The use of ozonation and biological fluidized bed treatment for the control of NOM in drinking water.

摘要

Bench-scale and pilot-scale studies were conducted using Huron River water taken at the Ann Arbor Water Treatment Plant. The major water quality parameters that were monitored in this study included TOC, BDOC, UV-254 absorption, THMFP, AMW distribution, humic and non humic fractions of NOM, turbidity, pH and alkalinity.; A combination of factors, including ozone dose, hydraulic retention time, and the concentration of dissolved ozone was identified, which controlled both the destruction of organic carbon and the production of low-molecular weight organic compounds and biodegradable organic matter during ozonation. The relationships between properties of THM precursors, including TOC, UV-254, humic substances, and THMFP were established and used to investigate the efficacy of the ozonation and biological fluidized bed treatment (FBT). A mathematical model that described the transformation of NOM during ozonation was developed and verified over a range of ozone doses of up to 3 mg/mg C, temperatures of up to 25°C, and hydraulic retention times of up to 20 minutes.; The biodegradable organic matter in Huron River water consisted of rapidly and slowly biodegrading fractions (“fast” and “slow” BDOC). The biodegradability of raw and treated waters was characterized by the maximum biodegradation rate of “fast” BDOC (R_max), the minimum biodegradation time that required to eliminate “fast” BDOC (EBCT_min), and by the minimum concentration of “slow” BDOC that remained in the water after biodegradation at EBCT_min (BDOC_slow).; The following treatment processes that included ozonation and FBT were investigated: (1) single-pass ozonation/FBT; (2) ozonation/FBT with recycle; (3) single-pass FBT/ozonation with biofiltration; (4) recirculating FBT/ozonation with biofiltration; (5) single-pass FBT/ozonation/biofiltration with the addition of acetate to the FBT column (“stimulated” FBT); and (6) recirculating “stimulated” FBT/ozonation with biofiltration. Among these processes, the recirculating “stimulated” FBT/ozonation process followed by biofiltration was most efficient in terms of the removal of NOM relative to ozone consumption and biodegradation time. The removal of NOM was comparable to that achieved at the Ann Arbor Water Treatment Plant, that uses lime softening, flocculation/sedimentation, ozonation and GAC filtration. For a design capacity of 1 MGD, the cost of treatment by the FBT/ozonation process followed by biofiltration was estimated to be at least 40 percent lower than that by a conventional flocculation/sedimentation process with ozonation and GAC filtration.