Chlorine disinfection of blended municipal wastewater effluents.

Blending is used in the wastewater industry to manage wet-weather events. Wastewater is treated through primary clarification, with flows in excess of the hydraulic capacity of the secondary system being directed to effluent disinfection. Before disinfection, the primary clarified effluent is "blended" with effluents that have been treated through the secondary system. The combined or "blended" effluents are then disinfected before being discharged to receiving waters. This study evaluated the effectiveness of chlorine to disinfect blended effluents. Experiments were conducted at bench-scale on primary and secondary effluents and three ratios of primary to secondary effluent (1:9, 3:7, and 5:5) from three publicly owned treatment works. Results from this study found that blending 10% or more primary effluent with secondary reduces the efficacy of chlorine disinfection, and coliphage survived chlorine disinfection better than bacterial indicator organisms. A simple empirical model for predicting indicator organism densities following chlorine disinfection was developed using data from this research.

Population diversity in model potable water biofilms receiving chlorine or chloramine residual.

Most water utilities use chlorine or chloramine to produce potable water. These disinfecting agents react with water to produce residual oxidants within a water distribution system (WDS) to control bacterial growth. While monochloramine is considered more stable than chlorine, little is known about the effect it has on WDS biofilms. Community structure of 10-week old WDS biofilms exposed to disinfectants was assessed after developing model biofilms from unamended distribution water. Four biofilm types were developed on polycarbonate slides within annular reactors while receiving chlorine, chloramine, or inactivated disinfectant residual. Eubacteria were identified through 16S rDNA sequence analysis. The model WDS biofilm exposed to chloramine mainly contained Mycobacterium and Dechloromonas sequences, while a variety of alpha- and additional beta-proteobacteria dominated the 16S rDNA clone libraries in the other three biofilms. Additionally, bacterial clones distantly related to Legionella were found in one of the biofilms receiving water with inactivated chlorine residual. The biofilm reactor receiving chloraminated water required increasing amounts of disinfectant after 2 weeks to maintain chlorine residual. In contrast, free chlorine residual remained steady in the reactor that received chlorinated water. The differences in bacterial populations of potable water biofilms suggest that disinfecting agents can influence biofilm development. These results also suggest that biofilm communities in distribution systems are capable of changing in response to disinfection practices.

Survival of Salmonella in waste egg wash water.

Waste wash waters from chicken egg-processing facilities can harbor high densities of bacteria, including salmonellae. For this study, we enumerated total coliforms, Escherichia coli, and Salmonella spp. in the egg wash waters of a large egg producer. We then determined how long these organisms would survive at temperatures of 5, 15, and 25 degrees C. We found that the fraction of salmonellae surviving over time at a given temperature was comparable to the fraction of indicator organisms that survived. We also found that the survival of these organisms varied with temperature, with 16, 8, and < 2 days being required for a 90% reduction of Salmonella in waste wash water held at 5, 15, and 25 degrees C, respectively. Finally, we noted that the response of laboratory-derived cultures to environmental stresses mimics the response of the indigenous microbial population, but individual cells within that population may survive for longer periods than laboratory-cultured strains.

Removal of PCBs from a Contaminated Soil Using CF-Systems® Solvent Extraction Process.

The U.S. Environmental Protection Agency's (EPA) Superfund Technical Assistance Response Team (START) in cooperation with EPA's Superfund Innovative Technology Evaluation (SITE) program evaluated a pilot scale solvent extraction process developed by CF-Systems. This process uses liquefied propane to extract organic contaminants from soils, sludges, and sediments. A pilot-scale evaluation was conducted in Golden, CO at Hazen Research, Inc., using CF-Systems' trailer-mounted organics extraction unit. Approximately 1,000 pounds of soil, with an average poly-chlorinated biphenyl (PCB) concentration of 260 mg/kg, was obtained from a remote Superfund site. Six 100-pound batches of the contaminated soil were extracted using multiple extraction sequences. Three of the six batch runs were subjected to three extraction sequences each, so that process variability could be evaluated. Results showed that PCB removal efficiencies varied between 91.4 and 99.4%, with the propane-extracted soils retaining low concentrations of PCBs (19.0-1.8 mg/kg). Removal efficiencies of oil and grease (O&G) were found to be 96.0 to 99.6% with propane-extracted soils retaining O&G concentrations from 279 to <20 mg/kg. Overall extraction efficiency was found to be dependant upon the numberof extraction cycles used.

Site Demonstration of Terra-Kleen Response Group's Mobile Solvent Extraction Process.

The U.S. EPA's Superfund Innovative Technology Evaluation (SITE) Program evaluated a pilot-scale solvent extraction process developed by the Terra-Kleen Response Group (TKRG). This process uses a proprietary solvent, or mixture of solvents, to extract organic contaminants from solids. A pilot-scale evaluation was conducted at Naval Air Station North Island (NASNI), near San Diego, CA, on soils which were contaminated with polychlorinated biphenyls (PCBs) and other organic substances. Five tons of soil with an average PCB concentration of 144 mg/kg were excavated, homogenized, and equally distributed to five extraction vessels. Eleven extraction cycles were used to produce a treated soil with an average PCB concentration of 1.71 mg/kg on a dry weight basis (98.8% removed). Oil and Grease (O&G) removal efficiencies were found to be 65.9%. This low O&G removal efficiency was attributed to solvent/solute relationships. Initial concentrations of hexachlorodibenzofuran (HxCDF) in soils averaged 0.697 jig/kg. Following solvent extraction, no HxCDFs were detected (<0.117 fxg/kg) in soil samples. A fullscale solvent extraction system was operated at a site in Stockton, California. Pesticides were extracted from 500 tons of contaminated soil using 19 extractors, each 20 cubic yards in volume. Three extraction cycles produced solids with <0.093 mg/kg residual pesticide (>99% removed). These results demonstrate that the TKRG's solvent extraction process is effective in removing organic contaminants from soils.