Functional Appraisal of Marine Outfall For Domestic Waste Disposal through Tracer Technique

Transcription

1 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 April 2014 SQU Muscat Oman

2 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

3 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.

4 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)] 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), 6 Latin America and the Caribbean Locations of Submarine Outfalls in the World Victoria, British Columbia, (Canada). Cartagena, Colombia, Ipanema beach from Rio de Janeiro (Brazil)*. Sosua (Dominican Republic).

5 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

6 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.

7 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.

8 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.

9 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

10 Mumbai Sewage Disposal Project

11 Service Zone Pollution Load through Organized Wastewater Discharges in Mumbai Organized Waste Water Flow (MLD) Method of Disposal Avg. BOD (mg/l) Total Flow collected through sewerage system = 1433 MLD Total pollution load = Kg/day Pollution Load (Kg/day) Colaba km Marine Outfall Worli km Marine Outfall Bandra km Marine Outfall Ghatkopar 120 Aerated Lagoon Bhandup 121 Aerated Lagoon Versova 190 Aerated Lagoon Malad 101 Marine outfall (Proposed)

12 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

13 Preliminary Treatment at WWTF Effluent EPS Screens Marine Outfall De-gritting Chambers ISO

14 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.

15 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.

16 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, NH 3 existing in wastewater tried as natural tracers. The effluent had BOD: 150 mg/l, NH 3 -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 ( 82 Br) radio tracer and Rhodamine fluorescent dye used. The tracers injected for 1 hour at effluent channel after grit chamber.

17 Methodology of Study (Contd..) DO, BOD, NH 3 N & 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.

18 Injection Methodology adopted for application of Radio Tracer 82 Br Half life of 82 Br is 36 Hrs.

19 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 LD 50 : 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

20 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

21 Tracer Tracking

22 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.

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

24 Existing Coastal Water Quality at Mumbai Low Tide BOD Low Tide (FC)

25 Dilution Factor of (BOD, NH 3 ) Dilution Factor during Flooding Tide with BOD, FC and NH 3 -N Dilution Factor of (FC) 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

26 Analytical Results for Dilution Experiment Conducted During Flooding Tide BOD FC NH 3 -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

27 Receding Tide Radiotracer Contours

28 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

29 Dilution Achieved at Various Locations During Tidal Conditions Location wrt diffuser Distance (m) Dye conc. (ppb) Dilution achieved Av. Dilution Time* (min) Center East pole Center West East pole Center West East pole Center West * Time after appearance of the dye

30 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

31 Conceptualization and Validation of Hydrodynamic Simulation and Water Quality Modeling for BOD and Dye

32 Observations Non compliance of BOD near the diffuser location in the mixing zone. The natural chemical and microbial tracers like BOD, FC, NH 3 N 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.

33 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)

34 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.

35 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.

36 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.

37 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.

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