Functional Appraisal of Marine Outfall
For Domestic Waste Disposal
through Tracer Technique
Dr. Shivani Dhage ,
Er. Ritesh Vijay and Dr. Prakash Kelkar
International Conference on Desalination, Environment
And Marine Outfall Systems
13-16 April 2014
SQU Muscat Oman
Marine Environment
Ocean : Biggest resource provider for mankind.
However it is also used as pollution sink for coastal
zone
Marine ecosystem:
experiencing the stress of
pollution, particularly in near shore regions of
coastal cities
Urban Settlement: By 2011, about 50% of World’s
urban population living in coastal cities.
17 out of 25 mega cities in coastal area
accommodating about 25% world’s population use
ocean for waste disposal
Marine outfall is one of the options for waste
discharges megacities
What is Marine Outfall
A pipeline or tunnel that discharges municipal,
industrial or desalination wastewater, storm water or
other effluent to the sea.
Common inclusions in the infrastructure of coastal
cities for sewage disposal.
Municipal wastewater discharged with no or only
preliminary treatment
Assimilative capacity of the sea used for further
treatment
The processes like diffusion, dispersion and
decomposition of wastewater are enhanced and
shifted away from the coastline.
Marine Outfall Installations in the World
>200 outfalls listed in an International database [Institute for Hydromechanics
at Karlsruhe University for the International Association of Hydraulic Engg. &
Research (IAHR) / (IWA)]
Locations of Submarine Outfalls in the World
Sr. No.
1
2
Continents
Africa
Asia
3
4
Australia
Europe
5
North America
6
Latin America
and the
Caribbean
Name of the Country / place
•
Casablanca (Morocco).
•
Manila Bay (Philippines).
•
Mumbai (India),
•
Mutwall, Wellawaththa, Lunawa (Sri Lanka).
•
Sydney.
•
Barcelona, San Sebastian, Spain
•
Costa do Estoril (Portugal),
•
the Marmara Sea near Istanbul (Turkey),
•
Split (Croatia), Edinburgh, Scotland.
•
the Thames Estuary downstream of London (UK),
•
Honolulu ,the New York Bight, Southern California
Bight (USA),
•
Victoria, British Columbia, (Canada).
•
Cartagena, Colombia,
•
Ipanema beach from Rio de Janeiro (Brazil)*.
•
Sosua (Dominican Republic).
Technology Details of Outfall in the World
Diameter of Outfalls: As narrow as 15 cm to as
wide as 8 m: Widest outfall : 8 m dia. at
Spain for industrial wastewater.
Length of Outfalls: As short as 50 m to as long as
55 km Longest outfall: At Boston - 16 km for
sewage. At Ankaleshwar (India) – 55 km for
industrial waste
Depth of outfall : As shallow as 3 m to as deep
as 60 m, Deepest municipal wastewater outfall
located in Venezuela
Advantages of Outfall System
Natural dilution & dispersion of pollutants
Ability to keep the sewage field submerged due to depth
available at release point
Greater die-off rate of pathogens due to greater salinity
Less expensive than advanced WWTF
Use natural assimilative capacity of the sea instead of
energy-intensive advanced treatment processes.
Preliminary treatment is sufficient for outfall and diffuser.
Costs of preliminary treatment are about one tenth of
advanced secondary treatment and also requires much
less land.
Disadvantages of
Marine Outfalls
Marine outfalls for partially treated or untreated
wastewater remain controversial for following reasons.
It was challenged by residents claiming that the
wastewater caused damage to the marine environment
and fisheries.
The design calculation & computer models for
modelling have been criticized, arguing that dilution is
overemphasized
Other mechanisms, such as bioaccumulation of
toxins, sedimentation of sludge work in the opposite
direction
Accumulative mechanisms include slick formation,
windrow formation, flocculate formation and
agglomerated formation.
Difficulties in Evaluation
Once the marine outfall is operational, it is
cumbersome to find its functional and operational
behavior in coastal region.
Evaluation of extent of dilution achieved is
complicated due to many reasons like, variation in
direction and buoyancy of upward flow, density,
currents, tidal effects and also the submergence of the
physical components of the diffuser.
Accurate information on compliance of the coastal
water standards is not readily computable.
Marine Pollutants
Marine Pollution: a degradation process of environment
due to inputs of chemicals, biological agents,
sediment, radiation, or heat
Coastal waters especially are highly affected by pollution
because they receive variety of pollutants like:
Non Point source - Discernable in terms of origin
Petroleum (Oil) : Oil refineries, oil tanker spills,
offshore oil well blowouts
Domestic waste & Sewage sludge: Human settlements
Insecticides: Agriculture & Pest Control
Mercury: industry
 Source pollution - Not defined or diffused sources,
Runoff harbours and marinas,
powerboat
Mumbai Sewage Disposal Project
Pollution Load through Organized
Wastewater Discharges in Mumbai
Service Zone
Method of
Disposal
Avg. BOD
(mg/L)
Pollution Load
(Kg/day)
312
10920
316
124188
170
80410
134
16080
Colaba
Organized Waste
Water Flow
(MLD)
35
Worli
393
Bandra
473
Ghatkopar
120
1.1 km Marine
Outfall
3.2 km Marine
Outfall
3.2 km Marine
Outfall
Aerated Lagoon
Bhandup
121
Aerated Lagoon
67
8107
Versova
190
Aerated Lagoon
85
16150
Malad
101
Marine outfall
(Proposed)
220
22220
Total Flow collected through sewerage system = 1433 MLD
Total pollution load = 278075 Kg/day
Pollutants & Effects of Waste Releases
from Domestic Waste Releases
POLLUTENTS
Biodegradable – Carbonaceous and Nitrogenous
Microbes – TC, FC, FS
Nutrients – Phosphorus and Nitrogen
Toxic - Detergents, Heavy Metals
IMPACTS
DO depletion
Ammonia toxicity
Microbial contamination
Alteration of phytoplankton and zooplankton
Reduction in primary productivity
Migration of fish
Preliminary Treatment at WWTF
Effluent EPS
Marine
Outfall
Screens
De-gritting Chambers
ISO 9001-2000
Marine outfalls with multiport
diffusers is a modern system
adopted to dispose off liquid waste
in coastal cities
About 900 mld preliminary
treated effluent is discharged
through two marine outfalls near
Worli and Bandra at a seaward
distance of 3.2 km.
Evaluation of Marine Outfall
Marine environment is very complex & dynamic. The mixing
behavior, dilution and dispersion of released wastewater is
governed by the interplay of ambient conditions of receiving
water.
It is complicated to find functional and operational behavior of
marine outfall & the extent of dilution achieved due to many
reasons. Factors like Temperature, chlorinity, re-aeration,
currents, tidal effects etc. play significant role in dilution.
Wastewater emerges to the surface through the risers at the
near-field, as non-merging surface plume: a character of a
shallow coastal marine outfall
Tracer studies and mathematical simulation provide valuable
tool to test the performance and adequacy of such systems. It is
essential to compare the actual field results for system
evaluation.
Methodology of Study
DO and BOD compliance status evaluated in ONE sq. km area
in near field diffuser region for flooding and receding tides of 12
hours duration.
Pollutants like BOD, FC, NH3 existing in wastewater tried as
natural tracers. The effluent had BOD: 150 mg/L, NH3-N: 14.0
mg/L and FC range :10E+07.
Water samples collected through boats for three hours after the
waste field appeared at the surface in the expected dispersion
zone
The studies using chemical and radioactive tracers carried out
to investigate the dilution and dispersion pattern of the waste
plume. Bromine 82 (82Br) radio tracer and Rhodamine
fluorescent dye used. The tracers injected for 1 hour at effluent
channel after grit chamber.
Methodology of Study (Contd..)
DO, BOD, NH3N & FC analyzed as per Standard analytical
procedures. Radiotracer monitored by scintillating detectors
& fluorescence with Shimadzu RF 5000 Spectrofluorometer.
S4 Current meter (Inter Ocean) was deployed to measure
temporal variation of ambient current velocities.
Mathematical model Mike 21 used for hydrodynamic and
water quality simulation for solute transport processes,
dilution & dispersion under variable tidal situation & time
intervals.
Simulation results calibrated and validated with the
experimental data of DO, BOD, FC and dye. The
Hydrodynamic & water quality validation of the model to
reproduce the agreement between the observed & predicted
water surface elevations, current velocities and directions.
Injection Methodology adopted for
application of Radio Tracer 82Br
Half life of 82Br is 36 Hrs.
Technical Information on Fluorescent Dye
Rhodamine, the fluorescent tracer is one of the most useful tracers for
quantitative studies because of minimum delectability, photochemical
and biological decay rates, good aqueous solubility, and adsorption.
It is the most conservative dye for streams or karsts tracing.
Toxicological Data: Oral mouse LD50: 887 mg/kg; investigated as a
mutagen, tumorigen, reproductive effector, hence the concentration of
dye used during study will not pose toxicity to most of the aquatic life.
The laboratory experiments on the impact of salinity, organic matter,
and turbidity on fluorescence property of Rhodamine indicated
marginal reduction of fluorescence (5 to 7%).
A corrective action was applied during measurement of dye
concentration by preparing calibration curve in artificially prepared
water with salinity, turbidity and organic content to match the field
conditions
“Tracer studies using fluorescent dye Rhodamine to evaluate dilution,
dispersion and travel path of the waste plume through
Bandra Marine Outfall”
“This study is quoted as one of the sixty achievements of CSIR”
Tracer Tracking
Simulation Studies
“Mike 21 model” was used to carry out hydrodynamic and
water quality simulation for solute transport processes
under different tidal conditions and time intervals.
This model simulates two dimensional distribution of
current, water surface elevations and water quality
parameters within the modeling domain as function of time
taking into account the hydraulic characteristics governed
by bed topography, surface wind effects and boundary
conditions.
Simulation results calibrated and validated with the
experimental data of DO, BOD, FC and Rhodamine dye.
Impact Zone of Outfall - DO and BOD Profile
DO (mg/L)
BOD (mg/L)
Existing Coastal Water Quality at Mumbai
Low Tide BOD
Low Tide (FC)
Dilution Factor of (FC)
Dilution Factor of (BOD, NH3)
Dilution Factor during Flooding Tide
with BOD, FC and NH3-N
Travel Time of Plume – Hrs.
Tide Conditions: LT 9.50 am, 1.42 m, HT 3.35 pm, 3.30 m
Time of travel through outfall tunnel for waste plume appearance
at surface: 1 hour 35 minutes
Analytical Results for Dilution Experiment
Conducted During Flooding Tide
BOD
FC
NH3-N
Tide Conditions: LT 9.50 am, 1.42 m, HT 3.35 pm, 3.30 m
Time of travel through outfall tunnel for waste plume appearance
at surface: 1 hour 35 minutes
Radiotracer Contours
Receding Tide
Performance of Radiotracer, Fluorescent Dye Rhodamine
and Mathematical Models for Estimation of Dilutions
 Dilution factors obtained
through tracer and
Mathematical Models
marginally differ at far field
locations
 Maximum dilution achieved
in field experiment differ
from the design value
Dilution Achieved at Various Locations During Tidal Conditions
Location wrt
diffuser
Distance
(m)
Dye conc.
(ppb)
Center
500
15-40
25-60
38
15-45
East pole
500-1300
12-26
37-82
54
40-70
Center
1000
14-38
26-62
40
45-60
West
400-900
8-16
24-129
87
35-70
East pole
1100-2950
11-20
51-93
72
100-130
Center
1100
17-20
51-58
54
100-150
West
850-2500
9-17
109-133
121
120-150
East pole
1000-2350
11-12
80-86
83
150-180
Center
1200
10-12
100-105
102
130-170
West
1150-2500
8-16
109-133
121
120-150
* Time after appearance of the dye
Dilution achieved Av. Dilution
Time*
(min)
Tracer Plume During
High & Low Tide
Dispersion Pattern at
Bandra Outfall
during flooding &
reseeding tide
 Conducted at Bandra
Outfall
 Input concentration of
Dye in Sewage: 1000 ppb
 Average dilution factor :
38 upto distance of 500 m
Conceptualization and Validation of Hydrodynamic
Simulation and Water Quality Modeling for BOD and Dye
Observations
Non compliance of BOD near the diffuser location in
the mixing zone.
The natural chemical and microbial tracers like BOD,
FC, NH3N did not offer exact dilution either at the
initial or far field location. The sea water available for
dilution already contaminated with selected
parameters and natural decay of these conservative
parameters.
The Rhodamine has minimum delectability,
photochemical and biological decay rates, toxicity (LD
50:887 mg/kg oral -Mouse) and good solubility. The
dose applied not harm aquatic life.
Observations
(Contd..)
The impact of salinity, organic matter & turbidity on
fluorescence of Rhodamine dye indicated marginal
reduction of fluorescence (5 to 7%). A corrective action
applied.
The appearance of dye noticed after 1 hr. 40 minutes
after injection confirm design travel time from WWTF
to diffuser.
The radiotracer and fluorescent dye provide analogous
results within ± 15% variation in the near field region
upto 625 mts away from diffuser pole
Comparable results for tracers & mathematical models
(Brooks for near field & DIVAST far field region)
Observations
(Contd..)
The calibration of model with correlation
coefficients 0.9 and 0.8 through simulated BOD
with observed values during high and low tide
respectively.
The simulation results established through
movement of waste plume represented by BOD
and dye follows the same trend of distribution and
dispersion in high and low tide.
Conclusions
Wastewater released through the diffusers got 30 to 60
times diluted in the near field areas up to 500 to 1000
meters from the centre of diffuser.
The dilution achieved is not adequate to comply the
designated receiving water quality standard of 3 mg/l
BOD at 3 km distance near the diffuser with discharged
quantity.
Dilution factor obtained through dye concentration at
east and west pole, indicates that the ten risers and ports
along the length of diffuser had uneven discharge rates.
This finding was attributed to the number and extent of
openings of the each port throughout the length of
diffuser. All the diffusers are not functioning equally.
Conclusions
(Contd..)
The waste plume from outfall moved parallel to the coast
demonstrating minimum risk of wastewater reaching the
coast thus achieving minimization the pollution on the
beaches through marine outfall system.
Before the reversal of the tide, the waste plume traveled up to
about 2.5 to 3.0 kilometers as the current was low.
Outfall impact zone for water quality deterioration extended
up to 5 km seaward distance.
In monsoon with high currents, strong winds & turbulence,
the waste field is likely to travel longer distance.
The movement of waste plume based on simulation results
through mathematical model follows observed pattern of dye
appearance monitored with the help of GPS locations.
Recommendations
The need for reorientation and alteration of the
degree of opening of ports at each riser to improve
the initial mixing.
Non-point discharges to be controlled as Ecosystem
of near shore region of Mumbai coast is at risk with
increased pollutants load
Efforts to achieve compliance of standards in coastal
region & corrective steps should be undertaken to
improve environmental status
Wastewater discharge standards to be more stringent
to achieve SW II at coastal zone.
Acknowledgements:
•
•
•
•
The Director, NEERI, for encouragement & support
Officials of Municipal Corporation of Greater Mumbai
Fellow Scientists from NEERI, Mumbai and Nagpur
BARC, Mumbai, India