Practicability of Using Biodigesters to Reduce GHG in NZ

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.  

Industry contributes 48% of the country’s total emissions and is facing mounting pressure to reduce GHG emissions. One solution offered is using a biodigester.

The study investigated the viability of biodigesters in New Zealand by examining its policies in power supply, dairy practices, and the availability of government subsidies and incentives that can affect biodigester uptake and comparing them 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 explicitly designed for the site and feedstock conditions. These reactors contain microbial communities that break down (or digest) the waste and produce resultant biogas and digestate, 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 made 19 billion litres.

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

Given New Zealand’s huge herd size, scaling up its biodigester application would seem feasible. However, because New Zealand practices traditional pasture-fed and free-range farming, collecting effluent becomes challenging and uneconomical.

According to the study, housing a herd for a large part of the year makes collecting effluent much easier in France. The French government wanted to increase the 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) 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 installation costs or provide farmers with an additional income source.

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, and less than ten competitors hold the remaining market share.

Since 2010, the government has 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.

Many companies generate and distribute power in New Zealand, but the five largest companies control 92% of the power generation and 95% of the 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. Switching from one power company to another in the country is also reasonably easy.

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 are the number of farmers investing in a feeding pad or herd shelter. The viability of AD in New Zealand is analysed using three scenarios:

• the gas being flared,
• gas being utilised 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 on a covered feed pad using a generator and over 1000 cows on a boiler.

NPV is used to analyse 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. Studies have concluded that to achieve the economic viability of AD, there should be a significant increase in manure collection for dairy cows (e.g., through feeding on hard-standing pads or animal housing for extended periods).

Relevant biogas technologies are fully embedded in European systems, while in New Zealand, it is still an emerging practice. Government subsidies make the viability of AD in France possible.

The study says that a significant uptake of the technology is unlikely in New Zealand unless the government chooses to subsidise investments.

To read the entire study, click the link below.

Farmers generating biogas in New Zealand

The EECA Business presents two case studies of New Zealand farmers who have built a biogas system. One is in Eyrewell, North Canterbury, operating a prototype biogas system from the effluent collected from the farm’s 900 cows. Another is a biogas system in a pig farm in Lepperton, Taranaki. Check the link to learn 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 on a 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 gathered up to 35,000 tonnes of food waste from supermarkets and factories and turned 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, which will be built right next to the biogas plant to supply greenhouse energy and CO2 for the vegetables’ growth.

To learn more about this project, click the link below.

Its greatest strengths are the multiple functions and benefits of biodigester and anaerobic digestion. 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 and its role in a circular economy, functions, challenges, and case studies of its application in Europe, click the link below: