Important Contaminants In Waste Water Biology Essay

Water is a of course happening substance and takes up approximately 70 % of the Earth ‘s surface. It is used for assorted activities including ingestion as drinkable H2O and in nutrient, rinsing, fabrication procedures and so on. When H2O has been used up, it becomes wastewater and is discharged into natural H2O beginnings such as lakes, rivers, and so on through sewage systems. To guarantee effluent discharged does non represent pollution of inland Waterss it is treated before discharge. Therefore, the primary purpose of effluent intervention is to guarantee human and industrial effluent is disposed of such that it does non represent wellness jeopardies to worlds or unacceptable harm to the natural environment ( Sonune & A ; Ghate, 2004 ) . Wastewater can therefore be defined as liquid waste made up of a mixture of both inorganic and organic substances including man-made or man-made substances ( Gray, 2005 ) , ensuing from family, commercial and industrial activities in add-on to groundwater, surface H2O and storm H2O ( Sonune & A ; Ghate, 2004 ) . In add-on to inorganic and organic substances, effluent besides contains high degrees of O using wastes, infective beings, foods and deposits, and in some cases toxic compounds ( Sonune & A ; Ghate, 2004 ) Table 1. Harmonizing to Gray, effluent can by and large be divided into domestic effluent besides known as sewerage, industrial effluent and municipal effluent ( Gray, 2005 ) , see Table 2 and Figure 1.

Table: Important contaminations in effluent

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Beginning: ( UN-ESCWA, 2003 )

Contaminants

REASONS FOR IMPORTANCE

Suspended solids ( SS )

SS can take to development of sludge sedimentations and anaerobiotic conditions when untreated effluent

is discharged to the aquatic environment.

Biodegradable organics

These are chiefly made up of proteins, saccharides and fats. They are normally measured in footings of BOD and COD. If discharged into inland rivers, watercourses or lakes, their biological stabilisation can consume

natural O resources and do infected conditions that are damaging to aquatic species

Pathogenic beings

Pathogenic beings found in waste-water can do infective diseases.

Precedence pollutants

Pollutants including organic and inorganic compounds, may be extremely toxic, carcinogenic, mutagenic or teratogenic.

Furnace lining organics

Refractory organics that tend to defy conventional waste-water intervention include wetting agents, phenols and

agricultural pesticides.

Heavy metals

These are normally added by commercial and industrial activities must be removed for reuse of the waste-water

Dissolved inorganic components

Dissolved inorganic components such as Ca, Na and sulphate are frequently ab initio added to domestic H2O

supplies, and may hold to be removed for waste-water reuse

Table 2: Types of effluent, beginnings and composing

Beginning: ( Aizenchtadt, Ingman, & A ; Friedler, 2008 )

TYPES OF WASTES

Description

Beginnings

Composition

DOMESTIC WASTEWATER

Blackwater

Greywater

this is wastewater discharged from families, commercial and institutional installations

Toilets

Kitchens, wash, washing/bathing

Urine, fecal matters, lavatory paper

MUNICIPAL WASTEWATER

Domestic effluent

Commercial effluent

Sanitary effluent

Commercial activity

Inflow and Infiltration

Storm flows/Street rinsing

Groundwater infiltration

this is derived chiefly from domestic activities but includes effluent discharged from commercial and industrial installations, infiltration and inflow into cloacas and storm overflows

Blackwater, greywater

Restaurants, workshops, etc

Combined systems, separate systems – cross-connections or illegal connexions in fractured pipes and manholes

Sand, grit, hydrocarbons, metals, etc. ; carnal wastes

INDUSTRIAL WASTEWATER

this is derived from assorted fabrication and industrial procedures

Manufacturing procedures, electrolysis, heavy metals, equipment cleansing, chilling systems

Figure: Beginnings of effluent

Beginning: ( Metcalf and Eddy, inc. , 2003 )

Wastewater intervention workss are made up of different intervention processes or units as shown on Table 3 and are designed to handle effluents of known composing and flow rate and finally generate wastewater of certain quality ( Gray, 2005 ) . In the UK the design of effluent intervention workss adheres to the Royal Commission Standard for wastewater of 20:30, that is, the wastewater has a biochemical O demand ( BOD ) of 20mg/l and a suspended solid concentration of 3omg/l ( Gray, 2005 ) , see Table 4.

Table 3: Some unit processes in effluent intervention

Beginning: ( Gray, 2005 ; UN-ESCWA, 2003 )

PROCESS UNITS IN WASTEWATER TREATMENT

Physical Unit procedure

Balancing

Screening

Deposit

Flotation

Hydrocyclone

Filtration

Centrifugation

Rearward osmosis

Ultrafiltration

Microfiltration

Chemical Unit procedure

Neutralization

Precipitation

Ion exchange

Oxidation decrease

Adsorption

Table 4: Typical composing of natural sewerage in the US and UK

Beginning: ( Gray, 2005 )

Parameter

US ( Mg/ )

UK ( Mg/l )

Ph

7

7

Biochemical O demand ( BOD )

250

350

Chemical O demand ( COD )

500

700

Suspended solids

250

400

Ammonia Nitrogen

30

40

Nitrate Nitrogen

& lt ; 1

& lt ; 1

Entire Phosphorus

10

15

The intervention method utilized for a peculiar effluent flow is dependent on the measure, composing and temperature of the effluent ( Rulkens, 2008 ) . Municipal effluent flow fluctuates with disparity in use and is affected by factors such as clime, community size, criterions of life, dependableness and H2O supply, cost of H2O and supply, preservation demands, degree of industrialisation, metre services and so on ( Liu & A ; Liptak, 2000 ) ; it is therefore expected to hold wide fluctuations in flow rates ( UN-ESCWA, 2003 ) . Unit flow rate informations can be utilized in gauging effluent flow rates from families, commercial and institutional installations ( Liu & A ; Liptak, 2000 ) . Industrial effluent flow rates vary and are a contemplation of the type and size of industry, dependable appraisal of industrial effluent flow rates can be obtained from specific information on each industry ( Liu & A ; Liptak, 2000 ) . Wastewater flow rates depict daily, hebdomadal and seasonal forms comparable to the forms H2O use exhibits ( Liu & A ; Liptak, 2000 ) . Table 5 shows information required by applied scientists when planing a effluent intervention works.

Table 5: Information required in planing effluent intervention works

Beginning: ( Liu & A ; Liptak, 2000 )

TYPES OF FLOW

Description

Average Daily Flow

This is the mean flow rate happening over a 24 hr period based on entire one-year flow rate informations. It is used by applied scientists to measure the capacity of a effluent intervention works and in developing flow rate ratios.

Maximal Daily Flow

This is the maximal flow rate that occurs over a 24 hr period based on one-year operating informations. The information is relevant when planing installations affecting keeping clip such as equalisation basins and chlorine-contact armored combat vehicles.

Peak Hourly Flow

This is the extremum sustained hourly flow rate that occurs during a 24 hr period based on one-year operating informations. The information obtained is required for planing aggregation and interception cloacas, effluent pumping Stationss, grit Chamberss, deposit armored combat vehicles, chlorine-contact armored combat vehicles and so on.

Minimal Daily Flow

This is the minimal flow rate happening over a 24 hr period based on one-year operating informations. It is of import when sizing conduits where solids deposition might happen at low flow rates.

Minimum Hourly Flow

This is the lower limit sustained hourly flow rate that occurs over a 24 hr period based on one-year operating informations. The information is required in finding the possible procedure effects and size effluent flow metres, peculiarly those that gait chemical-feed systems.

Sustained Flow

The sustained or exceeded flow rate value for a peculiar figure of back-to-back yearss based on one-year operating informations. Data obtained is used in sizing equalisation basins and other hydraulic constituents.

A good effluent intervention procedure is one that is capable of efficient riddance or change of assorted sorts of pollutants in a mode that is cost effectual, sustainable in footings of chemical and energy usage, release of pollutants and the coevals of energy and compounds of value including treated H2O for recycle ( Rulkens, 2008 ) . Wastewater intervention methods are a combination of colony procedures and either biological or physicochemical procedures. Treatment involves dividing solids that can settle, suspend and solubilize from effluent to organize big atoms that can be removed via colony ; these big atoms form sludge which is treated individually and so disposed ( Gray, 2005 ) . Conventional effluent intervention is a combination of physical, chemical and biological procedures and methods of taking solids, organic affair, and in some instances foods from effluent ( Sonune & A ; Ghate, 2004 ) . Treatment methods are by and large classified into four classs in order of increasing degree of intervention: preliminary intervention or pretreatment, primary intervention, secondary intervention and third or advanced intervention ( Idelovitch & A ; Ringskog, 1997 ) , Table 6.

Table 6: Methods of handling effluent

Beginning: ( Gray, 2005 )

TREATMENT METHODS

Description

Preliminary treatment/ Pretreatment

Removal and decomposition of gross solids, remotion of grit and separation of storm H2O. Large sums of oil and lubricating oil are besides removed here

Primary intervention

This follows pretreatment and involves remotion of substances that can settle and these are removed as sludge

Secondary intervention

Microorganisms are introduced at this phase to oxidise dissolved and colloidal stuffs

Tertiary/Advance intervention

here the biologically H2O is retreated to a quality beyond what is obtained with secondary intervention by taking left over BOD, suspended solids, bacteriums, toxic substances or foods. Chemical methods are employed in this case

Sludge intervention

Dewatering, stabilisation and concluding disposal of sludge takes topographic point

Figure: A effluent works demoing assorted intervention degrees

Beginning: ( UN-ESCWA, 2003 )

METHODS FOR TREATING WASTEWATER

2.1 PRETREATMENT

The aim of pretreating effluent is to take or cut down the size of solids and other substances which may interrupt intervention operations or harm works equipment. Solids such as wood, glass, vesture, plastics, grit and others such as fecal matters, oil and lubricating oil and even smells are removed during this phase. It involves physical unit processes such as showing, see Tables 3 and 7.

Table 7: Types of screens used for pretreating effluent

Beginning: ( UN-ESCWA, 2003 )

2.2 PRIMARY TREATMENT

This phase of intervention involves the uncomplete remotion of suspended solids and organic affair utilizing deposit and floatation physical procedures ( Sonune & A ; Ghate, 2004 ) . The aim of this intervention phase is to bring forth an wastewater, primary wastewater, appropriate for downstream biological intervention and to divide solids in the signifier of sludge that can be easy and cost-effectively treated before disposal ( UN-ESCWA, 2003 ) . It achieves the remotion of about 25-50 % BOD, 50-70 % of entire suspended solids and 65 % of oil and lubricating oil ; it to boot removes some organic N and P, heavy metals associated with solids but non colloidal or soluble constituents ( Sonune & A ; Ghate, 2004 ) . See Figures 3 and 4 and Table 8. At present, outflowing and H2O quality criterions demand the remotion of organic substances from effluent at greater degrees than can be achieved utilizing merely primary intervention ( Sonune & A ; Ghate, 2004 ) . Secondary intervention processes hence have to be employed.

Figure: Settling basin with horizontal flow used in deposit pretreatment

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

Figure: An illustration of a typical floatation armored combat vehicle

Beginning: ( Liu & A ; Liptak, 2000 )

Table 8: Quality of natural effluent and primary wastewater at specific intervention workss in California

Beginning: ( Sonune & A ; Ghate, 2004 )

2.3 SECONDARY TREATMENT

The intent of secondary intervention is to farther dainty primary wastewater by taking dissolved and colloidal organics and suspended solids that were missed during primary intervention ( Sonune & A ; Ghate, 2004 ) . It is a biological intervention procedure as it involves the usage of micro-organisms, Table 3, the assorted aerophilic biological methods employed vary chiefly in the manner O is supplied to micro-organisms and the rate at which organic affair nowadays in the effluent is broken down or metabolized ( Sonune & A ; Ghate, 2004 ) . Figure 5 depicts a trickling filter, the most often employed attached-growth biological intervention procedure for the remotion of organic substances from effluent ( UN-ESCWA, 2003 ) . The public presentation of secondary intervention works is about ever measured based on the remotion of BOD and SS. If well-constructed, it may take from 85-95 % of BOD and SS from effluent, however the BOD trial does non take into history all organic substances present on effluent ( Sonune & A ; Ghate, 2004 ) .on average a secondary intervention may incorporate BOD and COD of 20mg/l and 60-100mg/l respective but is estimated to take approximately 65 % of COD in effluent. Hence, the demand for a intervention procedure that can bring forth high quality wastewater when necessary by taking staying organic substances ( Sonune & A ; Ghate, 2004 ) .

Figure: A position of a trickling filter used in biological effluent intervention

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

2.4 ADVANCED TREATMENT

Although both primary and secondary effluent interventions take most of the BOD and suspended solids in effluent, it is going progressively evident that higher degrees of intervention are required as the two mentioned are incapable of protecting having Waterss or supplying reclaimable H2O for industrial and or domestic intents ( Sonune & A ; Ghate, 2004 ) . Advanced intervention is therefore an add-on to conventional intervention workss for taking N, P, biodegradable organics, foods, bacteriums and viruses, and toxic substances ( UN-ESCWA, 2003 ) . Harmonizing to Sonune & A ; Ghate, “ advanced effluent intervention can be defined as any procedure designed to bring forth an wastewater of higher quality than normally achieved by conventional secondary intervention procedure or incorporating unit operations non usually found in secondary intervention ” , see Table 9. The definition hence includes about all units non common in effluent intervention today ( Sonune & A ; Ghate, 2004 ) . Unlike conventional secondary intervention, which to some extent removes BOD and suspended solids, advanced intervention produces wastewaters that can be reused for industrial procedure or chilling H2O and may be recycled to increase the handiness of domestic H2O supply ( Sonune & A ; Ghate, 2004 ) .

Table 9: Types of advanced intervention

Beginning: ( Sonune & A ; Ghate, 2004 )

TREATMENT TYPE

Definition

Third Treatment

Any intervention procedure in which unit operations are added to the intervention procedure after the conventional secondary intervention phase. The added unit operation can run from a simple filtration to the add-on of several procedures for handling suspended solids, N, P and so on.

Physicochemical Treatment

A intervention procedure in which biological and physical-chemical procedures are intermingled to obtain wastewater of specified quality.

Combined biological-physical and chemical Treatment

This procedure differs from third intervention in that in third intervention unit procedures are added after conventional biological intervention while here biological and physicochemical procedures are combined.

2.4.1 MEMBRANE TECHNIQUES

In the past membrane intervention procedures were non frequently utilized in effluent intervention due to high cost and energy demand of membranes, and deficiency of experience. However, the industry of cheaper polymer-membrane stuffs holding high selectivity and efficient chemical, thermic and mechanical opposition has improved its use today ( Seo & A ; Vogelpohl, 2009 ) . The method is utilized in purifying and / or concentrating changing types of fluids including H2O, effluent, pharmaceutical and chemical merchandises ( Sonune & A ; Ghate, 2004 ) . The procedure is driven by force per unit area and depends on the membrane ‘s pore size to accomplish separation of constituents based on their pore sizes ( Sonune & A ; Ghate, 2004 ) . When compared to conventional physical-chemical intervention methods, its advantages include: decrease in installing infinite, cost, the usage of toxic chemicals ( Sonune & A ; Ghate, 2004 ) , sludge decrease and its simpleness ( Juang et al. , 2007 ) . However, harmonizing to Juang et al. , membrane procedures are limited by the issue of atom blocking, polariztion, membrane surface fouling after uninterrupted usage.

2.4.2 Desalination

The procedure of desalinization is used to take dissolved minerals from brackish H2O, saltwater, or treated effluent ( Sonune & A ; Ghate, 2004 ) . It is progressively being used to obtain drinkable H2O from brackish H2O and saltwater, better the fresh water quality for imbibing and industrial activities and in handling industrial and municipal effluent before discharge or recycle ( Sonune & A ; Ghate, 2004 ; Madwar & A ; Tarazi, 2002 ) . The combination of rearward osmosis with conventional or modern pretreatment engineerings are widely used in desalinization of effluent ( Madwar & A ; Tarazi, 2002 ) . See Tables 10 and 11 for illustrations of industrial application of desalinization and types of desalinization methods.

Table 10: Industries that apply desalinization methods

Beginning: ( Madwar & A ; Tarazi, 2002 )

INDUSTRIES THAT APPLY DESALINATION METHODS:

Power coevals industry

Glass fabrication industry

Electronicss industry

Fabric industry

Cooling systems

Construction industry

Metallic fabrication industry

mush and paper industry

Table 11: Types of desalinization methods

Beginning: ( Sonune & A ; Ghate, 2004 )

DESALINATION METHODS

Description

Rearward osmosis

Wastewater is passed through a semi permeable membrane under force per unit area, thereby dividing out the salts, Figure 6. The H2O is pretreated before being pumped through the membrane to except atoms that may blockade the membrane pores. The H2O quality obtained is dependent on force per unit area, salt concentration of feed H2O and pervasion invariable of membranes used.

Electrodialysis ( ED )

ED uses ion-permeable membranes and electricity to consequence separation of salts from effluent. The membranes are placed in a stack and those that permit cations are alternated with those that permit lone anions through. Electric current supplied serves to drag ions through the membrane concentrating them between each membrane. Change by reversaling the way of electric current AIDSs to forestall fouling of membranes

Ion exchange ( IX )

IX rosins are used to replace unwanted ions in H2O ( effluent ) with coveted ions, as the H2O passes through the rosin. The frequence at which rosins are replaces is dependent on the concentration of dissolved solids in the effluent. It is used in municipal effluent intervention to take Ca and Mg ions and in bring forthing pure H2O for industrial procedures.

Freeze desalinization

This method is based on the fact that as saltwater freezing, ice crystals are formed from pure H2O go forthing behind dissolved salt and other minerals. It uses less energy in concentrating a greater scope of effluent compared to distillment. Conventional freezing procedure involves the undermentioned stairss:

Precooking provender H2O

Crystallization of ice into slush

Separation of ice from seawater

Washing the ice

Melting the ice

Modern methods are looking into cut downing the figure of stairss peculiarly the rinsing measure.

Figure: A contrary osmosis system

Beginning: ( Sonune & A ; Ghate, 2004 )

BIOLOGICAL AND CHEMICAL TREATMENT METHODS

3.1 PHYSICO-CHEMICAL METHODS

Chemical methods of handling effluent involve the usage of chemical reactions to do alterations in effluent, Table 12. They frequently lead to a net addition in dissolved substances in effluent which is important if the effluent is to be recycled. Chemical methods are normally used with physical unit operations and biological methods ( UN-ESCWA, 2003 ) . In past old ages the primary ground for handling effluent was to bring forth an wastewater that met regulative criterions for the discharge of wastewater into inland Waterss ; which could be achieve with conventional biological procedures ( Rulkens, 2008 ) . However, the primary intent for handling effluent today is mostly to bring forth reclaimable H2O and recover of import compounds and energy from effluent ; advanced physic-chemical intervention methods are now utilized in accomplishing a intervention procedure that is environmentally sustainable ( Rulkens, 2008 ) . Some advantages of chemical intervention methods include ( Rulkens, 2008 ; Leentvaar et al. , 1978 ) :

Bettering the capableness of biological intervention procedures.

Recovering valuable substances and energy from effluent.

Achieving high quality necessary for the usage of wastewaters obtained from handling effluent.

Removing salt ( desalinate ) from brackish/ salty H2O and saltwater.

Treating concentrated liquid and sludge by merchandises of effluent intervention processes.

Reducing installing infinite.

Better meeting of extremum burden.

Insensitivity to toxic compounds in effluent.

Immediate start-up and shut-down.

Table 1: Chemical intervention processes for handling effluent

Beginning: ( Amudaa & A ; Amoo, 2007 ; MacCrehan, Bedner, & A ; Helz, 2005 ; Macauley, Qiang, Adams, Surampalli, & A ; Mormile, 2006 ; Lema, Omil, & A ; Suarez, 2009 ; UN-ESCWA, 2003 )

Method

Description

Chemical Precipitation

Coagulation/Flocculation

Compounds such as ferrous chloride are added to wastewater to enable suspended colloidal atoms aggregate into larger readily settleable flocs ( Amudaa & A ; Amoo, 2007 ) . it may be used for pretreating industrial effluent prior to dispatch into municipal sewage, primary intervention of urban effluent and so on ( Lema et al. , 2009 ) , see Figure 7.

Adsorption with activated C

Adsorption involves the adhesion of a gas, liquid or soluble substance to a surface, in this case activated C. This method normally follows biological intervention and is used to take left over soluble organic substances and other little atoms ( UN-ESCWA, 2003 ) , see Figure 8.

Disinfection

Disinfection of effluent involves the devastation or remotion of infective micro-organisms present in effluent, to cut down the hazard of human exposure ( UN-ESCWA, 2003 ; Macauley et al. , 2006 ) , Table 12. Methods used include:

Chemical substances such as Cl, ozone and so on

Radiation

Heat, visible radiation

Filtration, deposit and so on

Dechlorination

Chlorine used in disinfecting effluent is toxic to aquatic beings, therefore when used in disinfection it is removed by the procedure of dechlorination before outflowing discharge into surface Waterss. Reducing agents such as sulfite ( SO4 or HSO-3 ) is added in surplus to enable dechlorination ( MacCrehan et al. , 2005 ) .

Figure: A once-through chemical intervention system

Beginning: ( Liu & A ; Liptak, 2000 )

Figure: A Granular activated C contactor

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

Table12: Features of common disinfecting agents

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

3.2 BIOLOGICAL METHODS

Biological intervention of effluent involves the usage of micro-organisms to breakdown organic wastes in effluent ( Aytimur & A ; Atalay, 2004 ) ; it is normally used in combination with physical and chemical procedures ( Rulkens, 2008 ) . Biological procedures are categorized into the undermentioned: aerophilic procedures, anoxic procedures, anaerobiotic procedures, combined procedures, pool procedures ( UN-ESCWA, 2003 ) , Table 13 gives a sum-up of some of the commonly used methods. The following are advantages of biological intervention procedures ( Rulkens, 2008 ; El-Bestawy et al. , 2005 ; Chan et al. , 2009 ) :

Lower cost of intervention and absence of secondary pollution.

Ability to easy take P and N, which aid algae growing

Ability to handle about all effluent holding BOD/COD ratio of 0.5 or more.

Ability to easy change over compounds incorporating S into H2S, SO2-4 or S.

Ability to change over ammonium hydroxide and N incorporating compounds into N gas.

Table 13: some biological procedures used in effluent intervention

Beginning: ( Aytimur & A ; Atalay, 2004 ; Liu & A ; Liptak, 2000 ; Metcalf and Eddy, Inc. , 1991 ; Qasim, 1999 ; UN-ESCWA, 2003 )

Method

Description

Activated-sludge

Is an aerophilic procedure conducted in a continuous-flow aeration armored combat vehicle incorporating activated micro-organisms, activated-sludge, able to breakdown organic affair nowadays in effluent in the presence of O. Gram negative bacteriums including Nitrogen and C oxidants, floc and non-floc formers and so on are chiefly used for this procedure. A drawback to this procedure is sludge bulking due to the absence of P, N, hint elements, and fluctuations in pH, temperature and dissolved O, see Figure 9.

Trickling filter

This consists of a bed of extremely permeable media, made of stones and plastic wadding stuff, onto which micro-organisms are attached and through which effluent is percolated. Organic substances within effluent are degraded by surface assimilation onto the sludge bed formed by the micro-organisms, see Figure 5 and 10.

Activated Lagoon

An activated laguna is a basin within which effluent is treated either based on flow-through or solids recycling. Its biological science similar to activated-sludge procedure but differs in that its big surface country may do more temperature effects than is seen with traditional activated-sludge procedures, see Figure 11.

Stabilization pool

This is a shallow basin used to handle effluent without solids return due to finish commixture. It is usually classified as aerophilic, anaerobiotic or aerobic-anaerobic depending on the type of biological activity happening in it, see Figure 12.

Nitrification-Denitrification

In nitrification, Nitrosomonas bacterium and Nitrobacter are used to oxidise ammonium hydroxide and N into nitrite and so nitrate. It can be achieved by suspended-growth or attached-growth procedures such as dribbling filters and revolving biological contactors, see Figure 13.

Denitrification removes nitrogen as nitrate by change overing to nitrogen gas under anoxic status. It can be achieved utilizing suspended-growth or attached-growth procedures such as plug-flow activated-sludge and a column reactor incorporating media on which bacteriums can turn.

Phosphorus remotion

The procedure of taking P from effluent is based on exposing micro-organisms to jumping anaerobiotic and aerophilic conditions. This leads to emphasize and makes the micro-organism increase their consumption of P. A/O, PhoStrip and sequence batch reactor procedures are used to accomplish P remotion, see Figures 14 and 15.

Figure: A flow diagram demoing an activated sludge procedure

Beginning: ( UN-ESCWA, 2003 )

Figure: A flow diagram for dribbling filters

Beginning: ( UN-ESCWA, 2003 )

Figure: A flow diagram for aerated lagunas

Beginning: ( UN-ESCWA, 2003 )

Figure: A flow diagram for stabilisation pools

Beginning: ( Liu & A ; Liptak, 2000 )

Figure: The constellation of a revolving biological contactor

Beginning: ( Qasim, 1999 )

Figure: A/O procedure for taking P in effluent

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

Figure: PhoStrip procedure for P remotion in effluent

Beginning: ( Metcalf and Eddy, Inc. , 1991 )

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