Liquid Digestate Research Articles

Anaerobic digestion of chicken manure coupled with ammonia recovery by vacuum-assisted gas-permeable membrane process

To overcome the ammonia inhibition problem during anaerobic digestion of chicken manure, this study used a novel vacuum-assisted gas-permeable membrane (V-GPM) process for ammonia removal from liquid digestate prior to the liquid digestate backflow to the digester. Compared with the typical gas stripping process for ammonia removal, the V-GPM process could avoid several process problems, such as pH and dissolved oxygen increase, which harmed the anaerobic digestion process. Results show that more than 80% of the ammonia can be removed from the liquid digestate within 6 h under the conditions of 70 °C and 30 kPa. The low-ammonia-contained liquid digestate can be recycled to dilute the anaerobic feedstock. During the anaerobic digestion treatment of chicken manure, 75% of the feed solution can be replaced by this low-ammonia-contained liquid digestate. Compared with the case of liquid digestate recycling without ammonia removal, a higher biogas yield is obtained for the ammonia removal case, in which the specific methane production increases from 1.0 L/g-VS to 2.4 L/g-VS. Finally, the economic evaluation indicates that the ammonia recovery process could bring an extra benefit of $ 0.51/kg-N.

Evaluation on thermal treatment for sludge from the liquid digestion of restaurant food waste

During the anaerobic digestion of restaurant food waste, the sludge obtained as the sediment from the liquid digestate (LDS) is a high–yield solid waste. However, its valorization has not attracted sufficient attention. This study systematically detected the physicochemical properties of this sludge, proposed and evaluated thermal strategies of pyrolysis and combustion. Pyrolysis was a mild endothermic process with considerable H2O, CO2, and hydrocarbon releasing, and the LDS-derived biochar had pore structures and abundant functional groups. Combustion was exothermic in a broad temperature interval of 140 °C–580 °C with emissions of H2O, CO2, and NH3, but the process was mild and slow, revealing the poor combustibility of LDS, in addition, the ash had a medium deposition tendency. According to the results obtained in this study, pyrolysis was suggested as a more appropriate method for the reduction and reutilization of LDS. This work will be useful and helpful for LDS valorization, thereby, facilitating the spread and popularization of anaerobic digestion of food waste.

Effects of Organic Energy Crop Rotations and Fertilisation with the Liquid Digestate Phase on Organic Carbon in the Topsoil

Combining organic farming and biogas production from agricultural feedstocks has been suggested as a way of achieving carbon (C) neutrality in Europe. However, as the long-term effects of C removal for methane production on soil organic carbon (SOC) are unclear, organic farmers in particular have questioned whether farm biogas production will have a positive effect on soil fertility. Eight years of data from an organic long-term field trial involving digestate fertilisation and various crop rotations (CRs) with differing proportions of clover-grass leys were used to calculate C inputs based on the CANDY model, and these modelled changes compared with measured changes in SOC content (SOCc) over the same period. Measured SOCc increased by nearly 20% over the eight years. Digestate fertilisation significantly increased SOCc. Fertilised plots with the highest proportion of clover-grass in the CR had the highest SOCc. The C inputs from clover-grass leys, even if they only made up 25% of the CR, were high enough to increase SOCc, even with the removal of all aboveground biomass and without fertilisation. Our results show that biogas production based on clover-grass leys could be an important part of sustainable farming, improving or maintaining SOCc and improving nutrient flows, particularly in organic farming, while simultaneously providing renewable energy.

Expression and characterization of a novel single-chain anti-vascular endothelial growth factor antibody in the goat milk

Vascular endothelial growth factor (VEGF) has essential functions in angiogenesis, endothelial cell proliferation, migration, and tumor invasion. Different approaches have been developed to suppress tumor angiogenesis, which is considered a hallmark of cancer. Anti-VEGF monoclonal antibodies constitute an important strategy for cancer immunotherapy, which has been produced on several platforms. In this study, a novel single-chain anti-VEGF monoclonal antibody (scVEGFmAb) was produced in the goat mammary gland by adenoviral transduction. scVEGFmAb was purified by affinity chromatography. N-glycans were analyzed by exoglycosidase digestion and hydrophilic interaction ultra-performance liquid chromatography coupled to electrospray ionization mass spectrometry. The biological activity of scVEGFmAb was assessed by scratch and mouse aortic ring assays. scVEGFmAb was produced at 0.61 g/L in the goat milk, and its purification rendered 95 % purity. N-glycans attached to scVEGFmAb backbone were mainly neutral biantennary core fucosylated with Galβ1,4GlcNAc motif, and charged structures were capped with Neu5Ac and Neu5Gc. The chimeric molecule significantly prevented cell migration and suppressed microvessel sprouting. These results demonstrated for the first time the feasibility of producing an anti-VEGF therapeutic antibody in the milk of non-transgenic goats with the potential to counteract tumor angiogenesis.

Physico-chemical and multielemental traits of anaerobic digestate from Mediterranean agro-industrial wastes and assessment as fertiliser for citrus nurseries.

Previous researches have demonstrated the bioenergetic potential of agri-food Mediterranean wastes showing that anaerobic co-digestion is a valuable solution for Mediterranean areas. This implies a great interest for anaerobic digestates use in agriculture to replace fertilizers. The present study aimed at: i) producing knowledge on continuous anaerobic co-digestion of feedstock mixture composed by different Mediterranean agri-food wastes in terms of multielemental characterization and ii) assessing the agronomic value of industrial anaerobic digestate (AD) based on the potential as fertiliser in nursery condition for the citrus seedlings. Results have demonstrated that agro-industrial biomasses have great potentiality to be converted by anaerobic digestion in biofertilizer to be used in citrus nurseries as sustainable alternative to mineral fertilisers. Multielemental traits of the tested AD were valuable in terms of nutritional supply for the growth and development of the plant. AD was useful to replace the mineral fertilizers in terms of total N content (10.81±0.32%TS) and organic matter (43.32±0.80%TS). The seedlings nutritive status showed that no need for supplemental of nutrients was requested. Volkamer lemon highly benefited from the administration of liquid digestate, increasing the total chlorophyll level (2.97±0.31mgg-1 FW) presumably due to the higher ammonium content of the AD (59±0.08%TKN). Besides providing useful tools for citrus nurseries for conceiving new sustainable fertilization strategies, this study is a starting point for further in-depth works on physiological status and traits of citrus plants fertilized by using agro-industrial anaerobic digestate.

Lignolytic enzymes (laccase and peroxidase) production by pink oyster mushroom, Pleurotus djamor

This research work attempts the use of biogas digester liquid (BDL) as an inducer for lignolytic enzyme activity by Pleurotus djamor when grown in SSF culture condition. BDL rich in polyphenols and micronutrients can induce lignin degrading enzymes such as laccase and peroxidase. Spraying 100 ml BDL/bag (1kg paddy straw)/day was found to increase yields of Pleurotus djamor in SSF and also reduced the time for various stages of mushroom growth such as pin head formation, fruiting body formation and first flush by 3-5d. Of the 100ml BDL sprayed 70ml was collected as leachate and this showed highlignolytic enzyme (Laccase 150 U/L and Peroxidase 160U/L) activities in SSF and the enzyme activity coincided with the specific mushroom growth stages.

The Use of Flat Ceramic Membranes for Purification of the Liquid Fraction of the Digestate from Municipal Waste Biogas Plants

Due to the rising water deficit in agriculture, digestate is increasingly being considered not only as an alternative fertiliser but also as a potential source of water. The use of recycled water for crop irrigation requires that it be treated in such a way that contaminants from the fermented biomass are not returned to the environment. Membrane processes can provide promising results in this regard. This study seeks to achieve membrane filtration using flat ceramic membranes for effective digestate liquid fraction treatment from a municipal waste biogas plant. Membranes of 1, 5, 15, and 50 kDa, and 0.14 and 0.45 µm are examined. The results obtained show that the application of a sedimentation process, as a preliminary step in the purification of the digestate, allows for a significant reduction in the content of contaminants in the solution. By analysing the effectiveness of the liquid fraction of the digestate purification in the sedimentation-membrane filtration process using flat ceramic membranes, it can be stated that all the membranes tested can be applied in the digestate purification. With an increase in the cut-off value, a deterioration in the quality of the digestate can be observed. The use of the sedimentation process before the membrane process not only improves the final quality of the digestate but also reduces the intensity of membrane fouling.

Effect of Animal Waste Based Digestate Fertilization on Soil Microbial Activities, Greenhouse Gas Emissions and Spring Wheat Productivity in Loam and Sandy Loam Soil

The increasing quantities of organic residues are becoming one of the most important problems for climate change mitigation. Sustainable utilization technologies are required to minimize the effect of recycling on the environment. Nevertheless, treated residues should be part of the circular bioeconomy. One of the most promising processes is the biogas system, with the final products biogas and digestate, which contain valuable nutrients and are therefore suitable as agricultural fertilizers. However, there is lack of research data on the effectiveness of digestate on environmental factors including soil quality as well as crop productivity and quality. In this study, we compare the roles of different digestates (chicken manure digestate, cow manure digestate, and pig manure digestate) on spring wheat productivity, soil microbial activities, and greenhouse gas emissions in loam and sandy loam soil under controlled climate conditions. The liquid digestate applied was equivalent to 170 kg N ha−1 of total N presented. Overall, results showed that the two soil types responded differently to the addition of the digestates, and the benefits depended on soil characteristics as well as on the type of the digestate applied. There was a higher effect on soil microbial activity in sandy loam soil compared to that of loam soil. Chicken manure digestate had the highest value of dehydrogenase activity and soil microbial biomass C of 9.23 µg TPFg−1 h−1 and 175.6 µg g−1 across the two soil types. CO2 and N2O emissions were moderately higher in loam soil when compared to that of sandy loam soil. The highest CO2 peak emission at 0.0107 µg ha−1 h−1 occurred in pig manure digestate in the sandy loam soil, and regular peak patterns observed in loam soil fertilized with pig digestate manure. Chicken manure digestate had the highest peak emissions across both soil types at 0.007950 mg ha−1 h−1 and 0.5667 mg ha−1 h−1 in the loam and sandy loam soil, respectively. The biomass yield varied across the soil types irrespective of the digestate applied. The agricultural benefits of digestates in different receiving soil ecosystems supplying essential nutrients for crop productivity, coupled with its environmental benefits, makes it an encouraging prospect in temperate climate zones.

Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality.

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl− concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality.

Industrial symbiosis of anaerobic digestion and pyrolysis: Performances and agricultural interest of coupling biochar and liquid digestate

The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH4/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 °C, 1 h, and 10 °C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm3, respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates.

Farmyard manure application and associated root proliferation improve the net greenhouse gas balance of Italian ryegrass – Maize double-cropping field in Nasu, Japan

In Japan, most cows are fed indoors, so cow manure must be carefully treated and used to manage soil fertility. The objective of this study was to compare the net greenhouse gas (GHG) balance (NGHGB) of Italian ryegrass – corn (maize) double-cropping fields receiving farmyard manure (FYM), slurry, or methane fermentation digestion liquid (MFDL). FYM, Slurry, MFDL, mineral fertilizer only (Fert.), and no-N control (Cont.) plots were set up in a randomized block design (n = 3). FYM, slurry, or MFDL was applied to meet the K requirement for forage production, and then mineral fertilizers were supplemented to meet the N and P requirements. From September 2017 to September 2020, C inputs as manure and crop residue, heterotrophic respiration (RH), and emissions of methane (CH4) and nitrous oxide (N2O) from soil were determined. The similarity of the total yields in FYM, Slurry, MFDL, and Fert. plots reflected judicious fertility management. However, the residue-C input of Italian ryegrass was 38% greater in FYM plots than in the other plots. Manure-C input decreased in the order of FYM > Slurry > MFDL plots. RH was greater in FYM and Slurry plots than in MFDL plots. Net ecosystem C balance (NECB) ([residue-C + manure-C] − [RH-C + CH4-C]) decreased in the order of FYM > Slurry > MFDL plots. N2O emission was greater in Slurry and MFDL plots than in FYM plots. Consequently, NGHGB ([CH4 and N2O emissions] − NECB) in terms of CO2 equivalent decreased in the order of MFDL > Slurry > FYM plots, so FYM application contributed most to GHG mitigation. Yield-scaled NGHGB was smallest in FYM plots owing to the synergy of the greatest residue-C and manure-C inputs, less N2O emission, and the achievement of a high enough yield, reflecting judicious fertility management based on manure and mineral fertilizer.

Effects of different pretreatment methods on biogas production and microbial community in anaerobic digestion of wheat straw.

The pretreatment of wheat straw has been recognized to be an essential step prior to anaerobic digestion, owing to the high abundance of lignocellulosic materials. In order to choose economical and effective techniques for the disposal of wheat straw, effects of five pretreatment methods including acid, alkali, co-pretreatment of acid and alkali, CaO2, and liquid digestate of municipal sewage sludge on anaerobic digestion of wheat straw were investigated by analyzing biogas production and organic matter degradation in the study. The results showed that among these pretreatment methods, the methane yield was highest in the liquid digestate pretreated-wheat straw with 112.6mL gTS-1, followed by the acid, alkali, and CaO2 pretreatments, and the lowest was observed in the co-pretreatment of acid and alkali. Illumina MiSeq sequencing of the microbial communities in the anaerobic digesters revealed that the genera Ruminiclostridium including Ruminiclostridium and Ruminiclostridium 1, Hydrogenispora, and Capriciproducens were the main hydrolytic bacteria, acidogenic bacteria, and acetogenic bacteria, respectively, in the anaerobic digesters. Capriciproducens and Hydrogenispora dominated in the first and the later stages, respectively, in the anaerobic digesters, which could work as indicators of the anaerobic co-digestion stage of sludge and wheat straw. The total solid and SO42--S contents of the solid digestate and the NH4+-N concentration of the liquid digestate had a significant influence on the microbial community in the digesters. These findings indicated that liquid digestate pretreatment was a potential option to improve the anaerobic digestion of wheat straw, due to the low cost without additional chemical agents.

Coupling of Microalgae Cultivation with Anaerobic Digestion of Poultry Wastes: Toward Sustainable Value Added Bioproducts.

Third generation biofuels and high-value bioproducts produced from microalgal biomass have been considered promising long-term sustainable alternatives for energy and/or food production, potentially decreasing greenhouse gas emissions. Microalgae as a source of biofuels have been widely studied for bioethanol/biodiesel/biogas production. However, critical research is needed in order to increase the efficiency of microalgae production from high-N agri-waste, not only for biofuels but also for bio-based products, and thus enhance its commercial viability. The growth in the poultry industry has led to increased chicken manure (CM), which are rich in ammonia, phosphate, potassium, and other trace elements. These constituents could be used as nutrients for growing microalgae. In this research, a two-stage (liquid–solid) anaerobic digester treating CM at 20 ± 1 °C was performed, and liquid digestate (leachate) obtained after the digestion process was used as a substrate to grow the microalgal strain Chlorella vulgaris CPCC 90. Considering the high-N content (NH3-N: 5314 mg/L; TKN: 6197 mg/L) in liquid digestate, different dilutions were made, using distilled water to obtain viz. 10%, 30%, 50%, 70%, 90%, and 100% of the digestate concentrations for the microalgae cultivation. Preliminary results showed that Chlorella vulgaris CPCC 90 was able to grow and utilize nutrients from a 10% diluted CM digestate. Future research is underway to enhance microalgal growth at higher digestate concentrations and to optimize the use of microalgae/microalgae-bacteria consortia for better adaptation to high-N content wastes. An AD-microalgae coupling scenario has been proposed for the circulation bioeconomy framework.

Enhanced biomethane production from corn straw by a novel anaerobic digestion strategy with mechanochemical pretreatment

The biomethane production from lignocellulose via anaerobic digestion has always suffered from low carbon conversion rate, due to the stubborn structure of lignocellulose and the inefficiency of the current anaerobic digestion systems. The integrated two-phase anaerobic reactor can form a highly efficient anaerobic digestion system with an upper acidogenic phase and a lower methanogenic phase. However, the acidogenic phase can be overaccelerated, leading to acidification failure of the whole digestion system. In this study, the acidogenesis liquid digestate (ALD) generated from the acidogenic phase was applied to impregnate corn straw coupled with disc refining (DR) to enhance biomethane production by forming a thorough and stable integrated two-phase anaerobic system. The concentration of volatile fatty acids in the acidogenic phase is adjusted by this pretreatment technology to approximately match the efficiency of methanogenic bacteria in the methanogenic phase. The acetic acid in ALD was proved to be an effective acid to swell lignocellulose and improved the performance of the acid impregnation coupled with disc refining (AIDR) pretreatment. A 47.13% higher biomethane yield was obtained from corn straw after AIDR pretreatment. Moreover, energy conversion efficiency and economic analysis indicated this anaerobic digestion process with AIDR pretreatment had a $ 21.06 ton−1 higher net profit than that without any pretreatment. This novel anaerobic digestion process creates a synergistic processing technology that integrates biomass pretreatment with a two-phase anaerobic digestion system, resulting in destroying the compact structure of lignocellulose, enhancing biomethane production efficiency, and improving the economic competitiveness of biomass conversion to biomethane.

Digestion liquid based alkaline pretreatment of waste activated sludge promotes methane production from anaerobic digestion

This work proved an efficient method to significantly increase methane production from anaerobic digestion of WAS. This method is to reflux proper of digestion liquid into waste activated sludge pretreatment unit (pH 9.5 for 24 h). The yield of maximum methane improved between 174.2 ± 7.3 and 282.5 ± 14.1 mL/g VSS with the reflux ratio of digestion liquid increasing from 0% to 20%. It was observed that the biodegradable organics in the digestion liquid did not affect the biological processes related to anaerobic digestion but increased methane production through reutilization. The ammonium in the digestion liquid was the main contributor to the increase in methane production via promoting sludge solubilization, but refractory organics were the major inhibitors to anaerobic digestion. It should be emphasized that the metal ions present in the digestion liquid were beneficial rather than harmful to the biological processes in the anaerobic digestion, which may be connected with the fact that certain metal ions were involved in the expression and activation of key enzymes. In addition, it was found that anaerobes in digestion liquid were another potential contributor to the enhanced anaerobic digestion.

Performance Evaluation of a Developed Dried Grass Shredding Machine for Composting

In Nigeria Arable land covers approximately 745,000km2 of the total land area and at present organic farming is not prevalent, encouraged or facilitated despite its sustainability advantages. The anaerobic digestion process produces two main outputs (biogas and digestate). The digestate when properly harnessed can be used as a substitute for inorganic fertilizer. The digestate retains a high content of organic matter such as Nitrogen, Phosphorous and Potassium (K), as well as a range of other macro-and micronutrients like Calcium, Magnesium, Iron, Manganese, Zinc and ammonium. In this research work, a developed grass shredding machine for the composting of a digestate was evaluated for performance. Preliminary studies were undertaken to determine the liquid absorbability of non-shredded grass vise-visa dry shredded grass, the moisture content of fresh elephant and spear grass. An internal combustion powered shredding machine was developed to shred dry and sieve crushed grasses to be used as absorbent of digestate. The machine was evaluated for performance using different samples of properly dried elephant and spear grass. The shredded grasses samples were mixed with discharge digestate collected from a bio-digester to produce organic fertilizer. The shredding time, machine throughout capacity efficiency, mass of fibre and liquor were determined. The results of performance evaluation with elephant grass sample revealed that an average value of efficiency (90.97%), machine through put capacity (1.225g/sec), shredding time (126.54seconds), percentage loss (8.393%), fibre (288.58g) and liquor (119.83g) were established. Similar result were obtained with spear grass; efficiency (90.50%), machine through-put capacity (1.225g/sec), shredding time 126.54 seconds), percentage loss (8.32%), fibre (294.12g), and liquor (118.85g). The outcome of the results revealed that both solid fertilizer (fibre) and liquid fertilizer (liquor) were extracted from the digestate, and an average mass of 138.86g dried grass can absorb 269.55g of liquid digestate to produce organic fertilizer.

Application of Sugar Beet Pulp Digestate as a Soil Amendment in the Production of Energy Maize

This study aimed to determine the suitability of sugar beet pulp digestion by-products as soil amendments for maize grown for energy purposes. In a plot experiment, nitrogen fertilizer at a standard rate of 200 kg N ha−1 was applied as a control vs. treatment with solid and liquid digestate fractions. Digestate was obtained from a gasifier processing only sugar beet pulp. Following harvest, heating and calorific values were determined together with the yield and chemical composition of the maize cob and stover. It was found that soil amendment with crude (unseparated) digestate or its two fractions (separated into liquid and solid) produced higher yields of maize cobs and stover compared with the application of standard fertilizer. An analysis of the energy value of the maize plant revealed differences between the studied soil treatments. Cobs obtained from plots treated with the digestate showed higher calorific and heating values than those obtained from control plots; however, maize stover from control plots showed higher calorific and heating values compared with plants from other experimental plots. It can be concluded that by-products obtained from sugar beet pulp digestion can be alternatively used as a soil amendment for maize production in a crop rotation with sugar beet. Among studied amendments the solid fraction of the digestate was found to have the best performance.

Supplementation of Schwertmannite improves methane production and heavy metal stabilization during anaerobic swine manure treatment

Anaerobic conversion of animal manure to methane is an important bioenergy strategy. However, low methane productivity and heavy metal contamination hamper the sustainability of anaerobic swine manure treatment. In this study, we propose using Schwertmannite (Sch, Fe8O8(OH)4.5(SO4)1.75), a natural Fe-rich waste widely existing in acid mine drainage, to enhance biomethanation of swine manure. Results showed that the addition of 5 g/L Sch to the anaerobic digestion of swine manure loaded with Cu, Zn, and As improved the production of methane in batch and continuous-flow stirred tank reactors by 44.1% and 47.6%, respectively. The positive impact of Sch may be related to the stimulated enrichment of Methanosaeta (from 54.3% to 71.5%) and Methanospirillum (from 2.0% to 5.5%) for methanogenesis and the increased contents of extracellular polymeric substances (>2.6 times), especially aromatic and tryptophan-like proteins, for enhanced substrate degradation and anaerobic microbial aggregates formation. After anaerobic treatment by the addition of Sch, Cu, Zn, and As were dominantly bound to residual fractions and oxidizable fractions in solid digestate, and small amounts accumulated in liquid digestate, indicating that the stabilization of toxic metals in the treated swine manure improved greatly. These results demonstrate that Sch can be utilized as a viable and cost-effective enhancer to improve the anaerobic production of methane from heavy metal-bearing animal manure and reduce the risk of heavy metal pollution.

Agro-Environmental Sustainability of Anaerobic Digestate Fractions in Intensive Cropping Systems: Insights Regarding the Nitrogen Use Efficiency and Crop Performance

Digestate is an anaerobic digestion by-product rich in inorganic-nitrogen (N) that can be used as an organic fertilizer. Digestate agronomic efficiency and its impact on the environment have not yet been studied in detail, therefore this study tries to fill this gap. The agro-environmental sustainability of digestate fractions was evaluated in a holistic way by comparing the best management practices available in the Veneto Region agroecosystem. A farm experiment involving mineral fertilizer and both liquid and solid digestate fractions was established involving silage winter wheat and silage maize as main crops. Agro-environmental sustainability was investigated coupling crop performance analysis (e.g., yield, N uptake and N use efficiency (NUE)) with a novel proposed agro-environmental sustainability index (AESI) (i.e., product of the dry yield and NUE). The results showed that the liquid digestate fraction gave agronomic performances comparable to mineral fertilizers and a satisfying AESI while solid digestate showed lower performances. In conclusion, liquid digestate fractions might be an effective substitute for mineral fertilizers in the Veneto region agroecosystem reaching encouraging levels of agro-environmental sustainability. On the contrary, longer-term experiments are requested to evaluate solid digestate fraction sustainability.

Managing liquid digestate to support the sustainable biogas industry in China: Maximizing biogas‐linked agro‐ecosystem balance

AbstractBiogas industry in China is developing rapidly. This is particularly the case for livestock farm biogas plants, which are built to treat manure and wastewater. Managing the liquid digestate (LD) generated by anaerobic digestion of livestock wastes is becoming a bottleneck, restricting the sustainable development of the biogas industry in China. The separation of livestock breeding and arable farming, caused by rapid intensive animal husbandry development, is the main reason for the LD problem. Researchers, government representatives, and biogas plant operators in China have invested significant research efforts to maximize biogas‐linked agro‐ecosystem balance, which is considered as an important solution to the LD problem. This article reviewed these studies and proposed several solutions from the following four aspects: breeding mode, waste treatment mode, LD transportation mode, and LD utilization mode. One proposal is to reduce the scale of newly built livestock farms and disperse them in farmland, by promoting the “company + agent” livestock breeding mode. In this approach, farm scale would be based on the size of available farmland, and would allow for the use of LD in the near farmland. The second approach involves the intense separation of the livestock slurry and further transportation of the LD produced by the thick slurry. The third one is to expand the possible distances for transferring LD, using a pipe network or vehicle supervised by a professional third party. Finally, the development of high value‐added products and bringing them to market is the ultimate solution for the future.