BACKGROUND: The effect of acetic acid, a lignocellulose hydrolysis by-product, on lipid accumulation by activated sludge cultures grown on glucose was investigated. This was done to assess the possible application of lignocellulose as low-cost and renewable fermentation substrates for biofuel feedstock production. RESULTS: Biomass yield was reduced by around 54% at a 2 g L(-1) acetic acid dosage but was increased by around 18% at 10 g L(-1) acetic acid dosage relative to the control run. The final gravimetric lipid contents at 2 and 10 g L(-1) acetic acid levels were 12.5 +/- 0.7% and 8.8 +/- 3.2% w/w, respectively, which were lower than the control (17.8 +/- 2.8% w/w). However, biodiesel yields from activated sludge grown with acetic acid (5.6 +/- 0.6% w/w for 2 g L(-1) acetic acid and 4.2 +/- 3.0% w/w for 10 g L(-1) acetic acid) were higher than in raw activated sludge (1-2% w/w). The fatty acid profiles of the accumulated lipids were similar with conventional plant oil biodiesel feedstocks. CONCLUSIONS: Acetic acid enhanced biomass production by activated sludge at high levels but reduced lipid production. Further studies are needed to enhance acetic acid utilization by activated sludge microorganisms for lipid biosynthesis. (C) 2011 Society of Chemical Industry