River Bank Filtration- Overview and Experimental Applications with Cyanotoxins

für Mensch und Umwelt

River Bank Filtration- Overview and Experimental Applications with Cyanotoxins

Dakos Vasilis Federal Environment Agency (UBA), Berlin, Germany


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.

Part I.Part I.

DefinitionDefinition


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

HistoryHistoryPart I. Part I.

PAST

PRESENT

RBF employed in Europe since the 19th century

Along rivers Rhine and Elbe (Germany) for over 120 years potable drinking water


Principal

As water flows through the subsoil to the aquifer, pollutants can be retained or eliminated, partially or totally, in the porous medium.

DescriptionDescriptionPart I.Part I.

Feasibility

Strong hydraulic connection between recharging river and wellsHOW? pumping wells along the river banks


Processes during RBFProcesses during RBF

Part I.Part I.

Hydrodynamical convective-dispersive transfer, dilution

Physicochemical

complexation, flocculation/coagulation, redox reactions, precipitation

Biological microflora (biodegradation)

Mechanical filtration of particulate matter


BiodegradationBiodegradation

Key Role Microbiological activity

Biofilm: conglomerate of fully hydrated polymeric gel and bacteria

Part I.Part I.

catalysing many redox reactions

hydrolysis solubilisation of solid organic matter fermentative

anaerobic bacteria

mineralisation of organic matter


Treatment of Bank-filtrateTreatment of Bank-filtrate

Earlier years: No treatment- Direct drinking

Nowadays

(because of pollution)

Part I.Part I.


AdvantagesAdvantages

Surface (quantity) Groundwater (quality)

•High availability(even in dry periods)

•Saving of groundwater resources

•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

Part I.Part I.

•Easily applied

•Cost-effective drinking water pre-treatment step

In addition:


EfficiencyEfficiency 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

Part I.Part I.


ProblemsProblems

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

Part I.Part I.


Experimental Applications RBF and Removal of Experimental Applications RBF and Removal of CyanotoxinsCyanotoxins

Introduction

Why Cyanotoxins?

Since 1960‘s blooms of cyanobacteria in Lakes and rivers in

Berlin

Dangerous for health

Berlin‘s lake and river systems

intensively used for drinking water

via RBF.

Part II.Part II.

High scientific interest and

importance for public health


Characteristics of MicrocystinsCharacteristics 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

• 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

Part II.Part II.


H OCH3

H3C H

H

CH3

H

HH

H3C

HS

S O

HN

H COOH

O

N

R²

CH2

O

NH

H

H3C

R

O

XHN

COOHH

S

R1H

O

ZNH

X, Z: variable L-amino acids,R1, R2: H or CH3.

Cyclic heptapeptides

General Structure of Microcystins (MC)General Structure of Microcystins (MC)Part II.Part II.


A. Field Observations- Wannsee

Efficacy of Bank Filtration for the removal of microcystinsEfficacy of Bank Filtration for the removal of microcystins

Part II.Part II.


Materials and MethodsMaterials and Methods

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.

Part II.Part II.

•Samples from upper most aquifer

•Analysis of microcystis with ELISA (Measurement of MC content)

•HPLC(verification of results, distinguishes MC-variants)


Results/ConclusionsResults/Conclusions

•Typical values for blooms in the summer

•Very small fraction is recovered in the bank filtrate

Surface water Wells

Part II.Part II.


B. Field-scale experiments- MarienfeldeB. Field-scale experiments- Marienfelde

Simulating installation for RBF and Slow sand filtration (SSF)

In this case SSF was used to simulate RBF:

a) purification process depends also on biological activity of biofilm

b) similar mechanisms governing flow of water to the aquifer (dispersion, percolation, adsorption)

c) 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

Part II.Part II.


Description of installationDescription of installation

storage pond

> 2 m 1.5 - 2 m 1 – 1.5 m

55

.4 m

45.5 m

water surface area: 3294 m²total area: 5290 m²

88 m

8

1 7. 5

m

slow sand filters & infiltration ponds

bank filtration

8 piezzometersinlet

Part II.Part II.


5 m2 m 7 m22 m

piezzometersstorage pond

slow sand filter

about 4 m

gravel (8 - 20 mm)

gravel (2 - 8 mm)

sand (0.8 - 2 mm)

gravel (32 - 56 mm)

concrete

drainage pipe

Cross-section through the Bank Filtration SiteCross-section through the Bank Filtration Site

Part II.Part II.


AdvantagesAdvantages

a)a) experiments of hazardous substances can be carried out experiments of hazardous substances can be carried out on a field scale without adverse environmental impacts,on a field scale without adverse environmental impacts,

b)b) external conditions scale factors (e.g. weather conditions) external conditions scale factors (e.g. weather conditions) similar to real environment similar to real environment

c)c) elimination performance can be quantifiedelimination performance can be quantified

Part II.Part II.


2 m³/h

2 m³/h

initial concentration: 8 µg/L MC

average residence time:4.5 h

20 cm/h

lysed cells of Planktothrix agardhii ssp.

hourly samples of water body

hourly samples of effluent

1. Investigation of elimination of dissolved MC through SSF1. Investigation of elimination of dissolved MC through SSF

Methods and Materials

•Analyses by ELISA and HPLC

Part II.Part II.


Results in water body and effluentResults in water body and effluent

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25 30 35

hours after toxin application

su

m m

icro

cysti

ns i

n µ

g/L

(> 8

5 %

MC

-LR

)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0tra

cer c

on

cen

tratio

n

(µg

/L)

MC (HPLC) water body MC (HPLC) effluent

tracer in water body (calculated) tracer in effluent

Until 30 h after toxin application:applied MC: 267 mgrecovered MC: 4.3 mg=> elimination: 98.4 %

•Little adsorption (simultaneously appearance with tracer)

•In 33 hours 98,4 % elimination of toxin

•Values under WHO limit concs.

Part II.Part II.


2. Assessment of SSF performance in eliminating cell-bound MC2. Assessment of SSF performance in eliminating cell-bound MC

Methods and MaterialsMethods and Materials

0.5 m³/h

0.5 m³/h

live cells of Planktothrix agardhii ssp.

initially: 40 µg/L MC

average residence time:15 h

5 cm/h

daily samples of water body

daily samples of effluent

•Analyses by ELISA and HPLC

Part II.Part II.


ResultsResults

0.1

1.0

10.0

100

1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26days after application of cyanobacteria

mic

roc

ysti

ns

(µg

/L)

/ bio

volu

me

(cm

³/m

³)

0.1

1.0

10.0

100

biovolume of Planktothrix

MC (ELISA, total) in water body

MC (ELISA, total) in effluent

WHO guideline-value

•Elimination rate diminishes from 99% to 50% (lower biodegradation, release of MC by dying population)

•MC concs below WHO guidelines

Part II.Part II.


Conclusions/OutlookConclusions/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.

Documents

River Bank Filtration- Overview and Experimental Applications with Cyanotoxins