Resource recovery from pig manure via an integrated approach: A technical and economic assessment for full-scale applications

Enhancing swine manure treatment: A full-scale techno-economic assessment of nitrogen recovery, pure oxygen aeration and effluent polishing

In regions with intensive livestock production, managing the environmental impact of manure is a critical challenge. This study, set in Flanders (Belgium), evaluates the effectiveness of integrating process intensification measures into the treatment of piggery manure to mitigate nitrogen (N) surplus issues. The research investigates the techno-economic benefits of implementing three key interventions: pure oxygen (PO) aeration, ammonia (NH3) stripping-scrubbing (SS) pretreatment, and tertiary treatment using constructed wetlands (CW), within the conventional nitrification-denitrification (NDN) process. Conducted at a full-scale pig manure treatment facility, our analysis employs steady-state mass balances for N and phosphorus (P) to assess the impact of these process intensification strategies. Findings indicate that the incorporation of advanced treatment steps significantly enhances the efficiency and cost-effectiveness of the manure management system. Specifically, the application of PO aeration is shown to reduce overall treatment costs by nearly 4%, while the addition of an NH3 SS unit further decreases expenses by 1-2%, depending on the counter acid utilized. Moreover, the implementation of a CW contributes an additional 4% in cost savings. Collectively, these measures offer substantial improvements in processing capacity, reduction of by-product disposal costs, and generation of additional revenue from high-quality fertilising products. The study highlights the potential of advanced treatment technologies to provide economically viable and environmentally sustainable solutions for manure management in livestock-dense regions, emphasizing the cumulative economic benefit of a holistic approach to process intensification (10%).

Synergistic bioconversion of organic waste by black soldier fly (Hermetia illucens) larvae and thermophilic cellulose-degrading bacteria

Introduction

This study examines the optimum conversion of Wuzhishan pig manure by Black Soldier Fly Larvae (BSFL) at various phases of development, as well as the impact of gut microbiota on conversion efficiency.

Method and results

In terms of conversion efficiency, BSFL outperformed the growing pig stage (GP) group, with significantly higher survival rates (96.75%), fresh weight (0.23 g), and larval conversion rate (19.96%) compared to the other groups. Notably, the GP group showed significant dry matter reductions (43.27%) and improved feed conversion rates (2.17). Nutritional composition varied, with the GP group having a lower organic carbon content. High throughput 16S rRNA sequencing revealed unique profiles, with the GP group exhibiting an excess of Lactobacillus and Clostridium. Promising cellulose-degrading bacteria in pig manure and BSFL intestines, including Bacillus cereus and Bacillus subtilis, showed superior cellulose degradation capabilities. The synergy of these thermophilic bacteria with BSFL greatly increased conversion efficiency. The BSFL1-10 group demonstrated high growth and conversion efficiency under specific conditions, with remarkable larval moisture content (71.11%), residual moisture content (63.20%), and waste reduction rate (42.28%).

Discussion

This study sheds light on the optimal stages for BSFL conversion of pig manure, gut microbiota dynamics, promising thermophilic cellulose-degrading bacteria, and the significant enhancement of efficiency through synergistic interactions. These findings hold great potential for sustainable waste management and efficient biomass conversion, contributing to environmental preservation and resource recovery.

Environmental impact and optimization suggestions of pig manure and wastewater treatment systems from a life cycle perspective

With the rapid development of the pig farming industry in China, a large amount of pig manure is inevitably generated. The management and utilization of pig manure in a sustainable approach require a systematic analysis of the environmental impacts generated from the existing pig manure treatment and disposal routes. In this study, three typical pig manure treatment and disposal routes: pig manure solid-liquid separation, i) wastewater biological treatment, direct land application of manure/sludge; ii) black-film anaerobic digestion of wastewater, mono-composting of manure/sludge and land use; iii) wastewater biological treatment, co-composting of manure/sludge and land use, were comparatively assessed in terms of their environmental impacts using the life cycle assessment. The results show that the added chemicals in wastewater treatment and the consumed electricity in composting the manure/sludge are the two main contributors to all environmental impacts. Thus, using green chemicals, controlling the dosage of added chemicals accurately, and selecting composting types with low energy consumption will significantly reduce the environmental burden of pig manure treatment and disposal routes. For the global warming potential of the evaluated three pig manure treatment and disposal routes, direct emissions of greenhouse gases during the composting process contribute the most, accounting for 77 %, 95 %, and 79 %, respectively. Furthermore, the struvite recovery with anaerobic digestion from pig manure will bring excellent environmental benefits, which will markedly offset the toxicity impacts and carbon emissions derived from pig manure treatment and disposal process. Overall, this work quantitatively evaluates the potential environmental impacts of the existing pig manure treatment and disposal routes, providing insights on optimization for future technical improvement and development.

A thematic review on livestock manure treatment strategies focusing on thermochemical conversion

Livestock manure (LSM) management is emerging as a challenge due to increasing livestock consumption. Owing to the decreased agricultural land area, it is necessary to ensure LSM utilization in non-agricultural fields. LSM can be a valuable resource if managed as a circulating resource. This study discusses research trends based on a literature review and classifies LSM treatments. The analysis of each treatment is presented according to research trends, and implications for the future LSM processing are discussed. "Biological treatment" accounted for the largest portion at 48%, "manure management," which suggests improvement in manure treatment through systematic thinking or LSM management practices, accounted for 16%, and "thermochemical conversion" accounted for 11%. In addition, "life cycle assessment (LCA) research," "solid-liquid separation approach," and "nutrient-recovery/losses" were derived. Studies on biological treatments are increasing. Although anaerobic digestion (AD) is the most used method, it has the disadvantages of long processing time and waste generation after processing. As a key supplement, thermochemical conversion (TCC) technology, which could overcome the disadvantages of AD, was reviewed.

Multi-scale techno-economic assessment of nitrogen recovery systems for livestock operations

Intensive livestock farming generates vast amounts of organic materials, which are an important source of nitrogen releases. These anthropogenic nitrogen releases contribute to multiple environmental problems, including eutrophication of water systems, contamination of drinking water sources, and greenhouse gas emissions. Nitrogen recovery and recycling are technically feasible, and there exists a number of processes for nitrogen recovery from livestock material in the form of different products. In this work, a multi-scale techno-economic assessment of techniques for nitrogen recovery and recycling is performed. The assessment includes a material flow analysis of each process, from material collection to final treatment, to determine nitrogen recovery efficiency, losses, and recovery cost, as well as an environmental cost-benefit analysis to compare the nitrogen recovery cost versus the economic losses derived from its uncontrolled release into the environment. The results show that transmembrane chemisorption process results in the lowest recovery cost, 3.4-10.4 USD per kilogram of nitrogen recovered in the range of studied processing scales. The recovery of nitrogen from livestock material through three technologies, i.e., transmembrane chemisorption, MAPHEX, and stripping in packed bed, reveales to be cost-effective. Since the economic losses due to the harmful effects of nitrogen into the environment are estimated at 32-35 USD per kilogram of nitrogen released, nitrogen recycling is an environmentally and economically beneficial approach to reduce nutrient pollution caused by livestock operations.

Study on anaerobic phosphorus release from pig manure and phosphorus recovery by vivianite method

In this study, pig manure rich in phosphorus was used as the recovery object, In order to realize the maximum recovery of phosphorus resources in pig manure, this study established a phosphorus recovery route combining the electrochemical method with the Vivianite method using sacrificial iron anode. And in order to obtain phosphorus rich supernatant, pig manure was treated with different pH values, and the changes in phosphorus components and metal content in the liquid phase were mainly investigated; Graded phosphorus components and microbial communities in the solid phase; Finally, the effect of electrolytic recovery of phosphorus from fermentation supernatant was studied. The results showed that the highest total phosphorus (TP) content in the liquid phase follows a trend of acidity > control > alkalinity; The analysis of the results of solid-phase phosphorus fractionation extraction shows that acidic conditions are more conducive to the release of Non-apatite inorganic phosphorus (NAIP) and Apatite inorganic phosphorus (AP); The microbial community promotes the release of phosphorus by participating in the decomposition of fermentation substrates; The analysis of the change of metal content in the liquid phase before and after electrolysis showed that the two chamber electrolytic cell can not remove other metal components while recovering the vivianite; More than 90% of the phosphorus in the supernatant after fermentation was recovered by electrolysis. The characterization results showed that 84.66% of the precipitate was Vivianite.

Swine manure treatment technologies as drivers for circular economy in agribusiness: A techno-economic and life cycle assessment approach

Anaerobic digestion has been employed as a technology capable of adding value to waste coupled with environmental impact mitigation. However, many issues need to be elucidated to ensure the systems viability based on this technology. In this sense, the present study evaluated technically, environmentally, and economically, four configurations of swine waste treatment systems focused on the promotion of decarbonization and circularity of the swine chain. For this, a reference plant, based on a compact treatment process named SISTRATES® (Portuguese acronym for swine effluent treatment system) was adopted to serve as a model for comparison and validation. The results showed the importance of prioritization of the energy recuperation routes through anaerobic digestion, providing increased economic benefits and minimizing environmental damage. Thus, the SISTRATES® configuration was the one that presented the best designs in a circular context, maximizing the recovery of energy and nutrients, along with the reduction of greenhouse gas emissions, ensuring the sustainability of the pig production chain.

Comparison of the Ammonia Trapping Performance of Different Gas-Permeable Tubular Membrane System Configurations

The technology of gas-permeable tubular membranes (GPMs) is promising in reducing ammonia emissions from livestock manure, capturing NH₃ in an acidic solution, and obtaining final products suitable for valorization as fertilizers, in line with the principles of the circular economy. This study aimed to evaluate the performance of several e-PTFE membrane systems with different configurations for the recovery of NH₃ released from pig slurry. Ten different configurations were tested: only a submerged membrane, only a suspended membrane in the same chamber, only a suspended membrane in an annex chamber, a submerged membrane + a suspended membrane in the same chamber, and a submerged membrane + a suspended membrane in an annex chamber, considering in each case the scenarios without and with agitation and aeration of the slurry. In all tests, sulfuric acid (1N H₂SO₄) was used as the NH₃ capture solution, which circulated at a flow rate of 2.1 L·h^-1. The results showed that NH₃-N removal rates ranged from 36-39% (for systems with a single submerged or suspended membrane without agitation or aeration of the slurry) to 70-72% for submerged + suspended GPM systems with agitation and aeration. In turn, NH₃-N recovery rates were found to be between 44-54% (for systems with a single membrane suspended in an annex compartment) and 88-91% (for systems based on a single submerged membrane). However, when choosing a system for farm deployment, it is essential to consider not only the capture and recovery performance of the system, but also the investment and operating costs (ranging from 9.8 to 21.2 €/kg N recovered depending on the selected configuration). The overall assessment suggests that the simplest systems, based on a single membrane, may be the most recommendable.

Review on fate and bioavailability of heavy metals during anaerobic digestion and composting of animal manure

Anaerobic digestion and composting are attracting increasing attention due to the increased production of animal manure. It is essential to know about the fate and bioavailability of heavy metals (HMs) for further utilisation of animal manure. This review has systematically summarised the migration of HMs and the transformation of several typical HMs (Cu, Zn, Cd, As, and Pb) during anaerobic digestion and composting. The results showed that organic matter degradation increased the HMs content in biogas residue and compost (with the exception of As in compost). HMs migrated into biogas residue during anaerobic digestion through various mechanisms. Most of HMs in biogas residue and compost exceeded relevant standards. Then, anaerobic digestion increased the bioavailable fractions proportion in Zn and Cd, decreased the F4 proportion, and raised them more than moderate environmental risks. As (III) was the main species in the digester, which extremely increased As toxicity. The increase of F3 proportion in Cu and Pb was due to sulphide formation in biogas residue. Whereas, the high humus content in compost greatly increased the F3 proportion in Cu. The F1 proportion in Zn decreased, but the plant availability of Zn in compost did not reduce significantly. Cd and As mainly converted the bioavailable fractions into stable fractions during composting, but As (V) toxicity needs to be concerned. Moreover, additives are only suitable for animal manure treated with slightly HM contaminated. Therefore, it is necessary to combine more comprehensive methods to improve the manure treatment and make product utilisation safer.

Techno-Economic Assessment of Solid–Liquid Biogas Treatment Plants for the Agro-Industrial Sector

The urgent need to meet climate goals provides unique opportunities to promote small-scale farm anaerobic digesters that valorize on-site wastes for producing renewable electricity and heat, thereby cushioning agribusinesses against energy perturbations. This study explored the economic viability of mono-digestion of cow manure (CWM) and piglet manure (PM) in small manured-based 99 kWel plants using three treatment schemes (TS): (1) typical agricultural biogas plant, (2) a single-stage expanded granular sludge bed (EGSB) reactor, and (3) a multistage EGSB with a continuous stirred tank reactor. The economic evaluation attempted to take advantage of the financial incentives provided by The Renewable Energy Sources Act in Germany. To evaluate these systems, batch tests on raw and solid substrate fractions were conducted. For the liquid fraction, data of continuous tests obtained in a laboratory was employed. The economical evaluation was based on the dynamic indicators of net present value and internal return rate (IRR). Sensitivity analyses of the electricity and heat selling prices and hydraulic retention time were also performed. Furthermore, an incremental analysis of IRR was conducted to determine the most profitable alternative. The most influential variable was electricity selling price, and the most profitable alternatives were TS1 (CWM) > TS1 (PM) > TS3 (CWM). However, further studies on co-digestion using TS3 are recommended because this scheme potentially provides the greatest technical flexibility and highest environmental sustainability.

Recovery of nitrogen and phosphorus from livestock slurry with treatment technologies: A meta-analysis

The livestock industry has developed rapidly in recent decades, but the improper treatment of livestock manure, especially slurry, causes environmental pollution. Treatment technologies are considered to be effective in alleviating nitrogen (N) and phosphorus (P) losses from livestock slurry. Here, we used published research data to conduct a meta-analysis of the recovery efficiencies of N and P of five mainstream treatment technologies, including ammonia stripping, air scrubbing, membrane filtration, microalgae cultivation and struvite crystallization. Additionally, the agronomic effects of the recovered products of these treatment technologies were evaluated. The results showed that all technologies exhibited clear recovery effects on N and P. The N recovery efficiencies ranged from 57% to 86%, and those of P ranged from 64% to 87%. Struvite crystallization was the most efficient treatment technology for both N and P recovery; moreover, the ammonia stripping and microalgae cultivation technologies were less efficient. The pH levels and temperatures are the main factors that influence ammonia stripping, struvite crystallization and microalgae cultivation, while membrane filtration and air scrubbing are mainly affected by the membrane types and properties. When the equal amount of N or P input to fields, the recovered products (ammonium sulfate and struvite crystals) may achieve a similar crop yield, relative to commercial N or P fertilizers. Our findings can provide deep suggestions and parameters for designing proper treatment technologies to reduce nutrient discharge from livestock slurry in regions with high livestock density and also for identifying the research gaps that should be paid more attention in the future.

Phosphorus recovery from wastewater and bio-based waste: an overview

Phosphorus is one of the most important macronutrients needed for the growth of plants. The fertilizer production market uses 80% of natural, non-renewable phosphorus resources in the form of phosphate rock. The depletion of those deposits forces a search for other alternatives, including biological waste. This review aims to indicate the most important ways to recover phosphorus from biowaste, with particular emphasis on wastewater, sewage sludge, manure, slaughter or food waste. A comparison of utilized methods and directions for future research based on the latest research is presented. Combining biological, chemical, and physical methods with thermal treatment appears to be the most effective way for the treatment of wastewater sludge in terms of phosphorus recovery. Hydrothermal, thermochemical, and adsorption on thermally treated adsorbents are characterized by a high phosphorus recovery rate (over 95%). For animal by-products and other biological waste, chemical methods seems to be the most optimal solution with a recovery rate over 96%. Due to its large volume and relatively low phosphorus content, wastewater is a resource that requires additional treatment to recover the highest possible amount of phosphorus. Pretreatment of wastewater with combined methods seems to be a possible way to improve phosphorus recovery. A compressive evaluation of combined methods is crucial for future research in this area.

Maximising Societal Benefit From the Control of Neglected Zoonoses: Identifying Synergies and Trade-Offs in the Control of Taenia solium

Interventions to control or eradicate neglected zoonoses are generally paid for through the public purse and when these interventions focus on the animal hosts, they are often expected to be performed and financed through the state veterinary service. The benefits of control, however, accrue across the human, animal, and environmental spaces and enhance both public and private interests. Additionally, disease control interventions do not take place in a vacuum and the indirect impacts of our actions should also be considered if the societal benefit of interventions is to be maximised. With the caveat that unintended consequences can and will occur, pre-identifying potential synergies and trade-offs in our disease control initiatives allows for them to be considered in intervention design and monitored during programme roll-out. In this paper, using a One Health approach with the example of Taenia solium control, we identify potential indirect impacts which may arise and how these may influence both our choice of intervention and opportunities to optimise the animal, environmental, and societal benefits of control through maximising synergies and minimising trade-offs.

Nutrient recovery from swine wastewater at full-scale: An integrated technical, economic and environmental feasibility assessment

In this study, the technical, economic and environmental attributes of a full-scale nutrient recovery process connected to the centralized swine wastewater treatment facility (CSWTF) were evaluated. The performance of the process was assessed by introducing influent to the recovery reactor from different components of the CSWTF such as sedimentation tank (swine wastewater) and biological treatment reactor (biologically oxidized material and supernatant of the biologically oxidized material). The results of technical performance assessment revealed that the O-P recovery (87.1-90.7%) and NH₄-N removal (66.9-72.1%) efficiencies from the influent of biological treatment reactor were significantly higher than the influent from sedimentation tank (81.7 and 19.8%, respectively, p < 0.05). The economic evaluation elucidated that by increasing the treatment capacity of the recovery reactor from 30 m³/d to 100 m³/d, operating expenses could be covered through the commercialization of struvite, while it would take around seven years to get back the capital investment. Additional economic savings could also be possible when using the recovered struvite as a fertilizer raw material along with other environmental benefits. Considering the current farming practices in Korea, the complete recovery of O-P from CSWTFs as struvite could drop the soil phosphorus surplus by 40%, minimize the phosphatic fertilizer consumption by 6.4% and ultimately reduce CO₂ equivalent emissions of 6522 tons/year in comparison to chemical fertilizer production. However, during the continuous operation of the full-scale nutrient recovery process, influent characteristics need to be incessantly monitored and adjusted to the optimum conditions to improve the economics of recovered products. Overall, the nutrient recovery process at full-scale not only solves the problem of treating highly polluted swine wastewater but also helps to ensure societal and environmental sustainability.

Second-Generation Phosphorus: Recovery from Wastes towards the Sustainability of Production Chains

Phosphorus (P) is essential for life and has a fundamental role in industry and the world food production system. The present work describes different technologies adopted for what is called the second-generation P recovery framework, that encompass the P obtained from residues and wastes. The second-generation P has a high potential to substitute the first-generation P comprising that originally mined from rock phosphates for agricultural production. Several physical, chemical, and biological processes are available for use in second-generation P recovery. They include both concentrating and recovery technologies: (1) chemical extraction using magnesium and calcium precipitating compounds yielding struvite, newberyite and calcium phosphates; (2) thermal treatments like combustion, hydrothermal carbonization, and pyrolysis; (3) nanofiltration and ion exchange methods; (4) electrochemical processes; and (5) biological processes such as composting, algae uptake, and phosphate accumulating microorganisms (PAOs). However, the best technology to use depends on the characteristic of the waste, the purpose of the process, the cost, and the availability of land. The exhaustion of deposits (economic problem) and the accumulation of P (environmental problem) are the main drivers to incentivize the P’s recovery from various wastes. Besides promoting the resource’s safety, the recovery of P introduces the residues as raw materials, closing the productive systems loop and reducing their environmental damage.

Nitrogen recovery from pig slurry by struvite precipitation using a low-cost magnesium oxide

Ammonia nitrogen management is a recurrent problem in intensive livestock areas. Struvite precipitation stands as a mature technology to recover ammonia nitrogen and prevent associated environmental problems. However, the feasibility of struvite technology to recover ammonia nitrogen from pig manure is limited by the reagents cost. This research aimed to optimise the formulation of a stabilizing agent (SA) synthesised using an industrial low-grade MgO by-product (LG-MgO) and phosphoric acid for efficient TAN recovery via struvite precipitation. Experimental results showed that the H₃PO₄/LG-MgO ratio controls the magnesium phosphate mineral phase of the SA (bobierrite and/or newberyite). Newberyite-rich SA showed the highest TAN removal efficiency from pig manure (66-73%) compared to the SA formed by a mixture of newberyite and bobierrite (51-59%) and by bobierrite (26%). Particle size reduction of LG-MgO did not improve the SA's TAN removal efficiency, although XRD patterns showed that the precipitates from the TAN removal experiments contained some unreacted newberyite. The economic analysis showed that the higher reactivity of the SA formulated using higher H₃PO₄/LG-MgO ratios compensated reagent costs. The SA synthesised with a H₃PO₄/LG-MgO ratio of 0.98 showed the most economical treatment cost, which was estimated at 7.5 € per kg of ammonia nitrogen from pig manure. Finally, the optimum SA was successfully synthesised in a 200-L pilot plant, with a TAN removal capacity only 10% lower than the one synthesised at lab-scale.

Assessing the potential for up-cycling recovered resources from anaerobic digestion through microbial protein production

Anaerobic digesters produce biogas, a mixture of predominantly CH4 and CO2 , which is typically incinerated to recover electrical and/or thermal energy. In a context of circular economy, the CH4 and CO2 could be used as chemical feedstock in combination with ammonium from the digestate. Their combination into protein-rich bacterial, used as animal feed additive, could contribute to the ever growing global demand for nutritive protein sources and improve the overall nitrogen efficiency of the current agro- feed/food chain. In this concept, renewable CH4 and H2 can serve as carbon-neutral energy sources for the production of protein-rich cellular biomass, while assimilating and upgrading recovered ammonia from the digestate. This study evaluated the potential of producing sustainable high-quality protein additives in a decentralized way through coupling anaerobic digestion and microbial protein production using methanotrophic and hydrogenotrophic bacteria in an on-farm bioreactor. We show that a practical case digester handling liquid piggery manure, of which the energy content is supplemented for 30% with co-substrates, provides sufficient biogas to allow the subsequent microbial protein as feed production for about 37% of the number of pigs from which the manure was derived. Overall, producing microbial protein on the farm from available methane and ammonia liberated by anaerobic digesters treating manure appears economically and technically feasible within the current range of market prices existing for high-quality protein. The case of producing biomethane for grid injection and upgrading the CO2 with electrolytic hydrogen to microbial protein by means of hydrogen-oxidizing bacteria was also examined but found less attractive at the current production prices of renewable hydrogen. Our calculations show that this route is only of commercial interest if the protein value equals the value of high-value protein additives like fishmeal and if the avoided costs for nutrient removal from the digestate are taken into consideration.

A systematic comparison of commercially produced struvite: Quantities, qualities and soil-maize phosphorus availability

Production of struvite (MgNH₄PO₄·6H₂O) from waste streams is increasingly implemented to recover phosphorus (P), which is listed as a critical raw material in the European Union (EU). To facilitate EU-wide trade of P-containing secondary raw materials such as struvite, the EU issued a revised fertilizer regulation in 2019. A comprehensive overview of the supply of struvite and its quality is presently missing. This study aimed: i) to determine the current EU struvite production volumes, ii) to evaluate all legislated physicochemical characteristics and pathogen content of European struvite against newly set regulatory limits, and iii) to compare not-regulated struvite characteristics. It is estimated that in 2020, between 990 and 1250 ton P are recovered as struvite in the EU. Struvite from 24 European production plants, accounting for 30% of the 80 struvite installations worldwide was sampled. Three samples failed the physicochemical legal limits; one had a P content of <7% and three exceeded the organic carbon content of 3% dry weight (DW). Mineralogical analysis revealed that six samples had a struvite content of 80-90% DW, and 13 samples a content of >90% DW. All samples showed a heavy metal content below the legal limits. Microbiological analyses indicated that struvite may exceed certain legal limits. Differences in morphology and particle size distribution were observed for struvite sourced from digestate (rod shaped; transparent; 82 mass% < 1 mm), dewatering liquor (spherical; opaque; 65 mass% 1-2 mm) and effluent from upflow anaerobic sludge blanket reactor processing potato wastewater (spherical; opaque; 51 mass% < 1 mm and 34 mass% > 2 mm). A uniform soil-plant P-availability pattern of 3.5-6.5 mg P/L soil/d over a 28 days sampling period was observed. No differences for plant biomass yield were observed. In conclusion, the results highlight the suitability of most struvite to enter the EU fertilizer market.

An analysis on determinants of farmers' willingness for resource utilization of livestock manure

The increased manure produced in animal husbandry, especially in beef cattle farming, pose a great threat to the environment. Resource utilization of the manure is an effective way to solve the problem and is conducive to the sustainable development of animal husbandry. Based on the theory of planned behavior, this paper attempts to construct a model of farmers' willingness to utilize livestock manure from behavioral attitude, subjective norm and cognitive behavioral control, and makes an empirical test through a questionnaire on beef cattle farmers. As the findings show, farmers' behavioral attitude, subjective norm and cognitive behavioral control have a significantly positive impact on the resource utilization of the manure. Among them, behavioral attitude exerts the greatest impact, followed by cognitive behavioral control and subjective norm. Farmers surveyed share almost the same attitude towards the effects of resource utilization, who may actively or passively take into consideration the corresponding economic, social and ecological benefits. The pressure from the government plays an important role in farmers' subjective norm, while less pressure comes from village cadres and neighbors. Finally, time or labor endowment and economic strength are the core constraints on the resource utilization of livestock manure by farmers, with relatively little constraint on skill acquisition.

Life Cycle Assessment of Struvite Precipitation from Anaerobically Digested Dairy Manure: A Wisconsin Perspective

Recovering valuable nutrients (e.g., P and N) from waste materials has been extensively investigated at the laboratory scale. Although it has been shown that struvite precipitation from several manure sources contributes to nutrient management practices by recovering valuable nutrients and preventing them from reaching water bodies, it has not been widely applied in commercial (i.e., farm) scales. The purpose of this study is to evaluate the potential environmental impacts of the struvite recovery process from the liquid portion of the anaerobically digested dairy cow manure generated in Wisconsin, USA, dairy farms using life cycle assessment methodology for both bench- and farm-scale scenarios. The struvite precipitation process involves the use of additional chemicals and energy; therefore, investigating upstream impacts is crucial to evaluate the environmental costs and benefits of this additional treatment process. Results indicate that up to a 78% impact decrease in eutrophication potential can be achieved when P and N are recovered in the form of struvite and are applied in lieu of conventional fertilizers, rather than using the liquid portion of the anaerobically digested dairy manure as a fertilizer. Additionally, significant differences are identified in the majority of environmental impact categories when the struvite precipitation process is modeled and evaluated in a farm-scale setting. Future work should expand to evaluate the overall environmental impacts and trade-offs of struvite recovery application, including the anaerobic digestion system itself at the farm scale. Integr Environ Assess Manag 2021;17:292-304. © 2020 SETAC.

Sustainable Swine Manure Management: A Tale of Two Agreements

Intensification and concentration of swine farming has provided economic benefit to rural communities but also negative environmental and human health impacts, particularly from the use of the lagoon-sprayfield system for manure management. Although cost effective, this system is susceptible to poor management, unpleasant odor and other emissions, and inundation during extreme weather events. Competition for manure-spreading acres with other livestock or encroaching development can also pose a problem. This study examines two agreements between industry and government designed to develop and implement improved manure management technologies for swine farms: a voluntary agreement between the attorney general of North Carolina and Smithfield Foods and a consent judgment between the State of Missouri and Premium Standard Farms. Individuals involved in executing these agreements were interviewed to gain insight from their perspective on those processes and lessons they learned from their experience. Common themes among participant responses to support transition processes included the need to involve multiple stakeholder groups, clearly define goals, understand the system, allow time for incremental change, and provide adequate “protected space” for technology development and implementation. Viewing these themes through the lens of multi-level perspective theory identifies leverage points throughout the system to support transitioning farms to a more sustainable path of manure management.

Co-Digestion Biomethane Production and the Effect of Nanoparticle: Kinetics Modeling and Microcalorimetry Studies

To improve the production rate of methane, powder-activated carbon (PAC), granule activated carbon (GAC), titanium dioxide-anatase (TiO₂), and synthesized zeolite (permutit) were added in the co-digestion process. The co-substrates were corn stover (CS) and pig manure (PM) mixed in the ratio of 1:2 (w/w). The kinetic analysis model and ADM1da model were applied to obtain the kinetic parameters of the process. Besides, the heat flow analysis of the co-digestion process was determined using isothermal microcalorimetry. The addition of the PAC, GAC, TiO₂, and synthesized zeolite improved the methane cumulative yield by 40.12, 31.25, 31.17, and 43.74% respectively, as compared with the control reactor. The kinetic analysis and ADM1da model results indicated that the overall rate constant of the co-digestion process increased by 1.5 times averagely because of the effect of these materials. It was also observed that much higher heat energy released from the experimental sample compared with the control reactor, which indicated that the improvement of the metabolic process of the AcoD system. The addition of TiO₂-anatase improved methane production by 31.17%, which could be a promising method to improve the biomethane in a large-scale due to its availability and accessibility.

Pilot-Scale Demonstration of Membrane-Based Nitrogen Recovery from Swine Manure

Gas-permeable membranes technology presents a high potential for nitrogen (N) recovery from wastewaters rich in ammonia (NH₃). The EU project Ammonia Trapping (AT) is aimed at transferring knowledge from the lab-scale level to on-farm pilot-scale level, using this technology to recover NH₃ from livestock wastewaters. The goal of this study is to report the results of an on-farm pilot-scale demonstration plant using gas-permeable membranes to recover N from raw swine manure. After a setup optimization of the plant, stable, and continuous operation was achieved. The maximum NH₃ recovery rate obtained was 38.20 g NH₃-N m⁻² membrane day⁻¹. This recovery rate was greatly affected by the temperature of the process. In addition to its contribution to NH₃ emissions reduction, this technology contributes to the recovery of nutrients in the form of a concentrated stable ammonium sulphate solution. This solution contained 3.2% of N, which makes it suitable for fertigation. The economic approach revealed an economic feasibility of the technology, resulting in a cost of 2.07 € per kg N recovered.

Storage, fertilization and cost properties highlight the potential of dried microbial biomass as organic fertilizer

The transition to sustainable agriculture and horticulture is a societal challenge of global importance. Fertilization with a minimum impact on the environment can facilitate this. Organic fertilizers can play an important role, given their typical release pattern and production through resource recovery. Microbial fertilizers (MFs) constitute an emerging class of organic fertilizers and consist of dried microbial biomass, for instance produced on effluents from the food and beverage industry. In this study, three groups of organisms were tested as MFs: a high-rate consortium aerobic bacteria (CAB), the microalga Arthrospira platensis ('Spirulina') and a purple non-sulfur bacterium (PNSB) Rhodobacter sp. During storage as dry products, the MFs showed light hygroscopic activity, but the mineral and organic fractions remained stable over a storage period of 91 days. For biological tests, a reference organic fertilizer (ROF) was used as positive control, and a commercial organic growing medium (GM) as substrate. The mineralization patterns without and with plants were similar for all MFs and ROF, with more than 70% of the organic nitrogen mineralized in 77 days. In a first fertilization trial with parsley, all MFs showed equal performance compared to ROF, and the plant fresh weight was even higher with CAB fertilization. CAB was subsequently used in a follow-up trial with petunia and resulted in elevated plant height, comparable chlorophyll content and a higher amount of flowers compared to ROF. Finally, a cost estimation for packed GM with supplemented fertilizer indicated that CAB and a blend of CAB/PNSB (85%/15%) were most cost competitive, with an increase of 6% and 7% in cost compared to ROF. In conclusion, as bio-based fertilizers, MFs have the potential to contribute to sustainable plant nutrition, performing as good as a commercially available organic fertilizer, and to a circular economy.

Environmental life cycle comparisons of pig farming integrated with anaerobic digestion and algae-based wastewater treatment

This article shows environmental life cycle comparisons of four scenarios of manure management systems (MMS) for the intensive pig farming systems in terms of materials, transport, energy, and emissions. The MMS scenarios are categorized by different combinations of outside storage, anaerobic mono-/co-digester, and algae-based wastewater treatment (AWWT), where the conventional MMS scenario merely uses the outside storage (Scenario 1) or adopts an integrated anaerobic mono-digester and the outside storage (Scenario 2). The nonconventional MMS scenario uses an integrated anaerobic mono-digester and AWWT process (Scenario 3), notably the harvested algae biomass is used to fully substitute a few ingredients of swine diets. Using life cycle assessment (LCA) methodology, it is validated that Scenario 3 reduces the total environmental impact by 35.5%-40% as compared to Scenarios 1 and 2 and increases the nutrient recovery of nitrogen ratio from 58% (Scenario 1) to 81%. Scenario 4 uses an integrated anaerobic co-digester and AWWT process, where the harvested algae biomass is partially recycled to substitute the partial ingredients of swine diets and the remaining part is fed into the anaerobic co-digester for improving the biogas yield, to increase the algae biomass yield by 49% and also enhance the cogeneration of heat and power by 26.6% and 7%, respectively, as compared to Scenario 3.

Technical, Economic, and Environmental Assessment of a Collective Integrated Treatment System for Energy Recovery and Nutrient Removal from Livestock Manure

The aim of this 5-year study was to evaluate the technical, economic, and environmental performances of a collective-based integrated treatment system for bioenergy production and nutrients removal to improve the utilization efficiency and reduce the environmental impact of land applied livestock manure. The study involved 12 livestock production units located in an intensive livestock area designated as nitrate vulnerable zone with large N surplus. The treatment system consisted of an anaerobic digestion unit, a solid–liquid separation system, and a biological N removal process. Atmospheric emissions and nutrient losses in water and soil were examined for the environmental assessment, while estimated crop removal and nutrient utilization efficiencies were used for the agronomic assessment. The integrated treatment system achieved 49% removal efficiency for total solids (TS), 40% for total Kjeldahl nitrogen (TKN), and 41% for total phosphorous (TP). A surplus of 58kWh/t of treated manure was achieved considering the electricity produced by the biogas plant and consumed by the treatment plant and during transportation of raw and treated manure. A profit of 1.61 €/t manure treated and an average reduction of global warming potential by 70% was also achieved. The acidification potential was reduced by almost 50%. The agronomic use of treated manure eliminated the TKN surplus and reduced the TP surplus by 94%. This collective integrated treatment system can be an environmentally and economically sustainable solution for farms to reduce N surplus in intensive livestock production areas.

Environmental assessment of energy production from anaerobic digestion of pig manure at medium-scale using life cycle assessment

This study assessed the potential environmental effects of energy production from pig manure treatment by anaerobic digestion at medium-scale based on the Life Cycle Assessment of a farm in Puebla, Mexico. It also compared the results from common practices of biogas flaring and conventional management. The analysis was based on one ton of pig manure in 4 systems: two with energy production, one with biogas flaring, and the last one conventional management. The use of biogas for electricity production combined with composting techniques generated the lowest net impacts on climate change of 272 kg CO₂eq and photochemical oxidation of 0.056 kg ethylene eq, while the biogas flaring registered impacts of 344 kg CO₂eq and 0.095 kg ethylene eq. The systems with energy production had environmental benefits on fossil resources depletion by avoiding the consumption of -863 MJ and -1608 MJ, but systems that burned biogas required fossil fuel consumption of 246 MJ from the grid. The conventional management generated the greatest environmental impacts, with eutrophication being the most important negative effect due to the manure discharge into water bodies (5.97 kg PO₄eq). Sensitivity analysis shown that energy production could generate greater impacts on global warming compared to the case in which manure was used directly in crop fields, if emissions from unintentional releases and a poor digestate management are not avoided. Results are relevant for developing countries in which processes are carried out in rural and semi-industrial areas with lack of technical knowledge and economic resources.

Exploiting the unwanted: Sulphate reduction enables phosphate recovery from energy-rich sludge during anaerobic digestion

Anaerobic digestion is shifting from a single-purpose technology for renewable energy recovery from organic waste streams to a process for integrated resource recovery. The valorisation of high-rate energy- and phosphorus-rich sludge creates the opportunity for their combined recovery. This phosphate is present in a precipitated form in the sludge, and its release into the liquid phase is an important issue before recovery can be achieved. The objective of this research was to exploit the "unwanted" sulphate reduction process for the release of phosphate into the liquid phase during anaerobic digestion, thus, making it available for recovery. Two different treatments were considered, i.e., a control digester and a digester to which sulphate was added, each operated in triplicate for a period of 119 days. The control digester showed stable methane production at 628 ± 103 mL CH₄ L^-1 d^-1, with a feedstock COD (chemical oxygen demand) conversion efficiency of 89.5 ± 14.6%. In contrast, the digester with sulphate addition showed a 29.9 ± 15.3% decrease in methane production, reaching an "inhibited steady state", but phosphate release into the liquid phase increased to 58.7 ± 12.9% of total P, a factor 4.5 higher than the control digester. This inhibited steady state coincided with a clear shift from a Methanosaetaceae to a Methanosarcinaceae dominated methanogenic community. Overall, the sulphate reduction process allows phosphate release during the anaerobic digestion process, yet, at the cost of a reduced methane production rate.