H2 can also be viewed as an energy source and an intermediate towards the production of VFA which can be further transformed to polyhydoxyalkanoates (PHAs), or can be used for biohydrogenation of fatty acids into alcohols [120]. Polyhydroxyalkanoates (PHAs) are a group of biologically derived polyesters that represent a potentially sustainable replacement for fossil-fuel based conventional thermoplastics due to their biodegradability and capability of being produced from renewable resources. During growth-limiting conditions, bacteria produce PHAs as energy and carbon storage molecules. So far, many efforts have been made to pro­duce PHAs from commercial grade VFAs using pure cultures. However, the PHAs produced in this manner are more expensive than polyethylene due to their high production costs [121, 122]. Almost 30% of total PHA production cost is attributed to the carbon source [123]. VFA bound acid-rich waste generated from acidogenic process of H2 production can be used to produce PHAs using PHA accumulating organisms and is a promising approach to decrease the production cost. Production of PHA by mixed microbial cultures using wastes seems to have many advantages when compared to the existing well-known process where pure cultures and single defined substrates are used. Recently, the production of PHAs from the fermenta­tion of syngas was also reported which is economically viable than that from sugar fermentation [124].