Dairy and swine manure management - Challenges and perspectives for sustainable treatment technology

Biochar supplementation affects the microbiome of recycled manure solids for cow bedding: A metagenomic analysis

The widespread use of recycled manure solids (RMS) as cow bedding material is not without risks, because cattle manure may act as a vehicle for pathogenic and antimicrobial-resistant bacteria dissemination. Thus, our aim was to evaluate RMS supplemented with a pine biochar produced in Portugal as a new cow bedding material, because the use of biochar has been shown to have the potential to mitigate the effect of relevant bacterial species when added to animal manure microbiota. Our experimental setup consisted on fresh RMS samples that were collected on a commercial dairy farm and placed in naturally-ventilated containers for a total of 4 groups: (1) nonsupplemented RMS, (2) RMS supplemented with 2.5% (wt/wt) of biochar, (3) RMS supplemented with 5% (wt/wt) of biochar, and (4) RMS supplemented with 10% (wt/wt) of biochar. Sampling was performed at 4 different incubation times (0, 5, 15, and 30 d) and in 2 distinct seasons: April through May (humid season) and June through July (dry season). The resulting 32 samples were subjected to DNA extraction and their microbiome profile determined through complete 16S rDNA gene sequencing using Nanopore next-generation sequencing. We observed that biochar supplementation clearly altered the microbiome of RMS, which was reflected in changes in populations' diversity and the relative abundance of relevant pathogenic bacteria. In particular, we found that long-term storage (30 d) was more beneficial than short-term storage, an effect that was more evident for samples supplemented with 2.5% or 5% biochar. In both seasons, those concentrations of biochar led to a decrease in the levels of several mastitis-causing agents (Enterobacteriaceae, streptococci, enterococci, and staphylococci). In addition, we also observed a reduction in the levels of Salmonella spp. and gram-positive bacilli in the biochar-supplemented samples. Unexpectedly, however, those same conditions yielded an increase in the abundance of Brucella spp., a group that includes important infectious agents, highlighting the need for a deeper evaluation of the effect of biochar supplementation of RMS to ensure the future safe and sustainable use of this environmentally-friendly resource in animal production.

Potential of Pine Biochar to Mitigate Bacterial Hazards Present in Recycled Manure Solids from Dairy Cows

The use of recycled manure solids (RMS) as cow bedding in dairy farms poses concerns due to its potential to harbor pathogenic and antimicrobial-resistant bacteria. This study evaluated the impact of RMS supplementation with biochar at three concentrations (2.5%, 5%, and 10%) on bacterial counts and on the antimicrobial resistance and virulence profiles of Escherichia coli and Enterococcus isolates. The results show that biochar supplementation did not promote a significant reduction in bacterial numbers. Overall, there were no significant changes in the isolates' virulence or resistance profiles, and none of the isolates obtained were classified as high or moderate threats based on their MAR and VIR indexes. The most pathogenic Enterococcus isolates found were present in the control samples. A phylogenetic analysis of E. coli isolates allowed us to identify phylogroup D strains, predominantly in RMS supplemented with 2.5% and 10% biochar, which are associated with higher virulence and resistance. These findings indicate that the biochar concentrations tested were not effective in significantly reducing the bacterial risks associated with RMS. Further research is needed to evaluate different biochar formulations and concentrations, aiming to optimize its potential use for RMS supplementation.

Methodological study on carbon sequestration accounting for emission reductions from the whole-chain utilization of livestock and poultry manure

Effective livestock manure management is crucial for carbon neutrality. Scientific accounting methods and integrated management strategies can help guide reductions in carbon emissions and promote green development. To reduce greenhouse gas emissions by livestock manure, this study analyzed current accounting systems and focused on the complete chain of "collection-treatment-storage-use-returning" of manure based on the theoretical framework of greenhouse gas emissions accounting in the IPCC 2019 Guidelines. Combined with a life cycle assessment, the accounting list and boundaries were clarified, and the whole chain of livestock and poultry manure greenhouse gas accounting methodology system was proposed. Using swine breeding as a case study, this study evaluated the carbon emission reduction and sequestration effect of the whole manure chain using a typical technology model and a typical technological framework. It predicted the carbon reduction potential and sequestration benefits of utilizing swine manure in 2025 and 2030 in four scenarios. The findings indicated that the greenhouse gas emission factor of the whole chain of the six typical swine manure utilization modes in China was -48.82-40.54 kgCO2et-1. In 2022, the net greenhouse gas emissions from swine manure in China totaled approximately 2.0 × 107 tCO2e, with manure resource utilization reducing emissions by 3.2 × 107 tCO2e. Our projections suggest that emissions from swine manure in China may range from -1.8 × 107 to 1.3 × 107 tCO2e by 2025 and from -3.1 × 107 to 4.5 × 106 tCO2e by 2030. This can help guide optimal greenhouse gas emission reduction pathways for livestock and poultry farming and aid in the formulation of policies.

The role of geospatial technologies for sustainable livestock manure management: A systematic review

Optimal livestock production is a key contributor to the achievement of sustainable development goals. The management and disposal of livestock manure is one of the main issues facing the sector in terms of soil, water and air pollution. Proper and sustainable management of livestock manure also requires a systemic approach to the problem, considering it at different territorial levels. In order to identify existing strategies to support this issue, this review investigated the use of Geographic Information System (GIS) analysis as a support for livestock manure management, highlighting the several GIS methodologies used to provide insight into the complexity, power, and potential offered by these approaches in study areas with different economic, social, and environmental variables, and to provide insights for future research. The study was performed on 139 papers chosen from a literature screening. Three study themes were identified by co-word analysis: Bioenergy, Environmental pollution and Landscape management/development, with a percentage division of research articles of 38 %, 47 % and 15 %, respectively. This study provides a theoretical and prospective framework for the long-term expansion of the livestock sector, which is critical to promoting a balance between sector development and environmental impact. The use of spatial analysis, along with additional tools and methods such as modelling, multivariate and spatial statistics, life cycle assessment, machine learning and multi-criteria analysis, has proven to be widely applied.

Impact of lowering nitrogen content in pig manure through low crude protein diets on anaerobic digestion process stability, biogas yields, and digestate composition

Lowering crude protein in pig diets can reduce nitrogen (N) excretion and alter manure characteristics. Anaerobic digestion (AD) offers potential for converting pig manure into biogas and bio-based fertilizers (i.e., digestate). However, limited research exists on the effects of N content in pig manure on AD when pigs are fed diets with varying crude protein levels. This study investigated how lowering N content in pig manure through low crude protein diets may affect AD process stability, biogas generation, and digestate properties. Manures from different dietary treatments, named as control (CON), low N (LN), and very low N (VLN), with Total Kjeldahl Nitrogen concentrations of 5.87, 5.42, and 5.15 g/L, respectively, were investigated. Daily biogas production, composition (CH4, CO2, and H2S), and digestate properties were monitored over 13 fed-batch cycles (25 ± 4 days per cycle). The experiment was conducted at 20 ± 1 °C, a condition suited for milder climate regions, using six single-stage digesters operated in sequencing fed-batch mode. Data were analyzed by ANOVA using PROC MIXED with repeated measures. Results showed that the differences in N content in pig manure due to the three dietary treatments had a limited impact on biogas generation, with specific methane yields remaining similar over time. CH4 concentrations remained stable between 60 and 65 %, ensuring high-quality biogas despite dietary variations. Differences between treatments became more pronounced with increased organic loading rates (OLRs) due to variations in the amount of volatile solids fed. AD also remained stable (Total Volatile Fatty Acids/Total Alkalinity <0.25) even at an OLR of 2.15 g of chemical oxygen demand L-1 day-1, highlighting AD's robustness at lower temperatures. Digestate samples contained essential minerals beneficial for plant growth. More research is needed to explore varied manure compositions and feeding strategies to better understand the interactions of animal nutrition with AD.

Elucidating the role of sub-thermophilic temperature and pre-hydrolyzation for effective upgrading scheme of old swine manure digesters

Solids concentration, temperature, and digester configuration were subjected to biomethanation study to identify effective retrofitting schemes for old swine waste digesters. Batch assays were commenced to determine an appropriate scenario at 30-55 °C and total solids 1-3 %TS. Sub-thermophilic temperature (45 °C) was found desirable with an additional 11.1 % methane yield, while digestion at higher TS induced ammonium inhibition. Subsequent batch experiments lasted 72 hrs for hydrolytic-acidogenic assessment under various temperatures. Heating control at 45 °C and 55 °C for 24 hrs increased hydrolysis efficiency 4.6-5.7 folds above control but showed no significant difference (α = 0.05) between them. Limited heat supply from biogas engine dictated the continuous digestion study to operate pre-hydrolysis reactor at maximum temperature of 45 °C. The two-stage strategy demonstrated best overall performances at the sub-thermphilic combination, raising methane yield by 35.4 %. Next-Generation Sequencing indicated remarkable shifts in abundance and diversity, especially for hydrolytic organisms, which expanded from 54 to 70.2 % by sub-thermophilic temperature.

Effective microorganism combinations improve the quality of compost-bedded pack products in heifer barns: exploring pack bacteria-fungi interaction mechanisms

BACKGROUND

Compost-bedded pack barns (CBP) are getting huge attention as an alternative housing system for dairy cows due to their beneficial impact on animal welfare. Effective microorganisms (EM) inoculums are believed to enhance compost quality, improve soil structure and benefit the environment. However, little information is available on the impact of incubation with external EM combinations on the barn environment, compost quality and microbial diversity in CBP. This experiment was carried out to investigate the effect of inoculating different combinations of EM [Lactobacillus plantarum (L), Compound Bacillus (B) and Saccharomyces cerevisiae (S)] on compost quality and microbial communities of CBP products, as well as the relationship with the heifers' barn environment. CBP barns were subjected to the following four treatments: CON with no EM inoculum, LB/LS/LBS were Incubated with weight ratios of 1:2 (L: B), 1:2 (L: S), 1:1:1 (L: B: S), respectively.

RESULTS

The EM inoculation (LB, LS, LBS) reduced the concentration of respirable particulate matter (PM10 and PM2.5) in the CBP, and decreased the serum total protein and total cholesterol levels in heifers. Notably, LBS achieved the highest content of high-density lipoprotein compared to other treatments. Microbiome results revealed that EM inoculation reduced the bacterial abundance (Chao1 index) and fungal diversity (Shannon & Simpson indexes), while increasing the relative abundance of various bacterial genera (Pseudomonas, Paracoccus, Aequorivita) and fungi (Pestalotiopsis), which are associated with cellulose decomposition that ultimately resulted in accelerating organic matter degradation and humification. Furthermore, high nutrient elements (TK&TP) and low mycotoxin content were obtained with EM inoculation, with LBS showing a particularly pronounced effect. Meanwhile, LBS contributed to a decline in the proportion of fungal pathogen categories but also led to an increase in fungal saprotroph categories.

CONCLUSION

Generally, EM inoculation positively impacted compost product quality as organic fertilizer and barn environment by modifying the abundance of cellulolytic bacteria and fungi, while inhibiting the reproduction of pathogenic microbes, especially co-supplementing with L, B and S achieved an amplifying effect.

Phosphorus removal from fermented dairy manure concurrent with polyhydroxybutyrate-co-valerate synthesis under aerobic conditions

Wastewater phosphorus removal achieved biologically is associated with the process known as enhanced biological phosphorus removal (EBPR). In contrast with canonical EBPR operations that employ alternating anaerobic-aerobic conditions and achieve asynchronous carbon and phosphorus storage, research herein focused on phosphorus removal achieved under aerobic conditions synchronously with volatile fatty acid (VFA) storage as polyhydroxybutyrate-co-valerate (PHBV). 90.3 ± 3.4 % soluble phosphorus removal was achieved from dairy manure fermenter liquor; influent and effluent concentrations were 38.6 ± 9.5 and 3.7 ± 0.8 mgP/L, respectively. Concurrently, PHBV yield ranged from 0.17 to 0.64 mgCOD/mgCOD, yielding 147-535 mgCODPHBV/L. No evidence of EBPR mechanisms was observed, nor were canonical phosphorus accumulating organisms present; additionally, the polyphosphate kinase gene was not present in the microbial biomass. Phosphorus removal was primarily associated with biomass growth and secondarily with biomass complexation. Results demonstrate that concurrent PHBV synthesis and phosphorus recovery can be achieved microbially under aerobic dynamic feeding conditions when fed nutrient rich wastewater.

Effect of wheat crops on the persistence and attenuation of antibiotic resistance genes in soil after swine wastewater application

Swine wastewater (SW) application introduces antibiotic resistance genes (ARGs) into farmland soils. However, ARG attenuation in SW-fertigated soils, especially those influenced by staple crops and soil type, remains unclear. This study investigated twelve soil ARGs and one mobile genetic element (MGE) in sandy loam, loam, and silt loam soils before and after SW application in wheat-planted and unplanted soils. The results revealed an immediate increase in the abundance of ARGs in soil by two orders of magnitude above background levels following SW application. After SW application, the soil total ARG abundance was attenuated, reaching background levels at 54 days; However, more individual ARGs were detected above the detection limit than pre-application. Among the 13 genes, acc(6')-lb, tetM, and tetO tended to persist in the soil during wheat harvest. ARG half-lives were up to four times longer in wheat-planted soils than in bare soils. Wheat planting decreased the persistence of acc(6')-lb, ermB, ermF, and intI2 but increased the persistence of others such as sul1 and sul2. Soil type had no significant impact on ARG and MGE fates. Our findings emphasize the need for strategic SW application and the consideration of crop cultivation effects to mitigate ARG accumulation in farmland soils.

Swine manure management by hydrothermal carbonization: Comparative study of batch and continuous operation

Hydrothermal carbonization (HTC) is considered a promising technology for biomass waste management without pre-drying. This study explores the potential for swine manure management by comparing batch and continuous processes, emphasizing the benefits of the continuous mode, particularly for its potential full-scale application. The continuous process at low temperature (180 °C) resulted in a hydrochar with a lower degree of carbonization compared to the batch process, but similar characteristics were found in both hydrochars at higher operating temperatures (230-250 °C), such as C content (∼ 52 wt%), fixed carbon (∼ 24 wt%) and higher calorific value (21 MJ kg-1). Thermogravimetric and combustion analyses showed that hydrochars exhibited characteristics suitable as solid biofuels for industrial use. The process water showed a high content of organic matter as soluble chemical oxygen demand (7-22 g L-1) and total organic carbon (4-10 g L-1), although a high amount of refractory species such as N- and O-containing long aromatic compounds were detected in the process water from the batch process, while the process water from the continuous process presented more easily biodegradable compounds such as acids and alcohols, among others. The longer time required to reach operating temperature in the case of the batch system (longer heating time to reach operating temperature) resulted in lower H/C and O/C ratios compared to hydrochar from the continuous process. This indicates that the dehydration and decarboxylation reactions of the feedstock play a more important role in the batch process. This study shows the efficiency of the continuous process to obtain carbonaceous materials suitable for use as biofuel, providing a solution for swine manure management.

Physico-chemical assessment of on-farm bioconversion of organic waste in dairy farms in context to sustainability and circular bioeconomy

On a milk-producing dairy farm, milk production is correlated with manure production and the number of cattle, and manure is widely used as a soil fertilizer. However, excessive dairy manure production is linked with greenhouse gas emissions and water quality issues. On-farm planning of manure storage and application to enhance soil nutrients are essential in a circular economy to reduce environmental impact, where manure is not landfilled and incinerated. Instead, it creates a nutrient resource for crops and soil. Dairy manure, which is rich in nutrients, is a valuable fertilizer that contains many nutrients such as nitrogen (N), organic matter (OM), phosphorous (P), Potassium (K) and micronutrients. In this work, a pilot field research was conducted between 2016 and 2018 in various parts of California, USA (San Joaquin Valley, Sacramento Valley, Shasta Cascade, and the North Coast of California) to assess physio-chemical characteristics of solid fractions of dairy manure among various dairy farms. A total of 156 samples were collected from the gut (n = 107) and toe (n = 49) of the manure piles across California for determining total solid (TS), volatile solid (VS), temperature, moisture content and carbon-nitrogen ratio (C: N). Here, using the observations of field study and analysis, we show that C: N, OM and MC of solid fractions of dairy manure vary significantly among dairy farms. The average C: N ratio of manure (26-32) among various regions was close to an ideal C: N value of 24:1 for soil microbes to stimulate nutrient release to crops. Manure pH ranged between 7.0 and 8.0, which was close to an optimal pH range for common crops (6.0-8.0). Moreover, considering less cost and surplus availability, manure will likely continue providing a cost-effective organic fertilizer resource compared to commercial chemical fertilizers.

Recycling potassium from cow manure compost can replace potassium fertilizers in paddy rice production systems

The prevalence of K deficiency and negative K balance in rice production increases the demand for K fertilizer. However, the primary source of K fertilizer, potash rock, is limited. Recycling K from cow manure compost (CMC) is a sustainable solution. Nevertheless, the effects of substituting K fertilizer with CMC on rice yield, soil K fertility, and partial K balance (PKB) are not well understood. Therefore, a field experiment with four treatments (control - unfertilized, MNP K - CMC plus NPK fertilizer, MNP ½ K - CMC plus NP and 50 % K fertilizer, and MNP - CMC plus NP fertilizer) was conducted from 2020 to 2022 to study the effects of replacing K fertilizer with K from CMC on rice growth, yield, plant K uptake, soil K fertility, and PKB. The results indicated that K input from CMC exceeded the recommended K fertilizer level, sufficient for optimal rice growth and yield over three growing seasons and plant K uptake in the last two seasons. Plant K uptake increased with total K input and reached a plateau when total K input approached the maximum plant K uptake. In the MNP treatment, PKB was negative in the first two seasons but became positive in the last season, owing to the equivalence between K input from CMC and plant K uptake. Key factors influencing PKB in this treatment were K input from CMC and plant K uptake. Increasing the CMC application rate during the first two seasons could lead to a positive PKB. In this treatment, soil exchangeable K changed correspondingly with PKB, decreasing in the first two seasons but increasing in the last season. Overall, determining the appropriate amount of CMC application for a positive PKB is vital for the sustainability of substituting K fertilizer with K from CMC in paddy rice systems.

Production of Porous Biochar from Cow Dung Using Microwave Process

To valorize livestock manure, the present study investigated the production of biochar from cow dung (CD) by microwave pyrolysis. The pore properties and chemical characteristics of CD and CD-based biochar products were found to correlate with the process parameters like microwave power (300-1000 W) and residence time (5-20 min). The findings indicated that CD is an excellent biomass based on the richness of lignocellulosic constituents from the results of proximate analysis and thermogravimetric analysis (TGA). Higher calorific values were obtained at mild microwave conditions, giving the maximal enhancement factor 139% in comparison with the calorific value of CD (18.97 MJ/kg). Also, it can be concluded that the biochar product obtained at 800 W for a holding time of 5 min had the maximal BET surface area of 127 m2/g and total pore volume of 0.104 cm3/g, which were microporous and mesoporous in the nitrogen adsorption-desorption adsorption analysis. On the other hand, the CD-based biochar contained oxygen-containing functional groups and inorganic minerals based on the spectroscopic analyses by Fourier-transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDS), thus featuring to be prone to hydrophilicity in aqueous solutions.

Hotspots and bottlenecks for the enhancement of the environmental sustainability of pig systems, with emphasis on European pig systems

Although pig systems start from a favourable baseline of environmental impact compared to other livestock systems, there is still scope to reduce their emissions and further mitigate associated impacts, especially in relation to nitrogen and phosphorous emissions. Key environmental impact hotspots of pig production systems are activities associated with feed production and manure management, as well as direct emissions (such as methane) from the animals and energy use. A major contributor to the environmental impacts associated with pig feed is the inclusion of soya in pig diets, especially since European pig systems rely heavily on soya imported from areas of the globe where crop production is associated with significant impacts of land use change, deforestation, carbon emissions, and loss of biodiversity. The "finishing" pig production stage contributes most to these environmental impacts, due to the amount of feed consumed, the efficiency with which feed is utilised, and the amount of manure produced during this stage. By definition therefore, any substantial improvements pig system environmental impact would arise from changes in feed production and manure management. In this paper, we consider potential solutions towards system environmental sustainability at these pig system components, as well as the bottlenecks that inhibit their effective implementation at the desired pace and magnitude. Examples include the quest for alternative protein sources to soya, the limits (perceived or real) to the genetic improvement of pigs, and the implementation of alternative manure management strategies, such as production of biogas through anaerobic digestion. The review identifies and discusses areas that future efforts can focus on, to further advance understanding around the potential sustainability benefits of modifications at various pig system components, and key sustainability trade-offs across the environment-economy-society pillars associated with synergistic and antagonistic effects when joint implementation of multiple solutions is considered. In this way, the review opens a discussion to facilitate the development of holistic decision support tools for pig farm management that account for interactions between the "feed * animal * manure" system components and trade-offs between sustainability priorities (e.g., environmental vs economic performance of pig system; welfare improvements vs environmental impacts).

Occurrence and transformation of heavy metals during swine waste treatment: A full scale study

This study tracked the fate of nine detected heavy metals in an industrial swine farm with integrated waste treatment, including anoxic stabilization, fixed-film anaerobic digestion, anoxic-oxic (A/O), and composting. Results show that heavy metals exhibited different transformation behaviors in the treatment streamline with Fe, Zn, Cu and Mn as the most abundant ones in raw swine waste. The overall removal of water-soluble heavy metals averaged at 30 %, 24 % and 42 % by anoxic stabilization, anaerobic digestion and A/O unit, respectively. In particular, anoxic stabilization could effectively remove Cu, Mn and Ni; while A/O unit was highly effective for Fe, Cr and Zn elimination from water-soluble states. As such, the environmental risk of liquid products for agricultural irrigation decreased gradually to the safe pollution level in swine waste treatment. Furthermore, heavy metals in the solid (slurry) phase of these bioprocesses could be immobilized with the passivation rate in the range of 42-70 %. Nevertheless, heavy metals preferably transformed from liquid to biosolids to remain their environmental risks when biosolids were used as organic fertilizer in agriculture, thereby requiring effective strategies to advance their passivation in all bioprocesses, particularly composting as the last treatment unit.

Frequent export of pig slurry for outside storage reduced methane but not ammonia emissions in cold and warm seasons

Manure management is a significant source of methane (CH4) and ammonia (NH3), and there is an urgent need for strategies to reduce these emissions. More frequent export of manure for outside storage can lower gaseous emissions from housing facilities, but the longer residence time may then increase emissions during outside storage. This study examined CH4 and NH3 emissions from liquid pig manure (pig slurry) removed from the in-house slurry collection pits at three different frequencies, i.e., three times per week (T2.3), once per week (T7), or once after 40 days (T40, reference). The slurry from treatments T2.3 and T7 was transferred for outside storage weekly over four weeks, and slurry from treatment T40 once after 40 days, in connection with summer and winter production cycles with growing-finishing pigs. The slurry was stored in pilot-scale storage tanks with solid cover and continuous ventilation. Compared to T40, the treatments T2.3 and T7 increased CH4 emissions during outside storage, but in-house emissions were reduced even more, and the net effects on total CH4 emissions from manure management (housing unit and outside storage) were reductions of 18-41% in summer and 53-83% in winter. The frequent slurry export for outside storage led to more NH3 emissions, except for the treatment T2.3, which has slurry funnel inserts beneath the slatted floor. Measurements of in-vitro CH4 production rates suggested that shorter residence time for slurry in pig houses delayed the development of active methanogenic populations, and that this contributed to the reduction of CH4 emissions.

Trends in the management of organic swine farm waste by composting: A systematic review

Pig farming contributes to the economic development of nations and supplies human food demand; however, it generates a large amount of organic waste which, if not managed properly, becomes a risk to the environment and human and animal health. Considering the relevance of composting and its usefulness for the use of waste, this study aimed to determine the global trends in the management of composting manure, mortality and other organic waste produced on pig farms over the last five years (2017-2022). Systematic search involved four databases: ISI Web of Science, Scopus, Ebsco and Scielo. Of the total findings, 56 articles were included in the review, further classified into 14 categories for their respective analysis: co-substrates/additives, microbial communities, antibiotic resistance, heavy metals, polycyclic aromatic hydrocarbons, microbiological/parasitological quality, phytopathogens, nitrogen transformation, bioinoculants, comparison/combination with other waste management techniques, factors affecting composting, swine mortality and plant growth promotion/phytotoxicity. The review exemplified the importance of swine mortality composting as an alternative for organic matter management in pig farms, considering that the process also includes manure, vegetable waste and wood chips, among others. Controlled factors throughout the process are a requirement to obtain a stable product with physicochemical and microbiological quality that complies with national and international regulations and that will be useful and safe for application on crops, ensuring environmental, animal, and human health.

Response surface optimization of chemical coagulation for solid-liquid separation of dairy manure slurry through Box-Behnken design with desirability function

Discharging livestock manure slurry without proper treatment causes various environmental and sociological problems. Chemical coagulation is a widely used and easily applicable method for treating such wastewater. However, the technique requires optimization to enhance coagulation efficiency while minimizing chemical usage. In this study, we propose an efficient, low-cost, and environmentally safe chemical coagulation method for solid-liquid separation of dairy manure slurry. Experiments were conducted in laboratory jar tests using dairy manure slurry to investigate the impact of coagulants, specifically polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM), as well as pH, on the process of solid-liquid separation. Preliminary ranges of PAC, CPAM, and pH were estimated through single-factor experiments. Coagulation optimization and modeling were performed using the response surface methodology (RSM) with the Box-Behnken design (BBD), wherein the desired goal of each parameter was set to maximize solid-liquid separation efficiency while reducing chemical dosage to maintain residual aluminum (Al) concentrations below water quality standards. Numerical optimization predicted that the optimal dosages were 75 mg/L of PAC and 35 mg/L of CPAM at pH 7. Under these conditions, removal efficiencies of 99% for turbidity and 97% for chemical oxygen demand (COD) were achieved, with a minimal residual Al concentration of 0.045 mg/L. Positive zeta potential values in the treated water confirmed complete separation of negatively charged solids in the dairy manure slurry. The response values predicted by BBD aligned with the experimental results, and the analysis of variance (ANOVA) demonstrated the predictability and accuracy of the response models. Consequently, this study highlights the practical application of RSM with BBD in optimizing chemical coagulation using PAC and CPAM to achieve efficient solid-liquid separation in livestock wastewater while maintaining low residual Al concentrations.

Feasibility of Bio-Coagulation Dewatering Followed by Bio-Oxidation Process for Treating Swine Wastewater

The unsatisfactory performance of the conventional swine wastewater treatment is drawing increasing attention due to the large amount of refractory chemical oxygen demand (COD), nitrogen, and phosphorus attached to the suspended solids (SS). In this study, for the first time, a novel process based on bio-coagulation dewatering followed by a bio-oxidation (BDBO) system was developed to treat swine wastewater containing high-strength SS, COD, TN, and TP. Firstly, after the bio-coagulation process, the removal efficiencies of SS, COD, NH3-N, and TP reached as high as 99.94%, 98.09%, 61.19%, and 99.92%, respectively. Secondly, the filtrate of the bio-coagulation dewatering process was introduced into the subsequent bio-oxidation process, in which the residual COD and NH3-N were further biodegraded in a sequence batch reactor. In addition, the dewatering performance of the concentrated swine slurry was substantially improved, with the specific resistance to filtration decreasing from 17.0 × 1012 to 0.3 × 1012 m/kg. Moreover, the concentrated swine slurry was pressed and filtered into a semi-dry cake after pilot-scale bio-coagulation dewatering treatment. Finally, the concentrations of COD and NH3-N in the effluent after the BDBO process, ranging between 150-170 mg/L and 75-90 mg/L, met the relevant discharge standard. Compared to traditional treatments, the BDBO system has excellent large-scale potential for improving the treatment efficiency, shortening the operation period, and reducing the processing costs, and is emerging as a cost-effective alternative for the treatment of wastewater containing high concentrations of SS, COD, TN, and TP.

Low-Temperature Pretreatment of Biomass for Enhancing Biogas Production: A Review

Low-temperature pretreatment (LTPT, Temp. < 100 °C or 140 °C) has the advantages of low input, simplicity, and energy saving, which makes engineering easy to use for improving biogas production. However, compared with high-temperature pretreatment (>150 °C) that can destroy recalcitrant polymerized matter in biomass, the action mechanism of heat treatment of biomass is unclear. Improving LTPT on biogas yield is often influenced by feedstock type, treatment temperature, exposure time, and fermentation conditions. Such as, even when belonging to the same algal biomass, the response to LTPT varies between species. Therefore, forming a unified method for LTPT to be applied in practice is difficult. This review focuses on the LTPT used in different biomass materials to improve anaerobic digestion performance, including food waste, sludge, animal manure, algae, straw, etc. It also discusses the challenge and cost issues faced during LTPT application according to the energy balance and proposes some proposals for economically promoting the implementation of LTPT.

Valorization of pretreated biogas digestate with black soldier fly (Hermetia illucens, L; Diptera: Stratiomyidae) larvae

Increasing concerns related to the negative environmental impacts of food waste havemotivated the development of new solutions to complete the waste cycle of organic residues. One particular "waste" product, the solid digestate from anaerobic digestion, has been identified for further bioprocessing. Black soldier fly (BSF, Hermetia illucens) larvae are known for their great potential in the processing of organic waste. In this study, this potential was investigated to further process the digestate waste stream. Digestate is considered a low potential source of nutrients for larvae due to the presence of different fiber fractions. However, the lignocellulosic matter in this residue could be enzymatically hydrolyzed to release residual carbohydrates. For this study, digestate from a full-scale anaerobic digestion plant in Quebec (Canada) which processes a range of feedstocks (fruits, vegetables, garden wastes, sludge derived from dairy processing and wastewater treatment) was sourced. Digestate was treated with Accelerase® DUET enzyme complex to hydrolyze lignocellulosic matter and compared to a standard diet. For each treatment, 600 four-day old larvae were fed daily with 160 g (70% relative humidity) of diets for 6 days and harvested 3 days later. Although their growth and total biomass were significantly lower than the standard diet, larvae fed on hydrolyzed digestate were almost two times larger than the larvae fed on crude digestate. Furthermore, the content of organic matter, lipids and minerals in the diets and frass were analyzed. Finally, the feasibility of applying BSF treatment for digestate valorization is discussed. According to this study, enzyme-treated digestate does not allow efficient larval growth compared to the standard diet. The development of a more effective method of pretreatment is required for BSF larvae to become an eco-friendly solution for digestate valorization.

Dairy Trade Helps to Alleviate Global Carbon Emission Pressure

Global dairy production, consumption, and trade are growing rapidly, driven by population and per capita income growth and increasing health concerns mainly from developing countries, which has aroused concerns about the related carbon emission (mostly in the form of methane) increase. If all of the dairy products consumed were produced locally/domestically in the developing countries/economies (a counterfactual scenario), the carbon emissions in 2018 would be 28 Mt CO₂-equiv higher than its status quo (a factual scenario). The present study indicates that unlike in many global trade cases in which carbon leakages are from developed to developing countries, global dairy trade is characterized by net embodied carbon flows from developed to developing countries/economies due to the fact that there is an overwhelming one-way-flow of dairy products from developed to developing countries/economies. The differences in the carbon emission factors between the developed and developing countries/economies provide an opportunity that global dairy trade and production specialization can help to reduce carbon emissions from increasing dairy product demand, and the total reduction potential is estimated to be about 414 Mt CO₂-equiv from 2018 to 2030. Free trade agreements such as the Regional Comprehensive Economic Partnership will incentivize larger carbon emission reduction benefits through promoting dairy trade.

Recognition on characteristics and applicability of typical modes for manure & sewage management in pig farming: A case study in Hebei, China

Scale-up intensive pig farming can increase profitability by economies of large scale, but it also exacerbates environmental pollution caused by the disordered discharge of manure and sewage. Manure & sewage management (MSM) is critical to mitigate environmental pressure and reuse livestock waste. However, the corresponding MSM measures adopted by pig farmers are multitudinous in reality, due to the diversity of MSM methods and heterogeneity of farmers' characteristics and behaviors. Thus, this study empirically categorized five typical MSM modes (i.e., traditional simple mode (TSM), mixed processing mode (MPM), semi-biogas mode (SBM), professional processing with simple utilization mode (PPSUM) and professional processing with full utilization mode (PPFUM)) by clustering analysis, based on the field data from 406 pig farms, and further discriminated farmers' heterogeneous characteristics on corresponding mode adoption. Results revealed that each mode was distinctive. The applicability of the corresponding mode was reflected in the synthesis deliberation, involving farming structure, land, farmers' characteristic and their subjective awareness. Farmers' education level and pro-environmental perception are significantly promoted to adopt technology-intensive MSM modes. Scale upgrading has a positive effect on mechanization adoption and diversified strategies application. Land as an unalterable objective factor restricted the extension of MSM modes based on field returning. Conclusions clarified typical MSM modes and provided references to individual pig farms on appropriate mode selection, further enhancing the efficiency of MSM and contributing to the sustainability of green development of pig farming in China.

Assessment Impacts of Ozone on Salmonella Typhimurium and Escherichia coli O157:H7 in Liquid Dairy Waste

Liquid dairy manure, which is produced in enormous quantities in flush dairy manure management systems, is commonly used as an alternative to chemical fertilizers. It provides nutrient benefits to crops and soils. While dairy waste is a well-accepted and widely used fertilizer, the presence of indicator organisms and human pathogens in manure may lead to pathogen contamination in crops and soils. This study is focused on the examination of ozone gas-based sterilization. In the past, ozone (O3) has been used for sanitizing various foods and solid surfaces, but the potential of O3 for eliminating human pathogens in liquid dairy waste is not studied yet. Pathogens such as Salmonella Typhimurium and Escherichia coli O157:H7 are reported to be present in liquid dairy manure, and this research evaluated the effects of various levels of ozone on the survival of these two pathogens. We designed a continuous type O3 treatment system that has four major components: (1) ozone generator using oxygen; (2) ozone concentration control by mixing with pure air; (3) continuous monitoring of ozone concentrations; and (4) ozone experiment chambers. Various levels of ozone (43.26, 87.40, and 132.46 mg·L−1) were produced in the ozone system, and subsequently, ozone was diffused through liquid manure. Liquid manure was exposed to ozone for multiple durations (30, 60, and 120 min). To determine the effectiveness of O3 in eliminating pathogens, time-series samples were collected and analyzed for determining the levels of S. typhimurium and E. coli O157:H7. Preliminary results showed that ozone concentrations of 132.46 mg/L, and exposure time of 120 min resulted in the reduced levels of E. coli and Salmonella. Low levels of ozone and limited exposure time were found to be less effective in pathogen removal potentially due to high solid contents. Additional studies carrying out experiments to evaluate the impacts of solids in combination with ozone concentrations will provide further insights into developing full-scale ozone-based treatment systems.

Automatic temperature rise in the manure storage tank increases methane emissions: Worth to cool down!

A significant amount of CH₄ is emitting from livestock manure (LM) storage tank, which is being counted according to the guidelines provided by the Intergovernmental Panel on Climate Change (IPCC). Among various parameters affecting CH₄ conversion factor (MCF) of LM, temperature is known as the most influential factor. As a degree of temperature, atmospheric temperature (T_a), not the manure temperature (T_m), is used for determining the MCF. Currently, the closed-type tank is more common than open-type tank, which would cause the substantial difference between T_a and T_m, probably due to the automatic temperature rise (ATR). Here, we repeatedly observed the ATR by storing pig slurry (PS) in a pilot-scale tank (30 m³, surface/volume ratio of 1.9), and its consequent impact on the increased CH₄ emissions by comparing with the results from a lab-scale tank (1 L, surface/volume ratio of 72.2) controlled at 30 °C. As storage began, the T_m increased gradually from 16 to 23 °C to above 30 °C even in winter (-5 °C < T_a < 15 °C). During 30 d of storage, the CH₄ emissions of 1.3-2.5 kg CH₄/ton PS (MCF 26-29%) was observed in the lab-scale tank, while the emissions was increased to 2.6-4.2 kg CH₄/ton PS (MCF 40-50%) in the pilot-scale tank (Two-Tail test, |t_t|<|t_c|). For the first time, a detailed heat energy balance considering the waste heat from organic degradation, the heat requirement for warm up, and the heat loss by convection, was conducted, proving that the waste heat generated during storage was enough to reach above 30 °C. Cooling-down of LM at 20 °C was found to be effective for reducing CH₄ emissions by 90%, which sufficiently offset the greenhouse gas emissions in power consumption for cooling. Our findings strongly suggest that more CH₄ is emitting from LM storage tank than expected, and therefore, the IPCC needs to develop guidelines more accurately in determining MCF.

Comparative study on characteristics and mechanism of levofloxacin adsorption on swine manure biochar

This study evaluated the relationship between pyrolysis temperature (300-900 ℃), characteristics of swine manure (SM)-derived biochar (BC), and its adsorption of levofloxacin (LEV). The surface structure and chemistry of SM-derived BCs were characterized using Brunauer-Emmett-Teller analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. According to the characteristic analysis, the surface area and graphitization degree of SM-derived BC increased as temperature rose. The highest adsorption capacity was achieved by BC-900 (158 mg/g); this level was higher than that achieved in previous studies and comparable to that of commercial activated carbons. Characterization and adsorption experiments indicated that pore-filling, π-π stacking interaction, π-π electron donor-acceptor, H-bonding, and hydrophobic interactions each played a critical role in the adsorption of LEV on SM-derived BC. Collectively, this study confirms the potential utility of SM-derived BC for the removal of antibiotics.

When dewatered swine manure-derived biochar meets swine wastewater in anaerobic digestion: A win-win scenario towards highly efficient energy recovery and antibiotic resistance genes attenuation for swine manure management

This work explored the feasibility of dewatered swine manure-derived biochar (DSMB) as an additive to facilitate anaerobic digestion (AD) of swine wastewater for energy recovery and antibiotic resistance genes (ARG) attenuation enhancements. With 20 g/L DSMB assistance, the methanogenic lag time of swine wastewater was shortened by 17.4-21.1%, and the maximum CH₄ production rate increased from 40.8 mL/d to 48.3-50.5 mL/d, among which DSMB prepared under 300 °C exhibited a better performance than that prepared under 500 °C and 700 °C. Integrated analysis of DSMB electrochemical properties, microbial electron transfer system activity, and microbial community succession revealed the potential of DSMB-300 to act as redox-active electron transfer mediators between syntrophic microbes to accelerate syntrophic methanogenesis via potential direct interspecies electron transfer. Meanwhile, DSMB preparation by pyrolysis dramatically reduced ARG abundance by almost 4 logs. Adding DSMB into AD not only strengthened the attenuation efficiency of ARG in the original swine wastewater, but also effectively controlled the potential risk of horizontal gene transfer by mitigating 74.8% of the mobile gene elements abundance. Accordingly, we proposed a win-win scenario for bio-waste management in swine farms, highlighting the more advanced energy recovery and ARG attenuation compared to the current status.

Does policy cognition affect livestock farmers' investment in manure recycling facilities? Evidence from China

An increase in living standards and dietary changes have induced a rapid growth in the livestock sector worldwide, which has led to considerable environmental damages due inappropriate disposal of livestock manure. Using primary data from a field survey of cattle farmers in China, this paper empirically examines the impact of policy cognition on livestock farmers' investment in manure recycling facilities. The impact is tested through the multiple mediator model to accommodate two potential mediating mechanisms, which are the agricultural cooperative membership and land leasing. Three conclusions arise. First, policy cognition has a significant positive impact on both the diversification and amounts of farmers' investment in manure recycling facilities. Second, membership in agricultural cooperatives and participation in land leasing are two important mediating mechanisms for policy cognition to affect farmers' investment decisions on manure recycling. Finally, for the two mediating variables, leasing additional agricultural land promotes more investment in manure recycling facilities, but less in investment diversification, while cooperative membership has the opposite impact. This study contributes to three areas of literature on the factors affecting investment decisions, the mediating effects of policy cognition and the investment in non-production related assets. Regarding policy implications, we identify the importance of promoting policy awareness and agricultural cooperatives among livestock farmers, as well as developing land lease markets in agricultural regions in promoting investment in manure recycling facilities.