Removal of algal-derived organic material by preozonation and coagulation: Monitoring changes in organic quality by pyrolysis-GC-MS

This research examined the roles that algal populations, as sources of dissolved organic material (DOC), and water quality play in DOC removal during ozonation and coagulation processes. Algal monocultures were grown as suspensions in continuous-flow reactors to simulate bloom conditions and to provide a distinct type of DOC for treatment experiments. Jar tests were conducted with and without preozonation to assess DOC removal as a function of algal source, coagulant type and dose, pH and bicarbonate concentration. Overall, algal-derived DOC was difficult to remove; high coagulant doses were required and removal was strongly influenced by solution pH and algal source. Preozonation enhanced DOC removal to varying degrees depending on organic quality which was determined by the algal source. These results suggest that the unpredictable nature of ozone's ability to enhance coagulation in actual treatment practice may be related to changes in DOC caused by seasonal shifts in algal speciation and dominance. The technique of Pyrolysis (PY)-GC-MS was employed to explore the chemical basis for these differences in treatment performance. Preozonation produced dramatic changes in the chemical character of the organic matrix produced by algae as revealed by PY-GC-MS. These results suggest that, although use of ozone may not improve DOC removals in all cases, there may be advantages to ozone use which are related to desirable quality changes in the residual DOC. Furthermore, these results illustrate that PY-GC-MS is a powerful technique with which to characterize and monitor changes in organic quality so as to better understand chemical interactions in treatment. Copyright (C) 1996 Elsevier Science Ltd