either comparable or lower (0.04–0.09 %N applied) than the mineral fertilisers (0.10–0.14 %N applied). Nitrification of the initial ammonium-N present in the BBFs was likely the dominant biological process driving N2O production. The application of digestate and evaporator concentrates led to an increase in CO2 emissions (8–51 % of applied carbon (C)), mostly in the first days of the incubation. Meanwhile, the solid fraction of digestate exhibited slow mineralisation patterns (3–7 % of applied C). The variability in CO2 respiration was strongly influenced by the availability of labile C. Fertilisation had no effect on soil-borne CH4 emissions. Estimation of global warming potential, with respect to added N, suggests that BBFs obtained from the post-digestion treatment of digestate have a lower environmental impact compared to the unprocessed digestate, due to lower N2O emissions

Thermochemical upcycling of food waste into engineered biochar for energy and environmental applications: a critical review

Environmental issues caused by food waste are important concerns for human well-being and ecosystem health. Valorization of food waste into energy and carbon materials has been extensively investigated. Here, we reviewed the most recent advancements in the thermochemical conversion of food waste into engineered biochar. Synthesis routes and practical applications of the food waste-derived biochar was succinctly reviewed. Engineered biochar is a promising alternative for mitigating environmental pollution and alleviating energy crisis. The underlying relationships between engineered biochar properties and specific applications are still unclear, therefore, machine learning-aided engineered biochar design and process optimization was proposed. Moreover, before any industrial scale implementation, detailed assessments of the environmental benefits and economic feasibility must be conducted. In the context of carbon neutrality, thermochemical upcycling of food waste into engineered biochar for energy and environmental applications can significantly contribute to attaining sustainable food waste management, mitigating environmental pollution, and addressing the energy shortage crisis, and thus will eventually facilitate the fulfillment of United Nations Sustainable Development Goals (SDGs). Furthermore, the existing challenges in the practical valorization of food waste into engineered biochar are comprehensively discussed, and outlooks are proposed

The beneficial and hazardous effects of selenium on the health of the soil-plant-human system: An overview

Selenium (Se), which can be both hazardous and beneficial to plants, animals and humans, plays a pivotal role in regulating soil-plant-human ecosystem functions. The biogeochemical behavior of Se and its environmental impact on the soil-plant-human system has received broad attention in the last decades. This review provides a comprehensive understanding of Se biogeochemistry in the soil-plant-human system. The speciation, transformation, bioavailability as well as the beneficial and hazardous effects of Se in the soil-plant-human system are summarized. Several important aspects in Se in the soil-plant-human system are detailed mentioned, including (1) strategies for biofortification in Se-deficient areas and phytoremediation of soil Se in seleniferous areas; (2) factors affecting Se uptake and transport by plants; (3) metabolic pathways of Se in the human body; (4) the interactions between Se and other trace elements in plant and animals, in particular, the detoxification of heavy metals by Se. Important research hotspots of Se biogeochemistry are outlined, including (1) the coupling of soil microbial activity and the Se biogeochemical cycle; (2) the molecular mechanism of Se metabolic in plants and animals; and (3) the application of Se isotopes as a biogeochemical tracer in research. This review provides up-to-date knowledge and guidelines on Se biogeochemistry research.11Nscopu