AWWA WQTC60697

The main objectives of this research were to examine the effects of colloidal and particulate matter in fresh waters on dissolved organic carbon (DOC) and UV₂₅₄ determinations, and to develop some guidelines for filtering freshwater samples having widely varying turbidities. Over ninety percent of the organic matter in the natural waters tested in this study was in the dissolved form and filter cake formation did not have a significant impact on the DOC values of a sample. The experimental results showed that the level and characteristics of turbidity in a water sample, as well as the nature of pore structures and pore size distributions of a membrane filter selected for filtration play important roles in UV₂₅₄ and SUVA₂₅₄ determinations. Measuring turbidity in the filtrate of a sample is a simple way to validate the UV₂₅₄, and thus SUVA₂₅₄, results. The results indicated that when filtrate turbidities were below 0.3 NTU, no significant impact of filtration volume, filter cake formation, and separation (or pretreatment) processes occurred on DOC and UV₂₅₄ determinations, and thus calculated SUVA₂₅₄ values. However, when filtrate turbidities were higher than 0.5 NTU, UV₂₅₄ results were affected by residual turbidity values, which also adversely impacted calculated SUVA₂₅₄ values. These findings suggest that a conservative criterion for the turbidity of a filtered UV₂₅₄ sample, such as less than 0.3 NTU, can be adopted to minimize interferences on the results. Selection of small pore size filters (e.g., 0.2- or 0.1-µm) and pretreatment of samples (e.g., prefiltration, settling) may be used to alleviate the problems caused by colloidal materials in a sample. It was also found that a minimum of 25-mL filter-to-waste volume (i.e., for hydrophilic polyethersulfone filters or hydrophilic polypropylene filters of 47-mm disc size) would be applicable for various natural water samples with varying degree of turbidities prior to collecting samples for DOC and UV₂₅₄ determinations. Includes 11 references, tables, figures.