Innovation and Progress in Water Treatment Technology

Transcription

1 Innovation and Progress in Water Treatment Technology

2 Degree of separation of ultrafiltration Summary of the various processes The water will be pressed through the between the raw water side and the filtrate side caused by a pressure difference. The selection of the process is depending on the type of water ingredients who need to be eliminated. In principle a distinction is made between the following filtration processes: - reverse osmosis - nanofiltration - ultrafiltration - microfiltration product service pressure retention of 95 % demineralised water univalent ions reverse osmosis < 0,001 μm partially demineralised nanofiltration 0,01-0,001 μm bivalent ions organic compounds drinking water, service water, free of germs ultrafiltration 0,1-0,01 μm macromolecules viruses colloids service water, with germs microfiltration > 0,2 μm zooplankton algae turbidity bacteria suspended particles inlet raw water 2

3 Description and advantages Ultrafiltration (UF) In ultrafiltration the raw water will be pressed through small tubes in plastic material with an inner diameter of approx mm. The actual filter medium is the porous walls of these small tubes whose filter pores have a size of µm (for comparison: a human hair has a diameter of approx. 50 µm this is 5000 times as much). Contaminations larger than 0.05 µm will be kept back reliably and washed out again in regular time intervals. Dissolved matters and salts can pass through the s of the filter tubes. The big advantage of ultrafiltration compared to conventional filtration methods is the absolute sterility of the filtered water. The pores of the UF s are so tiny, that bacteria and even viruses are too large to be able to pass the UF. Bundling of many filtration tubes in filter modules creates the surface required for a higher water flow rate. Depending on the application, the modules have different sizes allowing different filter capacities. Therefore all water treatment requirements can be covered. Complete barrier for micro organisms and particles. Quality of the filtrate is independent from the quality of the water inlet. Ultrafiltration will also remove chlorine resistant germs such as cryptosporidium. The concentrate (waste water) will include only the materials removed from the raw water. The compact system can considerably reduce construction costs for new developments. Can be easily included with existing machinery. Full automation possible. By removal of almost all filmforming substances all subsequent processes, e.g. reverse osmosis, can be designed for a higher surface load and therefore reduced in size. Ultrafiltration (UF) in size comparison with known water germs Giardia approx µm Cryptosporidium approx. 4 6 µm Anthrax spores approx. 1 5 µm Legionella species 0,5-1,5 μm Escherichia Coli 0,5-1,5 μm B. Subtilis approx. 0,3 μm Virus / coliphage pore size UF approx. 0,05 μm 3

4 Ultrafiltration in practice Filtration and backwashing The shown sketches explain the principle of filtration and its backwashing. Filtration process: The raw water will be pressed into the filtration module from below. The shown process is called dead end process. During filtration, residuals will deposit on the inner side of the hollow fibres while the filtrate emerges on the outside of the hollow fibre. The clear water will be collected between the hollow fibres and discharged. Filtration Clean water Backwashing process: Raw water Primary backwashing (forward flush) cleaning of the inside of the hollow fibres flushing of the hollow fibre Main backwashing Backwash Waste water cleaning of the filter pores by inversion of the water flow direction from outside to inside Secondary backwashing (forward flush) Backwash Same procedure as for primary backwashing for removal of any possible residual contaminations. The entire backwashing procedure will be realised fully automatic Forward flush 4

5 Treatment procedure with ultrafiltration Cross flow and dead end There are two different procedures: In the cross flow procedure, a big water volume will be led by a circulation pump along the in a circle. A part of it will be pressed through the and another part will be disposed into the sewer as concentrate. These circulation losses will continuously be made up by means of the feed pump. The advantage of the cross flow is that there is no interruption of the treatment process for backwashing needed. The disadvantages are higher investment costs and higher energy consumption. Cross-Flow Waste water concentrate approx.10% Permanent extraction of concentrate (waste water) out of the loop In the dead end procedure the water will be pressed through the as in a dead end road. The contaminations will be collected in the capillaries; this is why the must be washed in regular intervals. Even though this procedure requires short interruptions for backwashing, the advantages are the lower energy consumption and the low-price compact construction of the treatment units. In W.E.T. ultrafiltration systems the water will be treated by means of capillary s in the dead end process. The ultrafiltration modules of the treatment unit contains several thousand hollow fibres who are accommodated in a pressure pipe. These ultrafiltration modules are arranged in lines, so that only a certain number will be operated or backwashed respectively. The number of modules and treatment lines depends on the water ingredients and the temperature. Recirculation approx. 80% Feed Raw water approx. 20% Dead-End Backwash approx. 5% Membrane Filtrate approx.10% Membrane cleaning by regular backwashing Feed Raw water 100% Filtrate approx. 95% Membrane 5

6 Filter types in use: Single pore Module Pressure pipe Hollow fibres Ø 1.5 mm Permeate collecting pipe Raw water distribution channels Raw water (feed) Filtrate (permeate) Waste water (concentrate) Backwash water Capillary s Capillaries grouted in resin for fixing PVC pressure pipe Perforated filtrate collecting pipe Inside diameter 0,5 or 2 mm Depending on the use Filtration layer with pores 0,01 0,05 µm Supporting material 6

7 Filter types in use: Muli pore PVC pressure pipe Grouting resin Multi pore hollow fibre 7 x 0,9 mm Ø Outlet treated water Raw water (feed) Filtrate (permeate) Waste water (concentrate) Capillary s Backwash water The filtrate will be collected in the external annular gap. Capillaries grouted in resin for fixing PVC pressure pipe Multi pore Supporting material Filtration layer with pores 0,01 0,05 µm Inside diameter 0,9 mm 7

8 Ultrafiltration in comparison Ultrafiltration Chlorine dioxide disinfection No 100 % disinfection (barrier) Elimination of Legionella in amoeba is not guaranted. Total failure of ClO 2 disinfection possible, all germs can pass without any treatment From bad to no disinfection in case of turbidity High operating costs caused by power and chemical consumption and work expenditure in case of failures (rejection of the prepared solution) The killed germs (dead bodies) will remain within the system Completely germ free in the filtrate Complete elimination of parasites, complete elimination of all particles > 0,05 micrometer Only partial failure possible e.g. in case of fibre rupture; the majority of germs will be held back Will remove turbidity completely, no disturbance of disinfection at all by turbidity Low consumption in power and chemicals, no regular changing of parts; no pumping energy required when used as bacteria barrier in drinking water networks Complete removal of the germs out of the drinking water Disinfecting effects in the distribution system Complete removal of the germs at the start, the distribution system will remain totally unaffected Copyright - W.E.T. GmbH 2005 No copying and/or propagation, also in extracts, without permission by the author. UV disinfection Author: W.E.T. GmbH No 100 % disinfection Not efficient for parasites (cryptosporidium) No effect on sheathed germs, e.g. legionella in amoeba Total failure of UV disinfection possible, all germs can pass without any treatment From bad to no disinfection in case of turbidity Operating costs caused by power consumption and spare lamps Damage to the germ DNS, but regeneration is possible Krumme Fohre 70 D Kasendorf Fon: +49 (0) 9228 / Fax: +49 (0) 9228 / [email protected] Internet: Completely free of germs Complete removal of parasites Complete removal of all particles > 0,1 micrometer Only partial failure possible e.g. in case of fibre rupture; the majority of germs will be held back Will remove turbidity completely, no disturbance of disinfection at all by turbidity Low consumption in power and chemicals, no regular changing of parts; no pumping energy required when used as bacteria barrier in drinking water networks Complete removal of germs