Removing suspended solids from effluent in the process of tertiary treatment by microfiltration in disk filters with flat and volumetric filtration

Summary

Mosvodokanal JSC carried out tests of a pilot microfiltration plant based on a disk filter with a fabric filter cloth. The pilot plant supplied by Mediana-Filter RPC JSC has been designed for removing suspended solids from effluent in the process of tertiary treatment. Disk microfiltration with fabric filter cloth (volumetric filtration type) provides for removing suspended solids to 4 mg/l in the effluent after biological treatment while using fabric filter cloth of 10 µm typical size and to 2 mg/l while using 5 µm filter cloth. At 8.5 m/h filtration rate the consumption of wash water for the pilot plant for 10 µm filter cloth was 0.7–1.4% of the water flow, and 5.8–6.8% for 5 µm filter cloth. Beside suspended solids present in the suspension, COD, BOD₅, total nitrogen and total phosphorus are also removed. Microfiltration plants of volumetric type are similar to the plants of flat type and can be used to ensure high quality tertiary treatment of effluent after biological treatment to remove suspended solids.

Key words

wastewater treatment , dragged particles , microscreening , disc filter , pile fiber filter cloth

The efficiency of removing suspended solids from biologically treated effluent by microscreening in disc filters

Summary

The article covers the results of studying the separation of suspended solids from biologically treated effluent and separation of mixed liquor from aeration tanks by microscreening method. The specialists of R&D Centre of «Mosvodokanal» JSC performed pilot testing of microscreening technology. The tests were carried out in a pilot plant designed on the basis of DynaDisc filter (Nordic Water Products AB, Sweden). The surface of filtration area was 2.8 m2. The tests were carried out at the Kur’ianovskie Wastewater Treatment Facilities in Moscow. In the course of studies it was shown that disc microscreening provided for effluent polishing with reducing suspended solids to 4 mg/l when using 18 µm sieve mesh and to 3 mg/l when using 10 µm sieve mesh. The concentration of suspended solids in backwash water is 0.5–1.4 g/l; backwash water flow rate does not exceed 1.2% of the installation capacity. Addition of Praestol 650 flocculant allows improving filtrate quality to 1 and 0.5 mg/l, respectively. The quality of filtrate during separation of mixed liquor from aeration tanks in DynaDisc filter with 50, 30 and 18 µm sieve mesh is, respectively, 140, 60 and 45 mg/l; suspended solids in backwash water – 30–70 g/l, backwash water flow rate – 6–8%. In the course of tests the optimal filter operational performance in effluent polishing and separating mixed liquor from aeration tanks by microscreening was determined.

Key words

wastewater treatment , flocculant , dragged particles , mixed liquor separation , microscreening , disc filter