Effect of pH on biodiesel production and the microbial structure of glucose-fed activated sludge

• The pH affected biomass accumulation of cultured sludge for biodiesel production.
• Cultured sludge with pH control produced higher biodiesel yields quickly.
• More unsaturated fatty acid esters were obtained without pH control.
• γ-proteobacteria dominated in activated sludge improved biodiesel production.

With the goal of reutilizing excess sludge, and decreasing the cost of lipid feedstocks, the effect of pH on enhancing biodiesel production via culturing special microbial communities from municipal activated sludge was investigated. The results indicated that controlling pH around 7.5 made biomass production and lipid accumulation more quickly under high initial glucose loading (40 g COD L−1) and COD:N ratio (90:1). Compared with the seed sludge (biodiesel yield of 5.2 ± 0.3 mg g−1 dry sludge), the cultivated sludge achieved higher biodiesel yields both with pH control and without. However, the biodiesel yield of the cultured sludge with pH control (69.3 ± 1.2 mg g−1 dry sludge) was higher than that of the sludge without (63.3 ± 0.4 mg g−1). More unsaturated fatty acid esters (64%, w/w total FAMEs) were obtained from the cultured sludge without pH control, which could improve the cold flow properties of biodiesel. The pH control did not make an essential difference in the microbial community at the end of cultivation. However, it improved the accumulation of Enterobacteriaceae and Shewanella in the cultured sludge. The dominant bacteria of Shewanella, Raoultella, Enterobacter, Kluyvera and two unclassified genera clustered with γ-proteobacteria within the cultured sludge possibly contributed to enhancing biodiesel production.