Manure-based Biogas Plants Research Articles

Methane emission rates averaged over a year from ten farm-scale manure storage tanks

Methane (CH4) emissions from animal manure stored in outdoor tanks are difficult to predict because of several influencing factors. In this study, the tracer gas dispersion method (TDM) was used to quantify CH4 emissions from ten manure storage tanks, along with the collection of supporting information, in order to identify its emission drivers. The dataset included two tanks storing dairy cattle manure, six holding pig manure, and two with digestate from manure-based biogas plants. CH4 emissions from the tanks were measured six to 14 times over a year. Emissions varied from 0.02 to 14.30 kg h−1, or when normalised by the volume of manure stored, emission factors (EFs) varied from 0.05 to 11 g m−3 h−1. Annual average CH4 EFs varied greatly between the tanks, ranging from 0.20 to 2.75 g m−3 h−1. Normalised EFs are similar to literature values for cattle and digested manure, but at the high end of the interval for pig manure. The averaged manure temperature for all tanks varied from 10.6 to 16.4 °C, which was higher than reported in a previous Danish study. Volatile solids (VS) concentration was in average higher for cattle manure (ranging from 3.1 and 4.4 %) than pig manure (ranging from 1.0 to 3.6 %). CH4 emission rates were positively correlated with manure temperature, whereas this was not the case for VS concentration. Annual average EFs were higher for pig than for cattle manure (a factor of 2.5), which was greater than digested manure emissions (a factor of 1.2). For the pig manure storage tanks, CH4 emissions were higher for covered tanks than for uncovered tanks (by a factor of 2.3). In this study, manure storage tanks showed a large disparity in emission rates, driven not only by physical factors, but also by farm management practices.

Energy recovery from wastewater microalgae through anaerobic digestion process: Methane potential, continuous reactor operation and modelling aspects

A mixture of piggery slurry and algal species (mainly composed of Nannochloropsis limnetica), grown in municipal wastewater, were used as substrates for biogas production. Mono- and co-digestion experiments were performed at batch and continuous reactor operation. The mono-digestion of wastewater microalgae led to the highest methane yield (408 ± 34 N mL/gVS). However, for manure-based biogas plants, a 60:40 v/v piggery slurry to wastewater microalgae ratio in terms of organic matter was identified as the most efficient mixture in batch assays (355 ± 27 N mL/gVS). The advantage of co-digestion was also evidenced under continuous reactor operation, which had markedly higher biogas production (23%, p < 0.05) compared to the mono-digestion of livestock manure. Moreover, it was demonstrated that the co-digestion process resulted in a more robust process as indicated by lower accumulation of acetate (i.e. presented during mono-digestion of piggery slurry) and propionate (i.e. recorded during mono-digestion of wastewater microalgae). The experimental data were compared with dynamic modelling (BioModel). A new set of biodegradability parameters was estimated and employed to improve the simulations of mono-digestion scenarios. Subsequently, the co-digestion scenario was used for model validation. Results obtained from simulations showed that the co-digestion can lead to relatively high methane productivity and prevent process instabilities.

A spatial analysis of biogas potential from manure in Europe

Anaerobic digestion is increasingly used worldwide to generate energy from biogas, bringing significant economic and environmental benefits. In particular, in the European Union (EU), biogas can contribute significantly in several countries to reach the renewable energy targets. This study provides an assessment of the spatial distribution of the biogas potential of farm manure from livestock and poultry in Europe, which is a key issue for the location and economic performances of a bioenergy plant. Biogas estimates provided in this study are computed through a spatial analysis algorithm that uses data of livestock and poultry, manure production and collection, leading to the evaluation of the spatial distribution of biogas potential at 1 km spatial resolution. Following this analysis, the theoretical biogas potential of manure was estimated at 26 billion m3 biomethane in Europe (23 billion m3 biomethane in the EU) and the realistic biogas potential, counting on collectible manure, was assessed at 18 billion m3 biomethane in Europe (16 billion m3 biomethane in the EU). Several maps provide the suitable locations and capacity of manure-based biogas plants in two different scenarios. Between 13,866 and 19,482 biogas plants could be built in Europe, with a total installed capacity between 6144 MWe and 7145 MWe, and an average capacity between 315 kWe and 515 kWe.

Anaerobic co-digestion of swine manure and crude glycerol derived from animal fat—Effect of hydraulic retention time

Crude glycerol (CG), an abundant by-product of bio-diesel production, has been identified as a suitable co-substrate for improving the biogas production of livestock manure through anaerobic digestion (AD). In this study, the potential of utilizing CG generated from the esterification of animal fats for biogas production was studied in both batch and continuous AD experiments, with emphasis on the importance of the hydraulic retention time (HRT). Batch experiments showed that the limiting step in the methane production rate during CG mono-digestion was the 1,3-propanediol uptake. Additionally, biochemical methane potential tests indicated that the addition of 1% w/w CG to swine manure-AD is more efficient in terms of percent of theoretical amount of methane obtained than the addition of 3% w/w. However, in continuous experiments, co-digestion of manure with 3% w/w CG did not exhibit any sign of inhibition within the HRTs tested (17–22 days). Moreover, a 222% increase of biogas productivity was observed with 3% CG supplementation at an HRT of 17 days, in contrast to a 146% increase at an HRT of 22 days. Based on this, and on the similar efficiency of soluble COD removal among the processes (ca. 93%), it was shown that it is possible to reduce the HRT without affecting negatively the efficiency of conversion of manure. Moreover, it was shown that CG from 2 nd generation biodiesel based on animal fat, is a suitable feedstock for boosting the methane production of manure-based biogas plants.

Comparative life cycle assessment of biowaste to resource management systems – A Danish case study

Waste to Energy combustion plants currently process most of the organic fraction of the household waste. This study presents an assessment of the environmental performance of an increased circular bioresource management system obtained by reallocating the organic fraction of the household waste from combustion (Reference Scenario) to biogas and fertilizer production (Alternative Scenario). The goals defined in the Danish National resource action plan for waste management, i.e. 33% reduction of organic fraction household waste dry weight, is taken as a case study. A comparative life cycle assessment of the diverting of the organic fraction of the household waste away from a Waste to Energy combustion plant towards sludge- and manure-based biogas plants in North Zealand (Denmark) shows a net increase in renewable electricity production of 39% at the expense of a reduction in heat production of 8%. Moving up the waste hierarchy results in a net greenhouse gas emission reduction of 100 kg CO2eq. per ton of dry weight biowaste treated, corresponding to a 10% of reduction in CO2 emission. The latter accompanied by a net reduction in depletion of fossil resources of 11% and a reduction in the impacts on Freshwater and Marine Eutrophication of 4.8 t P eq. and 3.6 t N eq., respectively. As such, the modelled increased circular bioresource management indicates significant improvement of the efficiency in use of resources in biowaste. However, trade-offs occur due to the presence of micropollutants in the natural fertilizers that results in future increased damage cost on terrestrial ecosystems and human health exists.

The energy balance of utilising meadow grass in Danish biogas production

This paper presents a study of the energy balance of utilising nature conservation biomass from meadow habitats in Danish biogas production. Utilisation of nature conservation grass in biogas production in Denmark represents an interesting perspective for enhancing nature conservation of the open grassland habitats, while introducing an alternative to the use of intensively cultivated energy crops as co-substrates in manure based biogas plants. The energy balance of utilising nature conservation grass was investigated by using: data collected from previous investigations on the productivity of meadow areas, different relevant geo-datasets, spatial analyses, and various statistical analyses. The results show that values for the energy return on energy invested (EROEI) ranging from 1.7 to 3.3 can be obtained when utilising meadow grasses in local biogas production. The total national net energy gain (NEG) was estimated to more than 600,000GJ corresponding to ≈15% of the total Danish biogas production in 2012.

Counteracting foaming caused by lipids or proteins in biogas reactors using rapeseed oil or oleic acid as antifoaming agents

Foaming is one of the major operational problems in biogas plants, and dealing with foaming incidents is still based on empirical practices. Various types of antifoams are used arbitrarily to combat foaming in biogas plants, but without any scientific support this action can lead to serious deterioration of the methanogenic process. Many commercial antifoams are derivatives of fatty acids or oils. However, it is well known that lipids can induce foaming in manure based biogas plants. This study aimed to elucidate the effect of rapeseed oil and oleic acid on foam reduction and process performance in biogas reactors fed with protein or lipid rich substrates. The results showed that both antifoams efficiently suppressed foaming. Moreover rapeseed oil resulted in stimulation of the biogas production. Finally, it was reckoned that the chemical structure of lipids, and more specifically their carboxylic ends, is responsible for their foam promoting or foam counteracting behaviour. Thus, it was concluded that the fatty acids and oils could suppress foaming, while salt of fatty acids could generate foam.

Optimizing the performance of a reactor by reducing the retention time and addition of glycerin for anaerobically digesting manure

Anaerobic digestion of manure is a widely accepted technology for energy production. However, only a minimal portion of the manure production in the EU is anaerobically digested and occurs predominantly in codigestion plants. There is substantial potential for biogas plants that primarily operate on manure (>90%); however, the methane yields of manure are less compared to coproducts, which is one of the reasons for manure-based biogas plants often being economically non-viable. Therefore, it is essential to begin increasing the efficiency of these biogas plants. This study investigated the effect of decreasing retention time and introducing a moderate amount of glycerin on the biogas production as methods to improve efficiency. An experiment has been conducted with two different manure types in four biogas reactors. The results of the study demonstrated that, first, it was possible to decrease the retention time to 10–15 days; however, the effect on biogas production varied per manure type. Secondly, the biogas production almost triples at a retention time of 15.6 days with an addition of 4% glycerin. The relative production-enhancing effect of glycerin did not vary significantly with both manure types. However, the absolute production-enhancing effect of glycerin differed per manure type since the biogas production per gram VS differed per manure type. Thirdly, the positive effect of the glycerin input declines with shorter retention times. Therefore, the effect of glycerin addition depends on the manure type and retention time.

Changes in Nitrogen Availability in Chernozemic Soils Amended with Anaerobically Digested Cattle Manure

Anaerobically digested manure (ADM) is a nutrient-rich coproduct from manure-based biogas plants. The ADM is often separated into a solid fraction, known as solid digestate (SD), and a liquid fraction, which could be applied to cropland at rates equivalent to those for raw manure. Application of SD could result in different nitrogen (N) mineralization patterns compared to raw manure due to biophysicochemical changes occurring during anaerobic digestion. The objective of this laboratory incubation experiment was to characterize changes in the availability of N in a Dark Brown Chernozem (Typic Haploboroll clay loam) and a Black Chernozem (Typic Haplocryoll silty clay) amended with raw beef cattle (Bos taurus) feedlot manure, SD, pelletized SD (PSD), and urea plus monoammonium phosphate (UMAP) at rates equivalent to 400 and 800 mg N kg⁻¹ soil. Across rates, net mineralized N concentrations after 70 d in soils amended with UMAP, manure, SD, and PSD were 44, 18, −5, and -13% of added N, respectively, in the Dark Brown Chernozem and 45, 29, 6, and -18%, respectively, in the Black Chernozem. The lower N mineralization potential of SD and PSD compared with manure implies that anaerobic digestion alters the nutrient release patterns of manure and suggests that these digested manure forms may have to be either applied at higher rates compared with raw manure or should be supplemented with inorganic N fertilizer to ensure adequate N supply for plants.

Biogas production from catch crops: Evaluation of biomass yield and methane potential of catch crops in organic crop rotations

Manure-based biogas plants in Denmark are dependent on high yielding biomass feedstock in order to secure economically feasible operation. The aim of this study was to investigate the potential of ten different catch crop species or mixtures as feedstock for biogas production in co-digestion with manure. The biomass yield per hectare and the specific methane yield of the catch crops in two different locations, namely Holstebro and Aabenraa, were investigated. The volatile solids (VS) yield per hectare was notably influenced by the differences in climate and soil conditions between the locations, being in the ranges of 1.4–3.0 t ha−1 and 0.3–1.7 t ha−1 for Holstebro and Aabenraa, respectively. Specific methane yields were in the range of 229–450 m3 t−1 of VS. Methane yields per hectare of up to 800 m3 ha−1 were obtained, making catch crops a promising source of feedstock for manure-based biogas plants in Denmark since this biomass is not competing with food/feed production.

Improving biogas yields using an innovative concept for conversion of the fiber fraction of manure

The potential of a new concept to enable economically feasible operation of manure-based biogas plants was investigated at laboratory scale. Wet explosion (WEx) was applied to the residual manure fibers separated after the anaerobic digestion process for enhancing the biogas yield before reintroducing the fiber fraction into the biogas reactor. The increase in methane yield of the digested manure fibers was investigated by applying the WEx treatment under five different process conditions. The WEx treatment at 180 °C and a treatment time of 10 min without addition of oxygen was found to be optimal, resulting in 136% increase in methane yield compared with the untreated digested manure fibers in batch experiments. In a continuous mesophilic reactor process the addition of WEx-treated digested fibers in co-digestion with filtered manure did not show any signs of process inhibition, and the overall methane yield was on average 75% higher than in a control reactor with addition of non-treated digested fibers.

Instrumentation, control and automation for full-scale manure-based biogas systems

In recent years manure-based biogas plants (MBBP) have won more and more importance, because of the numerous ecological advantages. The processes are similar to processes, which have been well known for many decades in anaerobic wastewater/sludge treatment. As a result of technical progress and permanently rising prices for non-renewable energy, MBBPs have become more and more economically reasonable. Because of the economies of scale law more and more larger MBBPs are being built (250-2000 kW(el)). With regard to investment costs, reactor volumes and complexity etc., these (centralized) plants are comparable with small wastewater treatment plants (WWTP). Consequently, as actually in the case of the small WWTPs a rising use of instrumentation, control and automation (ICA) for larger MBBPs can be observed.