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Removal of micropollutants and nutrients using filter beds for on-site sewage treatment – column and field experiments
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik.
2017 (Engelska)Konferensbidrag, Muntlig presentation med publicerat abstract (Övrigt vetenskapligt)
Abstract [en]

On-site sewage treatment facilities (OSSFs) are widely applied in rural areas in the Nordic countries. A potential amount of phosphorus (P) and nitrogen (N) are released from these systems every year. The concerns are also about micropollutants (MPs), i.e. pharmaceuticals and synthetic organic compounds which are contaminating the environment and can affect the ecosystem and human health (Luo, 2014). About 40% of the OSSFs in Sweden use soil-based systems to treat wastewater (Olshammar, 2015) and sand is the most commonly applied media. The aim of this study was to evaluate the removal efficiencies of P, N and a number of MPs in filter beds and to find out the potential additional treatment efficiency which could be achieved by combining sand with other commercial filter materials.

Two bench-scale column experiments were performed during 2016 (Table 1). The first experiment was operated with saturated flow conditions during two weeks. The second experiment applied unsaturated flow conditions and was operated during twelve weeks.

The wastewater used in the experiment was spiked with a number of MPs to investigate their removal by the sand filtration. The MPs included pharmaceuticals, pesticides, biocides, plasticizers, fragrances, surfactants, UV-stabilizers, rubber additives and food additives. Weekly samples were taken for N, P and MPs analysis. Other parameters measured during the experiments included dissolved organic carbon (DOC), pH, turbidity and electric conductivity.

A field pilot plant was constructed in 2013 (Kholoma, 2016) with three subsurface parallel filter beds. Each bed had a length and depth of 1.5 and 0.8 m, respectively, and an upper surface area of 0.75 m2. The three filter beds were filled with sand, biochar and sand, biochar and Sorbulite® (a product based on gas concrete), respectively. The system was maintained for two and a half years prior the sampling (November 2016), where 24-hour composite water samples were taken from the influent and the effluent.

The average removal efficiencies of DOC, NH4-N and Ptot in column and field samples are presented in table 2. Compared with the sand filter, the added biochar layer improved the removal of DOC by 18% and the added Sorbulite layer increased both the DOC and total phosphorus removal efficiencies by 7%.

The MPs in the column experiment showed different removal efficiencies: Firstly, biocides (hexachlorobenzene and triclosan), pharmaceuticals (acetaminophen and caffeine), fragrance (musk xylene) and preservative (propylparaben) have been efficiently removed with an average removal above 90%. Secondly, a few organophosphorus flame retardants such as tributylphosphate and triphenylphosphate, perfluoroaklyl substances, UV stabilizer (benzophenone) and fragrances (musk ketone and galaxolide) had lower removal efficiencies in the range 51% and 81%. The sand did not remove most of pharmaceuticals very efficiently. Seven out of the nine investigated pharmaceuticals had removal efficiencies ranging between 17% and 48%, whereas four of them (diclofenac, oxazepam, losartan and carbamazepine) had an average removal efficiency lower than 30%.

A number of 47 MPs were identified in the field experiment samples with concentrations ranging from 0.1 ng L-1 to 46285 ng L-1. The removal efficiency varied depending on the type of filter media and MPs. The dual layer filter with biochar and sand provided a better removal of MPs (on average, 68%) than the other two filters (on average, 65% and 56% for sand and biochar + Sorbulite, respectively). In the future, to improve the removal efficiency of nutrients and MPs, the application of new filter materials to optimize the traditional filter bed is needed. The life span of sand and alternative sorbents were not considered in the column experiments, however it is one of the essential research tasks for future work.

Ort, förlag, år, upplaga, sidor
2017.
Nationell ämneskategori
Vattenteknik
Forskningsämne
Mark- och vattenteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-234671OAI: oai:DiVA.org:kth-234671DiVA, id: diva2:1246524
Konferens
S2SMALL 2017 (International IWA Conference on Sustainable Solutions for Small Water and Wastewater Treatment Systems)
Forskningsfinansiär
Forskningsrådet Formas, 216-2012-2101
Anmärkning

QC 20180910

Tillgänglig från: 2018-09-07 Skapad: 2018-09-07 Senast uppdaterad: 2018-09-10Bibliografiskt granskad

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