Gaia EnviroTech

The Gaia EnviroTech business is the Bioenergy and Waste Management division of Gekko Systems, based in Ballarat, Victoria. The company has partnered with Jock Charles from the Berrybank Farm, who has successfully operated an Anaerobic Digester (AD) on piggery effluent in the Ballarat region for 30 years. The modular biodigester design was developed by Gaia EnviroTech and is manufactured onsite at their local facility. The expandable configuration is targeted to treat 5-20k tpa organic waste and upwards.

Objectives

The system in this case study was installed as a 12-month research and development project to establish the viability of an anaerobic digestion plant designed to convert dairy effluent to energy and minimise odour. The secondary objectives were to increase the nutrient value of the manure and ease handling constraints (e.g. allow longer-term storage). This was required to provide the dairy with a viable option for future herd expansion.

The family-owned dairy houses cattle in a large shed and periodically takes them to pasture. In addition to milk production, potatoes are grown on-site and benefit from the nutrient value of the manure. The operation milks 300 cows. Before the digester installation, raw manure was constantly scraped from this shed, loaded into tanker trailers, and spread onto farm paddocks, causing odour issues.

Installation design

The installation was fully automated and operated for a year, from November 2018 to 2019. The pilot unit is a 160m3 prototype system and is a novel modular multistage ‘biodigester’ to capture biogas released during anaerobic digestion. The sequential flow system ensures manure is effectively retained for a defined duration. During testing, up to 16m3 of liquid manure was fed to the biodigester unit daily. However, the average feed loading was 12m3/day and held in the system for 13 days, producing approximately 250m3 of biogas per day. The biogas stabilised at approximately 63% methane content. An H2S target level of less than 100ppm in the biogas for use in the system’s boiler and generator was targeted and typically controlled to below 50ppm.

Operation

The design centres around three 12 m-long biocells made from recycled shipping containers. Manure is pretreated from a collection pit at the end of the dairy shed to feed this unit. Feed is transferred from a small buffer tank and fed into the biodigester at a constant rate. A coarse fibre product is stockpiled in a bunker as a soil conditioner or compost.

During the deployment, the feed pretreatment equipment processed all the manure produced by stabled dairy cows (approximately 21m3/day). The standard feed throughput of the biodigester was a proportion of that processed manure. Generally, this was 12m3/day; however, rates as high as 16m3/day were achieved. The average biogas production rate was approximately 250m3/day, with a methane concentration of 63%. Biogas was conditioned by removing hydrogen sulphide and moisture before being used in a boiler or generator unit. This represents a total potential energy output of 1575kWh/day or approximately 550 and 630kWh/day of electrical and heat energy from a generator unit, respectively. This equates to 185MWh/year of electrical energy, worth roughly $37,000. This renewable electricity source can be on-demand and available when required by the farm’s equipment. Thermal energy is also a valuable resource that can substitute electrical or gas heating.

During the deployment, the overall uptime was 87%, and in the final six months of the project, it increased to 96%. This is equal to an average uptime of approximately 23 hours/day. However, on many days, the plant operated uninterrupted for 24 hours. Several technical hurdles related to feed preparation, additive dosing, biogas handling, and energy production areas were overcome, and they have now been successfully automated and implemented into the updated design.

The Anaerobic Digestion Process

The anaerobic digestion process enhances the nutrient value of the manure. Within the process, mineralisation occurs, transforming organic nitrogen (N) and phosphorus (P) into inorganic forms that have higher bioavailability (directly available to plants). This is not only of benefit to pastures and crops, it also reduces N and P runoff to waterways (potentially causing eutrophication and algal blooms).

The feed is broken down by microorganisms in several stages within the biodigester. Populations of Bacteria and Archaea work in unison to degrade and consume the complex organic matter. Approximately 40% of the original mass is released as carbon dioxide, methane (and other trace gases). This ‘biogas’ is captured and stored as an energy source. The liquid that exits the biodigester is called digestate and is stored in a large tank. This lower odour digestate has a high nutrient value and was spread to pastures when convenient.

Outcomes for Client

As residential areas encroach on traditional dairy farming land, odour becomes a significant issue, especially when the effluent needs to be stored. A biodigester effectively solves this issue. The odour emitted from the digestate is much lower than that of the raw manure. A lower-odour digestate will also allow longer-term storage prior to use and provide greater operational flexibility.

The system also operates at deficient noise levels using a low-energy system and shielded machinery inside containers. Although not quantified, the more excellent nutrient value in digestate will also benefit the site. Evidence suggests pastures and crops respond better to nutrients supplied in the digestate than raw manures. Nitrogen runoff is also less likely to occur due to being absorbed by the soil and plants more rapidly. In addition to N, P, K and other nutrients, digestate is also a tremendously beneficial source of organic carbon, especially in soils in drier regions. More carbon means higher microbial activity and healthier soil. The Gaia EnviroTech system has proven itself to be reliable and low maintenance. Uptime for the system >96%. Daily checks of the system can be completed in less than 30 minutes. Often, a walk-around with a simple checklist is all that is needed.

Gaia EnviroTech and Anaerobic Digestion

Environmental protection is a key driver for many projects involving anaerobic digestion technologies. This is not only because organic waste materials can pollute the environment directly (e.g., nutrient overloading of terrestrial and aquatic environments causes ecological imbalance) but also because they have the potential to generate greenhouse gas (GHG) emissions when stored or deposited in landfill facilities. An average Victorian household (adults with children, gas heating) requires approximately 15 kWh/day of electricity (CSIRO – Typical House Energy Use). Therefore, the installation in this case study would generate sufficient electricity to power 36 homes. Anaerobic biodigesters provide on-demand energy, contribute to waste management and circular economy outcomes and are minimally affected by weather conditions. Renewable energy sources, such as photovoltaic and thermal solar systems, require sunlight.

Wind turbines’ output is also dependent on atmospheric conditions. However, a biodigester plant will operate 24/7 as long as the feed is maintained, providing a reliable and uninterrupted resource for the dairy’s life.

Cattle contribute to GHG emissions by releasing gases as they digest food. Much of this is methane, over 28 times more potent than carbon dioxide as a GHG.

Cow manure is not the only organic feedstock suitable for the Gaia EnviroTech biodigester. Organic residues from several industries, including cheese whey, food manufacturing waste, fats, oils, and grease (FOG), flotation sludges from wastewater treatment plants, and food waste, can be anaerobically digested to produce biogas.

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