Monday, April 19, 2010
4-09

Effects of hydraulic and solids retention times on growth and settleability of microalgal-bacterial biomass for biofuel production

Julia M. Valigore1, Peter Gostomski2, and Aisling O'Sullivan1. (1) Civil and Natural Resources Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand, (2) Chemical and Process Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand

Microalgal-bacterial biomass grown on municipal wastewater can be highly productive, treats wastewater, requires low energy inputs, and it can be used in its entirety through 1) whole biomass conversion (e.g., thermochemical liquefaction) or 2) partial biomass conversion (e.g., lipid extraction for biodiesel) with valuable residual co-products such as fertiliser and animal feed.  These capabilities greatly increase the biomass’ sustainability for biofuel production.  Microalgal-bacterial biomass was grown in laboratory sequencing batch reactors on primary treated wastewater from the Christchurch Wastewater Treatment Plant (CWTP) in New Zealand to produce settleable biofuel feedstock.  Inoculums consisted of native, mixed cultures from an oxidation pond and the activated sludge process at CWTP.  Reactors were operated under simulated summer climate (i.e., 925 μmol/m2/s of photosynthetically active radiation for 14.7 hr/day at 21 °C mean water temperature) using a 4- or 8-day hydraulic residence time.  Solids retention times were controlled from 4 to 40 days by discharging different ratios of supernatant and completely mixed culture and internally recycling settled solids following bioflocculation.  Productivity increased as hydraulic and solids retention times decreased.  Variation of these parameters produced between 2 and 20 g/m2/day of solids.  Biomass settleability was generally 70 to 90%, and the microbes aggregated into stable, dense flocs as cultures aged up to 60 days.  The low lipid concentration of 10.5% indicated that the biomass was energetically more suited for biofuel pathways such as anaerobic digestion or thermochemical liquefaction rather than lipid extraction.


Web Page: www.civil.canterbury.ac.nz/postgrads/jvaligore.shtml

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