2 OXYGEN DEMANDING WASTES T.K. Liu
1
Marine Pollution
Dissolved oxygen and oxygen demand High in surface due to photosynthesis; Decrease under photic zone due to respiration; Increase in the bottom due to sinking oxygen rich polar water.
2
Dissolved oxygen in the ocean Gas
Percent of gas in atmosphere by volume
Percent of dissolved gas in seawater by volume
Conc. in seawater in ppm, by mass
N2
78.08%
48%
10-18 ppm
O2
20.95%
36%
0-13 ppm
CO2
0.03%
15%
64-107 ppm
Garrison, 2005
3
Oxygen solubility in ocean
(Metcalf & Eddy, 1991)
DO =fn(T,S,P) T: Temperature S: Salinity P: Pressure
4
Oxygen demand
Aerobic bacteria make use of O2 C6(H2O)6 + 6O2 → 6H2O + 6CO2 When DO >1~1.5 mg/L
organics + O2 → H2O + CO2 + stable end products (SO42-, PO43-, NO3-)
Anaerobic bacteria oxidize organics without O2
When DO < 1~1.5 mg/L Fe3+
Fe2+
organics + SO42- → HSNO3
-
CO2
+ unstable end products
NO2
FeS (black)
CH4
H2S (odor)
-
Inorganic wastes deplete O2 when get oxidized 5
Measurement of BOD
Biological oxygen demand (BOD): parameter of organic pollutants
Five-day BOD test (BOD5): Total O2 consumed by microorganisms during the first 5 days.
Measure DO @ t=0:
initial DO0
Put in dark room @ 20℃ for 5 days
Typically, background seawater BOD < 2 mg/L domestic wastewater BOD ≒ 200~300 mg/L
DO = 7.4 mg/L @ 20 ℃ & s a l i ni t y35‰ , us ua l l yne e dsdi l ut i on during BOD test. BOD = (DO0-DOf )/df
df=Vsample/(Vsample+Vdilution water)
6
Measurement of BOD Seeded BOD test (BOD5): To assure adequate bacteria population to carry out the biodegradation. Typically add 2 mL of wastewater to 1L of dilution water BODSVS + BODDVD =BODMVM
t=0
df = VS/VM
BODS = BODM (VM/VS) –BODD (VD/VS) = BODM/df –BODD (1-df)/df
M
D
DOi
Bi
t = 5 days
= [(DOi –DOf ) –(Bi –Bf )(1 - df)] / df S: sample; D: dilution; M: mixture
M
D
DOf
Bf 7
Ultimate BOD Ultimate BOD∞ (=L0) dLt/dt = - k Lt (assme 1st order decay) Lt = L0 e-kt (organics left after time t) L0 = BODt + Lt
L0 Organics as mgO2/L
BODt = L0 –Lt = L0(1-e-kt)
BODt
Lt t
BOD∞ BOD5
k @ 20℃ BODt
5
t
BOD5
Time
Ex. Domestic wastewater BOD5=200 mg/L assume k = 0.4 d-1 BOD∞= 200/(1-e-0.4*5) = 230
5
Time
day-1
Raw wastewater
0.35-0.7
Polluted river
0.10-0.25
Reaction constant is Temp dependent kT = k20 * (1.047) T-20 k5 (winter) = k20 * 0.5 8
Nitrogenous BOD Nitrification: typically observed from 5~8 days in BOD test Wastes (organic-N) → NH3 → (e.g., protein, urea)
NO2- → NO3-
Nitrification(硝化)
→
N2
Denitrification(脫硝)
BOD∞ Nitrogenous BOD
Nitrosonomas sp. (亞硝酸菌) 2NH3 + 3O2 →2NO2- + 2H+ + 2H2O
Carbonaceous BOD
Nitrobacter sp. (硝酸菌)
BOD5
2NO2- + O2 →2 NO35
Time
2NH3 + 4O2 →2NO3- + 2 H+ + 2H2O 1 mole NH3 oxidation need 2 mole O2 2*32 g O2/ 14g NH3-N ≒ 4.6 gO2/gNH3-N Ultimate NBOD = 4.6 TKN (Total Kjeldahl Nitrogen = Organic-N + NH3-N) 9
Other measures of oxygen demand Chemical oxygen demand (COD) Organics (CaHbOc) + Cr2O72- + H+ Cr 3+ + CO2 + H2O COD test only takes 3 hours (BOD needs 5 days) COD>BOD, some compounds only can be chemically oxidized COD usually correlate with BOD e.g., for domestic wastewater, COD/BOD = 1.25 ~2.5 Theoretical demand (ThOD) Completed oxidation (C → CO2; N → NO3-) Ex. ThOD of glycine (C2H5O2N) (1) C2H5O2N + 1.5 O2 → 2CO2 + NH3 + H2O (2) NH3 + 2O2 → H+ + NO3-+H2O ThOD = (1.5+2)*32 = 112 gO2/mole glycine 10
Dilution factor :
2
The solution to pollution is dilution
Saturated DO
freshwater
seawater
5℃
12.76
10.13
20 ℃
9.08
7.38
BOD of organic effluent is typically greater, dilution is needed . Current ocean outfall standards (mg/L)
BOD
COD
甲類海域
100
200
乙類海域
150
300
11
Dilution example Ex.
A 4day
Plant I
Plant II
B’ B
C’C
3day, k=0.15
k=0.2
BOD
Flow (cms)
k (d-1)
A
2
10
0.1
I
30
0.5
0.2
II
10
2
0.3
(1) Lo,A= 2/(1-e-0.1*4) = 5.08 Lo,B’= 5.08 e-0.1*4 = 3.41 BOD5,B’= 3.41(1-e-0.1*5) = 1.34 Lo,I = 30/(1-e-0.2*5) = 47.46 L0,B=(Q0L0,B’+ QIL0,I)/(Q0+QI) = 5.51 BOD5 BOD5,B = 5.51(1-e-0.15*5) = 2.91 3 (2) L0,C’= 5.51 e-0.15*3 = 3.51 2 BOD5,C’= 3.51 (1-e-0.15*5) = 1.85 1 Lo,II = 10/(1-e-0.3*5) = 12.87 L0,C={(Q0+QI) L0,C’+ QIIL0,II}/(Q0+QI +QII) = 5.01 A BOD5,C = 5.01(1-e-0.2*5) = 3.17
B
C 12
Oxygen budget
3
Source Incoming water Reaeration from atmosphere Photosynthsis
Sink Bacteria activity Respiration (aquatic organisms/algae) Reduced materials Release to atmosphere Sediments 13
Oxygen sag curve in river
Rate of deoxygenation (rD) Waste flow, QW
rD = k1 Lt = k1 L0 e-k1t
Rate of reaeration (rR) rR = k2 (O2 deficit) = k2 (S-C) = k2D
Upstream flow, Qr u
k1 : deoxygenation const. = BOD rate constant k2: reaeration coeff. =3.9 u0.5 /H1.5
Assuming Plug flow
S: saturation DO
Distant, x or Time, t
C: current DO
Rate of increase of the deficit = rD –rR dD/dt= k1L0e-k1t - k2D y’ +p(x)y=q(x) 14
Streeter-Phelps oxygen sag curve k1 L0 D = ─── ( e-k1t –e-k2t ) + D0 e-k2t k2 - k1 S
saturation Initial deficit D0
rR
D
rD DOmin xc or tc rD > rR
Time or distance rD = rR
rD < rR
15
Excessive BOD saturation
DO
Minimum acceptable DO, typically 1~2 mg/L
unhealthy
anaerobic
Distance
Fish driven elsewhere or die
Anaerobic process produces less desirable end products
Seasonal flow fluctuations change BOD concentration
Streeter-Phelps equation not applicable 16
Temperature effects DO
Waste outlet
Distance
When temperature increase, decay rate increase but saturated value drops and aeration slows down. Streams that have enough DO in winter may have unacceptable deficit during summer. Adverse impact from power plant. 17
4
Estuaries UNESCO definition A semi-enclosed coastal body of water having free connection to the open sea and within which sea water is measurably diluted with fresh water deriving from land drainage US NOAA/DOI definition (for MPA management purpose) Part of a river or stream or other body of water having unimpaired connection with the open sea, where the sea water is measurably diluted with fresh water derived from land drainage, and extending upstream to where ocean derived salts measure less than 0.5 parts per thousand during the period of average annual low flow. 18
Importance of estuary
Major populations reside on many of the estuaries around the world.
1/3 of U.S. population lives and works close to estuaries; 7 of the 10 largest metropolitan areas border estuarine areas (N.Y., Tokyo, London, Shanghai, Buenos Aires, Osaka, L.A.)
Intertidal grass and mangrove roots provide shelter for the small shrimp, crabs, lobster, and other marine life that need protection from predation by larger fish during the early stages of their life cycle. High primary and secondary productivity lead to increases in commercial fisheries. Estimated that 6080% of all commercial fishes depend on estuaries for part or all of their life cycle. 19
Geological formation type of estuary 1. 2. 3. 4.
Drowned river mouth (Ria 溺灣) Bar-build Fjord (峽灣) Tectonic
(Garrison, 2005) 20
Geological formation type of estuary
Drowned river mouth estuary
Formed at the mouth of a river when melting glaciers in temperate latitudes flooded river valleys Rising sea levels push seawater back during the last great rise in sea level. Typically resemble a V-shaped river channel, usually less than 20 m deep, with an accompanying floodplain
(Garrison, 2005)
21
Geological formation type of estuary
Bar-build estuary
A broad, shallow estuarine system where flow of water between the estuary and coastal ocean is restricted by a sand bar paralleling the shore line. Sand bar generally built up to the point where the wave action is stopped. The streams or rivers flowing into bar-built estuaries typically have a very low water volume during most of the year. The bars may grow into barrier beaches or islands and the estuary can become permanently blocked.
(Garrison, 2005)
22
Geological formation type of estuary
Fjord estuary
Forms when glaciers made a deep scouring cut in the coast line as they moved down toward the sea, usually deep with steep sides. A sill or rock bar is situated at the mouth of the fjord having been deposited there when the glacier receded. Fjords are found throughout Canada, Chile, New Zealand, Greenland, Norway, Siberia, and Scotland. Garrison, 2005
23
Geological formation type of estuary
Tectonic estuary
Result from major geological events such as faulting, volcanic eruption, and landslides when part of the coastline moves up or down. When depression sinks below sea level, ocean water may rush in and fill it. Typically very deep and surrounded by mountainous areas. San Francisco Bay is the best-known estuary formed by tectonic activity.
Garrison, 2005
24
Estuary comparison
Drowned river mouth and bar-built estuaries
depths generally less than 50 meters
sand or mud bottoms
found along older, tectonically passive coastlines
Fjords and tectonic estuaries
Fjords tend to have a moderately high input of freshwater. Very little seawater flows into the fjord because of the sill.
depths may extend far beyond 50 meters in some parts
rocky bottoms
found along rugged, tectonically active coastlines
25
Mixing in estuary Oceanographic classification: according to their circulation properties and the steady state salinity distribution
Most important types
Salt wedge estuary
Well-mixed estuary
Partially-mix estuary
Stratified estuary
Reverse estuary
The VR/VT ratio determines the estuary type, not the absolute values of VR or VT
VR, river volume: the volume of freshwater that enters from the river during one tidal period
VT, tidal volume: the volume of water brought into the estuary by the tide and removed over each tidal cycle
26
Mixing in estuary
Salt wedge estuary
VR >> VT, or there are no tides at all mixing is restricted to the thin transition layer between the fresh water at the top and the "wedge" of salt water underneath. Pool mixing for pollutants.
Well-mixed estuary
VT >> VR, tidal mixing dominates the entire estuary complete mix achieves locally between surface and bottom; uniform vertical salinity profiles show Better pollutants dissipation
(Garrison, 2005)
27
Mixing in estuary
Partially mixed estuary
share properties of both salt-wedge and well-mixed estuaries salt water is mixed upward and fresh water is mixed downward, but gradient not as sharp as with a salt wedge
Stratified estuary
Ex. Fjords: typically deep and have a large salt water reservoir below the upper layer Entrainment is a one-way process, so no fresh water is mixed downward Worse pollutants dilution
(Garrison, 2005) 28
Mixing in estuary
Reverse estuary Formed along arid coast when river cease to flow Evaporation at upstream will cause water to flow from the ocean to the estuary
Intermittent estuaries
(Garrison, 2005)
Many estuaries change their classification type because of highly variable rainfall over the catchment area of their river input 29
Resident time of estuary
Circulation in estuary
River flow out to sea
Tidal rise and ebb
Net seaward flow may be small
Ex. Thames estuary, London Ebbing tide: downstream 15 km Rising tide: upstream 13 km Net movement: 2 km seaward
(Clark, 2001)
Needs a month at the head of estuary to reach the ocean Small dilution capacity, pronounced O2 sag, anoxic zone may appear, migratory fish may not pass through
30
Settlement in estuary
Rate of settling of particles depends on the their size and de ns i t y ,andt hevi s c os i t yandve l oc i t yofwat e r .St oke s ’ equation can be used to calculate settling velocity. Flow velocity slow down at estuary Sudden change in salinity cause natural particles to flocculate and settle, i.e., compression of electric double layers. Sedimentation takes place in estuary, leading to the development of extensive mud-flats containing organic materials, metals, and so on. 31
Cheasapeake Bay
The largest estuary in the United States (166,534 km2) In the 1970s, the Bay contained one of the planet's first marine dead zones (hypoxia), oxygen was so depleted that it cannot support life, resulting in massive fish kills. Loss of aquatic vegetation has depleted the habitat for many of the bay's animal creatures. (Garrison, 2005)
32
Marine Eutrophication
5
(Clark, 2001)
33
Nutrient enrichment in natural waters
Enrichment
Many wastes entering sea are plant nutrients, i.e., nitrate and phosphate
Urban run-offs
Fertilizer from intensive farming area
Eutrophication
Natural eutrophication in regions of upwelling: nutrientrich deep ocean water rise to surface, e.g. E. China Sea Anthropogenic eutrophication is result of nutrient pollution of natural waters, e.g., lakes, rivers, estuaries, bays, coastal waters 34
Definition
NOAA definition (National Ocean & Atmosphere Admin.) a process in which the addition of nutrients to water bodies stimulates algal growth. In recent decades, human activities have greatly accelerated nutrient inputs, causing the excessive growth of algae and leading to degraded water quality and associated impairments
EEA Definition (European Environment Agency) Enhanced primary production due to excess supply of nutrients from human activities, independent of the natural productivity level for the area in question 35
Causes of eutrophication Perturbation of N & P biogeochemical cycles Synthetic fertilizers Burning of fossil fuels Forest burning Monoculture of legumes (豆類植物) Animal wastes and manure Sewage: Sewage treatment reduces BOD and some P inputs but no significant reduction of N Loss of wetland (main denitrifying)
36
Sources of nutrients
Point sources: Wastewater drains Domestic Sewage Sewage treatment plants Livestock production Storm sewers Can monitor & regulate or treat
Non-point sources: Agricultural runoff Manure spreading Atmospheric deposition Urban runoff & septic leachate Seasonal effects, e.g. rainfall, meltwater Major source of N & P to surface waters Diffuse, difficult to monitor or manage
37
Example of animal wastes
38
Important nutrients N, P, Si
Ratios N:P and N: Si are especially important Redfield ratio N:P = 16:1 N limited when < 16:1 P limited when >16:1 P most important in freshwater lakes N is usually limiting nutrient in coastal waters and estuaries. P limitation has been documented in coastal waters and estuaries: Si availability controls diatom growth. Dams and upstream eutrophication in rivers traps Si in sediments before it reaches estuaries which may shift algae community. 39
Consequences of eutrophication
Ecological
Ocean Hypoxia/Anoxia Increased harmful algae blooms (HAB) Increased turbidity Loss of sea grass and kelp beds Damage to coral reef Decreased biodiversity Marine mammal & seabird deaths
Socio-Economic
Decreased fisheries and aquaculture yields Contamination of aquifers, taste, odor, NO3- &NO2Increased risk of poisoning of animals including humans by algal toxins Loss of tourism revenues 40
Unexpected consequences of organic loading
Fisheries benefits with increase in organic discharges in Seto Sea Increase in seabirds in Wadden Sea with high organic inputs Number of sea ducks declines as Thames estuary restored. Ocean dumping of sewage sludge results in increase of sea bird. (Clark, 2001) 41
6
Public health risks Beach can be closed temporarily due to sewage contamination 80 million people visit the beaches of Los Angeles and Orange Counties each year, and according to a new study by researchers at UCLA and Stanford, as many as 1.5 million of those visitors are sickened by bacterial pollution, resulting in millions of dollars in public health costs. 42
Pathogens
Pathogens in sewage
Enteric bacteria, e.g., Salmonella, Shigella
Virus, e.g., polio, hepatitis virus, rotavirus
Protozoa, e.g., Giadia, Cryptosporidium
Eggs of intestine parasites
Routes of infection: contamination on bathing water or seafood
Through contacts with or incidental ingestion (cut/skin abrasion)
Consumption of contaminated seafood
Survival of pathogen in seawater
Bacteria can become dormant
Virus can be very persistent
43
Risk of contaminated food
Eggs of Parasites
High risk if sewage or sludge used in salad crops. Di s c har gewas t e st os e amayc ompl e t epar as i t e s ’ l i f ec yc l eandl e ad to infection of human when consuming infected sea products. Problems are greatest in tropical countries, e.g., Southeast Asia
Seafood
Hookworm and tapeworm are resistant to drying and may persist in crude sewage and sewage sludge
Higher risk for filter feeders, e.g., bivalve mollusks. Accumulate human pathogens on gills.
Depuration is required before marketing.
Crustaceans and fish do not presents risks.
Biotoxin:
Due to harmful algae 44
Beach monitoring in US
The BEACH Act (Beaches Environmental Assessment and Coastal Health) of 2000 required coastal states and states bordering the Great Lakes to adopt EPA's most current recommended bacteria criteria to better protect beach bathers from harmful pathogens.
E Coli.
Enterococci
Beach notification actions are usually either
A beach advisory, warning people of possible risks of swimming
Closing a beach for public swimming.
In 2007, of the 3,602 coastal beaches in US that were monitored, 1,167 (32%) had at least one advisory or closing. 94% of beach notification actions reported during the 2007 swimming season were a week or less.
45
Beach monitoring in Taiwan 項目
採樣日期 採樣天候
大腸桿菌群 腸球菌群 (菌落數/100毫升) (菌落數/100毫升) 30 小於10
試分級
福隆
97.9.1
陰
新金山
97.9.1
雨
33
小於10
優
崎頂
97.9.1
晴
450
290
尚可
通霄
97.9.1
晴
13
10
大安
97.9.1
晴
3100
280
馬沙溝
97.9.1
晴
小於10
小於10
優 不符甲類標 準 優
西子灣
97.8.31
晴
180
29
良
旗津
97.9.1
晴
11
12
良
杉原
97.8.31
晴
小於10
小於10
優
墾丁跳石 (南灣休憩 區海岸)
97.9.1
晴
小於10
小於10
優
優
46
Sewage treatment
7
The sewage treatment involves three stages, called primary, secondary and tertiary treatment. First, the solids are separated from the wastewater stream. Then dissolved biological matter is progressively converted into a solid mass by using microorganisms. Finally, the biological solids are neutralized then disposed of or re-used, and the treated water may be disinfected chemically or physically. The final effluent can be discharged into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. 47
Typical wastewater quality and treatment scheme Parameter
Conc. (mg/L)
BOD
100 ~ 300
COD
250 ~ 1000
TDS
200 ~ 1000
SS
100 ~ 350
TKN
20 ~ 80
TP
5 ~ 20
Water is typically > 99.9%
(Clark, 2001)
48
Primary treatment (physical)
Screening: remove large float objects that may damage pumps and clog pipes, e.g., bar screen, fine mesh screen Grit chamber:
Primary clarifier
Horizontal velocity typically 0.3 m/sec; detention time 45~90 sec Allow sand, grit (s.g. = 1.3~2.7) and other heavy materials to settle out. Flow speed is reduced sufficiently to allow most of the SS to settle out by gravity Detention time: 2~ 3 hours SS removal: 50~65 % BOD removal: 25~40 %
Odor/VOCs controls (volatile organic matters) Flow equalization 49
Secondary treatment (biological)
Trickling filter (滴濾池)
Biological tower: plastic media was used to increase the surface area of biofilm; equivalent treatment to rock beds with smaller land area.
Activated sludge process
WW is sprayed on the surface of coarse rocks, forming biofilm that adsorbs and consumes organics in the water as it percolates through the bed
Activated sludge and a large amount of air is pumped into the tank to enhance the biodegradation of wastewater
Remove more BOD than trickling filter
Detention time: 6 ~ 8 hours;
Secondary clarifier:
Effluent: BOD and SS typically 30/30
Sludge was recycled back to AS or diverted to further treatment.
50
Tertiary treatment (advanced)
Residual SS remove:
Nutrient removal
N: Ammonia oxidation; nitrification/denitrification; stripping P: Chemical precipitation; biological phosphors removal
Toxic compounds and refractory organics
granular medium filtration Membrane Microfiltration (MF); ultrafiltration (UF)
Carbon absorption Chemical oxidation
Dissolved solid
Chemical precipitation Ion exchange Nano filtration (NF); reverse osmosis (RO) 51
Disinfection
Selective destruction of disease causing organisms Chlorine and its compounds (Cl2, ClO2, NaOCl)
Ozone
Effective mixing, contact time, residual are important to achieve effective bacteria kill. Contact time: typically 15~45 min. CT value; N/N0 = (1+0.23CT)-3 Very reactive; deep and covered contact chambers are used Not persistent in the effluent
Ultraviolet (uv)
Safe, no hazardous chemicals are used Low contact time (20 ~ 30 seconds with low-pressure lamps) SS in the wastewater can render UV disinfection ineffective 52
River pollution
Greatest volume of organics to be disposed of: Urban: human sewage Intense farming: animal wastes
River water BOD Unpolluted: < 2 mg/L Grossly polluted: > 10 mg/L
River pollution index (RPI) BOD, DO, NH3-N, SS Four tiers
(www.epa.gov.tw) 53
River pollution index (RPI) Parameter
未(稍)受污染
輕度污染
中度污染
嚴重污染
DO
> 6.5
4.6~6.5
2.0~4.5
< 2.0
BOD
< 3.0
3.0 ~ 4.9
5.0 ~ 15
> 15
SS
< 20.0
20 ~ 49
50 ~ 100
> 100
NH3-N
< 0.5
0.5 ~ 0.99
1.0 ~ 3.0
> 3.0
Score
1
3
6
10
RPI
6
Ex. 96/5/3 鹽水溪橋(河口) DO=1.2; BOD=9.5; SS=34; NH3-N=14.8 RPI= (10+6+3+10)/4=7.25 (嚴重污染) 54
Ocean Outfall
8
Ocean and large lake, e.g., the Great Lake, provide extensive assimilation capacity that used by many communities for wastewater disposal. Typically, carries to an offshore discharge point by a laid on/buried pipe, or tunnel.
55
Density of seawater
Density of seawater frequently expressed in σt unit, σt = real density –1000 g/L
(Metcalf & Eddy, 1991) 56
Wastewater discharge plume in the ocean
Initial mixing zone (nearfield) Initial mixing involves effluent buoyancy, ambient stratification, and current. Buoyant plume forms and rapidly rise to the water column If ambient water stratified: Entrained deep denser water which reduces bouyancy If ambient water weakly or not stratified (as in winter): plume rises to surface Beyond initial zone (farfield) carries away by ambient current and dilute through diffusion
(Metcalf & Eddy, 1991) 57
Los Angeles Hyperion Treatment Plant
(From Hyperion Treatment Plant report)
58
(www.parsons.com)
59
San Diego South Bay Ocean Outfall
Project Duration: 1986 –2000
Constructed Value: $ 133 Million
Capacity: average dry weather flows of 660,000 CMD and peak flows of 1,260,000 CMD Extends 3.5 miles offshore and discharges effluent in approximately 100 feet of water
Tunnel boring machine was used to excavate the tunnel
The tunnel has an 11 foot diameter and is 19,000 feet long
Barges were used as platforms to trench the ocean floor, install pipe,
The 1.5 miles of exposed pipeline was covered with more than 400,000 tons of ballast rock to protect the outfall from ocean waves and ship anchors Tunneling minimized environmental impacts to a local salt marsh and barrier dune habitat, a major refuge for birds and wildlife 60
(Metcalf & Eddy, 1991) 61
(Metcalf & Eddy, 1991) 62
(Metcalf & Eddy, 1991) 63
(Metcalf & Eddy, 1991) 64
(Metcalf & Eddy, 1991) 65
(Metcalf & Eddy, 1991) 66
Consequence of organics charged to marine environment
9
67
Consequence of organics charged to estuaries Thames estuary case: a history of pollution and recovery Year
Conditions
~ 1820
Important Salmon river
1820~50
Progressed overloaded
1850s
Foul smelling and devoid fish
1890s
Outfalls reduced and sewer piped to treatment plants. Sludge dumped at sea
1900
Remarked improvement in water quality
1950s
Population growth out runs plant capacity. 30km of anoxic stretch
1964~76
Expansion of treatment plants
1979
Dramatic rise of oxygen, benthic fauna, and fish 68
Thames estuary case
(Clark, 2001) 69
Consequence of organics charged to sea
Case study of sludge dumping sites Barrow Deep Garroch Head New York Bight
Accumulation can be measured by Organic contents of sediments Heavy metal concentrations, e.g., silver Spores forming bacteria
70
Barrow Deep dumping site, outside Thames estuary UK
(Clark, 2001)
Dispersive site, strong bottom current and high water exchange 5 million ton/year since 1890s ~ 1998 No local effects, only some small patches of slightly elevated organics. Organic enrichment the southern North Sea
71
Garroch Head dumping site, west of Scotland
Cumulative site in area of weak current 1.5 million ton/year since 1974 ~ 1998 Severe but localized impact on the seabed
(Clark, 2001)
72
New York Bight dumping site
“12-mi l es i t e ”( 1924-86): 50 m deep, 10 million ton/year Evident of organic enrichment and metal accumulation “106-mile s i t e ”( 1985-92): 2500 m deep, 8 million ton/year Dispersed over 10,000 km2
(Clark, 2001)
73
(Clark, 2001)
74
Effect on benthic organisms
Ocean sludge dumping has a direct effect on the benthic fauna, which is exposed to he sedimentation of particulate matter rich in nutrients and bacteria. Smothering by PMs and reduction of DO due to enhanced bacteria activities excludes more sensitive species Opportunist species, e.g., Capitella capitata (小頭蟲), become dominant and outcompete other species; diversity decreases at the discharge site. Capitella can be indicator species for organic pollution
(Clark, 2001) 75
10
Regulations GESAMP put sewage discharge to sea top of its list of concern due to high public health risk. Many deaths reported annually in area with poor hygiene.
76
Standard for commercial/recreational uses
(Clark, 2001)
In Taiwan, coliform groups as indicator Effluent standards: < 200,000~300,000 CFU/100 mL Ocean outfall standards: < 5,000,000~10,000,000 CFU/100 mL Ocean environment: < 1000 CFU/100 mL
77