Comparative evaluation of biogas production from dairy manure and co‐digestion with maize silage by CSTR and new anaerobic hybrid reactor

This study aimed to investigate potential methane production through anaerobic digestion of dairy manure and co‐digestion with maize silage. Two different anaerobic reactor configurations (single‐stage continuously stirred tank reactor [CSTR] and hybrid anaerobic digester) were used and biogas production performances for each reactor were compared. The HR was planned to enable phase separation in order to improve process stability and biogas production under higher total solids loadings (≥4%). The systems were tested under six different organic loading rates increased steadily from 1.1 to 5.4 g VS/L.d. The CSTR exhibited lower system stability and biomass conversion efficiency than the HR. The specific biogas production of the hybrid system was between 440 and 320 mL/gVS with 81–65% volatile solids (VS) destruction. The hybrid system provided 116% increase in specific biogas production and VS destruction improved by more than 14%. When MS was co‐digested together with dairy manure, specific biogas production rates increased about 1.2‐fold. Co‐digestion was more beneficial than mono‐material digestion. The hybrid system allowed for generating methane enriched biogas (>75% methane) by enabling phase separation in the reactor. It was observed that acidogenic conditions prevailed in the first two compartments and the following two segments as methanogenic conditions were observed. The pH of the acidogenic part ranged between 4.7 and 5.5 and the methanogenic part was between 6.8 and 7.2.     

Pathogen removal in farm-scale psychrophilic anaerobic digesters processing swine manure

This study assessed the efficiency of commercial-scale psychrophilic anaerobic digestion in sequencing batch reactors (PADSBRs) for pathogen removal from pig manure. The impact of treatment cycle length and of hydraulic flow regimes on pathogen removal efficiency was investigated. Two conventionally operated SBRs (BR1 and BR2) and two SBRs simultaneously fed during the draw step (BR3 and BR4) were monitored over a two-year period. PADSBRs significantly decreased the concentration of coliforms, Salmonella, Campylobacter spp., and Y. enterocolitica, respectively from about 10⁶, 10³ CFU g⁻¹, 10³, and 10⁴ CFU g⁻¹ to undetectable levels in most samples. Densities of the gram-positive Clostridium perfringens and Enterococcus spp. remained high (10⁵ CFU g⁻¹) in the digesters throughout treatment. The PADSBRs maintained the same level of pathogen removal when the treatment cycle length was reduced from 2 to 1 week. Mass balances on volatile fatty acids (VFAs) revealed short-circuits of inlet flow respectively averaging 6.3% and 6.4% for BR3 and BR4, significantly reducing the overall performance of these reactors regarding pathogens removal. The results obtained in this study show the ability of low temperature anaerobic digestion to remove or significantly reduce indicator and pathogen concentration from raw pig manure.     

Ethanol production from maize silage as lignocellulosic biomass in anaerobically digested and wet-oxidized manure

In this communication, pretreatment of the anaerobically digested (AD) manure and the application of the pretreated AD manure as liquid medium for the simultaneous saccharification and fermentation (SSF) were described. Furthermore, fermentation of pretreated maize silage and wheat straw was investigated using 2 l bioreactors. Wet oxidation performed for 20 min at 121 °C was found as the most suitable pretreatment conditions for AD manure. High ammonia concentration and significant amount of macro- and micro-nutrients in the AD manure had a positive influence on the ethanol fermentation. No extra nitrogen source was needed in the fermentation broth. It was shown that the AD manure could successfully substitute process water in SSF of pretreated lignocellulosic fibres. Theoretical ethanol yields of 82% were achieved, giving 30.8 kg ethanol per 100 kg dry mass of maize silage.     

Nitrogen and phosphorus removal rates using small algal turfs grown with dairy manure

Conservation and reuse of nitrogen (N) and phosphorus (P) from animalmanure is increasingly important as producers try to minimize transport ofthesenutrients from farms. An alternative to land spreading is to grow crops ofalgaeon the N and P present in the manure. The general goal of our research is toassess nutrient recovery from animal manure using attached algae. The specificobjective of this study was to evaluate the use of small subsections of algalturfs for determining N and P removal rates by attached algae under differentloading rates of dairy manure. Algae were grown in a laboratory–scalealgal turf scrubber (ATS) operated by recycling wastewater and adding manureeffluent daily. Replicate subsections (0.032 m²) ofalgal turf screens were removed and treated with five different loadings ofanaerobically digested dairy manure containing 5 to 80 mgL^–1 NH₄-N and 1 to 20 mgL^–1 PO₄-P over a 2-h incubationperiod. NH₄-N removal rates were biphasic with a fast initial ratefollowed by a slower rate. Biphasic rates were more pronounced for the lowestloading rates but less so for the higher ones. PO₄-P removal rateswere linear throughout the incubation period for all loading rates. N and Premoval rates increased with increasing loading rate and biomass. Inincubationsusing 1% dairy manure NH₄-N and PO₄-P removal ratesaveraged 0.72 and 0.33 g m^–2d^–1,respectively. These rates were approximately 5 to 8-fold lower than ratesmeasured on laboratory-scale ATS units using undisturbed turfs.     

Molluscicidal and slug-repellent properties of anaerobically digested organic matter

Slug problems in arable crops and vegetables have increased drastically during the past few decades. Observations on slug damage to oilseed rape suggested that fresh, anaerobically digested organic material from a biogas production plant is molluscicidal. To find out whether digested matter can be used for the control of agricultural pest slugs, a series of exeriments were carried out. The laboratory experiments demonstrated strong mollusc repellent and molluscicidal effects of digested organic matter against the three most important pest slugs of Switzerland, Arion lusitanicus, A. distinctus and Deroceras reticulatum. The effects were restricted to fresh digested matter and were rapidly lost when the material was stored, and also after application in the field. In the field experiment, fresh digested matter greatly reduced slug damage to lettuce in comparison with the untreated plots. At present, the chemical nature of the molluscicidal compound(s) in digested matter is unknown, but environmental pollutants such as heavy metals can be ruled out. Current research aims at a new formulation which is easier to apply and has a longer-lasting molluscicidal or slug-repellent effect, and at optimising the dosage and number of applications.     

Ammonia inhibition in anaerobic digestion: A review

Even though ammonia is an essential nutrient for bacterial growth, it may inhibit methanogenesis during anaerobic digestion process if it is available at high concentrations. Therefore, ammonia is regarded as a potential inhibitor during anaerobic digestion, particularly when dealing with complex type of substrates such as manure or the organic fraction of municipal solid waste (OFMSW). Ammonia is produced through biological degradation of nitrogenous matter. Ammonium ion (NH₄⁺) and free ammonia (NH₃) are the two principal forms of inorganic ammonia nitrogen. Both forms can directly and indirectly cause inhibition in an anaerobic digestion system. Particularly, free ammonia (FAN) is a powerful inhibitor in an anaerobic digester above threshold concentrations. Process inhibition is related to the particular characteristics of the substrate to be anaerobically digested, pH, process temperature (mesophilic or thermophilic), type of the seed sludge (inoculum), the reactor configuration and to the concentrations of ammonium and ammonia. In this paper, ammonia inhibition in anaerobic digestion systems and the recovery efforts after inhibition are discussed. Furthermore, the impacts of ammonia inhibition on the microbial population available in anaerobic digesters, namely bacteria and Archaea, are also evaluated in detail.     

Development of a pilot scale anaerobic digester for biogas production from cow manure and whey mix

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaerobic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. The versatile and unique characteristics of the instrument allowed testing the methane production directly in the farm. The digester performance was evaluated with two calibration tests, the main for a period of 56 days. The study test was divided into three phases, one for each type of feeding operation (batch, fed-batch, batch). The initial phase of digestion resulted in 57 l-CH₄/kg-VS, the second phase had a yield of 86.6 l-CH₄/kg-VS and the third one had a production of 67 l-CH₄/kg-VS. The total methane yield was equal to 211.4 l-CH₄/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle, it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted tests did show that there is a good potential to the use of a cow manure and whey biomass mix for biogas production.     

Microbiological contamination of digested products from anaerobic co-digestion of bovine manure and agricultural by-products

Aims: This study was performed to investigate the microbiological contamination of digestate product (DP) obtained from the anaerobic co‐digestion of bovine manure and agricultural by‐products. Methods and results: Microbiological analyses were performed on bovine manure, fresh DP, liquid and solid fractions and stored liquid fraction of DP. A statistically significant reduction of faecal bacterial indicator was found after anaerobic digestion except for enterococci. After liquid/solid DP separation, bacteria tend to be concentrated in the solid fraction. Storage does not seem to influence the indicator parameters, except for enterococci. Escherichia coli O157:H7 and Yersinia were not found in any samples analysed. Salmonella was rarely detected in DP samples and its derivates, while Listeria monocytogenes was encountered in many samples. Conclusions: The results obtained indicate that the hygienic quality of DP is for almost all microbiological parameters better than that of the bovine manure (range of reduction 1.6–3.1 log₁₀) and suggest the need to identify specific pathogen indicators related to the hygienic characteristics of DPs. Significance and Impact of the Study: This study highlights that the anaerobic co‐digestion of bovine manure and agricultural by‐products in a field‐scale biogas plant does not increase human health risk with respect to the use of animal manure for agricultural fertilization.     

Bulk density and thermal properties of Moroccan dairy cattle manure

The bulk density, specific heat and thermal conductivity of Moroccan dairy cattle manure were studied with respect to total solids concentration. In the range of total solids studied regression equations were established relating each of these parameters to the percentage of total solids in cattle manure.     

Removal of nutrients from piggery wastewater using struvite precipitation and pyrogenation technology

In this paper, removal of nutrients from piggery wastewater by struvite crystallization was conducted using a combined technology of low-cost magnesium source in struvite precipitation and recycling of the struvite pyrolysate in the process. In the present research, it was found that high concentrations of K⁺ and Ca²⁺ present in the solution significantly affected the removal of nutrients. When the struvite crystallization formed at the condition of dosing the magnesite pyrolysate at a Mg:N:P molar ratio of 2.5:1:1, and having a reaction time of 6 h, a majority of nutrients in piggery wastewater can be removed. Surface characterization analysis demonstrated that the main components of the pyrolysate of the obtained struvite were amorphous magnesium sodium phosphate (MgNaPO₄) and MgO. When the struvite pyrolysate was recycled in the process at the pH range of 8.0-8.5, the precipitation effect was optimum. When the struvite pyrolysate was recycled repeatedly at pH 8.5 or without any adjustment of pH, the outcome of the removal of the nutrients in both cases was similar. With the increase in the number of recycle times, the performance of struvite precipitation progressively decreased. An economic evaluation showed that the combination of using low-cost material and recycling of struvite was feasible. Recycling struvite for three process cycles could save the chemical costs by 81% compared to the use of pure chemicals.     

Microbial removal from the separated liquid fraction of anaerobically digested pig manure in meso-scale integrated constructed wetlands

The aim was to investigate microbial removal from the liquid fraction of anaerobically digested pig manure in meso-scale integrated constructed wetlands (ICW’s) over a 13 month period. Four treatments were investigated: T1 (standard), T2 (effluent recycling), T3 (high nutrient loading), and T4 (high flow rate). Mean counts of yeasts and moulds and spore-forming bacteria were higher in T3 and T4 than in T1 and T2 (P < 0.05). Flow through the cells reduced mean counts of coliform, yeasts and moulds and spore-forming bacteria across all treatments (P < 0.01). Counts varied with season; coliform were highest in the Summer (P < 0.001), with yeasts and moulds highest in the Summer and Autumn (P < 0.01) and spore-formers lowest in the Autumn (P < 0.001). As Salmonella was undetectable in the influent and Escherichia coli and Enterococcus were rarely detected it is difficult to make conclusions regarding pathogen removal. Further investigations using marked strains would allow pathogen tracking within the ICW’s.     

Biochemical methane potential and biodegradability of complex organic substrates

The biomethane potential and biodegradability of an array of substrates with highly heterogeneous characteristics, including mono- and co-digestion samples with dairy manure, was determined using the biochemical methane potential (BMP) assay. In addition, the ability of two theoretical methods to estimate the biomethane potential of substrates and the influence of biodegradability was evaluated. The results of about 175 individual BMP assays indicate that substrates rich in lipids and easily-degradable carbohydrates yield the highest methane potential, while more recalcitrant substrates with a high lignocellulosic fraction have the lowest. Co-digestion of dairy manure with easily-degradable substrates increases the specific methane yields when compared to manure-only digestion. Additionally, biomethane potential of some co-digestion mixtures suggested synergistic activity. Evaluated theoretical methods consistently over-estimated experimentally-obtained methane yields when substrate biodegradability was not accounted. Upon correcting the results of theoretical methods with observed biodegradability data, an agreement greater than 90% was achieved.     

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.     

Ammonia emissions during the initial phase of microbial degradation of solid and liquid cattle manure

The maximum specific ammonia emissions from liquid manure (LM) and solid manure containing 2.5 kg straw/livestock unit (LU)/day (SM 2.5) or 15 kg straw/LU/day (SM 15) increased in the sequence LM < SM 2.5 < SM 15 (662.6 < 3163.7 < 6299.8 μg NH₃–N/h/kg). These emission levels were attained soon after the maximum temperatures (22.9°C < 34.3°C < 69.5°C) induced by microbial self-heating had been reached. After that, NH₄⁺ was microbially re-bound in amounts that increased with a higher C content and a widening C:N ratio, i.e. also in the sequence LM < SM 2.5 < SM 15. Over a period of 15 to 16 days, 6.0% (LM), 10.8% (SM 2.5) and 5.9% (SM 15) of the N_total was emitted. When the accumulated ammonia emissions were extrapolated beyond this period of investigation, it was concluded that, over longer storage periods, solid manure offers better biological conditions for low ammonia emissions than liquid manure.     

利用Chlorella vulgaris C9-JN2010去除蓝藻-猪粪沼液废水中氮磷的研究

利用普通小球藻Chlorella vugaris C9-JN2010处理蓝藻-猪粪沼液废水,以实现废水无害化利用。实验考察了氮磷比和沼液浓度对小球藻生长及处理废水效果的影响,结果表明:在氮磷比(20:1)和沼液浓度(5%)条件下培养小球藻,藻细胞生长和废水处理效果最佳,最高细胞干重及生产强度分别为900.1 mg·L~(-1)和85.1 mg·L~(-1)·d~(-1),废水中总氮、总磷、氨氮的去除率分别为84.6%、95.9%和90.5%,对应去除强度分别为5.43 mg·L~(-1)·d~(-1)、0.30 mg·L~(-1)·d~(-1)和4.75 mg·L~(-1)·d~(-1)。利用小球藻可较彻底的去除蓝藻-猪粪沼液废水中氮、磷等营养,达到污水处理效果。     

Factors in the determination of methanogenic potential of manure

The influence of the substrate concentration, the micro and macro nutrients and buffer requirements, the sludge origin (biomass that is acclimatized or not acclimatized to waste) and the inoculum/substrate ratio (ISR) were studied to determine their effects in the methanogenic potential of turkey manure, which is a solid waste. According to the results obtained, the methane production determination does not require the addition of nutrients (additional to the contents in the waste) and a buffer for this type of assay. The methane yield (Y_CH4) performance is given by the substrate concentration and the sludge origin, therefore it is better to carry out the assay with biomass that is already adapted to the waste. The methanogenic potential of this type of waste is not determined by the amount of sludge and it does not need an external inoculum (external to the waste contents).     

Dry anaerobic ammonia–methane production from chicken manure

The effect of temperature on production of ammonia during dry anaerobic fermentation of chicken manure (CM), inoculated with thermophilic methanogenic sludge, was investigated in a batch condition for 8 days. Incubation temperature did not have a significant effect on the production of ammonia. Almost complete inhibition of production of methane occurred at 55 and 65°C while quite low yields of 8.45 and 6.34 ml g⁻¹ VS (volatile solids) were observed at 35 and 45°C due to a higher accumulation of ammonia. In order to improve the production of methane during dry anaerobic digestion of CM, stripping of ammonia was performed firstly on the CM previously fermented at 65°C for 8 days: the stripping for 1 day at 85°C and pH 10 removed 85.5% of ammonia. The first-batch fermentation of methane for 75 days was conducted next, using the ammonia-stripped CM inoculated with methanogenic sludge at different ratios, (CM: thermophilic sludge) of 1:2, 1:1, and 2:1 on volume per volume basis at both 35 and 55°C. Production of methane improved and was higher than that of the control (without stripping of ammonia) but the yield of 20.4 ml g⁻¹ VS was still low, so second stripping of ammonia was conducted, which resulted in 74.7% removal of ammonia. A great improvement in the production of methane of 103.5 ml g⁻¹ VS was achieved during the second batch for 55 days.