No abstract

No abstract

Jar tests were conducted on six source waters from softening plants throughout the United States to evaluate the extent of softening, natural organic matter (NOM) removal, and reduction in disinfection by‐product (DBP) formation achieved by varying lime doses. Results demonstrated the effect of source water characteristics, e.g., specific ultraviolet absorbance (SUVA), bromide, and total organic carbon (TOC) on the potential for softening to remove NOM and reduce DBP formation. The source water exhibiting the lowest SUVA value had the lowest degree of NOM removal, and the source water with the highest bromide concentration showed substantial formation of bromine‐substituted DBPs. These results confirmed previous observations that enhanced softening improves removal of dissolved organic carbon, decreases SUVA values, and decreases formation of dissolved organic halogen. The research also showed that both calcium carbonate and magnesium hydroxide are responsible for NOM removal in softening. With the exception of Lake Austin (Texas) source water, the waters studied would require softening to the point of magnesium hydroxide precipitation to meet required TOC removals and (in some cases) to meet the maximum contaminant level for total trihalomethanes and the sum of five haloacetic acids with lime softening alone.

We compared the development of microalgal and bacterial-denitrifier communities within biofilms over 28 days in a restored-prairie stream (RP) and a stream receiving treated wastewater effluent (DER). Inorganic nutrient concentrations were an order of magnitude greater in DER, and stream waters differed in the quality of dissolved organics (characterized via pyrolysis-GC/MS). Biofilm biomass and the densities of algae and bacteria increased over time in both systems; however, algal and denitrifier community composition and the patterns of development differed between systems. Specifically, algal and denitrifier taxonomic composition stabilized more quickly in DER than RP, whereas the rates of algal and denitrifier succession were more closely coupled in RP than DER. We hypothesize that, under unenriched conditions, successional changes in algal assemblages influence bacterial denitrifiers due to their dependence on algal exudates, while under enriched conditions, this relationship is decoupled. Between-system differences in organic signatures supported this, as RP biofilms contained more labile, aliphatic compounds than DER. In addition, potential denitrification rates (DNP) were negatively correlated with the percentage of aromatic compounds within the biofilm organic signatures, suggesting a significant relationship between algal exudate composition and denitrification. These results are significant because anthropogenic factors that affect biofilm community composition may alter their capacity to perform critical ecosystem services.