Water Journal : Water Journal May 2011
wetlands for wastewater treatment water MAY 2011 103 Abstract Wastewater from CSBP, a chemical and fertiliser manufacturer in Kwinana, Western Australia, comprising stormwater and low-strength process effluent, is diverted to a wastewater containment pond and treated via a series of nutrient stripping wetlands, prior to discharge to the Sepia Depression Ocean Outlet Landline (SDOOL). Firstly, wastewater is successfully nitrified in two fill-and- draw wetland cells operated in parallel. Subsequently, denitrification takes place with the addition of external carbon in a constantly saturated wetland. In an example of industrial synergy, high organic carbon waste streams from neighbouring industries have been dosed into the saturated wetland in order to improve nitrogen removal. Introduction The recognition of constructed wetlands for reliably treating industrial effluents is on the rise in Western Australia. Evidence of this is the recent construction of two full-scale vertical flow (VF) wetlands at CSBP Ltd, a chemical and fertiliser manufacturer in Kwinana, 40km south of Perth. CSBP upgraded its wastewater treatment train in 2009 by adding two VF wetland cells of 8,000m2 each to the already existing 12,000m2 saturated surface VF wetland, expanding the total wetland area to 2.8ha (Figure 1). The inorganic wastewater generated is characterised by high nitrogen, predominantly NH3-N, phosphorus and TDS content (and low COD and TSS). The System The treatment system includes a containment pond which serves as an equalisation and settling basin. From the containment pond water is alternately pumped into the parallel VF wetlands. Rather than intermittently fed free- draining systems, these cells operate in a sequencing batch (fill and draw) mode. Batches are ideally up to 1,600m3/day, but can be higher than 2,000m3/day depending on rainfall and wastewater production. Operation is usually 12hr- filling, 12hr-full, 12hr-draining and 12hr- resting empty. While one cell is filling, the other one is emptying, then resting, and vice versa. The nitrified effluent from the parallel VF cells is pumped into the six-year-old saturated-surface VF system which has woodchips incorporated in the substrate and on the top of the sediment. A full description and performance data for this cell alone can be found in Domingos et al. (2009). The new VF wetlands have an HDPE liner covered by geotextile and incorporated a 20cm drainage layer of blast furnace slag covering the drainage pipes on the bottom (Figure 2). This layer consists of 15cm of 14mm slag on the bottom and a 5cm intermediate layer of 7mm slag on top (to avoid sand wash down into the slag layer). In an example of industrial synergy, CSBP has used slag from Kwinana neighbour HiSmelt (slag being a by-product of HiSmelt's smelting activities) as the aggregate for the new wetland cells. The sand used for the 50cm main filtering layer was locally available from the site (Kwinana sits on a sand dune). This fine sand (0--0.5mm), however, would not be suitable for VF wetlands treating wastewaters with a BOD and TSS content, due to clogging potential. The combination of the local carbonaceous sand and the furnace slag was to provide good phosphorus retention capacity and alkalinity to support nitrification in the VF wetlands. The inlet pipe has several spreaders to allow even distribution of water across the surface (Figure 3). Seedlings were sourced from a local nursery and included native Schoenoplectus sp., Juncus sp. and Isolepis sp. (Full aerial photographic coverage of the construction can be scrolled at www.nearmap.com/?II=- 32.237093,115.7631&z=18&t=k&n md=20110314.) SS Domingos, S Dallas, S Felstead The largest combination of vertical flow wetlands in Australia is at a chemical and fertiliser manufacturer in Kwinana VERTICAL FLOW WETLANDS FOR INDUSTRIAL WASTEWATER TREATMENT VF 8,000m2 ontainment pond Saturated VF 12,000m2 C Nitrification Denitrification Sepia Depression Ocean Outfall (Water Corporation) Influent 1 2 3 VF 8,000m2 Potential recirculation/reuse Figure 1: Treatment train at CSBP showing the two new VF wetlands operating in parallel and the six-year-old saturated surface VF wetland. The circle with the letter C going into the saturated VF cell indicates the addition of high carbon content wastewater into the wetland to favour nitrate removal. The numerals 1, 2 and 3 indicate sampling points. Figure 2: The drainage layer taking shape -- spreading the intermediate 7mm blast furnace slag on top of the 14mm layer. Note the "air" pipes which connect to the drainage system under the slag coming up in the centre and on the batter (far end).
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