## 1 Introduction  
Enhanced biological phosphorus removal (EBPR) is considered an efficient process for removing phosphorus from wastewater. However, microorganisms are responsible for phosphate removal, and the mechanisms by which they accumulate phosphorus are complex and not well-understood [1]. This process remains operationally unstable in many systems, and it is difficult to reliably meet low effluent limits [2]. Substrate type has been identified as an important factor affecting the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), which are usually dominant in a deteriorated EBPR system [3]. Past research has also shown high inhibition of heavy metal ions to biological carbon, nitrogen, and phosphate removal in EBPR [4; 5; 6; 7; 8]. Reduction in EBPR efficiency was observed in a municipal wastewater treatment plant at total tin concentrations greater than 4 \(\mu\)gL\({}^{-1}\) in the solids fraction of the mixed liquor suspended solid (MLSS) [9]. Nevertheless, no influence on carbon or nitrogen removal efficiency was observed at this concentration. However, a possible mechanism for the Sn inhibition of PAOs was not provided. A related study was conducted by [PERSON] et al. [6]. They tried to chronically and stepwise add heavy metal Cd(II) ions into an A\({}_{2}\)O pilot plant to examine the toxic effects on organism behaviors. The results showed that an addition of 2 mgCd L\({}^{-1}\) started to affect the efficiency of biological phosphate removal. About 76%, 64%, and 90% of the anaerobic P-release, the anoxic P-uptake, and aerobic P-uptake were inhibited, respectively. [PERSON] et al. [10] investigated the shock load effect of Cu(II) on PAO metabolism at various pH and biomass levels, especially focusing on the variations of intracellular polyphosphate (poly-P), polyhydroxyalkanoate (PHA), and glycogen. [PERSON] et al. [11] further experimentally showed that PAOs losing the abilities of PHA production and phosphate uptake under Cu(II) presence came from the inhibition of the enzyme activities of acetyl-CoA synthases (ACS) and poly-phosphate kinase (PPK), respectively. This is because Cu(II) has a higher affinity for free ACS than for the ACS-coenzyme A complex. Another experiment also showed that free PPK is more readily bound to Cu(II) than the PPK-adenosine triphosphate complex. The toxic effects of heavy metals on biological performances are complicated and correlated to other environmental conditions (e.g., pH, temperature, sludge retention time (SRT), carbon source, etc... ). [PERSON] et al. [3] investigated the effect of Pb(II) on the dominance systems in PAOs and GAOs fed with acetic acid or glucose as the major carbon source, respectively. The results showed abnormal aerobic phosphate release was observed in the presence of Pb(II) in a high concentration of acetic acid. [PERSON] et al. [12] showed that the endurance of PAOs to Cu(II) highly related to SRT. PHA storage in the anaerobic stage for SRTs at 5 d and 15 d were more easily influenced by Cu(II) than that at 10 d SRT. The reaction of PAO phosphate uptake for the sludge at 10 d SRT retained half of the ability to take up phosphate in the presence of 2 mgCu L\({}^{-1}\), whereas PAO phosphate uptake was completely lost for SRTs at 5 d or 15 d. Temperature is considered one of the most important factors affecting the performance of phosphate removal in an EBPR process [13]. Generally, the wastewater temperature fluctuates according to the weather, and it is difficult to control well in practice. Unfortunately, the competition between PAOs and GAOs is highly related to temperature [14]. There were many studies regarding the effects of temperature on phosphate removal in the absence of heavy metals. However, the effects of temperature on P removal mechanisms and PAO metabolism are still unclear, and some are even contradictory as a result of incomparable experimental designs. [PERSON] et al.