Advanced Bioretention Systems for Nutrient Removal from Kranji Reservoir

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1 Advanced Bioretention Systems for Nutrient Removal from Kranji Reservoir A Presentation to IWA Symposium on Lake and Reservoir Management August 5, 2015 William C. Lucas PhD, Cheng Hua (Michelle) SIM, PhD Public Utilities Board, Singapore Kok Hui (Alvin) GOH Public Utilities Board, Singapore

2 Background Kranji Reservoir is a major component of Singapore s water supply. However, it is the most impaired of all Singapore reservoirs due to heavy algae blooms from excess nutrients, particularly phosphorus (P). Nutrients come from non-point source runoff, particularly from agriculture. As a result, water must be extensively pretreated for use in water supply. Kranji is also shallow, with an average depth of 7m. Climate is humid tropical, with frequent thunderstorms all year.

3 Objective Overall System Approach: Lateritic lake sediments are very high in Al, so sediment P is tightly bound, and not very redox sensitive. Since shallow and warm, mixing or aeration seem unlikely to reduce algae. Therefore, removal of inflow P appears most important factor to reduce algae. Reduction of nitrogen will further reduce potential for algae blooms. Approach is to reduce nutrient loads by installing an Advanced Bioretention System (ABS) to intercept and treat runoff from agricultural lands. ABS processes and performance include the following: Media physical filtration and sorption effectively to remove TSS, metals and pathogens. Combination of biological uptake and microbial transformations to remove nitrogen species and Biological Oxygen Demand (BOD), by using innovative outlets to extend retention time without bypass. TN removal as high as 75%, with specific N removal of 3.2 g/m 2 /event. Media (and microbes) to irreversibly bind up phosphorus species. TDP discharge concentrations in long term experiment remained very low (<20 ug/l), even after retaining very high P loads (>125 gp/m 2 ).

4 Advanced Bioretention System Low Flow Regime Flow through Underdrain Flow through Media Inflow from street Plants Media Drain Stone Elevated Low Flow Outlet Low flows through Lower Outlet Impermeable liner if on sandy soils (>8-10cm/hr.) Permanent Saturated Zone when lined High flow rate (up to 100 cm/hr) media placed on pea gravel stone bed. Flows through stone are collected by underdrain and routed to outlet. Impermeable liner ensures flow rate is controlled by outlet if soil too sandy. Saturated zone stores runoff for denitrification/uptake after event. Flow through media and stone is controlled by dual stage outlet. Lower outlet throttled to 4-6 cm/hr. effective infiltration rate. This provides at least 4 hour retention time during small events. This increases TN retention to >70%, and NO x retention to >80%.

5 Advanced Bioretention System High Flow Regime Surface Overflow Only During Peak Flows of Extreme Events Surface Ponding at High Flows Inflow from Street Plants Media Inlet Outlet Drain Stone High Flows through Upper Outlet High Flows through Underdrain High Flows through Media Upper outlet controls rate of flow through media. Up to 50 cm/hr when ponded. Outlet lowered to maintain design flow rate as media accumulates sediments. This adaptive management enables hydraulic design to perform as intended as system ages and media flow rates decline. Upper outlet results in very little bypass flow, occurring only in extreme events. As a result, virtually all runoff is treated for N, P, TSS, metals, and pathogens. Due to HRT decreasing to ~2.5 hours, TN reductions are reduced. But still >50%, with NOx reductions >65%.

6 Advanced Bioretention System- Mesocosm Research INFLOWS OUTFLOWS The Advanced Bioretention System incorporates a media formulated for very high P retention using water treatment residuals (WTRs) to adsorb TDP. Original systems loaded with wastewater weekly to accelerate loads to decades. Systems dosed with synthetic stormwater (tap water & KH 2 PO 4 ) every 6 months. Initial research (2011) showed very low TDP discharge of mg/l after 125 gtdp/m 2 retained. Equal to ~40 years of urban runoff. Even after over almost 60 years of urban runoff, 96% SRP retained, and still discharged TDP below mg/l. SRP below mg/l.

7 Advanced Bioretention System- US Field Study P retention results from full scale 3,500 sq. ft. research facility treating 20 acres of farm and institutional uses installed at U. DE, using first generation ABS media. ABS media compared to DNREC media (sand, peat and wood chips), both with ABS outlet. ABS media makes very substantial improvement in P retention. System operating at up to 99% SRP removal, with up to 93% TP removal. TN reductions as high as 72%, and NO x reductions as high as 77%. So initial research has been field verified. But data collection very challenging.

8 Advanced Bioretention System- US Media Ortho-Phosphorus Total Dissolved Phosphorus Concentration (mg/l) Inflow Media 1 Media 2 Media 3 Media 4 Concentration (mg/l) Inflow Media 1 Media 2 Media 3 Media Run Results show outflow of SRP and TDP for 4 different US media. Initially excellent. Second loading run applies ~40 years of urban runoff load all at once. Third rinsing run washes off loosely bound P, followed by stormwater runs. Using the best available US WTRs, latest media formulation discharges TDP at mg/l after retaining 0.25 g P/kg media. SRP discharge was mg/l. The 125 gtdp/m 2 retained is close to amount of TDP applied in initial study. This is almost half century of urban runoff released at FOREST concentrations Run 4 5 6

9 Singapore ABS Facility 450 sq.m. treating 3.8 ha of agriculture/fish farm runoff (84:1 capture ratio) rainfall 3.44 m, with peak hourly rainfall 75mm. Higher than normal. Even so, system treats newrly all rainfall up to 55mm/h, and 73% of all rainfall. Base flow P as high as 6.0 mg/l, while stormflow P approaches 1.0 mg/l. Such extremely high P loads will require a lot of WTRs (35% v/v). 9

10 Singapore ABS Facility System divided into two cells with individual outlets to segregate flow regimes. This evaluates tradeoffs between retention time, N removal and interception. Each cell segregated into 10 individual underdrains to permit evaluation of different plant species on N (and P) retention as compared to the whole cell. Samplers moved from treatment to treatment to evaluate individual treatments. A wide variety of different plants to be evaluated, from biomass to landscape. Relative differences will emerge. 10

11 Advanced Bioretention System- Singapore Media Like US testing, all media is initially acceptable, even for the coarse media that failed after loading. This emphasizes need for long term analyses. Loading applies 3 decades of ag. source loads (~2 centuries of urban loads). Rinsing washes off loosely bound P, followed by series of stormwater runs. Best media formulation discharges TDP at mg/l after retaining 1.05 g P/kg media. SRP discharge was mg/l. The 531 gtdp/m 2 retained is 2.5x the amount of TDP applied in US and Australia research.

12 Advanced Bioretention System- Leaching Freshly blended media is unstabilized, so many stressors leach out at beginning. Therefore, must rinse out the initial stressors. Leachate that exceed the standards must be disposed. So methods to reduce leaching volume are important. By initial P dose, media meet standards, declining over an order of magnitude. At P loading, see increased leaching, due to massive ionic disturbance. At rinsing, see greatly increased leaching after a day of further ionic exchange. So these peaks in the leaching response not representative of typical systems.

13 Advanced Bioretention System- Leaching Initial Al response showed rapid rinsing, but then increased just prior to P dose. Initial Cu response also showed rinsing, with earlier increase prior to P dose. At P dose, Cu and Al leaching decreased, as P dose has low ionic concentration. At P loading, see increased leaching, due to massive ionic disturbance. At rinsing, see greatly increased leaching after a day of further ionic exchange. Again, these peaks in the leaching response not representative of typical systems. So attainment of acceptable concentrations would occur more rapidly.

14 Advanced Bioretention System- Leaching Initial Mn and Zn response showed clear initial rinsing trend. Data for dosing and P loading not collected, so response unknown. At rinsing, again see greatly increased leaching after further ionic exchange. Such peaks in the leaching response not representative of typical systems. Therefore actual stabilized leaching concentrations likely to be considerably lower. Mn below BC standards, but still higher than desired. Likely lower than shown. Zn greatly affected by P loading and rinsing, with coarse being the lowest, suggesting longer residual effect of P loading disturbance.

15 Advanced Bioretention System- Conclusions The performance of the ABS for removal of P from runoff is unmatched by any other technology, even those with much greater cost. While leaching does occur, it is much less than other media, especially typical compost based media which can leach N, P, TOC and Cu for years. As a result, there has been considerable research into WTR amendments by U.MD, WSU, VaTech, U.NH, U.DE., U.WA., U. Guelph, Rutgers, Villanova, Shenzhen U., and Singapore. So far, 19 peer reviewed papers have cited my original research, and 2 PhD dissertations and 4 Masters theses have been published on using WTRs. However, none of these studies report quite as effective retention performance. This is largely due to suboptimal WTR selection and preparation formulations. Optimizing WTR technologies is NOT a simple process. Using proper WTR technology, Singapore media formulation discharged TDP at mg/l after retaining 1.05 g TDP/kg media or 531 gtdp/m 2. TDP concentrations are much lower than conventional systems, for much longer. At NPV cost of $US420/m 2, life cycle cost per kg of TP removed is ~$US135.

16 Advanced Bioretention System- Contacts Thanks!!! For more information contact:

17 Advanced Bioretention System- Application Rouzan Tradition Neighborhood Project, Baton Rouge LA. Runoff from 88% impervious urban source area treated by ABS. Inflows pretreated by dual chamber stilling basin. Then runoff flows through ABS, so lake is flushed with clean water every storm. Lake water also recycled through ABS between storms. ~ 2 week recycling time. TerraSolve LLC