DEPARTAMENTO DE ENGENHARIA CIVIL E ARQUITECTURA

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PROJECTO DE INSTALAÇÕES DE TRATAMENTO / PROF. EDUARDO RIBEIRO DE SOUSA 1

DEPARTAMENTO DE ENGENHARIA CIVIL E ARQUITECTURA

MESTRADO INTEGRADO EM ENGENHARIA DO AMBIENTE

PROJECTO DE INSTALAÇÕES DE TRATAMENTO

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SCHEME OF TREATMENT

The treatment scheme is the set of actions which must be carried out in

various unit operations and processes in order to optimize the

treatment of water, technically and economically, taking into account the

physical, chemical and bacteriological raw water characteristics (in

accordance with the provisions laid out in Decree-Law 236/98 of 1

August) and the corresponding treated water quality (in accordance

with the provisions laid out in Decree-Law 306/2007 of 27 August).

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RAW WATER PARAMETERS

TREATMENT PROCESSES OR UNIT OPERATIONS

RAW WATER PARAMETERS PROCESSES OR UNIT OPERATIONS

Iron / manganese Oxidation + removal by chemical precipitation

Turbidity Clarification

Microbiological parameters Oxidation + clarification+ disinfection (chlorine)

Total suspended solids Clarification

Calcium-carbonic equilibrium Addition of lime, crushed limestone chambers Oxidation of organic matter Ozone, potassium permanganate, chlorine (but

not as the first treatment operation) Residual in treated water Chlorine addition

Synthetic organic compounds (pesticides and herbicides)

GAC (granular activated carbon) adsorption CAP (powered activated carbon) adsorption

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RAW WATER SOLIDS AND GRIT REMOVAL

The removal of solids is operated almost exclusively

when you want to treat surface water source (water

intakes from rivers, reservoirs, ponds, etc.);

The removal of sand is operated when you want to

treat surface water source lotic systems (flowing

water - rivers, springs, creeks and streams); is not

normally required in lentic systems (calm waters:

lakes, ponds, etc.)

SOLIDS REMOVAL

GRIT REMOVAL

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AREIAS DO VILAR (BARCELOS) WTP ÁGUAS DO NOROESTE, S.A.

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WATER INTAKE

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WATER INTAKE

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PRE-OXIDATION

Ozonation

Potassium permanganate

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PRE-OXIDATION

Chlorine should not be used as a pre-oxidant, since it can enhance the formation of organochlorine products, especially trihalomethanes THM (cancer precursors). The THMs are a group of organic compounds that are considered derivatives of methane (CH₄) in the molecules of which three of its four hydrogen atoms have been replaced by an equal number of atoms of the halogen elements (chlorine, bromine and iodine). The formation of THMs during the pre-oxidation of water with free chlorine, follows a complex mechanism by which chemical species, the halogens form with water, react with humic and fulvic substances that normally contained in raw water.

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POTASSIUM PERMANGANATE PRE-OXIDATION

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POTASSIUM PERMANGANATE PREPARATION

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PRE-OXIDATION / OZONATORS

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PRE-OXIDATION / OZONATION CHAMBERS

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CLARIFICATION

The clarification is an essential step in a WTP, including, usually, four

sub-steps:

FILTRATION RAPID

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CLARIFICATION / COAGULATION PROCESSES MIXING – DESTABILIZATION - FLOCCULATION

Coagulation processes are commonly included in WTP to promote aggregation of small particles into larger particles that can be subsequently removed by sedimentation and/or filtration processes.

Particulate suspensions commonly removed with coagulation processes include clay and silt-based turbidity, natural organic matter and other associated constituents, such as microbial contaminants, toxic metals, synthetic organic chemicals, iron, and manganese.

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CLARIFICATION / COAGULATION PROCESSES MIXING – DESTABILIZATION - FLOCCULATION

The coagulation process is comprised of three sequential steps. These steps include coagulation formation, particle destabilization, and particle aggregation.

Coagulation formation and particle destabilization are promoted in a rapid-mixing stage where treatment chemicals are added, hydrolyzed, and dispersed throughout the particulate suspension to cause destabilization.

Particle aggregation is then promoted in a flocculation stage where inter-particle collisions create larger amenable to separation from the treated water.

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CLARIFICATION / RAPID MIXING

RAPID MIXING

Chemical storage.

Most common chemicals used: aluminum sulfate Al₂(SO₄)₃14H₂O, ferric chloride FeCl₃, among others); synthetic organic polymers (cationic polymers) are sometimes used in addition to or in place of metal salt coagulants when jar tests demonstrate acceptable performance.

Solution or suspension preparation.

Chemical dosages (jar tests are generally performed to select coagulation process chemical dosages).

Rapid mixing chambers or other devices themselves (high velocity gradients – G value between 600 a 1000 s-1_{- concept developed by Camp and Stein in 1943).}

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CLARIFICATION / RAPID MIXING / EXAMPLE

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CLARIFICATION / FLOCCULATION

FLOCCULATION

Flocculation is typically performed in a basin baffled into three or more compartments with mechanical mixing (G value between 20 a 70 s-1_{) provided in each}

stage to promote inter-particle collisions and aggregation.

In an effort to reduce the capital and operating costs associated with traditional form of flocculation, contact flocculation performed within up-flow sludge blanket clarifiers, buoyant media roughing clarifiers, and granular media filters are gaining increased application.

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CLARIFICATION / FLOCCULATION CHAMBER/ EXAMPLE

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CLARIFICAÇÃO / FLOCULAÇÃO - COAGULAÇÃO CLARIFICATION / FLOTATION

Flotation is a solid-liquid gravity separation process, mostly used for algae removal.

Flotation processes introduce gas bubbles into the water that attach to solid particles and create bubble-solid agglomerates that float to the top of the water column where accumulated solids are removed.

Flotation is not generally used in place of sedimentation in water treatment.

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CLARIFICATION / FLOTATION / EXAMPLE

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CLARIFICATION / SEDIMENTATION

SEDIMENTATION

Sedimentation is a solid-liquid gravity separation process that promote gravity settling of solid particles to the bottom of the water column where accumulated solids are removed.

Sedimentation is generally used in combination with coagulation and flocculation to remove flock particles and improve subsequent filtration efficiency.

Sedimentation is particularly necessary for high turbidity and highly colored waters that generate substantial solids during the coagulation and flocculation processes.

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SEDIMENTATION

Sedimentation is sometimes unnecessary prior to filtration (direct filtration / water turbidity between15 a 20 mg/L) in instances where flocculation solids production is low and filtration can effectively handle the solids loading.

Sedimentation is also sometimes used at the head of a WTP in the form of a pre-sedimentation basin to allow gravity settling of denser solids that do not require coagulation and flocculation for promotion of solids separation.

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SEDIMENTATION

Sedimentation is most effective when hydraulic approach plug and laminar flow so that short circuiting and turbulence are minimized. Poor inlet flow distribution and effluent collection, wind or rising bubbles, and density differences caused by temperature or concentration all can contribute to flow instability.

Therefore, design of an effective sedimentation process is dependent on proper consideration of physical design factor such as surface loading rate, size and shape of proper tankage, inlet and outlet flow arrangements, baffling, and solids removal methods.

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SEDIMENTATION

Types of conventional sedimentation tanks: Horizontal-flow rectangular tank;

Circular radial-flow tanks; Square radial-flow tank.

Types of high-rate sedimentation (increase the available area for solids settling, decrease the solids settling depth, promote the flow stability, and decrease land requirements in comparison to more traditional tanks):

Tube settlers; Plate settlers.

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CLARIFICATION / SEDIMENTATION CIRCULAR RADIAL-FLOW TANK

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CLARIFICATION / SEDIMENTATION TUBE SETTLER

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CLARIFICATION / SEDIMENTATION PLATE SETTLER

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CLARIFICATION / FILTRATION

FILTRATION

Filtration, as it applies to water treatment, is the passage of water through a porous medium to remove suspended solids.

The granular media type, size, gradation, shape, and depth determine pore volume , pore size, and pore tortuosity that affect solids holding capacity, head loss, filtrate quality, and backwash requirements.

The most common materials used in granular media filters are sand, crushed anthracite coal, and granular activated carbon (GAC).

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CLARIFICATION / RAPID FILTRATION / NORMAL OPERATION

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CLARIFICATION / RAPID FILTRATION / BACKWASH OPERATION

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CLARIFICATION / RAPID FILTRATION / BACKWASH OPERATION

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CLARIFICATION / RAPID FILTRATION / CONTROL EQUIPMENT

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DISINFECTION

DESINFECTION

Disinfection is provided in water treatment to assure the production of a microbiologically safe finished water quality.

Disinfectants include free and combined chlorine (calcium hypochlorite Ca(ClO)₂ or sodium hypochlorite NaClO), chlorine dioxide ClO₂, ozone, ultraviolet (UV) irradiation, and other disinfectants.

Free chorine and combined chlorine are excellent biocides and provide a persistent residual to maintain the microbiological safety of the finished water as it passes through the transmission and distribution system.

Ozone is the most powerful disinfectant of those used in water treatment; however, ozone is highly unstable in water and lacks persistent residual.

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DISINFECTION / CHLORINE STORAGE

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TREATED WATER CISTERN