Oxidation of methane from manure storages in soils

Transcription

1 Journal of Integrative Environmental Sciences ISSN: X (Print) (Online) Journal homepage: Oxidation of methane from manure storages in soils Hans Oonk & Jan Koopmans To cite this article: Hans Oonk & Jan Koopmans (2012) Oxidation of methane from manure storages in soils, Journal of Integrative Environmental Sciences, 9:sup1, , DOI: / X To link to this article: Published online: 12 Sep Submit your article to this journal Article views: 392 Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at

2 Journal of Integrative Environmental Sciences Vol. 9, Supplement 1, November 2012, Oxidation of methane from manure storages in soils Hans Oonk a * and Jan Koopmans b a OonKAY!, Fabianusstraat 12, Apeldoorn, Netherlands; b PAS Mestopslagsystemen, De Giek 31, Drachten, Netherlands (Received 5 December 2011; final version received 12 July 2012) Dutch methane emissions from manure treatment and storage are estimated to be 115 Gg CH 4, which is about 1.5% of total greenhouse gas emissions. A possible option to reduce methane emissions from manure storages is to feed emissions into the soil next to the storage, where it is oxidized by methanotrophic bacteria, comparable to the way methane is oxidized in top-layers of landfills. A feasibility study is performed to evaluate the technical and economic viability of the method. An annual average methane oxidizing capacity of about 2 3 g m 72 h 71 seems to be feasible in sandy or loamy soils, without major modifications. A single manure storage will require a few 100 m 2 of soil to abate 70% or more of its methane. The system seems to be economically feasible and cost-effective. Additional investments are less than 5% of the total costs of a manure storage. Costs for emission reduction are e 1 to 4 per Mg CO 2 -eq. Proof of concept was no part of this feasibility study. The technology described is only expected and not demonstrated to work. Keywords: methane; manure; methane oxidation; methanotrophs; biocovers Introduction Treatment and storage of manure contributes to acidification and local odor nuisance through emissions of ammonia, H 2 S, other sulfuric components and organic esters. Apart from this, anaerobic conversion of residual organic material in animal manure results in formation and emission of methane. Total methane emissions from manure treatment and storage in the Netherlands is estimated to be 115 Gg CH 4 (Project Emissieregistratie 2010), which equals 2.7 Tg CO 2 -equivalents. Manure treatment and storage is responsible for almost 1.5% of total greenhouse gas emissions. Methane emissions from manure storages are released in relative small amounts, and show seasonal variability, depending on the amount of manure in storage. In the Netherlands, storages are generally emptied in spring and in autumn when manure fertilizer is applied in the fields. In between, manure storages are gradually filled again. Methane generation is also dependent on ambient temperature. As a result, methane generation in summer will be higher than methane emissions in winter (van der Hoek and van schijndel 2006). In this project, annual average methane emissions from manure storage near a stable of 80 milking cows are estimated to be about 300 *Corresponding author. hans@oonkay.nl ISSN X print/issn online Ó 2012 Taylor & Francis

3 226 H. Oonk and J. Koopmans g per hour, with a peak in summer up to about 1 kg per hour. So the source is small compared to, e.g. other sources of methane (e.g. landfills, waste water treatment or oil and gas industry) and this limits the possibilities for cost-effective abatement. Attempts are made to reduce methane emissions in biofilters, specifically for manure storages but also for other sources (e.g. Melse 2003). However, due to the poor solubility of methane in water, conversion is limited to about 0 20% for the residence times that are common in biofiltration. Scheutz et al. (2009) give a review of methane oxidation capacities of biofilters and report values in between 2 and 25 g h 71 per m 2 biofilter surface. Methane emissions from landfills are removed in the landfills top-layer by oxidation by methanotrophic bacteria. In the past decades, there has been an increasing interest in options to improve methane oxidation and engineered toplayers are developed, capable of removing 100% of the methane up to fluxes of 2 3 g m 72 h 71 (e.g. Huber-Humer et al. 2008; Scheutz et al. 2009). Important conclusion of this research is that many types of soil have adequate methane oxidation capacity. However, according to Huber-Humer et al. (2008) for an effective methane oxidizing top-layer, a dispersion layer is required to enable a homogeneous supply of methane from the bulk of the waste to the top-layer (see Figure 1). What works for landfills, can be expected to work for methane from manure storages as well. Therefore, a feasibility study was performed for removal of methane emissions from manure storages by methanotrophic bacteria in the soil near the manure storage. In such a system, the soil is used as a substrate for biofiltration. However, because of its design, residence times in such an oxidation field are much longer (about half an hour) in comparison to residence times in a biofilter (30 s to few minutes). For application near manure storages, methane might be collected from the manure storage and fed into a dispersion layer at about 1 m depth in the surrounding soil. When the gas migrates from this dispersion layer, through the soil towards the atmosphere, it is oxidized by methanotrophic bacteria. For a manure storage emitting 300 g CH 4 per hour, a methane oxidizing field of about 100 m 2 should suffice to mitigate most of the methane. This surface is not lost, but might be used for various purposes, e.g. grass can be grown to feed the cattle. For a further evaluation of the system a study was performed, evaluating both technical and economic feasibility of oxidation of methane from manure storages. The results of this feasibility study are presented in this article. Proof of concept was no part of this feasibility study. The technology described is only expected and not demonstrated to work. Figure 1. Enhanced methane oxidation in top-layers of landfills.

4 Journal of Integrative Environmental Sciences 227 Manure storages and methane emissions In the Netherlands, several different systems for manure storage are in use. Manure basins are rectangular shaped storages, consisting of dikes of about 3 5 m high. The bottom and the top of a basin is sealed with an impermeable liner in between which manure is pumped. The upper liner contains ventilation pipes as a result of which pressure is prevented from being built-up. Manure bags are also located between dikes, but the bags enable filling of the storage above the level of the dikes. Manure can also be kept in silos equipped with either a floating or a fixed roof. Stables are required to have sufficient storage room for six months of manure storage. However, large part of the manure is also stored away from the stables by agricultural farmers, near the fields where manure is used as a fertilizer. Those agricultural farmers purchase and transport the manure at a certain moment in time when they judge that prices are favorable. Methane emissions from a manure storage are quantified using a model, that describes methane emissions as a function of amount of manure in storage, the type of manure (cows, sows or slaughter pigs), the age of the manure and also the season (winter or summer storage). The model itself is a simple first-order decay model, in which methane generation is assumed to be proportional to the amount of biodegradable organic material in the manure in storage. The model parameters are based on the model used by Netherlands Environmental Assessment Agency (PBL) for quantification of Dutch methane emissions in the National Communications (van der Hoek and van Schijndel 2006). Table 1 gives an overview of model parameters used in this study. The model in itself has a limited accuracy. Inaccuracy in the national emission estimate is about 100% (Olivier et al. 2009; PBL 2010), so the interpretation of the PBL-model for quantification of methane emissions from a single storage will have similar accuracy. Methane oxidation As already mentioned in the introduction, methane oxidation in landfill top-layers received considerable attention in the last decade. Methane oxidation is governed by a number of factors:. The methane flux. The higher the flux, the more methane is converted in g m 72 h 71. The maximum methane conversion rate is governed by both the intrinsic capacity of the top-layer to develop methanotrophic activity and the rate of diffusion of air into the top-layer. Table 1. Model parameters for calculation of methane emissions from manure storage (based on van der Hoek and van Schijndel 2006). Manure production (ton/animal/year) 1 Initial methane potential (m 3 /ton manure) k summer (1/day) k winter (1/day) Milk cows Slaughter pigs Sows Note: 1 Including flushing water.

5 228 H. Oonk and J. Koopmans. The structure of the top-layer. The porosity needs to suffice, also under wet conditions. At the same time, the soil needs to have sufficient water-retaining capacity. The topsoil needs to be homogeneous with little or no tendency to form cracks.. Vegetation on the soil has a positive impact on moisture content and porosity of the top-layer.. Chemical composition is of importance. Essential nutrients are N and C amongst others.. Local weather conditions in general and ambient temperature and precipitation in particular. Under Dutch conditions, methane oxidation in winter will be less than in summer. Methane oxidation in top-layers of landfills has drawn the attention of many research groups throughout the world. In most cases, the objective is to increase methane oxidation. Three classes of cover materials might be distinguished, suited for methane oxidation:. One hundred percent organic material, such as compost was often proposed in the more early systems. However, most experiences indicate that this is not a preferred choice, since such cover material has limited life-time, since they decay and lose porosity. Moreover, decay of organic material might compete with methane for oxygen that diffuses into the top-layer, and also an excess of organic N might compete for oxygen. As a result, too high content of organic material might even hamper methane oxidation.. Mixtures of sand and stabilized compost are the preferred choice by most researchers. The compost supplies nutrients to methanotrophic bacteria and improves the water retaining properties of the soil. The sand improves porosity and permeability of the soil and provides mechanical firmness.. Sandy or loamy covers, without any additional material show sufficient methanotrophic activity. Since they are relatively cheap, inert and therefore have a long life-time, they are the preferred option by some researchers. Homogeneous supply of methane from the body of the waste to the top-layer, however, is essential for a proper oxidizing top-layer. For this purpose, a distribution layer is made, just below the top-layer, consisting of drainage sand, gas drainage mats, gravel or waste materials as glass or shredded car-tires. Developments in methane oxidizing top-layers have advanced that far, that the Austrian government already drafted guidelines on how to construct and operate methane oxidizing top-layers for landfills. A good methane oxidizing top-layer has a capacity of at least 3 g m 72 h 71, while actual capacity in summer might be considerably higher (Huber-Humer 2010). Application at manure storages Methane oxidation at manure storages might consist from the following parts:. Collection system: a manure storage normally has a few ventilation shafts that prevent pressure from being built-up in the manure storage. Ventilation shafts can be connected to a system of flexible hoses (see Figure 2);

6 Journal of Integrative Environmental Sciences 229 Figure 2. Capture of methane from a manure basin.. Injection into the soil: supply pipes might inject methane in a gas distribution layer below the soil. For such a distribution layer, similar materials might be used for distribution layers in landfills (see above);. As an oxidizing layer sandy or loamy soil might be used. Clay seems less well suited because of its low porosity, especially when wet. For landfills addition of organic material (e.g. stabilized compost) is proposed, but it is unclear whether this is a necessity. For methane from manure storages, the necessity of compost might be even less, since the waste gas from the manure storage contains ammonia, which can serve as a nutrient for methanotrophic bacteria. The thickness of a methane oxidizing layer will be about cm;. Pressure drop in the system (collection and sand) is estimated to be Pa and could be supplied by methane generation in the manure storage itself.. Effect of NH 3 and H 2 S is of concern. Waste gas from manure storages contains apart from methane CO 2,NH 3 and H 2 S. CO 2 and H 2 S also occur in landfill gas at comparable concentrations. At landfills, methane oxidation is still possible and therefore these components are most likely no complication for methane from manure storages. NH 3 does not occur in landfill gas and its effect on methane oxidation is unclear. At high concentrations, NH 3 might inhibit methanotrophic activity and NH 3 might also compete with methane for available oxygen. NH 3, however, also serves as a nutrient, increasing methanotrophic activity. A first estimate for nitrogen requirement during methane oxidation is one mole N per mole CH 4 converted with a N:CH 4 ratio of 1:40 as the most likely value. The NH 3 to CH 4 ratio in the waste gas of a manure storage is estimated to be 1:16 to 1:40, so most likely NH 3 is no problem in this application. However, the effect NH 3 is an important aspect of a project, demonstrating the proof of principle of this mitigation option.. Changes in methane supply occur when methane supply from a manure storage is not constant, but might fluctuate throughout the year. Normally, a manure storage is filled in the period April August, emptied in September, filled again from October to February and emptied again in March. Methane generation is proportional to the amount of manure in storage, so some fluctuation in methane formation can be expected. Methanotrophic bacteria seem to be able to react fast enough to this variation. In the lab accommodation to a higher content of methane often takes only a few days, especially when the soil has previously been exposed to methane.. The system seems to be safe for two reasons. In the manure storage, in the collection hoses and during injection in the distribution layer, waste gases from the manure storage are not diluted by air, so no explosive mixtures of methane

7 230 H. Oonk and J. Koopmans and air can be formed. Methane-air mixtures only occur in the top-layer itself. The system uses natural pressure build-up for transport and injection in the distribution layer. No electricity is used. So, in case leaks in the collection hoses do result in flammable mixtures of air and methane, there is no spark that can cause ignition.. Maintenance of a methane oxidizing top-layer seems relatively simple and is most likely limited to temporarily mowing of vegetation. For methane oxidation at landfills, it is recommended to leave mowed grass on the surface to keep nutrients in the system. For manure storages, this seems to be less critical since the most important nutrient, N, is supplied with the waste gas from the storage. Effectiveness The effectiveness of an oxidation field near a manure storage depends on supply of methane, the conversion rate in the oxidation field and the size of the field in m 2. Both methane supply and methane oxidation depend on the season. Figure 3 gives the result of a calculation for a manure storage near a stable for 80 milk cows. Methane generation is calculated using the parameters in Table 1. The size of the oxidation field is 100 m 2. Assumed rates of methane oxidation are based on minimum activities described by Huber-Humer et al. (2008). Methane oxidation is assumed to be temperature dependent, at 188C is6gm 72 h 71, and reduces by 50% when temperatures decrease by 108C. Methane oxidation capacity of the field suffices to abate all methane, except for some periods during the peak in methane production in summer and winter. Average annual effectiveness in this example is 82%. Annual average methane oxidation is 2.7 g m 72 h 71. Figure 4 gives the results for a manure storage for 2500 m 3 of manure, located away from the stables, near the area where manure is applied as a fertilizer. The 2500 m 3 is a common size in the Netherlands, since it is the maximum size that can be realized without additional permits. In this example, the manure storage is already filled early in the season with 80% pig manure and 20% cow manure. Average age of the manure at the moment of delivery is eight weeks. The size of the Figure 3. Methane generation from a manure storage (straight line) and methane oxidation (dotted line) in soil near a stable with 80 milking cows and a 100 m 2 oxidation field.

8 Journal of Integrative Environmental Sciences 231 oxidation field is 750 m 2. Annual average effectiveness in this example is 70%. Annual average methane oxidation is 2.9 g m 72 h 71. Economic feasibility Table 2 gives an overview of costs of methane oxidation at a manure storage. Costs for methane oxidation are few percent of the total investments of a manure storage. Table 3 gives cost-effectiveness of methane oxidation assuming an average methane conversion of 2 to 3 g m 72 h 71 and investment costs are about e 5 10 per m 2 of oxidation field (see Table 2). In this calculation, an annuity method of depreciation is assumed over 10 years period and an interest rate of 10%. Figure 4. Methane generation from a manure storage (straight line) and methane oxidation (dotted line) in soil for a 2500 m 3 storage basin in the field, with a 600 m 2 oxidation field. Table 2. Costs of methane oxidation near a manure storage. Manure silo (floating roof) Manure basin Capacity 1000 m m 3 Size oxidation field 100 m m 2 Costs manure storage e e Methane oxidation e 890 e Specification methane oxidation Gas collection at manure storage e 100 e 150 Dispersion layer e 530 e Work (digging) e 260 e 840 Table 3. Cost-effectiveness. Average effectiveness (g m 72 hr 71 ) Costs oxidation field (e m 72 ) Emission reduction (kg m 72 jr 71 ) Costs (e m 72 jr 71 ) Cost-effectiveness (e kg 71 methane) Cost-effectiveness (e Gg 71 CO 2 -eq.)

9 232 H. Oonk and J. Koopmans Cost-effectiveness varies in between e 1 and 4 per ton CO 2 -eq. and can be considered favorable. As a reference: compensation of CO 2 -emissies through purchase of certified emission rights (Gold Label certified CERs) costs about e 20 per ton CO 2 -eq. The industrial trading price for CO 2 was about e 20 per ton CO 2, has decreased somewhat due to the economic recession, but will rise again without any doubt to values well above e 20 per ton CO 2. Alternatives for greenhouse gas emission reduction, such as capture and storage of CO 2, cost about e 50 per ton CO 2. Conclusions Methane oxidation in the soil surrounding a manure storage seems to be technically feasible for all types of manure storage. The system was only evaluated in a feasibility study. Proof of concept was no part of this and the technology described is only expected and not demonstrated to work. The method itself is simple and adaptations to the manure storage are limited. Ventilation shafts of the manure storage are connected to a collection system of flexible hoses and pipes. The waste gases are fed into a distribution system of about 1 m under the surface. Methane is ultimately oxidized by methanotrophs in the soil. Main concern is the presence of ammonia in the waste gas, but at expected concentrations this is most likely facilitates methane oxidation. The effectiveness methane oxidation depends amongst others on the surface area of the methane oxidizing field. Yields in excess of 70% seem to be attainable. When fully implemented, a reduction of 1.9 Mton CO 2 -eq. per year might be possible, which is about 1% of total Dutch greenhouse gases. Besides methane, NH 3 and odor emissions are abated. This oxidation efficiency is based on information methane oxidation in soils, as described from literature. The oxidation efficiency has to be verified in a field demonstration. The system seems to be economically feasible and cost-effective. Additional investments are less than 5% of the total costs of a manure storage. Costs for emission reduction are e 1 to 4 per ton CO 2 -eq., which is cheap compared to other options that are currently considered for greenhouse gas emission reduction. Acknowledgments This feasibility study and the sequential demonstration are funded by the Small Business Innovation Research (SBIR) program on the reduction of methane emission from manure storages, executed by the Reduction programme for non CO 2 greenhouse gases (ROB) from NL Agency and the Ministry of Infrastructure and Environment. The authors would like to thank Arnoud Smit and Jan van Bergen of NL Agency in particular for their valuable and enthusiastic feedback in the course of the study. References Huber-Humer M Personal communication. Vienna, Austria: Universita t Wien. Huber-Humer M, Amann A, Bogolte T, Dos Santos M, Hagenauer I, Pauliny W, Reichenauer T, Watzinger A, Wimmer B Technischer Leitfaden Methanoxidationsschichten. Erstellt im Rahmen der O VA-Arbeitsgruppe Leitfaden Methanoxidationsschichten. Melse R Biologisch filter voor verwijdering van methaan uit lucht van stallen en mestopslagen. Wageningen: Agrotechnology and Food Innovations B.V.

10 Journal of Integrative Environmental Sciences 233 Olivier JGJ, Brandes LJ, te Molder RAB Estimate of annual and trend un-certainty for Dutch sources of greenhouse gas emissions using the IPCC Tier 1 approach. PBL Report Bilthoven: PBL. PBL Greenhouse gas emissions in the Netherlands PBL report / Bilthoven: PBL. Project Emissieregistratie Database available from: Scheutz C, Kjeldsen P, Bogner JE, De Visscher A, Gebert J, Hilger HA, Huber-Humer M, Spokas K Microbial methane oxidation processes and technologies for mitigation of landfill gas emissions. Waste Manage Res. 27: van der Hoek KW, van Schijndel MW Methane and nitrous oxide emissions from animal manure management, Background document on the calculation method for the Dutch National Inventory Report. RIVM report /2006. Bilthoven: RIVM.