Albrechtsen, Hans-Jørgen

Lee, Carson Odell

Nielsen, Peter B.

Smets, Barth F.

Tatari, Karolina

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 19, 2017Examining biological sand filters for drinking water treatment as biofilm reactors:experimental and modeling approachTatari, Karolina; Smets, Barth F.; Lee, Carson Odell; Nielsen, Peter B.; Albrechtsen, Hans-JørgenPublication date:2013Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Tatari, K., Smets, B. F., Lee, C. O., Nielsen, P. B., & Albrechtsen, H-J. (2013). Examining biological sand filtersfor drinking water treatment as biofilm reactors: experimental and modeling approach. Abstract from  IWA 9thinternational Conference on Biofilm Reactors, Paris, France.Examining biological sand filters for drinking water treatment as biofilm reactors: experimental and modeling approach Karolina Tataria, Barth F. Smetsa, Carson Leea, Peter B. Nielsen b and Hans-Jørgen Albrechtsena aDepartment of Environmental Engineering, Bygning 113, DTU, 2800 Lyngby, Denmark *kaot@env.dtu.dk b Krüger A/S, Gladsaxevej 363 Søborg, 2860 Denmark Rapid sand filtration is a widespread technology in drinking water treatment. Operation is simple and aims to retain particles and remove compounds such as NH4+, Fe and Mn. Filter design and operation is mainly based on rules of thumb. Lack of knowledge on the specific processes taking place in the filters limits optimization of filter performance. NH4+ is removed biologically by autotrophic microorganisms attached on the sand grains. The conventional approach considers a rapid sand filter as a homogenous unit and nitrification rate is averaged over filter depth. In this study we approach a rapid sand filter as a biofilm reactor aiming to interpret and predict filter performance. The study was composed of NH4+ depth profiling in a full scale filter, core sampling of sand and nitrification activity measurements in different depth layers with a lab scale assay. Experimental observations were interpreted with a biofilm model ultimately used to predict full scale filter performance.  Islevbro waterworks, Denmark was selected for the experimental investigations. The facility consists of two filtration stages. Influent NH4+ is mostly removed in the after filters to comply with the guideline value (0.05 mg/L). A multi level water sampler was installed in the full scale filter. Water samples were collected every 5-10 cm depth up to 40 cm to construct the NH4+ depth profile in the filter (Figure 1). Influent NH4+ was removed within the upper 10 cm of the filter in all sampling rounds. NH4+- N (mg/L)0.00 0.05 0.10 0.15Filter depth (cm)010203040 Figure 2: NH4+ depth profile in the full scale filter Sand was sampled from three depths of the full scale filter: 0-10 cm, 20-30 cm and 35-50 cm with a core sampler. Nitrification activity of the three filter regions was quantified in a lab scale assay. The experimental set up consisted of three independent columns, each packed with sand from one depth layer. Column dimensions were small (5 cm bed height and 2.6 cm inner diameter) to avoid stratification of nitrification activity within the lab-scale column. The columns were continuously fed with a 1 mg/L NH4+ solution and the influent flowrate was adjusted to obtain the same NH4+ volumetric loading rate of in the full scale filter. The effluent was monitored for all nitrogen species and dissolved oxygen.  To determine nitrification kinetics, the loading rate was increased for short periods of time (3-5 h) by increasing the influent flowrate. Volumetric removal rate was calculated from the NH4+ flux normalized over the packed sand volume in the for the three investigated filter depths (Figure 2). Loading rate (g NH4+- N/ m3 sand/ h)0 2 4 6 8 10 12 14Removal rate (g NH4+-N/ m3  sand/ h)02468100-10 cm20-30 cm 35-50 cm Figure 2: Volumetric NH4+ removal rate observed in the lab scale assay for sand obtained from three full-scale filter depths. Sand from the top 10 cm was significantly more active than deeper layers of the filter reaching removal rates up to 10 times higher compared with the middle and bottom filter layers. This clearly showed that nitrification activity was stratified with filter depth. These observations were supported by the full scale filter NH4+ profile, where NH4+ was mainly removed in the top 10 cm. Lower nitrification rates in the deeper layers were a result of low substrate concentration available for nitrifying microorganisms in these depths. However, nitrification activity detected here may function as extra nitrification capacity in case NH4+ is pushed deeper in the filter.  The lab scale observations were interpreted by a model that considered a biofilm attached on the external surface of the sand grains. Biofilm thickness was 30 µm as estimated by microscopic images. Cell abundance of specific microorganisms (ammonium and nitrite oxidizers) as determined by qPCR measurement was used to define the biofilm composition. The model assumed diffusion of substrates (NH4+ and O2) through a boundary layer with a calculated thickness of 40 µm. Two step nitrification with intermediate NO2- production was considered and the model was fitted to the experimental results to estimate kinetic parameters. The next step aimed to combine the lab scale column models for the different depth layers into a full scale filter model. Conceptually the full scale filter can be split into fractions, each of them approximated by one lab scale column model. Connecting the models of the different depths in series can simulate the performance of the full scale filter, predicting the NH4+ and NO2- effluent concentrations at a range of influent loading rate conditions. Loading rate variations are common due to switching between abstraction wells that have different water quality. These variations are a suspected cause of NH4+ breakthrough in several filters.  In this study we examined nitrification activity stratification in a filter. This differs from the traditional column approach, where NH4+ removal is averaged over filter depth. Nitrification activity was concentrated at the top of the filter. Physical observations were used to build a biofilm reactor model that interprets and predicts filter performance.  

Examining biological sand filters for drinking water treatment as biofilm reactors: experimental and modeling approach

http://orbit.dtu.dk/ws/files/59872757/prod21383666918205.Biofilm_13_proceedings_abstract.pdf

Examining biological sand filters for drinking water treatment as biofilm reactors: experimental and modeling approach

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology