fundmentals o wastewater treatment 1

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FUNDAMENTALS OF WASTEWATER TREATMENT TECNOLOGIES:

1 fundamentals of wastewater treatment FUNDAMENTALS OF WASTEWATER TREATMENT TECNOLOGIES Prepared By MAMDOUH ZAKI RAMADAN MANAGER OF WATER DIRECTORATE CENTRAL HEALTH LABS MINISTRY OF HEALTH AND POPULATION

TOPICS :

2 fundamentals of wastewater treatment TOPICS Objective Level of treatment Municipal wastewater constituents Municipal wastewater composition Conventional wastewater treatment processes Preliminary treatment Primary treatment Secondary treatment High rate biological process Suspended growth processes Attached ” fixed ” growth processes Low rate biological processes Pathogen removal Tertiary treatment

OBJECTIVE:

3 fundamentals of wastewater treatment OBJECTIVE Protection of public health and improve hygienic conditions within communities Prevention of pollution of environment, mainly receiving water bodies, such as surface and ground water Production of treated effluents that will not cause damage to crops and soils

LEVEL OF TREATMENT:

4 fundamentals of wastewater treatment LEVEL OF TREATMENT Level of treatment required dependent on the end use Irrigation purpose Vegetables Fodder crops Forestry Discharge to streams Wadies Reservoirs Ground water recharge

LEVEL OF TREATMENT:

5 fundamentals of wastewater treatment LEVEL OF TREATMENT Level of treatment required for agriculture and landscape uses depends on Soil characteristics Crop irrigated Types of distribution system Degree of public exposure

MUNICIPAL WASTEWATER CONSTITUENTS:

6 fundamentals of wastewater treatment MUNICIPAL WASTEWATER CONSTITUENTS Wastewater is composed of Domestic wastewater from residences Commercial buildings Industrial wastewater comes from manufacturing plants

CONSTITUENTS OF CONCERN:

7 fundamentals of wastewater treatment CONSTITUENTS OF CONCERN Suspended solids Biodegradable organic Pathogens Nutrients Hydrogen ion Heavy metals Dissolved inorganics Stable ( refractory ) organics

SUSPENDED SOLIDS:

8 fundamentals of wastewater treatment SUSPENDED SOLIDS Measured parameters Suspended solids (volatiles & fixed solids) Lead to Sludge deposits Anaerobic conditions when untreated wastewater is discharged in the aquatic environment Cause soil plugging

BIODEGRADABLE ORGANICS:

9 fundamentals of wastewater treatment BIODEGRADABLE ORGANICS Measured parameters Biochemical oxygen demand ( BOD ) Chemical oxygen demand ( COD ) Lead to Depletion of dissolved oxygen in receiving waters Development of septic conditions

PATHOGENS:

10 fundamentals of wastewater treatment PATHOGENS Measured parameters Indicator organisms Total and fecal coliforms bacteria Lead to Disease that can be transmitted by bacteria , virus , parasites

NUTRIENTS:

11 fundamentals of wastewater treatment NUTRIENTS Measured parameters Nitrogen , phosphorus , potassium Lead to Growth of undesirable aquatic life Nitrogen can lead to pollution of ground water

HYDROGEN ION:

12 fundamentals of wastewater treatment HYDROGEN ION Measured parameters ( PH ) Lead to Metal solubility is affected as well as alkalinity of soils Presence of industrial waste can alter PH significantly Normal PH range in municipal wastewater ( 6.5 ~ 8.5 )

HEAVY METALS:

13 fundamentals of wastewater treatment HEAVY METALS Measured parameter Specific elements ( Pb, Cd , Zn , Ni ,Hg , … .. ) Lead to Accumulate in the environment Toxic to plant and animals Limit the suitability of wastewater for irrigation

DISSOLVED INORGANICS:

14 fundamentals of wastewater treatment DISSOLVED INORGANICS Measured parameters Total Dissolved Solids ( T D S ) Specific elements ( Na , Ca , Mg , Cl , B ) LEAD TO EXCESSIVE SALINITY MY DAMAGE SOME CROPS SPECIFIC IONS SUCH AS CHLORIDE , SODIUM , BORON ARE TOXIC TO SOME CROPS SODIUM MAY CAUSE SOIL PERMEABILITY PROBLEMS

SODIUM:

15 fundamentals of wastewater treatment SODIUM Sodium Adsorption Ratio “ SAR ” is used to evaluate the suitability of water to irrigation High values of SAR indicate that the sodium in the irrigation water may be replace the calcium and magnesium ions in the soil, potentially causing damage to the soil structure Where concentration of sodium , magnesium and calcium are expressed in m . eq / L

SODIUM:

16 fundamentals of wastewater treatment SODIUM

BORON:

17 fundamentals of wastewater treatment BORON It is used in manufacturing of bleaching compounds used in household detergents It is an essential trace element for the growth of terrestrial crop plants, but can be toxic in excess Toxicity to plant can vary depending on life stage and environment Early stags are more sensitive to boron than later one The guidelines of maximum concentration of boron in reused wastewater for irrigation of crops depend on its sensitivity

BORON:

18 fundamentals of wastewater treatment BORON

STABLE (REFRACTORY )ORGANICS:

19 fundamentals of wastewater treatment STABLE (REFRACTORY )ORGANICS MEASURED PARAMETRS PHENOLS, PESTICIDES, CHLORINATED HYDROCARBONES THESE ORGANICS TEND TO RESIST COVENTIONL METHODS OF WASTEWATER TREATMENT LEAD TO TOXIC TO ENVIRONMENT LIMIT THE SUITABILITY OF WASTEWATER TO IRRIGATION

MUNICIPAL WASTEWATER COMPOSITION:

20 fundamentals of wastewater treatment MUNICIPAL WASTEWATER COMPOSITION COMPOSITION REFER TO ACTUAL AMOUNTS OF PHYSICAL, CHEMICAL , BIOLOGICAL CONSTITUENTS PRESENT IN WASTEWATER THE COMPOSITION OF UNTREATED WASTEWATER AND SUPSEQUENTLY TREATED EFFLUENTS DEPENDS ON THE COPOSITION OF THE MUNICIPLE WATER SUPPLY THE NUMBER AND THE TYPE OF COMMERCIAL AND IDUSTRIAL ESTABLISMENT THE NATURE OF RESIDENTAL COMMUNITY

MUNICIPAL WASTEWATER COMPOSITION:

21 fundamentals of wastewater treatment MUNICIPAL WASTEWATER COMPOSITION

Conventional wastewater treatment processes:

22 fundamentals of wastewater treatment Conventional wastewater treatment processes Consists of a combination of physical, chemical, and biological processes and operation It aims to remove solids, organic matter, nutrients from wastewater Different degree of treatment levels Preliminary Primary Secondary Tertiary and/or advanced Disinfection step to remove pathogens follows the last treatment step

PRELIMINARY TREATMENT :

23 fundamentals of wastewater treatment PRELIMINARY TREATMENT Amis to removal of coarse solids and other large materials often found in raw wastewater It includes the following processes Screening Comminution Grit removal Fat, oils & grease removal

SCREENING:

24 fundamentals of wastewater treatment SCREENING Protect plant against bulky matter (papers ,plastics ,rages )

COMMINUTION:

25 fundamentals of wastewater treatment COMMINUTION In the comminutor, wastewater passed through a rotating cutting screen This cutting screen shreds any large chunks of organic matter into smaller pieces This makes it easier for the microorganisms to use the organic matter as food

GRIT REMOVAL:

26 fundamentals of wastewater treatment GRIT REMOVAL Wastewater passes into a wide basin, which slows the wastewater s velocity The slower flow causes grit to settle out Elimination of gravel, sand , and other mineral particles(>0.2m) Protects pumps and other equipment against abarsion Avoid overloading subsequent treatment stages

PRIMARY TREATMENT:

27 fundamentals of wastewater treatment PRIMARY TREATMENT AIMS TO REMOVAL OF SETTABLE ORGANIC SOLIDS BY SEDIMENTATION FLOATING MATERIALS ( SCUM ) BY SKIMMING SOME ORGANIC NITROGEN , ORGANIC PHOSPHORUS AND HEAVY METALS ASSOCIATED WITH SOLIDS PERCENTAGE REMOVAL FROM THE INCOMING WASTEWATER BIOCHEMICAL OXYGEN DEMAND 25% OILS & GREASE 65% TOTAL SUSPENDED SOLIDS 40% THE MOST COMMON UNIT OPERATIONS EMPLOYED IN THE PRIMARY TREATMNT ARE PRIMARY SETTLING TANK ANAEROBIC STABILIZATION PONDS IMHOFF TANK

PRIMARY SETTLING TANK:

28 fundamentals of wastewater treatment PRIMARY SETTLING TANK SETTLED SOLIDS “ PRIMARY SLUDGE ” ARE NORMALLY REMOVED FROM THE BOTTOM OF THE PRIMARY SEDIMENTATION TANK “ CLARIFIERS ” BY SLUDGE RAKS THAT SCRAPE THE SLUDGE TO A CENTRAL WELL FROM WHICH IT IS PUMPED TO SLUDGE PROCESSING UNITS

ANAEROBIC STABILIZATION PONDS:

29 fundamentals of wastewater treatment ANAEROBIC STABILIZATION PONDS They are used to treat domestic and high strength organic wastewater that has high concentration of solids They are earthen basins with depth of up to 9 m The increased depth of deeper ponds helps to conserve energy and maintain anaerobic conditions Anaerobic ponds generate odor due to the formation of hydrogen sulphide gas during anaerobic digestion of settled solids by reducing sulphur bacteria ( spirlium and vibrio desulphuricans )

IMHOFF TANK:

30 fundamentals of wastewater treatment IMHOFF TANK IT IS A TWO STORY TANK THE INCOMING WASTEWATER FLOWS THE UPPER COMPARMENT, ALLOWING SOLIDS TO SETTLE TO THE BOTTOM OF THE CHAMBER, WHICH IS IN THE SHAPE OF THE HOPPER AT THE BOTTOM OF THE HOPPER, THE SOLIDS PASS THROUGH A BAFFLED OUTLET INTO THE LOWER CHAMBER IN WHICH ANAEROBIC DIGESTION OF THE SLUDGE TAKEPLACE IT IS CONSIDERED ECONOMICAL ONLY FOR RELATIVILY SMALL COMMUNITIES, WHERE THEIR SIMPICITY OFFERS SOME ADVANTAGES OVER SEPARATE SEDIMENTION AND DIGESTION

SECONDARY TREATMENT :

31 fundamentals of wastewater treatment SECONDARY TREATMENT THE OBJECTIVE IS A FURTHER TREATMENT OF THE EFFLUENT FROM THE PRIMARY TREATMENT TO REMOVE THE RESIDUAL ORGANIC AND SUSPENDED SOLIDS IT FOLLOWS PRIMARY TREATMENT AND INVOLVES THE REMOVAL OF BIODEGRADABLE DISSOLVED AND COLLOIDAL ORGANIC MATTER USING AEROBIC BIOLOGICAL TREATMENT PROCESSES IN AEROBIC BIOLOGICAL TREATMENT , THERE ARE TWO TECHNOLOGIES SUSPENDED GROWTH ATTACHED GROWTH REMOVAL PERCENTAGE BIODEGRADABLE ORGANICS 90% TOTAL SUSPENDED SOLIDS 85%

AEROBIC BIOLOGICAL TREATMENT :

32 fundamentals of wastewater treatment AEROBIC BIOLOGICAL TREATMENT IT IS PERFORMED IN THE PRESENCE OF OXYGEN BY AEROBIC MICRO ـ ORGANISM ( PRINCIPALLY BACTERIA ) THAT METABOLIZE THE ORGANIC MATTER IN THE WASTEWATER END PRODUCT MORE MICRO- ORGANISM INORGANICS ( CO 2 , NH 3 , AND H 2 O )

ANAEROBIC BIOLOGICAL TREATMENT :

33 fundamentals of wastewater treatment ANAEROBIC BIOLOGICAL TREATMENT IT IS PERFORMED IN THE ABSENSE OF OXYGEN BY ANAEROBIC MICRO- ORGANISMS END PRODUCT LESS ORGANISMS INORGANICS ( CH 4 , H 2 S, CO 2 AND NH 3 )

HIGH & LOW RATE BIOLOGICAL PROCESSES :

34 fundamentals of wastewater treatment HIGH & LOW RATE BIOLOGICAL PROCESSES SEVERAL AEROBIC AND/OR ANAEROBIC BIOLOGICAL PROCESSES ARE USED FOR SECONDARY TREATMENT THESE PROCESSES DIFFER PRIMARLY IN THE MANNER IN WHICH OXYGEN IS SUPPLIED TO THE MICRO - ORGANISMS THE RATE OF WHICH THE MICRO - ORGANISMS METABOLIZE THE ORGANIC MATTER SECONDARY BIOLOGICAL WASTEWATER TREATMENT PROCESSES MAY BE GROUPED ACCORDING TO THESE TWO FACTORES INTO TWO PROCESSES HIGH RATE BIOLOGICAL PROCESSES LOW RATE BIOLOGICAL PROCESSES

HIGH RATE BIOLOGICAL PROCESS:

35 fundamentals of wastewater treatment HIGH RATE BIOLOGICAL PROCESS THEY ARE CHARCTERIZED BY RELATIVELY SMALL REACTOR VOLUMES HIGH CONCENTATIONS OF MICROORGANISMS COMPARED WITH LOW RATE PROCESSES GROWTH RATE OF NEW ORGANISMS IS MUCH GREATER BECAUSE OF A WELL COTROLLED ENVIRONMENT MICROORGANISMS MUST BE SEPARATED FROM THE TREATED WASTEWATER BY SEDIMENTATION TO PRODUCE THE CLARIFIED SECONDARY EFFLUENT

:

36 fundamentals of wastewater treatment Sedimentation tanks used in secondary treatment, often referred to as secondary sedimentation tanks or clarifier operate in the same manner as the primary tanks Biological solids removed during secondary sedimentation (secondary sludge ) are normally combined with primary sludge for sludge processing Types of common high rate biological processes are Activated sludge processes Trickling filter Rotating biological contactors HIGH RATE BIOLOGICAL PROCESSES

ACTIVATED SLUDGE PROCESSES :

37 fundamentals of wastewater treatment ACTIVATED SLUDGE PROCESSES THE TERM ACTIVATED SLUDGE REFERRES TO THE MICRO ORGANISMS WHICH DEGRADE ORGANIC COMPOUNDS IN THE WASTE TO WATER AND CARBON DIOXIDE THIS WASTE CONVERSION TAKESPLACE IN A REACTOR , OR BASIN THIS PROCESS IS QUIT FLEXABLE AND MANY MODIFICATIONS HAVE BEEN DEVELOPED THE MAJOR ACTIVATED SLUDGE MODIFICATION ARE CONVENTIONAL PLUG FLOW EXTENDED AERATION OXIDATION DITCH SEQUENCING BATCH REACTOR

CONVENTIONAL PLUG FLOW :

38 fundamentals of wastewater treatment CONVENTIONAL PLUG FLOW AFTER PRIMARY CLARIFICATION, THE ORGANIC WASTE IS INTRODUSED INTO AN AERATION TANK WHERE A SUSPENDED “ MIXED LIQUOR ” IS AREATED THAT CONSISTING OF MICROORGANISMS DISSOLVED OXYGEN ORGANIC COMPOUNDS AND NUTRIENTS

CONVENTIONAL PLUG FLOW:

39 fundamentals of wastewater treatment CONVENTIONAL PLUG FLOW AFTER A SPECIFIED PERIOD OF TIME , THE MIXTURE IS PASSES ON TO A CLARIFICATION PROCESS , WHERE THE SUSPENDED SOLIDS IN THE MIXED LIQUOR SETTLE OUT TO FORM A BIOMASS , OR SLUDGE , AT THE BOTTOM OF THE TANK MOST OF THE SETTLED SLUDGE IS RECYCLED BACK INTO THE AREATION TANK TO ENSURE A CONSTANT POPULATION OF MATURE ACCLIMATED MICROORGANISMS A PORTION OF THE SLUDGE IS DISPOSED OF OR WASTED

CONVENTIONAL PLUG FLOW :

40 fundamentals of wastewater treatment CONVENTIONAL PLUG FLOW

EXTENDED AREARTION :

41 fundamentals of wastewater treatment EXTENDED AREARTION IT IS SIMILAR TO THE CONVENTIONAL OPERATION EXCEPT THAT IT REQUIRES A LOWER ORGANIC LOADING LONGER AREARION TIME IT IS USED WITHOUT PRIMARY CLARIFICATION EXTENDED AREATION PLANTS ARE TYPICALLY RUN WITH LONG SLUDGE AGES, AND THEY CAN ALSO PROVIDE AMMONIA NITROGEN REMOVAL ( NITRIFICATION ) IT REQUIRES MUCH MORE ENERGY FOR TREATMENT THAN THE CONVENTIONAL ACTIVATED SLUDGE PROCESS

OXIDATION DITCH :

42 fundamentals of wastewater treatment OXIDATION DITCH COSISTS OF A RING OR OVAL SHAPED CHANNEL EQUIPPED WITH ROTORS THE ONLY PRETREATMNT USED IS THE BAR SCREEN, AND THERE IS NO PRIMARY CLARIFICATION IT CAN BE CONSIDERDED AS A VARIATION OF THE EXTENDED AERATION PROCESS

OXIDATION DITCH :

43 fundamentals of wastewater treatment OXIDATION DITCH ADVANTAGES CAN BE EASILY MAINTAINED NOT EFFECTED BY LOAD FLUCTUATION REQUIRES RELATIVELY LITTLE ENERGY PERFORM NITRIFICATION AND PARTIALY DENTRIFICATION

OXIDATION DITCH :

44 fundamentals of wastewater treatment OXIDATION DITCH DISADVANTAGES IT REQUIRES ALARGE AREA LONG RETENTION TIME “ 2 DAYS ” IN COMPARISON TO ACTIVATED SLUDGE “ 2~4 HOURS ”

Sequencing Batch Reactor ( SBR ):

45 fundamentals of wastewater treatment Sequencing Batch Reactor ( SBR ) All steps in the activated sludge process occur in single reactor Wastewater fills the tank, the process runs its course and clarified effluent is decanted from the top of the tank In between batches , a portion of the settled sludge is wasted When wastewater is filling the tank , mechanical aerator mix the tank contents for a period of time to reactivate the sludge leftover the previous cycle

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46 fundamentals of wastewater treatment ADVANTAGES HIGH PERFORMANCE AND RELIABILITY HIGH DEGREE OF FLEXIBILITY NO OBNOXIOUS ODOR ARE GENERATED DISADVANTAGES HIGH OPERATIONALE AND MAINTENANCE COSTS HIGHLY SENSITIVE TO HYDROLIC AND ORGANIC SHOCKS LARGE QUENTITIES OF SLUDGE ARE PRODUCED AND HAVE TO BE HANDLED ACTIVATED SLUDGES PROCESSES

TRICKLING FILTER “ T . F ” :

47 fundamentals of wastewater treatment TRICKLING FILTER “ T . F ” TF CONSISTS OF A CIRCULAR TANK FILLED WITH THE PACKING MEDIA IN DEPTH FROM 1~2.5 m IN NATURAL MEDIA (ROCKS “ 2.5~10 cm ” ) OR 4.5~12.2m IN SYNTHETIC PACKING MEDIA WASTEWATER IS DISTRIBUTED OVER THE TOP OF THE MEDIUM AND SLOWLY MOVE DOWN THROUGH THE FILTER MEDIA

TRICKLING FILTER “ T . F ”:

48 fundamentals of wastewater treatment TRICKLING FILTER “ T . F ” MICROORGANISMS (AEROBIC , ANAEROBIC, FUCLTATIVE , BACTERIA, FUNGI , ALGEA , AND PROTOZOA ) ATTACH THEMSELVES TO THE FILTER MEDIA TO FORM A SLIME LAYER “ FIXED FILM ” ( 0.1 ~ 0.2mm THICK ) ORGANIC MATTER IN THE WASTEWATER DIFFUSES INTO THE BIOLOGICAL FILM , WHERE IT IS METABOLIZED

TRICKLING FILTER “ T . F ” :

49 fundamentals of wastewater treatment TRICKLING FILTER “ T . F ” PERIODICALLY, PORTION OF THE BIOLOGICAL FILM SLOUGH OFF THE MEDIA TREATED WASTEWATER AND ANY BIOLOGICAL SOLIDS ARE COLLECTED IN AN UNDER DRAIN SYSTEM THE COLLECTED LIQUID THEN FLOWS TO THE SECONDARY SETTLING TANK WHERE SOLIDS ARE SEPARATED FROM THE TREATED WASTEWATER

Slide50:

50 fundamentals of wastewater treatment ADVANTAGES SIMPLICITY OF OPERATION AND MAINTENANCE LOW POWER REQUIRMENT OF OPERATION LOW SLUDGE YEILD THAN THE ACTIVATED SLUDGE PROCESS RESISTANCE TO SHOCK LOAD HIGH DEGREE OF NITIFICATION IS ACHIEVED DISADVANTAGES SNAIL, MOSQUITO AND INSECT PROBLEMS OBNOXIOUS ODOR MAY BE GENERATED CLOGGING OF DISRIBUTOR SYSTEM LOW BOD REMOVAL ” 50 ~ 70% ” IN COMPARISON WITH ACTIVATED SLUDGE PROCESS HIGH SUSPENDED SOLIDS IN THE EFFLUENT ” 20 ~ 30 mg/l ” HIGH CAPITAL COST LOW TEMPERATURES REDUCE THE DEGRADING CAPACITY OF T F TRICKLING FILTER “ T . F ”

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51 fundamentals of wastewater treatment IT CONSISTS OF A SERIES OF CLOSELY SPACED CIRCULAR DISKS “ UP TO 3.5 M IN DIAMETER OF CORRUGATED LIGHT PLASTIC MATERIAL “ POLYVINYL CHLORIDE OR POLYSTYRENE ” THE DISKES ARE SUBMERGED IN THE WASTEWATER AND ROTATED SLOWLY “ 1~3rpm ” WHILE IMMERSED UP TO 40% IN THE WASTEWATER ROTATING BIOLOGICAL CONTACTORS ( R B Cs )

ROTATING BIOLOGICAL CONTACTORS ( R B Cs ):

52 fundamentals of wastewater treatment ROTATING BIOLOGICAL CONTACTORS ( R B Cs ) DURING OPERATION ,BIOLOGICAL GROWTHS BECOME ATTACHED TO THE WETTED SURFACE OF THE DISKS TO FORM A SLIME LAYER “ 1~4mm ” WHICH BIOLOGICALLY TREATS THE WASTEWATER THE ROTATION OF THE DISK ALTERNATELY CONTACTS THE SLIME LAYER WITH THE ORGANIC MATERIAL IN THE WASTEWATER AND THEN WITH THE ATMOSPHERE FOR ADSORPTION OF OXYGEN

ROTATING BIOLOGICAL CONTACTORS ( R B Cs ) :

53 fundamentals of wastewater treatment ROTATING BIOLOGICAL CONTACTORS ( R B Cs ) A SMALL PORTION OF THE BIOMASS REMAINS SUSPENDEDINTHE LIQUID WITHIN THE BASIN AND IS RESPONSIBLE IN MINOR PART FOR THE ORGANIC LOAD REMOVAL EXCESS SOLID ARE REMOVED “ TEARD OFF THE DISKS ” BY SHEARING FORCES AND ARE SEPARATED FROM THE LIQUID IN THE SECONDARY SETTLING TANK

ROTATING BIOLOGICAL CONTACTORS ( R B Cs ) :

54 fundamentals of wastewater treatment ROTATING BIOLOGICAL CONTACTORS ( R B Cs ) ADVANTAGES SHORT CONTACT PERIOD LOW POWER CONSUMPTION EASILY SEPARATES BIOMASS FROM WASTEWATER DISADVANTAGES NEED FOR COVERING UNITS INSTALLED IN COLD CLIMATE

LOW RATE BIOLOGICAL PROCESSES:

55 fundamentals of wastewater treatment LOW RATE BIOLOGICAL PROCESSES They are characterized by lower conversion rates as compared to high rate biological systems Micro-organisms are not usually separated from the liquid in a separate step Primary sedimentation prior to low rate processes is often omitted Low rate biological processes include Facultative wastewater stabilization ponds Aerated lagoons

FACULTATIVE WASTEWATER STABILIZATION PONDS:

56 fundamentals of wastewater treatment FACULTATIVE WASTEWATER STABILIZATION PONDS They have long retention times and do not have a mechanical mixing or aeration Stabilization of waste is achieved by a combination of aerobic, anaerobic and facultative bacteria They are earthen basins ( 1.2 ~ 2.5 m in depth ) that contain three zones A surface zone Bacteria and algae exist in symbiotic relation ship to aerobically degrade organic matter Intermediate zone Decomposition of organic wastes is carried out by facultative bacteria in parley anaerobic environment Bottom anaerobic zone Bacteria anaerobically digest the sludge layer formed by accumulation of large solids that have settled

AERATED LAGOON :

57 fundamentals of wastewater treatment AERATED LAGOON They are large basins ( 2.6 m in depth ) in which natural biological processes convert organic wastes to water and carbon dioxide , and have a retention time between 3 ~ 10 days A constant supply of oxygen from mechanical aeration is provided to maintain aerobic condition in the basin Sludge that is produced settles in certain unmixed zones of lagoons and forms a blanket on the bottom The sludge then becomes anaerobic and self digestion process takes place , which reduces the volume of the sludge considerably

AERATED LAGOON:

58 fundamentals of wastewater treatment AERATED LAGOON The lagoon requires sludge removal periodically to maintain hydraulic capacity The main difference between aerated lagoons and the activated sludge is that there is no secondary clarifier and, consequently, the sludge in the aerated lagoon is not recycled several types of aerated lagoons Complex mix aerated lagoons Partial mix aerated lagoons

AERATED LAGOON:

59 fundamentals of wastewater treatment AERATED LAGOON

COMPARISON OF LOW AND HIGH RATE BIOLOGICAL PROCESS:

60 fundamentals of wastewater treatment COMPARISON OF LOW AND HIGH RATE BIOLOGICAL PROCESS Low rate biological processes are important in many wastewater treatment and irrigation application in developing countries Less costly Require less process control Effluent quality is lower High suspended solids in wastewater stabilization pond effluent due to algal growth is a good example Provide a sufficient degree of treatment prior to reuse for agriculture for which secondary treatment is required Low rate processes such as stabilization ponds provide considerable pathogen and nitrogen removal

PATHOGEN REMOVAL:

61 fundamentals of wastewater treatment PATHOGEN REMOVAL Disinfection means destroying disease-causing organisms ( bacteria , viruses, intestinal nematodes eggs) of effluent from secondary treatment Different types of disinfectants are used, such as chlorine, ozone and ultraviolet A more important issue is the removal of intestinal nematode eggs , for this purpose, maturation ponds with a long retention time

ANAEROBIC TREATMENT :

62 fundamentals of wastewater treatment ANAEROBIC TREATMENT It is a conversion of organic compounds into methane and carbon dioxide by bacteria Without the aid of oxygen Removal of organic materials occurs by microbial conversion , first to hydrogen, carbon dioxide, and acetic acid which then act as a precursors to the final by-products of methane and carbon dioxide

ANAEROBIC TREATMENT:

63 fundamentals of wastewater treatment ANAEROBIC TREATMENT Three different but related groups of bacteria are involved, namely , acidogenic, acetognic and methanogenic bacteria

ANAEROBIC TREATMENT ADVANTAGES :

64 fundamentals of wastewater treatment ANAEROBIC TREATMENT ADVANTAGES Environmental acceptance No environmental nuisance because it is totally enclosed Low sludge production The very long solids retention time leads to low growth rate, and the solid production is also extremely low Energy production The carbon in the waste is available from methanogenesis in which the biogas ( ch4 ) is the main by-product The production of biogas is generally in excess of that needed to operate the anaerobic treatment system

TERTIARY TREATMENT:

65 fundamentals of wastewater treatment TERTIARY TREATMENT It is employed when specific wastewater constituents must be removed, but can not be removed by secondary treatment Individual treatment processes are necessary to remove nitrogen, phosphorous, additional suspended solids Advanced treatment processes are sometimes combined with primary or secondary treatment Chemical addition to primary clarifiers to remove phosphorous

TERTIARY TREATMENT:

66 fundamentals of wastewater treatment TERTIARY TREATMENT Suspended and colloidal solids must be removed by advanced treatment before disinfection step The sequence of treatment often specified is Secondary treatment Chemical coagulation Sedimentation Filtration disinfection

THANK YOU:

67 fundamentals of wastewater treatment THANK YOU

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