Leland Stanford Junior University

Allison J Pieja

Craig S Criddle

Curtis W Frank

Sarah Billington

Margaret C Morse

Sarah J Christian

A method for inexpensive and efficient PHA biosynthesis includes operating a sequencing bioreactor in alternating phases of nutrient deprivation and carbon feedstock deprivation to select for robust PHA-producing microbes. Preferably, the bioreactor is operated in a non-sterile manner with mixed cultures of methanotrophs. The method also preferably uses periodic biomass-wasting (PHA harvesting) at the end of the carbon feed phase, gradually lengthening the time period of carbon deprivation phase to create a penalty for rapid PHA degradation and incentive for PHA accumulation. Also, bacterial enrichment cultures may be introduced periodically. The PHA-accumulating bacteria are preferably grown on common anaerobic degradation products, specifically volatile fatty acids, such as acetate and propionate, and methane gas. The PHA has useful applications in bioplastics and other products.

Use of selection pressures to enable microbial biosynthesis of polyhydroxyalkanoates from anaerobic degradation products

A biocomposite is produced from natural fiber fabrics embedded in a matrix of biosynthetic polyhydroxy-alkanoate (PHA) polymers. The PHA is synthesized using aerobic microbial biosynthesis using mixed bacterial cultures and a feedstock containing anaerobic degradation products such as methane and volatile fatty acids derived from microbial biodegradation of organic waste materials, which may include waste biocomposites. Monomers may be added to the synthesized PHA polymer to control mechanical properties of the resulting biocomposite. The natural fibers and/or PHA may be pretreated using various techniques to improve the bond between the fibers and the PHA resin matrix and water absorption resistance of the fibers. The composite may be a laminate of treated and untreated fabric layers, or differently treated layers, to achieve good in-service performance as well as rapid and/or optimal biogas production when taken out of service and put in an anaerobic environment to degrade.

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Menlo Park, CA, United States of America

Allison J Pieja