The organic acid rich acidogenic liquid produced from waste sludge anaerobic fermentation was used as a potential feedstock for polyhydroxyalkanoates (PHA) production, which is a cost-effective and environmentally sustainable PHA production system. To analyze the effect of substrate on monomer composition of PHA, different acidogenic liquid generated from waste sludge fermentation in varied initial pH were used as external carbon source. The maximal PHA content accounted for 60.3 % of the dry cell with initial fermentation pH 10.0 sludge acidogenic liquid and the recovered polymer composition was 98.3 % polyhydroxybutyrate (PHB) and 1.7 % polyhydroxyvalerate (PHV) by mass. The utilization efficiency of soluble chemical oxygen demand (SCOD), protein, NH4+-N and volatile fatty acids (VFAs) was 95.4 %, 90.5 %, 98.0 %, 99.3 %, respectively. The tyrosine-like protein, tryptophan-like protein, fulvic acid-like organics and soluble microbial by-products were primary used for PHA production, while the humic acid-like organics used little. Furthermore, mass balance analysis was introduced to further illustrate the technology reliability. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.