Removal of Total Organic Carbon (TOC)/Dissolved Organic Carbon (DOC) and Trihalomethane Formation Potentials (THMFPs) from Surface Water using PreBiofilters

摘要

Biofiltration has long been used to treat drinking water in Europe and is becoming morewidespread in North America. PreBiofilters, or biofilters that operate as the first unit in asurface water treatment process train, are a cost-effective pretreatment for conventionalsurface water treatment and provide consistent downstream water quality. This paperdescribes a study which investigated the potential to remove total organic carbon(TOC)/dissolved organic carbon (DOC), and trihalomethane formation potential(THMFP) from surface water using PreBiofliters. Furthermore, the impact of differentmolecular weight fractions of TOC/DOC and THMFPs in the surface water and thefiltrates from the PreBiofilters were also investigated, respectively, in order to determinehow well the PreBiofilters can remove different fractions of TOC/DOC and THMFPs.Two bench-scale pilot plants of the PreBiofilters were operated in parallel under twodifferent modes: PreBiofilter-A (Column A) was half-exposed to air and half-submergedin water, whereas PreBiofilter-B (Column B) was fully submerged in water. TheCanoochee River in coastal Georgia, served as the source water. The raw water samplesand the filtrate samples from the two PreBiofilters were collected and water chemicalanalysis was performed for TOC/DOC, THMFP, turbidity and color. Generally, bothPreBiofilters represented similar removal efficiencies for all the tests. The PreBiofilters Aand B resulted in an average THMFPs reduction of about 20% and 30%, respectively. Asimilar average of TOC and DOC removal by 15-20%, turbidities removal by about 30-70%, and color removal by about 30-70% was also observed. The surface water samplesand filtrates from the Prebilfilters were ultrafiltrated in series, starting at 0.45 μm, 300KDaltons (KDa), then 100, 10, 3, 1, and 0.5 KDa pore size membranes to get differentmolecular weight fractions. The results showed that over 95% of TOC were DOC withtwo major fractions: <0.5 KDa : about 30%; 10K-100K: about 20% in the surface water.For the filtrates from the two PreBiofilters A and B, both had the same two majorfractions as the surface water: <0.5 KDa: about 30-40%; and 10K-100K: about 20-30%.On the other hand, the THMFPs were about 1,600, 1300, and 1,200 μg/L (ppb) in thesurface water, the filtrates A and B, respectively, while about 85-95% of the abovecorresponding THMFPs were contributed from DOC. There were two major fractionscontributing THMFPs in each of the surface water and filtrates from the PreBiofilters:<10 K: about 50-60% and 10K-100K: about 20%, respectively.Overall, the results of this study indicate that the PreBiofilter is an advantageous andpromising pretreatment process for removing TOC/DOC and THMFPs from surfacewater in drinking water treatment.