Waste remediation and value creation: the recovery of nutrients from dairy industry wastewater using the aquatic plant Lemna minor

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Walsh, Éamonn
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University College Cork
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The production of food is a major source of carbon emissions and environmental damage worldwide. The sector is also coming under significant stress from decreasing resource availability, climate change and soil erosion, among other things. In order to increase the sustainability of the sector action is required to maintain resources within the system. The circular economy (CE) is one economic model which can improve the recycling of resources within a system, particularly through the treatment of waste as a resource. The dairy industry is one significant component of the worldwide food production industry. As part of dairy processing, large amounts of wastewater are generated, in some cases up to ten times the volume of the processed milk. This large volume of wastewater must be treated for appropriate disposal. Usually this involves removal and disposal of the polluting components, such as organic compounds, N and P. However, there is a wealth of compounds contained within dairy processing wastewater which could be reused. This reuse is called valorisation, which can be part of a CE approach to waste treatment. There are different ways of valorising waste but a particularly interesting way in the context of dairy processing wastewater is phytoremediation, which was assessed in this thesis using aquatic Lemnaceae, i.e. duckweed. Accordingly, environmentally polluting compounds, such as N and P, are removed from the wastewater by plant action and in duckweed a valuable biomass is created which can be used as a feed or biofuel. In general, it was found that dairy processing wastewater is suitable for Lemnaceae cultivation. However, this research highlights how some adjustments to the wastewater are necessary for Lemnaceae survival, while other adjustments made to the growing conditions can optimise cultivation and remediation. Overall, high removal of N and P compounds was achieved and duckweed biomass with a high protein content was produced. Furthermore, the combination of duckweed cultivation with microbial digestion led to superior remediation of the dairy processing wastewater, particularly for organic components. These results will facilitate the integration of duckweed into the large-scale industrial remediation of dairy processing wastewater, which would improve the sustainability of the food production sector while also producing a versatile biomass that can be utilised in multiple ways.
Duckweed , Remediation , Wastewater , Circular economy , Valorisation
Walsh, É. 2021. Waste remediation and value creation: the recovery of nutrients from dairy industry wastewater using the aquatic plant Lemna minor. PhD Thesis, University College Cork.
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