Biogas Residue Research Articles

Coupling thermophilic composting and vermicomposting processes to remove Cr from biogas residues and produce high value-added biofertilizers

Removing pollutants and producing high value-added products are essential steps for sustainable disposal and utilization of biogas residues. Here, a coupled thermophilic composting and vermicomposting process was used to remove Cr from biogas residues, and the composting products were co-fermented with the plant growth-promoting fungus Trichoderma to produce high value-added biofertilizers. The results showed that thermophilic composting for 37 d markedly increased the total content of Cr but decreased the percentage of available Cr fractions. Synchrotron-radiation-based observations further provided direct evidence of the binding sites to support the results from traditional sequential extraction. At a density of 60 g earthworm/kg biogas residues, vermicomposting removed 23–31% of Cr from biogas residues. After vermicomposting, co-fermentation of biogas residues and Trichoderma was optimized, in which Trichoderma spores were 2–5 × 108 cfu/g substrates. Together, coupling thermophilic composting and vermicomposting processes is a promising technique to remove a portion of heavy metals from biogas residues.

Occurrence, Distribution, and Potential Role of Bacteria and Human Pathogens in Livestock Manure and Digestate: Insights from Guangxi, China

Livestock manure and digestate (biogas slurry [BS] and biogas residue [BR]) contain bacteria that can potentially destroy the environment microecology and affect human health. This is a problem in ...

Acidified Biogas Residues Improve Nutrient Uptake and Growth of Young Maize

Biogas residues (BGR) contain a variety of plant nutrients and are, therefore, valuable fertilizers. However, ammonia (NH3) emissions occur during slurry and BGR application. These emissions can be reduced by lowering the pH of the BGR. Acidification technology works well for slurry, but little is known about the effects on fertilizer properties of acidified BGR (ABGR). This study aimed to examine the impact of acidification on the chemical composition of BGR and its influence on plant growth of juvenile maize and the soil pH, as well as the soluble soil phosphorous (P) and manganese (Mn), after application of ABGR. The soluble amount of nutrients in BGR was compared with that in ABGR. In an outdoor pot experiment, BGR and ABGR were incorporated in soil, and maize was grown for 8 weeks. Two different BGR P levels were compared with (NH4)2HPO4 and a control treatment without additional P. BGR acidification increased dissolved amounts of P from 15% to 44%, calcium from 6% to 59%, magnesium from 7% to 37%, and Mn from 2% to 15%. The dry matter of ABGR-fertilized maize was 34%, 45% higher than that of BGR-fertilized maize. The soluble Mn content in the soil was 74% higher with the low ABGR dose and 222% higher with the higher ABGR dose than the BGR treatments. The fertilizer efficiency of ABGR was higher than that of BGR, indicating that the absolute amount of applied fertilizer could be reduced in systems using ABGR.

Life-cycle assessment of two food waste disposal processes based on anaerobic digestion in China

In the Chinese food waste disposal industry, the choice between using liquid-phase anaerobic digestion or solid–liquid mixed anaerobic digestion to effectively dispose of food waste has become a recent source of debate. However, no previous studies have compared or assessed the relevant technological parameters of these two processes for the same feedstock. In this study, the two processes were evaluated from the perspective of energy consumption and environmental impact. Here, hydrothermal pretreatment, anaerobic digestion, combined heat and power, and waste treatment were considered in the system boundaries. First, a biochemical methane potential test was conducted to obtain the liquid-phase and solid–liquid mixed anaerobic digestion methanogenic potential. Then, using the actual operating parameters of the food waste disposal plant, a life-cycle assessment was performed for the two treatment processes. For solid–liquid mixed and liquid-phase anaerobic digestion processes, the total energy inputs are 182.81 kWh/t and 192.67 kWh/t, respectively, and the net energy inputs accounts for 26.2% and 30.7% of the total energy input, respectively. Compared with solid–liquid mixed anaerobic digestion, liquid-phase anaerobic digestion demonstrates a higher potential for global warming (77.91 vs. 29.24 kg CO2-eq./t), eutrophication (0.4 vs. 0.19 kg PO43--eq./t), acidification (2.61 vs. 1.22 kg SO2-eq./t), and photochemical ozone creation (0.077 vs. 0.03 kg NMVOC-eq./t). According to the sensitivity analysis, the increased efficiency in total-solids degradation of anaerobic digestion and the total-solids content of the biogas residue were found to have a significant effect on the reduction of eutrophication potential, acidification potential, and photochemical ozone creation potential in solid–liquid mixed anaerobic digestion. For liquid-phase anaerobic digestion, the total-solids content of the separated solid phase is an important factor affecting its environmental impact. These results provide important reference values for the development of food waste treatment processes.

Effects of Organic Amendments on the Improvement of Soil Nutrients and Crop Yield in Sandy Soils during a 4-Year Field Experiment in Huang-Huai-Hai Plain, Northern China

To address the low productivity of sandy farmlands, our study aimed to conduct a comparative study on the effects of different organic amendment (OA) inputs for the potential improvement of crop yield and soil quality in sandy alkaline farmlands through the selection of a suitable OA. This study set up straw (ST) returning as control and chemical fertilizer (CF) treatment as a side control, and chose three OAs returning as treatments, including pig manure (PM), biogas residue (BR), and straw biochar (BC), for improving soil fertility, with all amendments having matched doses of nitrogen (N). The experiment was conducted at the Wuqiao Experimental Station (37°41 N, 116°37 E) of China Agricultural University in Hebei Province, China, from October 2012 to September 2016. The cropping rotation was the winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation system. Through a consecutive four-year field experiment, the principal results showed that three types of OA application significantly increased soil organic carbon from 1.46 g kg−1 to 8.24 g kg−1, soil total N from 0.21 g kg−1 to 0.64 g kg−1, soil available potassium from 55.85 mg kg−1 to 288.76 mg kg−1, and soil available phosphate from 4.86 mg kg−1 to 65.00 mg kg−1 in the 0–20 cm soil layer. The BR was the most effective in improving soil nutrients as compared with the ST. The PM and BR treatments were more conducive to promoting crop yield by 6–20% than ST, and the BC treatment significantly reduced the yield of winter wheat by 19% and summer maize by 8%. As the BR and PM treatments improved the soil nutrient content and significantly increased crop yield, these were the top choices for transforming the low-yield sandy farmlands.

Study of Occurrence Characteristics of Antibiotic Resistance Genes in Pig manure during Anaerobic Digestion and Digestate Fertilization

Antibiotic resistance genes (ARGs) existing in livestock and poultry manure have the risk to spread and proliferate. This might endanger people’s health. The common treatment of livestock and poultry manure is anaerobic digestion. But the change of ARGs during anaerobic digestion require further study, and the effect of digestate fertilization to the antibiotic resistance of cropland soil is still unclear. This study investigated the pig manure, biogas liquid, biogas residue, and cropland soils fertilized with and without digestate. The results showed that, the relative abundance of ARGs in biogas residue was much higher than other samples. The average relative abundance was 1.46×10-1 copy ratio (copy of ARG/copy of 16S rRNA gene), and the total relative abundance was 3.07 copy ratio. There were 21 ARGs detected in the 5 samples. 11 of them were shared by the 5 samples. The main ARGs were aminoglycoside, chloramphenicol, sulfonamide, tetracycline, and multidrug. Aminoglycoside had the highest relative abundance, and the total relative abundance in all samples was 1.18 copy ratio. Anaerobic digestion increased the total relative abundance of ARGs in pig manure from 1.14×10-1 to 1.70×10-1 copy ratio. Fertilization of digestate increased the total relative abundance of AGRs in soil from 3.27×10-1 to 7.29×10-1 copy ratio.

Biogas Residue Biochar Enhances Thermophilic Anaerobic Co-Digestion of Sewage Sludge and Food Waste

Biochar addition in anaerobic digestion (AD) systems generally improves the transformation of organic waste and the production of methane, yet little is known on further recycling of the biogas residue into biochar for AD. Here we prepared biogas residue biochar by heating the residue of food waste after AD at 500°C. We comprehensively compared the performance of this biochar with coconut shell biochar and corn stalk biochar on anaerobic co-digestion of sewage sludge and food waste, and explored the corresponding mechanisms. Results show that the biogas residue biochar has the highest mean methane daily yield, of 432.16 mL per g of volatile solids, versus 377.66-386.30 mL for coconut and corn biochars. This finding is in agreement with the structure of biogas residue biochar, whose structure shows more abundant functional groups, especially basic functional groups, which can effectively neutralize fatty acids and alleviate systematic acidification. Results are also supported by characteristics of the biogas residue biochar, which enriched the abundance of electroactive Clostridia , Methanobacterium and Methan o brevibacter in sludge under thermophilic condition, thus shortening the process of methanation.

Synthesis, Characterization and Application of Biogas Residue Biochar for Removal of Hg (II) from Aqueous Solution

Synthesis, Characterization and Application of Biogas Residue Biochar for Removal of Hg (II) from Aqueous Solution

Waste heat recovery from a data centre and 5G smart poles for low-temperature district heating network

The city of Espoo, Finland is planning to develop Kera as a green suburb with high level of energy efficiency and low CO2 emissions, using a high share of renewable energy and recycled or reused energy. For reaching this target, in this study, renewable energy resources such as solar, wind and waste heat are investigated for the study region. Two different technologies comprising heat pump (HP) and heat-only boiler (HOB) are investigated to retrieve waste heat from a data centre and LuxTurrim5G smart poles to use in a low-temperature district heating network. We investigate various scenarios to supply the required energy for the HP (which receives electricity from the electricity market, photovoltaic (PV) system, wind turbine (WT) and hybrid PV/WT; 4 scenarios) and HOB (which works with electricity, forest fuel wood, biogas, ammonia, wood pellets and industry wood residue; 6 scenarios). We found that the heat pump scenario is an efficient and cost-effective way to retrieve waste heat from the data centre and 5G smart poles with an LCOE of 3.192 ¢/kWh if electricity is produced by the PV system, and 3.516 ¢/kWh when the heat pump receives its electricity only from the electricity market.

Simultaneous elimination of H2S and NH3 in a biotrickling filter packed with polyhedral spheres and best efficiency in compost deodorization

With polyhedral spheres as the packing, a semi-pilot biological trickling filter reactor (BTF) inoculated by domesticated activated sludge is used to remove Hydrogen Sulphide (H2S) and Ammonia (NH3). The removal rate of H2S and NH3 by BTF was as high as 98.25% and 88.55%, and the maximum removal load was 84.57 g H2S m−3h−1 and 38.77 g NH3 m−3h−1 during the 61-day process. The inlet gas concentration ranges from 0 to 500 ppm, and the empty bed residence time (EBRT) is 31.8 s. When the EBRT reduced from 31.8s to 25.4s, the removal rate of H2S and NH3 decreased significantly, which was 67.21% and 81.36%, respectively. The results showed that EBRT significantly affected the removal rate of H2S and NH3. Microbial analysis indicated that Dokdonella, Ferruginibacter, Nitrosomonas, and Thiobacillus had high abundance at the genus level, showing that these genera play an important role in the degradation of H2S and NH3. When the optimized parameters applied to the on-site biogas residue compost, the removal rate of H2S and NH3 by BTF can reach 91.34%, which provides a feasible process for the deodorization project with compost.

Effects of substrate types on the transformation of heavy metal speciation and bioavailability in an anaerobic digestion system

Chemical speciation can fundamentally affect the potential toxicity and bioavailability of heavy metals. The transformation of heavy metal speciation and change of bioavailability were investigated in an anaerobic digestion (AD) system using four different substrates (pig manure (PM), cattle manure (CAM), chicken manure (CHM) and rice straw (RS)). The results obtained indicated that the total contents of heavy metals in PM, CHM and CAM were higher than in RS and decreased in the order Zn > Cu > Ni > Pb > As > Cd in all substrates. Moreover, the speciation with the largest proportion for each heavy metal was the same both in the different substrates and the biogas residues. Among them, Zn, Ni, Cd and As were mainly in the reducible fraction (F2), while Cu was mainly in the oxidizable fraction (F3) and Pb occurred predominantly in the residual fraction (F4). Our results further indicated that the AD process had a greater effect on the speciation of heavy metals in CHM and PM, but less on CAM and RS. The rates of change in bioavailability followed the order PM > CHM > CAM > RS. Changes in organic matter, humic acid or local metal ion environment as a result of AD were inferred as likely mechanisms leading to the transformation of heavy metal speciation. These results enhanced our understanding of the behavior of heavy metals in AD and provided a new perspective for the treatment and disposal of the substrates.

Identification and application of Streptomyces microflavus G33 in compost to suppress tomato bacterial wilt disease

Tomato bacterial wilt caused by Ralstonia solanacearum is the most destructive disease impacting production. Application of bioorganic fertilizer (BOF) containing antagonistic microorganism to suppress tomato bacterial wilt disease may be a promising disease control strategy. Here, we used organic waste materials, specifically biogas residues, cattle manure and rice straw, in composting with antagonistic strain G33 isolated from the rhizosphere soil of a healthy tomato plant to produce BOF. Strain G33 was identified as Streptomyces microflavus by morphological and culturing traits and by 16S rRNA gene sequence analysis. We conducted a field experiment with control treatment, organic fertilizer and BOF-G33 to characterize suppression of tomato bacterial wilt disease. Our results indicate that the optimal combination containing (w/w) 40% biogas residues, 40% cattle manure and 20% rice straw can increase the nutrient contents of the compost product, prolong the thermophilic period and increase the decomposition rate of organic matter and the humification degree. A combination of strain G33 and mature compost produced under optimal conditions resulted in the spore number of 5.75 × 109 CFU/g on the sixth day of fermentation. Field experiments showed that BOF-G33 significantly decreased the incidence of tomato wilt; the disease biocontrol efficiency was 64.4%. In addition, application of the BOF-G33 significantly reduced the pathogenic R. solanacearum populations and increased the abundance of beneficial indigenous flora in the rhizosphere soil, which might have been the key factors in constraining the disease. In conclusion, this study showed that bioorganic fertilizer with Streptomyces microflavus G33 is a potential biocontrol agent for controlling tomato bacterial disease.

Consumer Willingness To Pay for Proenvironmental Attributes of Biogas Digestate-Based Potting Soil

Biogas from anaerobic digestion has become an important element in the renewable energy portfolio of many countries. In anaerobic digestion, digestate is produced as a byproduct. This could be used to produce fertilizers and potting soils for home gardeners substituting mineral fertilizers or peat-based products. However, this depends on consumer willingness to pay (WTP) for such products, which we investigate in this study. To this end, we conducted a discrete choice experiment (DCE) with 507 private consumers. From the 6084 decisions made, we derived Bayesian part-worth utilities using a preference share model and so calculated the WTP for different proenvironmental attributes of potting-soil products. We also assessed the influence of proenvironmental attitudes on the WTP. We discovered five distinct consumer groups in our respondents. Some show a significant WTP for proenvironmental attributes such as “organic”, “peat free”, and “without guano”. Three descriptions of digestate as a “renewable resource”, a “fermentation residue”, or a “biogas residue” elicited three markedly different WTP responses across all classes, with “renewable resource” garnering the highest WTP and “biogas residue” the lowest. Consumers with a stronger proenvironmental attitude exhibited a higher WTP for proenvironmental attributes. Our results can help marketers of digestate-based potting soils discover suitable price points for their products and design differentiated pricing strategies across consumer groups.

Pellets from Biogas Digestates: A Substantial Source of N2O Emissions

The field application of pellets from biogas residues resulted in high N2O emissions which could not yet be parametrized through soil drivers. Therefore, the aim of this study was to determine potential N2O production from pellets themselves. N2O and CO2 release from the pure pellet body (in form of intact, crushed or finely ground pellets produced from biogas digestates) were measured during the first seven days after pellet wetting under constant laboratory conditions. Three pellet water contents were examined: 47, 62 and 72% water of the total fresh pellet weight. Additional replicates of similarly wetted intact pellets were used to determine NH4+, NO3− and DOC contents on days 0, 1 and 4 of incubation. Two further treatments of wet intact pellets (62% moisture) were sterilized prior or after moistening to investigate the emissions’ origin. N2O release was found to increase with decreasing pellet size fraction. A maximum of N2O fluxes within all three fractions was determined at 62% moisture, whereas lowest fluxes were measured at 72% moisture. The cumulative N2O emissions over seven days ranged between 1 µg N2O–N g−1 pellet (intact pellets at 72% moisture) and 166 µg N2O–N g−1 pellet (finely ground pellets at 62% moisture). In general, our findings indicate that denitrification was the main factor for N2O emissions, driven by indigenous microbial communities already present in the pellets. The results show that the N2O emissions released by the pellets themselves can explain a major portion of the N2O fluxes measured in situ.Graphic

Characteristics of Ammonia Emissions from Trough Composting of Swine Manure Biogas Residue and Corn Cob

Characteristics of Ammonia Emissions from Trough Composting of Swine Manure Biogas Residue and Corn Cob

Study on pollutant characteristics of different types of manure sludge drying condensate

In order to further study the characteristics of condensate contaminants generated during the drying of livestock manure and biogas residues, the three biogas residues were dried at different temperatures and at different time. The condensate produced in the experiment was collected and its pH, ammonia nitrogen and COD were measured. Exploring the effects of different temperatures and different times on the characteristics of condensate contaminants during the drying of manure sludge. And further comparing the characteristics of different types of biogas residue dry condensate. The results show that: the three biogas residue condensates are weakly alkaline; the three biogas residue condensates COD rises with the increase of drying temperature, the use of low temperature drying can reduce the organic content of the dry condensate; low temperature drying can significantly reduce Exhaust gas treatment load to prevent the loss of organic fertilizer efficiency; with the extension of the drying time, the NH3-N content of the dry condensate of pig manure and chicken manure biogas residues decreased, and the NH3-N content of the dry manure biogas residue dry condensate increased; comprehensive consideration of drying efficiency and drying for the characteristics of condensate. It is recommended that all three kinds of biogas residues be dried at 60°C at low temperature.

Effect of application of different biogas fertilizer on eggplant production: Analysis of fertilizer value and risk assessment

Anaerobic digestion (AD) is an important technology for manure treatment in livestock farms, but when a large amount of biogas slurry (BS), and biogas residues (BR) from large-scale farms are used as fertilizer, there are usually main ways to utilize the raw digestate (untreated BS, and BR), as a bio-based fertilizer. In this study, the effects of direct application of digestate and bio-based ammonium sulfate (AS) fertilizer obtained by ammonia stripping of BS on the cultivation of eggplant and crop yield were compared. Eggplant growth, nitrogen fertilizer efficiency, crop yield, and heavy metals accumulation were studied under the normal-dose application and double-dose application of digestate. In addition, the fertilizer efficiency and safety risk assessments of bio-based AS liquid fertilizer and bio-based AS solid fertilizer were also discussed. A comprehensive comparison of N-fertilizer efficiency and yield showed that the bio-based AS liquid fertilizer had the best fertilizer efficiency, followed by double-dose digestate, and the bio-based AS solid fertilizer, while the normal-dose digestate had poor efficiency. The application effect of bio-based AS liquid fertilizer was closer to the traditional urea N fertilizer. The results showed that compared with the bio-based AS solid fertilizer, the apparent recovery efficiency of N (ARE N ) of eggplant with bio-based AS liquid fertilizer increased by 2.8 times, and the eggplant yield increased by 24.5%. Moreover, the yield of eggplant with bio-based AS liquid fertilizer was increased by 28% compared to the direct application of digestate. Furthermore, no seedling burning and growth inhibition occurred with double application of digestate, but the content of heavy metal (Pb) increased significantly. The results can be used as a reference for understanding the effect of digestate and bio-based AS fertilizer on the cultivation of eggplant and the correlated safety risks assessment. • Comparison of application efficiency of biogas digestate and bio-based AS fertilizer. • Upgraded biofertilizer has the potential to replace digestate and synthetic nitrogen. • No seedling burning or growth inhibition with normal and double-dose of digestate. • Bio-based AS liquid fertilizer has the best comprehensive fertilizer effect. • Double-dose of digestate increases eggplant yield, but the heavy metal risk exists.

Waste-to-resources: Green preparation of magnetic biogas residues-based biochar for effective heavy metal removals

The agricultural wastes disposal and polluted water purification are always the key issues of environmental restoration. In this work, a magnetic biogas residue-based biochar (mBR-C) by direct pyrolysis and sonochemical method was prepared from biogas residue (BR). Response design methodology based on Box-Behnken design was used for the preparation parameters optimization. The characterization results identified that mBR-C had well-developed pore structure and surface area, which was beneficial to diffuse and capture heavy metal ions. Traces of toxic heavy metal in mBR-C was leached (˂0.04 mg/L) through TCLP method, indicating the environmental safety of the magnetic biochar. Meanwhile, the mBR-C exhibited excellent solid-liquid separation efficiency because of its strong magnetism. The series of adsorption experiments indicated that mBR-C could capture Cu2+ and Pb2+ rapidly, and the maximum adsorption capacity for Cu2+ and Pb2+ was 75.76 and 181.82 mg/g, respectively, which was higher than some other biochars previously reported. mBR-C was further applied in the synthetic wastewater treatment, which could effectively purify at least 600 mL (150 BV) to meet emission standards. After several column adsorption-desorption cycles, the adsorption capacity could still reach 85%, implying that mBR-C has good reusability and stability. Overall, the mBR-C can be used as an eco-friendly, desirable, economic and recyclable biosorbent in heavy metal polluted water treatment, providing a new idea for a combination of biogas residue recycle and wastewater treatment.

Biological removal of cadmium from biogas residues during vermicomposting, and the effect of earthworm hydrolysates on Trichoderma guizhouense sporulation

The removal efficiency of Cd from biogas residues (BR) by earthworms (Eisenia fetida) during vermicomposting and the optimum addition of earthworm hydrolysates for production of Trichoderma guizhouense NJAU 4742 spores were determined. The results showed that vermicomposting could effectively remove Cd (up to 18.9%) from the BR. Synchrotron radiation based FTIR spectromicroscopy demonstrated a weakened correlation between functional groups after vermicomposting, suggesting that the activity of earthworms affects the binding sites and bioavailability of heavy metals. Under optimum conditions, the hydrolysis rate of earthworms was ~97% and the removal efficiency of Cd was up to 93%. Furthermore, addition of 20% of earthworm hydrolysate promoted the largest production of Trichoderma sporulation (~2.95 × 108 cfu/g straw), indicating the possibility of earthworm hydrolysates promoting the growth of Trichoderma guizhouense is a suitable way to recycle earthworms after vermicomposting.

Mechanisms of potentially toxic metal removal from biogas residues via vermicomposting revealed by synchrotron radiation-based spectromicroscopies

Biogas residues (BR) contaminated with potentially toxic metals pose environmental risks to soils and food chains, and strategies are needed to decrease the concentration and bioavailability of potentially toxic metals in BR. Here, metal fractions and removal mechanisms were quantified by synchrotron radiation-based Fourier transform infrared and micro X-ray fluorescence spectromicroscopies on BR and earthworms subject to vermicomposting. Vermicomposting resulted in decreases in concentrations of potentially toxic metals in BR and increases in metal removal efficiencies due to uptake by earthworms. Prior to vermicomposting, Zn, Cu and Pb were associated with N-H, O-H, aromatic C, aliphatic C, and amide functional groups, but following maturation during vermicomposting, metals were associated with N-H, O-H, aliphatic C and polysaccharide functional groups. Following vermicomposting, Zn and Cu were mainly distributed in the dermal portions of earthworms, whereas Pb was more homogeneously distributed among the inner and outer portions of the earthworms, revealing that different metals may have different uptake routes. These findings provide a new strategy for safe utilization of BR by using earthworms via vermicomposting to remove potentially toxic metals and in situ insights into how metals binding and distribution characteristics in BR and earthworms during compost and vermicomposting processes.