NEW METHODS DEMONSTRATE RAPID BIODEGRADATION OF LAS
Scientists at the Ivorydale Technical Center of the Procter & Gamble Company (Cincinnati, Ohio, USA) have developed new test methods to measure the biodegradation of LAS under realistic environmental conditions. Results from five new studies using these new methods demonstrate that LAS biodegrades rapidly — and is extremely rapidly removed — under realistic test conditions. One of the studies has been published and four others were presented at the Society of Environmental Toxicology and Chemistry (SETAC) meeting in San Francisco, California, November 16-20, 1997.
• T.W. Federle and N.R. Itrich (Environmental Science & Technology, vol. 31, 1178-1184, 1997) reported the development of a test method for accurately measuring initial (primary) and complete (ultimate) biodegradation of a single pulse of material in “activated sludge” as used in most modern sewage treatment plants. Based on the rate constants observed for LAS, the half-life, or time period required for half the material to biodegrade, was only about 40 minutes for primary biodegradation and about 80 minutes for ultimate biodegradation (mineralization).
• N.R. Itrich and others (SETAC # PHA051) demonstrated that activated sludge becomes acclimated to LAS biodegradation and that biodegradation rates actually increase in activated sludge which previously was exposed to (and biodegraded) LAS. Initial rates of LAS removal, which more accurately predict LAS removal during sewage treatment, are extremely rapid, with half-lives of 60 to 80 seconds.
• B. Nuck and others (SETAC #PHA052) demonstrated that in realistic models of rivers polluted by disposal of untreated sewage LAS biodegrades more rapidly than the total organic material present, measured as the chemical oxygen demand (COD).
• D.W. Gledhill and others (SETAC #PHA053) confirmed that the 2-phenyl isomer of LAS biodegrades more rapidly than other isomers. However, the differences were not large enough to translate into different removal rates in realistic models of sewage treatment plants (CAS systems).
• S.K. Kaiser and others (SETAC #PHA048) observed that removal rates for LAS in model sewage treament plants (Continuous Activated Sludge, CAS, systems) realistically modeled LAS removal in activated sludge treatment plants.