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EXTENSIVE AND NATURAL SYSTEMS FOR WASTEWATER TREATMENT
Marcos von Sperling
Federal University of Minas GeraisBrazil
10th Specialized Conference on Small Water and Wastewater Treatment Systems
Venice, 18-22 April 2011
EXTENSIVE AND NATURAL SYSTEMS FOR WASTEWATER TREATMENT
• Cover only wastewater treatment
• Reflect more the experience at warm-climate regions, particularly Brazil
• Express some personal opinions
• Photos: not only small systems
PRESENTATION OUTLINE• Stabilization ponds
• Constructed wetlands
• UASB reactors + post-treatment
FEDERAL UNIVERSITY OF MINAS GERAIS - BRAZILCentre for Research and Training in Sanitation
UFMG - COPASA
IWA SPECIALIST GROUPS WITH GREATER INTERFACE WITH EXTENSIVE AND NATURAL SYSTEMS
• Anaerobic digestion
• Resources Oriented Sanitation (EcoSan)
• Sanitation and Water Management in Developing Countries
• Small Water and Wastewater Systems
• Use of Macrophytes in Water Pollution Control
• Waste Stabilisation Ponds
WASTE STABILIZATION PONDS
IWA Specialist Group on Waste Stabilization Ponds
8 international conferences(next one: Adelaide, Australia, 1-4 August 2011)
IWA Specialist Group on Waste Stabilization Ponds
Books published by IWA on stabilization ponds
FacultativeSTABILIZATION PONDS
Brazil
Anaerobic pond – Facultative pondSTABILIZATION PONDS
Brazil
South of France – Aerators on during wine production periods
Aerated lagoonSTABILIZATION PONDS
Northeast Brazil - 1 Anaer. pond + 1 Facult. pond + 3 Matur. ponds (100 ha)
Anaerobic – facultative - maturation pondsSTABILIZATION PONDS
UASB – POLISHING PONDS
Experimental WWTP UFMG/COPASA - 250 inhab
REMOVAL OF ORGANIC MATTER
FACULTATIVE PONDS
FACULTATIVE PONDSDesign criteria
• Surface organic loading rate• Depth • Hydraulic retention time• Geometry (length / breadth ratio)
Mara: Ls = 350 x (1.107 – 0.002.T) (T-25)
(T = mean air temperature in coldest month)
Surface organic loading rate - Ls
FACULTATIVE PONDSDesign criteria
Surface loading rate as a function of temperature
0
100
200
300
400
T (oC)
Ls (k
gBO
D/ha
.d)
Ls 100 124 152 183 217 253 291 331 350 350 350
10 12 14 16 18 20 22 24 26 28 30
FACULTATIVE PONDSEffluent BOD
Total BOD = Soluble BOD + Particulate BOD
FACULTATIVE PONDSHydraulic models
Plug flow Completely mixed
Cells in series Dispersed flow
-K.t0eS=S
K.t+1S
=S 0
n0
)ntK+(1
S=S
4K.t.d1a
ea)(1ea)(1
4ae.SSa/2d2a/2d2
1/2d0
+=
−−+=
−
FACULTATIVE PONDSEffluent soluble BOD concentration
Completely mixed:
• Primary ponds: K = 0.30 to 0.40 d-1
• Secondary ponds: K = 0.25 to 0.32 d-1
FACULTATIVE PONDSHydraulic models
Relationship between reaction coefficients (K)
FACULTATIVE PONDSHydraulic models
CFD modelling
5 10 15 20 25 30 35 40 45 50 55
5
10
15
20
25
(e.g. studies on the influence of baffles)
Tracer studies
(long time for field trials)
1 mgSS/L = 0.3 to 0.4 mgBOD5/L
Pond effluents: 60 to 100 mgSS/L (for design)
1 mgSS/L = 1.0 to 2.0 mgCOD/L
FACULTATIVE PONDSEffluent particulate BOD concentration
No adequate models for predicting effluent BOD and SS
FACULTATIVE PONDSEffluent polishing (algae removal)
Coarse rock filter:Experiments UFMG:Stones: 3 to 8 cmH = 0.40 mHLR: 0.5 to 1.5 m3/m3.d
Floating macrophytes – duckweed (Lemna)
Experimental WWTP UFMG/Copasa
FACULTATIVE PONDSEffluent polishing (algae removal)
PRIMARY FACULTATIVE PONDSSand accumulation
Brazil
Prior grit removal is recommended
Colombia
FACULTATIVE PONDSSludge accumulation
0.03 to 0.08 m3/inhab.year
2 to 3 cm per year
FACULTATIVE PONDSSludge accumulation
Operation for 20 years without need of sludge removal
Complex operation when removal is necessary
REMOVAL OF PATHOGENIC ORGANISMS IN PONDS
REMOVAL OF PATHOGENIC ORGANISMS
Removal of bacteria and viruses
Die-off mechanisms (high UV radiation, high pH, high DO, ...)
Substantial research in the past years
(source: Nelson, 2009)
REMOVAL OF PATHOGENIC ORGANISMSRemoval of bacteria and viruses
Molecular biology methods (PCR, FISH, Quantitative PCR)
Detection of actual pathogenic organisms, not only indicators
(source: Godinho et al 2009)
b c
RSRS P1RS P1RS
a
PCR products from amplification of DNA from: a) Escherichia coli, b) Salmonella enterica subsp. enterica,c) Enterococcus spp., d) Shigella dysenteriae.Legend: RS (raw sewage), UASB (UASB effluent), P1 (polishing pond 1 effluent)
Coliform removal efficiency (log units)186 ponds around the world
FACULTATIVE AND MATURATION PONDS
LOG UNITS REMOVED IN EACH POND OF THE SERIES
Median 25%-75% 5%-95%
PRIM SEC MAT1 MAT2 MAT345
CATEGORY
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
LOG
UN
ITS
RE
MO
VE
D
MATURATION PONDS
Baffled ponds
Samambaia, Brazil (180,000 inhab)
MATURATION PONDS
Ponds in series
Experimental WWTP UFMG/Copasa (250 inhabitants)
MaxMin75%25%Median
EFFLUENT E. COLI CONCENTRATIONSPHASE 1
E. c
oli (
MPN
/100
ml)
1
10
100
1000
10000
1e5
1e6
1e7
1e8
1e9
1e10
RAW UASB POND1 POND2 POND3 POND4
Depth of ponds: H: 0.4 to 0.8 m (shallow ponds)
Coliform die-off coefficient (Kb) - dispersed flow186 ponds around the world
FACULTATIVE AND MATURATION PONDS
Kb disp (20o C) vs depth H
0,0
1,0
2,0
3,0
4,0
5,0
6,0
0,00 1,00 2,00 3,00H (m)
Kb (1
/d)
Effluent coli estimated x observed
1,E+00
1,E+02
1,E+04
1,E+06
1,E+08
1,E+10
1,E+00 1,E+02 1,E+04 1,E+06 1,E+08 1,E+10
Obs
Estim
FACULTATIVE AND MATURATION PONDS
For the same surface area A:
Increase H increase V increase HRT
But Kb decreases Efficiency does not increase
H
2H
A A
V
V
REMOVAL OF PATHOGENIC ORGANISMS
Removal of protozoan cysts and helminth eggs
Mechanism: sedimentation
Helminth eggs removalAyres et al model (2002)
] 0,14.e [1 . 100E 0,38.t)(−−=Mean removal efficiency:
WHO (irrigation):< 1 egg/L
FACULTATIVE AND MATURATION PONDS
REMOVAL EFFICIENCY OF HELMINTH EGGS
0,0
1,0
2,0
3,0
4,0
5,0
6,0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Hydraulic detention time(d)
Log
units
rem
oved
Average values95% confidence level
Helminth eggs removalAyres et al model (2002)
FACULTATIVE AND MATURATION PONDS
HELMINTH EGGS - FIRST PONDESTIMATED (AYRES) AND OBSERVED EFFICIENCY
80
85
90
95
100
0 5 10 15 20 25RETENTION TIME (d)
EFFI
CIE
NC
Y (%
OBS
ESTIM
Average values from five different ponds in Brazil
Helminth eggs removal
Baffled maturation pond in Brazil (4 baffles)Helminth eggs in the sludge after two years
FACULTATIVE AND MATURATION PONDS
Avoid population access!
STABILIZATION PONDS
NITROGEN REMOVAL
FACULTATIVE AND MATURATION PONDSNitrogen removal
NITROGEN REMOVAL EFFICIENCY
0
20
40
60
80
0 5 10 15 20 25 30 35 40
HDT (d)
Effic
ienc
y (%
)
pH=7,0
pH=7,5
pH=8,0
pH=8,5pH=9,0
T= 20oC
• Values from one of the equations available in the literature• Assumption that NH3 volatilization is the prevailing mechanism• Considerable debate over the mechanisms• Removal efficiencies are not high
FACULTATIVE AND MATURATION PONDSNitrogen removal
• Capture of ammonia escaped through the surface of a pond, in order to measure volatilization rate• Studies with marked nitrogen isotopes (15N)
Volatilization does not seem to be a major mechanism
Experimental WWTP UFMG, Brazil Experimental WWTP UK (Miller et al, 2009)
MATURATION PONDSNitrogen removal
Experimental WWTP UFMG-Copasa
• N fraction removed: ammonia• Poor nitrification
NITROGEN FRACTIONS
MATURATION PONDS x WETLANDSAmmonia removal
H
1.0m0.5m
Experiments from Univ. São Paulo, Brazil(two ponds in parallel):
For the same surface area A:
Greater H Higher V Higher HRT
Lower ammonia removal efficiency
Pond with H=0.5m (L/B = 16)
PONDS: FUTURE CHALLENGES
PONDS: FUTURE CHALLENGES
• Reduction of required area
• Better understanding of the removal mechanisms(e.g. pathogen decay; nitrogen removal)
• Implementation of rational models design optimization (but not much scope for operationalcontrol)
• Carbon sequestration and energy production(biodiesel, hydrogen production from cyanobacteria...)
• ...
CONSTRUCTED WETLANDS
IWA Specialist Group on Use of Macrophytes in Water Pollution Control
12 international conferences
Next conference: Perth, Australia - 2012
IWA Specialist Group Use of Macrophytes in Water Pollution Control
Books published by IWA on constructed wetlands
Constructed Wetlands for Pollution Control
Processes, Performance, Design and Operation
Author(s): R. Kadlec, R. Knight, J. Vymazal, H.
Brix, P. Cooper, R. Haberl
Publication Date: 2000
New Zealand (pond effluent polishing)
Surface flow constructed wetlands
Experimental WWTP UFMG / COPASA (50 inhab each unit)
Planted(Typha)
Unplanted
Horizontal subsurface-flow constructed wetlands
Surface hydraulic loading: 0.1 m3/m2.d
Hydraulic retention time (V.porosity/Q): 1.2 d
Measured filtered COD concentrations along the length
020406080
100120140
0% 25% 50% 75% 100%
CO
D c
once
ntra
tion
(mg/
L)
Planted wetland
25%
50%
90%
10%
Min
Max
75%
Relative distance
020406080
100120140
0% 25% 50% 75% 100%
CO
D c
once
ntra
tion
(mg/
L)
Unplanted wetland
25%
50%
90%
10%
Min
Max
75%
Relative distance
Horizontal subsurface-flow constructed wetlands
• Water losses (evapotranspiration): increase in effluent concentrations
• Compute removal efficiencies in terms of loads (and not concentrations)
• Actual role of plants? (debate in the literature)
• Capacity for N and P removal?
Clogging surface flow
Horizontal subsurface-flow constructed wetlands
• Modelling of clogging development and hydraulic conductivity reduction• Refurbishment / cleaning of the beds
Source: Knowles et al (2010)
Experimental WWTP UFMG-Copasa
Vertical flow constructed wetlands
Experimental WWTP UFMG / COPASA (100 inhab)
French (CEMAGREF) system
Tifton
Vertical flow constructed wetlands
Experimental WWTP UFMG / COPASA (100 inhab)
Hydraulic behaviour
0,0000
0,0005
0,0010
0,0015
0,0020
0,0025
0,0030
0,0035
0,0040
0,0045
0 200 400 600 800 1000 1200E
(t)
Initial tests (clean filter)
After a 11 months operation (used filter)
Time(min)
Tracer studies - DTD curve
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Tempo (horas)
Q (L
itros
/min
uto)
Teste 5 (FV-NP) Teste 11 (FVP-2)
Outflow as a function of time
Vertical flow constructed wetlands
Experimental WWTP UFMG / COPASA (100 inhab)
Potential for nitrification
0
5
10
15
20
25
30
Raw Unplanted Planted
Nitr
ogen
fract
ions
(mg/
L) N nitrate
N ammonia
N organic
UASB REACTORS AND POST-TREATMENT OF ANAEROBIC
EFFLUENTS
SMALL UASB REACTORS
Experimental WWTP UFMG / COPASA (250 inhab)
UASB REACTORFrom small to large installations
Hundreds of inhabitants One million inhabitants
Experimental WWTP UFMG / COPASA Onça WWTP – COPASA (Brazil)
UASB + POST-TREATMENT
Any of the technologies for treating raw sewage can be used as post treatment with advantages (in warm climate regions)
Advantages:
• Certain reduction in construction costs• lower volume/area of the units
• Large reduction in operating costs• less energy consumption• less quantity of sludge to be produced
Polishing ponds
Lagoa depolimento
ReatorUASB
WWTP UFMG – Copasa (250 inhab)
UASB + POST-TREATMENT
UASB
Pond
Overland flow
Overland flowUASB + POST-TREATMENT
Itabira, Brazil(300 inhab)
Loading rate: 0.2 to 0.5 m3/h per meter widthLength: 30 to 45 mSlope: 2 to 8%
Experimental WWTP UFMG / COPASA (50 inhab each unit)
Planted
Unplanted
Horizontal subsurface-flow constructed wetlandsUASB + POST-TREATMENT
Activated sludgeUASB + POST-TREATMENT
Rio Claro, Brazil - 100,000 inhab
Trickling filterUASB + POST-TREATMENT
Itabira, Brazil - 70,000 inhab
Trickling filterUASB + POST-TREATMENT
Experimental WWTP UFMG / COPASA (500 inhab)
Trickling filterUASB + POST-TREATMENT
Experimental WWTP UFMG / COPASA (UASB: 500-700 inhab; TF: 300 inhab)
CONCLUDING REMARKS
There is no overall best treatment process
In each particular case, select the system with the bestperformance from the technical and economical studies
THANK YOU VERY MUCH!
ENJOY THE CONFERENCE!