Executive Summary: Mixed Culture PHA Production with TERAXTM Liquor as Substrate – Proof of Concept

Summary of Project and Key Findings:
The problem
The objective of this study was to demonstrate the concept of mixed culture PHA production potential using nutrient rich TERAXTM liquor as substrate.

Client Initiatives
Mixed culture bio polymer production is an attractive proposition for industries that face sludge disposal issues. Pulp mill owning companies such as Norske Skog and District Councils are closely looking at alternatives to sludge landfilling and options for converting sludge to a value added material.

This project
This project specifically investigated the feasibility of using biosolid hydrolysate as a feedstock for mixed culture biopolymer (PHA) production. The proof of this concept could potentially reduce the major cost component of bio polymer production (the substrate) and also add further downstream value to sludge treatment processes using wet oxidation technologies such as the TERAXTM process.

A two-step approach of PHA producing culture enrichment and PHA accumulation was used with TERAXTM liquor derived from municipal biosolids as substrate. Batch accumulation studies were run with PHA enriched culture to demonstrate and compare PHA accumulation potential with high and low nutrient TERAXTM liquors with synthetic organic substrates.

Key Results
The main result of the study was the demonstration of the feasibility of using solely TERAXTM liquor as substrate for PHA production without any external carbon or nutrient sources. The nutrient rich liquors were not an impediment for PHA accumulation and the liquors matched the PHA accumulation potential of single synthetic carbon sources such as acetate. A maximum PHA accumulation of 40% based on dry cell weight was obtained with TERAXTM liquor in seven hours. The diversity of volatile fatty acids and other organic compounds in liquor enabled the production of PHA containing 25% of PHV and 75% PHB whereas the single synthetic substrate produced only PHB.

Implications of Results for Client
These initial results show the potential to further increase PHA accumulation in sludge using nutrient rich liquors such as TERAXTM liquor. The successful demonstration of the concept to produce a value added product from a waste stream opens exciting possibilities for industries to benefit from their current costly disposal options.

Further Work
Continuation of this study would enable further optimisation of process conditions for PHA accumulation and evaluation of long term stability of mixed cultures grown under short solid retention time to produce high PHA producing cultures. Ways to improve volumetric productivities are needed to match those of pure culture based commercial PHA production processes.