Practicability of Using Biodigesters to Reduce GHG in NZ

Home / Adaptation Strategy / Practicability of Using Biodigesters to Reduce GHG in NZ
climate adaptation biodigesters new zealand

A 2015 study from the Waikato Management School of the University of Waikato examined the potential of anaerobic digestion to reduce GHG emissions from the agriculture sector in New Zealand.  

The industry contributes to almost half of the countries total emissions at 48% and is facing mounting pressures to reduce its GHG emissions. One solution offered is using a biodigester.

The study investigated the viability of biodigesters in New Zealand by looking at its policies in power supply, dairy practices, and the availability of government subsidies and incentives that can affect biodigester uptake and compares it to what France is doing.

Biodigester and anaerobic digestion.

A biodigester system uses anaerobic digestion, a process in which bacteria break down organic matter—such as animal manure, wastewater biosolids, and food wastes—without oxygen. Anaerobic digestion for biogas production occurs in a sealed vessel called a reactor, which is designed specifically for the site and feedstock conditions. These reactors contain microbial communities that break down (or digest) the waste and produce resultant biogas and digestate, a solid and liquid end-products from the digester that can be used as fertiliser (How does anaerobic, 2021).

According to the study, an anaerobic digestion system has the potential to assist with:

  • decreasing the production of GHG;
  • producing renewable energy, reducing consumption of heat, fuel, and fertiliser on the farms;
  • improving use efficiency of nitrogen produced on the farm;
  • diversifying the income of farmers and increasing the integration of the farm activities in the region.

France and New Zealand are both important milk producers. Comparing the milk production of both countries, France produced almost 23.7 billion litres in 2013 and New Zealand, 19 billion litres.

However, the two counties show a big difference in the average herd size—France with 52 cows and New Zealand, 402. Data was taken in 2013/2014.

New Zealand’s huge herd size would seem feasible for it to scale up its biodigester application. However, because New Zealand applies traditional pasture-fed and free-range farming, collecting effluent becomes challenging and uneconomical.

In France, the housing of its herd for a big part of the year means that collecting effluent is so much easier, according to the study.

According to the study, the French government wanted to increase their proportion of renewable energy to 20%, reduce emissions, and create energy from biological materials.

To achieve this, it provided incentives through the “Plan Energie methanisation Atutonomie Azote” (a plan for creating energy and nitrogen autonomy through methanisation of biological materials) that was launched in 2013. The target is to develop 1000 anaerobic digestion (AD) systems by 2020.

The French government subsidised the development of the AD units for up to 30% of the investment’s cost with tax exemptions for five years after the installation.

The payback period for an AD plant of 30kW capacity ranges from 29 to 6 years with or without government contribution. The AD system uses 20 to 40% of the heat produced, while the remaining 80 to 60% is used to heat houses, cheese factories, sheds, dry crops, hay, or wood which can offset the cost of installation or provide an additional income source to farmers.

Energy context in France and New Zealand

The price of power in France is the same across regions, and there is little price difference between what other competitors offer. The EDF holds a 93.8% share of the electricity residential market share, and less than ten competitors hold the remaining market share.

Since 2010 the government also made it mandatory for these electric companies to buy electricity produced through renewable sources with the price for purchasing set by the French Government. This power policy proved helpful in securing investments in renewable energy.

In New Zealand, many companies generate and distribute power, but the largest five company controls 92% of the power generation, 95% of power distribution. Transpower, a state-owned company, operates the core electricity grid.

These companies operate in different regions, which affects the difference in electricity prices around New Zealand.  It is also reasonably easy to switch from one power company to another in the country.

In 2012, 25,000 consumers changed their electricity provider per month. According to the study, there is also no mechanism for individuals to contribute or sell electricity from renewable sources to the national grid, nor any financial support or incentive from the government to encourage people to generate power from renewable sources or contribute to the national grid.

Feasibility of AD in New Zealand

Herd sizes are increasing in New Zealand, and so is the number of farmers investing in a feeding pad or herd shelter. The viability of AD in New Zealand is analyzed using three scenarios:

  • the gas being flared,
  • gas being utilized with a generator, and
  • the gas used with a boiler.  

Results show that a herd of more than 1000 cows is required to produce a net present value (NPV) for farms without a covered feed pad, but only with 600 cows with a covered feed pad using a generator, and over 1000 cows with a boiler.

NPV is used to analyze the profitability of a projected investment by calculating the difference between the present value of cash in the inflows and the cash outflows over time (Investopedia, 2021).

In New Zealand, an alternative option to “tanks” is covered anaerobic ponds. To achieve the economic viability of AD, studies have concluded there should be a significant increase in manure collection for dairy cows (e.g., through feeding on hard standing pads or animal housing for longer periods).

In Europe, relevant biogas technologies are fully embedded into their systems which in New Zealand is still an emerging practice. The viability of AD in France is made possible through the provision of government subsidies.

In New Zealand, it is unlikely there will be significant uptake of the technology unless the New Zealand Government chooses to subsidise investments, the study says.

To read the entire study, click the link below:

Farmers generating biogas in New Zealand

The EECA Business presents two cases studies of New Zealand farmers who have set up a biogas system. One is in Eyrewell, North Canterbury, operating a prototype biogas system from the effluent collected from the farm 900 cows. Another one is a biogas system in a pig farm in Lepperton, Taranaki.  Check the link to know more about it: Biogas on your farm

A Kiwi turning food waste into natural gas

Also, check out this news about Andrew Fisher, a man with a big mission to turn New Zealand’s food waste into natural gas.  His company Ecogas has started building a $10 million-plus anaerobic digestion plant in Reporoa, just 39 km south of Rotorua in the Waikato region of the North Island.

In the last 12 years, his other company has also been gathering up to 35,000 tonnes of food waste from supermarkets and factories and turns it into animal feed.

The Ecogas anaerobic digester will collect around 20,000 tonnes of organic food waste from dairy factories, commercial bakeries, milk sheds, fruit graders, and the like in the Rotorua and Taupo area and break it down in the digester, collecting methane and CO2 and turning it into useable natural gas.

The biogas produced will be piped across a massive greenhouse, just built right next to the biogas plant to supply the greenhouse energy and CO2 for the vegetables to grow.

To know more about this project, click the link below:

The multiple function and benefits from biodigester and anaerobic digestion is its greatest strength. It turns our waste into renewable energy, reduces our GHG emissions, and provides biofertiliser as a by-product while protecting our environment. Anaerobic digestion and biodigesters embody a circular economy.

As demands for bio-based resources will grow in the coming years, our wastes will increasingly be transformed into valuable products like fuels, power, and heating, and biogas facilities will have an important role to play.

To know more about Anaerobic digestion and biogas its role in a circular economy, functions, challenges, and case studies of its application in Europe, click the link below:

Source Citation:

Milet, A., Rowarth, J.S., & Scrimgeour, FG (2015). Potential for anaerobic digestion of dairy farm effluent in New Zealand. Waikato Management School, The University of Waikato. Retrieved from

How Does Anaerobic Digestion Work? (2021, January). EPA. Retrieved from

Net Present Value (NPV). (2021, April 9). Investopedia. Retrieved from

Biogas on your farm (2009, August). EECA. Retrieved from

Fagerström, A., Al Seadi, T., Rasi, S., Briseid, T, (2018). The role of Anaerobic Digestion and Biogas in the Circular Economy. Murphy, J.D. (Ed.) IEA Bioenergy Task 37, 2018: 8. Retrieved from

Leave a Reply

Translate »