Microbial filters

T0475 Lawrence Livermore National Laboratory, In Situ Microbial Filters... 

Laboratory development of the in situ microbial filter has been completed. According to LLNL, the key engineering design parameters have been measured under controlled conditions, and scaled laboratory experiments have demonstrated the success of the approach. A field demonstration of the biofilter concept was conducted at a contaminated site in Chico, California. 

According to the technology developer, the total cost for using the in situ microbial filter technology is approximately half of the estimated pump-and-treat cost, while involving only about 10% of the usual volume of groundwater used in pump-and-treat remediation (D152103, p. 1). 

Groundwater — Dynamic underground stripping, in situ bioremediation, biosorption of uranium, recirculating wells, and microbial filters... 

V etated microbial filters increased removal [26] of both aromatics and aliphatics. 

Biowalls, also referred to as permeable reactive biowalls, or in-line microbial filters, are essentially in situ... 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

Verification of the microbial retention efficiency of the membrane filters may be undertaken using either Hquid or aerosol challenge tests. A Hquid challenge test is more stringent. Furthermore, this test can provide retention information for process conditions such as extreme moisture after sterilization or air entrained with water drops. A Hquid challenge is performed using a protocol similar to that described for Hquid filtration. 

Raw juice is heated, treated sequentially with lime (CaO) and carbon dioxide, and filtered. This accomplishes three objectives (/) microbial activity is terminated (2) the thin juice produced is clear and only lightly colored and (J) the juice is chemically stabilized so that subsequent processing steps of evaporation and crystalliza tion do not result in uncontrolled hydrolysis of sucrose, scaling of heating surfaces, or coprecipitation of material other than sucrose. 

The importance of the final settling, or humus, tank can be seen by an examination of what occurs in the trickling filter itself. A new filter is broken in by applying settled sewage as in the normal operation. After a period of time the microbial, or zoogleal, mass forms on the filter medium and stabilizes the waste. Waste material is first adsorbed, and then assimilated by the microorganisms. 

Microstrainers. Microstrainers are rotating steel screens with extremely fine stainless steel mesh (85—170 perforations per square centimeter (13—26/in. )). The flowing Hquid enters the open end of the dmm and passes through the mesh to the effluent end. The mesh traps soHd impurities and rotates with the dmm. A wash-water spray washes the trapped soHds into a hopper for final disposal. The mesh is washed with filtered effluent discharged from jets fitted into the dmm and then exposed to uv radiation to inhibit microbial growth. The mesh is washed with chlorine water at intervals of 7 to 28 days in order to control slime growth removal efficiencies are 30—55% of the appHed BOD and 40—60% of suspended soHds. 

Removal of particulates, colloidal matter, iron and organics. Multimedia, manganese, greensand, diatomaceous earth, brim, or carbon filter. Caution carbon filters not recommended unless absolutely required for the removal of color and odor (as they provide a medium for microbial growth). 

Removal of dissolved materials. If operated at ambient temperatures, regenerate mixed bed at least once a week for microbial control. Use 4.5-10 pm absolute filters after mixing bed to stop resins and particulates from entering distribution system. 

Because systems are normally not designed for use with this type of fluid, certain aspects should be reviewed with the equipment and fluid suppliers before a decision to use such fluids can be taken. These are compatibility with filters, seals, gaskets, hoses, paints and any non-ferrous metals used in the equipment. Condensation corrosion effect on ferrous metals, fluid-mixing equipment needed, control of microbial infection together with overall maintaining and control of fluid dilution and the disposal of waste fluid must also be considered. Provided such attention is paid to these designs and operating features, the cost reductions have proved very beneficial to the overall plant cost effectiveness. 

About 5 ml of sample is withdrawn for every 4-6 hours. The absorbance reading of the sample at 580 nm was measured using a Hitachi U-2000 spectrophotometer. The sample is filtered in a vacuum through Whatman filter paper with a pore size of 2.5 pin and diameter of 47 mm. The dry weight of cells is measured to monitoring microbial cell population and cell density. A plot of optical density reading from the spectrophotometer against cell dry... 

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