Full Description

In order to maintain strict compliance with the turbidity requirements of the Surface Water Treatment Rule (SWTR), algae levels in finished water is to be minimized. To better characterize the algae in the source and finished waters, an alternative technique employing centrifugation for algae concentration was developed and compared to the standard technique using sand filtration for algae recovery and enumeration. Lugol's solution, a preservative, was added to 200 mls of raw and partially treated water samples or 2 liters of finished water samples. The preserved algae samples were concentrated by means of a centrifuge in which they were spun at 1000 g or RCF for 20 minutes to become sample pellets with supernatants. The feasibility of using the centrifuge method as an alternative to the sand method was determined based on the total number of algae and the total number of blue-green, taste/odor offenders, filter cloggers, and green algae identified from water samples. The study was conducted from August through October 1998, and March through November 1999 for a total of 12 months of quantitative data. One hundred and fifty-six (156) water samples from various sources were collected and analyzed; 78 samples were processed by each method. The standard sand method was used for the comparison as described in Standard Methods by pouring 500 mls of an unpreserved water sample through a Sedgwick- Rafter sand filter. Algae enumeration and identification was done using a Sedgwick- Rafter counting cell (S-R cell) and a Palmer-Maloney counting cell (P-M cell) or the nanoplankton counting cell. The amount of debris within a sample was an important variable that was observed for evaluating both methods. Higher total algae counts were obtained in raw and in both types of finished water samples after centrifugation. Filter cloggers, T/O offenders, blue-green algae, and the majority of 37 algae genera were all detected better with the centrifuge method. This is attributed to an enhanced ability to see internal structures, a new approach to working around debris, and other advantages. Paired t-tests were conducted to determine statistical significance between the two methods. The centrifuge method was strongly recommended and is being used routinely in the Washington Aqueduct laboratory. However, when the treatment problems occur due to significant populations of larger green algae, the sand method will be utilized as well. In preparation for compliance with future pending regulations, the centrifuge method can be relied upon as a standard cell counting method for the detection of Cyanobacteria (blue-green algae), other freshwater algae and their toxins. Includes 9 references, tables, figures.

Product Details

Edition: Vol. - No. Published: 01/01/2001 Number of Pages: 19File Size: 1 file , 12 MB