Inhibition of methanogenesis and its reversal during biogas formation from cattle manure

The composition of volatile fatty acids in the biogas digester based on cattle manure as substrate and stabilised at 25°C showed that it contained 87–88% branched chain fatty acids, comprising of isobutyric and isovaleric acids, in comparison to 38 % observed in the digester operating at 35°C. Mixed cellulolytic cultures equilibrated at 25°C (C-25) and 35‡C (C-35) showed similar properties, but rates of hydrolysis were three times higher than that observed in a standard biogas digester. The proportion of isobutyric and isovaleric were drastically reduced when C-25 was grown with glucose or filter paper as substrates. The volatile fatty acids recovered from C-25 (at 25°C) inhibited growth of methanogens on acetate, whereas that from C-35 was not inhibitory. The inhibitory effects were due to the branched chain fatty acids and were observed with isobutyric acid at concentrations as low as 50 ppm. Addition of another micro-organismRhodotorula selected for growth on isobutyric completely reversed this inhibition. Results indicate that the aceticlastic methanogens are very sensitive to inhibition by branched chain fatty acids and reduction in methane formation in biogas digester at lower temperature may be due to this effect.     

Eugenol stimulates lactate accumulation yet inhibits volatile fatty acid production and eliminates coliform bacteria in cattle and swine waste

AIM: To determine how eugenol affects fermentation parameters and faecal coliforms in cattle and swine waste slurries stored anaerobically. METHODS AND RESULTS: Waste slurries (faeces:urine:water, 50:35:15) were blended with and without additives and aliquoted to triplicate 1-l flasks. Faecal coliforms were eliminated in cattle and swine waste slurries within 1 or 2 days with additions of eugenol at 10.05 mm (0.15%) and 16.75 mm (0.25%). At these concentrations volatile fatty acids (VFA) were reduced ca 70 and 50% in cattle and swine waste, respectively, over 6-8 weeks. Additionally, in cattle waste, eugenol stimulated the accumulation of lactate (>180 mm) when compared with thymol treatment (20 mm lactate). In swine waste, lactate accumulation did not occur without additives; eugenol and thymol stimulated lactate accumulation to concentrations of 22 and 32 mm, respectively. CONCLUSIONS: Eugenol added to cattle waste may be more beneficial than thymol because not only does it effectively control faecal coliforms and odour (VFA production), it also stimulates lactate accumulation. This in turn, causes the pH to drop more rapidly, further inhibiting microbial activity and nutrient emissions. SIGNIFICANCE AND IMPACT OF THE STUDY: Plant essential oils have the potential to solve some of the environmental problems associated with consolidated animal feeding operations. Thymol and eugenol reduce fermentative activity, thus, have the potential to reduce emissions of greenhouse gases and odour, and curtail transmission of pathogens in cattle and swine wastes.     

Phenylacetic acid in an anaerobic swine manure digester

Summary The presence of phenylacetic acid (PAA) in an anaerobic swine manure digester was determined by gas chromatography of the butyl ester and confirmed by mass spectroscopy. PAA concentration increased during start-up of a digester and with low carbon, high nitrogen loading. Unlike acetate, propionate and butyrate, the concentration of PAA varied little through the day in a stable digester loaded once per day. The laboratory scale digester was loaded at 4 g of swine manure solids/liter digester volume per day. The retention time and temperature were 15 days and 37°C. PAA is a microbial intermediate which is produced by one group of anaerobic bacteria and converted to methane by other members of the bacterial community in the digester. As such, it may be a useful indicator of the relative metabolic activity of the bacterial groups and thus of the overall stability of the anaerobic process.     

Influence of temperature on the performance of anaerobic fixed-film reactors utilizing screened dairy manure

Thermophilic (55°C) and mesophilic (35°C and 22°C) anaerobic digestions in laboratory scale (4 litre) fixed-film reactors fed with screened dairy manure were successfully operated over a range of hydraulic retention times, from 1 to 20 days. Maximum methane production rates of 1·82, 1·68 and 1·28 litres CH₄ litre⁻¹ day⁻¹ occurred at 1, 1·5 and 1 days HRT for the respective 55°C, 35°C and 22°C reactors. Both thermophilic and mesophilic digestions achieved maximum biodegradation efficiency at 10 days HRT. The thermophilic fixed-film reactor performed better than completely-mixed reactors in terms of methane production at HRTs shorter than 2 days. From the results, mesophilic fixed-film reactor operated at 35°C provided optimum methane production and net energy output between 1 and 5 days HRT.     

Digestion of sand-laden manure slurry in an upflow anaerobic solids removal (UASR) digester

Studies on the performance of a laboratory scale upflow anaerobic solids removal (UASR) digester were carried out using sand-laden cow manure slurries having total solids (TS) concentration as 50 and 100 g/l. Hydraulic retention time (HRT) was maintained as 32.4 days, which resulted in the volatile solids (VS) loading rates of 1 and 1.64 g/l d. The UASR system was designed to remove sand from the manure slurry, while anaerobically digesting biodegradable solids inside a single reactor. To enhance the contact of microorganisms and substrate, the liquor from the top of the digester was recirculated through the bed of settled solids at its bottom. Volatile solids reduction through this process was observed to be 62% and 68% in the case of feed slurries having TS concentration as 50 and 100 g/l (referred in the text as 5% and 10% feed slurries), respectively. The methane production rates were observed to be 0.22 and 0.38 l/l d, while methane yield was 0.21 and 0.27 l CH₄/g VS loaded, for 5% and 10% feed slurries, respectively. This indicates that the increase in the VS loading had a positive impact on methane production rate and methane yield. It would be of interest to study the performance of a UASR digester at higher solids loadings and with longer solids retention times. Nonetheless, the presented study showed that sand-laden manure slurries can be successfully digested in a UASR digester producing methane energy equivalent to 4 kW h per m³ of digester volume per day.     

Operating a full-scale poultry manure anaerobic digester

A full-scale, completely-mixed digester, with a liquid capacity of 587 m³, was constructed to process the manure from 70 000 caged layers. Biogas from the digester was used as fuel for an engine/generator set. The operating temperature was maintained at 35°C using waste heat from the engine. The digester was operated on a 22–24 day HRT. Digester influent averaged 5·90% TS, 5250 ppm TKN, and 3790 ppm NH₃N. Digester effluent averaged 3·11% TS, 5090 ppm TKN, and 4060 ppm NH₃N.Sustained operation of the digester was achieved during the period of study (8/83−4/85). During this period biogas production averaged 0·38 m³ kg⁻¹ VS added (0·58 m³ kg⁻¹ VS destroyed). The CH₄ content averaged 58·0%. The major operational problem encountered was grit accumulation in the digester. This problem was reduced by settling most of the grit from the manure prior to the digester. Biogas production was reduced when concentrated lagoon-liquid was used as make-up water. Approximately 22% of the electricity produced was required for operating the system.     

Reduction of indicator and pathogenic microorganisms by psychrophilic anaerobic digestion in swine slurries

The objective of this study was to evaluate the efficiency of a low temperature anaerobic treatment to reduce viable populations of indicator microorganisms (total coliforms, Escherichia coli) and the presence of selected pathogens (Salmonella, Yersinia enterocolitica, Cryptosporidium and Giardia) in swine slurries from different sources. Experiments were carried out in 40 l Sequencing Batch Reactors (SBRs). Experimental results indicated that anaerobic digestion of swine manure slurry at 20 degrees C for 20 days in an intermittently fed SBR: (1) reduced indigenous populations of total coliforms by 97.94-100%; (2) reduced indigenous populations of E. coli by 99.67-100%; (3) resulted in undetectable levels of indigenous strains of Salmonella, Cryptosporidium, and Giardia. It can be considered as a promising method for reducing indigenous indicator and pathogenic microorganisms populations in liquid swine manure slurries.     

Survival of Salmonellas and Ascaris Suum Eggs in a Thermophilic Biogas Plant

In a continuous biogas plant, receiving manure from 200 dairy cows and 400 calves and young stock, survival of salmonellas and Ascaris suum eggs was studied. The bacteria and parasite eggs were kept in filter sacs in the manure that had a temperature of 55°C. No viable salmonellas or Ascaris suum eggs could be found after 24h in the digester. Survival of salmonellas and Ascaris suum eggs was also studied in the manure pit where the manure was stored after digestion. The temperature in the manure pit varied between 22–27°C. Salmonellas survived 35 but not 42 days. On day 56, when the experiments had to be stopped, 60% of the Ascaris eggs were viable.     

Minimally managed composting of beef manure at the pilot scale: Effect of manure pile construction on pile temperature profiles and on the fate of oxytetracycline and chlortetracycline

Oxytetracycline (OTC) and chlortetracycline (CTC) are broad-spectrum antibiotics used in livestock production. Although laboratory-scale studies have shown that extractable concentrations of these compounds decrease over time within treated and untreated manures and soils, there is relatively little information from farm-scale experiments. The objective of this study was to determine the effect of different levels of management on manure pile temperature profiles and on the fate of OTC and CTC in manure from therapeutically treated calves. Four treatments were designed to span a range of management options – from simply piling up the manure to amending it with straw to increase aeration and adding insulating layers of straw. Replicate samples of antibiotic-containing calf manure were held at ambient temperature or placed in three locations within replicate 3 m³ piles of beef manure. During the 28-day incubation period, concentrations of buffer-extractable OTC and CTC/ECTC (the summed concentrations of CTC and its epimer 4-epi-chlortetracycline (ECTC)) in manure samples incubated at ambient temperature (11–24 °C) decreased 75% (from 18 to 4.6 mg kg⁻¹ dry weight (DW)) and 90% (from 192 to 16 mg kg⁻¹ DW), respectively. Concentrations of the CTC metabolite iso-chlortetracycline (ICTC) decreased 90% (from 37 to 3 mg kg⁻¹ DW). OTC and CTC/ECTC concentrations in samples incubated for 28 days within a non-amended manure pile decreased 91% and >99%, respectively. During that period, the manure pile temperature ranged from 36 °C to 45 °C. Manure piles insulated with a blanket of straw and/or amended with straw (3:1, v/v) attained temperatures up to 70 °C and contained very low levels of OTC, CTC/ECTC, and ICTC (ranging from <0.1 to 0.4 mg kg⁻¹ DW) after 28 days.     

Impact of chlortetracycline on sequencing batch reactor performance for swine manure treatment

Treatment of aged (500 day, 4 °C stored) chlortetracycline (CTC; 0, 20, 40, 80 mg/L CTC)-amended swine manure using two cycle, 22 day stage anaerobic sequencing batch reactors (SBR) was assessed. Eighty milligrams per liter CTC treatment inhibited SBR treatment efficiencies, although total gas production was enhanced compared to the no-CTC treatment. The 20 and 40 mg/L CTC treatments resulted in either slight or no differences to SBR treatment efficiencies and microbial diversities compared to the no-CTC treatment, and were generally similar to no-CTC treatments upon completion of the first 22 day SBR cycle. All CTC treatments enhanced SBR gas generation, however CH₄ yields were lowest for the 80 mg/L CTC treatment (0.111 L CH₄/g tCOD) upon completion of the second SBR react cycle. After a 22 day acclimation period, the 80 mg/L CTC treatment inhibited methanogenesis due to acetate accumulation, and decreased microbial diversity and CH₄ yield compared to the no-CTC treatment.     

Influence of manure from pigs fed chlortetracycline as growth promotant on soil microbial community structure

Chlortetracycline (CTC), an antimicrobial compound used in animal production, is not sorbed or degraded in the animal, and may enter the field environment through manure land-spreading. This study determined the influence of a single application of manure with or without CTC on field soil microbial community characteristics. Manures from swine fed unamended or CTC-amended rations were applied at 7,000 kg solid ha⁻¹ to a Brandt silty clay loam soil that had no known prior history of manure application. Soil samples taken 1, 7, 28, or 42 days after treatment (DAT) were analyzed for aerobic culturable counts on R2A agar and most probable number using 2,4-D as sole carbon source. Soil extracts of 1, 7, and 42 DAT samples were subjected to polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) analysis of the V3 region of the 16S rRNA gene pool. Gels were analyzed by Neighbor Joining based on Euclidean distance and Raup–Crick multivariate statistical analysis, and selected bands were extracted to identify predominant community members. Both manure applications initially changed soil microbial diversity, however, communities appeared to converge over time, so that no long-term significant effect was detected with this single application.     

Comparison of saccharification process by acid and microwave-assisted acid pretreated swine manure

The saccharification process of swine manure by conventional and microwave-assisted acid pretreated were investigated using cellulose enzymes, respectively. The optima for microwave-assisted acid pretreated swine manure is achieved when swine manure of 50 g l⁻¹ of substrate concentration and water amount 40 ml was pretreated by 4% H₂SO₄ concentration with 445 W microwave powers for 30 min at pretreatment period, and temperature 50 °C, enzyme loading 2 mg g⁻¹ substrate, substrate concentration 5 g l⁻¹ and initial medium pH 4.8 at enzymes hydrolysis period by microwave-assisted acid pretreated, respectively. The optimal conditions by conventional acid pretreated is obtained when 50 g l⁻¹ swine manure was submerged in 40 ml, 4% H₂SO₄ maintained at 130 °C for 3 h at pretreatment period, and temperature 45 °C, enzyme loading 2 mg g⁻¹ substrate, substrate concentration 15 g l⁻¹ and initial medium pH 5.2 at enzymes hydrolysis period, respectively. Under the optimum conditions microwave-assisted acid pretreatment could achieve higher yield of reducing sugar, short reaction time, and lower energy consumption than from the conventional acid pretreatment, which indicates that microwave-assisted acid pretreatment is more suitable for swine manure pretreatment than by acid alone.     

The behavior of tetracyclines and their degradation products during swine manure composting

The purposes of this study were to investigate the behavior of three tetracyclines including chlortetracycline (CTC), oxytetracycline (OTC) and tetracycline (TC) and their degradation products in a pilot scale swine manure composting, and also to study the degradation kinetics of CTC, OTC and TC. During the pilot scale composting, CTC, OTC and TC were degraded by 74%, 92% and 70%, respectively. Several degradation products were found like 4-epitetracycline (ETC), 4-epioxytetracycline (EOTC), 4-epichlortetracycline (ECTC), demeclocycline (DMCTC) and anhydrotetracycline (ATC). Both the simple and the adjusted first-order kinetic models successfully fit the degradation process of CTC, OTC and TC during the composting, but the adjusted first-order kinetic model fit much better with the calculated half-lives of 8.2, 1.1 and 10.0 days, respectively.     

Comparison of two-stage thermophilic (68 degrees C/55 degrees C) anaerobic digestion with one-stage thermophilic (55 degrees C) digestion of cattle manure

A two-stage 68 degrees C/55 degrees C anaerobic degradation process for treatment of cattle manure was studied. In batch experiments, an increase of the specific methane yield, ranging from 24% to 56%, was obtained when cattle manure and its fractions (fibers and liquid) were pretreated at 68 degrees C for periods of 36, 108, and 168 h, and subsequently digested at 55 degrees C. In a lab-scale experiment, the performance of a two-stage reactor system, consisting of a digester operating at 68 degrees C with a hydraulic retention time (HRT) of 3 days, connected to a 55 degrees C reactor with 12-day HRT, was compared with a conventional single-stage reactor running at 55 degrees C with 15-days HRT. When an organic loading of 3 g volatile solids (VS) per liter per day was applied, the two-stage setup had a 6% to 8% higher specific methane yield and a 9% more effective VS-removal than the conventional single-stage reactor. The 68 degrees C reactor generated 7% to 9% of the total amount of methane of the two-stage system and maintained a volatile fatty acids (VFA) concentration of 4.0 to 4.4 g acetate per liter. Population size and activity of aceticlastic methanogens, syntrophic bacteria, and hydrolytic/fermentative bacteria were significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. The density levels of methanogens utilizing H2/CO2 or formate were, however, in the same range for all reactors, although the degradation of these substrates was significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. Temporal temperature gradient electrophoresis profiles (TTGE) of the 68 degrees C reactor demonstrated a stable bacterial community along with a less divergent community of archaeal species.     

Spatial and temporal variations of microbial community in a mixed plug‐flow loop reactor fed with dairy manure

Mixed plug‐flow loop reactor (MPFLR) has been widely adopted by the US dairy farms to convert cattle manure to biogas. However, the microbiome in MPFLR digesters remains unexplored. In this study, the microbiome in a MPFLR digester operated on a mega‐dairy farm was examined thrice over a 2 month period. Within 23 days of retention time, 55–70% of total manure solid was digested. Except for a few minor volatile fatty acids (VFAs), total VFA concentration and pH remained similar along the course of the digester and over time. Metagenomic analysis showed that although with some temporal variations, the bacterial community was rather stable spatially in the digester. The methanogenic community was also stable both spatially and temporally in the digester. Among methanogens, genus Methanosaeta dominated in the digester. Quantitative polymerase chain reaction (qPCR) analysis and metagenomic analysis yielded different relative abundance of individual genera of methanogens, especially for Methanobacterium, which was predominant based on qPCR analysis but undetectable by metagenomics. Collectively, the results showed that only small microbial and chemical gradients existed within the digester, and the digestion process occurred similarly throughout the MPFLR digester. The findings of this study may help improve the operation and design of this type of manure digesters.     

Combination of a urease inhibitor and a plant essential oil to control coliform bacteria, odour production and ammonia loss from cattle waste

AIM: To evaluate urea hydrolysis, volatile fatty acid (VFA) production (odour) and coliforms in cattle waste slurries after a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and a plant oil component (thymol) were added. METHODS AND RESULTS: Faeces from cattle fed a diet of 70% corn silage and 30% alfalfa haylage, urine and distilled water in the ratio 50 : 35 : 15 were blended at high speed for 1 min. Triplicate aliquots of 750 ml were amended with NBPT plus or minus thymol and reblended for 1 min, and were poured into 1.6 l wide-mouth jars covered 90% with a lid. After 56 days, thymol (2000 mg kg(-1) waste) in combination with NBPT (80 mg kg(-1) waste) retained 5.2 g of an initial 9.2 g of urea in cattle waste slurries, compared with less than 1 g of urea retained when NBPT was the only additive (P < 0.05). Another experiment using excreta from cattle fed 76.25% high moisture corn, 19.25% corn silage and a 4.5% supplement, blended at a low speed, gave a similar response with urea hydrolysis; and the two treatments, thymol alone and thymol in combination with NBPT, reduced VFA production (P < 0.01) and eliminated all coliform bacteria by day 1. A third experiment indicated coliforms disappeared in the no addition treatment after 8 days; however, they were viable at 6.6 x 10(4) CFU g(-1) waste beyond 35 days in the NBPT treatment. CONCLUSIONS: Thymol supplements the effect of NBPT by increasing the inhibitory period for hydrolysis of urea in cattle waste slurries and nitrogen retention in the waste. SIGNIFICANCE AND IMPACT OF THE STUDY: Thymol and NBPT offer the potential to reduce odour and pathogens in cattle manure, and increase the fertilizer value.     

Optimization of biogas production from co-digestion of whey and cow manure

Anaerobic co-digestion is effective and environmentally attractive technology for energy recovery from organic waste. Organic, agricultural and industrial wastes are good substrates for anaerobic co-digestion because they contain high levels of easily biodegradable materials. In this paper enhancement of biogas production from codigestion of whey and cow manure was investigated in a series of batch experiments. The influence of whey ratio on specific biogas production in a mixture with cow manure was analyzed at 35 and 55°C, for different initial pH values and for different concentrations of supplemental bicarbonate in experiments carried out over 12 days. Good biogas production (6.6 dm³/dm³), methane content (79.4%) in a biogas mixture and removal efficiencies for total solids (16%) were achieved at optimum process conditions (temperature of 55°C, 10% v/v of whey and 5 g/dm³ NaHCO₃ in the initial mixture). In order to validate optimized conditions for co-digestion of whey and cow manure in the one-stage batch process, the experiments were performed within 45 days. The high biogas production (21.8 dm³/dm³), a good methane content (78.7%) in a biogas mixture as well as maximum removal efficiencies for total solids (32.3%), and chemical oxygen demand (56.3%), respectively indicate that whey could be efficiently degraded to biogas in a onestage batch process when co-digested with cow manure.     

The potential of biological methane generation from chicken manure

The potential for biological methane generating from the manure of laying hens was investigated in the laboratory. Fresh manure was collected, analyzed, and used to prepare medium for bacterial growth. At 55°C and under anaerobic conditions, methanogenic cultures were initiated by incubating the medium with different inoculations from various natural environments. Since there were no significant differences in gas production among these initiated cultures after 40 days of acclimation, they were mixed to maintain a genetic pool. The mixed culture was then challenged with different retention times (RT) and different volatile solid (VS) concentrations for the selection of optimal conditions and cultures. The conditions were finally selected to be 4-day RT and 6% VS for the maximal rate of gas production. The optimal pH and temperature were determined to be 7.5 and 50°C, respectively. Under such conditions the selected culture produced total gas at a rate 4.5 L/L day and methane (70% of total gas) 3.2 L/L day. The chicken manure therefore was able to support the methane yield at 270 L/kg of VS, a value comparably higher than other kinds of livestock wastes.     

煤矿区复垦土壤中有机肥的分解动态及其驱动因素

基于煤矿区不同复垦年限土壤,研究有机肥的分解动态及其驱动因素,可为有机肥合理施用和矿区土壤培肥提供科学依据。本研究以山西煤矿复垦区为试验平台,采用尼龙网袋填埋法,在复垦年限为1年(复垦初期阶段,R₁)、10年(复垦中期阶段,R₁₀)和30年(复垦长期阶段,R₃₀)的土壤中进行有机肥分解试验(有机肥碳量与土壤重量比例为4∶100)。供试有机肥为牛粪和猪粪,以不添加有机肥为对照(CK),填埋深度为15 cm。在填埋后的第12、23、55、218、281和365 d采集尼龙网袋样品,测定有机肥残留量、土壤微生物生物量碳(MBC)和可溶性有机碳(DOC)含量,采用方差分解分析(VPA)量化土壤性质、有机肥性质和水热条件对有机肥分解的贡献率。结果表明: 猪粪的分解速率显著高于牛粪。猪粪的腐殖化系数(46.3%)显著低于牛粪(71.7%);猪粪在复垦30年的土壤中的腐殖化系数(44.5%)显著低于复垦1年和10年的土壤(47.2%);而牛粪在3种复垦年限土壤中的腐殖化系数无显著差异。猪粪和牛粪的易分解碳库占总碳库的比例分别为52%和26%,易分解碳库分解速率常数分别为0.00085和0.00074 ℃^-1,且差异显著。在0~218 d填埋时间段内,猪粪还田对复垦土壤MBC和DOC的提升作用显著高于牛粪,在281~365 d填埋时间段内,两者差异不显著。有机肥还田下,3种复垦年限土壤中MBC和DOC的增长幅度均表现为R₁ >R₁₀ ≈ R₃₀。在土壤性质、物料性质和水热条件中,有机肥性质是其分解的主要影响因子,对有机肥分解的单独贡献率最大,为17.9%。综上,猪粪的分解受到土壤复垦年限的影响,而牛粪的分解不受土壤复垦年限的影响。在不同复垦年限土壤中,牛粪的腐殖化系数显著高于猪粪,在煤矿复垦区建议选择腐熟的牛粪进行有机肥还田,以提高土壤肥力。     

The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure

In order to obtain basic design criteria for anaerobic digesters of swine manure, the effects of different digesting temperatures, temperature shocks and feed loads, on the biogas yields and methane content were evaluated. The digester temperatures were set at 25, 30 and 35 degrees C, with four feed loads of 5%, 10%, 20% and 40% (feed volume/digester volume). At a temperature of 30 degrees C, the methane yield was reduced by only 3% compared to 35 degrees C, while a 17.4% reduction was observed when the digestion was performed at 25 degrees C. Ultimate methane yields of 327, 389 and 403 mL CH(4)/g VS(added) were obtained at 25, 30 and 35 degrees C, respectively; with moderate feed loads from 5% to 20% (V/V). From the elemental analysis of swine manure, the theoretical biogas and methane yields at standard temperature and pressure were 1.12L biogas/g VS(destroyed) and 0.724 L CH(4)/g VS(destroyed), respectively. Also, the methane content increased with increasing digestion temperatures, but only to a small degree. Temperature shocks from 35 to 30 degrees C and again from 30 to 32 degrees C led to a decrease in the biogas production rate, but it rapidly resumed the value of the control reactor. In addition, no lasting damage was observed for the digestion performance, once it had recovered.