Alastair James Ward

Comparison of near infra-red spectroscopy, neutral detergent fibre assay and in-vitro organic matter digestibility assay for rapid determination of the biochemical methane potential of meadow grasses.

This paper investigates near infra-red spectroscopy (NIRS) as an indirect and rapid method to assess the biochemical methane potential (BMP) of meadow grasses. Additionally analytical methods usually associated with forage analysis, namely, the neutral detergent fibre assay (NDF), and the in-vitro organic matter digestibility assay (IVOMD), were also tested on the meadow grass samples and the applicability of the models in predicting the BMP was studied. Based on these, regression models were obtained using the partial least squares (PLS) method. Various data pre-treatments were also applied to improve the models. Compared to the models based on the NDF and IVOMD predictions of BMP, the model based on the NIRS prediction of BMP gave the best results. This model, with data pre-processed by the mean normalisation method, had an R(2) value of 0.69, a root mean square error of prediction (RMSEP) of 37.4 and a residual prediction deviation (RPD) of 1.75.

Real time monitoring of a biogas digester with gas chromatography, near-infrared spectroscopy, and membrane-inlet mass spectrometry.

Four methods of monitoring the anaerobic digestion process were studied at pilot scale. The methods employed were Micro Gas Chromatography (μ-GC) and Membrane Inlet Mass Spectrometry (MIMS) for measurements in the gas phase, Near Infrared Spectroscopy (NIRS) and pH in the liquid phase. Micro Gas Chromatography accurately measured H(2), CH(4), H(2)S, N(2) and O(2) in the headspace whereas the MIMS accurately measured CH(4), CO(2), H(2)S, reduced organic sulfur compounds and p-cresol, also in the headspace. In the liquid phase, NIRS was found to be suitable for estimating the concentrations of acetate, propionate and total volatile fatty acids (VFA) but the error of prediction was too large for accurate quantification. Both the μ-GC and NIRS were low maintenance methods whereas the MIMS required frequent cleaning and background measurements.

Identification of syntrophic acetate-oxidizing bacteria in anaerobic digesters by combined protein-based stable isotope probing and metagenomics

Inhibition of anaerobic digestion through accumulation of volatile fatty acids occasionally occurs as the result of unbalanced growth between acidogenic bacteria and methanogens. A fast recovery is a prerequisite for establishing an economical production of biogas. However, very little is known about the microorganisms facilitating this recovery. In this study, we investigated the organisms involved by a novel approach of mapping protein-stable isotope probing (protein-SIP) onto a binned metagenome. Under simulation of acetate accumulation conditions, formations of 13C-labeled CO2 and CH4 were detected immediately following incubation with [U-13C]acetate, indicating high turnover rate of acetate. The identified 13C-labeled peptides were mapped onto a binned metagenome for improved identification of the organisms involved. The results revealed that Methanosarcina and Methanoculleus were actively involved in acetate turnover, as were five subspecies of Clostridia. The acetate-consuming organisms affiliating with Clostridia all contained the FTFHS gene for formyltetrahydrofolate synthetase, a key enzyme for reductive acetogenesis, indicating that these organisms are possible syntrophic acetate-oxidizing (SAO) bacteria that can facilitate acetate consumption via SAO, coupled with hydrogenotrophic methanogenesis (SAO-HM). This study represents the first study applying protein-SIP for analysis of complex biogas samples, a promising method for identifying key microorganisms utilizing specific pathways.

Thermophilic anaerobic co-digestion of separated solids from acidified dairy cow manure.

This study examined the potential for partly substituting dairy cow manure (DCM) with solids from solid to liquid separation of acidified dairy cow manure (SFDCM) during thermophilic anaerobic digestion. Three different substituting levels with a maximum of 30% substitution were tested. All digesters substituting DCM with SFDCM showed a stable biogas production with low volatile fatty acid concentrations after a short transition period. An increased methane yield in terms of digester volume compared to DCM alone was obtained with increasing amount of SFDCM and about 50% more methane was achieved when 30% of DCM was substituted with SFDCM. The digestates were subsequently digested in a post digestion, during which the methane yield increased proportionally with increasing amounts of SFDCM. It can be concluded that SFDCM is a suitable biomass for co-digestion and can be used to increase methane yield in terms of digester volume at ratios up to at least 30%.

Quantifying Contribution of Synthrophic Acetate Oxidation to Methane Production in Thermophilic Anaerobic Reactors by Membrane Inlet Mass Spectrometry

A unique method was developed and applied for monitoring methanogenesis pathways based on isotope labeled substrates combined with online membrane inlet quadrupole mass spectrometry (MIMS). In our study, a fermentation sample from a full-scale biogas plant fed with pig and cattle manure, maize silage, and deep litter was incubated with 100 mM of [2-(13)C] sodium acetate under thermophilic anaerobic conditions. MIMS was used to measure the isotopic distribution of dissolved CO2 and CH4 during the degradation of acetate, while excluding interference from water by applying a cold trap. After 6 days of incubation, the proportion of methane derived from reduction of CO2 had increased significantly and reached up to 87% of total methane, suggesting that synthrophic acetate oxidation coupled to hydrogenotrophic methanogenesis (SAO-HM) played an important role in the degradation of acetate. This study provided a new approach for online quantification of the relative contribution of methanogenesis pathways to methane production with a time resolution shorter than one minute. The observed contribution of SAO-HM to methane production under the tested conditions challenges the current widely accepted anaerobic digestion model (ADM1), which strongly emphasizes the importance of the acetoclastic methanogenesis.

Evaluation of near infrared spectroscopy and software sensor methods for determination of total alkalinity in anaerobic digesters

In this study two approaches to predict the total alkalinity (expressed as mg L(-1)HCO(3)(-)) of an anaerobic digester are examined: firstly, software sensors based on multiple linear regression algorithms using data from pH, redox potential and electrical conductivity and secondly, near infrared reflectance spectroscopy (NIRS). Of the software sensors, the model using data from all three probes but a smaller dataset using total alkalinity values below 6000 mg L(-1)HCO(3)(-) produced the best calibration model (R(2)=0.76 and root mean square error of prediction (RMSEP) of 969 mg L(-1)HCO(3)(-)). When validated with new data, the NIRS method produced the best model (R(2)=0.87 RMSEP=1230 mg L(-1)HCO(3)(-)). The NIRS sensor correlated better with new data (R(2)=0.54). In conclusion, this study has developed new and improved algorithms for monitoring total alkalinity within anaerobic digestion systems which will facilitate real-time optimisation of methane production.

Rapid Assessment of Mineral Concentration in Meadow Grasses by Near Infrared Reflectance Spectroscopy

A near infrared reflectance spectroscopy (NIRS) method for rapid determination of nitrogen, phosphorous and potassium in diverse meadow grasses was developed with a view towards utilizing this material for biogas production and organic fertilizer. NIRS spectra between 12,000 cm−1 and 4,000 cm−1 were used. When validated on samples from different years to those used for the calibration set, the NIRS prediction of nitrogen was considered moderately useful with R2 = 0.77, ratio of standard error of prediction to reference data range (RER) of 9.32 and ratio of standard error of prediction to standard deviation of reference data (RPD) of 2.33. Prediction of potassium was less accurate, with R2 = 0.77, RER of 6.56 and RPD of 1.45, whilst prediction of phosphorous was not considered accurate enough to be of any practical use. This work is of interest from the point of view of both the removal of excess nutrients from formerly intensively farmed areas and also for assessing the plant biomass suitability for conversion into carbon neutral energy through biogas production.

Characteristics of Animal Slurry as a Key Biomass for Biogas Production in Denmark

Climate change has become an important global issue and animal manure has been pointed out as a major source of greenhouse gas (GHG) emissions. The Danish government targets animal manure as a key biomass with the aim of producing renewable fuels and reducing GHG emissions. Animal manure is a mixture of excreta and materials added during management. Apart from the major part of animal slurry which is feces and urine, animal slurry is composed of many materials, i.e., sand, water from cleaning, small branches and straw from the bedding materials. Thereby a wide variation of characteristics can be found depending on different management systems, animal type and diet, etc. which make for difficulties in the estimation of manure quality for biogas production.

Biogas potential from forbs and grass-clover mixture with the application of near infrared spectroscopy

This study investigated the potentials of forbs; caraway, chicory, red clover and ribwort plantain as substrates for biogas production. One-, two- and four-cut systems were implemented and the influence on dry matter yields, chemical compositions and methane yields were examined. The two- and four-cut systems resulted in higher dry matter yields (kg [total solid, TS] ha(-1)) compared to the one-cut system. The effect of plant compositions on biogas potentials was not evident. Cumulative methane yields (LCH4kg(-1) [volatile solid, VS]) were varied from 279 to 321 (chicory), 279 to 323 (caraway), 273 to 296 (ribwort plantain), 263 to 328 (red clover) and 320 to 352 (grass-clover mixture), respectively. Methane yield was modelled by modified Gompertz equation for comparison of methane production rate. Near infrared spectroscopy showed potential as a tool for biogas and chemical composition prediction. The best prediction models were obtained for methane yield at 29 days (99 samples), cellulose, acid detergent fibre, neutral detergent fibre and crude protein, (R(2)>0.9).

Effects of high-temperature isochoric pre-treatment on the methane yields of cattle, pig and chicken manure

Cattle manure, dewatered pig manure and chicken manure were pre-treated in a high-temperature reactor under isochoric conditions for 15 min at temperatures between 100 and 225°C with 25°C intervals to study the effect on their methane yield. After 27 days of batch incubation, cattle manure showed a significant improvement in its biochemical methane potential (BMP) of 13% at 175°C and 21% at 200°C. Pig manure showed improvements at temperatures of 125°C and above, with a maximum 29% increase in yield at 200°C. The BMP of chicken manure was reduced by 18% at 225°C, but at lower temperatures there were no significant changes. It was found that this method of pre-treatment could be feasible if sufficient surplus energy was available or if the energy used in the pre-treatment could be recovered.