An aerator membrane

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References

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Gilbert, V. L. et al., Metabolic uptake of phosphorus by wastewater organisms. Journal WPCF, 1965, 37(6), 800-821. EPA Design Manual, Phosphorus Removal. EPA/625/1-87/001, September 1987. 16 US patent publications.

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flowing into the anoxic zone may be as high as 100% of solids settled from the oxic zone effluent stream. The recycle anoxic effluent stream may range between 50 and 100% of the influent wastewater entering the anoxic zone.

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An aerator membrane

(European patent application 0 761 294 to Bontec A G, Schmerikon, Switzerland; in German)

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An anoxic effluent stream is discharged from the anoxic zone and is directed into the oxic zone. A recycle anoxic effluent stream is introduced into the anaerobic zone. An anaerobic effluent stream is discharged from the anaerobic zone and is directed to the anoxic zone. A recycle oxic cffluent stream is introduced into the anoxic zone. Activated sludge from the oxic effluent stream is separated from the mixed liquor to form a return activated sludge stream. The return activated sludge stream is introduced into the anoxic zone. The environmental conditions in the anoxic zone must bc frcc of residual dissolved oxygen, and the anoxic zone preferably contains dissolved oxygen

concentrations less than 0.5 mg/litre. These conditions in the anaerobic zone must be free of residual dissolved oxygen and NO,, both of which are preferably held at concentrations less than 0"5 mg/litre. The environmental conditions on the oxic zone must be such that sufficient concentrations of dissolved oxygen are present to permit metabolic oxidation of carbonaceous organic material, and dissolved oxygen concentrations of at least 0-5 mg/litre are preferably maintained. The flow of recycled oxic effluent entering the anoxic zone may range between 200 and 400% of the wastewater influent entering the anoxic zone. The return activated sludge stream

Urs Heck, a bioengineer of the above company, developed an aerator having a perforated membrane and a sheetlike carrier. The membrane together with a second non-perforated membrane form a cushion in which an air space is formed. The advantage of such an aerator is deemed to reside in that the use of a special frame for holding the membrane assembly is avoided. Figures 3 and 4 show a longitudinal section of the aerator proposed by Heck. Both membranes are referred to by numerals 7 and 8 and are connected to each other by high frequency welding or by vulcanizing. Membranes 7 and 8 consist of a plastic material and membrane 7 has a textile web embedded therein to restrict its elasticity. Consequently, membrane 8 cannot be stretched because it extends against carrier 5. Instead of a textile web, a netting can also be used that is laid over membrane 7 and, together with that membrane, is welded at its periphery. Screw threaded busing 11 is provided with a collar 13 and is inserted into a boring 14 of carrier 5 and secured by bolt 12. Bolt 15 serves for connecting the U-profile 9 for reinforcing the aerator in the aerator assembly. Thc countersunk mounting of the screw-threaded bushing 11 is for preventing contact corrosion when the carrier 5 or parts thereof are made of a metal instead of a plastic material (see Fig. 3). To restrict the elasticity of membrane 7, it is provided with holes 2 (see Fig. 5) at the welding sites, the holes being surrounded by circular welding beads 16. Figure 5 is a top view of the aerator assembly.

Patent survey

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To reduce the tension in the area of f i e holes, plastic or metal elements 17 (]'ig. 4) having circular recesses 19 are p,ovided. The recesses hold the welding b, ads so that the tension around holes 2 will be reduced. With an aerating assembly of 1 < 1-5 m normally 12 connecting sites a~e provided so that 12 elements are n~'eded to connect both membranes 7

and 8 to carrier 5. The air feed connection, as usual, is located at the carrier. By connecting both membranes to each other such as by welding, protrubances 16 (Fig. 4) are formed which inside a recess 21 of edge element 20 is positioned so that tension on membrane 7 due to air pressure is reduced. Air feed is effected through carrier 5 and membrane 7 so that no dewatering devices are needed. The inventor states that with his aerator the swell of the airspace can be reduced to 75% with respect to conventional systems.

Refercnces 3 German patent publications. 3 European patent publications.

A high yield process for producing thermophilic microorganisms belonging to the species Pyrobaculum islandicum and Pyrococcusfuriosus under steady state conditions, particularly for the production of a biomass (US patent 5 624 841 to Microhiol~gical Research Authority Centre for Applied Microbiology & Research. Wiltshire, UK) Neil D. H. Raven, John D. Cossar, Narendra M. Ladwa and Richard J. Sharp, all of Salisbury, England, have previously developed a process for the growth of anaerobic thermophilic heterotrophic methanogens belonging to the above species, by continuously growing the bacterium in a nutrient