River Bank Filtration- Overview and Experimental Applications with Cyanotoxins

1. River Bank Filtration- Overview and Experimental Applications with Cyanotoxins Dakos Vasilis Federal Environment Agency (UBA), Berlin, Germany

2. Part I. Definition • River Bank Filtration (RBF) is the naturally occurring influx of surface water to the groundwater. The water flows from the bed and banks of the river body through sand and gravel aquifers into wells or filtration galleries adjacent to the river. • Bank Filtrate is river water that has passed through the river banks and proceeded to the groundwater. • From a water resources perspective, this process is characterized by an improvement in water quality, thus RBF is considered as pretreatment of surface water for drinking purposes.

3. Part I. History PAST RBF employed in Europe since the 19th century Along rivers Rhine and Elbe (Germany) for over 120 years potable drinking water • At present Rhine, Ruhr, Danube, Elbe, Ohio, Great Miami and Thames • France 50% of the total drinking water production • Netherlands 5% of the total drinking water supply (=62,4 million m3/y) • USA quite limited- renewed interest (alternative water treatment technology) • Germany approximately 16% of drinking water PRESENT

4. Part I. Feasibility Strong hydraulic connection between recharging river and wells HOW? pumping wells along the river banks Description Principal As water flows through the subsoil to the aquifer, pollutants can be retained or eliminated, partially or totally, in the porous medium.

5. Part I. convective-dispersive transfer, dilution Hydrodynamical filtration of particulate matter Mechanical complexation, flocculation/coagulation, redox reactions, precipitation Physicochemical Biological microflora (biodegradation) • Processes during RBF

6. Part I. Key Role Microbiological activity catalysing many redox reactions mineralisation of organic matter hydrolysis solubilisation of solid organic matter fermentative anaerobic bacteria Biodegradation Biofilm:conglomerate of fully hydrated polymeric gel and bacteria

7. Part I. Nowadays (because of pollution) • Treatment of Bank-filtrate Earlier years: No treatment- Direct drinking

8. Part I. In addition: • Easily applied • Cost-effective drinking water pre-treatment step • Advantages Surface (quantity) Groundwater (quality) • Removal of bacteria, viruses, parasites • Removal of particles • Removal of easily biodegradable compounds • Reduction of persistent organic contaminants and heavy metals • Constant composition and temperature • Absence of faecal contamination • Compensation of concentration peaks • Barrier against shock loads • High availability(even in dry periods) • Saving of groundwater resources

9. Part I. • Efficiency • Depends on: • Soil-related conditions • quality and porosity of the soil • residence time of the water in the underground • water’s temperature • pH conditions • oxygen concentration • Riverwater-related conditions • quality quantity changes in the river (particles, concentration of dissolved organic matter, oxygen, ammonia, nutrients, microorganisms other pollutants) Must be noted: specific claims impossible. HOWEVER Bank filtrate can be regarded as good groundwater

10. Part I. Problems • Low efficiency for the elimination of: • endocrine disrupting agencies • non-biodegradable pharmaceuticals from hospitals • c. alkynophenoles used in special detergents • Reason:polar molecules with hydrophilic groups, penetrate banks endangering drinking water supplies BUT: It is the long-term contamination by persistent compounds that affects negatively the bank filtrate. Solution: should be removed from wastewater plants at point of production or replaced by biodegradable less hazardous substances

11. Part II. High scientific interest and importance for public health Experimental Applications RBF and Removal of Cyanotoxins Introduction Why Cyanotoxins? Berlin‘s lake and river systems intensively used for drinking water via RBF. Since 1960‘s blooms of cyanobacteria in Lakes and rivers in Berlin Dangerous for health

12. Part II. Characteristics of Microcystins • cyclic heptapeptides • about 70 structural variants • occur in different Cyanobacteria (Microcystis aeruginosa) • water soluble • highly hepatotoxic • tumor promoters • max. reported concs along Havel river: 25 000 µg/L • usually between 1 and 10 µg/L during algal blooms • WHO guideline value: 1 µg/L

13. Part II. Cyclic heptapeptides R² O COOH H N NH HN H O CH2 R H3C H3C S O O H H H OCH3 H S R1 H HN NH X H Z S H H H3C CH3 COOH H O X, Z: variable L-amino acids, R1, R2: H or CH3. General Structure of Microcystins (MC)

14. Part II. Efficacy of Bank Filtration for the removal of microcystins A. Field Observations- Wannsee

15. Part II. Materials and Methods • Samples from upper most aquifer • Analysis of microcystis with ELISA (Measurement of MC content) • HPLC(verification of results, distinguishes MC-variants) ELISA (Enzyme-Linked ImmunoSorbent Assay) specific immunological assay based on the reaction of all microcystins with antibodies. HPLC (High Performance Liquid Chromatography) separates individual microcystin variables by their absorption spectrogram in a photodiode array detector.

16. Part II. Results/Conclusions Wells Surface water • Typical values for blooms in the summer • Very small fraction is recovered in the bank filtrate

17. Part II. B. Field-scale experiments- Marienfelde Simulating installation for RBF and Slow sand filtration (SSF) In this case SSF was used to simulate RBF: • purification process depends also on biological activity of biofilm • similar mechanisms governing flow of water to the aquifer (dispersion, percolation, adsorption) • slow flow regime of the rivers in the area around Berlin, especially during the summer months when cyanobacterial blooms occur make RBF and SSF similar

18. Part II. slow sand filters & infiltration ponds water surface area: 3294 m² total area: 5290 m² 45.5 m bank filtration 88 m storage pond 55.4 m > 2 m 1.5 - 2 m 1 – 1.5 m 17.5 m 8 inlet 8 piezzometers Description of installation

19. Part II. piezzometers slow sand filter storage pond about 4 m sand (0.8 - 2 mm) gravel (32 - 56 mm) gravel (2 - 8 mm) concrete gravel (8 - 20 mm) drainage pipe 22 m 2 m 5 m 7 m Cross-section through the Bank Filtration Site

20. Part II. Advantages • experiments of hazardous substances can be carried out on a field scale without adverse environmental impacts, • external conditions scale factors (e.g. weather conditions) similar to real environment • elimination performance can be quantified

21. Part II. lysed cells of Planktothrix agardhii ssp. hourly samples of water body 2 m³/h initial concentration: 8 µg/L MC average residence time:4.5 h 20 cm/h hourly samples of effluent 2 m³/h 1. Investigation of elimination of dissolved MC through SSF Methods and Materials • Analyses by ELISA and HPLC

22. Part II. Results in water body and effluent • Little adsorption (simultaneously appearance with tracer) • In 33 hours 98,4 % elimination of toxin • Values under WHO limit concs.

23. Part II. live cells of Planktothrix agardhii ssp. daily samples of water body 0.5 m³/h initially: 40 µg/L MC average residence time:15 h 5 cm/h daily samples of effluent 0.5 m³/h 2. Assessment of SSF performance in eliminating cell-bound MC Methods and Materials • Analyses by ELISA and HPLC

24. Part II. 100 100 MC (ELISA, total) in water body MC (ELISA, total) in effluent biovolume of Planktothrix 10.0 10.0 microcystins (µg/L) / biovolume (cm³/m³) WHO guideline-value 1.0 1.0 0.1 0.1 1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 days after application of cyanobacteria Results • Elimination rate diminishes from 99% to 50% (lower biodegradation, release of MC by dying population) • MC concs below WHO guidelines

25. Conclusions/Outlook • RBF cost-effective pretreatmnet for drinking water supply • High efficiency in removing hazardous contaminants from groundwater, even cyanobacterial toxins • THOUGH: • There is need for more investigations on: • MC cyanobacterial cells sedimented to the bottom of a river body. • microcystin degrading bacteria • the efficacy of microcystin degradation during RBF also in conditions of fast flowing rivers and under anaerobic conditions • In the experimental field of the German Federal Environment Agency in Berlin these issues are to be examined in future projects.