Consistent production of high quality PHA using activated sludge harvested from full scale municipal wastewater treatment – PHARIO

Abstract

Production of polyhydroxyalkanoate (PHA) biopolymers by mixed microbial cultures concurrent to wastewater treatment is a valorization route for residual organic material. This development has been at pilot scale since 2011 using industrial and municipal organic residuals. Previous experience was the basis for a PHA production demonstration project: PHARIO. PHARIO was centred on processing surplus activated sludge biomass from the Bath full-scale municipal wastewater treatment plant in the Netherlands to produce PHA. Full-scale surplus activated sludge was fed to a pilot facility to produce PHA rich biomass using fermented volatile fatty acid (VFA) rich liquors from industry or primary sludge sources. A PHA rich biomass with on average 0.41 gPHA/gVSS was obtained with reproducible thermal properties and high thermal stability. A routine kilogram scale production was established over 10 months and the polymer material properties and market potential were evaluated. Surplus full-scale activated sludge, over four seasons of operations, was a reliable raw material to consistently and predictably produce commercial quality grades of PHA. Polymer type and properties were systematic functions of the mean co-polymer content. The mean co-polymer content was predictably determined by the fermented feedstock composition. PHARIO polymers were estimated to have a significantly lower environmental impact compared to currently available (bio)plastics.

Polyhydroxyalkanoates (PHAs) Production: A Feasible Economic Option for the Treatment of Sewage Sludge in Municipal Wastewater Treatment Plants?

“…This wide range of prices hinders the comparison of the obtained values with the previously reported ones. In any case, prices obtained in this work are lower than current market prices (4.9 US$/kg or higher [32]).…”

“…Capital costs could be drastically diminished if secondary sludge is directly used to accumulate PHAs from VFAs, which would only be generated from the primary sludge, avoiding the capital costs related to biomass enrichment [10]. In this sense, Werker et al [32] tested the PHAs-accumulation potential of secondary sludge from several WWTPs. They found that secondary sludge was able to accumulate around 40% of PHA, a value that meets the minimum value required for a downstream economic recovery of the polymer.…”

“…According to Bluemink et al [10] the PHAs purification process would increase production costs by around 25%, so the minimum price of the processed product would be 1.58 and 2.83 US$/kg PHA-pure for the large and small treatment plants, respectively. Different bioplastic production costs from wastewater can be found in the literature ranging from 1.40-11.80 US$/kg PHA-pure [10,20,31,32], which can be associated to the scale and plant configuration proposed. This wide range of prices hinders the comparison of the obtained values with the previously reported ones.…”

Downstream processing and characterization of polyhydroxyalkanoates (PHAs) produced by mixed microbial culture (MMC) and organic urban waste as substrate

“…Very few examples have reported PHA production and characterization from larger plant dedicated to waste management and services of wastewater treatment. In this context, PHA with M w of 400-500 kDa has been produced from surplus full-scale activated sludge [9,40]. There are no examples describing the pilotscale MMC-PHA production and characterization from OFMSW-WAS mixture as carbon source.…”

“…PHA-storing organisms can grow by applying aerobic dynamic feeding conditions (ADF) through the wellknown feast-famine regime [7]. In the last decade, MMC-PHA production using different types of waste has been the topic of several applied researches; moreover, recent investigation has been conducted at pilot scale to demonstrate the technical feasibility of the technology [8,9]. In particular, PHA production from the organic fraction of municipal solid waste (OFMSW) has been assessed in order to quantify the process PHA productivity (g PHA/L day) potentially achievable and final polymer quality, also in consideration of a possible integration in the existing wastewater WWTP [10][11][12].…”