Patent ID: 8641908

Claim:
A method of recovering polyhydroxyalkanoates (PHAs) from municipal waste sludge, comprising: (a) removing coarse particles in the municipal waste sludge and measuring a mass of a solid content in the municipal waste sludge in terms of a volatile suspended solid in the municipal waste sludge; (b) removing a supernatant from the municipal waste sludge; (c) freezing the municipal waste sludge to deactivate polyhydroxyalkanoates (PHAs) producing microbial species present in the municipal waste sludge to obtain a frozen sludge; (d) conducting a pretreatment of the municipal waste sludge that has been frozen, the pretreatment including addition of sodium hypochlorite solution, followed by centrifugation to remove a supernatant therefrom and to obtain a pretreated sludge; (e) adding a surfactant into the pretreated sludge to obtain a slurry, followed by centrifugation to remove a supernatant therefrom; (f) adding a controlled amount of sodium hypochlorite solution to the municipal waste sludge obtained in step (e) so as to digest the PHAs producing microbial species and to release PHAs, wherein a ratio of the mass of the solid content of the municipal waste sludge to a volume of the sodium hypochlorite solution added ranges from 0.67 mg/ml to 1.25 mg/ml; and (g) separating PHAs from non-PHAs substances in the municipal waste sludge obtained in step (f).