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Author:Zolas, Sophia
Title:Mixed bed -suodatus osana vedenpuhdistusprosessia
Mixed bed filtration as a part of water treatment process
Publication type:Master's thesis
Publication year:2010
Pages:114      Language:   fin
Department/School:Insinööritieteiden ja arkkitehtuurin tiedekunta
Main subject:Vesihuoltotekniikka   (Yhd-73)
Supervisor:Vahala, Riku
Instructor:Hiillos, Kirsi
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto     | Archive
Keywords:alkalinization
filtration
limestone
mixed bed
surface water
water treatment
alkalointi
kalkkikivi
mixed bed
pintavesi
suodatus
vedenpuhdistus
Abstract (eng): This research is about studying the feasibility of a mixed bed filter to the water treatment process of Pitkäkoski water treatment facility at HSY Vesi in process scale.
The filter bed of the mixed bed filter consisted of 1/3 of Nordkalk Parfihl 2/1500 crushed limestone and 2/3 of crushed quartz sand.
The grain size of the crushed limestone was approximately 0,5 - 1,5 mm and of the quartz sand about 0,5 - 1,0 mm.
In the beginning of the study the height of the filter bed was about 1,1 m.
The functioning of the mixed bed filter was compared to that of a plain sand filter.
The water that was filtrated by both filters came from the clarification process.

The mixed bed filter reduced particles from the water far better than the sand filter.
This showed by high turbidy and iron reduction.
Due to the excellent particle constraint the head loss in the mixed bed filter increased more rapidly than iii the sand filter.
The back wash interval of the mixed bed filter was over twice the time compared to that of the sand filter.

Due to the dissolution of the limestone the pH, alkalinity and hardness of the water increased as it streamed through the filter bed.
Simultaneously some of the carbon dioxide in the water was consumed.
As the limestone dissolved the height of the filter bed decreased leading to an ever briefer contact period.
Consequently the filter's ability to raise the pH, alkalinity and hardness of the water decreased as the limestone dissolved away.
The dissolution rate of the limestone was approximately 24 g/m3.

According to this study it is recommendable to replace as many sand filters in the process as possible with mixed bed filters.
The crushed limestone should he added frequently and small amounts at a time to avoid pH peaks.
The higher the pH of the filter appartment can be raised to the higher the alkanity of the water will be.
Thus during the rest of the treatment process the need for alkalinisation decreases and less chemicals are needed, which leads to decreasing chemical costs.
Abstract (fin): Tutkimuksessa tutkittiin laitosmittakaavassa mixed bed -suodatuksen soveltuvuutta osaksi HSY Veden Pitkäkosken vedenpuhdistuslaitoksen pintavedenpuhdistusprosessia.
Mixed bed -suodattimen suodatinmateriaali oli 1/3 Nordkalk Parfill 2/1500- kalkkikivirouhetta ja 2/3 murskattua kvartsihiekkaa.
Kalkkikivirouheen raekoko oli noin 0,5 - 1,5 mm ja hiekan 0,5 - 1,0 mm.
Suodatinpatjan lähtökorkeus oli noin 1,1 m.
Mixed bed -suodattimen toimintaa verrattiin hiekkasuodattimen toimintaan.
Suodattimille tuleva vesi oli selkeytettyä vettä.

Mixed bed -suodatin poisti huomattavasti hiekkasuodatinta paremmin partikkeleita vedestä.
Tämä näkyi sameuden poistossa ja rautareduktiossa.
Erinomaisesta partikkelien pidätyskyvystä johtuen mixed bed -suodattimen paine-ero kasvoi nopeammin kuin hiekkasuodattimen.
Mixed bed -suodattimen pesuväli oli yli kaksinkertainen hiekkasuodattimen pesuväliin verrattuna.

Kalkin liukenemisesta johtuen veden pH, alkaliniteetti ja kovuus nousivat sen virratessa suodatinmateriaalin läpi.
Samalla vedestä kului hiilidioksidia.
Kalkin kuluessa suodatinpatjan korkeus pieneni, jolloin kontaktiaika myös lyheni.
Siitä johtuen suodattimen pH:n, alkaliniteetin ja kovuuden nostokyky pieneni tasaisesti sitä mukaa, kun kalkkia kului.
Kalkin kulumisnopeus oli noin 24 g/m3.

Tutkimuksen perusteella olisi suositeltavaa korvata mahdollisimman moni suodatusosaston hiekkasuodattimista mixed bed -suodattimilla.
Kalkkia kannattaa lisätä suodattimiin usein ja pieniä määriä kerralla, jotta vältytään pH- piikeiltä.
Mitä korkeammaksi suodatusosaston pH:n voidaan antaa nousta, sitä korkeampi on alkaliniteetti lähtevässä vedessä ja sitä vähemmän alkaloivia kemikaaleja veteen tarvitsee syöttää prosessin loppuosassa, mikä alentaa kemikaalikustannuksia.
ED:2010-09-27
INSSI record number: 40978
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