methane emission project - a guide for pig producers reducing...

1

A Guide produced for the Pig Research & Development Corporation. By : Agribiz Engineering, 96 Yarra St (P.O. Box 279), Geelong 3220, Ph. (03) 5229 7300 Fax (03) 5229 7566

DISCLAIMER :

The publisher believes that the information contained in this report to be accurate at the time of publication. We take no responsibility and will not be liable for any damage suffered by any person, for any actions or investment, financial or otherwise taken by any person reading or relying on any of the text in this publication. No part of this report may be reproduced without prior approval.

M e t h a n e E m i s s i o n P r o j e c t - A G u i d e f o r P i g P r o d u c e r s

REDUC ING The Greenhouse GAS Effect

Table of Contents Table of Contents ................................................1 What is the Greenhouse Effect?.........................1 Is Climate Change Happening?..........................2 What are the Possible Consequences? .............2 What is Being Done? ..........................................2 About the Science ...............................................3 Greenhouse Emissions from Pig Production......4 Options for Emission Reduction in Piggeries5 A. Pig Production.................................................5 B. Effluent Collection ...........................................6 C. Waste Management Systems ........................6

1 Direct Land Application ........................................... 7 2 Anaerobic Lagoons ................................................. 7 3 Aerobic Treatment Systems.................................... 7 4 Covered Lagoons.................................................... 7 5 Anaerobic Digester.................................................. 8 6 Straw-based System............................................... 8 Greenhouse Gas Emission Reduction Strategies......... 8

Relative Costs of Different Waste Management Systems.............................................................10

Appendix A Land Application Systems for Small Piggeries ..................................................................... 11 Appendix B Covered Lagoons for Large Piggeries .... 12 Appendix C Biogas Digesters for Large Piggeries .... 14

Require More Information? ...............................18

What is the Greenhouse Effect? The Earth’s atmosphere allows solar radiation to pass through to the surface, where much of it is re-emitted as heat. The term greenhouse refers to the processes whereby gases in the atmosphere trap infrared (heat) radiation released from the Earth’s surface. This effect of the atmosphere has operated for billions of years due to the naturally occurring greenhouse gases: water vapour, carbon dioxide, methane, ozone and nitrous oxide. The amount of warming of the planet depends in large part on the concentrations of these and other human produced greenhouse gases in the atmosphere. Without the greenhouse effect the Earth would be cold and uninhabitable. Over the past few hundred years, the concentrations of greenhouse gases have increased considerably due to human activities such as burning fossil fuels, industrial and agricultural activity, and clearing of forests and other vegetation. For example, the concentration of carbon dioxide in the atmosphere has increased from 280 to 358 parts per million by volume since the Industrial Revolution, while the concentration of methane has more than doubled. The continuing increase in the concentrations of these gases is expected to lead to warming of the lower atmosphere and the Earth’s surface, with likely negative impacts on human activities. This additional warming is of great concern to the global community, and is referred to as the “enhanced greenhouse effect”.

This booklet is part of a range

of programs, services and products which support

“no-regrets” forms of greenhouse response.

Methane Emission Project Guide for Pig Producers

2

15%

6%2% 3%

48%

17%

8%

0%

10%

20%

30%

40%

50%

60%

Stationaryenergy

Transport Fugitive Industrialprocesses

Agriculture Land UseChange andForesetry

Waste

Is Climate Change Happening? While there is some dissent, the overwhelming balance of scientific opinion is that: • climate has changed over the past

century, • scientific evidence suggests a discernible

human influence on global climate, • climate is expected to change in the

future as greenhouse gases in the atmosphere increase, and

• for many regions and systems, the effects of climate change are likely to be adverse

What are the Possible Consequences? Australia is vulnerable to a range of possible consequences of climate change including: • An increase in severe storms, floods

and droughts, • More intense and longer cyclones, • Erosion of coasts due to sea level rise, • Risks for human health, • An increase in the range and spread of

tropical diseases and pests, and • Adverse impacts on agricultural

industries, biodiversity, manufacturing industry and social and economic infrastructure.

Figure 1 : Share of Net CO2 Equivalent Emissions by Source Category - 1996. Note 1: Fugitive emissions are those which occur, for example, during the storage of fuel; from leaks due to breakages in pipelines etc. Note 2: Forestry and other, excludes land clearing, but includes forestry and other subsectors. Source: Greenhouse Gas Inventory, 1996.

What is Being Done? Australia is a party to the Framework Convention on Climate Change and took an active part in negotiating the Kyoto Protocol to that Convention. Australia has signed the Kyoto Protocol. If, as expected, we proceed to ratification of the Protocol, Australia will be committed to restricting the growth in its net greenhouse gas emissions to 108% of 1990 levels, measured as the average of annual emissions in the years 2008 to 2012. A National Greenhouse Strategy has been developed by the Commonwealth and State Governments, in consultation with the Australian Local Government Association, industry and the community. The development of the Strategy is based on a comprehensive approach to greenhouse abatement, across all the greenhouse gases, including the development of sinks (using vegetation management to absorb carbon dioxide from the atmosphere), and involving all sectors of the economy. In developing specific forms of greenhouse response, the initial focus is on measures which also contribute to industry productivity and competitiveness, and ecological and economic sustainability. Another important consideration is equity in sharing benefits and any necessary burdens. Emissions from the agriculture sector were around 20% of the national total emissions in 1996. Primary producers are therefore expected to play a significant role in reducing emissions, and in contributing to the development of sinks. In most agricultural sectors there is already a strong awareness of the need for integrated management practices which include more sustainable farming systems to enhance productivity and long term sustainability. The information presented in this booklet shows that, through the effective management of wastes and judicious selection of inputs. Pig producers can make an important contribution to reducing greenhouse gas emissions, as well as improving farm productivity and profitability.


3

Figure 3 : Share of Net CO2 Equivalent Emissions by Source Agriculture Category Source: Greenhouse Gas Inventory, 1996

69.8%

0.8%

11.9%

0.3%

17.2%

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

Livestock Rice Cultivation AgriculturalSoils

SavannaBurning

AgriculturalResidueBurning

Figure 2 : Share of Net CO2 Equivalent Emissions by Source Livestock Category Source: Greenhouse Gas Inventory, 1996

About the Science The main greenhouse gases of interest to primary industry in Australia are carbon dioxide, methane and nitrous oxide. Carbon dioxide is a product of aerobic decomposition or burning of organic matter, combustion of fossil fuels such as coal or petroleum products in engines, coal and gas-fired electricity generation, and respiration by living organisms. Methane is a gas produced by decaying organic matter (plants) in places where there is very little air (anaerobic decomposition), typical of ruminant digestion as occurs in beef and sheep production, with large quantities being released to the atmosphere through the digestive tract (burps) and small quantities through anal flatulence. Rice cultivation, venting of natural gas, and waste decomposition in land fills are some other major sources of methane emissions. Effluent ponds and lagoons also produce large quantities of methane. Nitrous oxide (commonly referred to as laughing gas) is used as an anaesthetic and as a propellant in aerosol products. Nitrous oxide is produced naturally in the nitrogen cycle, where denitrifying bacteria convert some of the nitrates in soil back into gaseous nitrogen or nitrous oxide. Aerobic treatment of pig effluent can also release nitrous oxide into the atmosphere.

The different greenhouse gases have different relative contributions to the global warming effect. This is expressed relative to the greenhouse potency of carbon dioxide. The Global Warming Potential (GWP) has been developed as an index for quantifying the relative contributions of different gases to the greenhouse effect. The GWP is the sum of the radiative forcing from the release of one kilogram of the particular greenhouse gas expressed relative to that of one kilogram of carbon dioxide. (Radiative forcing is an alteration in the balance between incoming and outgoing atmospheric radiation causing climatic temperature changes.) So one kilogram of nitrous oxide released to the atmosphere is similar to the effect of releasing 310 kilograms of carbon dioxide. The relative future global warming potential of a greenhouse gas emission is the product of the appropriate GWP and the amount of gas emitted. Thus it is possible to express on a common scale the emissions of different greenhouse gases. Greenhouse Gases *Global Warming

Potential Carbon Dioxide 1

Methane 21 Nitrous Oxide 310

* Global Warming Potentials (GWP)

1.8%

11.5%

31.1%

1.6%

53.4%

0.6%0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

pigs dairy sheep feedlot beef other


4

Greenhouse Emissions from Pig Production

The range of on-farm greenhouse gas emissions associated with the production of a kilogram of pigmeat (kg carcass weight) are: Table 1: Range of greenhouse gas emissions associated with pig production.

grams/kg pigmeat Carbon Dioxide Methane Nitrous Oxide

Digestion (The Living Pig) *2391 8.9 -

Facilities (Waste Collection) - 1.6 4.9 - 10.8

Waste Management System 14 –1543 0 - 132.3 0 -2.3

RANGE OF TOTALS 3107-4636 10.5 - 142.8 4.9 - 10.8

As CO2 Equivalent 3107-4636 221 - 2999.0 1550 - 3348.0 * As mentioned previously the respiration of CO2 by animals is not included in any inventories as it is considered as part of the natural carbon cycle. The greenhouse gas emissions associated with various waste management systems are shown below which explains the large variation between systems: Table 2: Greenhouse gas emissions attributed to different waste management systems

grams/kg pigmeat Waste Management System Carbon Dioxide Methane Nitrous Oxide

Direct Land Application 14 0.0 0.4

Anaerobic Lagoon 32 132.0 0.0

Aerobic Treatment 1543 14.0 2.3

Covered Lagoons & Cogeneration

(269) 20.0 0.0

Covered Lagoons & Flare 384 20.0 0.0

Digester & Cogeneration (412) 0.0 0.0

Straw-based 613 7.6 N/A** ** Is accounted for in the collection system table above at 10.8 grams/kg meat. ( ) These represent a credit, as the system has generated electricity which would normally result in a contribution to the carbon dioxide of the atmosphere from thermal electricity generation.


5

Average daily weight gain in grams

Methane released (g / kg meat)

500 550 600 650 700 750 8007.0

7.5

8.0

8.5

9.0

Grower Liveweight Feed Conversion

Methane released (g / kg meat)

2.0 2.2 2.4 2.6 2.8 3.0 3.25.5

6.0

6.5

7.0

7.5

8.0

8.5

Options for Emission Reduction in Piggeries

A. Pig Production Piggeries with efficient pig production systems will achieve emission reductions: any management decision which reduces feed use, through delivering higher daily weight gain, higher numbers of piglets born alive per litter, or lower pig mortalities, will reduce methane emissions per kilogram of pigmeat produced. The quantity of methane released by the digestion of feed is dependent on the quantity of energy fed to the pigs. An increase in the feed conversion causes a linear increase in methane released per kilogram of meat. Efficient usage of feed is an active contribution to environment protection as well as providing an economic gain. Each decrease of 100 grams of feed (18.6 megajoules of Gross Energy/kg (dry matter)) needed to produce a kilogram of pigmeat

decreases in the digestion process of methane released by 0.13 grams. This emission is only that of the digestion. Usually more efficient feed conversion is associated with a higher daily weight gain. The influence on the methane emission of differences in the rate of weight gain is shown in the figure 5. Two sources of methane emission are considered here: the metabolism/digestion and the husbandry system. As the daily weight gain increases, the necessary quantity of energy decreases, because less feed is required for maintenance. The growing period shortens, therefore the pigs occupy the shed for less time and that source of emission decreases too. The weaner weight is assumed to be 25 kilograms and the final weight 95 kilograms.

Figure 4 : Methane release as a function of Grower Liveweight Feed

Conversion

Figure 5 : Methane release as a function of Average Daily Weight

Gain in grams.


6

B. Effluent Collection The effluent collection system has a small influence on the methane emissions while nitrous oxide emissions are constant except for the straw based system which includes

the waste management system (composting of the manure and bedding). The following table shows the relative emissions for different collection systems.

Table 3: Relative greenhouse gas emissions for different effluent collection systems. Effluent Collection System Methane Released,

grams/kg meat Nitrous Oxide grams/kg meat

Hosed or flushed concrete surface 0.0 4.9

Partly slatted floor 1.4 4.9

Fully slatted floor 2.1 4.9

Straw-based 7.6 10.8

C. Waste Management Systems The intensive production systems used by the pig industry mean that the wastes are collected at a point source and there is potential to reduce greenhouse gas emissions by the selection of appropriate waste management systems. The chart on the following page shows the alternative waste management systems available for the Australian Pig Industry. In choosing a waste management system, a number of issues must be considered: size of piggery, climate, area of land available, water for irrigation, buffer distances to neighbours, water table, soils, catchment hydrology, odours and now greenhouse gas emissions. For information on choosing and designing waste management systems for

piggeries, the book Effluent at Work by Ian Kruger, Graeme Taylor and Megan Ferrier, published by NSW Agriculture and also available from the Pig Research & Development Corporation, Canberra, is recommended reading. The six waste management systems assessed in this study for greenhouse gas emissions were: 1. Direct Land Application; 2. Anaerobic Lagoons; 3. Aerobic Treatment Systems; 4. Covered Lagoons; 5. Anaerobic Digestion; and 6. Straw-based System.

Figure 6 : Potting Mix (Just Bagged)


7

Figure 7: Waste management Options 1 Direct Land Application The wastes are collected in a sump, for smaller piggeries. They are then tankered or pumped out and spread over land at a rate which will provide an equivalent phosphorus fertiliser as required on the particular soil. For larger piggeries, the wastes are screened, and the solid fraction is sold off-site or spread on land. The liquid is pumped and spread on land as a fertiliser as above. 2 Anaerobic Lagoons The wastes are collected by gravity flow into a primary anaerobic lagoon for small piggeries, while for larger piggeries the wastes are screened before lagooning. The outflow from anaerobic lagoons is then stored for up to six months before land application at fertiliser equivalent rates for phosphorus.

3 Aerobic Treatment Systems The wastes are collected, screened and then mechanically aerated to provide an aerobic breakdown of the biological wastes. This requires about 2 kw-hr of electricity per kilogram of pigmeat produced. The outflow from the aeration basin is then stored for up to six months before land application at fertiliser equivalent rates for phosphorus. 4 Covered Lagoons The wastes are collected (screened for larger piggeries), and treated in an anaerobic lagoon with an 80 day hydraulic retention time and a membrane cover to collect the gases. The gases are flared or scrubbed and then used for heating or electrical generation. The outflow from the lagoon is then stored for up to six months before land application.

Collection

Land Solids Separation

Storage

Recycled Flush Water

Lagoons Covered

Anaerobic

Solids For Offsite Sale

Anaerobic Digestion

Land

Long Term Short Term

Lagoons Covered Aerobic

Aeration Oxidation Ditch

Floating Aerators

Land Land Land Land Land

Solids Offsite Sale


8

5 Anaerobic Digester Piggery wastes are collected and concentrated to at least 5% solids and placed inside a sealed tank where the air is excluded, the contents are thoroughly mixed at a controlled temperature, the wastes are then digested by anaerobic bacteria to produce biogas (methane, carbon dioxide), water and sludge.

6 Straw-based System This is a new variation of an old system, raising pigs on straw. Pigs are housed in plastic, igloo-style greenhouses with quantities of straw bedding (40-60 kilograms of straw per grower pig reared over a 16 week period). At the end of the growing cycle, the straw, manure and urine (soaked into straw) are removed and composted or applied direct to land. The total greenhouse gases and their equivalence in carbon dioxide (CO2) for the different waste management systems available are:

Table 4: Total greenhousegas emissions from Pig metabolism, effluent collection and waste treatment and land application

Waste Management System

CO2

grams/kg meat

Methane

grams/kg meat

CO2 equivalent

grams/kg meat

Nitrous Oxide

grams/kg meat

CO2 equivalent

Grams/kg meat

Total CO2 equivalent

grams/kg meat

Direct land application 14 10.5 221 2.4 744 979 Anaerobic lagoons 32 132.0 2999 2.0 620 3651

Aerobic lagoons 1543 23.5 494 4.3 1333 *3370 Covered Lagoons (269) 17.0 358 2.0 620 709

Digester (412) 10.5 221 2.0 620 429 Straw-based 613 18.1 381 12.8 3968 4962

( ) These represent a credit, as the system has generated electricity which would normally result in a contribution to the carbon dioxide of the atmosphere from thermal electricity generation.

*This value should include another 1141 grams of CO2 which is stored in the treated liquid.

Greenhouse Gas Emission Reduction Strategies From a greenhouse gas emission perspective, the best practice waste management system will be a biogas digester with co-generation (electric power generation and hot water production from engine cooling). Which produces a credit of 412 grams of carbon dioxide per kilogram of pig meat produced because of the electricity produced as a substitute to coal fired electricity. When added to the other gas emissions of pig production gives a debit of 429 grams carbon dioxide equivalence per kg meat. The worst practice is the use of mechanically aerated lagoons, which produce about 4.5 kg of carbon dioxide equivalent for each kilogram of pigmeat produced, due to the emissions attributable to electricity generation to run aerators.

The covered lagoon option has considerable potential to provide a cheaper methane collection system than the conventional enclosed digester, as well as odour minimisation and still collect worthwhile quantities of methane for power generation. In selecting a best practice waste management system, other factors to consider are costs (capital and operating), income and environmental sustainability for the particular piggery location. Appendices A , B & C outline the best practice waste management systems for small and large piggeries for achieving greenhouse gas emission reductions.


9

Figure 8 : Methane release per kg meat as a function of daily weight gain for lagoon

system

A v e r a g e d a i ly w e ig h t g a in in g ra m s /d a y

M e th a n e r e le a s e d (g / k g m e a t )

5 0 0 6 0 0 7 0 0 8 0 0 9 0 01 2 7

1 3 0

1 3 3

1 3 6

1 3 9

1 4 2

The Influence of growth rate on reducing greenhouse gas emissions using an anaerobic lagoon system is shown in figure 8. The selected fattening period was 25 to 95 kg. The husbandry conditions were a pig building with a fully slatted floor and the manure was stored in an anaerobic lagoon at an average storage temperature. This example shows that under the given average conditions an increase in the daily weight gain from 571 g, which is the Australian average (Pigstats 96), to 670 g corresponds to a decrease in methane emissions from 137 g to 132 g / kg meat produced. There are three reasons for the decrease of emissions: 1. The decrease in feed required

decreases the rate of production of metabolic methane.

2. The shorter time the pig is in the shed

decreases the quantity released during the growing stage.

3. The decrease in feed required

decreases the quantity of organic material in the faeces available to ferment.

Of interest are not the absolute values which might be different under different conditions, but the decrease in emissions which is about 4 % for an increase in daily weight gain of 100 grams. (i.e. from 570 g / day to 670 g / day) The feed conversion rate has a greater effect on the economic outcome than growth rate, because a high daily weight

gain can be achieved either with an efficient use of feed or with a waste of feed. The feed conversion is a measure of the efficiency. Again a husbandry system with a slatted floor and an anaerobic lagoon is considered.

Feed conversion ratio

Methane released (g/kg meat)

2.0 2.2 2.4 2.6 2.8 3.080

100

120

140

160

180

200

220

Figure 9 : Methane release per kg meat as a function of feed conversion

Figure 9 shows a remarkable decrease in emissions with a decreasing feed conversion. The decrease of emissions is about 12 grams per 0.1 change of the feed conversion ratio. The vast majority of the cutback in the emissions is due to less organic fermentable material in the faeces, whereas only 0.1 grams of the 12 grams is the contribution of the decrease of metabolic release. Therefore for production systems with an anaerobic lagoon, efficient use of foodstuffs is essential from an environmental point of view. It is certainly difficult to sell pigs with a higher final weight and to achieve simultaneously a good feed conversion. However, appropriate protein quantity and quality for the fattening stage, a high energy concentration of the feed ration and an appropriate feeding regime are required to achieve a feed conversion under the Australian average of 2.47. Improving the breeding herd performance by : • a higher rate of pigs born alive per litter • a lower weaner mortality rate • a lower pig mortality rate can also help to decrease emissions due to the contribution of the sow and boar being spread over more kilograms of pig meat produced.


10

Relative Costs of Different Waste Management Systems The different waste management systems have been costed on an annualised capital component based on a 12 year life and 10% interest rate, operating costs and income derived on the basis of actual nutrients available as fertiliser replacement in the year of application.

The total of the different greenhouse gases and their equivalence in carbon dioxide for the different waste management systems available are shown below. For each waste management system except for the straw based system, average values have been taken for the enteric emission and for the effluent system.

Table 5: Net costs of different waste management systems and their greenhouse gas contribution.

Net Cost Cents/kg meat

Waste

Management Systems 2000 Pig Place

Piggery

Rank

20,000 Pig Place Piggery

Rank

Greenhouse Gas

Emissions CO2 equiv. Grams/kg

meat

Direct Land Application:

Tanker 7.9 4 (0.1) 5 979

Irrigated 0.5 2 (3.1) 3

Anaerobic Lagoon 0.9 3 0.5 6 3651

Aerobic Lagoon 12.0 6 5.5 7 *3370

Covered Lagoon 9.7 5 (0.9) 4 709

Biogas Digester 12.2 7 (5.8) 1 429

Straw-based System (0.5) 1 (2.1) 2 4962 ( ) This represents the value in using this system after deducting costs. *This value should include another 1141 grams of CO2 which is stored in the treated liquid.


11

Appendix A Land Application Systems for Small Piggeries For small piggeries a well designed and managed land application waste management system can minimise greenhouse gases, be environmentally friendly and not be an economic barrier to continuing in pig production. A well designed and managed land application system will have a collection sump with pump and mixer, and a low-

profile travelling effluent applicator, or a tractor-drawn vacuum tanker. To ensure environmental standards are maintained, first flush runoff collection facilities should be provided for the land application areas. Adequate vegetative buffers of at least 100 metres to any water course, and odour buffers of 500 metres to any house must also be provided.

Figure 10 : Tanker with soil injection equipment applying effluent to land, the injection of the nutrients in the effluent into the soil reduces odour emissions and improves nutrient

use.


12

Appendix B Covered Lagoons for Large Piggeries

Figure 11 : Covered Lagoon waste management system in America, Royal Farms, Tulare, California USA

Royal farms installed a covered lagoon biogas system in 1982 as part of their 3 lagoon system. Initially, one-third of the primary lagoon was covered to treat the flushed manure from the 700 sow farrow -to-finish operation. The cover trapped this biogas before being transmitted to a 75 kW engine generator. In 1985, Royal Farms covered the remainder of the lagoon and added a 100 kW engine/generator in response to an increase in pig numbers to 1500 sow farrow-to-finish. This technology continues to provide 80-90 % of the electricity used at the operation and reduces problems associated with odour, dust, and flies. In addition, this system continues to offset energy prices which to this point have saved almost one million dollars US!

The installation cost of the covered lagoon system was about $220,000US in the early to mid 1980s, with annual benefits of about $84,000US (including electricity savings, heat savings, and sale of electricity). Annual operating costs are about $8000 and are principally for routine engine oil changes and periodic engine overhauls. The Royal Farms covered lagoon system paid for itself within 4 years. Reprinted from AgSTAR Program U.S. EPA literature.


13

Heat Energy

Gas Recycled Flush Water Covered Lagoon(s) Sludge Storage Lagoons

Figure 12 : Flow chart - covered lagoon system

Pig Buildings Flushed

Land or Value Added

Products Land Application


14

Appendix C Biogas Digesters for Large Piggeries The production of biogas from the piggery wastes in a temperature controlled fully mixed process, the gas is used to generate electricity, the sludge is further processed and bagged for the nursery garden industry and the liquid nutrients used on farm.

Figure 13 : Anaerobic Digester, Berrybank Farm, Ballarat. The main digester is the large white insulated tank, the secondary digester and gas bell is the structure to the left. The shed in the foreground is used for further processing and packaging the digested sludge into garden products.


15

The Biodigestion Process

The Grit Removal Machine and Homogenisation Pit In Australian conditions, the removal of grit from the slurry is important. Meat and bone meal fed to the pigs contains granules of bone and this passes through the pig and into the effluent. These granules will destroy the stators in the pumps and may deposit in the primary digester, so it is necessary to remove them. This is achieved with a specially designed Grit Removal Machine. The gritty material removed from the

effluent is sold to a local worm farmer who is producing worm castings for use as a fertiliser. The Homogenisation Pit is where the degritted effluent is agitated before it is pumped to the screen. This is necessary to ensure that the solids do not settle to the bottom and block the pump, and, so a consistent mix passes over the screen for separation of the coarse solids.

Pig Buildings Flushed Mixed Pumping Grit

Grit Removal Recycling Liquid Biofiltration (land) Screen DAF Digester 1 Solids Digester 2 Humus Heat Electricity Nutrients Nutrient Gas Filtration Rich Dehumidification Liquor Cogeneration

Figure 14 : Flow chart - “Berrybank Farm” total waste management system


16

The Screen To achieve a good production of gas it is necessary to thicken the effluent so that there is a higher concentration of solids than would normally exist. The concentration of solids in the effluent on a typical Australian pig farm is approximately 1.5%. The thickening plant, of which the screen is the first component, increases the percentage of solids in the effluent passing to the Primary Digester up to 5% by separating the water. Dissolved Air Flotation Unit The underflow from the screen is then processed by a DAF (Dissolved Air Flotation) Unit, where chemicals and flocculants are added to the liquid, which is then charged by small bubbles of air which float the solids to the surface. The solids are skimmed off the surface and then fed into the Primary Digester. The liquid fraction is used for flushing the piggery and/or applied to crop land. The Primary and Secondary Digesters The Primary and Secondary Digester are where the anaerobic digestion takes place. Anaerobic digestion is a biological process very similar to that occurring naturally in swamps where bacteria breaks down the rotting vegetation to produce marsh gas. A digester simply provides the ideal conditions for the process to proceed at a faster, more controlled rate, by excluding air, thoroughly mixing the contents and keeping the temperature at an optimum level. The Gas Bell The Gas Bell is located above the Secondary Digester and is constructed of steel. There is a constant pressure of gas in the Bell and it moves up and down the railing according to the volume of gas being stored.

Recirculation of the Digested Solids Effluent consists of fully digested, partially digested and totally undigested material. Obviously, it will take the bacteria longer to break down the totally undigested material. In fact, to design a digester to achieve this would require it to be big enough to hold the equivalent of 40 days’ sludge. The normal practice is to design a digester with a hydraulic retention time of about 20 days, thus achieving total digestion of only about 60-70% of the sludge. The Berrybank digester was developed with a recirculation system which ensures greater digestion of the sludge in the same size digester. Purification of the Biogas Biogas needs to be cleaned because it has levels of sulphur which can damage the cogeneration units. The purification plant consists of gas scrubbers, condensation traps and a dehumidifier. These items were developed in the farm workshop. The Cogeneration Plant and Thermic System Here the purified Biogas is used as fuel for gas engines which drive generators to produce (a) electricity for the farm’s use and sale to the Electricity Grid, and (b) thermal heat (from the gas engines’ cooling water), which is used to heat the Primary Digester, and is also available for other heating purposes such as pig buildings or hydroponic liquids and/or greenhouses. Fertiliser Extraction and Collection The solid and colloidal part of the digested slurry is separated from the water by way of a centrifuge. This reduces the bulk of the slurry by up to ten times and increases its fertiliser value by the same amount. This composted material or humus can be sold as an organic fertiliser or utilised on the property for crop production. The separated water, which still contains some fertiliser compounds, can be used for irrigation


17

An Anaerobic Digester System for 20,000 Pigs The system includes: • collection of approximately 400,000 litres of effluent per day at 2.3% solids;

• removal of approximately 2 tonne of grit material per week which has been sold as a feedstock to worm farmers for $8/tonne;

• separation of 98% of the solids from the liquid effluent;

• recirculation of the calirified water (0.06% solids) for flushing;

• conversion of solids into approximately 2700 cubic metres of biogas per day and 7 tonnes of organic sludge per day via the process of anaerobic digestion;

• conversion of the biogas into a continuous supply of 220 kilowatts of electricity (5336 kwh/day), which may be sold for 14.8 cents/kwh during peak periods;

• conversion of the anaerobic sludge into 20 tonnes of bagged soil conditioner per day, which can be sold for up to $160/tonne.

Costs • The capital cost of the system is approximately $2,000,000.

• The operating costs are approximately $250,000 per year.

• The potential income is approximately $650,000 per year.

• The break-even size of a biogas digester is for a piggery with about 11,000 pigs, based on typical capital, operating and income costs. If odour and other environmental factors are given a cost, the economic size of the piggery will reduce accordingly.


18

Require More Information? Suppliers / Who to Contact -

Covered lagoon facilities, suppliers of liners and covers: Pacific Lining Co Aust Pty Ltd 1689 Pacific Highway Wahroonga NSW Ph. 02 9489 4800

Curtis Barrier Pty Ltd 91 Carlingford Road Epping NSW Ph. 02 9876 1799

GTI Level 1, 24 Glenferry Rd Malvern VIC Ph. 03 9576 3188

PMP (Gordon Services Pty Ltd) P.O. Box 142 Ringwood East VIC Ph. 03 9879 2379 Fax 03 9879 1489

SLT Advanced Lining Technology Pty Ltd 24 Regent Cres Moorebank NSW Ph. 02 98212977

Reef Industries Inc P.O. Box 750245 Houston TX 77275-0245 USA Ph 713 507 4200 Fax 713 507 4295

Digester & Co-generation Systems BioResources Australia can supply designs and consultancy services for establishing digester type facilities. They can be contacted on (03) 5343 2344.

Suppliers of Tankers Agriwaste 940 Old Port Wakefield Rd Two Wells SA Ph. 08 5202 555

Pearson Engineering Mangawhero Rd Matamata NZ Ph. 1800 122 900 (Australia)

Axon 5 Rembrant St Carlingford NSW Ph. 02 9873 3840

Travelling Manure Irrigators Vaughan Irrigators P.O. Box 387 Yankalilla SA Ph. 08 8558 3151

Trailco Irrigation P.O. Box 1278 Eagle Farm QLD Ph. 07 3260 1828

Upton Engineering Federation Ave Corowa NSW Ph. 02 60331844

Illawara Irrigators Ph. 02 6272 5139

Further Reading

KRUGER, I.; TAYLOR, G.; FERRIER, M.; (1995), Effluent at Work, Pul, N.S.W. Agriculture. The National Greenhouse Strategy, Australian Greenhouse Office www.greenhouse.gov.au/pub/ngs Ph. 1800 803 772 (Australia)

methane emission project - a guide for pig producers reducing...

Documents