Constructed wetroof for the treatment and reuse of domestic wastewater

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CONSTRUCTED WETROOF: A NOVEL
APPROACH FOR THE TREATMENT AND
REUSE OF DOMESTIC WASTEWATER
Presented by,
Vineetha Rose Vincent
Asst. Professor
Dept of Civil Engineering
11/12/2018

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CONTENTS
• INTRODUCTION
• NEED OF A CONSTRUCTED WETROOF (CWR)
• COMPONENTS OF A CWR
• CLASSIFICATION OF CWR
• TECHNICAL ASPECTS OF CWR
• ADVANTAGES AND LIMITATIONS OF CWR
• CASE STUDY
• CONCLUSION
• REFERENCES
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INTRODUCTION
➢ CONSTRUCTED WETROOF (CWR)
❖ Combination of Green Roof and Constructed Wetlands
❖ Placed over the roof of a building
❖ Used for the treatment of pretreated domestic wastewater
❖ First introduced in Netherlands
❖ The treated water is used for irrigation, toilet flushing etc
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Fig 1 : Schematic Representation of a
Constructed Wetroof
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NEED OF A CONSTRUCTED
WETROOF (CWR)
▪ Population growth
▪ Urbanization
▪ Lack of land
▪ Lack of green spaces
▪ Depletion of fresh water sources
▪ Increased production of wastewater.

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COMPONENTS OF A CONSTRUCTED
WETROOF
The major components of a CWR are:
1)Turf mat / vegetation
2)Stabilization plate
3)Substratum
4)Drainage
5)Insulation
6)Bituminous waterproofing
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1) Turf mat / vegetation
• An immediate vegetation cover on top of the system
• Substrate depth dictates vegetation diversity and the
range of possible species
➢ Function
o Protects the substratum by withstanding heavy rain,
snow or wind.
o Provides an immediate presence of plants for further
root colonization.
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2) Stabilization plate
• Recycled-plastic stabilization plate
• It is placed in between the turf mat and substratum.
➢ Function
o Increase lifespan of the system
o Helps to support even sloped roofs during
seasonal events (e.g. rain) and walking of people
(during maintenance)
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3) Substratum
• Important component of CWR
• Major parameter- Load bearing capacity (LBC) of the
building or roof - limits the amount and type of
material to be used
• The material should provide enough surface area for
biofilm development and appropriate water purification
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• Very fine material like sand is preferred, but heavy and can
affect the LBC of the building
• So Light and high-surface-area materials (e.g. Light
expanded clay aggregates (LECA), biodegradable polylactic
acid (PLA) beads etc) should be considered for this purpose.
➢Function
• Water purification
• Act as a support for biofilm development
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4) Drainage layer
• Controls the drainage properties of the roof in combination with
the substrate
• Composed of either granular materials (e.g. sand and/or gravel,
lava and pumice, crushed brick etc.) or modular/ sheet systems.
➢ Function
o drains water off the roof
o protects the root proof layer from being mechanically damaged
o retains water for times of drought
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5) Insulation
• A root membrane is provided
•The membranes specification depends on the planned
landscape and the slope of the roof.
•The root barrier could either be a biocide or a copper/
heavy grade polythene-based material
➢ Function
o Root membrane prevents plant roots from damaging the
waterproofing.
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6 ) Bituminous water proofing
• Bitumen is a mixed substance made up of organic
liquids that are highly sticky, viscous, and waterproof.
• Sometimes used to construct roofs, in the form of
roofing felt or roll roofing products.
➢ Function
o Designed to protect residential and commercial
buildings
o Provides an extra weather barrier in case of blow
offs or water penetration through the roofing or
flashings.
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Fig 2 : Components of a CWR matrix
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Fig 3: Bituminous waterproofing layer
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CLASSIFICATION OF CWR
a) Based on Green Roof
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Characteristics Extensive Roof Intensive Roof
Purpose Functional; storm-water
management, thermal
insulation, fireproofing
Functional and aesthetic;
increased living space
Structural requirements Typically within standard
roof weight-bearing
parameters; additional 70
to 170 kg/m2
Planning required in
design phase or structural
improvements necessary;
additional 290 - 970 kg/m2
Substrate type Lightweight; high
porosity, low organic
matter
Lightweight to heavy;
high porosity, low organic
matter
Average substrate depth 2 to 20 cm 20 or more cm

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Plant communities Low-growing
communities of plants and
mosses
selected for stress-
tolerance qualities
No restrictions other than
those imposed by
substrate depth, climate,
building height and
exposure and irrigation
facilities
Maintenance Little or no maintenance
required; some weeding or
mowing as necessary
Same maintenance
requirements as similar
garden at ground level
Accessibility Generally functional
rather than accessible; will
need basic accessibility
for maintenance
Typically accessible;
bylaw considerations
Characteristics Extensive Roof Intensive Roof
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b) Based on Constructed Wetland
Three types:
i. Horizontal Surface Flow
Fig 4: Horizontal Surface Flow CW
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ii. Subsurface Horizontal Flow
Fig 5: Subsurface Horizontal Flow
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iii. Vertical flow CW
Fig 6 : Vertical Flow CW
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TECHNICAL ASPECTS OF CWR
1) THE TREATMENT TRAIN
Toilet
flushing,
Irrigation
etc
Source Primary Secondary
Fig 4: The Treatment Train
Treatment
Kitchen,
bathroom,
laundry
Septic
Tank
Constructed
wetroof
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2) AEROBIC CHARACTERISTICS OF CWR
• Functions as highly aerobic system
• Main reason – shallow depth of CWR bed and presence of
vegetation
• The roots in the CWR occupy∼12% of the whole media
• Thus, the grass could provide a great part of the oxygen
• A shallow bed results in a high root density that contributed
to a higher water-root contact, hence increasing the chances
for oxygen release from the roots to the water.
• Also, the highly oxygenated rain water creates mixing in
the bed that can facilitate oxygen transfer.
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3) MICROBIAL ACTION IN CWR
• Microbial activity in the turf mat was greater than
substratum
• The turf mat is composed of organic soil and roots, both
being an ideal support of an active biofilm
• Hence the turf mat provides an immediate ideal condition
for biofilm development until the system gets adapted to
new conditions
• Along the length of the bed, inlet region showed the
higher microbial activity as compared to the rest of the bed
• During dry days, lack of water along the whole bed affects
the microbial activity and reduces treatment performance.
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4) EFFECT OF SEASONAL CHANGES ON CWR
➢ EFFECT OF RAIN
• During rainy days, the excess of water accelerated the
DWW movement, thus highly reducing the system’s
HRT.
• At the same time the rain highly dilutes all type of
pollutants
• Hence in terms of concentration, the water quality
was not negatively affected.
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➢ EFFECT OF SUMMER
• During hot summer days, the DWW close to the inlet
area get almost evapotranspirated , due to the shallow depth
and large area, turning the system often into a zero-
discharge CW.
• This causes serious plant drought, deteriorating the CWR
aesthetics in such period
• To cope up this situation intermittent irrigation can be
done.
• The surplus effluent water (overflow) that goes to the
infiltration pond can be used for this purpose.
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ADVANTAGES AND LIMITATIONS OF CWR
➢ ADVANTAGES
• Helps in storm water management
• Reduces heat island effect
• Noise insulation
• Protects the building from thermal effect
• No land area is required for wastewater treatment
• Improves the quality of air
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• Decreases the amount of water to be treated in a wastewater
treatment plant
• Increase oxygen levels
• Reduces carbon dioxide quantities
• Protects the building from UV radiations
• Enhances the aesthetics of the area
• Generates self-efficient buildings that are capable to recycle the
water
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➢ LIMITATIONS
• Load bearing capacity (LBC) of the building
• Installation cost is high.
• Pretreatment is required to avoid clogging.
• Periodic maintenances should be done.
• Requires expert design and supervision.
• Not all parts and materials may be available locally.
• Long startup time to work at full capacity
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CASE STUDY
• A CWR was built in April 2012 at the Van Helvoirt
Groen projecten facilities, Netherlands done by Zapater-
Pereyra
• The company ECOFYT conducted the hydraulic design
of the CWR as a subsurface horizontal flow CW.
• Had a depth of 9 cm
• LBC of building: 100 kg/ m2
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Fig 4: CWR Constructed at Van Helvoirt, Netherlands
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➢ COMPONENT STRUCTURE
• Turf mat in 1.5cm depth at top composed of 20% Lolium
perenne,50% Festuca rubra and 30% Poa pratensis
• Stabilization plate in 3.5cm depth
• 7.5 cm of Substrate
• volcanic sand (0-4mm)
• LECA
• PLA
• fine sand (0–0.5 mm)
• The material proportion was 33:17:22:28
• Load applied on the building was 90kg/m2 (Zapater-Pereyra et.al,
2013)
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Parameter Value
Constructed wetland type
Bed Area (m × m)
Depth (m)
Number of beds
Roof angle
Flow type
Water pulses per bed per day
Volume of each pulse /m of bed
(L )
Wastewater type
Pre-treatment
Retention time (d)
Resting period
Horizontal subsurface flow constructed
wetland
3.00 × 25.50
0.09
4
14.3°
Intermittent
2
` 3.45-4
Pre-treated domestic wastewater
Septic tank (Expected)
2-3
1.5 d per week (Weekend) ,When roof
temperature < 2°C.
Table 1: Features of the Constructed Wetroof
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`Parameter Influent Effluent % removal
DO (mg L-1 ) 0.3 ± 0.1 3.2 ± 1.8 –
BOD (mg L-1) 217 ± 16 11 ± 1 94.9
TSS(mg L-1 ) 186 ± 22 26 ± 5 86
COD (mg L-1 ) 859 ± 76 129 ± 31 85
NH4 + -N (mg L-1 ) 187 ± 9 0.2 ± 0.1 99.9
NO3 - -N (mg L-1 ) 0.08 ± 0.02 8.05 ± 3.28 –
Total N (mg L-1 ) 225 ± 8 7 ± 2 97
Total P (mg L-1 ) 27 ± 3 8.7 ± 2.7 79.1
Table 2: Water Quality in the Influent and Effluent of the full-scale Constructed Wetroof
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CONCLUSION
• Lack of water, lack of space and lack of green areas have
stimulated new solutions for wastewater treatment like the
Constructed Wetroof
• Combines the benefits of a constructed wetland for wastewater
treatment with those of a green roof in a single system, providing
green areas in unused spaces.
• It has proven to deliver an appropriate effluent quality for
irrigation, toilet flushing or disposal into water bodies while it
also provides a green area.
•This system is adaptable to different urban requirements but it is
best seen as a way to solve some of the problems of megacities
where the need for sanitation, water and green areas are critical
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REFERENCES
• Abdou A. et.al (2016); “Constructed Wetlands as a Sustainable Wastewater
Treatment Methods in Communities”; Procedia Environmental Sciences 34 (2016),
605 – 617.
•Andreas Thon et.al (2010); “Constructed Wetlands on Roofs as a Module of Sanitary
Environmental Engineering to Improve Urban Climate and Benefit of the Onsite
Thermal Effects”; Journal of Environmental Science 2010 1(7), 191-196.
•Arthur F M et.al (1999); “Wetlands for Wastewater Treatment: Oppurtunities and
Limitations”; Ecological Engineering 12 (1999), 5–12.
•Chris C Tanner (1996); “Plants for Constructed Wetland Treatment Systems- A
comparison of the Growth and Nutrient Uptake of Eight Emergent Species”;
Ecological Engineering 7(1996), 59-83.
•Corrie Clark et.al (2008); “Green Roof Valuation: A Probabilistic Economic Analysis
of Environmental Benefits”; Environmental Science Technology (2008) 42, 2155–
2161.
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• García J.A. et.al (2013); “Effect of plants and the combination of
wetland treatment type systems on pathogen removal in tropical climate
conditions”; Ecological Engineering, 58, 57-62.
• Jim C Y et.al (2015); “Assessing climate-adaptation effect of extensive
tropical green roofs in cities”; Landscape and Urban Planning 138
(2015), 54–70.
• Kuschk P et.al (2003); “Effects of plants and microorganisms in
constructed wetlands for wastewater treatment”; Biotechnology
Advances 22 (2003), 93– 117.
• Zapater-Pereyra et.al (2013); “Material selection for a constructed
wetroof receiving pre-treated high strength domestic wastewater”; Water
Science and Technology, 68 (10), 2264-2270.
• Zapater-Pereyra et.al (2016); “Constructed wetroofs: a novel approach
for the treatment and reuse of domestic wastewater”; Journal of
Ecological Engineering (2016) 94, 545 – 554.
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