Towards development of biogas production for New Zealand on-farm greenhouse gas reduction

The current non-circular approaches to farm dairy manure management in New Zealand (NZ) have prompted research into alternative strategies. Anaerobic digestion (AD), by capturing methane as biogas and producing biofertiliser, offers a promising solution to reduce greenhouse gas (GHG) emissions and displace harmful chemical fertilisers. While AD technology is well-established in Europe, its application in New Zealand remains limited, with underdeveloped research on dairy cow and goat manure AD. This study aimed to develop and optimise AD systems for maximised resource recovery and GHG emissions reduction from New Zealand farm dairy manure. The research focused on four key areas: a critical literature review of conventional manure management systems compared to AD, a comparative assessment of New Zealand dairy goat and cow manure properties and biogas potential, an experimental assessment of New Zealand dairy cow and goat manure processing routes including application of ultrasonic pretreatment (UP) to enhance biogas production, and a comprehensive carbon emission reduction assessment, comparing AD with traditional manure management systems and quantifying the environmental benefits. Physicochemical analyses revealed that New Zealand dairy goat manure had higher initial bioconversion potential (16% volatile solids) than cow manure (10%) but slower hydrolysis rates due to complex lignocellulosic structures. This resulted in its lower biodegradability (26% vs 81% for cow manure) and consequently lower biogas production. Baseline AD testing demonstrated that conventional AD is effective for New Zealand dairy cow manure digestion, achieving over 81% of the maximum biomethane potential. However, UP was recommended for dairy goat manure to overcome its slow hydrolysis. The research demonstrated that UP (2,200-4,200 kJ/kg total solids) increased methane content from 29% to 54% and methane yield by 90% while reducing hydrogen sulphide content. Results further indicated that implementing conventional AD for New Zealand cow farms and ultrasonic-enhanced AD for New Zealand goat farms could potentially reduce carbon emissions from manure management, farm electricity, and fertiliser use by up to 84% and 56%, respectively. The research provides crucial insights into the potential of AD for mitigating GHG in the New Zealand dairy sector, offering a promising pathway to delay peak warming temperatures and support climate change mitigation efforts.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemical and Materials Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2025

Author dc:creator

• Nleya, Yvonne

Advisors dc:contributor.advisor

• Baroutian, Saeid
• Young, Brent
• Nooraee, Eeman

• Anaerobic digestion
• biogas
• Manure management
• Dairy cow manure
• Dairy goat
• Manure
• Greenhouse gas
• IPCC Modelling
• Ultrasound pretreatment
• Biochemical methane potential
• Techno economic
• Technological readiness level

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/75238

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/75238