Stress Testing an Activated Sludge Plant To Determine Toxicity Removal Capacity

Inland Empire Utilities Agency (IEUA) operates four publicly owned treatment works in the western end of San Bernardino County in Southern California. In 1995 and 1996, IEUA experienced toxicity at its Regional Water Recycling Plant No. 2 (RP-2). In 1996, using Ceriodaphnia dubia as the test organism, twenty-four of the acute or chronic survival toxicity tests performed (approximately one-half) showed toxicity. All of the observed 1995 and 1996 toxic events occurred between April and November. In late September 1996, as a result of these events, the California State Regional Water Quality Control Board issued a notice of violation (NOV) to IEUA. The NOV required IEUA to conduct weekly whole effluent toxicity monitoring of the effluent and extensive sampling of the trunklines for heavy metals and pesticides.