2012/07/25
Site Evaluation of
Wastewater Treatment Plants
Green Drop Symposium
Pretoria
July 25, 2012
WHY SITE INSPECTIONS?
• Alignment of audit portfolio with reality
• Engagement with other professionals
• Specification philosophy
– Specification of procedures
– Specification of performance
(best practice)
(compliance)
• Green Drop programme employs both
philosophies
A SIMPLE ANALOGY
• Is it safe for my child to travel with the DirtCheap
Bus Company from Pretoria to Cape Town?
• Compliance
– Accident record
– Record of punctuality
– Roadworthiness of vehicle
• Best practice
–
–
–
–
Driver experience / exchange
Which route / quality of the road?
Time of day / week
Age of the bus / condition
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DURING A SITE VISIT …..
• A standard site inspection form is used with
about 100 questions to force a systematic audit
• Questions are answered by
– Own observations
– Interviews with site staff
• Each question scored from 0 to 1:
– 1.00
Fully satisfied
– 0.00
Absent / completely unacceptable
– Low scores are accompanied by comments
• Deficiencies not covered not by the standard
questions are noted
SEVEN AUDITING CATEGORIES
1.
2.
3.
4.
5.
6.
7.
Physical appearance
Preliminary treatment
Primary treatment
Secondary treatment
Tertiary treatment
Solid waste management
Operation / Administration
1. PHYSICAL APPEARANCE
• Entrance signposted?
• State and tidiness of terrain?
• State and tidiness of bathroom, lockers, food
area?
• Serious OHS contraventions?
• Workplace satisfactory?
• Facility fenced without access for people and
animals?
• Relevant safety signs posted?
• Electricity use measured and recorded?
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2. PRELIMINARY TREATMENT
• Screening
– Manual screens
– Automated screens
• Degritting
– Manually cleaned channel
– Automatically cleaned channel
– Automated de-gritters
• Disposal of screenings and grit
• Flow measurement
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QUESTIONS - SCREENING
• Screens in place and free of debris and
obstructions?
• Hand rake clean, wheelbarrow in working
order?
• No unusual sound and vibrations?
• Screenings are measured, properly stored and
disposed?
• Maintenance schedule available and
implemented?
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QUESTIONS – GRIT REMOVAL
• Channels and equipment are in working
order?
• Channels are clear of grit?
• Grit is stored and disposed of correctly?
• Maintenance schedule is available and
implemented?
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QUESTIONS – FLOW METERING
• Flow metering device in place and functional?
• Flow rate recorded, converted and
interpreted?
• Means of flow verification?
• Inflow samples taken and analysed according
to schedule?
• Wet weather flows and night flows recorded?
• Flow balancing / mixers / aerators working?
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3. PRIMARY TREATMENT
• Primary sedimentation
• Flow balancing
• Pond systems
QUESTIONS – PRIMARY SETTLING
• Mechanical equipment moving and
operational?
• Flow evenly distributed and gates and valves
working?
• Weirs in good condition?
• Layers of scum, floats, fats or grease?
• Desludging schedule being followed?
• Safety railings present, in good condition?
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QUESTIONS – OXIDATION PONDS
•
•
•
•
•
•
Ponds operated in series, how many?
Short-circuiting, aerators working?
Anaerobic pond desludged?
Desludging schedule being followed?
Appropriate diversion when desludging?
Pond banks clear of weeds?
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4. SECONDARY TREATMENT
• Biological reactors
– Attached growth reactors
• Trickling filters
• Rotating biological contactors
– Activated sludge
• Secondary settling
• Chemical coagulant dosing
QUESTIONS – BIOFILTERS
•
•
•
•
•
Safe ladder to the top?
Even flow distribution?
No ponding?
Underdrains clear of debris?
Outer shell without cracks or properly
contained?
• Schedule for turning of filter media?
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QUESTIONS – ROTATING CONTACTORS
•
•
•
•
•
•
•
Discs turning at steady rate?
Current meter working?
Motors hot or noisy?
Sludge recycle pumps working?
Return sludge volume or ratio recorded?
Clarifier clear of floating sludge?
Maintenance schedule followed?
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QUESTIONS – ACTIVATED SLUDGE
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•
•
•
•
•
•
•
•
Sludge age recorded?
MLSS monitored and within range?
Scum on the surface?
Dead zones in reactor?
Liquor has visual floc and right colour?
An earthy smell present?
Chemical dosing position / recorded?
Process monitoring (COD, pH, NO3, etc)
Aerators working?
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QUESTIONS – ACTIVATED SLUDGE
(continued)
•
•
•
•
•
•
Aerator downtime / repair time?
Recycle pumps working?
Recycle rates known and recorded?
Motors or pumps hot or noisy?
Maintenance schedule followed?
Handrails in position and safe?
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QUESTIONS – SECONDARY SETTLING
•
•
•
•
•
•
•
•
Troughs, weirs, baffles clean?
Sludge withdrawal working?
Overflow is clear?
Weirs and channels clean?
Launders clean?
SVI tested and interpreted?
Scum on surface?
Overflow is clear?
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CHEMICAL DOSING PRINCIPLES
• Five Things About ChemicalS
•
•
•
•
•
F
T
A
C
S
Flow
Target dosage
Adjustment
Control
Stock
How much water?
What concentration?
How to set it?
Target correct?
Enough on site?
COAGULANT
•
•
•
•
•
F
T
A
C
S
From flow meter
From laboratory tests
Dosing pump
Check phosphate / turbidity
Liquid level in storage tank(s)
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LIME
•
•
•
•
•
F
T
A
C
S
From flow meter
From laboratory tests
Screw feeder speed
Check pH
Count bags / Level in bulk silos
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CHLORINE
•
•
•
•
•
F
T
A
C
S
From flow meter
Feedback from residual chlorine
Adjust rotameter on gas flow
Measure residual chlorine
Count and weigh cylinders
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DOSING CALCULATION
• Dosing calculations require expressions for
MASS (the chemical), VOLUME (the water into
which the chemical is dosed, and the TIME
(used to express flow rate or dosing rate)
• Mass: kilogramme; gramme; milligramme
• Volume: Megalitre; cubic metre; litre; millilitre
• Time: days; hours; minute; seconds
• Calculations sometimes tricky because
different units are freely mixed
CONVERSIONS
RATIO
VALUE
g/kg or mg/g
1000
m3/Mℓ or ℓ/m3 or mℓ/ℓ
1000
hours/day
24
minutes/day
1440
seconds/day
86400
To remove a unit above the line, divide by that unit
To remove a unit below the line, multiply by that unit
FOR EXAMPLE:
To convert kg/day to g/day, divide by kg and multiply by g
EXAMPLE
Flow rate 15 Mℓ/day; Feed rate 50 g/minute –
concentration ?
Convert flow rate to m3/day:
15 * 1000 / 1440 = 10.4 m3 / minute
Concentration:
50 / 10.4 = 4.8 g/m3 = 4.8 mg/ℓ
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ENERGY CALCULATION (1)
•
•
•
•
•
•
•
Capacity 40 Mℓ/day
Average flow 32 Mℓ/day
Electricity cost 30 c/kWh in summer
Electricity cost 50 c/kWh in winter
12 Aerators @ 90 kW each
12 x 90 x 24 = 25920 kWh / day
810 kWh / Mℓ
• R243 / Mℓ = R0.24 / kℓ or m3 in summer
• R405 / Mℓ = R0.41 / kℓ or m3 in winter
ENERGY CALCULATION (2)
• Average flow 8 Mℓ/day
• Electricity cost 50 c/kWh
• Monthly electricity usage 260 000 kWh
•
•
•
•
Cost = 260000 x 0.5 = R130 000 / month
Volume = 8000 x 30 = 240 000 m3/month
Unit cost = 130000/240000 R/month
Unit cost = R0.54 / m3
TYPICAL OPERATIONAL COSTS
• Small treatment plants
– R1.50 to R2.50 per kℓ or m3
• Large treatment plant
– R0.70 per kℓ or m3
• Comparable with water treatment costs
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5. TERTIARY TREATMENT
•
•
•
•
Chemical disinfection
Constructed wetlands
Maturation ponds
Final discharge
QUESTIONS – DISINFECTION
•
•
•
•
•
•
•
•
Disinfection practiced / chemical?
Contact tank clean?
Residual chlorine tested / recorded?
Sufficient stock on site?
Training for handling chlorine?
Safety signs?
Safety equipment / PPE?
Correct final sampling point?
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QUESTIONS – MATURATION PONDS
• Overflow is clear?
• Good housekeeping?
• Active bird and plant life?
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6. SOLID WASTE MANAGEMENT
• Thickening
– Gravity thickening
– DAF thickening
• Dewatering
– Filter / belt press
– Drying
• Stabilisation
– Anaerobic digestion
QUESTIONS – DRYING BEDS
•
•
•
•
•
Sludge on bed level / free of weeds?
Walls intact without cracks?
Sand replaced per schedule?
Drainage system, pipes and valves working?
Monitoring schedule for TSS, drying time,
sludge layer thickness, etc?
• Dried sludge stored / safe disposal?
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7.
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•
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•
•
•
•
•
•
•
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•
•
OPERATION / ADMINISTRATION
Personal Protective Equipment
First aid equipment
Storage areas
Workplaces
Food storage and preparation areas
Classification and operator certificates
Process diagram
Operation and Maintenance Manual
Laboratory and Instrument Manual
Operations logbook
Monitoring results
Incident register
Incident management procedures
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THE END
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