Dr. Shivani Dhage , Er. Ritesh Vijay and Dr. Prakash Kelkar

Functional Appraisal of Marine Outfall

For Domestic Waste Disposal through Tracer Technique

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

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.

What is Marine Outfall

Sr. No. Continents Name of the Country / place 1 Africa • Casablanca (Morocco). 2 Asia • Manila Bay (Philippines).

• Mumbai (India), • Mutwall, Wellawaththa, Lunawa (Sri Lanka).

3 Australia • Sydney. 4 Europe • 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),

5 North America • Honolulu ,the New York Bight, Southern California Bight (USA),

• Victoria, British Columbia, (Canada). 6 Latin America

and the Caribbean

• Cartagena, Colombia, • Ipanema beach from Rio de Janeiro (Brazil)*. • Sosua (Dominican Republic).

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

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

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.

Advantages of Outfall System

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.

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.

Difficulties in Evaluation

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

Total Flow collected through sewerage system = 1433 MLD Total pollution load = 278075 Kg/day

Pollution Load through Organized Wastewater Discharges in Mumbai

Service Zone Organized Waste Water Flow

(MLD)

Method of Disposal

Avg. BOD (mg/L)

Pollution Load (Kg/day)

Colaba 35 1.1 km Marine Outfall

312 10920

Worli 393 3.2 km Marine Outfall

316 124188

Bandra 473 3.2 km Marine Outfall

170 80410

Ghatkopar 120 Aerated Lagoon 134 16080

Bhandup 121 Aerated Lagoon 67 8107

Versova 190 Aerated Lagoon 85 16150

Malad 101 Marine outfall (Proposed)

220 22220

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

Pollutants & Effects of Waste Releases from Domestic Waste Releases

ISO 9001-2000

Screens

Marine Outfall

De-gritting Chambers

Effluent EPS

Preliminary Treatment at WWTF

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.

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.

Evaluation of Marine Outfall

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.

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.

Methodology of Study (Contd..)

Half life of 82Br is 36 Hrs.

Injection Methodology adopted for application of Radio Tracer 82Br

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

Technical Information on Fluorescent Dye

“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

“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.

Simulation Studies

Impact Zone of Outfall - DO and BOD Profile DO (mg/L) BOD (mg/L)

Low Tide (FC)

Low Tide BOD Existing Coastal Water Quality at Mumbai

Dilution Factor of (FC

) D

ilutio

n Fa

ctor

of (

BO

D, N

H3)

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

Dilution Factor during Flooding Tide with BOD, FC and 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

Analytical Results for Dilution Experiment Conducted During Flooding Tide

BOD FC NH3-N

Receding Tide

Radiotracer Contours

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

Performance of Radiotracer, Fluorescent Dye Rhodamine and Mathematical Models for Estimation of Dilutions

Location wrt diffuser

Distance (m)

Dye conc. (ppb)

Dilution achieved Av. Dilution Time* (min)

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

Dilution Achieved at Various Locations During Tidal Conditions

* Time after appearance of the dye

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

Tracer Plume During High & Low Tide

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.

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.

Observations (Contd..)

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

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.

Conclusions (Contd..)

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.

Recommendations

Acknowledgements: • The Director, NEERI, for encouragement & support • Officials of Municipal Corporation of Greater Mumbai • Fellow Scientists from NEERI, Mumbai and Nagpur • BARC, Mumbai, India