Carbon reduction and resource recycling from on-farm dairy waste in Australia

Carbon reduction and resource recycling from on-farm dairy waste in Australia

The aim of this thesis is to develop circular manure management strategies to reduce environmental risks and improve the sustainability of the Australian dairy farming sector. Circular technologies target the beneficial recycling of resources contained in dairy manure residues, such as nutrients and organic matter, for bioenergy production. Measurements are performed on liquid manure residues (effluent) from various dairy farms across Australia and reveal material amounts of nutrients, but there are no significant differences in nutrient concentrations amongst different dairy production system types (i.e. grazing vs. intensive dairies). However, there are notable differences in total nutrient capture rates (recovery potential) between different systems. Unfortunately, measurements confirmed dairy effluent is usually heavily diluted, making its transport, further processing, and beneficial use less viable. Cleaning strategies also affected dilution, requiring recovery methods such as solid-liquid separation. A modular solid-liquid separation technology is applied at full-scale at a commercial dairy. Without chemicals (lime and flocculant), only 25.9% particulate matter and 33.4% organic particle matter are recovered into the solid fraction, but the filtrate is more usable for irrigation. The solid fraction is also stackable and easily transportable for further processing and reuse. Lime and polymer flocculant enabled nitrogen and phosphorus recovery into the solid fraction, at ~54% and up to 91%, respectively. This provides circular options for farmers. A first biochemical methane potential of grazing dairy effluent is reported, specifically 161 LCH4 ·kg-1 volatile solids. Important effects of on-farm manure separation were also evaluated. This is important to evaluate renewable biogas recovery potential and is essential for sector emissions accounting. Overall, the data and findings of the thesis were invaluable to understand closed-loop system options, estimating recovery potential, and evaluating approaches to reduce manure-management greenhouse gas emissions across Australian dairy farms.

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