AWWA WQTC69489

Treatment of groundwater sources with undesirable levels of reduced iron and manganese andwith significant levels of natural organic matter (NOM) to yield a free-chlorinated finished watercan be challenging. This paper reports on results of field, pilot and benchscalestudies directed at meeting this treatment challenge for the existing Aquarion WaterCompany (AWC) Lantern Hill water treatment plant (LHWTP) located in Mystic, Connecticut. Treatment consists of three parallelpressure media filters, each with 21 inches of anthracite over 24 inches of a greensand media;hydraulic loading rates vary from 1 to 3 gallons per minute per square foot of filter surface area.In-line chemical addition prior to filtration includes free chlorine, potassium hydroxide,potassium permanganate and a synthetic cationic polymer, in sequential order. Prior to April2007, pre-filter chlorine was dosed to achieve a post filter residual of 1 to 1.4 mg/L as no postfilterchlorine addition was possible; post-filtration chlorine addition was practiced after April2007. The experimental approach involved assessment of levels of metals, organic matter and DBPs asa function of treatment process at full, pilot and bench scales. For example, water samples werecollected across a full-scale treatment plant, and were fractionated using 0.4 µm pore size filtersand 30,000 apparent molecular weight cut-off ultrafilters to determine particulate, colloidal anddissolved fractions of metals and TOC. The Mn and Fe concentrations in the filtered sampleswere typically measured using Hach colorimetric methods. The impact of pre-filter chlorinationon DBP levels (trihalomethanes and haloacetic acids) was investigated using various methods.Water samples were collected immediately before and after pre-filter chlorination was turned on, turned off, or decreased in dose at the treatment plant. The samples were collected at variouslocations across the treatment plant; plant effluent samples were held for 24 hours to simulatedistribution system DBP formation. Jar tests and a small filter column filled with filter mediaobtained from the full-scale Lantern Hill filters were used to assess the effectiveness of usingKMnO₄ to oxidize Fe and Mn rather than free chlorine and the related impacts on DBPformation. Media cores (anthracite, sand) were collected, drained of water, and subdivided into4 to 8 inch depth increments. Media characterization included extraction of metal coating andsieve analysis. Extracted metals (Mn, Al, Fe and Ca) were measured using ICP with atomicemission spectroscopy. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

7

File Size:

1 file , 830 KB