Challenge
The City of Hudson, New York had aging slow-sand and diatomaceous earth (DE) filter systems which had been struggling to meet effluent water quality treatment goals. Total organic carbon (TOC), disinfection by-product precursors and turbidity reduction were the key problem areas. Turbidity spikes were caused by the DE filters failing periodically and in addition Haloacetic Acid and Total Trihaolomethane exceeded regulatory limits.
Knowing that they needed to improve treatment performance and expand their plant capacity the City hired Stearns & Wheler, LLC (Cazenovia, New York) to evaluate a number of treatment technologies. In 2001 they selected the Trident® process to be pilot tested.
Solution
The Trident process consists of upflow Adsorption Clarification followed by Mixed Media Filtration in a packaged treatment system. Prior to entering the Adsorption Clarifier® system coagulant and polymer are added for coagulation. Flocculation and solids capture occur in a bed of buoyant clarifier media contained in the clarifier section. The clarified water is then filtered through a Mixed Media bed consisting of anthracite, sand and garnet. Each layer of filter media has a progressively smaller effective size and increasing specific surface area to form an ever tightening filter bed. Both the clarifier and filter are periodically cleaned using an air-water flushing system.
During the pilot study the source water ranged from 1.8-3.0 NTU turbidity, 4-15.7 color units, and ph of 7.1-8.1. The two stage Adsorption Clarification and Mixed Media Filtration provided with the packaged Trident system was found capable of producing exceptional filter effluent quality and good net water production. More specifically, the filter effluent quality met the protocol requirements with turbidities less than 0.1 NTU and filter effluent color of < 5 color units. During testing the clarifier run lengths ranged from four to six hours while filter run lengths approached 24 hours.
Results
Construction of the 2.8 MGD facility was finished in the spring of 2006 with four TR-420 stainless steel Trident units installed. The chemical treatment process includes PCH-180 poly-aluminum chloride to coagulate soluble organic materials and Cytek 1986 and Polyamine polymer as a filter aid. The Trident system is cleaned based on time duration with the Adsorption Clarifier system flushed every four hours and the filters backwashed every 40 hours of operation. Finished water is pumped to a 2.5 million gallon storage tank from a 350,000 gallon on-site clearwell. Chlorine is added as a disinfection agent prior to the distribution system. The entire system is PLC controlled including automatic coagulant feed adjustment based on water quality produced. A SCADA system provides up-to-date real time graphic visual displays and report generation.
The City is conducting monthly TOC measurements and currently meets the required 50% removal consistently with this new water plant. Further refinements to the pre-chlorination system are in process at this time.
The new drinking water treatment plant services the 7,500 residents and businesses. The design capacity will also meet the City’s growth needs for the foreseeable future. The total cost of the project was $9.6 million. Drinking Water State Revolving Fund assisted the community with a low interest loan and a portion in a hardship grant.