Pressure filtration has the capability of removing a wide variety of particulate contaminants. The pressure filter treatment process typically consists of a steel pressure vessel(s) with water to be filtered entering under pressure and leaving under a slightly reduced pressure due to headloss within the vessel (AWWA, 1999). Pressure filtration is commonly utilized in small water systems like Chignik Lake. Additionally, since the filtrate is leaving the vessel under pressure it can be distributed to the community system without the need for additional pumping.
The purpose of the WTP pilot testing was to perform the following:
1. Evaluate different pre-treatment chemicals to promote effective contaminant removal in the pressure filters prior to distribution to the community.
2. Select and optimize operating parameters including chemical type, chemical dosage and sequencing of chemical addition to meet the State of Alaska Department of Environmental Conservation (ADEC) primary and secondary drinking water quality standards in the most economical manner (maximizing filter run times).
The contaminants of concern for the pilot test were as follows:
- Arsenic (As);
- Manganese (Mn); and,
- Hydrogen Sulfide (H2S [taste and odor]).
Prior to and during the pilot testing activities, a series of jar tests were conducted to evaluate the contaminant removal effectiveness and dosage rates for several different water treatment chemicals. Jar testing is the most common method for obtaining data on contaminant removal effectiveness for a water treatment process short of full-scale pilot testing. Jar testing mimics full-scale operation by simulating both flow through oxidation and solids removal processes.