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

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

MAJOR AEROBIC BIOLOGICAL PROCESSES

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

Primary Clarifier

Trickling Filter Solids Contact BoxSecondary Clarifier

Humus

Trickling Filter/Solids Contact Treatment Process

Trickling Filter Integrated with Ponds (Petro'M)

Type of Growth

Common Name Use

SUSPENDED GROWTH

ACTIVATED SLUDGE (AS) COD REMOVAL (NITRIFICATION) / P REMOVAL

AERATED LAGOONS COD REMOVAL (NITRIFICATION)

ATTACHED GROWTH

TRICKLING FILTERS COD REMOVAL. NITRIFICATION

ROUGHING FILTERS (TRICKLING FILTERS WITH HIGH HYDRAULIC LOADING RATES)

COD REMOVAL

ROTATING BIOLOGICAL CONTACTORS

COD REMOVAL (NITRIFICATION)

COMBINED SUSPENDED & ATTACHED GROWTH

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

PST

BIO-REACTORSSST

SLUDGE TREATMENT

DISINFECTION

DISPOSAL

RAS

WASTING

EFFLUENT RE-USE

ATHLONE WWTW

POTSDAM WWTW: SURFACE AERATION

ADVANTAGES / DISADVANTAGES OF THE ACTIVATED SLUDGE PROCESS

ADVANTAGES

CAN ADAPT TO MINOR PH,

ORGANIC AND TEMP

CHANGES.

SMALL AREA REQUIRED.

DEGREE OF NITROGEN

REMOVAL IS

CONTROLABLE.

MINOR ODOUR PROBLEMS.

DISADVANTAGES

HIGH OPERATING COSTS.

SKILLED OPERATIONAL

STAFF REQUIRED.

ELECTRICITY COST HIGH.

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 FILTERDISTRIBUTOR ARMS

STONES

FEED

EFFLUENT

ADVANTAGES AND DISADVANTAGES OF TRICKLING FILTERS

ADVANTAGES

GOOD QUALITY COD

REMOVAL ( 80%-90%).

MODERATE OPERATING

COSTS ( LOWER THAN

ACTIVATED SLUDGE).

WITHSTANDS SHOCK

LOADS BETTER THAT

OTHER BIOLOGICAL

PROCESSES.

DISADVANTAGES

HIGH CAPITAL COSTS.

CLOGGING OF

DISTRIBUTOR ARMS OR

BEDS.

POSSIBLE ODOUR

PROBLEMS.

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 SEMI-

SKILLED. 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..

SUMMARYWE 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

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