Energy production, nutrient recovery and greenhouse gas emission potentials from integrated pig manure management systems

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.

Optimization of Screw Mixer to Improve Drying Performance of Livestock Manure Dryer Using CFD Analysis

Scarcity of fossil fuels and their emissions of fossil fuel pollutants, such as carbon dioxide, into the atmosphere, and the resulting consequences, have led energy policymakers to look for alternative renewable and clean energy sources. The use of animal wastes is one of the very promising renewable energy alternatives paving the way for a more sustainable energy network. Animal manure produced by livestock farms has a moisture content of about 80%, and such livestock manure is dehydrated to a moisture content of 20–25% and solidified to be used as biomass and fuel for thermal power plants. Previous studies on manure dryers have been concentrated on convection-type dryers, but this type of dryer has the disadvantage of inadequate processing capacity per hour because it cannot agitate manure. In this study, to deal with the drawbacks of conventional livestock manure drying methods, a screw-type dryer was proposed. CFD analysis of the dryer was performed by selecting the viscosity of livestock manure and design parameters of the screw using Ansys Workbench. Through the response surface method, optimal design of the screw shape for the improvement of drying efficiency and smooth discharge of residual manure was carried out.

Agricultural wastes co-densification: A solution for seasonal feedstock storage and anaerobic digestion performance improvement

Rice straw and pig manure pellets (RPP) and sorghum straw and pig manure pellets (SPP) were used to identify their competition as the flexible feedstock of anaerobic digestion with one-year indoor storage. The results indicated the effect of time on their characteristic was tiny during storage period, such as density, calorific value, total solid, volatile solid, ratio of carbon and nitrogen, and lignocellulosic components. Biogas yields of stored RPP and SPP were 8.8% and 26.7% lower than that of fresh pig manure (PM), and 45.4% and 56.1% higher than the sum of corresponding straw and PM digestion alone, respectively. Improvements in biodegradability were observed in co-densified biomass anaerobic digestion. Net biogas yield of RPP was 24.2% higher than that of rice straw, considering volatile matter loss and biogas yield decline during densification and storage stage. Priority of manure and supplement of co-densified biomass were proposed for feedstock supply on demand.

The removal of moisture and antibiotic resistance genes in dairy manure by microwave treatment

To characterize the drying of dairy manure during microwave (MW) heating, and to determine the impacts of microwave radiation on reductions of antibiotic resistance genes (ARGs), this study investigated on understanding the effects of microwave heating on solid streams of flushed dairy manure. A series of experiments were performed to determine the rate of drying, moisture removal percentages, change in solids, and the level of ARGs. Manure was exposed to microwave radiation for 30-300 s at a frequency of 2450 MHz. The results showed moisture removal rate (U) up to 0.63-g water per minute per gram of dairy manure. During MW treatment, volatile solid (VS) content was relatively stable. The MW treatment resulted in reduction of ARGs such as sulII, intI1, and tnpA. The ARG concentrations (sulII, intI1, and tnpA) were reduced by 2 orders of magnitude in less than 1 min of microwave heating. The preliminary results of this study showed that MW treatment can be a viable option for drying of dairy manure and reducing ARGs in manure.

Structure of Microbial Communities When Complementary Effluents Are Anaerobically Digested

Olive oil and pig productions are important industries in Portugal that generate large volumes of wastewater with high organic load and toxicity, raising environmental concerns. The principal objective of this study is to energetically valorize these organic effluents—piggery effluent and olive mill wastewater—through the anaerobic digestion to the biogas/methane production, by means of the effluent complementarity concept. Several mixtures of piggery effluent were tested, with an increasing percentage of olive mill wastewater. The best performance was obtained for samples of piggery effluent alone and in admixture with 30% of OMW, which provided the same volume of biogas (0.8 L, 70% CH4), 63/75% COD removal, and 434/489 L CH4/kg SVin, respectively. The validation of the process was assessed by molecular evaluation through Next Generation Sequencing (NGS) of the 16S rRNA gene. The structure of the microbial communities for both samples, throughout the anaerobic process, was characterized by the predominance of bacterial populations belonging to the phylum Firmicutes, mainly Clostridiales, with Bacteroidetes being the subdominant populations. Archaea populations belonging to the genus Methanosarcina became predominant throughout anaerobic digestion, confirming the formation of methane mainly from acetate, in line with the greatest removal of volatile fatty acids (VFAs) in these samples.

Co-composting of forest and industrial wastes watered with pig manure

Co-composting of forest-derived wastes (chestnut forest burr, CST; scrubland biomass, SRB; industrial sludge, MDFS, from the Medium Density Fibreboard production process) watered with pig manure (PM) may constitute a feasible management technique for both solid and liquid streams. PM provided water and improved the carbon to nitrogen (C/N) ratio. Four piles of 1.8-2.4 m³ were conformed: A (SRB, with compaction bulk density), B (SRB, without compaction), C (SRB and MDFS at a volumetric ratio of 3:1) and D (CST). Thermophilic temperatures were maintained for 8 (B), 16 (A), 28 (C) and 40 (D) days. Stable compost was obtained after 35 (A, B, C) and 48 (D) days. Hygienization was only complete in piles C and D. N losses were higher in piles A (39.3%) and B (33.6%) in relation to C (17.0%) and D (8.9%) which could be attributed to the characteristics of MDFS and CST. Increasing the matrix size from 340 L to around 2000 L led to a higher intensity of the thermophilic phase. Besides, compaction significantly increased the temperature during composting. PM was added at ratios ranging from 1.8 to 2.5 L/kg dry matter, being favoured by pre-drying of solid wastes.

Composting of pig manure and forest green waste amended with industrial sludge

The aim of this research was to study the composting of chestnut forest green waste (FGW) from short rotation chestnut stands amended with sludge resulting from the manufacture of Medium Density Fibreboard (MDFS) and pig manure (PM). Both FGW and MDFS presented low biodegradation potential but different characteristics in granulometry and bulk density that make its mixture of interest to achieve high composting temperatures. PM decreased the C/N ratio of the mixture and increased its moisture content (MC). Three mixtures of MDFS:FGW at volume ratios of 1:1.3 (M2), 1:2.4 (M3) and 0:1 (M4) were composted after increasing its MC to about 70% with PM. A control with food waste (OFW) and FGW (1:2.4 in volume) (M1) was run in parallel. Watering ratios reached 0.25 (M1), 1.08 (M2) 1.56 (M3) and 4.35 (M4) L PM/kg TS of added solids wastes. Treatments M2 and M3 reached a thermophilic phase shorter than M1, whilst M4 remained in the mesophilic range. After 48days of composting, temperature gradients in respect to ambient temperature were reduced, but the mineralization process continued for around 8months. Final reduction in total organic carbon reached 35-56%, depending mainly on the content in MDFS. MDFS addition to composting matrices largely reduced nitrogen losses, which range from 22% (M2) to 37% (M3) and 53% (M4). Final products had high nutrient content, low electrical conductivity and low heavy metal content which make it a valuable product for soil fertilization, right to amend in the chestnut forests and as a pillar of their sustainable management.

The financial attractiveness assessment of large waste management projects registered as clean development mechanism

This study illustrates the financial analyses for demonstration and assessment of additionality presented in the project design (PDD) and enclosed documents of the 431 large Clean Development Mechanisms (CDM) classified as the 'waste handling and disposal sector' (13) over the past ten years (2004-2014). The expected certified emissions reductions (CER) of these projects total 63.54 million metric tons of CO2eq, where eight countries account for 311 projects and 43.36 million metric tons. All of the projects declare themselves 'not financially attractive' without CER with an estimated sum of negative results of approximately a half billion US$. The results indicate that WM benchmarks and indicators are converging and reducing in variance, and the sensitivity analysis reveals that revenues have a greater effect on the financial results. This work concludes that an extensive financial database with simple standards for disclosure would greatly diminish statement problems and make information more comparable, reducing the risk and capital costs of WM projects.

Life cycle assessment of pig slurry treatment technologies for nutrient redistribution in Denmark

Animal slurry management is associated with a range of impacts on fossil resource use and the environment. The impacts are greatest when large amounts of nutrient-rich slurry from livestock production cannot be adequately utilised on adjacent land. To facilitate nutrient redistribution, a range of different technologies are available. This study comprised a life cycle assessment of the environmental impacts from handling 1000 kg of pig slurry ex-animal. Application of untreated pig slurry onto adjacent land was compared with using four different treatment technologies to enable nutrient redistribution before land application: (a) separation by mechanical screw press, (b) screw press separation with composting of the solid fraction, (c) separation by decanter centrifuge, and (d) decanter centrifuge separation with ammonia stripping of the liquid fraction. Emissions were determined based on a combination of values derived from the literature and simulations with the Farm-N model for Danish agricultural and climatic conditions. The environmental impact categories assessed were climate change, freshwater eutrophication, marine eutrophication, terrestrial acidification, natural resource use, and soil carbon, nitrogen and phosphorus storage. In all separation scenarios, the liquid fraction was applied to land on the pig-producing (donor) farm and the solid fraction transported to a recipient farm and utilised for crop production. Separation, especially by centrifuge, was found to result in a lower environmental impact potential than application of untreated slurry to adjacent land. Composting and ammonia stripping either slightly increased or slightly decreased the environmental impact potential, depending on the impact category considered. The relative ranking of scenarios did not change after a sensitivity analysis in which coefficients for field emissions of nitrous oxide, ammonia and phosphorus were varied within the range cited in the literature. Therefore, the best technology to implement in a given situation depends on the environmental problem in question, local policy, cost and practicality.

Modelling the potential of slurry management technologies to reduce the constraints of environmental legislation on pig production

Limits on land applications of slurry nitrogen (N) and phosphorus (P) are used to restrict losses of nutrients caused by livestock production. Here, we used a model to assess technologies that enable a more even geographic distribution of slurry nutrients to land. Technologies included were screw press slurry separation, with or without solid fraction composting, centrifuge separation with or without liquid fraction ammonia (NH3) stripping, and anaerobic digestion. Regulatory constraints were placed first on the application in slurry of N, then P, then N and P both on the producing (donor) and receiving (recipient) farms. Finally, a constraint preventing an increase in donor farm NH3 emissions was imposed. Separation had little effect on N losses per unit mass of slurry, but NH3 stripping led to a reduction. Centrifuge separation allowed a greater increase in pig production than a screw press, especially with P regulation. NH3 stripping was only advantageous with N regulation or when combined with NH3 scrubbing of pig housing ventilation air, when donor farm NH3 emissions were a constraint. There was a production penalty for using composting or anaerobic digestion. The choice of appropriate slurry management option therefore depends on the focus of the regulation. Nuanced and therefore complex regulations are necessary to take advantage of synergies and avoid cross-policy conflicts and incongruencies.

The influence of the pig manure separation system on the energy production potentials

Energy recovery from pig manure offers an opportunity for waste utilisation and financial benefit. Samples of the solid fraction of separated pig manure and samples which had undergone chemical or biological pretreatment prior to separation were pyrolysed. A beech wood sample was pyrolysed for comparison. The chemically pre-treated and anaerobically digested materials had similar properties and showed similar behaviour during thermogravimetric analysis. However, the energy content of the gas arising from pyrolysis in a batch reactor at 600 °C comprises about 30% of the original energy of the feedstock in the case of the anaerobically digested materials and double that of the chemically pre-treated material. Therefore, the overall energy balance showed a loss of 595.9 MJ/t for the pyrolysis of the chemically pre-treated manure, while very small positive values of 351.7 MJ/t, 817.3 MJ/t and a significant value of 8935 MJ/t were found for anaerobically digested sample, un-pretreated solid and for wood, respectively.

Dual purpose microalgae-bacteria-based systems that treat wastewater and produce biodiesel and chemical products within a biorefinery

Excess greenhouse gas emissions and the concomitant effect on global warming have become significant environmental, social and economic threats. In this context, the development of renewable, carbon-neutral and economically feasible biofuels is a driving force for innovation worldwide. A lot of effort has been put into developing biodiesel from microalgae. However, there are still a number of technological, market and policy barriers that are serious obstacles to the economic feasibility and competitiveness of such biofuels. Conversely, there are also a number of business opportunities if the production of such alternative biofuel becomes part of a larger integrated system following the Biorefinery strategy. In this case, other biofuels and chemical products of high added value are produced, contributing to an overall enhancement of the economic viability of the whole integrated system. Additionally, dual purpose microalgae-bacteria-based systems for treating wastewater and production of biofuels and chemical products significantly contribute to a substantial saving in the overall cost of microalgae biomass production. These types of systems could help to improve the competitiveness of biodiesel production from microalgae, according to some recent Life Cycle Analysis studies. Furthermore, they do not compete for fresh water resources for agricultural purposes and add value to treating the wastewater itself. This work reviews the most recent and relevant information about these types of dual purpose systems. Several aspects related to the treatment of municipal and animal wastewater with simultaneous recovery of microalgae with potential for biodiesel production are discussed. The use of pre-treated waste or anaerobic effluents from digested waste as nutrient additives for weak wastewater is reviewed. Isolation and screening of microalgae/cyanobacteria or their consortia from various wastewater streams, and studies related to population dynamics in mixed cultures, are highlighted as very relevant fields of research. The species selection may depend on various factors, such as the biomass and lipid productivity of each strain, the characteristics of the wastewater, the original habitat of the strain and the climatic conditions in the treatment plant, among others. Some alternative technologies aimed at harvesting biomass at a low cost, such as cell immobilization, biofilm formation, flocculation and bio-flocculation, are also reviewed. Finally, a Biorefinery design is presented that integrates the treatment of municipal wastewater with the recovery of oleaginous microalgae, together with the use of seawater supplemented with anaerobically digested piggery waste for cultivating Arthrospira (Spirulina) and producing biogas, biodiesel, hydrogen and other high added value products. Such strategies offer new opportunities for the cost-effective and competitive production of biofuels along with valuable non-fuel products.

Fluidized-bed gasification of dairy manure by Box-Behnken design

Application of excessive animal manure to the land may cause some environmental problems such as eutrophication of surface waters, degradation of ground water quality, and threats to human health. This paper reports an experimental study on the technology of biomass gasification to treat animal waste by analysing the effects of key operating parameters on gasification. In this research, dairy manure from the University of Nebraska dairy farm was first collected and dried, and then gasified in a fluidized-bed, laboratory-scale gasifier to generate syngas. The effects of three parameters, namely temperature, steam to biomass ratio (SBR) and the equivalence ratio (ER), on the gasification were described by a Box-Behnken design (BBD). Results showed that increasing the temperature favoured the formation of all three combustible gases, but the composition of each gas behaved differently according to the changing parameters. The lower heating value of the syngas varied from 2.0 to 4.7 MJ m(-3), indicating gasification could be used as a waste management option to produce bioenergy, and potentially reduce problems associated with the disposal of animal waste.

Escherichia coli inactivation kinetics in anaerobic digestion of dairy manure under moderate, mesophilic and thermophilic temperatures

Batch anaerobic digestion experiments using dairy manure as feedstocks were performed at moderate (25°C), mesophilic (37°C), and thermophilic (52.5°C) temperatures to understand E. coli, an indicator organism for pathogens, inactivation in dairy manure. Incubation periods at 25, 37, and 52.5°C, were 61, 41, and 28 days respectively. Results were used to develop models for predicting E. coli inactivation and survival in anaerobic digestion. For modeling we used the decay of E. coli at each temperature to calculate the first-order inactivation rate coefficients, and these rates were used to formulate the time - temperature - E. coli survival relationships. We found the inactivation rate coefficient at 52.5°C was 17 and 15 times larger than the inactivation rate coefficients at 25 and 37°C, respectively. Decimal reduction times (D10; time to achieve one log removal) at 25, 37, and 52.5°C, were 9 -10, 7 - 8 days, and < 1 day, respectively. The Arrhenius correlation between inactivation rate coefficients and temperatures over the range 25 -52.5°C was developed to understand the impacts of temperature on E. coli inactivation rate. Using this correlation, the time - temperature - E. coli survival relationships were derived. Besides E. coli inactivation, impacts of temperature on biogas production, methane content, pH change, ORP, and solid reduction were also studied. At higher temperatures, biogas production and methane content was greater than that at low temperatures. While at thermophilic temperature pH was increased, at mesophilic and moderate temperatures pH were reduced over the incubation period. These results can be used to understand pathogen inactivation during anaerobic digestion of dairy manure, and impacts of temperatures on performance of anaerobic digesters treating dairy manure.

Carbon, nitrogen, and phosphorus distribution in particle size-fractionated separated pig and cattle slurry

Solid liquid separation of animal slurry is a method to reduce the excess nutrient loads from intensive livestock production. Five different separation technologies (sedimentation, centrifugation, pressurized filtration, polymer flocculation and drainage, and iron chloride addition + polymer flocculation and drainage) were applied to pig and cattle slurry in a laboratory study. Separation efficiencies of mass, dry matter (DM), N, and P were measured. Particle size fractionation of the solid fractions was performed by subjecting them to wet fractionation and C, organic N (N(org)), and P contents were subsequently measured. Chemical pretreatment with polymer before gravity drainage separated DM, total N, and P from raw pig and cattle slurry with the highest efficiencies. Sedimentation and centrifugation separated P from pig and cattle slurries with higher simple separation efficiencies (0.77 and 0.70, respectively) compared with pressurized filtration (0.15 and 0.37). Pressurized filtration transferred the lowest masses (14 and 18%) to the solid fractions. Solid fractions from pig slurry generally contained higher concentrations of P and C compared with cattle slurry solid fractions. The majority of C in solid fractions was present in particles > 25 microm, whereas N and P were present in larger proportions in particles < 25 microm. Chemical pretreatment increased the capture of smaller N(org)- and P-rich particles into larger particles between 25 and 1000 microm.