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how to build a methane digester?

  • Put a chicken in your tank: "You just put about three buckets of manure into a sealed oil drum. Put a small oil heater under the drum to keep the manure at a steady 80 degrees. There are two microbes in the manure which, when heated, eat each other - this produces the gas. You can collect the gas in bottles or in plastic balloons for storage. Then all you do is feed the methane through an adapter into your carburetor - and you've got chicken power. I keep replenishing my manure supply. I run my car for about six months before I clean out the tank and start with fresh dung."
digester designs

 

Small scale
  • in a bucket
  • tin for doggie dooly
  • in a plastic foil  (DIY PDF)
  • in a barrel (see also below) 
  • Wood Power Pallets: Integrated Gasifier-Genset Skids with DIY Options
  • lots of DIY solutions
  • "A manufacturer of renewable energy micro generation systems has recently developed a self-contained anaerobic digester they call the “Muckbuster” that converts horse manure and bedding into energy, mulch, and fertilizer. The manufacturer, a Muckbuster sized to process 200 liters of manure and bedding per day (about 4 horses worth) generates about 7,148 Kilowatt hours (kWh’s) of energy annually and costs about $28,000. Additionally, they make manure management easy, thereby helping to protect water quality of nearby streams and rivers, as well as your farm’s groundwater resources.  These systems are also very beneficial from a resource reuse perspective, as the by-products are fertilizer which can be used in your garden, and mulch which can be used as bedding in stalls or footing in paddocks." (sourceclay@sustainablestables.com) 
  • bio waste collection in townsCommunity Composting Network (CCN) is the UK-wide organisation that supports and promotes community groups, social enterprises and individuals which are involved in producing compost from green/food waste and using it in their local communities. "The food waste, cooked meat included, is loaded into the Rocket and composted for two weeks. The correct nitrogen/carbon ratio is achieved by adding cardboard (which previously used to block the chutes) and wood chips. The mix is kept constantly at a temperature of 60°C and heated to over 70°C for 1h daily to ensure that the time and temperature requirements of the ABPR are met."

chicken manure digesterprinciple of chicken manure digestermaterial: rubber stopper, plastic tubing, stainless steel, copper tee fittings, a heavy plastic bag, a brass stop cock, copper tubing manometer: To measure and maintain pressure in the system, I created a manometer with some plastic hose. After experimenting with different lengths, I settled on an 8 inch loop filled with water. As the pressure in the system increased, water would rise on the right hand side of the manometer. If too much pressure built up, the water would be forced out of the manometer thereby relieving the pressure and preventing other parts of the system from exploding. burner tip: I tapered one end of the copper tubing, then flattened the end around a sewing needle. This created a small orifice which acted as a burner tip. temperature: Methane production is best at 90-100 degrees Fahrenheit. To keep the mixture at a high enough temperature, I used an aquarium heater and a water bath. I partially submerged the jar in the water, resting it on top of some canning rings to keep the slurry level at or above the water level. I installed the aquarium heater in the pot, and set it on its highest setting. The temperature stayed at about 85 degrees, not optimal, but high enough to faciliate methane production. I also used some foam packing material to retain the heat and reduce water loss due to evaporation. I monitored the water level every day to keep it at the appropriate depth for the aquarium heater. collector: I added a collection bag to store the gas as it was produced. My bag was actually an empty heavy-duty plastic bag (once used to store rawhide dog chews), with copper tubing clamped onto the end and sealed with silicone. A Mylar ballon or an empty milk bag would probably have made better a collection bag, as suggested by some of the other project sites listed in the Resources section. ratio for 5L bucket: 1 pound chicken manure : 1 hand composted horse manure, rest water Barrel Digester

 

the following quotes are mostly from this page (see also algae biodiesel)

On a municipal level, rubbish tips act as biogas digesters and are prodigious methane generators. In fact, because un-burnt methane released into the atmosphere is a powerful greenhouse gas, 10% of our personal impact on the climate comes from the food refuse we put in our garbage bins that ends up decomposing under landfill. In a small scale waste to energy situation it is possible to generate methane from manure or even sewerage.

Each kilogram of biodegradable material yields around 0.4 m³ (400l) of gas. 2 gas rings for a couple of hours a day will use between 1-2 m³. Gas lights need around 0.1 m3 (100l) per hour.

For example, where 55 kg of dung a day is available a 8 m3 plant is warranted; where it’s only 6 kg of dung a day, a 1 m3 plant will suffice. For a family of 8 with a few animals (say 8-10 cows), a 10m³ digester is a commonly used size in India, with 2 m³ gas storage.

How long you leave the material in a batch digester depends on temperature (2 weeks at 50°C up to 2 months at 15°C). The average is around 1 month – so gauge how much material you will add each day, and multiply it by 30 to calculate the size of the digester.

While anaerobic digestion occurs between 32° F (0°C) and 150° F (65°C), the optimum temperature range for methane generating microbial activity is 85°F (29°C) to 95° F (35°C).

Little gas production occurs below 60°F (16°C). In colder climates placing the digester in a greenhouse, and perhaps using some of the methane to warm the system, are possible strategies.

Needed parts:

  • The biogas digester is the system component where the animal, human and other organic wastes are introduced, usually as a slurry with water, to break down anaerobically.
  • storage container is used to hold the gas produced, from which it is piped for burning as a fuel. Variable volume storage (i.e. flexible bag or floating drum) is easier, cheaper and more energy efficient than high pressure cylinders, regulators or compressors. 

Process:

  • Waste material is put into the oil drum, neoprene cover rises when full of gas, gas is tapped into container (upside-down plastic drum with water seal) which rises as more gas enters.
  • When full, gas can be tapped off and used with the little gas ring.
  • Batch digesters based on a container (see photo: http://www.small-farm-permaculture-and-sustainable-living.com/images/biogas_experimental_process.jpg) are feasible on the domestic scale.
  • When the digester is emptied, the spent effluent is dried for later reuse as a fertilizer.
big scale
  • Trockenfermentation: Biogas aus der Komfortgarage, Stand der Entwicklungen und weiterer F+E-Bedarf
  • optimized single batch processors using carriers
  • zorg-biogas.com: Biogas reactor is composed of steel panels with high quality glass enamel cover made using technology of high temperature sintering. This enamel cover has long operational lifetime period, is extremely chemically-proof, corrosion and shock resistant. Biogas reactor can be quickly installed and dismantled. The advantage of steel reactor with cover as compared with concrete one is in long operating life, absence of formwork necessity, reduction of construction period, possibility of round-year construction. Stainless steel manholes, reinforced holes for mixing devices, access holes – everything is designed taking into account the specifics of biogas industry. Main advantage of steel digester is that it can be easily dismantled and considered as best mortgage by banks. (Mitglied im Fachverband Biogas)
  • Aikan Technology allows for batch processing of waste, producing biogas and compost, without moving around the solid waste fraction
Resources
    • WP: use of feces and horse manure
    • german: WP:BiogasanlageWP:Trockenfermantation im Batchbetrieb
    • Generating Methane Gas From Manure
    • The quest for “horse-Powered” Bioenergy, Faculty Voices, Donna E. Fennell, Ph.D. Assistant Professor, Enviromental Science, Rutgers University
    • Biogas Production from Co-Digestion of Horse Manure and Waste Sewage Sluge, E. Agayev, A. Ugurlu: Biogas yield of horse manure was evaluated in batch and continous digesters. Studies were carried out in three stages. The biogas yields of horse manure in the batch studies after 35 days of the digestion period for the concentrations of 0,5 %, 1%, 2% and 4% were 343 ml/gVS, 376 ml/gVS, 382 ml/gVS, 393 ml/gVS respectively. In the second stage, biogas formation from co-digestion of horse manure with waste sewage sludge was investigated in batch systems. The horse manure was mixed with waste sewage sludge and the biogas production was investigated under two different starting concentrations of %2 and %4 (VS). The methane yields after 35 days were 412 ml/gVS and 430 ml/gVS respectively. These results show that co-digestion of horse manure with sewage sludge is beneficial. The biogas production was improved when the manure was mixed with sewage sludge even in the ratio of 10%. In the third stage, co-digestion of horse manure and sewage sludge mixture was investigated in a lab scale continuous digester. 250 ml of the content was removed each day and replaced with fresh horse manure and sewage sludge mixture with 4% VS content. The methane content of the biogas produced was abot 67 %. (In: Clean Technology 2011, published June 23th, £82, Chapter 3: Bio Energy & Bio Fuels)
      • anaerobe conditions (no oxygen)
      • constant temperature, highest methane production is between 25 to 35 C
      • enough moisture with bacteria
      • PH between 7.5 and 8.5
      • Moisture: The weight of water lost upon drying at 220°F (105°C) until no more weight is lost.
      • Total Solids (TS): The weight of dry material remaining after drying as above. TS weight is usually equivalent to "dry weight." (However, if you dry your material in the sun, assume that it will still contain around 30% moisture.) TS is composed of digestible organic or "Volatile Solids" (VS), and indigestible residues or "Fixed Solids."
      • Volatile Solids(VS): The weight of organic solids burned off when dry material is "ignited" (heated to around 1000°F, 538°C). This is a handy property of organic matter to know, since VS can be considered as the amount of solids actually converted by the bacteria.
      • Fixed Solids (FS): Weight remaining after ignition. This is biologically inert material.
      • For horeses VS is 80% of TS
      • Temperature: the higher the temperature, the shorter the retention time. It has no effect on the absolute biogas yield, which is a constant that depends only on the type of biomass in the digester.
      • moisture / TS: The most advantageous TS for the digester of a continuoustype biogas plant is 5-10%, compared to as much as 25% for a batch-operated plant. A TS of 15% or more tends to inhibit metabolism. Consequently, most substrates are diluted with water before being fed into the digester.
      • C/N: An important operating parameter is the ratio between carbon content (C) and nitrogen content (N), i.e. the C/N-ratio, which is considered favorable within the range 30 :1 to 10: 1. A C/N-ratio of less than 8: 1 inhibits bacterial activity due to an excessive ammonia content.
      • pH: The pH is the central parameter of the biochemical bacterial environment. 7-7.2 optimum 
      • monitoring temperature and transfer produced energy away with a water bed - digestion does not produce much warmth and wather bath is insuitable for our rusty barrels
      • insulation as frost and heat protection by earth or with some kind of organic material
      • constantly feed drums with tempered moisture 
      • The biogas digester is the system component where the animal, human and other organic wastes are introduced, usually as a slurry with water, to break down anaerobically. In this case three oil drums.
      • storage container is used to hold the gas produced, from which it is piped for burning as a fuel. Variable volume storage is easier, cheaper and more energy efficient than high pressure cylinders, regulators or compressors. In our case a combination shall be used with an open oil drum put upside downfor temporary storage and a currently unused metal cylinder for high pressure storage.
      • Waste material is put into the oil drums and kept there for several days stirred every some hours
      • gas floats into container (upside-down oil drum with water seal) with brass and manometer at the top (tubes filled with water)
      • When the mano shows high pressure, gas can be tapped off and used with the little gas ring or stored somewhere else
      • When the digester is emptied, the spent effluent is dried for later reuse as a fertilizer. 
      • Ende des 19. Jahrhunderts entdeckte man, dass Abwasser mittels anaerober Vergärung geklärt werden kann. Ab 1906 entstanden im Ruhrgebiet Abwasserreinigungsanlagen mit beheizten Fermentern. Ziel war damals (wie später auch) eigentlich NICHT die Biogasgewinnung, sondern die Abfallverringerung. Erst von etwa 1922 an wurde Biogas aufgefangen und in das städtische Gasnetz eingespeist. Einige Klärwerke verdienten damit soviel, daß sie ihre Betriebskosten decken konnten. Bis 1937 hatten einige deutsche Städte ihren Fuhrpark auf Biogas umgestellt. Die Müllabfuhr der Stadt Zürich fuhr bis 1973 mit Biogas.
      •  Erste Versuche, Biogas nicht nur aus Abwasser zu gewinnen, wurden in den späten 30er und in den 50er Jahren zuerst mit Festmist und später mit Gülle gemacht. Es entstanden damals ca. 50 Anlagen. Wegen des damals immer billigeren Erdöls hat man diese Versuche wieder eingestellt. In der Energiekrise von 1973 wurde die Biogastechnik wieder aktuell. Aber durch fallende Erdölpreise wurde die weitere Entwicklung dann erneut gebremst.
      •  Durch die große Menge landwirtschaftlicher Abfälle und Gülle haben die Niederlande, Schweiz (Kompogas, kein Substratanbau) und Schweden die meisten Erfahrungen mit Biogas. In diesen Ländern werden BHKW seltener genutzt. Hier wird das Biogas zu Biomethan aufbereitet. In den Niederlanden und in der Schweiz wird es in das Erdgasnetz eingespeist. In Schweden wird es für Kraftfahrzeuge genutzt.
    • Methane Production Potential of Horse Manure and Stall Waste {Biomass and Bioenergy
    • Thermophilic Anaerobic Co-Digestion of Equine Stall Waste and Food Waste (BioCycle)
    • Pilot-Scale Anaerobic Co-digestion of Food Waste and Horse Waste (BioCycle)
    Motivation

    Many horse farms utilize or store manure on-site, and the application of manure and stall waste on fields and pastures is the primary means of disposal (Warren, 2003).  Land application or nursery use of the manure often follows composting (Romano et al., 2006). Horse waste mixed with straw bedding is preferentially sought for use in mushroom production. However, not all owners wish to use straw bedding and not all equine facilities are within a geographic area that could serve mushroom facilities (Malinowski, 2007). Equine facilities are seeking economical and environmentally friendly options for manure disposal. As part of 

    horse waste handling, anaerobic digestion could be employed to increase the value of horse manure and offset disposal costs through production of a biofuel (methane). One horse, defined as a 454 kg (1000 lb) animal, produces 17 kg (37 lb) feces and 9 L (2.4 gal) of urine per day, for a total of about 27 kg (60 lb) of waste (Romano et al., 2006; Westendorf and Krogmann, 2004; Wheeler and Zajaczkowski, 2002). Stalled horses require up to 9 kg (20 lb) of bedding per day (Westendorf and Krogmann, 2004; Wheeler and Zajaczkowski, 2002).  Combined, this accounts for up to 12,000 kg (13 tons) of waste per horse per year. [1f]

    With the methane production values obtained from the batch bottle experiments, the energy potential of horse manure alone (per month of peak activity) can be estimated to be 4 to 5 x 105 kJ/metric ton wet weight (Table 2.7).  With the values obtained from our batch bottle experiments, it was estimated that the energy potential of stall waste was 2 to 4 x 105 kJ/metric ton wet weight (Table 2.7). For the 125 L high solids batch reactors, this value was approximately 1.3 x 105 kJ/metric ton wet weight.  Since a horse produces approximately 13 wet tons (~ 14.3 metric tons) of stall waste per year (with bedding) (Westendorf et al., 2007; Wheeler and Zajaczkowski, 2002), this amounts to theoretical values of 2.87 to 5.73 GJ (106 kJ) generated per horse per year.  In comparison, a typical home might consume 50 to 80 GJ per year for heating (Smil, 2005; Zambini, 2006). [48]

    Summary

    The methane production potential for horse manure at 35°C averaged 139 ± 65 L/ kg VS (average ± standard deviation) and 29 ± 15 L/ kg wet weight, corresponding to 9.2 ± 4.8 x 105 kJ / metric ton wet weight.  The energy production potential of stall waste with softwood chip bedding ranged from 4.0 ± 0.4 x 105 kJ / metric ton wet weight to 6.6 ± 0.8 x 105 kJ / metric ton wet weight, depending upon the relative amount of bedding present.

    The methane production from these digesters was 356 ± 61 L/kg VS-d. The loading rate increased over time to 1.7 kg VS/m3-d.  The methane content of the biogas was 55.7 ± 5.2 %. Total ammonia nitrogen approached 5 g/L, suggesting a higher C:N ratio feed stock mixture than that afforded by the waste food and horse manure mixture might be necessary for future applications.

    2.2.4. Solid State Batch Reactors:  Setup and Operation (S. 21, Image S. 88)

    Anaerobic digestion of stall waste from Oxbow Stables, Hamburg, NJ (section 2.2.1) was performed in high solids, batch stainless-steel water-jacketed reactors covered with foam-insulation as described previously in detail (Hull, et al., 2002; Krogmann, et al., 2003; Hull, et al., 2005). The reactors were equipped with stainless-steel screens near the bottom so that a waste pile could be held in place while free liquid could drain and be collected in the bottom of the reactor.  Prior to use, reactors were tested for ability to hold pressure at approximately 14 kPa (2 PSI).

    At start-up, each reactor was filled to approximately 100 L with 29 kg wet weight (9.8 kg VS) stall waste plus 2 L of inoculum (2% volume:volume amendment). Reactors were separately initiated seven days apart.  

    On Days 50 and 43, respectively, each reactor was opened and 10 L additional inoculum (10% volume:volume amendment) was added.

    The top of each reactor was equipped with four ports. One port was connected by 1.3 cm. diameter braided Tygon® tubing to a wet test meter (Precision Scientific, Chicago, IL) through which the biogas flow from the reactor was continually measured. Measured biogas was discharged to a chemical fume hood. The second port accommodated a temperature probe that was extended to just above the bottom of the reactor. The third port was connected to a liquid distribution manifold on the inside of the lid of the reactor and was connected by Tygon® tubing and a pump to a port at the bottom of the reactor.  This system was used for re-circulating leachate that drained from the waste pile to the bottom of the reactor, back to the top of the reactor every 2 to 5 days to maintain moisture in the pile. During each leachate re-cycling event, a 50 to 200 mL sample was collected for pH and ammonia-N determination.  The fourth port was connected to a pressure gauge, which was used initially to assure proper sealing conditions and later to ensure no pressure buildup occurred (e.g., from clogging of lines).

    The internal reactor temperature was maintained between 34.0°C and 36.0°C for both reactors during the course of the experiment.

    Other components of the biogas were not analyzed but were assumed to be primarily CO2 as the other main digestion end product and N (from purge gas), along with trace amounts of NH and HS. 

    Efficiencies of methane production based on the input of feed stock biomass VS was estimated by assuming 1 g COD stabilized = 0.35 liters of methane at STP and that 1 g COD = 1.42 g VS (Rittmann and McCarty, 2001). 

    Results

    Methane production at 25°C was 1.2 ± 1.1 L/d and the percent methane was 30.8 ± 17 %.  Methane production increased approximately 5-fold when the temperature was increased from 25°C to 35°C after Day 55. At 35°C with a substrate of horse manure alone the methane production rate averaged for the two CFRs was 7.7 ± 2.8 L/d and the percent methane was 57.9 ± 6.6 %. The highest estimated yield of methane from the volatile solids loaded during operation at 35°C with horse manure only (VS estimated to be converted to methane) was approximately 35% for reactor 1 and 38% for reactor 2. The methane production potential of the horse manure, based on a VS loading of 42 g VS/d, was thus 183 ± 67 mL methane/g VS. (S.28 Diagramm)

    On Day 82, both digesters were switched from horse waste without bedding to stall waste (horse manure intermingled with softwood bedding). The horse stall waste with bedding contained about 25% wood chips by wet weight or approximately 0.4 g bedding VS per g manure VS. Methane production indeed declined upon switching to stall waste, and reached levels that were lower than those observed during operation at 25°C. The overall biogas production declined to approximately 14% of that produced by manure alone after Day 82. The methane content of the biogas also decreased from 57 ± 13% from Day 60 to 96 to 9 ± 9% from Day 103 to 123 for reactor 1 and 59 ± 6% from Day 60 to 96 to 39 ± 1% from Day 112 to 123 for reactor 2. On some days following addition of stall waste in reactor A, the percent methane in the biogas was <1%. It was hypothesized based on these results that addition of stall waste (including the softwood chips) may have inhibited the microbial community and methane production, through the presence of anti-microbial compounds (Belmonte et al., 2006; Savluchinske-Feio et al., 2006). [31]

    In each of these experiments, the cumulative methane production from horse manure was determined over incubation times ranging from 33 to 79 days.  The methane produced ranged from 70 to 120 mL over 40 to 60 days in the batch tests with 0.5 g horse manure VS added (Exp. 1, 2, and 3) and from 135 to 620 mL over 33 to 79 days in the batch tests with 2.38 g horse manure VS added (Exp. 4 and 5).  The methane production potential for horse manure at 35°C ranged from 45 ± 13 L/ kg VS to 114 ± 73 L/ kg VS over approximately 40 days of incubation to 134 ± 7 L/ kg VS over 79 days of incubation. (Note: one additional experiment produced 215 ± 17 L/ kg VS over 59 days.)  The methane production potential of horse manure averaged over all batch experiments was 139 ± 65 mL methane per g horse manure VS, similar to that observed during CFR operation. [32]

    Wood+Straw-Mixes

    Taken together, these results indicated that regardless of the amount of fresh softwood bedding present in the stall waste mixture, the full amount of potential methane production would be realized from the degradable horse manure fraction contained in the waste mixture.  No apparent toxicity or inhibition was observed. [33]

    Methane production from Woody Pet® alone (0.75 ± 0.19 mL) was nearly identical to that observed from fresh softwood bedding alone (0.85 ± 0.22 mL), yet all bottles containing a mixture of Woody Pet® and manure produced approximately 40% more methanethan did bottles with manure alone, with similar methane concentrations (<1% different).  Bottles containing manure and straw bedding produced 75 ± 33 mL methane over 46 days of incubation (Figure 2.6) or 111 ± 58 mL methane per g VS.   Straw alone produced nearly identical methane volumes (27 ± 6 mL) as manure alone (26 ± 8 mL) and bottles containing manure and straw produced two to almost five times as much methane as mixtures of manure with softwood bedding depending upon the manure to bedding ratio. [34f]

    Exp4: Moreover, the presence of the bedding contributed positively to methane production with the manually separated, used softwood bedding producing 39 ± 

    10 mL methane per g VS added.  This confirmed that not only is the softwood bedding non-inhibitory to the anaerobic digestion process, but suggests that separation of the bedding from the manure prior to recovery of bioenergy, a process that could be desirable to reduce reactor volumes or avoid mechanical problems caused by wood particles, would result in a loss of recoverable energy.  Whereas it was initially presumed that the increase in methane production from the presence of the manually separated, used softwood bedding was due to small manure remnants that adhered to the wood particles, visual observations indicating particle breakdown suggested the possibility of anaerobic breakdown of the softwood bedding itself. [35]

    It is important to note that methane concentration did not change with increasing concentration of wood, showing again that the presence of wood was not inhibitory to methanogenesis. [36]

    The methane production potential of the softwood bedding was 20.0 ± 4.6 mL methane over 33 days of incubation (Figure 2.9) or 8.4 ± 1.9 mL methane per g VS added. [39]

    Changes over time

    Methane production over time during Exp. 4 appears to have peaked shortly after Day 10 for all bottle types, with a decline in methane production evident near Day 30 [39]

    Biogas production from static piles of waste that were initially amended with inoculum at only 2% volume:volume ratio began almost immediately after reactor startup.   The biogas production was initially 30 ± 3 L/d from Days 6 to 12 

    The reactor temperature reached approximately 46°C several times prior to switching to a new sensor.  Immediately prior to changing the faulty sensor, 

    digester #2 was producing 42 L/d from Days 5 to 7.  Following installation of the new sensor, 25 L/d biogas was produced from Days 8 to 9 and then the biogas production decreased gradually over the next 34 days.  Beginning on Day 13, biogas production from digester #1 also began a gradual decline over the next 36 days.  It was expected that as the waste digested, solids content would decrease and the moisture content of the pile would increase.  However, little leachate was observed in the reactors and the dry conditions were confirmed when the lid of each digester was removed and it was observed that only the top layer of the pile (perhaps moistened by initial 2 L of inoculum) had been at least partially degraded.  The remaining stall waste appeared to resemble its initial condition.

    On Days 50 and 43, each digester was reinoculated with 10% volume:volume inoculum.  After the addition of inoculum biogas production increased and was greater than 30 L/d. Methane concentrations exceeded 40% after approximately 12 days into each digester’s run (Figure 2.12).  Methane concentrations approached 50% (for digester #1) between Days 21 to 37, but then a slow but gradual decline in methane content occurred between Days 37 to 47.  For digester #2, methane concentrations approached 45% between Days 12 to 21, but then a slow but gradual decline in methane content occurred between Days 21 to 37.  It was hypothesized that the relatively low methane production  could be a result of the low moisture content.

    After 63 days, the cumulative amount of biogas produced was 1320 L for digester #1 and 1097 L for digester #2. Since 9.83 kg VS were initially loaded into each digester, 101 L biogas/kg VS and 78 L biogas/kg VS, or

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