Meat processing dissolved air flotation sludge as a potential biodiesel feedstock in New Zealand: A predictive analysis of the biodiesel product properties

Abstract

This paper examines the potential of utilising dissolved air flotation sludge obtained from a local meat processing plant in New Zealand as a viable biodiesel feedstock. In this study the dissolved air flotation sludge was characterised and the physicochemical properties of the lipid extract were assessed. The fatty acids present in the lipid extract were explored as a precursor to the estimation of the fuel properties of the biodiesel produced. This study has demonstrated the insufficiency of the traditional alkaline catalysed transesterification biodiesel pathway when meat processing dissolved air flotation sludge is utilised as a biodiesel feedstock. Therefore an alternative integrated hydrolysis and esterification production process has been proposed. The fluid behaviour (Newtonian or non-Newtonian) of the lipid extract was investigated to facilitate an improved understanding of the nature and physical state of the extract. Using a thermodynamic model and experimental data from the literature, the fuel properties, viscosity, density, oxidative stability, heating value and cetane number, of the produced biodiesel as a function of the fatty acid methyl ester profile were estimated. These properties satisfy the existing biodiesel fuel property standards. A preliminary economic assessment of the biodiesel production process using the dissolved air flotation sludge as the feedstock was also conducted. The initial favourable financial results provided a compelling basis for further investigations into the techno-economic feasibility of the production process. The poor cold flow properties of the produced biodiesel were however identified as significant considerations that may limit the utilisation of the dissolved air flotation sludge as a biodiesel feedstock in a temperate climate region like New Zealand. Possible solutions to this problem were initially discussed. In addition, health and safety concerns with the utilisation of this feedstock were identified. Approaches to limit the harmful effects of possible pathogenic content and unpleasant smell of this feedstock were also explored.