Two innovative devices for depth sampling in granular filtration systems Natalia Belkin a, 1 , Edo Bar-Zeev a, 1 , Tom Berman b , Ilana Berman-Frank a, ⁎ a Bar Ilan University, Mina & Everard Goodman Faculty of Life Sciences, Ramat Gan, Israel b Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, P.O.B. 447, Migdal 14950, Israel abstract article info Article history: Received 12 September 2011 Received in revised form 15 October 2011 Accepted 18 October 2011 Available online 20 November 2011 Keywords: Particulate and interstitial water sampler Dissolved oxygen sampler Rapid Sand Filtration Filter bed sampling Biofiltration Appropriate devices for obtaining either interstitial water or grain particle samples or for measuring dis- solved oxygen (DO) at depth within the interior of large-scale, industrial granular bed filters are currently lacking. We developed two innovative samplers for studying a Rapid Sand Filter (RSF) at an operational SWRO plant: the first for water and granular material, the second for DO measurements. 1. The particle and interstitial water sampler is based on a corer that retains grain particles inside a chamber using water suction created by an external peristaltic pump. 2. The DO sampler incorporates a temperature compensated oxygen measuring optode over which laminar water flow is maintained by an external peristaltic pump. To test these samplers, an operational, full-scale RSF at a SWRO plant was monitored at various depths within the filter bed over several months. Additionally, DO profiles within the filter bed were followed during and after a backwash cycle. These samplers enable efficient and precise collection of DO data, interstitial water, and granular material from previously inaccessible depth layers within the filter bed without interruption of the filter operation, providing information on microbiological processes such as biofilm development, mi- crobial community structure and organic matter cycling. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Gravity based granular medium filtration is widespread as a treat- ment procedure in wastewater purification [1] and pretreatment for seawater reverse osmosis (SWRO) desalination [2, 3]. To date various types of Rapid Sand Filters, (RSF) have been developed by the desali- nation industry as pretreatment to improve the quality of feed water prior reaching UF or RO membranes. The main mechanisms acting in these filters are mechanical retention, adsorption, sedimentation, chemical and microbiological processes [4, 5]. Several types of filter bed media are currently used; sand, anthra- cite [1] and activated carbon [6]. Full-scale granular filters normally operate with a media bed depth of 2 to 4 m [7, 8] overlaid with a 1 to 2 m water layer. The granular character of the filter bed makes it extremely difficult to sample either interstitial water or particulate medium at depths within the filter bed. Providing access by specially constructed sampling ports or sampling only upon complete draining of the filter [9] is either complicated to apply or interrupts the normal operation. As a result, most sampling has been limited to the upper 0.1-0.5 m of the filter bed [4, 9] and therefore relatively little detailed information is available about chemical or biological processes occur- ring within the filter bed of operational RSF's [10]. The operational efficiency of a granular filter depends on the optimal integration of many factors (media type, composition, hydraulic loading rates, fil- ter backwash intervals, extent of microbial degradation) [11]. De- tailed monitoring of chemical and biological processes occurring throughout the entire depth of the filter bed can provide important information on filter function during routine operation as well as suggesting possible strategies for improved design. In this paper we describe two new devices that enable accurate in situ sampling at all depths within granular filter beds. The first sam- pler enables the precise retrieval of interstitial water and granular particulates from any desired depth within the filter bed. The second device allows on line determination of in situ dissolved oxygen (DO) concentrations at any desired depth. Both samplers can be used in full scale RSF without interrupting filter operation. 2. Materials and Methods 2.1. Sampler description 2.1.1. Filter bed medium and interstitial water sampler The combined particulate and water sampler is shown in Fig. 1. The hollow segmented body of the sampler is constructed from two segments of a solid brass block. The inner part of the lower segment forms a tapered chamber in which particulate grain samples of the media are retained. The chamber opening at the bottom is narrower at the lower end (8 mm diameter) than at the upper end (12 mm di- ameter). During insertion into the filter bed, this increases the down- ward pressure of the water jet (see 2.1.1.1) and prevents any grains of Desalination 286 (2012) 115–119 ⁎ Corresponding author. Tel.: + 972 3 5318214; fax: + 972 4 6914842. E-mail address: ilana.berman-frank@biu.ac.il (I. Berman-Frank). 1 Contributed equally to this work. 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.10.031 Contents lists available at SciVerse ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal