Hotspots and future trends of phosphorus recycling from livestock manure: A bibliometric review.

In recent decades, the importance of managing the earth's dwindling phosphorus (P) has grown exponentially, as have efforts to develop a circular economy. Livestock manure represents a P-rich waste product, so recycling P from livestock manure has garnered the attention of scholars worldwide. Based on a global database from 1978 to 2021, this study presents the current status of recycling P from livestock manure and proposes strategies for efficient P utilization. Unlike traditional review articles, this work establishes a visual collaborative network on P recycling from livestock manure of research areas, countries, institutions, and authors through a bibliometric analysis using Citespace and VOSviewer software. The co-citation analysis of literature revealed the development of the main research content in this field, and further clustering analysis illustrated the current key research directions. Keyword co-occurrence analysis identified the hotspots and new frontiers of research in this field. According to the results, the United States was the most influential and actively contributing nation, and China was the country with the tightest international ties. The most popular research area was environmental science, and the Bioresource Technology published the largest number of papers in this area. The research priority was the technologies development of P recycling from livestock manure, of which the most used method was struvite precipitation and biochar adsorption. Subsequently, evaluation is also essential, including the economic benefits and environmental impacts of the recycling process by life cycle assessment and substance flow analysis, as well as the agronomic efficiency of the recycled products. New directions for technological innovation in recycling P from livestock manure and potential risks in the recycling process are explored. The results of this study may provide a framework for understanding the mechanisms of P utilization in livestock manure, and support the overall popularization of P recycling technology from livestock manure.

Comparison of phosphorus species in livestock manure and digestate by different detection techniques.

Phosphorus (P) species characterize the effectiveness of the P fertilizer. In this study, the P species and distribution in different manures (pig manure, dairy manure and chicken manure) and their digestate were systematically investigated through combined characterization methods of Hedley fractionation (H2OP, NaHCO3-P, NaOH-P, HCl-P, and Residual), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) techniques. The results from Hedley fractionation showed that >80 % of P in the digestate was inorganic and the HCl-P content in manure increased significantly during anaerobic digestion (AD). XRD manifested that insoluble hydroxyapatite and struvite belonging to HCl-P were presented during AD, which was in agreement with the result of Hedley fractionation. 31P NMR spectral analysis revealed that some orthophosphate monoesters were hydrolyzed during AD, meanwhile the orthophosphate diester organic phosphorus like DNA and phospholipids content has increased. After characterizing P species by combining these methods, it was found that chemical sequential extraction could be an effective way to fully understand the P in livestock manure and digestate, with other methods used as auxiliary tool depending on the purpose of studies. Meanwhile, this study provided a basic knowledge of utilizing digestate as P fertilizer and minimizing the risk of P loss from livestock manure. Overall, applying digestates can minimize the risk of P loss from directly applied livestock manure while satisfying plant demands, and is an environmentally friendly P fertilizer.

Datasets on material properties and energy yields of lab-designed organic fraction of municipal solid waste (OFMSW) components.

The organic fraction of municipal solid waste (OFMSW) is a complex material with different ingredients characterized by varying properties depending on parameters such as season or geographical region of origin. Consequently, studies on OFMSW are hard to compare due to the changing characteristics of the samples. Therefore, this article presents data on the physico-chemical composition of standardized, recipe-based OFMSW components divided into the categories "Paper", "Green waste" and "Food waste", and further subcategories. Data presented in this article include (1) dry matter, (2) organic dry matter, (3) C, H and N concentrations, (4) gross calorific values, (5) ash melting behavior, (6) specific biogas yield and (7) methane concentration. An application example of an experiment requiring the same starting material properties is represented by storage experiments, as performed within the original scientific article [1]. Thus, this Data in Brief article also provides additional data on recipe-based storage experiments complementing the original article. The datasets cannot only be used to estimate biowaste potentials but they can also be used for the design and execution of experiments that require standardized OFMSW samples.

Methane production of banana plant: Yield, kinetics and prediction models influenced by morphological parts, cultivars and ripening stages.

Banana trees and fruits with three ripening stages, including green, ripe, and overripe, of two cultivars, namely Nam wa and Hom were separated into different morphological parts for biogas yield determination. Specific methane yields (SMY) were significant different among banana parts (p ≤ 0.05). High non-structural carbohydrates and high non-lignocellulosic residual in substrates promoted high SMY. Pseudostem showed the highest share of energy yields among farm wastes which Nam wa cultivar provided higher energy potential than Hom. Peel presented the major energy source from fruit wastes which ripening stages did not have a significant effect on its SMY. Modified Gompertz model presented the best fit for methane production of most substrates. The SMY prediction models based on chemical constituents were developed to obtain conveniently used methane estimating tool which showed that a combination of lignin, hemicellulose, non-lignocellulosic residual, and crude fiber contents presented the highest performance for banana substrates.

Two-stage anaerobic digestion: State of technology and perspective roles in future energy systems.

Two-stage anaerobic digestion (TSAD) systems have been studied on a laboratory scale for about 50 years. However, they have not yet reached industrial scale despite their potential for future energy systems. This review provides an analysis of the TSAD technology, including the influence of process parameters on biomass conversion rates. The most common substrate (35.2% of the 38 selected studies) used in the analysed data was in the category of rapidly hydrolysable industrial waste with an average dry matter content of 7.24%. The highest methane content of 85% was reached when digesting food waste in a combination of two mesophilic continuously stirred tank reactors with an acidic (pH 5.5) first stage and alkaline (pH 7) second stage. Therefore, the review shows the limitations of the TSAD technology, future research directions, and the effect of integration of TSAD systems into the current strategy to reduce greenhouse gas emissions.

pH-depended flushing in an automatized batch leach bed reactor system for volatile fatty acid production.

In a two-stage CSTR system, the anaerobic digestion effluent from the second stage (methane reactor) can be used for pH-control in the acidification reactor. But using batch leach bed reactors, controlling the pH-value is key affecting factor due to dynamic process conditions. The aim of this work was to study, an automatized technical-scale leach bed reactor system for VFA-production with pH-dependent flushing. It was developed and tested at mesophilic and thermophilic operating conditions and compared to a time-controlled flushing mode. The reactors were fed with grass silage and the experiments were run for 35 days. Total cumulative VFA yields up to 270 g kg-1VS were achieved and extracted from the reactor. The methane formation in the leach bed reactors was successfully suppressed with a pH-controlled flushing mode. As a result of the extraction of the VFA from the leach bed reactors, the methane potential decreased by up to 50 %.

Response of phosphorus speciation to organic loading rates and temperatures during anaerobic co-digestion of animal manures and wheat straw.

The world is facing huge phosphate (P) shortage and anaerobic digestion (AD) is a recognized technology to promote nutrient (N and P) recycling. The composition of P speciation in the digestate is essential for the fertilizing effect. However, how P speciation in the digestates interacts with the AD process conditions is unknown. Therefore, interaction of P speciation in digestates with AD process conditions was investigated by using a chemical sequential extraction method (Hedley fractionation) and X-ray diffraction; specifically, the effects of organic loading rate (OLR), temperature, and substrate composition were investigated. The results showed that OLR and feedstock affected P speciation in the digestate significantly due to different ion species and ionic strengths. The H2O-P concentration in chicken manure with straw (CMS) and dairy manure with straw (DMS) digestates decreased by 44.04-48.76% and 48.88-50.49%, respectively, as the OLR increased from 2 to 4 kg VS m-3 d-1. Simultaneously, HCl-P increased by 38.02-44.01% in the CMS digestates due to Ca-P and Mg-P formation, indicating that Ca-P and Mg-P formation was positively correlated with OLR, whereas P mobility decreased. Further, thermophilic temperature conditions were more conducive for the formation of insoluble P than mesophilic temperature conditions in the digestates due to the thermodynamic driving force of the reactions. The results would facilitate the understanding of P transformation in the AD process under the influence of feedstock, OLR, and temperature. From the viewpoint of nutrient management, lower OLR and temperature are more beneficial for a fast P availability, whereas higher OLR and temperature are more helpful for storage and export because of P precipitated into solid phase of digestate.

Improving the energetic utilization of household food waste: Impact of temperature and atmosphere during storage.

Food waste (FW) from households represents a major fraction of municipal waste and it is often collected in separate biowaste bins. Until waste collection is carried out, storage conditions in the biowaste bin influence FW properties. To draw conclusions for an optimized waste utilization in anaerobic digestion (AD), the aim of this study was to evaluate the impact of storage duration (20 to 40 days) and temperature (5 °C and 20 °C) on inherent energy potentials of household FW during aerobic and anaerobic storage. Therefore, physico-chemical parameters of recipe-based FW samples with reproducible initial compositions were monitored. After 20 days of aerobic storage, water contents (WC) were reduced from 61.9% to 39.5% (20 °C) and from 63.9% to 50.3% (5 °C) while organic dry matter (oDM) concentrations were lowered by 4.3% (20 °C) and 1.1% (5 °C). Increased pH-values of 6.6 (initially 5.5) were only measured for FW stored aerobically at 20 °C. In total, the energy potential was decreased by 31% (20 °C) and by 16% (5 °C). Thus, storage temperature and duration are crucial parameters for optimized aerobic FW storage leading to higher energy yields in AD. Instead, anaerobic storage of FW decreased pH-values to <5 while increasing WC in all samples (up to 67% at 20 °C). As oDM concentrations were preserved almost completely, the energy potential losses were only marginal proving that energy contents of FW could be preserved at household level. Consequently, energy yields in AD of FW could be increased through anaerobic storage conditions.

Dataset for a full-year time series characterization of separately collected organic fraction of municipal solid waste from rural and urban regions in Germany.

In the municipal context and depending on the collection scheme, different waste streams are of relevance. This article contains year-round data on the chemical composition of organic fractions of municipal solid waste (OFMSW) of rural and urban origins. All samples were collected in the municipality of Tübingen, which is located in southern Germany. The sampling procedure was executed in accordance with standard procedures mentioned in the German Biowaste Ordinance. The data presented in this article include (1) sampling area and process specifications (2) organoleptic examinations (3) dry matter and organic dry matter contents (4) impurity concentrations and (5) elemental compositions (major, minor and trace elements). All datasets are presented as a time series for the year 2018. Thus, this article especially presents the influence of season and settlement structure on the physico-chemical characteristics of OFMSW. Researchers, waste management companies and municipalities can compare and expand their own OFMSW data with those presented in this article. The dataset can also be used to calculate energy yields of OFMSW when utilized in anaerobic digestion. Based on the data, it is also possible to discuss and to evaluate the material utilization of OFMSW-based digestates and compost products, especially with regard to concentrations of major, minor and trace elements. For further discussion, please refer to the original scientific article Sailer et al. (2021).

Characterization of the separately collected organic fraction of municipal solid waste (OFMSW) from rural and urban districts for a one-year period in Germany.

Knowledge on material properties is beneficial to fully exploit inherent utilization potentials of the organic fraction of municipal solid waste (OFMSW). The objective of this study was to analyze and compare the physico-chemical characteristics of separately collected OFMSW (biowaste bin) originating in southwestern Germany. Therefore, 22 rural and 20 urban OFMSW samples, each from the same location were analyzed in the course of one year. Next to the basic characteristics such as the impurity, dry matter (DM) and organic dry matter (oDM) contents, this study focused on the analysis of 37 major, minor and trace elements. In addition, stoichiometric CH4 potentials for the anaerobic digestion were calculated. The fresh mass (FM) based DM contents were significantly (p = 0.001) higher in rural OFMSW (32.86 ± 2.35% vs. 30.50 ± 1.75%) while the DM based oDM content was higher (p = 0.07) in urban OFMSW (84.59 ± 3.90% vs. 82.22 ± 4.16%). The impurities in rural OFMSW were significantly lower (2.83 ± 1.67% DM vs. 5.07 ± 2.71% DM with p = 0.004) while oDM based CH4 potentials were higher for urban OFMSW (533 ± 22 L/kg vs. 519 ± 26L/kg). For both OFMSW types, contents >1000 mg/kgDM were detected for Ca, K, Si, Na, Al, Fe, Mg, P and S while Ti, Mn, Ba, Zn, Sr, Cr, Cu, V, Ni, Li, Pb and B were measured between 1 and 1000 mg/kgDM. The determined element concentrations are useful for an improved classification of OFMSW as a biorefinery resource.

Anaerobic digestion beyond biogas.

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.

Optimal conditions for high solid co-digestion of organic fraction of municipal solid wastes in a leach-bed reactor.

Anaerobic co-digestion of organic fraction of municipal solid waste with solid content greater than 20% and chicken manure was investigated using leach-bed reactors in the framework of Middle East and North African countries. The objectives of the experiments were to determine the optimal ratio of organic fraction, chicken manure and solid inoculum, to compare temperature conditions and usage of liquid inoculum or water in percolation process. The highest specific methane yield (SMY) (236 LN ∙ kg-1 VS) was received in the reactors with 20/80 organic fraction/solid inoculum ratio under thermophilic conditions with liquid inoculum percolation. Under the same conditions but mesophilic temperature, SMY dropped by 12%. Replacing liquid inoculum by water led to 172 LN ∙ kg-1 VS. Addition of chicken manure to the substrate mixture positively influences a start-up phase and keeps pH in optimal range 6.5-8, despite the high ammonia concentration.

Adapted Hedley fractionation for the analysis of inorganic phosphate in biogas digestate.

The major share of phosphate in biogas digestate is inorganic. For optimized nutrient recovery, inorganic phosphate must be analyzed adequately. Therefore, the photometric spectra of extracts from Hedley fractionation were measured and analyzed for their peaks using the molybdenum blue method. The ideal wavelength was 709 nm. The lower calibration limit needed to be raised from 15 µg L-1 to 50 µg L-1 to avoid underestimation of phosphate concentration. Drying digestate before extraction increased H2O-P by 78.4% and NaHCO3-P by 44.9% compared to undried digestate. The filter paper of the filtration between extractions was added to the next extraction to avoid phosphate losses. This made it necessary to rinse the samples with 30 mL deionized H2O after the H2O extraction, with 60 mL NaHCO3 after NaHCO3 extraction and 60 mL NaOH after the NaOH extraction. Ultimately, the results showed that the phosphate concentration in extracts was independent of extraction time.

Effect of residence time during hydrothermal carbonization of biogas digestate on the combustion characteristics of hydrochar and the biogas production of process water.

The biogas digestate from anaerobic digestion of cow manure and energy crops was treated by hydrothermal carbonization (HTC) at 210 °C for 0.5 to 5 h to understand the effect of HTC residence time on the combustion characteristics of hydrochar and the biogas production of process water. The increase in HTC residence time slightly reduced the higher heating values (16.3-16.0 MJ/kg) but improved most slagging and fouling indices of the hydrochar. However, the slagging and fouling during hydrochar combustion were almost impossible to avoid. The specific methane yield of the process water was not significantly influenced by the HTC residence time. Energy assessment demonstrated that HTC for 0.5 h achieved the highest process efficiency and net energy gain when the combustion energy was obtained from hydrochar and CH4 (from process water). Therefore, the HTC condition of 210 °C, 0.5 h is suggested to valorize biogas digestate for energy production.

Biological methanation of injected hydrogen in a two-stage anaerobic digestion process.

In the field of biological hydrogen methanation, ideal process parameters are underexplored for continuous two-stage systems with anaerobic filters. The present study aims at filling this gap for continuous in-situ reactors while applying different hydrogen injection rates. The results of the study demonstrate an almost complete acid degradation on the output side of the anaerobic filter fed by hydrolysate from maize silage and silage effluent. Most of the oxidizable substances were transferred to methane, but hydrogen could not be completely converted. With fully stoichiometric hydrogen addition, a methane production rate of 0.88 ± 0.06 m3d-1 per m3 reactor volume was reached. With half stoichiometric hydrogen addition, a hydrogen conversion rate of 75.53 ± 3.77% was obtained. The present approach proved to be a promising contribution to power-to-gas technology, as a considerable amount of hydrogen had to be converted into methane while carbon dioxide was fixed.

Demand-oriented biogas production and biogas storage in digestate by flexibly feeding a full-scale biogas plant.

This work studied the demand-oriented biogas production and the biogas storage in digestate by flexibly feeding a full-scale research biogas plant. The investigated continuous stirred tank reactor (CSTR) was equipped with a fast-moving submersible motor mixer and a slow-moving inclined shaft agitator. A model for the biogas storage in digestate was introduced and tested in full scale using temporally highly resolved volume flow measurements. An increase in mixing time led to a faster biogas production: A two to five hours reduction of the time to reach the maximum biogas production after feeding occurred in our experiments. However, no influence of the rheology and of the mixing regime on the methane yield could be derived from the measurements. Further, a 30% reduction of the stored biogas in the digestate occurred when the viscosity was lowered by 66%. This knowledge can be used to enhance the existing biogas formation models.

Influence of anaerobic digestion on the labile phosphorus in pig, chicken, and dairy manure.

Phosphorus (P) loss from livestock and poultry industry causes serious threat to agro-ecological environments. Anaerobic digestion (AD), through recycling of P-containing resources and biogas production, prevails as a promising solution to the resource, energy, and environment trilemma. In this study, the dynamic transformation of P in batch AD processes fed with chicken, pig and dairy manures was investigated. Results showed that the Labile-P of total phosphorus (TP) in pig, chicken and dairy manure digestates decreased from 37.35% to 23.79%, 36.79% to 17.29%, and 60.47% to 20.39%, respectively, and was associated with an increase of NaOH-P during the AD process. However, the Labile-P in raw manures ranging from 64.67% to 81.10%, indicated that AD could reduce the pollution risk caused by the overuse of high Labile-P animal manure as fertilizer. Metal ions had a significant influence on P transformation because of their ability to combine with PO43-/HPO42-. During AD, the species of phosphates increased: AlPO4, FePO4, Mg3(PO4)2, CaHPO4, Mg(NH4)PO4·6H2O and Ca10(PO4)6(OH)2 were the main phosphates qualified by X-ray diffraction (XRD). AD produced a satisfactory fertilizer for plants that were able to activate the precipitated P, which could provide readily available N and slow-release P. This study provides a meaningful theoretical guide for recycling P from animal manure resources.

Datasets on chemical composition and anaerobic digestion of organic fraction of municipal solid waste (OFMSW), digested sewage sludge (inoculum) and ashes from incineration or gasification.

This article contains data on the chemical composition and anaerobic digestion of different residue streams including OFMSW, digested sewage sludge, low-carbon (LC) ashes from incineration subdivided into LC coarse and LC fly ash as well as high-carbon (HC) ashes from gasification subdivided into HC reactor and HC fly ash. All materials were collected in accordance to standard procedures in southern Germany. The data presented in this article include (1) dry matter (2) organic dry matter (3) elemental analysis (4) trace elements and (5) cumulative biogas and CH4 yields. Researchers and waste management companies on lab-/pilot-/industrial-scale can rely on the presented data for classification and comparison of biogenic waste streams. For further discussion, please refer to the scientific article entitled "Optimizing anaerobic digestion of organic fraction of municipal solid waste (OFMSW) by using biomass ashes as additives" [ 1 ].

Optimizing anaerobic digestion of organic fraction of municipal solid waste (OFMSW) by using biomass ashes as additives.

The purpose of this study is to test alternative additives for trace element (TE) supplementation and process stabilization during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and sewage sludge. Process instabilities due to acidification are a typical problem in waste fermentation. Provision with minerals and TE is crucial for microorganisms in AD to work effectively, allowing higher organic loading rates within the digester without risking acid accumulation. In batch-fermentation tests, different mixture configurations of OFMSW, digested sewage sludge and biomass ashes were evaluated. Based on an extensive characterization of the TE contained in wood ashes, suitable combinations of digested sewage sludge and OFMSW as a baseline substrate together with ash additives were derived. While high dosages of ash reduced biogas production, 1:1 mix of ash and OFMSW facilitated higher CH4 yields (6%). The supplementation of ashes increased the pH-value within AD and CO2 precipitation through metal oxides in situ elevated the CH4 concentration in biogas up to 98%. Therefore, ashes may increase the efficiency of AD and serve as a basis for a new gas purification method, minimizing technical effort. Additional investigations are needed to examine long-term effects as well as financial and legal aspects such as possible ways of digestate usage. As a further area of research, the transferability of batch-test results into practical applications is identified.