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Passaic Valley Water Commission has instituted a major upgrade of its Little Falls WaterTreatment plant that incorporates advanced treatment concepts to achieve high qualityfinished water originating from a surface water source. The upgrade was necessary inorder to achieve compliance with the Stage 1 Disinfectant/Disinfection Byproduct Ruleand Interim Enhanced Surface Water Treatment Rule. The Little Falls Water TreatmentPlant is located in northeastern New Jersey and has a design capacity of 110 MGD. Theoriginal conventional treatment process with aluminum-based coagulation followed byprimary and secondary Cl2-disinfection and dual-media anthracite/sand or granular activated carbon (GAC)/sandfiltration is being replaced with high-rate sand-ballasted pretreatment using iron-basedcoagulation, intermediate ozonation and dual media GAC/sand biological filtration. Thusthe process chemistries are significantly different from the conventional route and arebeing implemented in a multi-phased approach.The first phase of the upgrade was initiated in February 2003. In the spring of 2003,numerous discolored water customer complaints seemed to correlate with a rise infinished water manganese levels. Although manganese is present in the source waters, theincrease in finished water total manganese from 0.01 to 0.04 ppm during this upgrade isattributed to the use of ferric chloride as the primary coagulant, elimination of prechlorinationand the replacement of existing anthracite/sand filters with GAC/sand mediaand the associated changes in plant conditions. Manganese is a known impurity in ferricchloride, where the impurity concentration is in the range of 600 to 700 mg/L for a 40%solution.After this discolored water event, a systematic study for the evaluation and control ofmanganese was undertaken. The study design was to monitor both insoluble and solublemanganese in the source waters, through individual unit treatment processes and in thedistribution system. In addition, since the upgrade of the LFWTP consisted of phasing inthe new unit treatment processes in stages while in production, provisions for effectivemanganese control strategies for the intermediate phases of the upgrade was undertaken.Mass balance analysis indicated the major sources of manganese in the treatment processto be those discussed above. The contribution from recycle streams consisting of filterbackwash water and residuals thickening process decant, among others, is noteworthy.Process changes that affect pH, detention times and chemicals used impact manganeseoxidation due to different oxidation states and the corresponding soluble/insoluble formsof manganese that can result from oxidation. This paper explores the phased processchanges of the upgrade as it relates to manganese oxidation and subsequent removal ofthe oxide. Includes 5 references, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 20File Size: 1 file , 1.8 MB