“Dairy Manure Waste Management at Petit Merlo Dairy Farm - Composting and Biogas to Energy Recovery Facility”
“Dairy Manure Waste Management at Petit Merlo Dairy Farm - Composting and Biogas to Energy Recovery Facility”

The operation of a dairy farm in Mauritius will be beneficial for the product of fresh milk for local supply and hence reduce dependence on importation. The Petit Merlo farm intends to start with 50 cows initially, to reach 400 cows within 7 years with a yearly production of 1.2M litres of milk in year 7. The project is in line with the objective of the government to increase our self-sufficiency from the actual two percent, corresponding 3.2M litres to twelve percent in 2015( Blueprint for a Sustainable Diversified Agri Food Strategy for Mauritius (2008-2015). The milk production from January to June 2008 was 1,750,000 litres (CSO, Economic and Social Indicators 2008).

However, it will lead to the production of solid and liquid wastes that requires proper treatment and disposal. Traditional practices mainly relied on the agronomic use of dairy wastes which include storage and spreading in the fields and use of the liquid effluent for irrigation for crop production. Although these methods are highly effective in nutrients recycling, it has been reported as being objectionable in terms of odour and to cause nitrates pollution of underground water and water bodies.

Furthermore, the dairy farm proposed by the cooperative is situated in proximity to a water table. Hence, the management of wastes, be it solid or liquid is of crucial importance to avoid contamination, which is irreversible. This project will ensure adequate protection through the composting and biogas treatment of the dairy wastes.

Another major pollution from dairy farms is the emission of methane. A review of agricultural emission data shows that the majority of CH4 from dairy farms is created through enteric fermentation, followed by emissions from manure storages. In fact, it is believed that 63% are from enteric fermentation and 30% from manure storages (Energy Information Administration, 2006).

The intergovernmental Panel on Climate Change (IPCC, 2007) reported that it is “extremely likely” (i.e representing a 95% confidence interval or higher) that anthropogenic emissions of greenhouse gases (GHGs) are causing a change in global climate. Although many mitigation plans currently focus on reducing carbon dioxide (CO2) emissions, methane (CH4) is a stronger greenhouse gas and has a global warming potential around 23 times that of CO2 (IPCC, 2007). The Food and Agriculture Organisation of the United Nations has claimed that livestock emit more CH4 in CO2 equivalents than is emitted through the burning of fossil fuels for transportation (FAO, 2006). Hence it is important that all efforts be done to quantify and reduce CH4 emissions from livestock.

There are several sources of emissions of CH4 from dairy farms; the main ones are from enteric fermentation in the animals and microbial processes in deposited manure. In addition to these major sources, less significant emissions result from field-applied manure and from manure deposited by animals inside the barns or on pasture. Field-applied slurry can result in significant emissions for a few days after application (Chadwick and Pain, 1997; Sherlock et al. 2002). A study by Sedorovich et al. (2008) used the Integrated Farm System Model to simulate a 100-cow dairy farm in Pennsylvania, and the model predicted a total average annual emission of 20 Mg CH4. This included an average annual emission of 135 kg CH4 per cow from the Holstein herd and an average emission of 5.4 kg CH4 per m3 of stored slurry manure.

Objectives of proposed project

This project has as objective to design the solid and liquid wastes management facility with a view of preventing environmental pollution as well as recovery of useful resources such as compost and feed material for the generation of heat and electricity. It will comprise of two parts. The initial part will involve the design and operation of a solid waste composting plant, further to separation of the liquid and solid fractions. With time, as the number cows is increased from 50 to 400, the amount of wastes generated will become more significant and will justify construction of an anaerobic digester. Hence, in the second part, the design of an anaerobic digester, the composting plant for stabilising the digested cake (which contains less decomposable organic matter) and the recovery, purification and conversion of the biogas to electricity will be considered.


The NGO is a cooperative society (Petit Merlot Farm Cooperative Society Ltd) regrouping 6 dairy keepers. It is specialised in the rearing of cows for the production of milk.

Suitability of project

The project seeks to address key environmental concerns related to cow farming, namely land contamination, odour and greenhouse gas emissions and ground and surface water pollution. The use of composted manure will serve to enrich the land for growing of grass for fodder, and reduce use of chemical fertilisers. In addition, the use of compost will support organic farming and possibly enable production of organic milk. It is thus in line with the focal areas of the GEF’s operational programme No.10 for International Waters (Contaminant-based program), as well as under the focal area of GEF’s operational programme No. 6 for Climate change; and under the GEF/SGP category of demonstration and capacity building.

The project is also in accordance with the 'Maurice Ile Durable' project which aims to reduce the country's dependence on petroleum fuel, and hence increasing the use of renewable energy sources with a target is to attain 65% in terms of renewable energy by the year 2018, with 35 % from biomass (sugar cane, and biogas from fermentation), 15% solar energy, 6% wind energy, 3% hydro energy, 3% geothermal and 3% from other sources. Anaerobic digestion of the manure will produce methane gas, which will be cleaned and converted to electricity. It is estimated that 240,900 m3/yr of methane, with an electricity potential of 61kwh, will be produced.

This will help in reducing methane emission to the atmosphere and help produce useful energy for the farm and neighbouring industries. Furthermore, the project can be a useful component in line with the new Electricity Bill of Mauritius, whereby independent users will be encouraged to produce their own electricity.

Intended End Results

The overall project consists of two major parts and with effective implementation the following results would be obtained:

Part I – First year of operation
? Safe disposal of 183 tons/year of cow manure produced during the first year of operation of the dairy farm with 100 cows, under the assumption that a typical cow of 635 kg generates around 50.8 kg of solid wastes per day.
? Compost produced will be used in grass plantations to be used for fodder and will have reduced the use of chemical fertilisers as the compost will provide the nutrients to fertilize plant growth
? Wastewater will be given a preliminary treatment, mainly by sedimentation and retention before use for irrigation.
? Provide training to farmers on compost making from cow manure

Part II – Second year of operation
? Set up a state of the art anaerobic digestion plant
? Anaerobic digestion of 7300 tons of cow wastes and all liquid wastes annually
? Separate and compost digestate from digester to a stabilised state
? Provide training in compost making from digested cow manure
? Produce a compost safe to be used in agriculture
? Production of electricity using a gas motor for use on the farm and for sale of excess electricity to the grid; and provide training/troubleshooting on using gas motor
? Revenue obtained from sale of compost and electricity

Site identification
The Petit Merlo Cooperative Society has obtained about 22.5 hectares of land on lease from the Government for the dairy farm project. It is far from commercial, residential and industrial activities. The site is judged to be appropriate for the compost or anaerobic digestion facility. It is to be noted that the cooperative society has already obtained their PER (Preliminary Environmental Report).

Risks for successful implementation

The risks that could occur would be non- availability of cow wastes, community finding difficult to understand and monitor the composting process and environmental impact such as runoff being not properly managed and odour problem, and the anaerobic digestion plant being unable to produce sufficient amount of electricity to justify connection to the grid. It is the first time in Mauritius that a digester together with the electricity production facility with a capacity of 60 kWh will be installed and reported, and would therefore serve as an interesting learning platform for other future projects.

Result dissemination

A half-day workshop will be held at the beginning to present the project and expected results to all stakeholders and representatives of the local community. A seminar will be held at the end of the project to present the key outcomes. A report based on the experience gained in “Cow wastes composting, anaerobic digestion and electricity production” will be produced for wide dissemination. This report will be made accessible to all GEF/Small Grants Program and will be shared on the GEF/SGP website, the MID website and the internet in general.


The total budget of the project is estimated to be Rs 12,395,988 (US$ 390,425) for the Part I and II. A request of US$ 48,850 is being submitted to the GEF/SGP.

It is to be noted that 4 NGOs have secured Rs 4.4 M from AREU under a Decentralized Cooperation Programme/EU funding. Amongst these NGOs, the Petit Merlo Dairy Farm Cooperative Society Ltd is expected to receive around Rs 1 million at least for land preparation and fodder plantation. The Petit Merlo Dairy Farm Cooperative Society Ltd. has also obtained a total of 22.5 acres of land from the government, for which a lease of Rs 1045/acre per year is being paid by members. The value of the agricultural land in Mauritius is estimated to be around Rs 300,000 per acre and this value has been included as the contribution by the NGO. Likewise the Food Security Fund has earmarked Rs 45M for 3 Cooperatives amongst which The Petit Merlo Dairy Farm Cooperative Society Ltd for its dairy farm project (Budget Speech 22 May 2009). From this amount, it is proposed that Rs 834,900 will be a direct contribution to this project. In any case the full co-funding that the NGO has received will be communicated to the GEF SGP in due course. Furthermore, the society has already spent around Rs 500,000 from their own funds for land preparation, plantation, purchase of equipment and administrative expenses such as payment for permit, licensing, preliminary environment report (PER), etc.

The project comprises of two parts; Part I and II. It is proposed to develop Part I with the GEF/SGP and part of the Food Security funds to manage mainly the pollution from solid waste and liquid effluent associated with dairy milk production. For the second part of the project, it is intended to look for additional funds from:

? The ‘Maurice Ile Durable’ fund
? Ministry of Agro Industry and Development

The part II will only be possible with funds from the MID fund, and others, as it will involve the construction and commissioning of the complete anaerobic digestion and biogas to energy plant which requires a high capital investment.
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Project Snapshot

Petit Merlo Farm Cooperative Society Limited
Area Of Work:
Climate Change Mitigation
International Waters
Grant Amount:
US$ 48,823.00
Co-Financing Cash:
US$ 289,502.00
Co-Financing in-Kind:
US$ 225,577.00
Project Number:
Satisfactorily Completed
Project Characteristics and Results
Policy Impact
Expected to be high and to show the way to several other dairy farms in the country
Capacity - Building Component
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Grantee Contact

Mr System Administrator



SGP Country office contact

Mrs. Pamela Bapoo-Dundoo
(230) 213 53 84
(230) 212 14 11


2nd Floor, Sugar Industry Pension Fund Building, 1 Remy Ollier Street
Port Louis, Mauritius

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