Strategies for PHA production by mixed cultures and renewable waste materials

Abstract

Production of polyhydroxyalkanoates (PHA) by mixed cultures has been widely studied in the last decade. Storage of PHA by mixed microbial cultures occurs under transient conditions of carbon or oxygen availability, known respectively as aerobic dynamic feeding and anaerobic/aerobic process. In these processes, PHA-accumulating organisms, which are quite diverse in terms of phenotype, are selected by the dynamic operating conditions imposed to the reactor. The stability of these processes during long-time operation and the similarity of the polymer physical/chemical properties to the one produced by pure cultures were demonstrated. This process could be implemented at industrial scale, providing that some technological aspects are solved. This review summarizes the relevant research carried out with mixed cultures for PHA production, with main focus on the use of wastes or industrial surplus as feedstocks. Basic concepts, regarding the metabolism and microbiology, and technological approaches, with emphasis on the kind of feedstock and reactor operating conditions for culture selection and PHA accumulation, are described. Challenges for the process optimization are also discussed.

Effect of feeding regimens on polyhydroxybutyrate production from food wastes by Cupriavidus necator

“…The predominance of lactic acid at pH lower than 4 and the relative increase in acetic acid and propionic acid concentrations after the adjustment of pH to around 6 were consistently shown in triplicate experiments (data not shown) and in previous studies (Du and Yu, 2002). PHB seems to be effectively produced from acetic acid (Serafim et al, 2008). Moreover, propionic acid production is also beneficial because it leads to the synthesis of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-PHV) copolymer (Du and Yu, 2002), which is more ductile and tougher than the PHB homopolymer .…”

“…This technique is more energy-efficient than that involving pure cultures (Kek et al, 2008;Lee et al, 2008). However, the PHA content in the mixed cultures was not high (<65%) (Serafim et al, 2008). In contrast, PHA production by pure cultures yields a very high PHA content (ca.…”

“…Therefore, bio-based and biodegradable polymers such as polyhydroxyalkanoates (PHAs) have attracted considerable attention as alternatives to the petroleum-based plastics (Castilho et al, 2009). In almost all established industrial processes for PHA production, the substrates used are sugar-based compounds, which have a high market price (Serafim et al, 2008). Therefore, more cost-effective technologies are required.…”

Combining the enrichment and accumulation step in non-axenic PHA production: Cultivation of Plasticicumulans acidivorans at high volume exchange ratios

“…7). Still, the PHB content of the harvested biomass ranks among the higher values reported for non-axenic PHB production (Jiang et al, 2012;Serafim et al, 2008).…”

“…To reduce the production cost of PHA and allow broad application, various researchers investigated the use of open microbial communities and waste organic carbon as substrate (Albuquerque et al, 2010;Bengtsson et al, 2008;Coats et al, 2007;Dionisi et al, 2005;Jiang et al, 2012). The process for non-axenic PHA production from organic waste comprises three steps: (1) acidogenic fermentation of the waste stream, (2) enrichment of a PHA-producing culture, and (3) production of the PHA (Dionisi et al, 2004;Serafim et al, 2008). The first or acidogenic fermentation step (Temudo et al, 2007) aims to convert the waste organic carbon, primarily carbohydrates, to a mixture of volatile fatty acids.…”