THE USE OF STORMDMT TECHNOLOGY AS A LOW COST SOLUTION TO REMOVE METALS FROM STORMWATER RUNOFF

Transcription

1 THE USE OF STORMDMT TECHNOLOGY AS A LOW COST SOLUTION TO REMOVE METALS FROM STORMWATER RUNOFF. A BULK STORAGE FACILITY CASE STUDY IN PORT OF TOWNSVILLE Dr Konstantinos Athanasiadis 1, Paul McFadyen 1, Martin Brennan 2 1. GHD Pty Ltd, Brisbane, QLD 2. GHD Pty Ltd, Townsville, QLD ABSTRACT A full scale pilot trial was undertaken at a bulk storage facility in the Port of Townsville handling the following chemicals: Magnetite Concentrate Copper Concentrate Zinc Concentrate and Ammonium Sulfate Fertiliser. Aim of the pilot trial study was to evaluate the performance of the StormDMT technology, a low cost passive multi barrier treatment system, for the treatment of the stormwater runoff generated onsite. Factors such as hydraulics (0 to 100 l/s), stormwater runoff quality, and metal speciation (particulate, dissolved and colloidal) were investigated. StormDMT metal removal efficiency for zinc mass was 90%, Copper 85% and lead 80%. Metal concentrations at the outlet of the StormDMT filter were always lower than the regulated site discharged limits. Considering the site relevant stormwater runoff rates of copper, zinc and lead, the StormDMT technology demonstrated a minimum maintenance life of two years. INTRODUCTION The pilot trial catchment at the Bulk storage facility in the Port of Townsville covers a total area of 3,000 m 2. Pilot Plant Descripiton Pilot plant trials treated: stormwater runoff exceeding first flush capacity of the relevant sump first flush water (first 15 mm of stored stormwater runoff) after precipitation with lime and process water after precipitation with lime. The process water is generated during the washdown of the catchment/equipment between rain events (long dry weather periods) to minimise the contamination of stormwater runoff. In a rainfall event the sump was capturing approximately the first 15 mm of the stormwater runoff generated across the sump s catchment, including the runoff from a zinc metal roof. The excess stormwater runoff was overflowing the existing weir into the StormDMT filter system via a penstock and then the treated stormwater was gravitating into the existing stormwater pipeline network system. First flush water was captured in the sump from either rainfall events or catchment washdown cleaning process (process water). The first flush or the process water was then tested for ph, dosed with lime if necessary to raise the ph to 8.3 and tested for a suit of metals before being pumped to the StormDMT filter to remove remaining metal concentrations. The StormDMT multi barrier filter (see Figure 1) comprised three filtration media which have been designed to remove fine solids, colloidal bound and dissolved contaminants such as metals and nutrients such as Nitrogen and Phosphorous. The first media is a porous polypropylene/polyethylene mixture. This material removes Oil & Grease and fine particulate matter which may foul subsequent media. The second media is chemically conditioned natural zeolitic material, clinoptilolite.this material removes dissolved positively charged metals. The third media, laterite, also removes dissolved metals, including negative charged and performs an additional function as a polishing step. Figure 1: The StormDMT Filter System Monitoring Process Flow based auto samplers were installed at three different tube intake strainers: The inflow stormwater pipeline to the StormDMT multi barrier filter system The outlet stormwater pipeline of the StormDMT multi barrier filter system and

2 A sampling channel at the downpipe of the rainwater tank receiving the roof runoff water from an old zinc roof. All three autosamplers were programmed to sample on the same flow basis. Sampling initiated on flows greater than 2 L/s, measured by an installed flowmeter. While flows remained above 2 L/s sampling continued at a rate of one sample every 3 minutes. Samples were taken for up to a maximum of 144 minutes of a rainfall event (3 minute intervals * two samples per sample bottle * 24 bottles). Each sample was analysed for: ph, temperature, electrical conductivity, total dissolved solids, total oxidised sulphur, total suspended solids, total and dissolved metals, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, total phosphorous, chemical oxygen demand, total petroleum hydrocarbons, total recoverable hydrocarbons and BTEX surrogates. DISCUSSION AND RESULTS Catchment Quality Six rain events were sampled from the respective catchment stormwater runoff during the 2012/2013 wet season. The ph value of stormwater runoff varied from 4.5 to 7.1 with an average value of 6.6. The average concentration of suspended particles in the first 15mm of a rain event was 20.7 mg/l and remained constant for the rest of the rain event. Similar results were obtained for the metal concentrations of concern. This indicates stormwater runoff quality is reaching the average concentration much earlier than the 15 mm sump storage rain event capacity, thus any reduction of the sump storage capacity down to 5 mm may not significantly affect the stormwater runoff quality entering the StormDMT multi barrier filter system. Similar results in regard to the first flush effect with respect to metal concentration in stormwater runoff have been reported by Lee et al., (2002), Sansalone et al., (1997) and by Athanasiadis et al., (2010). As expected, the amount of metals washed off the catchment surface area during sampled rain events depended on the dry period preceding rain events and any applied operational wash-down regimes for the specific catchment. The major pollutant in stormwater runoff for the catchment was zinc. The minimum concentration of zinc was 1.08 mg/l and the maximum concentration 13.8 mg/l. The phase distribution of zinc concentration in the stormwater runoff was almost equally divided between particulate (44.8%) and dissolved (55.2%). The copper concentration in stormwater runoff varied from 0.28 mg/l to 1.59 mg/l. The copper phase distribution was 62.1% particulate and 37.9% dissolved. The lead concentration in stormwater runoff varied from 0.19 mg/l to 1.73 mg/l. As expected, the phase distribution of lead concentration was dominated by the particulate phase (79.3%). The concentrations of other metals such as cadmium and nickel were either under the detection limit or extremely low. Particle size distribution measurements were undertaken to define treatment requirements (Table 1). The results illustrate a requirement for a fine filtration step to comply with the site regulated metal discharged limits. Table 1: Particle Size Distribution in Samples Sample 90 th percentile (µm) 50 th percentile (µm) 10 th percentile (µm) Roof Water Quality Four rain events were sampled from the zinc roof runoff during the pilot. The ph value varied from 6.2 to 6.6; the mean value was 6.3 which is considered typical for runoff from a zinc metal roof. The average concentration of suspended particles was 7.9 mg/l. This concentration increased up to 29 mg/l at the beginning of a rain event and reduced by up to six times during the remaining rain event. Similar results have been reported by Gromaire et al. (1999), and Athanasiadisis et al. (2004), for the city of Paris and Munich respectively. The copper concentration in roof runoff, mainly originating from dust deposit on the roof between rain events, varied between and 7.12 mg/l with a mean copper concentration of mg/l. As was expected, high amounts of zinc were washed from the oxidised zinc roof surface during all rain events. After rainwater contacting the roof material the concentration of zinc in roof runoff increased significantly. At the beginning of the rain event the concentration of total zinc in the roof runoff varied from 1.54 to 84.2 mg/l and remained as high as 11.2 mg/l (mean value) throughout the rain event. The phase distribution of zinc concentration in roof runoff was clearly dominated by the dissolved phase (65.1% at the beginning of the rain event and almost 94.3% during the remaining rain event). He et al., (2001) reported zinc concentrations in roof runoff for newly coated zinc sheets ranging between 2.8 and 4.7 mg/l. Depending on the type of roofing material and the pre-treatment process (e.g. coated zinc, painted zinc, pure zinc, galvanised zinc) runoff concentrations between 0.1 and 10 mg/l are also reported. Gromaire et al., (1999) as well as Athanasiadis et al., (2004) reported concentrations of zinc in roof runoff varying from 5.6 to 38.1 mg/l with the concentration of zinc remaining as high as 7 mg/l throughout the rain event. It is anticipated that the extremely high zinc concentrations observed in roof

3 runoff during this trial are the result of the deteriorating roof condition (see Figure 2). The concentration of lead in roof runoff varied from mg/l to 4.5 mg/l with a mean concentration of mg/l. The high concentration of lead in the roof runoff is believed to result either from the sealing material used to seal the zinc sheets or from lead polluted dust deposited on the roof between rain events. The phase distribution of the lead concentration in the roof runoff was dominated by the particulate phase at the beginning of the rain event (87.4%), reduced to almost 62% for the remaining of the rain event. Figure 2: Zinc Roof Remains in Roof Water The concentrations of the rest of the metals were of limited significance as they were either under the detection limit or extremely low such as arsenic and nickel. Particle size distribution measurements were undertaken to define the treatment requirements (Table 2). The results demonstrated a requirement for a fine filtration step in order to comply with the site regulated metal discharged limits. Table 2: Particle Size Distribution in Roof Samples Sample 90 th percentile (µm) 50 th percentile (µm) 10 th percentile (µm) Pilot Plant Performance During the 2012/2013 wet season pilot trials of the StormDMT TM multi barrier treatment system were conducted on treatment of: stormwater runoff overflowing from the relevant sump during the recorded rain events process washdown water and first flush water stored in relevant sump. Details of the trials are provided in Table 3 below. Pilot Plant Trial Table 3: Pilot Plant Trial Details Type of Trial Limed Process Wash-down Water Limed First Flush Water Volume of entering the StormDMT Filter (m 3 ) 436 The retention capability of the multi barrier filter concerning copper concentration is illustrated in Figure 3. The copper concentration exiting the StormDMT multi barrier filter system was significantly below the discharged limit of 0.1 mg/l for almost all trials. Two outlier samples during the 1st recorded rain event exceeded the discharged limit resulting from particulate bound copper forcing its way through the barrier filter materials as a result of the high stormwater runoff flow rates. It should be noted that during the same rain event the dissolved copper concentration was by far lower than the discharged limit. The result demonstrates the importance of fine filtration such

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5 Figure 3: Performance of StormDMT Multi Barrier Filter System Concerning Copper Elimination

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7 Figure 4: Performance of StormDMT Multi Barrier Filter System Concerning Lead Elimination

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9 Figure 5: Performance of StormDMT Multi Barrier Filter System Concerning Zinc Elimination

10 as sand/cloth filtration prior to the barrier filter system to trap copper bounded particles. Additionally, the copper concentration in two samples at the outlet of the StormDMT filter system during the limed first flush water trial was slightly higher than the discharged limit. The causal analysis for this result is presented in conjunction with the discussion of zinc concentration results below. Copper load entering the StormDMT multi barrier filter during the pilot trials was g. The filter system retained g, a copper mass removal efficiency of 85%. The retention capability of the StormDMT multi barrier system for lead is presented in Figure 4. Lead concentration at the outlet of the StormDMT multi barrier filter system was lower than the regulated lead discharged limit of 0.1 mg/l for all trials except during the 1st recorded rain event. As identified above in our analysis of copper concentrations the cause was identified as particulate bound lead forcing through the filter as a result of the high flow rates. Dissolved lead concentration exciting the filter system were far lower than the discharged limit. Fine filtration upstream of the StormDMT multi barrier system is required to ensure compliance with the regulated site discharged limit. The lead load entering the multi barrier system during the pilot trials was g, with the StormDMT multi barrier filter system retaining g, a lead removal efficiency of 80%. The retention capability of the filter system concerning the zinc concentration is illustrated in Figure 5. It can be seen that the zinc concentration exciting the StormDMT filter system was always lower than the regulated zinc discharged limit both for total and dissolved for all trials including trial number 9. The zinc load entering the StormDMT filter system was 2,655.2 g and was able to retain 2,393.6 g, thus achieving zinc mass removal efficiency of 90.1%. During the 10 th trial (Limed First Flush Water), a clear breakthrough of zinc concentration from the StormDMT filter system occurred, demonstrating the clinoptilolite barrier material reached its saturation limit for the specific feed concentration, ph and flow rate. Zinc concentrations exciting the StormDMT filter system during the 14 th trial fluctuated around the total zinc regulated discharged limit and was clearly lower during the 15 th rain event trial, although the feed flow rate and the ph remain similar with the 10 th trial. This is due to the feed zinc concentration dropping from 30 mg/l on the 10 th trial to 7 mg/l for the 14 th trial and to approximately 3 mg/l for the 15 th trial. Such behaviour is typical of all zeolitic systems in regard to the impact of speciation concentration (linear relation) on the operating sorption capacity of the zeolitic material (Athanasiadis 2005). The high feed zinc concentration of 30 mg/l on the 10 th trial was due to inappropriate liming process of the stored stormwater runoff in the relevant sump. Although it was reported that the ph of the stormwater in the sump after liming was 8.3, the laboratory results have reported a feed ph to the StormDMT filter system of 6.7. The zinc load contribution to the sorption capacity of this specific trial was 900 g and it demonstrates the importance of automating the procedure of adding lime to precipitate the extremely high metal concentrations in the first flush stormwater runoff and in the process washdown water stored in the sump. CONCLUSION The following key conclusions can be drawn from the pilot trial study undertaken: The StormDMT multi barrier filter system has demonstrated metal removal efficiency of 90% in regard to zinc, 85% for copper and 80% for lead, with concentrations at the outlet of the filter system always lower than the regulated discharged limits. The stormwater runoff quality is reaching the average contaminant concentration significantly earlier than the 15 mm storage rain event capacity. Any reduction of the storage sump capacity down to 5 mm may not affect stormwater runoff quality variability. The major pollutant in stormwater runoff is zinc with a minimum concentration of 1.08 mg/l, a maximum of 13.8 mg/l and an average 4.06 mg/l. The phase distribution of zinc concentration in the stormwater runoff was almost equally divided between particulate (44.8%) and dissolved (55.2%). The copper concentration in stormwater runoff varied from mg/l to 1.59 mg/l with the average concentration at mg/l. The copper phase distribution was similar to zinc with 62.1% particulate and 37.9% dissolved. The lead concentration in stormwater runoff varied from mg/l to 1.73 mg/l with the average concentration at mg/l. As expected, the phase distribution of lead concentration was dominated by the particulate phase (79.3%). High amounts of zinc were washed from the zinc roof surface during all rain events. After contacting the roof material the concentration of zinc in roof runoff increased significantly. At the beginning of the rain event the concentration of total zinc in the roof runoff varied from 1.54 to 84.2 mg/l and remained as high as 11.2 mg/l (mean value) throughout the rain event the phase distribution of zinc concentration in roof runoff was clearly dominated by the dissolved phase (65.1%) at the beginning of the rain event and almost 94.3% during the remaining rain event there is a requirement for a fine filtration step to successfully treat the catchment stormwater runoff as well as the roof runoff because of the particulated bound metal concentration the limiting factor for the final design of the site stormwater treatment system is the zinc concentration and its phase distribution both in

11 the stormwater runoff as well as in the roof runoff. REFERENCES Athanasiadis, K., Helmreich, B., & Wilderer, P. A Elimination of zinc from roof runoff through geotextile and clinoptilolite filters. Acta Hydrochimica Et Hydrobiologica, 32(6), Athanasiadis, K., Horn, H., & Helmreich, B A field study on the first flush effect of copper roof runoff. Corrosion Science, 52, Gromaire-Mertz, M.C., Garnaud, S., Gonzalez, A., & Chebbo, G Characterisation of urban runoff pollution in Paris. Water Science and Technology, 39(2), 1-8. He, W., Wallinder, I. O., and Leygraf, C A laboratory study of copper and zinc runoff during first flush and steady state conditions. Corrosion science, 43(1), Lee, J.H., Bang, K.W., Ketchum, L.H., Choe, J.S., & Yu, M.J First flush analysis of urban storm runoff. Science of the Total Environment, 293, Sansalone, J.J., & Buchberger, S.G Partitioning and first flush of metals in urban roadway stormwater. Journal of Environmental Engineering ASCE, 123, ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support of this project by Glencore. Special thanks to Glencore personnel for their unlimited support: Greg O Shea Manager Townsville Projects Daniel Christie Projects & Engineering Kevin Hemmett Project Manager

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