Obtaining reliably high compaction characteristics and low SVI values has enormous economic consequences on activated sludge plant design and operation. Now that use of selectors has become more common for achieving low SVI values, the assessment of the full-scale performance characteristics of activated sludge plants incorporating selectors has high value for the design and operation of future plants. Treatment plant effluent quality is seldom analyzed solely on an average basis and the impact peak events have on effluent quality must be considered in design and operation. Descriptive statistics should also be used to assess selector performance, so that the influence of infrequently occurring values on plant design and operation can be assessed. The performance of 21 activated sludge plants incorporating selectors was evaluated. All the selector plants for which post installation data were available showed that the operating SVI values were significantly improved. One plant studied in detail showed that final effluent quality was significantly better after the selector installation. As a group, activated sludge plants with anaerobic selectors outperform those with anoxic selectors. Dissolved oxygen control is just as important in activated sludge plants with selectors as in conventional activated sludge plants.

No abstract

The City of San Diego, California, evaluated the performance capabilities of biological aerated filters (BAFs) at the Point Loma Wastewater Treatment Plant. The City conducted a 1-year pilot-plant evaluation of BAF technology supplied by two BAF manufacturers. This paper reports on the first independent oxygen-transfer test of BAFs at full depth using the offgas method. The tests showed process-water oxygentransfer efficiencies of 1.6 to 5.8%/m (0.5 to 1.8%/ft) and 3.9 to 7.9%/m (1.2 to 2.4%/ft) for the two different pilot plants, at their nominal design conditions. Mass balances using chemical oxygen demand and dissolved organic carbon corroborated the transfer rates. Rates are higher than expected from fine-pore diffusers for similar process conditions and depths and clean-water conditions for the same column and are mostly attributed to extended bubble retention time resulting from interactions with the media and biofilm. Water Environ. Res., 80, 663 (2008).

The City of San Diego (City) operates the Point Loma Wastewater Treatment Plant (PLWTP) which can normally treat up to 240 million gallons per day (MGD) of chemically enhanced primary treated (CEPT) effluent for ocean disposal. The City wanted to understand the performance capabilities of Biological Aerated Filters (BAFs) in treating CEPT effluent to secondary standards. To this end, the City conducted a one year pilot plant evaluation of BAF technology supplied by the two leading BAF manufacturers with experience in providing and operating BAFs greater than 30 MGD capacity. The pilot test results, which were reported at the 2005 WEFTEC conference, confirmed that the BAF technology is capable of producing secondary treated effluent that meets anticipated discharge requirements during simulated wet weather and dry weather conditions. This paper reports on oxygen transfer efficiencies, which were measured twice during the pilot study using the off-gas method. The first set of tests was largely unsuccessful due to mechanical problems that were unrelated to aeration equipment. The second set of tests was successful and showed process water oxygen transfer efficiencies (OTE) of 1.3 to 1.8 %/ft (4.1 to 5.7 %/m) and 1.8 to 2.4 %/ft (6 to 7.9 %/m) for the two different pilot plants at their nominal design conditions. A mass balance using chemical oxygen demand and dissolved organic showed similar transfer rates. These rates are higher than can be expected from fine pore diffusers for similar process conditions and depths.

Obtaining reliably high compaction characteristics and low SVI values has enormous economic consequences on activated sludge plant design and operation. Now that use of selectors has become more common for achieving low SVI values, the assessment of the full-scale performance characteristics of activated sludge plants incorporating selectors has high value for the design and operation of future plants. Treatment plant effluent quality is seldom analyzed solely on an average basis and the impact peak events have on effluent quality must be considered in design and operation. Descriptive statistics should also be used to assess selector performance, so that the influence of infrequently occurring values on plant design and operation can be assessed. The performance of 21 activated sludge plants incorporating selectors was evaluated. All the selector plants for which post installation data were available showed that the operating SVI values were significantly improved. One plant studied in detail showed that final effluent quality was significantly better after the selector installation. As a group, activated sludge plants with anaerobic selectors outperform those with anoxic selectors. Dissolved oxygen control is just as important in activated sludge plants with selectors as in conventional activated sludge plants.