In this study a porous pot reactor was used to simulate an activated sludge stage and an anaerobic granule biosensor (AGB), as an upset early warning system for activated sludge treatment process, was configured in a down-flow mode with a side-stream of the influent wastewater fed to the top. The hydraulic retention time (HRT) for the porous pot and AGB systems was 12 hours and 6 hours, respectively. The influent was made up of synthetic wastewater. In the first group of toxic loading tests, the prepared cupric chloride solutions were separately injected into both the porous pot and AGB systems at six different concentrations (5, 10, 15, 20, 30, and 45mg Cu²⁺/L), and phenol solutions were used at four different concentrations (10, 20, 30, and 45mg phenol/L) in the second group of toxic loading tests. In addition, a control study was included for reference. The porous pot reactor and AGB were monitored for pH, ORP, COD, solids, and ammonia concentrations following a simulated toxic event. The COD removal efficiency of porous pot system decreased dramatically in response to the addition of Cu²⁺ and phenol. The greatest decrease in COD removal efficiency was from 92% to 52% at a Cu²⁺ concentration of 30 mg/L, and was from 98% to 76% at a phenol concentration of 45mg/L. The longest time of COD removal efficiency continuous decreasing was 23 hours at a Cu²⁺ concentration of 45 mg/L, and 7 hours at a phenol concentration of 10mg/L. Similar to the response in COD removal, the ammonia removal efficiency decreased significantly after the Cu ²⁺ shock loading. As the porous pot reactor was challenged with the Cu²⁺ or phenol shock load, the AGB received an equivalent dose. The most sensitive parameter reflecting the toxic shock load in the AGB was the ORP. The ORP changed more rapidly and uniformly than the pH over both the range of Cu²⁺ concentrations and phenol concentration tested. The shortest response time to peak was 1 hour after Cu ²⁺ injection at 5 and10 mg/L, and was 1 hour after phenol injection at 10, 20, and 45mg/L. The longest response time was 5 hours at 15 and 30 mg/L during Cu²⁺ shock loading tests, and was 3 hours at 30mg/L during phenol shock loading test. Surprisingly, the change of pH in the AGB following Cu²⁺ or phenol addition was not as noticeable and reliable as the change in the ORP.