Biopolymers from Urban Organic Waste: Influence of the Solid Retention Time to Cycle Length Ratio in the Enrichment of a Mixed Microbial Culture (MMC)

Abstract

In this study, the performance of the selection process for polyhydroxyalkanoate (PHA) production from mixed microbial cultures (MMCs) at pilot scale was deeply investigated with the solid retention time (SRT) to cycle length (CL) ratio as main affecting parameter. Four different runs were tested by varying the SRT/CL ratio maintaining the same organic loading rate (OLR). The pilot-scale selection and accumulation reactors were fed with a fermented mixture of source-selected organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS), refined with a centrifuge and membrane unit for the coarse solid removal. The selected biomass obtained in the most performing run was characterized by a specific storage rate of 375 mg COD P /g COD Xa h and a storage yield of 0.46 COD P /COD SOL . Accumulations performed with the same biomass were characterized by a storage yield of 0.62 COD P /COD VFA . The microbiome composition was assessed. In the most performing run, putative PHA-storing bacteria affiliated with Paracoccus genus were found at high abundance (36.8%), in contrast to all other runs. An overall PHA yield of 110 g PHA/kg VS was estimated for the best scenario, revealing an interesting perspective for biorefinery technology chains based on the three-stage process for PHA production.

Combined Strategies to Boost Polyhydroxyalkanoate Production from Fruit Waste in a Three-Stage Pilot Plant

“…The PHA-producing process using MMC was recently implemented at a pilot scale. − However, the low global volumetric productivity obtained is considered as one of the major constraints for full-scale application, given the great impact of the capital costs on the polymer end-price . Techno-economic analyses have indicated that other critical parameters to be maximized to increase the viability of the process are the overall PHA yield, to minimize the waste of resources, and the PHA content on biomass at the end of production, to reduce extraction costs. , Lastly, the recovery and purification of the polymer is a time-consuming process known to require large amounts of chemicals that also contribute significantly to increase the overall manufacturing costs of the product …”

“…3 Technoeconomic analyses have indicated that other critical parameters to be maximized to increase the viability of the process are the overall PHA yield, to minimize the waste of resources, and the PHA content on biomass at the end of production, to reduce extraction costs. 3,9 Lastly, the recovery and purification of the polymer is a time-consuming process known to require large amounts of chemicals that also contribute significantly to increase the overall manufacturing costs of the product. 10 Several individual factors have been found to contribute to improving the global process performance.…”

From Organic Wastes and Hydrocarbons Pollutants to Polyhydroxyalkanoates: Bioconversion by Terrestrial and Marine Bacteria

“…In the context of waste utilization, MMC-PHA production can be easily integrated into existing infrastructures for the biological treatment of organic waste residues and wastewaters [45]. In the last decade, many research groups have contributed to the scalingup of the process from laboratory-scale experiments to new and integrated pilot-scale facilities [46][47][48][49][50][51][52][53][54]. Regardless of the operating conditions and the adopted scale of the application, the inoculum typically used for MMC systems is the activated sludge from municipal wastewater treatment plants [25].…”

“…Both of these conditions force a physiological adaptation in those microorganisms that are fast enough and able to thrive under such unbalanced growth conditions-accumulating the external C source as PHA in the feast phase and using it as C-reserve to grow in the famine phase [22]. The optimal operating conditions of each single stage have been largely investigated in the literature (at the laboratory and pilot scale)-the overall process performance is basically calculated as the overall yield of synthetized PHA per kg of VS (volatile solids) in the waste feedstock [49,50,58]. An essential requirement for efficient microbial selection is the application of dynamic feeding conditions, which are generally characterized by transient C source availability, whereby microorganisms are faced with an alteration between high (feast) and low or zero (famine), concentrations of external organic substrate.…”

“…This type of configuration generally does not require nutrient removal. In fact, the integrated approach recently used for waste treatment includes a section for anaerobic overflow recovery, wherein biogas is produced and nutrients are recovered in the composting section of the digestates [49].…”