waste ferric sludge wetland substrates for tertiary ... · incomplete removal during wastewater...
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Waste ferric sludge wetland
substrates for tertiary treatment
of recalcitrant substances in
wastewater
Devin Sapsford and Akintunde Babatunde,
Cardiff School of Engineering, Cardiff University
Constructed Wetalnds Established use of constructed wetalnds for removal of N
species, P – species and BOD etc
Do they have a role in treating ‘emerging contaminants’ and
other recalcitrant contaminants?
Why ‘emerging’ contaminants?
‘Emerging’ determined by whether the contaminant is persistent or has potentially harmful human or ecological effects
Perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and other
perfluorinated compounds
Pharmaceuticals, Hormones, and Endocrine Disrupting Compounds (EDC)
Drinking Water Disinfection Byproducts
Sunscreens/UV Filters
Brominated Flame Retardants
Benzotriazoles
Dioxane
Naphthenic Acids
Pesticide Degradation Products and New Pesticides
Perchlorate
Gasoline Additives: MTBE and EDB
Algal
Naphthenic acids
PharmaceuticalsPharmaceuticals, hormones, and EDCs are present in water due to incomplete removal during wastewater treatment.
Possible estrogenic and other effects, both to wildlife and humans.
Bacterial resistance from overuse and release of antibiotics into the environment.
Pharmaceuticals are introduced via use by
humans and in vetenary care and farming
(Source: Richardson, 2007, Anal. Chem. 79, 4295-4324)
Removal mechanisms for
wastewater treatment Sorption (e.g. GAC),
Biodegradation, dilution, and volatilization
Reductive or oxidative attack
Direct photolysis
Advanced Oxidation Processes
Heterogeneous photocatalysis employing semiconductor
catalysts (TiO2, ZnO, Fe2O3, CdS, GaP and ZnS) or Fenton’s or Photofenton’s processes
Previous work on use of
constructed wetlands for treatment
of pharmaceuticals
Caffiene, salicyclic
acid > Ibuprofen,
naproxen
Identified mechanisms for removal
of pharmaceuticals in wetlands
Complex systems – difficult to identify mechanisms
Sorption and hydrophobically driven interactions with organic
matter, some biodegredation
Reactive Media in Constructed
Wetlands (for enhanced P removal)
Alum sludges
Zhao, Y. Q., X. H. Zhao, and A. O. Babatunde. "Use of dewatered alum sludge as main substrate in treatment reed bed receiving agricultural wastewater: Long-term trial." Bioresource technology 100.2 (2009): 644-648.
Iron sludges
Heal, K. V., et al. "Enhancing phosphorus removal in constructed wetlands with ochre from mine drainage treatment." Water Science and Technology 51.9 (2005): 275-282.
Hydrous Ferric Oxide Sludges
From water treatment works (from groundwater or from added
coagulants), or from coal mine drainage. Generally XRD-
amorphous/ferrihydrite. Iron not toxic in this form.
Thickened sludge
Air-dried sludge
Liquid sludge
Samples of water treatment sludges
Elemental compositionChemicalComposition
Unit Pontsticill(Alum)
StrataFlorida(Alum)
Court Farm
(Ferric)
BontGoch
(Ferric)Aluminium as Al203
mg/g 236 225 93.0 13.7
Iron as Fe203 mg/g 11.0 19.5 244 381
Calcium as Ca0 mg/g 4.0 0.8 16.9 8.6Magnesium as Mg0
mg/g 2.1 0.3 15.6 0.7
Humic Acid as TOC
mg/g 230.6 nd 80.2 nd
Cl- mg/l 39.3 2.0 4.9 1.3S04
2 mg/l 59.9 2.0 65.2 4.34H2 O at 105oC % 84.8 86.0 79.7 81.6
Sludge Compositions
Ad
so
rptio
n c
ap
acity (
mg
-P/g
)
P capacities (v pH)
HFO also is an excellent sorbent for heavy metals such as Zn, Cu,Pb at
circumneutral pH
Why use HFO as a reactive media
in constructed wetlands?
Re-use of a common waste sludge but also possess several
useful properties...
Removal Mechanisms for
recalcitrant pollutants:
1. ‘Trapping’ with HFO
R1
R2
R3
1
2 3 45
6
Image taken from google Earth
20m
PAH Compound Sample L1-1 (mg/kg) Sample L1-2 (mg/kg) Sample L1-3 (mg/kg)
Naphthalene 953.5 10.72 0.866
Acenaphthylene 355.9 31.10 n.d.
Acenaphthene 199.8 26.18 n.d.
Fluorene 871.8 146.6 0.720
Phenanthrene 1460 354.6 7.738
Anthracene 403.6 n.d. 3.366
Fluoranthene 518.1 122.1 23.40
Pyrene 280.6 66.21 14.06
Benz(a)anthracene 156.8 37.02 8.833
Chrysene 146.3 29.95 7.425
Benzo(k)flouranthene 30.72 5.972 0.926
Benzo(a)pyrene 97.15 18.42 4.667
Indeno (1,2,3-cd) pyrene 32.15 4.880 0.006
Benzo(g,h,i)perylene 27.35 5.280 n.d.
TOTAL 5534 859.0 72.00
TPH Compound Sample L1-1
(mg/kg)
Sample L1-2
(mg/kg)
Sample L1-3
(mg/kg)
Sample L1-4
(mg/kg)
Dodecane 23.76 n.d. n.d. n.d.
Tetradecane 13.19 1.757 n.d. n.d.
Octadecane 1486 345.0 7.989 2.201
Docosane 5.278 n.d. n.d. n.d.
Tetracosane 20.15 n.d. n.d. n.d.
Hexacosane 3.541 n.d. n.d. n.d.
TOTAL 1552 346.8 7.989 2.201
Removal Mechanisms for
recalcitrant pollutants:
2. Photocatalytic Oxidation It is a well known fact that many metallic oxides exhibit photo
catalytic properties due to their semiconductor properties
Mechanism of a photocatalyst
(Bahnemann. D. W. 2004)
Fe2O3 + hv hVB+ + eCB
-
hVB+ + H2O OH*
eCB- + O2 O2*
- + H2O OH*
Pharamaceutical process effluent,
phenol (0.1% w/w) and Mn tested
Component
Component percentage
(%)
Piperazine 8.7
N-methyl-2-pyrrolidone 4.3
Quetiapine chloroimine 1.7
Toluene 0.8
Aryl piperazine 0.2
Samples in the environmental chamber
underwent extreme irradiation from a full
spectrum of light with an equivalent intensity
approximately to that of midday sun around
the equator, this equates to approximately
900W/m2.
Absorption spectrum for iron oxides is below
600nm, so there is potential for a large
amount of photo activity in the presence of
iron.
-1.00E+00
0.00E+00
1.00E+00
2.00E+00
3.00E+00
4.00E+00
5.00E+00
6.00E+00
280 320 360 400 440 480 520 560 600 640 680 720 760 800
Irra
dia
nce (
W/m
²)
Wavelength (nm)
Pre Test
% Decrease in measured COD (or
concentration for Mn) with 24 hrs
RTContaminant 5g/L HFO 10 g/L HFO 5g/L HFO
+ daylight
10 g/L HFO
+ daylight
25% v/v
solution of
pharmaceutic
al wastwater
0% 3% 53% 68%
0.1% Phenol 16% 19% 69% 44%
100 mg/L Mn 75% 76% 95% 99%
Holder, N. 2011Performed similar to the addition of H2O2 to mix
and some cases better
Removal Mechanisms for
recalcitrant pollutants:
3. (Bio)geochemical reduction by
Fe(II)-HFO
The redox intensive cycling
in wetalnd conducive to
regeneration of surface
bound Fe(II)
Key Questions Are wetlands compatible with iron sludges?
Is the iron non-toxic?
Will dissolved iron be released?
Rates and specificity of breakdown
Summary There seems substantial opportunity to use WASTE hydrous
ferric oxides from water treatment and mine water treatment as reactive media for constructive wetalnds for enhanced removal of conventional contaminants of concern such as P and heavy metals but also for a range of ‘emerging’ recalcitrant pollutants.
Number of mechanisms to utilise including photocatalysed oxidation and biogeochemical reduction with sorbed Fe(II)
Further research in this area is now underway.
Thank you
Dr Devin Sapsford,
Dr Akintunde Babatunde,
Cardiff School of Engineering, Cardiff University