Edward W. Wilde

Screening of algal strains for metal removal capabilities

Eight algal species were tested for their ability to remove five toxic metalsduring 30-min exposures to single-metal (1 mg L-1) solutions at pH7. Efficacy of metal bioremoval varied according to algal species and metal. Al+3 was best removed by the thermophilic blue-green alga(cyanobacterium) Mastigocladus laminosus, Hg+2 and Zn+2 by the thermophilic and acidophilic red alga Cyanidiumcaldarium, and Cd+2 by C. caldarium and the green alga Scenedesmus quadricauda. All of these alga/metal combinations resultedin >90% metal removal. However, none of the eight algal speciesremoved more than 10% of Cr+6. Results indicate that some toxicmetals are more readily removed than others are by algae and that selectionof appropriate strains could potentially enhance bioremoval of specificmetals from wastewater at neutral pH.

Cultivation of algae and nutrient removal in a waste heat utilization process

A process providing a beneficial use for waste heat and excess nutrients in the cooling waters of nuclear reactors and fossil-fueled power generating plants has been developed. The process involves the cultivation of selected strains of thermotolerant microalgae in heated discharge waters and the subsequent harvesting of the algal biomass for nutrient removal, recovery of energy and fertilizer, and extraction of high value products. The design of such a process is presented for a large cooling reservoir receiving a discharge of 1091−1 d−1 of secondary cooling water containing 100 μg 1−1 of available P and 400 μg 1−1 of available N. Based on this nutrient load, with a 1% P content in the algal biomass and a productivity of 10 g m−2 d −1, a 100 ha region would be needed for the process. Hydraulic barriers (submerged plastic curtains) would isolate the 100 ha algal production area “cultivation zone” in the influent end of the reservoir to create a hydraulic and thermal environment conductive to the selective growth of filamentous, thermotolerant, nitrogen-fixing, blue-green algae. The algal culture would be inoculated into the thermal plume and harvested near the distal barrier of the cultivation zone with rotating, backwashed, fine mesh screens (“microstrainers”). A portion of the harvested biomass would be recycled to the inoculation site to maintain a dense culture. This process could mitigate both thermal and nutrient loadings on receiving bodies of water.

Evaluation of biodegradation potential of foam embedded Burkholderia cepacia G4

Foam embedded Burkholderia cepacia G4 removed up to 80 % and 60 % of a 3 mg/l solution of trichloroethylene (TCE) and a 2 mg/l solution of benzene, respectively. Removal of TCE and benzene decreased more than 50% when readily metabolizable carbon sources were present. TCE degradative activity was observed with G4 cells induced with phenol or benzene prior or after immobilization of cells.

Growth and production of thermophilic cyanobacteria in a simulated thermal mitigation process

A cyanobacterial cultivation process, designed to mitigate impacts of thermal effluents by reducing their nutrient content, was simulated in bench-scale tests using semicontinuous cultures of the nitrogen fixing thermophile Fischerella (formerly Mastigocladus laminosus). The cyanobacterial strains were isolated from and grown in water from nuclear reactor cooling reservoirs at the Savannah River Site near Aiken, South Carolina. Major limiting factors for biomass production under various scenarios included temperature, light, carbon and phosphorus. The amount of biomass recycling needed to maintain a stable biomass in the mitigation (nutrient removal) zone of the mock reservoir varied with different light and temperature scenarios that were tested. In the worst case scenario, when biomass was repeatedly recycled into heated water at the end of the light cycle rather than at the beginning, stable daily production could be maintained only when 75% of the biomass was recycled. Otherwise, the inoculated biomass was able to maintain one doubling per day, allowing a daily recycle of 50% of the biomass. Overall, the growth rates and primary production capabilities needed for successful operation of a proposed process for nutrient removal from thermal effluents were demonstrated in these laboratory simulations.

Exposure of Fischerella (Mastigocladus) to high and low temperature extremes: strain evaluation for a thermal mitigation process

In conjunction with a proposed algal cultivation scheme utilizing thermal effluent, twelve Fischerella strains were tested for tolerance to temperatures above and below their growth range. Exposure to 65 °C or 70 °C for 30 min caused bleaching and death of most or all cells. Effects of 60 °C exposure for periods of up to 2 h ranged from undetectable to severe for the various strains. Chlorophyll a content typically decreased 21–22% immediately following 60 °C or 65 °C (1 h) exposure. However, the 60 °C-shocked cultures regained normal Chl a content after 24 h at 45 °C, whereas Chl a in 65 °C-shocked cultures immediately lost visible autofluorescence and was later degraded. Exposure to 15 °C virtually stopped growth of all strains during a 48 h exposure period. Most strains grew as rapidly as 45 °C controls when restored to 45 °C, while a few strains recovered more slowly. Comparison with dark-incubated controls indicated that photooxidative damage did not occur during cold shock. Certain strains exhibited relatively rapid recovery from both heat and cold exposure, thus meeting the temperature tolerance criteria for the proposed algal cultivation process.

Immobilization of Burkholderia cepacia in polyurethane-based foams: embedding efficiency and effect on bacterial activity

Immobilization of the trichloroethylene-degrading bacterium Burkholderia cepacia was evaluated using hydrophilic polyurethane foam. The influence of several foam formulation parameters upon cell retention was examined. Surfactant type was a major determinant of retention; a lecithin-based compound retained more cells than pluronic- or silicone-based surfactants. Excessive amounts of surfactant led to increased washout of bacteria. Increasing the biomass concentration in the foam from 4.8 to 10.5% dry weight per wet weight of foam resulted in fewer cells being washed out. Embedding at reduced temperature did not significantly affect retention, while the use of a silane binding agent gave inconsistent results. The optimal formulation retained all but 0.2% of total embedded cells during passage of 2 L of water through columns containing 2 g of foam. All foam formulations tested reduced the culturability of embedded cells by several orders of magnitude, but O2 consumption and CO2 evolution rates of embedded cells were never less than 50% of those of free cells. Nutrient amendments stimulated an increase in cell volume and ribosomal activity in immobilized cells as indicated by hybridization studies using fluorescently labeled ribosomal probes. These results indicate that, although immobilized cells were mostly nonculturable, they were metabolically active and thus could be used for biodegradation of toxic compounds.

Comparison of three methods for measuring residual chlorine

Abstract Three EPA-approved residual chlorine detection methods were compared using standard solutions and water collected from the Savannah River which is used to cool reactors at the Savannah River Site (SRS) near Aiken, S.C. The testing was part of an experimental program to develop baseline data for the design of a proposed cooling tower for the K-reactor at the SRS. A series of total residual chlorine (TRC) measurements made simultaneously by three methods revealed that for the river water samples, the DPD method (Hach DR-100 kit) and the amperometric titration method produced statistically similar results while an ion-selective electrode method, standardized according to the manufacturers instructions, provided significantly lower values. The DPD method (utilizing a Hach DR-100 kit) was the recommended method for future monitoring of the water evaluated because this method is simple, provides quick results, measures both total residual chlorine (TRC) and free residual chlorine (FRC) and is equally suitable for measurements in the field and laboratory.

Bioremediation of coal pile run off waters using an integrated microbial ecosystem

The pH of coal pile run off was elevated from <2 to >7 and dissolved heavy metal concentrations were brought within or below drinking water standards following batch treatments utilizing a mixed culture of bacteria. Treatment tanks containing the wastewater were inoculated with the bacterial culture and appropriate media for growth. Remediation (i.e. elevated pH, change in redox, and metal precipitation) occurred in both aerated and non-aerated treatment tanks inoculated with bacteria. The bacterial culture included specific strains of Bacillus and Pseudomonas. Remediation did not occur in treatment tanks containing growth nutrients alone.

Chlorination and dechlorination of nuclear reactor cooling water

Abstract Effects from chlorination and dechlorination of Savannah River water were studied during the development of biofouling countermeasures for a proposed cooling tower system required for thermal mitigation of nuclear reactor cooling water effluent. Testing was conducted to assess chlorine demand and dissipation rates as well as the environmental acceptability of using sodium sulfite as a dechlorinating agent. Chlorine demand varied significantly, but in an unpredictable manner during seven seasonal sampling dates. A chlorine dosage of 3–5 mg/l was generally adequate to provide a free chlorine residual of 1 mg/l. Static 48-h bioassays with bluegill showed no acute toxicity for chlorinated/dechlorinated cooling water containing up to 64 times the calculated stoichiometric concentration of sodium sulfite required for dechlorination. Experiments measuring the depletion of dissolved oxygen and flow-through (96-h) bioassays with bluegill and largemouth bass further substantiated the environmental acceptability of using sodium sulfite as a dechlorinating agent.

Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l−1 daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec−1 m−2) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO3− + NO2−−N, 71% of NH3-N, 82% of PO43− −P, and 70% of total P from effluent water samples containing approximately 400 μg l−1 combined N and 60 μg l−1 P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO3− + NO2− removal, 38–45% P removal and no net NH3 removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.