Digestate Storage Research Articles

Survival of plant seeds in digestate storage—with and without prior anaerobic digestion

IntroductionPlant seeds from weeds and energy crops have the potential to survive anaerobic digestion (AD). Species able to form physically dormant, i.e., hardseeded (HS) seeds seem particularly resistant. However, it is not yet known to what extent the storage of the digestate after AD affects seed viability.MethodsSeed survival of five HS and six non-HS (NHS) species was investigated in three combinations of digestate storage (DS) and AD. First, untreated seeds were exposed to DS for maximum 12 weeks. To simulate short-circuited AD (ADshort) in biogas reactors, seeds were second subjected to lab-scale AD for 1 day before DS. Third, seeds of six species were exposed to full-scale AD (ADfull) followed by DS. Seed viability was determined using a combination of germination tests and tetrazolium staining. Viability was modeled as a function of exposure time.Results and discussionSeed viability was affected by DS, AD and AD + DS, but responses varied greatly between species and treatments. With increasing exposure time, viability decreased after a lag-phase, remained stable or even increased. The NHS species Cichorium intybus, Daucus carota, Echium vulgare, and Verbascum thapsus were most susceptible, with seed-killing close to 100% if DS was involved. The HS species Malva sylvestris, Melilotus albus and Melilotus officinalis were most resistant. They survived all treatments and were alive after 35 days of ADfull plus 3 months of DS. The resistance potential of the HS species Abutilon theophrasti and Malva alcea and of the NHS species Chenopodium album and two tomato varieties was intermediate. None of them survived ADfull + DS, but except A. theophrasti they were viable after ADshort + DS. With few exceptions, seed-killing by AD + DS was higher than that by AD alone. In conclusion, DS and AD + DS have the potential to reduce seed viability, but do not completely inactivate all species. Therefore, digestate can be contaminated with viable seeds and may lead to the spread of weeds, especially after a short-circuited AD. In order to ensure the sustainable use of digestates in terms of weeds, we recommend to investigate the factors contributing to seed inactivation and the quantity of seed introduced to AD.

An Effective Biochar Application for Reducing Nitrogen Emissions from Buffalo Digestate Storage Tank

Open manure storage contributes to the release of ammonia (NH3) into the atmosphere. Tank floating covers represent an effective technique to reduce NH3 emissions and biochar has been gain attention as a floating cover and as manure additive. Nevertheless, the mechanisms involved in the process still need to be elucidated since they are influenced by the biochar specific properties, application methods and dose. This work aims to study: (i) the biochar adsorption performances in an NH3 aqueous solution under conditions relevant to manure storage and (ii) the effect of different biochar application methods and dosage on NH3 emissions from buffalo digestate storage. The results show that a 43% reduction in NH3 emissions can be achieved by using biochar as a floating cover of 2 cm rather than as an additive. Moreover, the results show that the biochar produced at 550 °C acts as an adsorbent material for both NH4+ and NH3, by being adsorbed on the biochar surface in the form of NH4+ after H+ abstraction from the acid groups. A minimum cover height of 2 cm is required to give compactness and provide an additional resistance to the gas transfer, which is even more relevant than the adsorption in reducing NH3 emissions.

Monitoring CH4 Fluxes in Sewage Sludge Treatment Centres: Challenging Emission Underreporting

In this manuscript, CH4 emissions from sludge treatment centres are quantified using an unmanned aerial vehicle (UAV) framework, with particular focus on anaerobic digesters and digestate storage tanks. The outcomes are compared to those obtained using the carbon accounting workbook (CAW), which is the most commonly used industry tool by UK and Irish water companies to estimate the annual greenhouse gas emissions from their process operations. Path integrated concentrations are monitored with the use of an open-path tuneable diode laser absorption spectroscopy sensor embedded on a UAV. Measurements are interpolated using geostatistics (Kriging) and coupled with the mass balance approach to estimate emissions. The findings show that the CAW seems to underestimate emissions from digestate storage tanks by up to an order of magnitude. The results also show that CH4 emissions are linked with the residence time in the tank and temperature of the digestate. This study highlights the limitations of assumptions made using current reporting methods based on the carbon accounting workbook. This study proves that the UAV framework, together with the mass balance approach, provides high spatial resolution data; it captures the dynamic nature of emissions compared to the CAW and can be a cost-effective solution to estimate CH4 fluxes compared to other sensor-based systems.

Dairy manure nutrient recovery reduces greenhouse gas emissions and transportation cost in a modeling study

Technologies that separate manure or digestate into fractions with different solids and nutrient contents present interesting options to mitigate manure storage emissions (by reducing the quantity of carbon stored anaerobically) and to improve nutrient distribution (by reducing the quantity of water transported with nutrients). In this study, the dairy farm model, DairyCrop-Syst, was used to simulate storage emissions of methane (CH4), nitrous oxide (N2O), and ammonia (NH3), and to simulate nutrient distribution for a case-study farm in Canada. The farm used several types of manure processing, including: anaerobic digestion (AD), solid-liquid separation (SLS), and nutrient recovery (NR). Simulations were done with combinations of the above technologies, i.e., a baseline with only AD that produced a single (unseparated) effluent, compared to AD+SLS, and AD+SLS+NR that produced two separate fractions. With AD+SLS+NR, the processing system isolated a solid fraction with a high concentration of N and P, and a liquid fraction containing less nutrients. Compared to the baseline system, the addition of solid liquid separation and nutrient recovery (i.e. SLS+NR) reduced CH4 emissions from outdoor liquid digestate storage by 87%, with only a small offset from higher N2O and NH3 emissions from storing the solid fraction. The solid fraction was simulated to be transported to fields at least 30 km away from the dairy barns, while the liquid fraction was transported by dragline to fields adjacent to the barn. The advanced nutrient separation system resulted in much lower transport costs for manure nutrients and the ability to transport N and P to greater distances.

Decision support tool for the construction and seasonal operation of farm-scale anaerobic digestion plants

Optimal plant design and management are critical components for the successful operation of farm-scale anaerobic digestion (AD) plants. However, this often proves challenging due to difficulties in designing and sizing the plant based on specific site conditions. The current investigation aims to address these difficulties by developing a universal decision support tool to assist in the optimal design and management of agriculture-based AD plants, accounting for site-specific practicalities and implications. The tool consists of various mathematical functions, which enable numerous simulations to be created and run. The developed tool was applied to a case study, located in Ireland, to test its usefulness, where the analysis showed the optimal, site-specific, plant design with key assessment indicators. For this case study, the feedstock availability assessment determined that the lignocellulose and non-lignocellulose biomass within a 10 km distance of the site. Based on the local energy demand of the area, the tool modelled an optimal AD plant design, including feedstock storage, digester volume, engine capacity, and digestate storage. The tool applied various technical, economic, and ecological assessment indicators to the plant to gauge its viability. Therefore, demonstrating the tool's usefulness in assisting stakeholders to make informed decisions and reducing costs by optimising plant design and performance.

The Danish national effort to minimise methane emissions from biogas plants

In total, 69 biogas plants representing 59 % of Danish biogas production participated in a national effort to reduce methane (CH4) emission. Measurements in terms of total plant CH4 emissions, quantification of emissions from point sources, leak surveys and conceptual design plans to mitigate emissions were performed. Plant-level CH4 emission rates varied between 1.3 and 81.2 kg CH4 h−1, and CH4 losses expressed in percentages of production varied between 0.3 and 40.6 %. Agricultural plants generally had lower CH4 loss rates compared to wastewater treatment plants. Biogas plants with a smaller gas production emitted a larger fraction of their production compared to larger plants, which was partly explained by the absence of gas collection from digestate storage tanks at smaller plants. A very commonly observed source of emission was pressure relief valves, where this source of leakage was observed at 53 % of the plants. A national emission factor (sum of CH4 emissions/sum of CH4 productions) was determined at 2.5 % for the Danish biogas production, whereof it was 2.1 % for agricultural biogas production and 6.7 % for biogas production at wastewater treatment plants. Measurements of total CH4 emissions at six plants performed before and after implementation of mitigating actions showed that emissions were reduced by 46 % by carrying out relatively minor technical fixes and adjustments. An economic evaluation showed that, in some cases, mitigating actions could be economically beneficial for the biogas plant (positive net present value over a 10 year time frame), due to an increase in revenue.

Methane losses from different biogas plant technologies

Biogas and biomethane production can play an important role in a fossil-fuel-free energy supply, provided that process-related methane (CH4) losses are minimized. Addressing the lack of representative emission data, this study aims to provide component specific CH4 emission factors (EFs) for various biogas plant technologies, enabling more accurate emission estimates for the biogas sector and supporting the identification of low emission technologies. Four measurement teams investigated 33 biogas plants in Austria, Germany, Sweden and Switzerland including mainly agricultural and biowaste treating facilities. For the first time, a harmonized measurement procedure was used to systematically survey individual on-site emission sources and leakages. Measurements revealed a large variability in technology specific emissions, especially for biogas utilization and upgrading. Median loss from combined heat and power (CHP) plants was 1.6 % for gas engines (n = 21), and 3.0 % for pilot injection units (n = 3) of the input CH4. Biogas upgrading units showed median CH4 slips of < 0.1 % (chemical scrubbers, n = 4), 0.1 % (after exhaust gas treatment, n = 3) and 2.9 % (water scrubbers, n = 2). Not-gastight digestate storage (n = 8) was identified as a major emission source with maximum 5.6 % of the produced CH4 emitted. Individual leakages (n = 37) released between 0.0 and 2.1 % (median 0.1 %) relative to the CH4 production. All measurement and secondary data are provided in a harmonized dataset (294 datapoints). A review of IPCC default EFs indicate an underestimation of emissions from biogas utilization (reported in the energy sector) while the impact of leakages on overall plant emissions (waste sector) may be overestimated for European biogas plants.

Life Cycle Assessment and Techno-Economic Analysis for Anaerobic Digestion as Cow Manure Management System

Clean electricity is generated by the anaerobic digestion of biomass waste. The environmental impacts of various biomass waste feedstocks vary, while co-digestion has been reported to improve anaerobic digestion performance. A consequential life-cycle assessment (LCA) and techno-economic analysis (TEA) are carried out for cow manure waste management for a cow farm. Three scenarios are considered in this study: (S1) mono-digestion of cow manure, (S2) co-digestion of cow manure and maize silage, and (S3) co-digestion of cow manure with cow feed waste, sewage sludge, and returned dairy products. The LCA aims to quantify the environmental impact of each MWh of electricity generated, assuming the plant is located in Malaysia, using OpenLCA software. The TEA economic parameters are quantified and compared between the three scenarios. Net present value (NPV), Internal Return Rate (IRR), and Return of Investment (ROI) are examined. Among the three scenarios, S2 with maize cultivation has a higher environmental impact due to its higher energy requirements. With the integration of closed digestate storage and renewable energy-powered electricity, S3 has the best environmental performance in global warming, eutrophication and acidification. S3 is found to be most economically viable, with MYR 1.28 million NPV, 14% IRR, and 15% ROI, and a Payback Period of 6.56 years with an OPEX of MYR 3491.82/MWh.

A comparative life cycle assessment of anaerobic mono- and co-digestion of livestock manure in Bangladesh

Proper management of biogenic residues, particularly livestock manure and food waste, is a major challenge for Bangladesh. While mono-digestion has traditionally been used on farms for treating manure, inadequate energetic output limits its applicability. Food waste, however, is typically landfilled in current practice. Co-digestion of biowaste emerged as an alternative due to synergistic yield and capacity to handle multiple waste streams. However, its environmental performance is underreported, particularly in developing countries. This study aimed to compare the environmental implications of co-digestion and mono-digestion of livestock manure (poultry and cow manure) with food waste from a life cycle assessment perspective for the regional context of Bangladesh. Two inventory cases were considered, accounting for mechanistically calculated (case M) and experimentally reported synergistic biogas yield (case E). Co-digestion scenarios showed net benefits by reducing three of the five impact categories-considerably reducing climate change (up to 117%), eutrophication potential, and terrestrial ecotoxicity in both cases (54.5 % and 55.7 %, respectively). The highest decrease occurred for climate change by diverting food waste landfilling. However, when synergistic biogas yield was considered, acidification potential and malodor air emissions increased by co-digestion owing to a higher amount of hydrogen sulfide and ammonia in the produced gas, thus entailing significant environmental burdens. The key hotspot in most categories was open storage of digestate, necessitating appropriate post-treatment.

Environmental impact of milk and electricity production from dairy farms with biogas plants of different size and feeding system

Anaerobic digestion is an effective method to decrease the environmental impact of milk production and to generate renewable energy. A dairy farm with an annexed biogas plant produces three outputs, milk, meat and electricity, and should be considered as a single system for the evaluation of the environmental impact. The aim of this study was to investigate to what extent the size and feeding methods of the biogas plants in three dairy farms with different features affect the environmental impact related to the milk and electricity produced. The first farm was characterized by a biogas plant of 300 kW fed only with cattle manure, the second farm had a plant of 526 kW fed with cattle manure, maize silage and waste of maize grain production, while the third farm had a biogas plant of 999 kW fed with cattle and poultry manure, maize and triticale silage, and fats from slaughterhouse waste. The Life Cycle Assessment involved the environmental impact of Fat Protein Corrected Milk (FPCM), in the first instance with meat and electricity from biogas considered with an economic allocation, and then considered a credit. Successively, the environmental consequences of electricity were evaluated considering milk and meat as credits. With the economic allocation, Carbon Footprint (CFP) of one kg of FPCM was 0.82, 0.85 and 0.72 kg CO2 eq in the first, second and third farm, respectively. In all the three farms, electricity generation from biogas determined a reduction in the environmental impact of milk production thanks to a credit of emissions provided by the production of renewable energy. Milk CFP in the three farms was 0.82, 0.91 and 0.13 kg CO2 eq respectively, with mitigation from biogas of 11%, 11% and 85%. The best performances were obtained in the third farm thanks to higher levels of electricity generation, covered digestate storage and the large use of agri-industrial waste. Electricity CFP in the farms was −0.74, −0.68 and −0.06 kg CO2 eq/kWh respectively. Environmental consequences of electricity production from biogas plants were compensated in all the farms thanks to the credits provided by milk; this compensation was as greater as the ratio between milk and electricity production and the first farm reached better outcomes. In the context of reducing the environmental impact of animal foods and implementing an ecological transition to reach national and European goals for renewable energy production, the work could be beneficial to assess which combination between dairy and energy products should be promoted.

Possibility of using tannins to control greenhouse gas production during digestate storage

The presented paper deals with the testing of a possibility to reduce emissions of undesirable greenhouse gases (CH4, CO2; NOx) and their mixture (biogas) during the storage of digestate using applications of secondary plant metabolites (tannins). The experiment was conducted in laboratory conditions in which the digestate was placed in fermentation chambers. Prior to the fermentation process, preparations were applied to the digestate, which contained tannins: Tanenol Antibotrytis (TA), Tanenol Clar (TC) and Tanenol Rouge (TR) in three concentrations (0.5, 1.0 and 2.0% w/w). The application of these preparations demonstrably affected the production of biogas and the contents of CH4, CO2 and N therein. The application of TR preparation in the concentration of 1.0% and 2.0% significantly reduced the production of biogas as compared with all variants. The preparation further inhibited the process of CH4 development. In contrast, the other preparations with the content of different kinds of TA and TC increased the production of biogas (on average by 15%), CH4 (on average by 7%) and CO2 (on average by 12%) as compared with the control variant and TR variant. These two variants reduced the concentration of N in biogas on average by 38%. Thus, the tested Tanenol tannin preparations can be used in different concentrations either to control emissions of greenhouse gases during the storage of digestate or, in case of increased production of CO2 for its reuse in order to increase methane yields in the process of anaerobic fermentation.

Fugitive methane emissions from two agricultural biogas plants

This study quantified fugitive methane (CH4) losses from multiple sources (open digestate storages, digesters and flare) at two biogas facilities over one year, providing a much needed dataset integrating all major loss pathways and changes over time. Losses of CH4 from Facility A were primarily from digestate storage (5.8% of biogas CH4), followed by leakage/venting (5.5%) and flaring (0.2%). At Facility B, losses from digestate storage were higher (10.7%) due to shorter hydraulic retention time and lack of a screwpress. Fugitive emissions from leakage were initially 3.8% but were reduced to 0.6% after the dome membrane was repaired at Facility B. For biogas to have a positive impact on greenhouse gas emissions and provide a low-carbon fuel, it is important to minimize fugitive losses from digestate storage and avoid leakage during abnormal operation (leakage, roof failure).

A comparison of digestate management options at a large anaerobic digestion plant

Increased biogas production from increasing numbers of anaerobic digestion (AD) facilities has increased the mass of digestate applied to agricultural land close to AD plants and has led to an oversupply in some regions. This necessitates long distance digestate transportation accompanied by economic, environmental, and social drawbacks. This work assesses the performance of three different digestate management options (MOs); land application of whole digestate (MO1), digestate separation (MO2), and digestate separation and evaporation (MO3), combined with centralised or decentralised digestate storage. All MOs required the same landbank area, whilst MO2 and MO3 reduced digestate management costs by 9% and 37% (if recovered heat is used) respectively. GHG emissions from MO2 were 41% lower than MO1 if renewable electricity was used. MO3 reduced GHG emissions by 63% compared to MO1, if renewable electricity and recovered heat were used. MO2 required the same centralised digestate storage volume as MO1 while MO3 required 44% of the centralised storage volume. Centralised digestate storage required a maximum of 79 days for digestate transportation (33 trucks/day, 20 m3 capacity) to land for MO1 and MO2, and 35 days for MO3. Decentralised digestate storage required 63 storage tanks and 15 trucks/day for MO1, 69 tanks and 15 trucks/day for MO2, and 68 tanks and 7 trucks/day for MO3. Tank size ranged from 500 m3 to 20,000 m3. MO3 combined with decentralised storage could reduce the cost and GHG emissions (if recovered energy is used), vehicle movements, and the number of storage tanks required for digestate management.

Methane emissions along biomethane and biogas supply chains are underestimated

Methane emissions along biomethane and biogas supply chains are underestimated

Nutrient recovery abates methane emissions from digestate storage

Farm-based anaerobic digestion is a promising source of renewable natural gas (RNG), but the carbon intensity of RNG is influenced by methane (CH4) emissions from digestate storage. This study evaluated whether a nutrient recovery system could minimize digestate CH4 emissions from uncovered storage. Nutrients were concentrated in the solid fraction, which contained 82% of the Phosphorus (P) and 39% of the Nitrogen (N) with only 7% of the water. Laboratory results showed that the CH4 emission potential from digestate was 113 ± 6 mL g−1 volatile solids (VS), which was reduced to zero in the liquid fraction after nutrient separation. Measurements from the 0.4-ha uncovered outdoor liquid storage showed CH4 emissions were low, with annual emissions being 1.5% of the CH4 collected by the biodigester. Storage emissions could be further reduced by ensuring that all manure passed through the nutrient recovery system. Overall, the combination of biogas and nutrient recovery reduces the carbon intensity of RNG and improves nutrient distribution.

Untargeted Metabolomics Profiling of Bioactive Compounds under Varying Digestate Storage Conditions: Assessment of Antioxidant and Antifungal Activity.

The rapid development of biogas plants in China has generated large quantities of digestate. The disparity between the continuity of biogas plant operation and the seasonality of digestate utilization has led to the need to store digestate. Therefore, untargeted profiling of bioactive compounds in the digestate stored under aerobic and anaerobic conditions was performed. The antioxidant and antifungal activity of digestate stored under varying conditions was likewise assessed. The results delineated that digestate storage under varying conditions brought about the degradation of organic acids, alkenes, aldehydes, alcohols, ketones, ethers, amino acids and their derivatives, and esters, leading to the stabilization of digestate components. Together, these new data revealed that digestate storage for up to 20 days under aerobic conditions promotes glycine, serine, and threonine degradation pathways and enhances biotin and vitamins production. In contrast, anaerobic storage enhances the taurine and hypotaurine metabolic pathways and increases the derivation of antimicrobial substances, such as indole alkaloids. Moreover, digestate storage under anaerobic conditions promotes antioxidant and antifungal activity more than storage under aerobic conditions. These findings can contribute to the future development of high-value agricultural products from digestate and the sustainability of biogas plants. Further studies are required for the untargeted metabolomic of digestate under storage to explore the underlying mechanisms of promoting disease resistance by the digestate upon land application.

Digestate Post-Treatment Strategies for Additional Biogas Recovery: A Review

Anaerobic digestion (AD) is a process in which microorganisms, under oxygen-free conditions, convert organic matter into biogas and digestate. Normally, only 40–70% of biomass is converted into biogas; therefore, digestate still contains significant amounts of degradable organic matter and biogas potential. The recovery of this residual biogas potential could optimize substrate utilization and lower methane emissions during digestate storage and handling. Post-treatment methods have been studied with the aim of enhancing the recovery of biogas from digestate. This review summarizes the studies in which these methods have been applied to agricultural and wastewater digestate and gives a detailed overview of the existing scientific knowledge in the field. The current studies have shown large variation in outcomes, which reflects differences in treatment conditions and digestate compositions. While studies involving biological post-treatment of digestate are still limited, mechanical methods have been relatively more explored. In some cases, they could increase methane yields of digestate; however, the extra gain in methane has often not covered treatment energy inputs. Thermal and chemical methods have been studied the most and have yielded some promising results. Despite all the research conducted in the area, several knowledge gaps still should be addressed. For a more thorough insight of the pros and cons within post-treatment, more research where the effects of the treatments are tested in continuous AD systems, along with detailed economic analysis, should be performed.

Evaluation of pathogen concentration in anaerobic digestate using a predictive modelling approach (ADRISK)

Farmyard manure and slurry (FYM&S) is a valuable feedstock for anaerobic digestion (AD) plants. However, FYM&S may contain high concentrations of pathogens, and complete inactivation through the AD process is unlikely. Thus, following land application of digestate, pathogens may contaminate a range of environmental media posing a potential threat to public health. The present study aimed to combine primary laboratory data with literature-based secondary data to develop an Excel-based exposure assessment model (ADRISK) using a gamma generalised linear model to predict the final microorganism count in the digestate. This research examines the behaviour of a suite of pathogens (Cryptosporidium parvum, norovirus, Mycobacterium spp., Salmonella spp., Listeria monocytogenes, Clostridium spp., and pathogenic Escherichia coli) and indicators (total coliforms, E. coli, and enterococci) during mesophilic anaerobic digestion (M-AD) at 37 °C, pre/post-AD pasteurisation, and after a period of storage (with/without lime) for different feedstock proportions (slurry:food waste: 0:1, 1:3, 2:1, and 3:1). ADRISK tool simulations of faecal indicator bacteria levels across all scenarios show that the digestate can meet the EU standard without pasteurisation if the AD runs at 37 °C or a higher temperature with a higher C:N ratio (recipe 3) and a hydraulic retention time ≥ 7 days. The storage of digestate also reduced levels of microorganisms in the digestate. The Irish pasteurisation process (60 °C for 4 days), although more energy-intensive, is more effective than the EU pasteurisation (70 °C for 1 h) specification. Pre-AD pasteurisation was more effective for C. parvum, norovirus, Mycobacterium thermoresistibile. However, post-AD literature-based pasteurisation is most likely to assure the safety of the digestate. The information generated from this model can inform policy-makers regarding the optimal M-AD process parameters necessary to maximise the inactivation of microorganisms, ensuring adverse environmental impact is minimised, and public health is protected.

Environmental impacts of a rice-beef-biogas integrated system in the Mekong Delta, Vietnam evaluated by life cycle assessment

It is essential to increase the production of foods to meet the increasing future food demand, but this should be done in an environmentally sustainable manner. Integrated crop-livestock systems have been suggested to balance the reduction of environmental impacts and the increase in food production. Here we assessed and compared the environmental impacts of specialized (SPC) and integrated (ITG) rice and beef production systems in the Mekong Delta, Vietnam, using a life-cycle assessment (LCA). The productions of rice and beef are separated in the SPC, whereas they are integrated in the ITG: cattle manure is treated by a biodigester for biogas production, its digestate is applied to rice paddy fields as fertilizer, and part of the rice straw is used as cattle feed. We developed an LCA model based on data collected by site investigations of rice and beef farms and the relevant literature and LCA databases. Our evaluation of the ITG and SPC rice-beef production systems using the LCA revealed that among the four environmental impact categories investigated herein, the ITG had less environmental impacts on climate change (22%), energy consumption (22%), and eutrophication (14%) compared to the SPC. With the ITG, the reduction of methane emissions from paddy fields, the avoided energy consumption by the biogas produced, and the lower ammonia, nitrate, and phosphorous emissions from cattle manure and no eutrophying pollutant emissions from grassland were the main contributors to the lower greenhouse gas emissions, energy consumption, and eutrophication potential of this system, respectively. A sensitivity analysis showed that the use of cover for digestate storage resulted in lower environmental impacts of the ITG system compared to SPC system in all of the impact categories investigated here. These results provide helpful information to develop a circular and resource-efficient rice and beef production system that balances increasing productivity with environmental sustainability in rice-producing countries, particularly in Asia.

The Effect of Untreated and Acidified Biochar on NH3-N Emissions from Slurry Digestate

The development of new options to reduce ammonia (NH3) emissions during slurry manure storage is still required due to the shortcomings of the current technologies. This study aimed to identify to what extent untreated and acid-treated biochar (BC) and pure acids could reduce ammonia nitrogen (NH3-N) volatilization and increase nitrogen retention in slurry digestate. The NH3-N emissions were effectively reduced by H2SO4 and H3PO4 acids, untreated BC when applied mixed into the digestate and acidified BC treatments applied on the surface of the digestate. Acidification increased the specific surface area and number of O-containing surface functional groups of the BC and decreased the pH, alkalinity and the hydrophobic property. Compared to untreated BC, the ability of BC to reduce NH3-N emissions was greater when it was acidified with H2SO4 and applied to the digestate surface. The effect on digestate pH of acidified BC when applied mixed into the digestate was not different, except for H2O2, from that of the addition of the respective pure acid to digestate. The total N concentration in digestate was not significantly correlated with NH3-N emissions. These findings indicate that acidified BC could be an effective conditioner to reduce NH3-N emissions from slurry digestate storage.