Hello there! Welcome to Wastewater Treatment Training. In this blog post we will be introducing you to the first topic of the Wastewater Treatment. Here, you will understand the basic concepts related to water and waste treatment, before we go into a more detailed approach of each of the treatment process steps This presentation will also help you understand the process of treating in-fluent water and wastewater, setting up control measures to maximize the effect of treatment programs, and as well as to maintain safe surroundings and environment First we need know what is the definition of influent water, wastewater and effluent water, as I will be using these terms a lot during the course Influent water is essentially all the water that flows into the plant, to be used in its industrial processes In-fluent water may come from towns water, underground bore water, or river water

It may come from anywhere, but it has to meet the purity specifications before use Wastewater on the other hand, is all the water that has been used by industries for industrial operations This water is usually highly contaminated and contains high levels of dissolved or suspended matter Wastewater needs to be treated and purified to meet the safety regulations before it is discharged into sewage and streams This discharged water can otherwise be called effluent water

There are many reasons to which we need to treat water and wastewater Firstly, it is to have good quality influent water Many industries requires good quality influent water to avoid contamination with the processes and to avoid process equipment damages After water has been used in an industry, impurities in the wastewater must be removed before the water is discharged The effluent water must not contain anymore than the permissible limits for impurities before it is being discharged

Without proper treatment, the wastewater will pollute the water body it is being discharged into as wastewater may contain high levels of hydrocarbons and chemicals Many of these substances are toxic, poisonous, or even carcinogenic Without proper treatment, contaminated water will harm marine life, and eventually affect all life forms There are also situations where wastewater is treated not only to a quality that is safe for the environment but to a higher quality that is fit for use by the manufacturing processes This enables the manufacturing plants to conserve water by reusing the treated water

In some countries where the water resources are scarce and the water price is high, many industries are driven to look at some new ways to conserve and recycle wastewater It is important to recycle the wastewater to ensure continuous running of the plant at the desired capacity In certain industries, contaminants in the wastewater may be of high value materials such as, the gold in wastewater from the gold-plating plant or the oil in the wastewater from oil refineries It makes sense to recover these contaminants from the wastewater stream as much as possible If these precious materials are not recovered from the wastewater, high wastage may occur and profitability could suffer

Three Types of Contaminants in Water

There are mainly 3 types of contaminants in wastewater, in which we deal each one differently Suspended solids are particles that do not dissolve in water and can be seen with the naked eye or through an ordinary microscope They contribute to turbidity and can be removed quite easily by using physical or mechanical means, such as sedimentation or filtration Dissolved solids is a measure of total amount of dissolved matter, determined by evaporation Various softening process such as lime softening and cation exchange via hydrogen zeolite, will reduce dissolved solids

Colloidal suspended solids are solids that are not truly dissolved and yet do not settle readily These are somewhat loosely defined as the differences between the total suspended solids and the settleable solids There is at present, no simple or standard laboratory test to specifically determine colloidal matter Most colloids will not settle out even after long quiescent periods of settling Many colloidal particles remain suspended in wastewater because of their small size and electrostatic repulsion

Electrostatic repulsion is the mechanism that controls particle stability At the interface of hydrophobic surfaces, excess anions or cations may accumulate With hydrophilic surfaces, surface charges exist and it attracts ions of the opposite charge of the surface The electrostatic and Van der Waal’s forces strongly bind these ions to the surface The layer of accumulated ions at the surface produces an electrical potential that repels particles from each other and causes the particles to remain suspended in water due to mutual repulsion

So, the negative surface charge together with Van der Waal’s force of attraction develops a layer of ions next to the particle surface and builds an electrical potential, which prevents particles from agglomerating into larger particles When lemon juice is added to milk the stable particles of milk destabilizes and curdles It now coagulates to form cheese In influent or wastewater treatment Coagulation is used to chemically increase the size of the particles so that impurities can settle out faster

Particle size is built by neutralizing the negative surface charges on these particles Initially the layer of ions or charged molecules accumulate at the particles surfaces and create the electrostatic potential When the negative surface charges are neutralized the electrostatic potential diminishes and so does the electrostatic repulsion Now the particles agglomerate naturally Cationic polymers and inorganic coagulants can be used to neutralize surface charge of these particles

Self-precipitating polymers not only neutralize the surface charges, they also link particles together with their long chain molecular structure As the long polymer molecules sweep through the solution they catch more particles and binding them together to form the sweeping floc effect This therefore serves a dual purpose of coagulant and flocculant I will cover more about flocculation soon All 3 of these balls are made of the same material and hence have the same density

When the balls are released, which of the 3 balls will travel faster down the tube? Have a guess! The speed which the balls travel down to the tube of liquid is known as the settling velocity It is determined by the size and density of the balls Similarly the solid particles in wastewater, have a settling velocity that is governed by the Stoke’s Law According to Stoke’s Law, bigger and denser particles travel and settles down faster than smaller and less dense particles as they fall through a fluid under gravity This is the formula expressing Stoke’s Law

The settling velocity of particle is directly proportional to the square of the particle’s diameter The settling velocity is also directly proportional to the difference of the densities between the particle and the fluid that it is in Although, the settling velocity is inversely proportional to the fluid’s viscosity However at this point, you only need to look at the concept of particle size as the particle size is something we can chemically influence Note that as particle size doubles, the settling velocity will increase to 4 times and as the particle size triples, the settling velocity will increase to 9 times

Hence, increasing the particle size is an efficient way to improve the separation of the impurities And this can be acheived easily by coagulation “There are 2 types of coagulants The inorganic salts and the organic polyelectrolytes Inorganic salts of aluminum or iron, neutralize the charge on the turbidity particle

These also hydrolyze to form insoluble precipitates which entrap additional particles With the exception of sodium aluminate, all common iron and aluminate coagulants are acid salts which lower the pH of the treated water So depending on the initial raw water alkalinity and pH, an alkali, such as lime or caustic, must be added to counteract the pH depression of the coagulant Organic polyelectrolytes are mainly water soluble that can be used alone or in conjunction with inorganic coagulants They are water-soluble organic polymers with numerous ionized sites for both coagulation and flocculation

Now let’s compare the two types of coagulants Organic coagulants have some advantages over inorganic coagulants Organic coagulants create a smaller volume of sludge This means the sludge disposal cost is lower with organic coagulants Secondly, unlike inorganic coagulants the performance of organic coagulants is less pH dependent

Hence, operationally it is easier to operate without having to closely monitor and control the pH Most of the inorganic coagulants except Sodium Aluminate have low pH which makes it less safe to handle Also the equipment needs more maintenance due to corrosion On the other hand, organic coagulants are weakly acidic Much less acidic than inorganic coagulants

Additionally, organic coagulants are biodegradable and hence, are more environmentally friendly Although the unit prices of organic coagulants are generally much higher than inorganic coagulants, the dosage requirement for organic coagulants is typically 10 to 20 times lower the dosage requirement for organic coagulants is typically 10 to 20 times lower than that of inorganic coagulants and the overall cost may still be lower by using organic coagulants Even if the overall treatment cost with organic coagulants is higher, its use may still be justifiable with the all the other benefits However, the final choice of coagulants would depend on customer requirements After coagulation, the coagulated particles will come together to form larger lumps

This process is called flocculation Flocculation is a method to chemically increase the size of the coagulated particles so that impurities in wastewater settle out During flocculation, the physical inter-particle bridging mechanism relies mainly on the size and structure of the flocculant molecule rather than its charge density High molecular weight polymers work primarily via inter-particle bridging Polymers of long chain and branch structure increase the efficiency of the flocculation

Selecting the right flocculant is greatly influenced by its molecular structure, charge, molecular weight and form With the advancedment of technologies, the manufacturing of polymers that have precise placement of charges are possible The optimum spacing between the charges ensures that all charge sites are used and that expensive charge is not wasted Different molecular structures have its use for a range of unique applications Polymers might have different charges either cationic, anionic or nonionic

The charge density of different polymer molecules may be different For contaminant particles that have a low charge, you need flocculants of low charge density and vice versa Molecular weight affects the selection of the flocculant Flocculants have different molecular weights ranging from low, medium to high The molecular weight indicates the size of the polymeric molecule

A large molecule tends to do a better job in inter- particle bridging mechanism Polymers are available in four different forms: powders, liquids, emulsions and dispersions Powder forms are highly concentrated Emulsion polymers are composed of water, polymer and oil Brine dispersions are cationic flocculant liquid

Powder and emulsions tend to have higher molecular weight Powder is the most concentrated form of flocculant It is the most expensive on a unit price basis, but it is the least expensive to use However, it is difficult to feed It requires a special makedown or chemical mixing system

It is available as a high molecular weight cationic, anionic and nonionic polymer There are 2 methods to makedown a dry polymer powder Manual and automatic A manual makedown system consists of a makedown tank, an eductor, an agitator, a feed pump, and a calibration cylinder A feed tank is optional but advisable

If a feed tank is available, it should have an agitator running continuously at a slow speed This will keep the makedown solution homogeneous When a feed tank is used, a transfer pump is required And this must not be a centrifugal pump as it will degrade the polymer, resulting in poorer performance The dry powder polymer is introduced into a mixed tank through an eductor with water

The eductor ensures that the polymer particles are wetted properly The agitator must not run any more than 350 RPM and normally for no more than 30 minutes Once the solution of dry polymer becomes clear and the polymer is fully dissolved, the agitator should stop The solution could then be transferred into a feed tank if there is one This gradually reduces the solution level in the mixed tank and increase the solution level in the feed tank

An automatic power feed system is expensive However, it allows hands off operations and ensures consistent makedown quality In the automatic makedown process, the polymer is fed from helix feeder It is evenly distributed over the rotating drum through the spreader The thoroughly wet polymer is then brought to the eductor in the state of suspension

When the polymers added to the mixed tank through the eductor, the mixer starts rotating The polymer is then totally mixed and the transfer pump starts pumping The polymer is then fed to the point of application Here are some tips on handling dry powder polymers First of all dry powder polymer needs to be stored in a low humidity environment

Otherwise it may absorb moisture from the air and becomes caked up For the same reason containers of dry polymer should be sealed with cover The makedown polymer solution should be consumed within 24 hours after preparation That is why the feed tank is normally sized for 8 to 24 hours capacity An eductor is used for powder transfer to ensure that the dry powder polymers are individually wetted

Otherwise, undissolved polymer globules commonly called “fisheyes” may be formed The maximum solution strength for anionic dry polymer should not be more than 05% and for cationic dry polymers it should not be more than 1% We can further dilute the solution to a lower concentration for better performance with an in-line mixing arrangement Liquids cost more than powders, but are much easier to handle

You may need to dilute it to feed it in In many cases it can be fed neat without dilution It is usually available as a cationic low molecular weight material with high charge density The liquid polymer may be injected neat into the water treatment processes However, for better mixing effect or better pumping rate at convenient strength, it can be diluted in batches or to an in-line mixer

A batch dilution system for liquid polymer is normally used for high viscosity solution The system consists of a tank, an agitator, a feed pump and a calibration cylinder A feed tank with a transfer pump is optional The liquid polymer is added to the dilution water in the mixed tank while the agitator is running Once the dilution is homogenous, the agitator should stop

The solution could then be transferred into a feed tank if there is one In the in-line dilution process, a metering polymer pump is used to feed neat undiluted polymer solution into a dilution waterline where an in-line mixer is installed The in-line mixer creates turbulence to ensure good mixing of the concentrated polymers solution with the dilution water There are also some special precautions that should be taken with respect to the handling of liquid polymers The liquid polymer should be stored at moderate temperature between the range of 60 – 120°F or 15 – 50°C

It is important to protect the polymer from freezing, because some polymers can suffer irreversible damage when frozen Liquid polymer solution does not require periodic mixing to prevent separation before use However, some liquid polymer solutions have a short shelf life Hence, inventories should be well planned accordingly For high viscocity polymer solution, the dilution should be 20% or less

A further 10:1 dilution with an in-line mixer would be a good practice especially for sludge dewatering applications Always try to avoid making down more than 24 hours supply Emulsion is another type of flocculant that has a higher concentration than the liquid form The polymeric molecules are encased in fine water droplets that are in turn emulsified in a continuous oil phase Before a molecule can serve its purpose it needs to be activated from the water droplets to open up the molecular structure

To activate a molecule it requires an inversion process and needs a special makedown or a chemical mixing system The polymer molecules are initially coiled within very fine water droplets in a water in oil emulsion where the water is dispersed in the continuous oil phase During the makedown a lot more water is added and agitation action breaks the oil into fine droplets The emulsion turns into an oil and water emulsion where oil is dispersed in continuous water phase As a result, coiled polymers uncoils in the continuous water phase

The batch makedown system for emulsion polymer is exactly the same as that for the liquid polymer The system also consists of a tank, an agitator, a feed pump, and a callibration cylinder Except, that it is important to have the feed tank as it allows time for the inversion process to happen In a batch makedown system, the feed tank should have an agitator running continuously at a slow speed This will ensure homogeneity of the makedown solution

Use a diaphragm pump for transferring polymer solution from the mix tank to the feed tank The emulsion polymer is added to the dilution water in the mix tank while the agitator is running Once the solution is homogenous the agitator should stop The solution could then be transferred into a feed tank A continuous makedown system uses a float valve to control the water supply

The flow of water supply in turn activates a flow switch to turn on the pump that transfers emulsion polymer from the chemical storage to the chemical tank This automates the makedown process Whenever the liquid level in the chemical tank is low enough, the float valve initializes the automation cycle The chemical tank itself provides the resident time for the inversion process to happen The polymer solution pump delivers the makedown polymer to the application point

Where necessary, secondary dilution can be made using an in-line mixer Here are some precautions that you need to keep in mind when handling emulsion polymers It is important to store the neat emulsion polymer in a low humidity environment Also try to protect the storage drum from having condensation inside the drum because a small quantity of water can cause the emulsion to gel up Like dry polymer it is best stored at a moderate temperature range of 60 – 120°F or 15 – 50°C

During the makedown process, the initial makedown strength should not be more than 1 – 2 vol% For best performance, a further dilution to 02 – 05 vol% is recommended Like other types of polymers, avoid making down more than 24 hours supply

If makedown stock has been standing still for some time, always mix before use Remember always add polymer to water while agitation action is on Adding water to polymer would gel up the polymer and it will not be possible to dilute it further Brine based dispersions are available as cationic flocculants The makedown for this form of flocculant is fast and easy

It only need to be diluted with water However, dispersion need to be mixed periodically in bulk storage to prevent separation and gelling of the product According to the dispersion model, the initial form of dispersion is a brine solution of individually coiled polymers each being stabilized with some surfactant or stabilizer on its surface This stability is maintained by high salt concentration That is why dispersion polymers are kept in brine solution

When the polymer product is diluted, the salt concentration surrounding the dispersed polymer particles reduces significantly As a result, it is difficult to keep the surfactant on the particle’s surface This causes the polymer to slowly open up The batch dilution system is the same as that for the liquid and emulsion polymer The system consists of a tank, an agitator, a feed pump and a calibration cylinder

A feed tank with a transfer pump is optional The brine dispersion polymer is added to the dilution water in the mixed tank while the agitator is running at not more than 350 RPM for 10 – 20 minutes Once the dilution is homogeneous, the agitator should stop The solution could then be transferred into a feed tank if there’s one The in-line dilution is also the same as that used by any liquid polymer solution

A metering polymer pump is used to feed neat undiluted brine dispersion polymer into a dilution waterline where an in-line mixer is installed The in-line mixer creates turbulence to ensure good mixing of the concentrated polymer solution with the dilution water Here are some tips that you need to keep in mind when handling a brine dispersion polymer Firstly, it should be stored under a moderate temperature range of 40 – 90°F or 4 – 32°C and be protected from condensation The initial makedown strength should be 0

5 – 5 vol% Further dilution with in-line mixer to 03 vol% is recommended for a better performance Before use the neat product should be agitated or recirculated for 30 to 60 minutes to ensure homogeneity It is recommended that the dispersion polymer storage tank be slowly and continuously mixed

As the polymer is brine based, it is corrosive Hence, carbon steel or copper alloy should be avoided as material of construction in the feed system Suitable material for a tank piping and pump are High Density Poly Ethylene (HDPE) or rigid Poly Vinyl Chloride (PVC) Natural rubber, Buna N, or Teflon may be used for tubing material The high speed rotating action of a centrifugal pump can degrade the polymer

So it should not be used for chemical transfer Gear pump or diaphragm pump is recommended Mixing is an important operation in the coagulation and flocculation processes which directly affect the treatment performance Initial mixing intensity is critical to accomplish optimum polymer dispersions and polymer-to-particle contact Coagulation and flocculations are done under different mixing conditions

During coagulation, fast mixing is required for coagulant distribution This is because turbulence created in the mixing operation increases the polymer-to-particle contact In the case of flocculation, slow and gentle mixing is required to encourage particle-to-particle contact If the mixing during flocculation is too fast, the aggregates that are already formed will break up Performing a jar test is important to simulate the conditions of the plant and to determine the mixing rate

The jar test is recognized throughout the water industry as the most valuable and most commonly used tool for realistically simulating coagulation control at a full-scale treatment plant This test is routinely performed by water treatment plant operators as well as consultants and researchers It basically involves duplicating, sequentially in a single vessel, conventional treatment steps that occur simultaneously at different locations in the plant The jar test is a standard laboratory simulation for wastewater treatment and influent clarification Jar test is used to determine the optimum chemical program, establish the best order of chemical addition, establish the approximate chemical dosage, and it is also to determine the best equipment operations, such as the most effective mix cycle for a given chemical program

While performing a jar test ensure that waste water samples used in the jar tests are representative or untreated samples Hence, the water samples should be collected from the upstream of the chemical injection point In addition, ensure that you vary only one parameter at a time while testing You should not vary the chemical and mixing rate at the same time You should simulate the same mixing sequence in the plant

In other words, if the polymer is first mix to a certain length of piping and then through a mixing tank and thereafter further mix through another length of piping then you should determine the mixing energy in each of these three mixing modes separately Jar testing may be used to evaluate the effects of changes in chemical doses and points of application, choosing alternative coagulants, adding polymeric coagulant aids, implementing alternative preoxidation strategies, varying mixing intensities and times, and changing overflow rates on the removal of particles, natural organic matter, or other water quality parameters of concern The key parameters include: Velocity gradient/mixing intensity in the rapid mix and flocculation basins, effective retention times in the rapid mix and flocculation basins, surface loading rate of the sedimentation basin, and actual retention time in basins if jar testing is being done to evaluate time-dependent reactions for which full-scale reaction time influences results The intensity of mixing is generally quantified by the velocity gradient, G, with units of s-1 (seconds to the minus 1 power) The velocity gradient is calculated using the energy dissipation rate in the fluid, or it can be interpolated from calibration curves

In order to attain jar test results that are relevant to the treatment plant, mixing intensities and therefore velocity gradients during jar tests should correspond to those in the treatment plant The mixing speed of the jar test is expressed in RPM or revolutions per minute The mixing energy varies for coagulants and flocculants The appropriate mixing energy of inorganic coagulants is 200 – 300 per second of velocity gradient, 300 – 400 per second of velocity gradient for organic coagulants, and 60 – 90 per second of velocity gradient for flocculants” The jar tests helps you determine the flocculants that can be used under specific conditions

For this flocculant jar test, you need to first fill a jar with a fresh sample of water and then mix rapidly at a speed that duplicates plant conditions After that you may need to chlorinate the water if this is practiced in the plant This is an optional step and is based on the plant’s operating conditions Next you need to measure the water pH with a pH probe while the mixer still running You may need to adjust the water pH with drops of acid or caustic to the actual plant pH or to the desired pH level

This pH adjustment is needed if there are pH adjustments at the plant and your water sample is collected from the upstream In jar tests for investigating the impact of various pH, this is especially important Some inorganic coagulants can lower the water pH significantly In such cases, the water pH should be adjusted higher such that the final pH will fall within the desired range after coagulant addition For practical purposes, the amount of caustic agent needed for pH adjustment can be predetermined by separate titration test with coagulant added

Now add the coagulant to the jar at the desired dosage The coagulant should be prediluted to the same strength as practiced in the plant or to a strength if you would like to investigate its impact on the treatment performance Now the mixing of the coagulant starts Keep the mixing running at the original high speed for the duration that simulates the mixing of the coagulants in the plant At this stage, tiny pin floc should start to form if the coagulant is effective

After the mixer has run at a high speed for the required duration of time, reduce the agitator speed to 40 – 50 RPM and add the flocculant The flocculants should be prediluted to the same strength as practiced in the plant or to a strength you would like to investigate its impact on the treatment performance After you have added the flocculant, immediately reduce the speed and run for duration that simulates the mixing of the flocculants in the plant This is usually 20 – 30 RPM for 5 – 10 minutes During this stage, if the flocculants work effectively, you should see flocs starting to grow in size

Stop the mixer and record the floc size and settling rate for each jar The floc size is normally recorded as a comparative scale of 1 to 5 with one being the worst and five being the best After 5 – 10 minutes, draw some water from the bulk and measure the supernatant turbidity This process is normally carried out in 4 – 6 jars in parallel at the same time Test different flocculants first to select the most effective one

After the most effective flocculant is selected, vary it’s dosage to determine the minimum dosage requirement You may also evaluate combinations of different amounts of coagulants and flocculants to determine the most economical combination In these tests, you may want to add the present plan treatment amounts to establish the first jar as a control sample Other studies with jar tests may also be carried out to assess the impact of different pH, different mixing energy, or different temperatures on the treatment performance Remember that you should only vary one parameter at a time

Now that you know the various types of contaminants and wastewater and how to deal with it, and how to deal with it, let’s have a look at the most common treatment programs Influent water clarification uses processes such as coagulation, flocculation, clarification, and filtration Influent water clarification ensures that influient water meets purity requirements before it can be used in industrial process Coagulants and flocculants are commonly used to aid the clarification processes Similarly, coagulants and flocculants are typically used to improve the efficiency of the sedimentation and flotation processes

Wastewater treatment also commonly involves the removal of heavy metals We now have reached the end of Introduction to Wastewater Treatment module in the Wastewater Treatment Series Thank you for listening and watching this webinar If you think you got value out of this webinar, please feel free to share this video to your friends and colleagues Thank you very much again, and I look forward to seeing you again in the next webinar

Bye!