EFFECTS OF SHOCK 2,4‐DICHLOROPHENOL (DCP) AND COD LOADING RATES ON THE REMOVAL OF 2,4‐DCP IN A SEQUENTIAL UPFLOW ANAEROBIC SLUDGE BLANKET/AEROBIC COMPLETELY STIRRED TANK REACTOR SYSTEM

Abstract

The treatability of 2,4‐dwichlorophenol (DCP) was studied in an anaerobic/aerobic sequential reactor system. Laboratory scale upflow anaerobic sludge blanket (UASB) reactor/ completely stirred tank reactors (CSTR) were operated at constant 2,4‐DCP concentrations, and increasing chemical oxygen demand (COD) loading rates. The effect of shock organic loading rates on 2,4‐DCP, COD removal efficiencies and methane gas production were investigated in the UASB reactor. When the organic loading rate was increased from 3.6 g l−1 d−1 to 30.16 g l−1 d−1, the COD and 2,4‐DCP removal efficiencies decreased from 80 to 25% and from 99 to 60% in the UASB reactor. The optimum organic loading rates for maximum 2,4‐DCP (E=99–100%) and COD (E=65–85%) removal efficiencies were 25–30 and 8–20 g‐COD l−1 d−1, respectively. The percentage of methane of the total gas varied between 70 and 80 while the organic loadings were 18 g‐COD l−1 d−1 and 20.36 g‐COD l−1 d−1, respectively. During 80 days of operation, 2,4‐DCP concentration was found to be below 0.5 and 0.1 mg l−1 in aerobic reactor effluent resulting in 78 and 100% removal efficiencies. When the hydraulic retention time (HRT) was 18.72 h, the 2,4‐DCP removal efficiency was 97% in the aerobic reactor. The optimum COD removal efficiency was 78.83% in anaerobic reactor effluent at an influent COD loading rate of 7.238 g‐COD l−1 d−1 while 83.6% maximum COD removal efficiency was obtained in the aerobic reactor, resulting in a total COD removal efficiency of 96.83% in the whole system. The 2,4‐DCP removal efficiency was 99% in the sequential anaerobic (UASB)/aerobic (CSTR) reactor system at COD loading rates varying between 11.46 and 30.16 g‐COD l−1d−1.