Biodiesel production using oil from fish canning industry wastes

•A process was established to produce biodiesel from fish canning industry wastes.•Biodiesel production was enabled by an acid esterification pre-treatment.•Optimization studies showed that the best catalyst concentration was 1wt.% H2SO4.•There was no advantage when a two-step alkali transesterification was employed.•Waste oil from olive oil bagasse could be used to improve fuel quality. The present study evaluated biodiesel production using oil extracted from fish canning industry wastes, focusing on pre-treatment and reaction conditions. Experimental planning was conducted to evaluate the influence of acid catalyst concentration (1–3wt.% H2SO4) in the esterification pre-treatment and the amount of methanolic solution (60–90vol.%) used at the beginning of the further two-step alkali transesterification reaction. The use of a raw-material mixture, including waste oil obtained from olive oil bagasse, was also studied. The results from experimental planning showed that catalyst concentration mostly influenced product yield and quality, the best conditions being 1wt.% catalyst and 60vol.% of methanolic solution, to obtain a product yield of 73.9wt.% and a product purity of 75.5wt.%. Results from a one-step reaction under the selected conditions showed no advantage of performing a two-step alkali process. Although under the best conditions several of the biodiesel quality parameters were in agreement with standard specifications, a great variation was found in the biodiesel acid value, and oxidation stability and methyl ester content did not comply with biodiesel quality standards. Aiming to improve fuel quality, a mixture containing 80% waste olive oil and 20% of waste fish oil was evaluated. Using such mixture, biodiesel purity increased around 15%, being close to the standard requirements (96.5wt.%), and the oxidation stability was in agreement with the biodiesel quality standard values (⩾6h), which are promising results clearly showing the potential of using such wastes, of very low value, for biodiesel production.