Anaerobic Digestion Of Swine Waste Research Articles

Effect of Ecuadorian natural zeolite on the performance of anaerobic digestion of swine waste in semicontinuous regime

This study explores the potential of zeolite as an amendment to mitigate ammonium inhibition in the anaerobic digestion of swine waste. Two 50 L reactors, one with and one without zeolite amendment were operated at an OLR of 3.0 g VS L−1d−1 for 130 days, and fed with swine waste from a full-scale pig farm. Under these conditions, zeolite doses of 4 g L−1 allowed total ammonia nitrogen (TAN) concentrations to be kept below 1000 mgNH3-N L−1. The zeolite-amended reactor not only showed an average increase of 8% in methane production under stable conditions but also exhibited 34% reduction in H2S concentrations in the biogas, compared to the reactor without zeolite. The community of archaea originating from the inoculum was conserved in the reactor with zeolite amendment, particularly the acetoclastic methanogens of the genus Methanosaeta. On the other hand, in the reactor without zeolite addition, the microbial community went from being dominated by the acetoclastic methanogen Methanosaeta to having a high relative abundance of hydrogenotrophic methanogens. The zeolite addition also favoured the reactor stability, prevented foaming, and produced an enriched natural zeolite with N, P and K. However, additional studies on the potential of enriched zeolite as a fertilizer are required, which could make the use of zeolite in Anaerobic Digestion of swine waste not only energetically favourable but also economically feasible.

Natural Ecuadorian zeolite: An effective ammonia adsorbent to enhance methane production from swine waste

Anaerobic digestion (AD) of swine waste allows obtaining renewable energy, biofertilizer and the reduction of environmental impacts. However, the low C:N ratio of pig manure generates high concentrations of ammonia nitrogen in the digestion process, reducing methane production. Zeolite is an effective ammonia adsorbent; thus, in this research the ammonia adsorption capacity of natural Ecuadorian zeolite was studied under different operating conditions. Subsequently, its effect on methane production from swine waste was evaluated using three doses of zeolite, 1.0, 4.0 and 8.0 g, in 1 L batch bioreactors. The results showed that the Ecuadorian natural zeolite has an adsorption capacity of around 19 mgNH3-N gZ−1 when using ammonium chloride solution and, an adsorption capacity between 37 and 65 mgNH3-N gZ−1 using swine waste. On the other hand, the addition of zeolite had a significant effect on methane production (p < 0.01). The zeolite doses that provided the highest methane production were 4.0 and 8.0 g L−1, which led to values of 0.375 and 0.365 Nm3CH4 kgVS−1, compared to the values of 0.350 and 0.343 Nm3CH4 kgVS−1 that were obtained for the treatments without addition of zeolite and using a dose of 1.0 g L−1, respectively. Addition of natural Ecuadorian zeolite meant not only a significant increase on methane production in the AD of swine waste, but also a better quality of the biogas with higher percentages of methane and lower concentrations of H2S.

Effect of organic loading rate on the anaerobic digestion of swine waste with biochar addition.

The aim of this study was to investigate the impact of biochar addition on the mesophilic semi-continuous anaerobic digestion of swine waste with a focus on the effects of the organic loading rate (OLR) on biogas production, methane yield, total volatile fatty acids (TVFA), alkalinity, ammonium, volatile solids (VS) removal efficiency and process stability. Four reactors, two with amended biochar (R1 and R2) and two without biochar addition as controls (R3 and R4), were operated at OLRs in the range of 2-7 g VS/(L d), which corresponded to hydraulic retention times (HRTs) in the range of 7-2 days, respectively. The addition of biochar initially caused an increase in the generation of biogas and methane when compared to the control reactors when the process operated at OLRs of 2 and 3 g VS/(L d). This behaviour could be attributed to the presence of several trace elements (such as Fe, Co, Ni and Mn) in the biochar, which are involved in the action of acetyl-CoA synthase and methyl coenzyme M reductase to catalyse key metabolic steps, especially the methanogenic stage. The pH, alkalinity, TVFA and TVFA/Alkalinity ratio values for the effluents remained within the optimal ranges for the anaerobic digestion process. It was also found that the increase in OLR in the range of 2-5 g VS/(L d) determined a proportional increase in the VS removal rate. However, when the OLR increased up to 7 g VS/(L d), a drastic decrease in the VS removal rate was found for the control reactors. Biochar amendment contributed to a more balanced state of the anaerobic process, preventing biomass washout.

Abundances of Tetracycline Resistance Genes and Tetracycline Antibiotics during Anaerobic Digestion of Swine Waste.

The impact of anaerobic digestion of animal waste on the persistence of antibiotic resistance genes (ARGs) and antibiotics is not widely studied. Two identical, 800-L digesters seeded with swine slurry were followed up to 100 d in three separate trials. The trials received varying amounts of antibiotic-free corn ( L.) mixed with water to maintain the digestion process. Biogas production, seven tetracycline resistance () genes, and three tetracyclines and their transformation products were measured. Biogas production proportionally increased as the feeding loads increased between trials. In Trial 1, log gene copies showed small but statistically significant ( < 0.01) increases during digestion. In Trial 2, anaerobic digestion did not have a significant ( > 0.05) effect except for significant reductions in B ( < 0.0001) and G ( = 0.0335) log gene copies. In Trial 3, which received the highest amount of corn mix, log copies of the 16S ribosomal RNA and the genes significantly ( < 0.0001) reduced over time during digestion. Up to 36 μg L tetracycline, 112 μg L chlortetracycline, 11.9 mg L isochlortetracycline, and 30 μg L 4-epitetracycline were detected both in the liquid and solid digestates. Results of this study revealed that although anaerobic digestion of swine waste can produce useful biogas, it does not result in complete removal of bacteria, ARGs, and antibiotics regardless of differences in the feeding loads between trials. Further effluent and sludge treatments are required prior to their downstream use in crop production to minimize emergence and environmental dissemination of antimicrobial-resistant bacteria through animal manure.

Bioregeneration of Chabazite During Nitrification of Centrate from Anaerobically Digested Livestock Waste: Experimental and Modeling Studies.

Nitrification of high total ammonia nitrogen-strength wastewaters is challenging due to free ammonia (FA) inhibition of nitrification. FA inhibition can potentially be alleviated by temporarily adsorbing ammonium (NH4+) to natural zeolite, such as chabazite, followed by direct zeolite bioregeneration via nitrification. In this research, the effectiveness of chabazite addition for reducing nitrification inhibition during treatment of centrate from anaerobic digestion of swine waste was quantified. A mathematical model was developed that accounts for ion exchange of NH4+ and sodium at the chabazite surface, surface diffusion of adsorbed NH4+ within the chabazite grains, sequential nitrification of aqueous NH4+ to nitrite and nitrate, and inhibition of nitritation and nitratation rates by NH4+. The model was calibrated using results of abiotic ion exchange and nitrification studies. Subsequently, nitrification tests were carried out with synthetic wastewater with a NH4+-N concentration of 1000 mg L-1, with and without chabazite. A chabazite dose of 150 g L-1 decreased the FA concentration to below the inhibitory level and increased the nitrification rate from 0.16 to 0.36 mg-N (g-VSS)-1 h-1. Following calibration, the model could predict the experimental data with no additional fitting parameters or parameter adjustment, in both the presence and absence of chabazite. The results suggest that the mathematical model provides a theoretically sound conceptual understanding of ion exchange assisted nitrification.

Effects of an iron oxide–zeolite additive on process performance of anaerobic digestion of swine waste at mesophilic, ambient and psychrophilic temperatures

The improved process performance of AD of swine waste at mesophilic, ambient and psychrophilic temperatures by an iron oxide–zeolite additive.

Anaerobic Co-digestion of Swine Manure and Microalgae Chlorella sp.: Experimental Studies and Energy Analysis

Integration of algae production with livestock waste management has the potential to recover energy and nutrients from animal manure, while reducing discharges of organic matter, pathogens, and nutrients to the environment. In this study, microalgae Chlorella sp. were grown on centrate from anaerobically digested swine manure. The algae were harvested for mesophilic anaerobic digestion (AD) with swine manure for bioenergy production. Low biogas yields were observed in batch AD studies with algae alone, or when algae were co-digested with swine manure at ≥43 % algae (based on volatile solids [VS]). However, co-digestion of 6–16 % algae with swine manure produced similar biogas yields as digestion of swine manure alone. An average methane yield of 190 mL/g VSfed was achieved in long-term semi-continuous co-digestion studies with 10 ± 3 % algae with swine manure. Data from the experimental studies were used in an energy analysis assuming the process was scaled up to a concentrated animal feeding operation (CAFO) with 7000 pigs with integrated algae-based treatment of centrate and co-digestion of manure and the harvested algae. The average net energy production for the system was estimated at 1027 kWh per day. A mass balance indicated that 58 % of nitrogen (N) and 98 % of phosphorus (P) in the system were removed in the biosolids. A major advantage of the proposed process is the reduction in nutrient discharges compared with AD of swine waste without algae production.

Coupling Nitrogen Removal and Anaerobic Digestion for Energy Recovery from Swine Waste Through Nitrification/Denitrification

Abstract As a major swine-producing state, North Carolina (United States) has adopted incentives for energy recovery from swine waste and environmental performance standards for new swine facilities. However, there are no treatment performance requirements for existing farms; therefore, management of swine waste in open lagoons with spray irrigation for disposal is nearly universal in North Carolina. Emissions of nitrogen to the atmosphere and the landscape from large industrial swine farms have led to concerns over the impact on environmental quality and human health. Accordingly, there has been increasing interest in developing alternate treatment methods for swine waste, including methods that allow for energy recovery. To evaluate the technical feasibility and limitations of coupling biological nitrogen removal with anaerobic digestion of swine waste for energy recovery, we operated a pilot nitrification/denitrification system at an 8,000-head finishing farm already practicing full-scale anaerobic dig...

Fate of 17β-Estradiol in Anaerobic Lagoon Digesters

The fate of [C]17β-estradiol ([C]E2) was monitored for 42 d in triplicate 10-L anaerobic digesters. Total radioactive residues decreased rapidly in the liquid layer of the digesters and reached a steady-state value of 22 to 26% of the initial dose after 5 d. High-performance liquid chromatography and liquid chromatography-tandem mass spectrometry analyses of the liquid layer of the anaerobic digesters indicated a rapid degradation of E2 to estrone (E1), which readily adsorbed to the sludge layer subsequent to its formation. Estrone was the predominant steroid identified under anaerobic digestion in the liquid layer or sorbed to sludge at 42 d. Methane formation represented 11.1 ± 5.7% of the initial E2 fortification with 0.3 to 0.5% of the starting E2 mineralized to carbon dioxide. Maximum [C]methane production appeared between Days 4 and 7. An estimate of estrogenicity of the final product based on reported estrogen equivalents for E1 and E2 was 2% of the original in active digesters. Anaerobic digestion of swine waste has several management benefits; moreover, this study demonstrated that it reduces the potential of environmental release of estrogens, which are known endocrine disruptors.

Implications of Urine‐to‐Feces Ratio in the Thermophilic Anaerobic Digestion of Swine Waste

Thermophilic anaerobic digestion of swine manure represents a potential waste treatment technology to address environmental concerns, such as odor emissions and removal of pathogenic microorganisms. However, there are concerns relative to the stability of this process when swine manure is the sole substrate. In this study, the potential of biogas production from swine manure as the sole substrate under thermophilic (50 degrees C) conditions was investigated in the laboratory, to determine whether separation of urine and feces as part of the waste collection process would benefit anaerobic digestion. Effluent from a continuously stirred tank reactor was used as the inoculum for batch tests, in which the substrate contained three different concentrations of urine (urine-free, as-excreted urine-to-feces ratio and double the as-excreted urine-to-feces ratio). Inocula were acclimated to these same urine-to-feces ratios to determine methane production. Results show that both urine-free and as-excreted substrates were not inhibitory to anaerobic inocula. Anaerobic microorganisms can be readily acclimated to substrate with double the as-excreted urine concentration, which contained nitrogen concentrations up to 7.20 g/L. Cumulative methane production reached similar levels in the batch tests, regardless of the substrate urine concentration.

Effect of Potassium Inhibition on the Thermophilic Anaerobic Digestion of Swine Waste

The inhibition effects of high potassium concentration on thermophilic anaerobic digestion of swine waste were studied. A continuous stirred tank reactor (CSTR), operated at a hydraulic retention time of 10 days and chemical oxygen demand loading of 7.2 to 7.5 g/L/d, was used to digest swine waste and cultivate thermophilic anaerobic microorganisms. To evaluate the toxicity of potassium, batch inhibition tests were also conducted. Without acclimation to potassium, the inhibition threshold beyond which methane production decreased significantly was 3 g K+/L. Volatile fatty acids accumulation was observed during the decline of methane production. Propionic acid was the dominant fatty acid, indicating that propionic acid utilizers were more sensitive to potassium inhibition than acetoclastic methanogens. To test the effect of acclimation on potassium inhibition, the potassium concentration in the CSTR was increased to 6 and 9 g K+/L. Acclimation to 6 g K+/L increased the tolerance of anaerobic inocula to potassium inhibition without significantly reducing the methanogenic activity. The inhibition threshold was increased from 3 g K+/L for unacclimated inocula, to 6 g K+/L for inocula acclimated to 6 g/L of potassium. Acclimation of inocula to 9 g/L potassium further increased the inhibition threshold to 7.5 g K+/L. However, the overall methanogenic activity in the last case was lower than that of unacclimated and 6 g K+/L acclimated inocula.

Bio-Retentive Properties of Synthetic Media for Anaerobic Digestion of Animal Waste

The results from a three-year study involving three types of synthetic media for process intensification of anaerobic digestion of swine waste are reported. The three media types were a polyurethane foam, a woven nylon mesh and a polypropylene felt. The physical durability of the different media for the three six-month runs and the ability of each media type to retain bacterial growth within the reactors are reported. Evaluation of the three media types showed that the polyurethane foam material was effective in retaining bacterial culture, but was subject to physical degradation in a mixed reactor environment, and approximately 98% of the original media was lost during the study. The woven nylon mesh was extremely durable but its bio-retentive characteristics were the lowest of the three types. The polypropylene felt proved to be the best media material, showing good physical durability (i.e., no breakdown or loss) and excellent bio-retentive properties.

Digester stress as related to iso-butyric and iso-valeric acids

A recently published study on the long chain volatile fatty acid (VFA) relationships in anaerobic digestion of swine waste using CST reactors proposed using iso-butyric and iso-valeric acid levels as indicators of impending digester failure. The data suggested that individual levels of these acids below 5 mg liter −1 signified good, healthy digestion. Levels between 5 and 15 mg liter −1 suggested that problems were developing and failure was imminent, while a level greater than 15 mg liter −1 indicated failure had already occurred to the extent that a long recovery period would be necessary. When iso-butyric and iso-valeric acids were in the 5–15 mg liter −1 range, the study suggested that this was a signal that provided as much as a week's advance notice of the failure. This short communication gives further supporting data of those relationships from a completely independent study using two different reactor types.

Long chain volatile fatty acid relationships in anaerobic digestion of swine waste

Volatile Fatty Acid (VFA) relationships have been receiving increased attention in anaerobic digestion in recent research due to their important role as precursors in methane fermentation and because they are known inhibitors in excess concentrations. Most recently, VFAs have received considerable attention as performance indicators, with particular emphasis on developing stress/failure indices using the short chain acetic and propionic acids. Longer chain VFAs, such as butyric, iso-butyric, valeric and iso-valeric, have received little attention, primarily because they are either completely non-detectable or they are present in low concentrations in the properly functioning digester. Stress/failure indices that would give the operator sufficient time to adjust operating parameters of a digestion system would be an invaluable aid in fortelling impending process failure. Given a simple test that would indicate stress, the operator could reduce the chance of complete failure and thus avoid a 6 to 8 week recovery period. Reported here are promising results of such a test using the relationship of the longer chain branched (iso) VFAs. The relationship developed involves iso-butyric and iso-valeric acids and appears to give as much as 7 days advance notice of digestion failure using methane yield <0·25 liter CH 4 per g VS added as the failure criteria.

Carbon/Nitrogen Ratio and Anaerobic Digestion of Swine Waste

ABSTRACT THE greatest volume of methane production was observed in digesters operating on a sub-strate of high carbon/nitrogen (C/N) ratio. How-ever, these digesters tended to be unstable ecologically and operated on the verge of failure. Digesters operated on a low C/N ratio (high nitrogen) substrate, although exhibiting lower gas production, were seen to become highly buffered and more stable. The low C/N digesters, because of their stability, were better able to adjust to increases in organic loading. The C/N range of 15.5/1 to 19/1 was found to be the optimum range in terms of maximum methane production based on variation in loading rates. Maximum gas production (690 mL CH4/g organic carbon loaded) occurred at a loading rate of 2.24 g volatile solids (VS)/L/day and a C/N ratio of 19/1. Due to unstable operating conditions observed at high C/N ratios, it is suggested that a C/N ratio of 16/1 may provide more operational stability with minimum loss in gas production. This corresponds to a 55 to 60 percent reduction in total organic carbon (TOC).

Two-Phase Anaerobic Digestion of Swine Waste

An effort was made to design and construct an anaerobic filter for use in the production of CH/sub 4/ and volatile acids substrate from swine waste to obtain a substrate relatively free of suspended solids and with a high concentration of volatile acids. In the CH/sub 4/ digester, after reaching equilibrium with a constant flow rate and concentration of substrate, there was a mass balance between the total gas production and the decrease in volatile acids from the influent and effluent concentrations and the mass flow rate of wastewater. Determinations were made of the specific daily gas yield as a function of the mass flow rate or detention time and the influent volatile acids concentration. After achievement of steady-state operation in 2 to 3 days, it was possible to set up equations to describe the relation. The reaction process, however, could be drastically influenced by such things as pH, C:N:P balance, and the presence of many known agents that are toxic, synergistic, or antagonistic.