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

Abstract

Sludge is a by-product of municipal wastewater treatment plants (WWTPs) and its management contributes significantly to the operating costs. Large WWTPs usually have anaerobic sludge digesters to valorize sludge as methane and to reduce its mass. However, the low methane market price opens the possibility for generating other high value-added products from the organic matter in sludge, such as polyhydroxyalkanoates (PHAs). In this work, the economic feasibility of retrofitting two types of WWTPs to convert them into biofactories of crude PHAs was studied. Two cases were analyzed: (a) a large WWTP with anaerobic sludge digestion; and (b) a small WWTP where sludge is only dewatered. In a two-stage PHA-production system (biomass enrichment plus PHAs accumulation), the minimum PHAs cost would be 1.26 and 2.26 US$/kg PHA-crude for the large and small WWTPs, respectively. In a single-stage process, where a fraction of the secondary sludge (25%) is directly used to accumulate PHAs, the production costs would decrease by around 15.9% (small WWTPs) and 19.0% (large WWTPs), since capital costs associated with bioreactors decrease. Sensitivity analysis showed that the PHA/COD (Chemical Oxygen Demand) yield is the most crucial parameter affecting the production costs. The energy, methane, and sludge management prices also have an essential effect on the production costs, and their effect depends on the WWTP’s size.

The Effect of Static Magnetic Field on Methanogenesis in the Anaerobic Digestion of Municipal Sewage Sludge

“…The operation of sewage treatment plants directly necessitates optimal sludge management. The municipal sewage sludge (MSS) generated during wastewater treatment must be converted, then properly neutralized and/or managed [1]. Although MSS management techniques and methods are clearly being continuously explored, a universal, economicallyviable technology for its effective neutralization has yet to be developed.…”

Conversion of Starchy Waste Streams into Polyhydroxyalkanoates Using Cupriavidus necator DSM 545

“…Indeed, the accumulation of PHAs occur when strains grow in an unbalanced environmental condition, such as limitation of macroelements and a rich carbon source [ 17 ]. The price of PHAs is between 2.4 and 5.5 USD/kg, while the cost of petroleum-based plastics ranges from 0.8 and 1.2 USD/kg [ 18 ]. Thus, PHAs substitution of conventional plastics is limited by their expensive manufacturing; in fact, the substrates alone represent up to 50% of the total production costs [ 13 ].…”

Integrating dairy manure for enhanced resource recovery at a WRRF: Environmental life cycle and pilot‐scale analyses

“…However, the WRRF concept should be expanded beyond a focus on energy neutrality and phosphorus capture—but not at the expense of deteriorated wastewater treatment. In this regard, while the concept of integrating bioplastics production within wastewater treatment has been investigated at a pilot scale (Bengtsson et al, 2017; Conca et al, 2020; Crutchik et al, 2020), investigations have focused on the feasibility and economics of PHA production and not associated impacts on wastewater treatment and effluent.…”