Microscreens

Blinding The clogging of the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become sealed off due to a buildup of grease or the material being filtered. 

Houk VS, DeMarini DM. 1988. Use of the microscreen phage-induction assay to assess the genotoxicity of 14 hazardous industrial wastes. Environ Mol Mutagen 11 13-29. 

This is mechanical separation process for removal of suspended sohds by passing the waste-water through a microscreen. A removal efficiency for TSS is 50-80% depending on the pore size of the microscreen to be used. 

Rossman TG, Molina M, Meyer L, et al. 1991. Performance of 133 compounds in the lambda prophage induction endpoint of the Microscreen assay and a comparison with IS. typhimurium mutagenicity and rodent carcinogenicity assays. Mutat Res 260 349-367. 

In the integrated membrane system fed with seawater (Figure 12.4A) the pretreatment consists of two rotating microscreens of 150 pm used to remove the larger suspended particles from the water. Successively 8MF units (polypropylene (PP) hollow membranes placed in a vertical position and operated according to the deadend principle) are used to remove the suspended solids completely, algae and to disinfect the water. The MF section is designed to filter 700-750 m3/h [15]. 

Introduction Microscreening Process Design Criteria Backwashing Design oe Microscreens Energy and Costs Design Example Nomenclature Reeerences Appendix... 

Microscreening is a method of filtration that uses fabric as the filtering medium. Microscreens (microstrainers) usually consist of a special metallic or plastic fabric mounted on the periphery of a revolving drum. The untreated water flows into the drum and radiates outward through the microfabric, leaving behind the suspended solids removed by the cloth. The solids retained on the inside of the rotating screen are carried upward to a row of backwash jets that flush them into a hopper, which is mounted on a hollow axle of the drum, for return to the treatment plant. 

Individual microscreening manufacturers have specific designs and sizes for various types of installations, and much of the design information is proprietary in nature. Design elements required for nficroscreening include (9) ... 

Tables 1 and 2 (10) summarize the microscreen sizes available from two manufactures. A schematic of a microstrainer appears in Fig. 1.

According to The Colorado Department of Public Health (11), the design of microscreening should take the following into consideration ... 

Table 1 Microscreens Removal from Secondary Effluents ...

Table 2 Microscreen Sizes from Glenfield and Kennedy ...

Hot water. Where oil and grease are present, hot water and/or steam treatment can be used to remove these materials from the microscreens. Plastic screens with grease problems are cleaned monthly with hot water at 1200 F to prevent damage to the screen material. Downtime for cleaning may be up to 8 hours. 

The design procedure for microscreens is detailed in the following steps (18). 

The annual energy consumption by microscreens is shown in Fig. 2 (9). Electrical energy requirements include backwash water pumping and screen drive (10). 

The microscreens construction and operation and maintenance costs (1979 dollars, Utilities Index = 257.20) are illustrated in Figs. 3 and 4, respectively (9). To obtain the values in terms of the present 2004 US dollars, using the Cost Index for Utilities (Appendix A), multiply the costs by a factor of 506.13/257.20 = 1.97 (20). The costs are based on the following assumptions ... 

Sidsmerged Screen Area, ft Fig. 2. Microscreens energy consnmption (Sonrce US EPA). 

WMT, Mechanical Filtration—Microscreening, Water Management Technologies, Aquaculture System Design, Integration and Eqnipment Snpply, Hydrotech Drum Filter, URL http //www.w-m-t.com., 2004. 

D. G. Bordien and R. L. Stenburg, Microscreening effectively polishes activated sludge effluent. Water and Wastes Engineering, 3, 74-77 (1966). 

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