Endotoxins in drinking water: Mechanisms of release from biofilms and response to treatment technologies.

摘要

Endotoxins are a component of the lipopolysaccharide (LPS) complexes that make up a part of the outer layer of the cell walls of most gram-negative bacteria and some cyanobacteria. LPS complexes are macromolecules composed of three main regions: lipid A, core polysaccharide, and "O" antigens. The lipid A component is critical for all biological responses to endotoxin.; To-date, outbreaks of water-borne endotoxin-related illness have been only infrequently documented. Given the fact that the cause of many outbreaks of fever-related illness associated with drinking water are never identified by routine medical and bacteriolgical analyses, and that endotoxin-related fever symptoms are typically short-lived, it may be prudent to investigate more closely the role of drinking water treatment processes with respect to endotoxin. In particular, given the trend of drinking water utilities toward delayed chlorination, and the use of ozone followed by a biological treatment step to reduce the formation of chlorination byproducts, emphasis should be placed on operational issues associated with the use of biological filters and GAC contactors.; A series of bench-scale investigations involving oxidants to assess endotoxin inactivation rates were conducted. Oxidants examined were those that would normally be applied following biofiltration or could potentially influence bioactivity in such filters. They included free chlorine, monochloramine, and potassium permanganate. It was found that none of the oxidants were particularly efficient at inactivating endotoxin with the maximum inactivation rate being 1.4 endotoxin units (EU)/mL.h for free chlorine. Medium pressure ultraviolet (UV) irradiation was also investigated. It was found that UV irradiation was somewhat effective 00.55 EU/mL per mJ/cm2), albeit at higher dosages than currently being employed in drinking water treatment. Escherichia coli (E. coli) O111:B4 endotoxin was used in all experiments.; Laboratory filter column tests to identify conditions under which endotoxins can be released from biologically active anthracite/sand filters were also conducted. Relationships between endotoxin release rates and heterotrophic plate count bacteria (HPC) levels, potassium, and dissolved oxygen were identified. Biofilm bacteria were isolated and identified, and the ratio of Gram-negative to Gram-positive bacteria was estimated. It was determined that about 80% of the identified species were Gram-negative. Endotoxin was produced in greatest quantities during periods of optimal bacterial growth in the first few hours following shutdown of biologically active filters. (Abstract shortened by UMI.)