The application of ozone and biologically active filters (BAFs) for dissolved organic carbon (DOC) removal and trihalomethane (THM) control has proven challenging in high-DOC surface waters. This dissertation investigates DOC removal and transformation across various treatment processes, including coagulation/softening, ozonation, and BAFs. This research addresses the limitations of current DOC fractionation methods, developing a novel fractionation method using two solid phase extraction cartridges to assess major DOC fractions of hydrophilic neutral (HPIN), total acidic (TA), and hydrophobic neutral (HPON) without requiring the recovery of sorbed compounds. Applying this method to a full-scale coagulation/softening plant revealed that while HPON decreased, the remaining HPIN exhibited lower specific UV254 absorbance (SUVA), higher specific THM formation potential (STHMFP), and a shift towards lower molecular weights below 1 kDa. The results did not confirm the exclusive removal of any DOC fraction and highlighted the importance of characterizing changes in DOC quality beyond simple quantification, as the contribution of HPIN to SUVA and STHMFP in treated water was higher than that of HPON. Further investigation in a full-scale plant revealed that the typical ozone dose (0.4 mg O₃/mg-C) applied to coagulated/softened water with predominantly hydrophilic DOC (72%) did not affect DOC biodegradability or STHMFP. However, increasing the ozone dose to 1 mg O₃/mg-C in lab-scale experiments enhanced biodegradability from 6.3 to 26%, transformed all DOC to hydrophilic, and reduced STHMFP from 69.4 to 11.2 µg/mg-C. Subsequent 28-day batch biodegradation offset the lower STHMFP achieved by the higher ozone dose, increasing it to 60 µg/mg-C due to the formation of low-molecular-weight byproducts. Finally, the performance of full-scale anthracite/silica sand (BAS) and granular activated carbon (BAC) filters was assessed across summer and winter, considering temperature, empty bed contact time, and backwashing effects. BAC filters achieved greater DOC and BDOC removal during summer, particularly post-backwashing. A specific ATP level of 13×10⁻⁶ ng per bacterial 16S rRNA gene copy number corresponded to this maximum DOC removal. This research provides critical insights into DOC removal and transformation throughout various treatment processes and highlights the complex interplay between operational parameters and BAF performance.