Why wastewater treatment? Policy on Wastewater Separation Types of sanitation systems

transcript

IMPROVED RURAL SANITATION CONCEPTS

Dhanesh GunatillekeSPECIALIST (SEWARAGE

DESIGNS)NWSDB

1st April 20141

1 Why wastewater treatment?

2 Policy on Wastewater Separation

3 Types of sanitation systems

4 Design of onsite sanitation systems in compliance to SLS 745 Part II:2009

5 Further Treatment Options

Presentation Outline

1 WHY WASTEWATER TREATMENT ?

Protect the environment from;high loads of suspended solids & organic mattereutrophication & groundwater pollutionSubstantial load of hazadous and non biodegradable compoundsSerious contamination with microorganisms

…in order to establish/maintain healthy environment for flora & faunaallow mankind to use water resources for different purposesprevent transmission of waterborne diseases/improve public health 3

Definition of Safe Sanitation

Ref: water supply and sanitation collaborative council

Collection, Transport, Treatment &

Disposal or reuse of human excreta,

domestic wastewater and solid waste,

and associated hygiene promotion

Pollution from human beings

45-60 g BOD/person/day

8- 14 g N/person/day

0.6-2.5 g P/person/day

Medical residues

Eutrophication & it’s impactsIncrease in rate of supply of organic matter

to an ecosystem resulting nutrient built up (N, P)

Massive algae growth, anaerobic conditions, oxygen depletion

Changers in the structure and functioning of the lake and marine ecosystem

Reduction in biodiversity, fish and shellfish harvesting

Increase risk of poisoning by algal toxins11

DO Sag CurveWastewater

Distance (Km)

7.83mg/lat 280C

Health Problems

In some areas in the developing world, 75 -80% of human illness is related to water and water pollution

Discharge of wastewater represents the greatest risk for pollution of potable water

Ref: A.J. Arcivala

Ref: Metcalf & Eddy

2. Wastewater Separation

RainwaterRainwater Harvesting/Surface Drainage System

Hazardous WW

Separate them in concentrated formin separate plumbing system

Treat/Dispose as Hazardous WW

Restaurants Grease Interceptor Onsite/Sewerage

Reticulation SystemWW of Domestic Nature

X-Ray Processing AgCl+NaOH AgO

Dental Wastewater (Amalgam) Ag, Pb, Sn

Radioactive Iodine Treatment Mutagenic

Full Blood Count Test (Cn) Blood Urea Test Total Protein Test Albumin Test Liver Functional Test Cholesterol Test Sugar Test Skin Preparation (Salicylic, Benzoic Acid, yellow parafin) Bottle Washing (Antibiotics) Molecular Biology Research

(Ethidium Bromide Mutagenic) Formalin (preservative for biological specimens)

CONCEPT FOR HOSPITAL To the Existing Surface

Drainage System Storm Water/ Rain Water

Rat/ Mora WWTP

Retention(As per CEA/AEA Recommendation)

Grease Trap Kitchen WW Sewerage System

Other WW of Domestic Nature

Effluent from Radiation Treatment(Iodine)

Pumping Station

• X- Ray Processing (Dark Room)• Dental WW• Laboratory WW

Collection to Containers in concentrated form with separate plumbing system

Disposal as Hazadous Wastewater (GeoCycle)

Existing Oxidation Ditch & Settling tank will be converted to a Floting wetland

Hazardous WW Disposal-Preconditioning

Ref: National Institute of Minamata Disease

3. Types of Sanitation Systems

• On site sanitation systems (>90%)– Septic tank associated effluent disposal systems

• Off Site Sanitation Systems (>2.5%)– Wastewater collection, treatment & Disposal

• Decentralized System

PRODUCTION PRE TREATMENT DISPOSAL

EVAPOTRANSPIRATION

WATER TABLE

PURIFICATION

GROUND WATER

SOIL ABSORBTIONSEPTIC TANK

GREASE TRAP Drainage field

Unsaturated Zone

Saturated Zone

Schematic cross-section through a conventional septic tank soil disposal system for on-site

disposal and treatment of domestic liquid waste

How it Works

Onsite Sanitation Systems

SIMPLE PIT LATRINE

Manual 1:Latrine Construction

Technical Manual Series on Rural Water Supply & Sanitation

NORAD-Helvetas Sri Lanka

VENTILATED IMPROVED PIT LATRINE

On Site Sanitation

WATER SEAL POUR – FLUSH LATRINE (Off-set Pit Type)

NWSDB through ADB 3rd Project

Puttalam 10,112

Kegalle 11,634

Kalutara 8,745

Hambantota 12,675

Monaragala 23,128

Total 81,333

Total 164,000

DRY COMPOST LATRINES Environmentally friendly Designed to keep the faeces separate from the urine and water used for anal cleansing Is usually an elevated construction Urine/water drained into an evaporative plant bed or a cultivation plot To eliminate bad odour and nuisance from flies a handful of ash, lime or soil has to be sprayed into the pit

NWSDB About 100

NGO’s About 100

ECOSAN-BANGALIDESH/TAMIL NADU

Onsite Sanitation SystemsSEPTIC TANK / SOKAGE PITS/SOKAGE TRENCES

NORAD-Helvetas Sri Lanka34

GREAZE INTERCEPTOR

Service StationsPrimary treatment by Grease InterceptorsSubsequent Pre treatment by

CoagulationFlocculationSedimentation

Muthugala Service Station- Kurunegala

Disposal of OilAs furnace oil

Nippon Steel Cor.

38Frazer Thomas-NZ

Frazer Thomas-NZ

BIO TOILET-JAPAN

Problems in on site systems?• Faulty design & construction of septic

tanksInadequate water depth for solid separationFailure in construction/water tightness

• Faulty design of soakage arrangementsSeasonal high ground water tablePresence of non favorable soilsPresence of shallow rockProne for floodingOverloading

4. Treatment Options

SLS 745:Part I: 2004 • Part I- Small systems disposing to ground

SLS 745:Part II: 2009 • Part II- Systems Disposing To Surface, Systems For

On-site Effluent Reuse And Larger Systems Disposing To Ground

SECTION

Inspection port150mm

Partition

Access openings500mm min.

Vent pipedia. 25mm min.

Free board200mm min.

Dia.100mmmin.

Min. 20% of liquid depth

50mm min.

Opening100mm min.

Liquid level 300mm min.

To further treatment

First compartment approx. 2/3 length Second compartmentapprox. 1/3 length

Total length between 2 – 4 times width

Opening25mm min.

Dia.100mmmin.

To further treatment

SEPTIC TANK

Ref: SLS745 Part II

SEPTIC TANKS

Design Requirements

SLS 745:Part I: 2004 SLS 745:Part II: 2009

• Main functions • Free board• Vent pipe & cowl • Access• Commissioning• Desludging

2 to 4=Length to Width Ratio

0.75m=Minimum width of Septic Tank

1m=Minimum depth of septic tank

55%=Assume reduction in BOD

mg/l200=Assume initial BOD

Septic Tank

m3/day0.56=Q

112 * 5 =Q Average daily WW flow

liters/person/day 140 * 0.8=Per Capita Wastewater Flow

liters/person/day 140=Per capita Water Consumption

5=No of members in a family

Design for All Wastewater

The Design and Construction of Septic Tank and Associated Effluent Disposal Systems (SLS 745 Part I : 2004)

DESIGN CRITERIA

SEPTIC TANK DESIGN FOR 5 PERSONS (DE-SLUDG PERIOD 5 YEARS)

m30.092=Vd

Q(m3/day) / 0.2(m3/p/day)=pPopulation equivalent for all wastewater

(for an ambient Temperature of 20 0C) days33=tdTime required for sludge digestion

(for all wastewater)m3/day0.001=qsVolume of fresh sludge per person

qs. Td. P=Vd

1.2) Volume required for sludge digestion Vd (All Waste)

m3 0.88 =Vs

Should be > 0.2 d

days 1.58 =

days(1.5-0.3 log Q)=tsTime required for settling

ts.Q=Vs

1.1) Volume required for settling, Vs (All Waste)

46td =1853T-1.25

47mg/l90=BOD of effluent

55%=Assume rate of BOD removal in septic

Hence ok

( 2<L/W<4 ) 3.23 =L/W

m 2.42 =Then Length L

m0.75=Assume width, W

m2 1.81 =Then, Surface Area A

( Minimum Depth 1m)m1=Take Depth, H

( 1m3 < V < 12m3 )m3 1.81 =V

Vs+Vd+1.5*Vst

=1.5)Total Volume required for septic tank

Vst0.5= Volume required for scum storage

1.4) Volume required for scum storage

m30.56=Vst

year5=nDesludging interval>1

m3/year0.04=rVolume of digested sludge per person per year for all wastewater

r.p.n=Vst

1.3) Volume required for sludge storage Vst (All Waste)

De-sludging Interval (Years) 2 5

No of Occupants /House 5 7 10 5 7 10

ST Volume (m) 1.31 1.80 2.52 1.81 2.51 3.53

ST Height (m) 1.00 1.00 1.20 1.00 1.00 1.20

ST Width (m) 0.75 0.75 0.80 0.75 0.90 1.00

ST Length (m) 1.75 2.40 2.63 2.42 2.78 2.94

Length / Width 2.33 3.20 3.28 3.23 3.09 2.94

Surface Area (m2) 1.31 1.80 2.10 1.81 2.51 2.94

SIZING OF SEPTIC TANKS

49Sludge Judge

Sludge judge

SOKAGE PITS

Soakage pits• Soak septic tank effluent• Effluent get treated before reaching GW

Applicability– GWT below 2.5m (seasonal fluctuation)– Soil percolation rate between 25mm/h to

125mm/h

Location– At least 18m away from nearest well/drinking

water source– At least 5m away from the nearest building

dia. 100 mm min.

Minimum1.2 m

GWT (Seasonal high )

SECTION

Impermeableliner / wall

Between 900mm & 3000mmImpermeable

Minimum 1000 mm

Inlet pipe

300 mm min.

Minimum2.5 mOpen jointed

brick / cementblock

Ground level

PLAN (CIRCULAR TYPE) PLAN (SQUARE TYPE)

PLAN (RECTANGULAR TYPE)

900mm <

Dia. < 3000mm

900mm < Length < 3000mm

Width > 900 mm

Length < 3000mm

Inlet pipe

SOKAGE PIT

Ref: SLS745 Part II

Minimum Distance Between Soakage PitsRef :table 2,SLS 745 part 2

Average daily flow(m3/d)

Minimum distance between soakage pits (m)

2-5 15

5-10 20

10-30 36

Specific Effective Areas for Soakage Pits Ref :table 3,SLS 745 part 2

Percolation Rate mm/hr

Specific Effective Area (m2 / m3 per day)

100 8.4

125 6.653

Minimum depth to groundwater table from bottom of soakage pit

Ref :table 4,SLS 745 part 2

Percolation rate(mm/hr.)

Minimum depth to GWT (m)

25-50 1.2

50-75 1.8

75-100 2.4

100-125 3.054

Existing surface

Topsoil

Finished surface

Perforated distributor pipesdia.100mm min.Soil barrier

Settlementallowance

Level floorarea

Prepared aggregate(20 – 40mm)

100mm min.

300mm min.

1000mm max.From wall

2000mm max. spacing 1000mm max.From wall

Level site – slope less than 5 %

TYPICAL ARRANGEMENT OF SEEPAGE BED

Length < 20m

SECTION

75mm min.

Septic tank

Distributor pipes

SEEPAGE BED

The maximum bed length

shall be 20 m.

SLS 745 Part II:200955

100mm min.

300mm min.

Topsoil

Ground surface

Perforated pipedia.100mm min.

Soil barrier

Settlement allowance

Finished surface

Prepared aggregate(20 – 40mm)

300mm min.

75mm min.

TYPICAL ARRANGEMENT OF SEEPAGE TRENCH

ax.Septic tank

Disposal field trenches

SECTION

Ground slope 5% max.

20m max.

SEEPAGE TRENCH

Specific effective areas for seepage beds and seepage trenches

Ref :table 5, SLS 745 part 2

Percolation rate(mm/hr)

Specific effective area(m2 / m3 per day)

100 12.5

125 10

150 8.3

175 7.1

200 6.25

225 5.6

250 5.057

Minimum, maximum and typical dimensions of seepage beds

Ref :table 6, SLS 745 part 2Bed dimension Typical

Range(mm)

Maximum(mm)

Minimum(mm)

Width 1000-6000 6000 1000

Depth of aggregate

300-600 600 300

Depth of topsoil 100-150 N/A 100

Spacing between beds (sidewall to sidewall)

- N/A 1000

Typical dimensions of seepage trenches Ref :table 7, SLS 745 part 2

Trench dimension Typical Range(mm)

Maximum(mm)

Minimum(mm)

Width 300-600 600 300

Depth of aggregate

300-600 600 300

Depth of topsoil 100-150 N/A 100

Spacing between beds (sidewall to sidewall)

1000-2000 N/A 1000

MOUND SYSTEMS

Cross-section of a mound system for slowly permeable soil on a sloping site (US EPA, 1980)

ROCK STRATA OR IMPERMEABLE SOIL LAYER

PLOUGHED LAYER OF TOP SOIL

ABSORBTION BED

DISTRIBUTION LATERAL

STRAW, HAY OR FABRIC

MOUND SYSTEMS

Cross-section of a mound system for a permeable soil with hight ground water or shallow creviced bed rock (US EPA, 1980)

ROCK STRATA OR IMPERMEABLE SOIL LAYER

PLOUGHED LAYER OF TOP SOIL

ABSORBTION BED

DISTRIBUTION LATERAL

STRAW, HAY OR FABRIC

Frazer Thomas-NZ62

Frazer Thomas-NZ

In compliance to Disposal StandardsInland Water BodySea OutfallRe Use For Non Potable Uses

Faecal Coliform

Further Treatment

OUTLET

Dia.100mmmin.

OUTLET

Dia.100mmmin.

SECTION

Access opening500mm min.

Vent pipe dia. 25mmmin.

Liquid level

Dia. 50mmmin.

TYPICAL ARRANGEMENT OF ANAEROBIC FILTER

Washed & graded filterMedia (min. size 2mm).

200mm min. Perforated filter floor

Perforations dia.10mm min.

Inletchamber

Access opening500mm min.

ANAEROBIC FILTERS

The minimum design HRT shall be 0.6 days and the maximum shall be 1.5 days.

Surface loading rate (m/d) = Average daily flow (m3/d) Plan area of filter (m2)

SLR ≤ 2.8

Total volume of void space in the bed > 35 per cent

Volume of the bed

0.6m < h > 1.8m

invert of the outlet shall be at least 50 mm below the invert of the inlet

WETLANDS

• FREE WATER SURFACE WETLANDS

WETLANDS

• SUBSURFACE WETLANDS

Typical Wetland Plants

Cattails

Kok mota

SUBSURFACE WETLANDRATMALANA TSUNAMI RESETTLEMENT HOUSING

SCHEME AT FOOD STORES LAND

Free Floating Aquatic Plants

Floating Treatment Wetlands72

Floating Wetlands

Biofilm covered roots

Variable water depth

Floating mat

Leaf litter

3. Floating Wetlands

1. Duckweed

2.Salvinia74

Natural Floating Wetlands cont...

3. Water lettuce

Common Features

Self buoyant root structureUncontrolled rapid growthCutoff sunlight 75

Natural Floating Wetlands cont..4. Eichhornia crassipes

Floating Wetlands

Removal glycol from de-icing water at Heathrow Airport

JHOKASOU(private sewage treatment system)

Jhokasou

Anaerobic contact aeration type

Sludge Return Pipe

Blue valve for aeration

Blue valve for aeration Yellow valve for air-

release

Yellow valve for air-release

White or Grey valve for air-Lift

Red valve for Back-washing

Sludge Return Equipment ( Air-Lift )

Disinfection Tank ( Disinfectant )

Sedimentation TankSedimentation Tank

Anaerobic contact aeration type

contact aeration type

(3) Separate aeration type

(4) Total aeration type

aeration

chambersettling

chamber

disinfection

chamber

inflow

effluent

air pump

sludge

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Sprinkling filter bed type

sludge

Filtermedia Filter

Exhaust pipe

Sprinkling weir

inflow

effluent← 　 anaerobic tank 　→ ← 　 aerobic part 　→

Why wastewater treatment? Policy on Wastewater Separation Types of sanitation systems

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