Municipal Solutions

Stormwater treatment

Secondary/tertiary wastewater treatment

Reclaimed water for reuse

Potable water treatment

Primary wastewater treatment

Hydrotech Municipal solutions Hydrotech Municipal solutions

32

Hydrotech filtrationMicroscreens are used in a variety of different applications within water and wastewater treatment. Pretreatment to sand filters at potable water treatment works was one of the first applications. Just after the Second World War the first drum filters were installed for treatment of trickling filter effluent in the UK (Isaac & Hibberd 1972). Treatment of effluents from final clarification after activated sludge treatment was soon to come. Today, the Hydrotech Discfilter and the Hydrotech Drumfilter can be found in applications ranging from primary to tertiary wastewater treatment, and from reclamation of water for reuse to potable water treatment. A selection of feasible and tested solutions are introduced in the following pages.

Hydrotech develops, manufactures and markets high performance filter systems. Today the company is the world’s leading manufacturer of microscreens and there are more than 6000 Hydrotech Discfilter and Drumfilter units installed all over the world. The company is based in Vellinge, Sweden and is represented world-wide by a network of professional, highly qualified partners. Hydrotech is part of the Veolia Water Solutions & Technologies group of business.

The Hydrotech Discfilter™ Entering the Discfilter, water flows by gravity into a cen-tral drum supporting vertically mounted discs with filter cloth on each side. During filtration particles are retained on the inner side of the filter panels and the flow of water through the filter is impeded. Conse-quently, the water level inside the Discfilter rises and eventually backwashing is initiated by a level sensor. During backwashing, and only then, the discs rotate and nozzles spray the filter cloth thereby removing separated particles for discharge via a sol-ids collection trough. Filtration is continuous and not stopped during backwashing.

The maximum operational differential pressure is typically in the range of 250 to 300 mm and filters can be placed in a gravity line or in a pumped feed system. The actual filtration process is gravity based. Available disc diameters range from 1,7 up to 3,1 m and the maximum filtration area for one unit with 24 discs is 134 m². The Discfilter can be supplied in two versions – a self-contained tank version or a frame version for installation in a concrete chamber.

1. The function of the Hydrotech Discfilter™

2. Discfilter in self-contained tank version. 3. Discfilter in frame version.

Table of contents

Hydrotech filtration 3

The Hydrotech Discfilter™ 3

The Hydrotech Drumfilter™ 4

The Hydrotech Beltfilter™ 4

Primary wastewater treatment 5

Stormwater treatment 6

Secondary/tertiary wastewater treatment 7

Activated sludge treatment 7

Biofilm processes 8

Reclaimed water for reuse 9

The Hydrotech design 11

Design example 11

Delivery and installation 12

Pilot testing 12

Reports and articles 13

Hydrotech Municipal solutions Hydrotech Municipal solutions

54

The Hydrotech Drumfilter™Similar to the Discfilter, water flows into a cen-tral drum covered with filter cloth. During filtra-tion particles are retained on the inner side of the filter panels. The water level inside the drum rises and eventually backwashing is initiated by a level sensor. During backwashing the drum ro-tates and nozzles spray the filter cloth. Transpor-tation of separated particles up from the water and to the spray nozzles is facilitated by the sup-porting frame construction on the filter panels. Separated particles are finally removed via the solids collection trough. Filtration is continuous and not stopped during backwashing.

The maximum filtration area for one unit is 21.6 m² and available drum diameters range from 0.5 up to 2.4 m. Also the Drumfilter can be supplied in two versions – a self-contained tank ver-sion or a frame version for installation in e.g. a concrete chamber.

The Hydrotech Beltfilter™The Beltfilter is an automatic, self-cleaning gravity belt thickener, specially designed for efficient filtration of sludge or wastewater. The filter belt is designed as a slowly moving con-veyer and separated particles are drained on the belt to a high dry matter content. Dewa-tered sludge is removed at the top of the filter by a scraper and discharged into a hopper. The belt is cleaned by a high-pressure backwash system and the backwash reject is lead into a separate sludge trough.

The Beltfilter can be used for thickening of re-ject streams from the Discfilter, the Drumfilter or from other processes such as the Actiflo® process.

4. Drumfilter in self-contained tank version.

5. Drumfilter in self-contained tank version. 6. Drumfilter in frame version.

7. Beltfilter in frame version.

Primary wastewater treatmentAfter preliminary treatment with grit and grease removal it is possible to use the Drumfilter or the Discfilter for primary treatment. In such applications pore size ranging from 40 μm up to more than 100 μm are typi-cally used.

Primary treatment based on microscreening can provide effluent results comparable to primary clarifiers but with a significantly lower foot-print. Full-scale sites can be found in Denmark, Norway and Sweden.

The Drumfilter can be combined with cationic polymer addition for increased particle removal resulting in an SS-reduction of approximately 90 % (Ljunggren et al 2007).

Another option is addition of a metal salt and polymer for phosphorous removal thus providing a system for chemically enhanced primary treatment (CEPT) based on microscreening instead of primary clarification (Ljunggren et al 2007).

Secondary treatment

Bar screenInlet pumping station

RecipientGrit chamber

Figure 8. Primary treatment with the Drumfilter

Drumfilter Secondary treatment

Secondary treatment

DrumfilterBar screenInlet pumping station

RecipientGrit chamber

Figure 10. Primary treatment with coagulation and flocculation

Secondary treatment

Coagulation Flocculation

Al/Fe Polymer

Secondary treatment

Bar screenInlet pumping station

RecipientGrit chamber

Figure 9. Primary treatment with polymer addition

Drumfilter Secondary treatment

Flocculation

Polymer

Hydrotech Municipal solutions Hydrotech Municipal solutions

76

Stormwater treatmentAssociated with options for primary treatment are applications for stormwater treatment at the wastewa-ter treatment plant. It is possible to use both the Drumfilter and the Discfilter with a wide range of pore size in various treatment configurations – with or without chemical pre-treatment.

Below are two possibilities (fig. 11), treating water before and after primary clarification, illustrated.

Another option is stormwater treatment in the sewage network. In Copenhagen, Denmark, Drumfilters and Discfilters have been combined with subsequent UV-treatment (Andersen 2005) in order to fulfil stringent bathing water criteria. The Filters are preceded by a 3 mm screen.

Bar screenInlet pumping station

RecipientGrit chamber

Figure 11. Treatment of sewer overflow before and after primary clarification

Drumfilter

Secondary treatment

Secondary treatment

Primaryclarification

Discfilter

Figure 12. Treatment of combined sewer overflow

Secondary/tertiary wastewater treatmentBoth the Discfilter and the Drumfilter can be used in various process configurations for secondary and terti-ary wastewater treatment. Typically nominal pore size openings of 10 – 30 μm are used.

Activated sludge treatmentTertiary filtration after activated sludge treatment and secondary clarification, sometimes referred to as “ef-fluent polishing”, is one of the most common Discfilter applications. The largest plant (10 m³/s) of this type is under construction in Sweden. The Discfilter has been installed after various activated sludge processes, including for example bio-P removal, simultaneous P-precipitation and nitrogen removal with either pre- or post-denitrification.

In the case of stringent effluent requirements on phosphorous it is possible to extend the treatment with post precipitation. However, flocs need to be strengthened by polymer addition prior to filtration in the Discfilter.

Discfilter Recipient

Figure 13. Tertiary treatment with the Discfilter

Primary treatment

Primarytreatment

Activated sludgetreatment

Secondarysettling

Discfilter Recipient

Figure 14. Phosphorus removal, chemically assisted Discfilter

Coagulation Flocculation

Primary treatment

Primarytreatment

Activated sludgetreatment

Secondarysettling

Al/Fe Polymer

Hydrotech Municipal solutions Hydrotech Municipal solutions

98

Biofilm processesThe Discfilter or the Drumfilter can be combined with a variety of biofilm processes, ranging from trickling filters to processes based on suspended carriers.

The Moving Bed™ Biofilm Process can be used in several process configurations, either as a combined or as a stand-alone process. By using the Discfilter for particle removal space and energy can be saved compared to other separation processes. The Discfilter combined with a post denitrifying MBBR-process is described by Persson et al (2003).

Recipient

Figure 15. MBBR + Discfilter

Primary treatment

Primarytreatment *

DiscfilterMoving Bed™ Biofilm Process (MBBR)

*Could include secondary treatment

Recipient

Figure 17. Trickling filter + Discfilter

Primary treatment

Primarytreatment

Trickling filter

Discfilter

Recipient

Figure 16. RBC + Discfilter

Primary treatment

Primarytreatment

RBC Drumfilter

Recipient

Figure 18. Trickling filter + Humus tank + Discfilter

Primary treatment

Primarytreatment

Trickling filter

DiscfilterHumustank

Drum filtration after trickling filters was one of the first ap-plication types within wastewa-ter treatment. Today there are numerous exam-ples of trickling filters followed by the Discfilter, with and without an intermediate humus tank.

There are several full-scale instal-lations with mi-croscreens, either Drumfilters or Discfilters, following rotating biological contactors (RBC).

The Biostyr® process has been succesfully combined with the Discfilter in a number of full-scale installa-tions.

Reclaimed water for reuseThe well defined filter media enables the Hydrotech Discfil-ter to be considered as a barrier, which is beneficial in water reclamation and reuse applications where it is critical to remove specific pathogens of certain sizes. The suitability of the Hydrotech Discfilter for removal of Helminth eggs has for example been demonstrated by Quinzanos et al (2008).

The Hydrotech Discfilter meets the California Department of Health Services Title 22 criteria for the unrestricted reuse of treated effluent.

The ACTIDisk® - a combination of Actiflo® and Hydrotech Discfilter™ - is an example of an advanced treat-ment process suitable for applications with very high effluent quality demands, for example in reuse ap-plications (Sanz et al 2007). One of the largest reference plants for reuse can be found in Barcelona (4 m³/s) where the process is combined with UV-disinfection.

20 μm

Figure 20. Egg from intestinal worm (Helminth) blocked by a filter cloth (10 μm)

Recipient

Figure 21. ACTIDisk® (Actiflo® + Discfilter)

Discfilter

Hydrocyclone

Polymer

Micro-sand

Coagulant

Lamellasedimentation

MMMMMMMM

Actiflo®WWTP UV-Disinfections

WWTP

Figure 19. Biostyr®+ Discfilter

Primary treatment

Primarytreatment

Biostyr® RecipientDiscfilter

Hydrotech Municipal solutions Hydrotech Municipal solutions

1110

Tertiary treatment based on the Discfilter or the Drumfilter is also suitable also as a membrane pre-treat-ment technology. One of the largest plants of this type (375 000 m3/d) is located in Sulabija, Kuwait, where Discfilters with pore size openings of 60 μm are used prior to UF (ultrafiltration) and RO (reverse osmosis).

Potable water treatmentBoth Discfilters and Drumfilters are used for filtration of intake water from rivers and lakes at potable water treatment works. A wide range of pore size openings are used, from 10 to 500 μm. Drumfilters or Discfilters are also suitable in the case of downstream membrane treatment, i.e. as a membrane pre-treatment tech-nology.

ScreenRiver/Lake

Figure 23. Filtration of intake water

DrumfilterPumping station

Recipient

Figure 22. Membrane prefiltration

Discfilter

WWTP

WWTP

WWTP

Membrane filtration

Water treatment

Water treatment

The Hydrotech designWith straining being the dominant separation mechanism there is basically only one chance to remove a particle. However, large enough particles is not the only condition that needs to be fulfilled, certain floc strength is also required. Furthermore, the separated solids – attached to the panels – should be efficiently removed, that is transported to the spray bar and washed off the panels in order for the filter to provide high effluent quality and maximum hydraulic capacity. These and other factors have all been considered in the Hydrotech patented design where key parameters like differential pressure, peripheral speed and back-wash pressure are based on years of R&D and operations experience and with consideration to experiences found in the literature (Ljunggren 2006).

A twill weave monofilament polyester filter cloth is the standard filter media for the Discfilter and the Drumfilter. Apart from being light and mechanically very strong, polyester has a good resistance against chemicals. Filters can be equipped with filter panels with nominal pore sizes ranging from 10 up to 1000 μm (for special applications, larger openings can be used).

Design exampleA tertiary treatment installation designed for a peak flow of 1100 m³/h and a maximum influent SS of 20 mg/l. 20 mg/l would, according to Hydrotech design guidelines, require a Discfilter HSF 2220, either in frame or tank version. The filter has a total filtration area of 112 m² and a footprint of 14 m² (walkways around the filter excluded).

The production of reject water, will be less than 1.4 % of the peak flow at maximum loading conditions. Compared to a sand filter the foot-print is very low, 6 – 7 times less area is required for the filters only.

Recipient

Figure 24. Tertiary treatment example

Primary treatment

Primarytreatment

Activated sludgetreatment

Secondarysettling

Discfilter

Peak flow: 1100 m3/hMaximum SS: 20 mg/l

Reject flow < 1. 5 %TS-content ~ 0. 1 %

5 mg SS/l

Hydrotech Municipal solutions Hydrotech Municipal solutions

1312

Delivery and installationHydrotech provides technical guidance notes for correct instal-lation of filter units. In order to prevent contamination of the fil-tered water in case of excessive flows or power failure, a separate by-pass facility is recommended. The tank versions, are available with an internal emergency by-pass and an outlet weir integral to the tank maintains the filtered water level.

Ideally the filters should be gravity fed however many installa-tions are pump fed due to lack of available head in the system.

Pilot testingWhere appropriate pilot testing can be carried out. The pilot filters are basically full-scale filters of the smallest models. Discfilter pilots are for example based on one or two discs, whereas in full-scale plants the number of discs and filters are extended in order to achieve the desired filtration area. There-fore, critical parameters in the pilot correspond to those in full-scale meaning that up-scale problems can be minimised. Pilot filters, instructions and test protocols are available from Hydrotech. Furthermore, technicians and engineers can assist in installation and start-up of pilot tests.

Figure 25. Tertiary treatment installation in the UK (tank version)

Figure 27. Test filter at pilot test

Access platform level

Emergency by-pass channel

Backwash pump Backwash strainer

Filtered water chamber

Final effluent channel

Influent channel

Backwash water outlet pipe

Figure 26. Typical lay-out of a Discfilter installation (frame version)

Reports and articles

Andersen, N. K., Cronqvist, C., Nielsen, P. Mathiasen, L. L., Albrechtsen, A., Bentsen, L. Construction and testing of a CSO treating combined sewage to bathing water quality standards. 10th International Conference on Urban Drainage, Copenhagen/Denmark, 21-26 August 2005.

Isaac, P. C. G., Hibberd, R. L. (1972). The use of microstrainers and sand filters for tertiary treatment. Water Research, Vol. 6, 1972.

Ljunggren, M. (2006). Microscreening in wastewater treatment – an overview. VATTEN 62, 2006.

Ljunggren, M., Alm L-G., Nilsson, B., Persson, E., Strube, R., Svensson, L., Jansen, J. la Cour. (2007). Microscreening in chemically enhanced primary treatment. Chemical Water and Wastewater Treatment IX.

Persson, E., Ljunggren, M., Jansen, J. la Cour, Strube, R., Jönsson, L. (2006). Disc filtration for separation of flocs from a moving bed biofilm reactor. Water, Science & Technology, vol. 53, No. 12, 2006.

Quinzanos, S., Dahl, C., Strube, R., Mujeriego, R. (2008) Helminth eggs removal by mi-corscreening for water reclamation and reuse. Water, Science & Technology, vol. 57, No. 5, 2008 (in press).

Sanz, J., Guerrero, L., Ortega, J. M., Ferrer, C., Miguel, D., Martinez, F. Application of the new solution ACTIDisc® on secondary effluent reclamation in Castellón de la Plana. Desalination 204, 189-197, 2007.

Hydrotech Municipal solutions Hydrotech Municipal solutions

1514

Reusing waste water

Baix Llobregat wastewater treatment plant in Barcelona, Spain

The plant is an activated sludge plant and one of Europe’s larger plants treat-ing the wastewater for approx. 2 million people and having a capacity of 420,000 m³ wastewater/day.

Approx. 4 million people live in and around Barcelona and also the majority of the Catalonian industry is located in this area.

The water supply to the town comes from groundwater as well as treated water from the river of Llobregat that is relatively saline.

Final effluent first treaden in 3 Actiflo units, followed by 10 Hydrotech’s Disc-filters before passing through a UV plant and sent for re-use.

10 Discfilters, HSF2220/18-2FN.

Baix Llobregat wastewater treatment plant

Hydrotech AB, A Veolia Solutions & Technologies CompanyMejselgatan 6, 235 32 Vellinge, SwedenPhone: +46 (0)40 - 42 95 30Fax: +46 (0)40 - 42 95 31E-mail: mailbox@hydrotech.seWeb site: www.hydrotech.se Copyright © All rights reserved

Hydrotech develops, manufactures and sells high performance filter systems. Our systems are used in more than 5000 installa-tions around the world, proof of the quality, re-liability and professionalism our customers have come to expect from Hydrotech.

Effluent polishing, stormwater, waterworks, pro-cess plants and fish farms are just some of the areas using Hydrotech’s water purification filters.