Transcript The City of Cape Town’s Role in Creating a Better Life for All

THE COMPARISON OF
WASTEWATER
TREATMENT METHODS
AND THEIR USE FOR
IRRIGATION
Presented by: Michael Fynn
Date: Tuesday 3rd September 2007
CONTENT
1. WATER – THE CURRENT SITUATION IN SA.
2. WHY TREAT WASTEWATER?
3. TREATMENT OBJECTIVES.
4. CURRENT TREATMENT OPTIONS.
5. CURRENT TRENDS.
6. THE ACTIVATED SLUDGE PROCESS.
7. THE TRICKLING FILTER.
8. COMPARISON OF ACTIVATED SLUDGE AND TRICKLING
FILTERS .
9. EFFLUENT RE-USE .
CURRENT SITUATION
SA SITUATED IN SEMI-ARID PART OF AFRICA
450mm RAIN/YEAR ; WORLD AVERAGE IS 860mm/YEAR
TOTAL FLOW FROM ALL RIVERS IN SA IS 49200 million
cu.m WHICH IS LESS THAN ½ TOTAL ANNUAL FLOW
FROM ZAMBEZI RIVER.
GLOBAL WARMING AN EVER PRESENT REALITY
WHY TREAT WASTEWATER?
THE MOST BASIC ANSWER IS TO CLEAN DIRTY WATER.
TREATMENT FACILITIES SIMPLY COMPRESS THE ORGANIC
DECOMPOSITION PROCESSES WHICH TAKE PLACE IN NATURE.
THIS IS PERFORMED BY A COMBINATION OF PHYSICAL,
BIOLOGICAL, AND CHEMICAL TREATMENT STAGES.
NATURE (RECEIVING WATERS) CAN ONLY ACCEPT SMALL
AMOUNTS OF SEWAGE BEFORE BECOMING POLLUTED, THAT IS,
NATURAL BACTERIA FEED ON THE SEWAGE ORGANICS AND
CREATE AN ABNORMAL AMOUNT OF DISSOLVED OXYGEN UPTAKE.
BIOLOGICAL TREATMENT OBJECTIVES
IN THE CASE OF DOMESTIC WASTEWATER TREATMENT THE
OBJECTIVE OF BIOLOGICAL TREATMENT IS
TO STABILIZE THE ORGANIC CONTENT.
TO REMOVE SUCH NUTRIENTS SUCH AS PHOSPHORUS
AND NITROGEN.
PROCESS TYPES
AEROBIC
ANOXIC
ANAEROBIC
COMBINED PROCESSES
MAJOR AEROBIC BIOLOGICAL
PROCESSES
THE TREATMENT OF THE WASTEWATER IS ACHIEVED BY
BILLIONS OF NATURALLY OCCURING BACTERIA
THESE BACTERIA REQUIRE MEDIA ON OR IN WHICH TO GROW
IN ORDER TO BE IN THE BEST POSITION TO UTILIZE THE
WASTEWATER AS FOOD
TWO TYPES OF GROWTH ENVIRONMENTS
SUSPENDED GROWTH ENVIRONMENT
FIXED GROWTH ENVIRONMENTS
Several alternative process configuration using trickling
filter technology are available.
• conventional bio-filter
• biofiltration solids contact (BFSC) process
• biofiltration with high rate circulation
• pond enhanced treatment and operation (PETRO)
process
• integrated anaerobic pond biofiltration process
• integrated biofiltration activated sludge (BFAS)
process
Dual Stage Trickling Filtration Process
Polishing Nitrification Trickling Filter Process
Trickling Filter Solids Contact Box
Primary Clarifier
Secondary Clarifier
Humus
Trickling Filter/Solids Contact Treatment Process
Trickling Filter Integrated with Ponds (Petro'M)
Type of
Growth
SUSPENDED
GROWTH
ATTACHED
GROWTH
COMBINED
SUSPENDED &
ATTACHED
GROWTH
Common Name
Use
ACTIVATED SLUDGE (AS)
COD REMOVAL (NITRIFICATION) / P
REMOVAL
AERATED LAGOONS
COD REMOVAL (NITRIFICATION)
TRICKLING FILTERS
COD REMOVAL. NITRIFICATION
ROUGHING FILTERS
(TRICKLING FILTERS WITH
HIGH HYDRAULIC LOADING
RATES)
COD REMOVAL
ROTATING BIOLOGICAL
CONTACTORS
COD REMOVAL (NITRIFICATION)
ACTIVATED BIOFILTER
PROCESS
COD REMOVAL (NITRIFICATION)
SUSPENDED GROWTH ---THE
ACTIVATED SLUDGE PROCESS
ACTIVATED SLUDGE HAS BEEN THE SUSPENDED MEDIA
TREATMENT OPTION OF CHOICE. WHY?
EXCELLENT COD REMOVAL.
COMPLETE NITRIFICATION IS ACHIEVABLE.
LOWER PHOSPHATE DISCHARGE IS POSSIBLE.
IMPROVED DISINFECTION DUE TO LOWER AMMONIA
AND SUSPENDED SOLIDS IN FINAL EFFLUENT.
BRIEF OVERVIEW OF THE AS PROCESS
RAW
IN
SCREENS
GRIT
REMOVAL
BIO-REACTORS
SST
PST
DISPOSAL
RAS
WASTING
DISINFECTION
SLUDGE
TREATMENT
EFFLUENT RE-USE
ATHLONE WWTW
POTSDAM WWTW: SURFACE AERATION
ADVANTAGES / DISADVANTAGES OF
THE ACTIVATED SLUDGE PROCESS
ADVANTAGES
DISADVANTAGES
CAN ADAPT TO MINOR
HIGH OPERATING
PH, ORGANIC AND TEMP
COSTS.
CHANGES.
SKILLED OPERATIONAL
SMALL AREA REQUIRED.
STAFF REQUIRED.
DEGREE OF NITROGEN
ELECTRICITY COST
REMOVAL IS
HIGH.
CONTROLABLE.
MINOR ODOUR
PROBLEMS.
SENSITIVE TO SHOCK
LOADS.
REQUIRES CONTINUOUS
AIR SUPPLY.
ATTACHED GROWTH ---- THE TRICKLING
FILTER
WHAT IS A TRICKLING FILTER?
A WASTEWATER TREATMENT SYSTEM THAT BIODEGRADES
ORGANIC MATTER AND CAN ALSO BE USED TO ACHIEVE
NITRIFICATION.
THE WASTEWATER TRICKLES THROUGH A CIRCULAR BED OF
COARSE STONES OR PLASTIC MATERIAL..
ATTACHED GROWTH ---- THE
TRICKLING FILTER. CONT
•A ROTATING DISTRIBUTOR) EVENLY DISTRIBUTES THE WASTEWATER
FROM ABOVE THE BED.
•THE MICROORGANISMS IN THE WASTEWATER ATTACH THEMSELVES TO
THE BED (ALSO KNOWN AS THE FILTER MEDIA), WHICH IS COVERED WITH
BACTERIA .
•THE BACTERIA BREAK DOWN THE ORGANIC WASTE AND REMOVE
POLLUTANTS FROM THE WASTEWATER .
A TYPICAL TRICKLING FILTER
STONES
FEED
EFFLUENT
DISTRIBUTOR ARMS
ADVANTAGES AND DISADVANTAGES
OF TRICKLING FILTERS
ADVANTAGES
DISADVANTAGES
GOOD QUALITY COD
HIGH CAPITAL COSTS.
REMOVAL ( 80%-90%).
CLOGGING OF
MODERATE OPERATING
DISTRIBUTOR ARMS OR
COSTS ( LOWER THAN
BEDS.
ACTIVATED SLUDGE).
POSSIBLE ODOUR
WITHSTANDS SHOCK
PROBLEMS.
LOADS BETTER THAT
OTHER BIOLOGICAL
PROCESSES.
COMPARISON OF THE TWO SYSTEMS
CAPITAL COSTS … ACTIVATED SLUDGE LOWER.
OPERATING COSTS … BIOFILTER LOWER.
ENERGY COSTS…. BIOFILTER LOWER .
CALIBRE OF OPERATIONAL STAFF… FOR TF CAN BE SEMISKILLED. ASP …REQUIRES FAIRLY SKILLED PROCESS
CONTROLLERS. THIS INCURS HIGHER OPERATING COSTS.
EFFLUENT QUALITY …. ASP PRODUCES A BETTER QUALITY
FINAL PRODUCT.
EFFLUENT NUTRIENT VALUE … TF EFFLUENT HAS MORE
NITRATE AND PHOSPHATES THUS HAVING A GREATER
FERTILIZER VALUE.
WHERE WOULD TRICKLING FILTER BE
AN APPROPRIATE TECHNOLOGY ?
SMALL RURAL COMMUNITIES.
WHEN ONLY SKILLED STAFF ARE AVAILABLE
NO SLUDGE AGE CALCULATIONS NEEDED
NO SLUDGE WASTING REQUIRED.
WHEN ELECTRICITY SUPPLY IS LIMITED.
WHEN A WELL NITRIFIED EFFLUENT IS REQUIRED FOR
IRRIGATION.
ENERGY COST OF TREATMENT
TRICKLING FILTER - 250 KWH/ML
ACTIVATED SLUDGE - 350 KWH/ML
ADVANCED TREATMENT WITH NITRIFICATION - 504 KWH/ML
EFFLUENT RE-USE
IRRIGATION HAS TWO REQUIREMENTS.
THE WATER REQUIREMENTS OF THE PLANT.
THE NUTRIENT REQUIREMENTOF THE PLANT.
WITH FULLY NITRIFIED EFFLUENT FROM A TRICKLING FILTER
WORKS ONE CAN EXCEED THE NUTRIENT REQUIREMENT
BEFORE ONE REACHES THE WATER REQUIREMENT OF THE
PLANT. AS A RESULT NITRATES MAY INFILTRATE THE
UNDERGROUND WATER SUPPLY WHICH MUST BE AVOIDED.
THEREFORE TRICKLING FILTER WASTEWATER APPLICATION
RATES MUST BE CAREFULLY MONITORED.
WITH ACTIVATED SLUDGE ONE CAN CONTROL THE NITRATE
AND THE WATER REQUIREMENT OF THE PLANT AT THE SAME
TIME.
POTSDAM WWTW: EFFLUENT RE-USE
APPROPRIATE TECHNOLOGY
REQUIRES TRAINED STAFF
STAFF TO BE TRAINED IN THE OPERATION OF THEIR
WORKS.
OPERATIONS STAFF TO BE OBSERVANT AND USE
THEIR FIVE SENSES WHEN EVALUATING THEIR
PROCESS.
COUNTER-PRODUCTIVE TO HAVE APPROPRIATE
TECHNOLOGY OPERATED BY POORLY TRAINED STAFF.
MAINTENANCE CRITICAL..
SUMMARY
WE HAVE DISCUSSED ONLY TWO OF MANY TREATMENT
OPTIONS.
IT IS CLEAR THAT THE BEST SOLUTION IN A
PARTICULAR CASE IS OFTEN A COMPROMISE
BETWEEN MORE THAN ONE OPTION AS WELL AS
ECONOMIC AND ENVIRONMENTAL CONSIDERATIONS.
LOOKING BACK ON THE SHORT HISTORY AND
SUCESSES OF OUR YOUNG DEMOCRACY I AM SURE
THAT WE ARE WELL UP TO THE TASK OF CHOOSING
APPROPRIATE TECHNOLOGIES.
THANK YOU FOR YOUR ATTENTION
Conclusion
Let us work together
for a better city