Henrik Bjarne Møller

A new algorithm to characterize biodegradability of biomass during anaerobic digestion: Influence of lignin concentration on methane production potential

We examined the influence of fibrous fractions of biomass on biochemical methane potential (BMP) with the objective of developing an economical and easy-to-use statistical model to predict BMP, and hence the biodegradability of organic material (BD) for biogas production. The model was developed either for energy crops (grass, maize, and straw) or for animal manures, or as a combined model for these two biomass groups. It was found that lignin concentration in volatile solids (VS) was the strongest predictor of BMP for all the biomass samples. The square of the sample correlation coefficient (R(2)) from the BMP versus lignin was 0.908 (p<0.0001), 0.763 (p<0.001) and 0.883 (p<0.001) for animal manure, energy crops and the combined model, respectively. Validation of the combined model was carried out using 65 datasets from the literature.

Methane and carbon dioxide emissions and nitrogen turnover during liquid manure storage

Animal slurry stored in-house and outside is a significant source of atmospheric methane (CH4). The CH4 source strength of stored slurry is greatly affected by temperature. To improve emission calculations on a global scale there is a need for knowledge about the relationship between production of CH4 in slurry and temperature. In this study, the filling of slurry channels was reproduced in the laboratory by gradually filling 1xa0m-high PVC vessels during 9xa0days followed by incubation for 100–200xa0days. A preliminary test showed that little CH4 was produced from animal slurry during 10xa0days of incubation at 20°C, if no inoculum (slurry incubated anaerobically at the test temperature for 1.5–2xa0months) was present. However, the addition of 7.6% inoculum supported an immediate production of CH4. Vessels amended with inoculum and gradually filled with cattle or pig slurry were then incubated at 10, 15 and 20°C. Methane production from stored pig and cattle slurry was not significant at temperatures below 15°C, where CO2 was the main product of decomposition processes. In contrast, the anaerobic production of CH4 was high and significant relative to the production of CO2 at 20°C. Peak emissions of CH4 averaging 0.012 and 0.02xa0gxa0Cxa0h−1xa0kg−1 volatile solids (VS) were reached within about 10xa0days at 10 and 15°C, respectively. At 20°C, the emission of CH4 from pig slurry was about 0.01xa0gxa0Cxa0h−1xa0kg−1 for 10xa0days, and thereafter emissions increased to about 0.10xa0gxa0Cxa0h−1xa0kg−1 VS. For cattle slurry a peak emission of 0.08xa0gxa0Cxa0h−1xa0kg−1 VS was measured after 180xa0days. Degradation of organic nitrogen (N) in cattle slurry was related to the reduction of organic material as reflected in CO2 and CH4 emission. The mineralization of organic N during storage represented 10–80% of organic N in cattle slurry, and 40–80% of the organic N in pig slurry.

Extrusion as a pretreatment to increase biogas production

Application of an extruder to increase the methane yield in a biogas production was examined, and large potential was proved. An extruder was tested on five agricultural biomass types, represented by 13 samples. The samples were analyzed for temperature, maximum particle size, biogas potential, and energy consumption. The extruder treatment increased biomass temperature by 5-35 °C. Large particles (>1mm) were most affected by the extruder. Extrusion accelerated the degradation of slowly degradable organic compounds, and some otherwise nondegradable organic compounds were also degraded. The methane yield increased significantly: by 18-70% after 28 days, and by 9-28% after 90 days. The electrical energy equivalent of the extra methane, after subtracting the energy used by the extruder, resulted in energy surpluses of 6-68%. By day 90, the energy-efficiency of the extrusion process was ranked as follows: grass = straw = solids of flocculated manure < solids of screw-pressed manure

Cultivation of Ulva lactuca with manure for simultaneous bioremediation and biomass production.

The potential of liquid manure as sole nutrient source for cultivation of Ulva lactuca was investigated with the perspective of utilizing the produced biomass for feed and/or energy. Algae grown with manure demonstrated equal growth rates to algae grown with standard f/2-medium. The optimum manure concentration, expressed as ammonium concentration, was 25xa0μM. At these conditions, the biomass produced was potentially suitable for anaerobic digestion, due to a relative high carbon/nitrogen ratio (approximately 19). At higher manure concentrations, tissue concentrations of nitrogen, phosphorus, proteins, and amino acids increased, making the biomass less suitable for anaerobic digestion but potentially interesting as a feed supplement. Cultivating U. lactuca with manure as nutrient source has potential in terms of bioremediation as well as production of bioenergy and protein-feed.

Chemical composition and methane yield of reed canary grass as influenced by harvesting time and harvest frequency

This study examined the influence of harvest time on biomass yield, dry matter partitioning, biochemical composition and biological methane potential of reed canary grass harvested twice a month in one-cut (OC) management. The regrowth of biomass harvested in summer was also harvested in autumn as a two-cut management with (TC-F) or without (TC-U) fertilization after summer harvest. The specific methane yields decreased significantly with crop maturity that ranged from 384 to 315 and from 412 to 283 NL (normal litre) (kgVS)(-1) for leaf and stem, respectively. Approximately 45% more methane was produced by the TC-F management (5430Nm(3)ha(-1)) as by the OC management (3735Nm(3)ha(-1)). Specific methane yield was moderately correlated with the concentrations of fibre components in the biomass. Larger quantity of biogas produced at the beginning of the biogas assay from early harvested biomass was to some extent off-set by lower concentration of methane.

Mesophilic versus thermophilic anaerobic digestion of cattle manure: methane productivity and microbial ecology

In this study, productivity and physicochemical and microbiological (454 sequencing) parameters, as well as environmental criteria, were investigated in anaerobic reactors to contribute to the ongoing debate about the optimal temperature range for treating animal manure, and expand the general knowledge on the relation between microbiological and physicochemical process indicators. For this purpose, two reactor sizes were used (10u2009m3 and 16u2009l), in which two temperature conditions (35°C and 50°C) were tested. In addition, the effect of the hydraulic retention time was evaluated (16 versus 20 days).

Heavy Metal and Phosphorus Content of Fractions from Manure Treatment and Incineration

Alternative uses of pig manure are being considered, including separation and eventual incineration of the solid fraction to produce energy and ash. The efficiency of a screw press, a decanting centrifuge and chemical treatment in transferring N, P and heavy metals from slurry to a solid fraction were compared. Chemical treatment by coagulants and flocculants removed heavy metals most efficiently; they were transferred to the solid fraction in the order Zn > Cu > Cd by all three types of equipment. With centrifugation the heavy metal load on land where the solid fraction was applied was very low, whereas on land where the liquid fraction was applied it was only slightly less than that from un-separated manure. Conversely, chemical treatment resulted in a heavy metal load similar to that from un-separated manure with the solid fraction, while with the liquid fraction it was reduced to 20% of that from un-separated manure. Incineration of the solid fraction produces bottom ash and fly ash containing high levels of P. Most of the P and less than 10% of Cd is present in the bottom ash, producing an ash low in Cd content and a fly ash high in Cd. However, Cu and Ni tend to accumulate in the bottom ash. Chemical extraction procedures revealed that P-availability was high in all liquid and solid fractions except the bottom ash from incineration where ∼80% of the P was transformed into a form of apatite. Since more bottom ash than fly ash is being formed, significant amounts of P may be immobilized by incineration of solid fractions.

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.

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%.

Process performance of anaerobic co-digestion of raw and acidified pig slurry.

The effect of incorporating different ratios of acidified pig slurry on methane yield was evaluated in two scales of anaerobic digesters: Thermophilic (50 °C) pilot scale digester (120 l), operating with an average hydraulic retention time of 20 days and thermophilic (52 °C) full-scale digesters (10 and 30 m(3)), operating with an average hydraulic retention time of 30 days. In the lab-scale digester, different inclusion levels of acidified slurry (0-60%) were tested each 15 days, to determine the maximum ratio of acidified to non-acidified slurry causing inhibition and to find process state indicators helping to prevent process failure. In the full-scale digesters, the level of inclusion of the acidified slurry was chosen from the ratio causing methane inhibition in the pilot scale experiment and was carried on in a long-term process of 100 days. The optimal inclusion level of acidified pig slurry in anaerobic co-digestion with conventional slurry was 10%, which promoted anaerobic methane yield by nearly 20%. Higher inclusion levels caused methane inhibition and volatile fatty acids accumulations in both experiments. In order to prevent process failure, the most important traits to monitor in the anaerobic digestion of acidified pig slurry were found to be: sulfate content of the slurry, alkalinity parameters (especially partial alkalinity and the ratio of alkalinity) and total volatile fatty acids (especially acetic and butyric acids).