Henriksdals reningsverk ägs av Stockholm Vatten och är ett av Europas störstaavloppsreningsverk som är helt beläget under marken. Grundläggande för att den biologiska reningsprocessen skall fungera är att en stor mängdmikroorganismer eller slam hålls kvar i de biologiska bassängerna. Detta sker idag genom attslammet får sjunka i eftersedimenteringsbassänger varifrån det cirkuleras tillbaka tillbiobassängerna. Periodvis, när flödena in till verket är höga, räcker inte kapactiteten i det biologiskareningssteget till. Vid sådana tillfällen finns idag två drifttekniska möjligheter:- Försedimenterat avloppsvatten leds förbi det biologiska reningssteget till sandfilter.- Försedimenterat avloppsvatten förbileds både det biologiska reningssteget ochsandfilter, d.v.s. bräddas till utloppet. Konsekvensen av förbiledning och bräddning är att utsläppshalterna av föroreningar ökar ivattnet som släpps ut. I det fall då vattnet endast leds förbi det biologiska steget, ökarbelastningen på sandfiltren samt risken för igensättning. För att lösa dessa problem på längre sikt kommer en stor ombyggnation ske där ny teknikska sättas in i det biologiska reningssteget. Under ombyggnaden kommer kapaciteten förden biologiska reningen att minska eftersom delar av den biologiska reningen måste tas urdrift när den nya tekniken installeras. Detta leder till att förbiledning och bräddning blir ännustörre under ombyggnaden. På grund av detta finns det ett intresse att öka reningen av förbigående och bräddat vattengenom att utöka den befintliga förfällningen med andra typer av fällningskemikalier. Uppgiften var därför att undersöka och jämföra två fällningskemikalier i stor skala genom atttillsätta dem, var för sig, direkt till försedimenteringen. Kemikalierna som testades varjärn(III)klorid (PIX-111) och polyaluminiumklorid (PAX-21). Först gjordes flockningstester ilabbskala för att bestämma hur stor dos som skulle doseras vid de storskaliga försöken. Resultaten från labbförsöken visade att en bra dos för PIX var 0,12 ml PIX/l vatten och att enbra dos för PAX var 0,10 ml PAX/l vatten.Resultaten från det storskaliga försöket med PAX visade en hög reduktion av turbiditet ochSS halt. Både reduktion av turbiditet och reduktion av SS låg mellan 50-75%.Resultaten från det storskaliga försöket med PIX visade inte en lika stor reduktion som PAX.Reduktionen av turbiditet låg runt 20 % vid de flesta proverna, med ett maxvärde på 36,8%.Reduktionen av fosfat var desto tydligare och låg mellan 70-80%. Under projektets gång vardet endast PAX som testades under högflöden på grund av uteblivet regn. Detta medför attingen rättvis jämförelse kan göras mellan kemikalierna innan PIX också testats vid högflöden. / Henriksdal wastewater treatment plant is one of the largest plants in Europe located underthe ground. The wastewater is treated mechanically, chemically and biologically. The basic concept for the biological treatment to work properly is that the amount ofmicroorganisms is kept at a high level. This is done by recirculating some of the sludge backto the biological pools. Periodically, when the flow into the plant is very high, the capacity ofthe biological step is not sufficient. At these times, there are currently two possible options:- Pretreated water is directed past the biological treatment to the sand filters.- Pretreated water is directed past the biological treatment and the sand filtersstraight out to the recipient. To solve these problems, Henriksdal is planning a reconstruction of the biological treatment.During the reconstruction, the capacity of the biological treatment is going to be even lessthan it is today. Hence there is an interest, at high flows, to increase the purification in the pre-precipitationstep with new types of precipitation chemicals. The aim of this project is to examine two different precipitation chemicals in lab- and in largescale. This was done by flocculation tests in the lab with a flocculator to determine thedosage for each chemical to be tested in large scale. The two chemicals that were testedwere iron chloride (PIX-111) and polyaluminiumchloride (PAX-21). The results from the labtests showed that an optimal dose for PIX was 0,12 ml PIX/l water.While the optimal dose for PAX was 0,10 ml PAX/l water. The results from the large scale test with PAX showed a high reduction in both turbidity andsuspended particles. The reduction of both was between 50-75 %. The results from the large scale test with PIX did not show as high reduction as that of PAX.The reduction of turbidity was around 20 %, with a maximum value of 36,6 %. The reductionof phosphate was between 70-80 %. During the project there were only a few days of high water flows and only PAX could betested during these conditions. Hence, the two chemicals cannot be compared accuratelyuntil also PIX is tested during high water flows

The aluminium content of water extracts is an important aspect for the food safety of paper board, as the content indicates the ability of the paper board material to transfer aluminium to the packaged food product. Aluminium intake in humans and its health effects have been discussed for many years as some research has seen potential links between, among other things, high aluminium levels in the brain and the development of hereditary Alzheimer's.BfR's method and recommendation is the one that is generally followed by producers around the world, as there is no common international law. The method involves leaving small pieces of the paper board in Milli-Q water for 24 hours, before a content determination of Al is made in the formed water extract. In 2021, BfR halved its recommended limit for aluminium in aqueous extracts from 2 mg/L to 1 mg/L. For Stora Enso Skoghall, this led to some of their paper board grades not meeting this limit.A specific liquid packaging board grade that previously did not meet BfR's new limit was selected and alum as a flocculant was replaced with PAC, among other things. The aim was to investigate whether the change in flocculation chemical, as well as varying dosages, could affect the Al content in water extracts and whether PAC could possibly result in a lower Al content. The method for the water extracts and their effect on the final Al content have also been investigated further. This is done by performing the BfR method with artificial tap water as well, and then comparing the Al content in these extracts.PAC as a flocculant instead of alum did not result in lower levels of Al in the water extracts. Variations in dosage and production without aluminium-containing flocculants also did not significantly affect the Al content of the extracts. The type of water used in the analysis turned out to play a major role in how much aluminium migrated from the board. All samples extracted in artificial tap water resulted in Al levels less than the 1 mg/L limit. For the majority of the samples extracted in Milli-Q water, the Al levels were instead closer to 2 mg/L. The difference in Al content between the water extracts is believed to be mainly due to differences in pH and thus varying amounts of soluble aluminium.The results showed a relatively large variation between the two external laboratories used. This is believed to be mainly due to variations in method and measuring equipment, but one must also consider the small sample size that was tested and what variations it entails.