Polyhydroxyalkanoate (PHA) production from sludge and municipal wastewater treatment

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with comparable properties to some petroleum-based polyolefins. PHA production can be achieved in open, mixed microbial cultures and thereby coupled to wastewater and solid residual treatment. In this context, waste organic matter is utilised as a carbon source in activated sludge biological treatment for biopolymer synthesis. Within the EU project Routes, the feasibility of PHA production has been evaluated in processes for sludge treatment and volatile fatty acid (VFA) production and municipal wastewater treatment. This PHA production process is being investigated in four units: (i) wastewater treatment with enrichment and production of a functional biomass sustaining PHA storage capacity, (ii) acidogenic fermentation of sludge for VFA production, (iii) PHA accumulation from VFA-rich streams, and (iv) PHA recovery and characterisation. Laboratory-and pilot-scale studies demonstrated the feasibility of municipal wastewater and solid waste treatment alongside production of PHA-rich biomass. The PHA storage capacity of biomass selected under feast-famine with municipal wastewater has been increased up to 34% (g PHA g VSS-1) in batch accumulations with acetate during 20 h. VFAs obtained from waste activated sludge fermentation were found to be a suitable feedstock for PHA production.

Wastewater and waste treatment plants, traditionally considered solely as end-of-pipe processes, can be utilised as residuals bio-refineries in which raw wastewater and its organic/inorganic content are transformed into renewable products, such as energy, minerals and chemicals. Polyhydroxyalkanoates (PHA) are a family of completely biodegradable polyesters that can be produced as a novel adjunct to biological wastewater treatment in mixed-microbial activated- sludge systems. PHA have attracted much interest due to their thermoplastic properties and biodegradability. The possibility of producing PHA from renewable resources, especially, from municipal, industrial, and agricultural residuals, has further spurred advancements in biological processes for PHA production. As the opportunities, PHA are recognised as platform chemical raw materials within bio-refinery frameworks. In particular, in the management of wastewaters and solid wastes, PHA production via mixed microbial activated sludge represents an opportunity for recovering raw wastewater organic carbon by means of biological treatment.