Assessing Biofiltration without Ozonation for Removal of Trihalomethane Precursors in Drinking Water at the Beaver Water District Drinking Water Treatment Plant

Biofiltration without pre-ozonation has the capability to remove natural organic matter (NOM) fractions that serve as precursors of disinfection byproducts (DBPs), which include the four regulated trihalomethanes (THMs) and dichloroacetonitrile (DCAN). Rapid small-scale column tests (RSSCTs) and Pilot Plant filters operated at empty-bed contact times (EBCTs) of 4, 8, and 16 minutes were used to evaluate the performance of nutrient-amended (free ammonia and phosphorus) biofiltration for THM and DCAN precursor removal, as measured using formation potential (FP) tests. NOM surrogates – which include dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA254) and fluorescence-PARAFAC components – were measured weekly throughout the 30-week study to assess their suitability to track DBP precursor removal. RSSCTs containing DOC-exhausted granular activated carbon (GAC) removed up to 25% of the DOC with removal increasing (=0.01) with EBCT between 4 and 16 mins. During the 11-week period of active nitrification in the RSSCTs, average removals of total THMFP and DCANFP were 21% and 44%, respectively. However, statistically similar removals (=0.01) were observed at 8 and 16 mins EBCT, indicating that EBCTs in excess of 8 mins would not be helpful unless additional pretreatment steps such as pre-ozonation or a higher chlorine dioxide dose were added prior to the biofilters to increase the amount of biodegradable NOM. Relative to the RSSCTs, the Pilot filters achieved higher average removals of DOC, SUVA254, TTHMFP and DCANFP because their GAC media was not exhausted with respect to DOC and thus NOM was sorbed by physical-chemical mechanisms. Weak linear correlations observed between NOM surrogates and TTHMFP (R2 \u3c 0.27) during the active nitrification period in the RSSCTs indicate that these surrogates are not useful for monitoring THM precursor removal in nutrient-enhanced biofilters and therefore DBPFP tests are required to assess biofiltration performance

The Links Between the Neighborhood Food Environment and Childhood Nutrition

Identifies key studies on the availability of, and residents' access to, healthy foods and how they influence the choices of low-income children and their families. Discusses efforts to bring about improvements and new research and policy priorities

Explicit Conditions for the Convergence of Point Processes Associated to Stationary Arrays

In this article, we consider a stationary array $(X_{j,n})_{1 \leq j \leq n, n \geq 1}$ of random variables with values in \bR \verb2\2 \{0\} (which satisfy some asymptotic dependence conditions), and the corresponding sequence $(N_{n})_{n\geq 1}$ of point processes, where $N_{n}$ has the points $X_{j,n}, 1\leq j \leq n$. Our main result identifies some explicit conditions for the convergence of the sequence $(N_{n})_{n \geq 1}$, in terms of the probabilistic behavior of the variables in the array

A Cluster Limit Theorem for Infinitely Divisible Point Processes

In this article, we consider a sequence $(N_n)_{n \geq 1}$ of point processes, whose points lie in a subset $E$ of \bR \verb2\2 \{0\}, and satisfy an asymptotic independence condition. Our main result gives some necessary and sufficient conditions for the convergence in distribution of $(N_n)_{n \geq 1}$ to an infinitely divisible point process $N$. As applications, we discuss the exceedance processes and point processes based on regularly varying sequences