AWWA MTC57646

The New York City Department of Environmental Protection is in the preliminary design stage of a new 7 to 9 million gallon per day (MGD) drinking water plant. This plant will be located in the borough of Queens and will utilize groundwater from the Upper Glacial Aquifer (approximately 80-foot deep aquifer) as its sourcewater. The water has high levels of iron (Total: 1 to 15 mg/l), manganese (1 to 1.5 mg/l), tetrachloroethene (PCE - 5 to 160 ug/l), MTBE (1 to 140 ug/l), and hardness (150 to 600 mg/l as CaCO3). The proposed full-scale treatment train for this plant includes pH adjustment, iron/manganese oxidation, membrane filtration, membrane softening, two-stage air stripping, and final chemical conditioning. As only the groundwater wells but no treatment plant currently exists on the site, a 100- gpm pilot plant was constructed within an empty storage building. The pilot plant process train includes parallel trains of pH adjustment via induced draft tray aerator or caustic soda addition, parallel trains of iron and manganese oxidation by potassium permanganate or ozone, parallel trains of microfiltration (MF) and ultrafiltration (UF) skids (Ionics, Pall, & Zenon are manufacturers), and membrane softening (one Osmonics skid will alternately test Koch nanofiltration (NF) and Osmonics low-pressure reverse osmosis (RO) membranes). Once a suitable pH-oxidation strategy was conceived and run through the MF/UF filters, the NF and RO membranes were put to the test to remove hardness and VOCs. One of the stated goals of the pilot plant was to evaluate the effectiveness of NF and RO membranes to remove hardness and VOCs from the groundwater. Two NF/RO membranes were alternately tested: Koch's NF and Osmonics' low-pressure RO membranes, each for a continuous period of at least three weeks. New York City's upstate water supply (Catskill-Delaware systems) satisfies more than 90% of the City's drinking water needs. This sourcewater is relatively soft (average hardness of 22 mg/l as CaCO3); therefore, the City desired that groundwater from this new plant would closely resemble the water which the end users currently received. With high hardness levels present in the Upper Glacial Aquifer, the NF and RO membranes were tasked with this responsibility. In addition to hardness removal, it was also hoped that the NF and RO membranes could remove some of the volatile organic compounds (VOCs) present in the groundwater. The NF and RO membranes' ability to remove VOCs such as MTBE, PCE, and TCE is important in evaluating design objectives for a full-scale facility. Includes tables, figures.