Digestate (effluent of biogas plants) became the main bottleneck for biogas industry expansion because it often exceeds the capacity of surrounding croplands as fertilizer. Nutrients recovery from ...digestate is a promising solution for closing nutrients cycles and generating high value-added byproducts. In fact, numerous nutrients recovery technologies were reported and utilized for that purpose. However, each technology has optimum working conditions, while digestates have different characteristics due to the different substrates, digestion conditions, and handling methods. On the other hand, no protocol has been reported yet for selecting the optimal nutrients recovery technology or sequenced technologies for different digestates regarding their characteristics and the surrounding environmental conditions. In this study, an interactive flowchart was suggested and discussed for selecting the most appropriate technology or sequential techniques among the different alternatives. The whole digestate utilization technologies, solid-liquid separation technologies, liquid and solid processing technologies were included.
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•Digestates have very wide characteristics range.•An interactive flowchart was planned to select the best application.•Whole digestate utilization applications have use priority.•Vacuum, Membrane, NH3 strip, P recovery, Ion ex., Microalgae are used for liquids.•Composting, Pelletizing, Pyrolysis, Gasification, Incineration are used for solids.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, a suite of Fe-rich biochars derived from Fenton-like treated digestate (Fe-BC) were fabricated under different pyrolysis temperatures (300, 500, and 800 °C), which were firstly ...utilized as peroxymonosulfate (PMS) activators for promoting digestate dewaterability with wide applicability. Results showed that compared to the Fe-BC300/Fe-BC500 + PMS treatments, Fe-BC800 + PMS process performed superior digestate dewaterability in which specific resistance to filtration reduction and water content reduction improved by > 12.5% and > 130%, respectively, under the optimal conditions. Mechanistic results demonstrated that in Fe-BC800 + PMS system, HO• and SO4•− oxidation played a pivotal role on promoted digestate dewaterability, while HO• and 1O2 oxidation was dominated in Fe-BC300/Fe-BC500 + PMS treatments. Fe-BC800 containing higher Fe and CO contents could efficiently interact with PMS to generate numerous HO• and SO4•− via iron cycle. These highly reactive oxygen species proficiently reduced the hydrophilic biopolymers, protein molecules, and amino acids in extracellular polymeric substances, leading to remarkable decrease in particle size, hydrophilicity, adhesion, network strength, and bound water of digestate. Consequently, the flowability and dewaterability of digestate could be significantly enhanced. The cost-benefit result indicated the Fe-BC + PMS treatment possessed desirable reusability, applicability, and economic viability. Collectively, the Fe-BC + PMS is a high-performance and eco-friendly technique for digestate dewatering, which opens a new horizon towards a closed-loop of digestate reutilization.
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•Fe-rich digestate biochar at 800 °C was effective in PMS activation for ROS production.•Fe-BC800 + PMS remarkably enhanced digestate dewaterability at wide applicability.•Fe-BC800 + PMS promoted strong oxidation and flocculation for digestate dewatering.•Hydrophilic biopolymers, functional groups, and amino acids in EPS were degraded.•A closed-loop utilization of anaerobic digestate was proposed and evaluated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Biogas is mainly discussed in the context of renewable energy, digestate is playing a minor role. However, in the upcoming EU Fertilizer Product Regulation digestate as eligible component material is ...in line with the circular economy action plan. This article discusses the quality of raw digestate based on analysis data from Austrian biogas plants regarding to the current Austrian as well as the European fertilizer regulatory framework. Therefore, a survey among Austrian biogas plant operators for results of digestate analysis and substrate input and energy output is used. The results show, that the legislative framework applies to a minimum of 1.5 million tonnes of digestate. Austrian digestate is of high quality with regards to the nutrient content, required limit values for heavy metals and is also safe with respect to their hygienic parameters. The following European fertilizer product function categories are available for international trade of digestate: “organic soil improver”, “growing medium”, and “organic, non-microbial plant biostimulant”. Establishing legal criteria determining End-of-Waste and subsequently the product status for digestate is another important step in the European circular economy.
•Austria produces at least 1.5 million tonnes of digestates.•Three different fertilizer categories are suitable for digestates.•Digestates cannot be classified as organic fertilizers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Anaerobic digestion technology has gained significant attention as an organic solid waste treatment method due to its favorable economic and environmental benefits. However, after digestion, the ...digestate still contains a significant amount of underutilized organic matter. Sustainable management and resource utilization of digestate plays a crucial role in achieving resource circularity and implementing a circular economy. Previous reviews have mainly focused on improving the operational efficiency and stability of anaerobic digestion, with limited exploration of sustainable management and resource utilization of digestate. To address this gap, this review provides a systematic summary of the sustainable management and resource utilization of digestate. First, the basic characteristics of digestate are outlined. Then, based on a visual analysis of literature on digestate management from the past decade, the review highlights the hotspots in sustainable management and circular utilization of digestate. Finally, it summarizes the relevant policies on digestate management in different regions and outlines the challenges in digestate treatment and disposal. The challenges in digestate management remain a significant issue that requires further exploration and solutions. This review aims to promote the standardization of digestate management, provide direction for further in-depth research on digestate, and contribute to the continued development of resource cycling of anaerobic fermentation products.
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Hydrothermal pretreatment was used for dewatering food waste digestate residue, and biochar/biogas were generated from the separated solid and liquid phases via pyrolysis and anaerobic digestion, ...respectively. Increasing hydrothermal pretreatment temperature (110–200 °C) clearly improved dewaterability, whereas enhancing treatment duration (30–90 min) had little impact. The optimal condition of 160 °C/30 min gave the best dewatering performance with relative lower energy consumption and was chosen for pilot-scale verification achieving 61.7 wt% dry weight content after mechanical squeezing. Moreover, the filtrate and filter cake obtained at optimal condition were applied for biogas and biochar production in lab scale. The methane yield of the filtrate was 335 mL/g COD. Pyrolysis temperature of 500 °C gave better biochar performance and was verified in a pilot scale test. Additionally, the heavy metals in digestate were effectively immobilized during hydrothermal dewatering and pyrolysis processes. In the end, mass/energy balance calculated using pilot-scale data presented the combined systems provided a promising strategy for accomplishing energy recovery and resource reuse of digestate residue.
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•HTPT, pyrolysis and anaerobic digestion were used for DR treatment.•°C and 500 °C performed better performances in DR dewatering and biochar production.•The optimal conditions were successfully verified at pilot-scale tests.•Mass/energy balance showed slight energy deficit of the whole process.•t biochar was produced from 100 t DR.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Environmental assessment of five digestate treatment technologies using LCA.•Environmental benefits observed for treatment of digestate vs. direct spreading.•Highest environmental benefits observed ...when treating raw digestate.•Spreading techniques (e.g. injection or incorporation) influence overall impacts.•The use of mixing triangles was performed to aid in decision making.
The production of biogas from energy crops, organic waste and manure has augmented considerably the amounts of digestate available in Flanders. This has pushed authorities to steadily introduce legislative changes to promote its use as a fertilising agent. There is limited arable land in Flanders, which entails that digestate has to compete with animal manure to be spread. This forces many anaerobic digestion plants to further treat digestate in such a way that it can either be exported or the nitrogen be removed. Nevertheless, the environmental impact of these treatment options is still widely unknown, as well as the influence of these impacts on the sustainability of Flemish anaerobic digestion plants in comparison to other regions where spreading of raw digestate is allowed. Despite important economic aspects that must be considered, the use of Life Cycle Assessment (LCA) is suggested in this study to identify the environmental impacts of spreading digestate directly as compared to four different treatment technologies. Results suggest relevant environmental gains when the digestate mix is treated using the examined conversion technologies prior to spreading, although important trade-offs between impact categories were observed and discussed. The promising results of digestate conversion technologies suggest that further LCA analyses should be performed to delve into, for instance, the appropriateness to shift to nutrient recovery technologies rather than digestate conversion treatments.
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•A closed-loop system coupling with AD, pyrolysis and adsorption was established.•More than 95% of antibiotics and benzenes in actual liquid digestate were removed.•80.5% of C and ...94.7% of N in pig manure was effectively recovered and recycled.•The system enabled clean biogas production and safe biofertiliser recycling.
Anaerobic digestion of livestock manure as a carbon-negative practice yields bioenergy and biofertilizer. However, substantial antibiotics and benzenes contained in liquid and solid digestate hinder its large-scale applications. In this study, a novel closed-loop treatment strategy was proposed to integrate the synthesis benefits of anaerobic digestion, pyrolysis of solid digestate, and adsorption. The solid digestate-derived biochar (S-biochar) was successfully prepared by coupling pyrolysis and H2SO4 activation. The S-biochar possessed a polycyclic aromatic structure, abundant micropores (0.8–1.0 nm), various functional groups (–COOH, Aro–OH), and a higher absolute zeta potential value. These characteristics contributed to the excellent adsorption of tetracycline (51.3 mg/L), oxytetracycline (32.9 mg/L), benzene (86.0 mg/L) and toluene (74.1 mg/L), wherein pore filling, electrostatic interactions, H-bonding, surface partition, and π-π conjugation mechanisms were involved. The adsorption of antibiotics was more sensitive to pH, in comparison with benzenes, and displayed a declining trend (pH>7). Under actual liquid digestate conditions, >95% adsorption of antibiotics and benzenes were reached at the dosage of 1.5 g/L, in a company with >80% of nitrogen and phosphorus. In the end, a carbon and nitrogen flow analysis was performed to elucidate that more than 80% of carbon in pig manure can be settled as biochar and biogas, and up to 94.7% of nitrogen remained in the biochar and liquid digestate. This study not only developed a S-biochar with excellent performance in removing organic pollutants from liquid digestate, but also established a closed-loop strategy as an alternative carbon sequestration approach using anaerobic digestion side-products.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A mass-balance tool enables estimation of anaerobic digestion systems outputs.•All inputs have significant impact on, at least, one tool output.•Model evaluation shows an accurate ...prediction for raw digestates and liquid phases.•Phase separation and storage leads to prediction uncertainty for solid phase.•Suitability of the tool for technical, economic and environmental applications.
The increase in anaerobic digestion systems has profoundly affected the waste management of territories, particularly for agricultural systems. Changes in cultural practices and imports of organic waste modify the carbon (C) and nitrogen (N) fluxes on territories where anaerobic digestion is implemented. Successful anaerobic digestion can increase the economic and ecological efficiency of the waste management system. Conversely, poor anaerobic digestion leads to low economic and environmental efficiency due to greenhouse gas emissions and nutrient loss. Modeling the impact of anaerobic digestion on the systems integrating anaerobic digestion can improve the efficiency of these practices. The aim of this study was to develop, analyze, and evaluate a simple mass balance tool able to predict carbon and nitrogen fluxes in anaerobic digestion systems. The tool is composed of an exhaustive substrate database used by three models: (i) an anaerobic digestion model that predicts C and N contents in biogas and digestate; (ii) a phase separation model that predicts C and N content in liquid and solid phase digestates; and (iii) a storage model that predicts C and N content in raw, liquid phase, and solid phase digestates, as well as C and N emissions during storage. Sensitivity analyses were performed on the tool to determine critical inputs. Sensitivity analysis showed that outputs were highly sensitive to their respective inputs and to total inputs of solids. Performance evaluation showed that the tool can provide good quality predictions with R2 correlations between observation and prediction varying from 0.72 to 0.99 with the best predictions obtained for raw digestate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•P-AnMBR's operational stability in treating digestate was elucidated.•P-AnMBR had various retention effects on various pollutants.•The contamination mechanism of AnMBR membranes was unveiled.•The ...membrane fouling situation during operation was quantified.
Anaerobic Membrane Bioreactor (AnMBR) are employed for solid-liquid separation in wastewater treatment, enhancing process efficiency of digestion systems treating digestate. However, membrane fouling remains a primary challenge. This study operated a pilot-scale AnMBR (P-AnMBR) to treat high-concentration organic digestate, investigating system performance and fouling mechanisms. P-AnMBR operation reduced acid-producing bacteria and increased methane-producing bacteria on the membrane, preventing acid accumulation and ensuring stable operation. The P-AnMBR effectively removed COD and VFA, achieving removal rates of 82.3 % and 92.0 %, respectively. Higher retention of organic nitrogen and lower retention of ammonia nitrogen were observed. The membrane fouling consisted of organic substances (20.3 %), predominantly polysaccharides, and inorganic substances (79.7 %), primarily Mg ions (10.1 %) and Ca ions (4.5 %). To reduce the increased transmembrane pressure (TMP) caused by fouling (a 10.6-fold increase in filtration resistance), backwash frequency experiment was conducted. It revealed a 30-min backwash frequency minimized membrane flux decline, facilitating recovery to higher flux levels. The water produced amounted to 70.3 m³ over 52 days. The research provided theoretical guidance and practical support for engineering applications, offering practical insights for scaling up P-AnMBR.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Anaerobic digestion produces a biologically stable and high-value fertilizer product, the digestate, which can be used as an alternative to mineral fertilizers on crops. However, misuse of digestate ...can lead to annoyance for the public (odours) and to environmental problems such as nitrate leaching and ammonia emissions into the air. Full field experimental data are needed to support the use of digestate in agriculture, promoting its correct management. In this work, short-term experiments were performed to substitute mineral N fertilizers (urea) with digestate and products derived from it to the crop silage maize. Digestate and the liquid fraction of digestate were applied to soil at pre-sowing and as topdressing fertilizers in comparison with urea, both by surface application and subsurface injection during the cropping seasons 2012 and 2013. After each fertilizer application, both odours and ammonia emissions were measured, giving data about digestate and derived products' impacts.
The AD products could substitute for urea without reducing crop yields, apart from the surface application of AD-derived fertilizers. Digestate and derived products, because of high biological stability acquired during the AD, had greatly reduced olfactometry impact, above all when they were injected into soils (82–88% less odours than the untreated biomass, i.e. cattle slurry). Ammonia emission data indicated, as expected, that the correct use of digestate and derived products required their injection into the soil avoiding, ammonia volatilization into the air and preserving fertilizer value. Sub-surface injection allowed ammonia emissions to be reduced by 69% and 77% compared with surface application during the 2012 and 2013 campaigns.
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•Anaerobic digestion produced useful fertilizers, i.e. the digestate.•Digestate misuses led to odours and ammonia impacts.•Pre-sowing and topdressing use of digestate substituted completely N-fertilizers.•Subsurface injection of digestate reduced greatly odour and NH3 emissions.•Digestate use allowed producing maize silage as well as using urea.
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