Manure Biodigesters and CLEAN-BIODIG method

Pork farming and biodigesters in Vietnam:

Since 2005, Zebunet led 24 projects supporting pork farming with Vietnamese rural families. In partnership with our local partners, farmers benefited from microcredit to develop family farming in order to increase and diversify their revenues. Up to 1,500 families starting with 4 pigs could eventually reach an average stock of 8-10 pigs and 2 sows.
Since it complements crop farming, this activity can produce a virtuous cycle at the local level. Leftover crops constitute a food base for animals; and during hunger gap, animal farming brings significant additional revenues to cover family expenses.
This type of farming also produces a significant amount of manure. When tossed directly into the environment without being processed, it can produce negative consequences, including pollution to ground soil, ground waters and water networks in the vicinity.
Yet, this waste can have some value: when processed in a biodigester (methanization process), manure ferments and rejects methane. This gas, produced from waste natural degradation, can be used in cooking and as a source of energy (fridge, light bulb, etc.).

This process closes the loop: families can complement their revenues with a stable activity over the year; crop and animal farming complement one another; and waste from these activities produces energy.

Based on this assessment, Zebunet has chosen to develop biodigester projects as a follow-up to pork farming projects led in Vietnam over the years.



Originally, Zebunet did not have the technical skills to oversee biodigesters’ installation. The association contacted specialists in the field to benefit from scientific expertise. In 2010, we started a collaboration with an IRD researcher, and a methodology was implemented to install "clean" biodigesters limiting waste discharge from methanization.

First, a plan was established to collect the slurry by-product in a tank. Slurry is a leftover from the methanization process that has high potential as an organic fertilizer but is also a nitrogen concentrate which can have negative effects if misused. Currently, this type of tank is not mandatory and not always required during the construction of a biodigester. Yet, the absence of such tank leads to slurry being disposed of directly into the environment, although this waste has a high polluting potential for the ground and for standing and ground waters. Moreover, slurry is an excellent natural fertilizer, available at no cost, which makes it even more important to collect it.

The next step was to carry out environmental controls on the various projects. The objective was to measure if there was any pollution to waters near the farms and fields where slurry is being spread. In order to run these tests, the IRD-Zebunet partnership connected with IAE, the Institute for Agriculture and Environment at the Vietnamese Academy of Agricultural Science. Since 2011, a researcher from the Institute works on our projects in Vietnam, where he performs controls twice a year, and delivers educational sessions to farmers on using and managing biodigesters and slurry.



Since 2010, Zebunet supported the installation of 213 biodigesters with families who took part in one of our previous pork projects. The most recent biodigester project was launched in May in Ha Giang province, as a follow-up to « Quan Ba 2014 pigs » project, which had just finished.
This led to our initial partnership with IRD and IAE to be expanded to include Epurtek, a French-Vietnamese business specializing in methanization and purification systems.
With the help of research findings, environmental controls and our partners expertise, the
CLEAN-BIODIG project was drafted.

The goal is to provide a method, a framework and support to limit the negative impacts of the methanization process:

First, in order to be selected to install a biodigester, families must meet a number of criteria: number of animals, surface of the home, commitment met during the last project, etc. Then, a study is conducted with each family to evaluate the relevance of such installation. This allows to assess for instance if the family can use the slurry in its fields (what is grown, how much, how far from where slurry is produced, etc.). 

Once this phase is over, the conditions of the project are defined under an agreement between partners and beneficiaries. For example, how much is funded directly by farmers, how much is subsidized by Zebunet or another partner, and how much is funded through micro-lending.

Providing access to micro lending for families on a range from 20% to 60% of the infrastructure budget is essential, and it allows to implement the next steps of the project thanks to a PES system.

The PES method - Payments for Environmental Services - is implemented throughout the reimbursement phase. Conditions may vary from a project to another, but the goal of the system is to be provide incentives with a win-win approach among stakeholders:

Throughout the Zebunet project, IRD, IAE and Epurtek offer monitoring, education sessions and analyses to beneficiaries to enable them with the tools and skills to best use their biodigesters. In order to participate in the project, beneficiaries are asked to take part in an education program of their choice -several programs are offered to meet the multiple needs: rice farming, market gardening, fish farming, gardening, etc. Environmental controls help with measuring pollution and if needed, adapting the use of the system or providing further education to families.

Over the 24- or 36-months period of the project, the PSE system requires the micro lending reimbursement rate to be caped proportionally with results: if results are positive (correct use of the biodigester and slurry, no dumping, etc.), the micro lending has a 0% interest rate. On the other hand, if a pollution or bad management is observed and negative effects are still visible after further education sessions are provided, the family will be required to pay some interest rates over the remaining balance due from the micro lending (from 3 to 10% annually according to the level of pollution and motivation). Therefore, the PSE method provides incentives in a win-win perspective: with no pollution, there is no interest rates for the farmer, and the project is a success for all, with limited costs and no impact on the environment.

The CLEAN-BIODIG model is versatile and replicable for other projects and actors. By providing a methodology to limit pollution from biodigesters, the objective of CLEAN-BIODIG is to promote the installation of clean biodigesters within small farms.


Funding :

So far, Zebunet has funded various biodigester projects by combining budgets from its own capital, as well as diverse grants received from Foundations or Institutions (Brageac Solidarité Foundation, French Embassy in Hanoi, Véolia).

Within the next few months, Zebunet will implement a new type of subscription on its website, through an internal system similar to crowdfunding. It will be possible for any individual member, whether a private person or a business, to participate in the funding of future support projects such as biodigesters or even agroforestry. If you are interested in these projects, do not hesitate to write to us and to follow our news!


Competitions and 2016 Convergence forum:

Zebunet, IRD, IAE and Epurtek participated in the Prix Convergences by submitting the CLEAN-BIODIG project in June 2016. This annual competition aims at highlighting development projects initiated by multi-actor partnerships, promoting a fair and sustainable world.
We did not win the prize in the international category, but we were selected for the final among six national nominees. The value of the CLEAN-BIODIG method was recognized and we hope that it will help to promote best practices.