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Biological Wastewater Treatment

Biological Wastewater Treatment. Wastewater treatment Importance Type of Pollutants Methods of Treatment Biological process as Wastewater Treatment

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Page 1: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Biological Wastewater Treatment

Page 2: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Wastewater treatment ImportanceType of PollutantsMethods of TreatmentBiological process as Wastewater TreatmentMicroorganisms (Type, Applications and

Working)BOD removal Activated sludge process (Components,

Monitoring & Operation)

Page 3: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Wastewater TreatmentWastewater Treatment

Page 4: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Environmental EffectsEnvironmental Effects Reuse ImplicationsReuse Implications

PotablePotable IndustrialIndustrial

Regulatory RequirementsRegulatory Requirements

Page 5: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Types of Pollutants

Page 6: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

1) Suspended Solids1) Suspended Solids2) Dissolved Solids2) Dissolved Solids3) Colloidal Solids3) Colloidal Solids

Solids may be organic (eg. Phenol, oil, bacteria) Solids may be organic (eg. Phenol, oil, bacteria) or inorganic (eg. Salts, Ca, Mg, silt) in natureor inorganic (eg. Salts, Ca, Mg, silt) in nature

Page 7: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Oxygen (BOD, COD, DO)Solids content (TS)Nutrients (phosphorus, nitrogen) Acidity (pH)Bacteria (e.g., fecal coliform)Temperature

Page 8: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Metcalf & Eddy

TS = TVS + TFSTS = organic + inorganic

TS = TSS + TDS

TSS=VSS+FSS TDS=VDS+FDS

Page 9: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Dissolved Oxygen (DO)Biochemical oxygen demand (BOD)

Chemical oxygen demand (COD)

Total organic carbon (TOC)

Page 10: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment
Page 11: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

BOD: Oxygen is removed from water when organic matter is consumed by bacteria

Low oxygen conditions may kill fish and other organisms

http://www.lcusd.net/lchs/mewoldsen/Water_Pollution_LCHS.ppt

Page 12: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

The quantity of oxygen used in biological and non-biological oxidation of materials in wastewater

The determination of chemical oxygen demand (COD) is used in municipal and industrial laboratories to measure the overall level of organic contamination in wastewater. The contamination level is determined by measuring the equivalent amount of oxygen required to oxidize organic matter in the sample

BOD/COD ratio – the greater the ratio, the more oxidizable (biologically treatable) the waste. Ratios rarely exceed 0.8-0.9.

Page 13: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Measure of WW pollution characteristicsBased on the chemical formulaTest methods use heat and oxygen, UV

radiation, and/or chemical oxidants to convert organic carbon to carbon dioxide, which can then be measured

Can be assessed in 5 to 10 minutesTheoretical > Measured

Page 14: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Methods of Methods of TreatmentTreatment

Page 15: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

1) Clarification, Sedimentation, Flocculation are used for suspended and/ or colloidal pollutants

2) Evaporation, Reverse Osmosis etc, are used for dissolved inorganic pollutants

3) Oxidation/ Synthesis by Micro-organisms is carried out (Biological Treatment) for Dissolved Organic Pollutant

Page 16: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Biological Processes...Biological Processes... cell: derives energy from oxidation of reduced food sources (carbohydrate, protein & fats)

Requires….. Requires…..

microbes with the ability to degrade the waste microbes with the ability to degrade the waste organicsorganics

contact time with the organicscontact time with the organics favorable conditions for growthfavorable conditions for growth

Page 17: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

To stabilize the organic matter (Soluble To stabilize the organic matter (Soluble and none settleble)and none settleble)

To reduce the amount of dissolved To reduce the amount of dissolved phosphorus and nitrogen in the final phosphorus and nitrogen in the final effluenteffluent

Page 18: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

MicroorganismsMicroorganisms

Page 19: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Microorganisms = single-celled organism Microorganisms = single-celled organism capable of performing all life functions capable of performing all life functions independently independently

Basic unit of life = cellBasic unit of life = cell

Cell WallEnzymes

C, N, PH2OO2

WastesH2OCO2

Page 20: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

animal cell

virus

bacterial cell

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Cocci– spherical cells, often in chains or tetrads

Rods – most common shape– vary in shape & size

Spiral Rod – curved rods

Page 23: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Growth = cell division Growth = cell division one cell divides to produce two equal one cell divides to produce two equal

daughter cellsdaughter cells

Generation time Generation time length of time required for length of time required for bacterial population to doublebacterial population to double

Page 24: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

single cell

cell elongates

cell produces cell wall

two daughter cells produced

The cell replicates all its components, reorganizes it into two cells, forms a cell wall,

and separates.

Page 25: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

log phase

stationary phase

death phase

lag phase

cell c

ou

nt

time

Page 26: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Percentage by weightPercentage by weight CarbonCarbon 5050 OxygenOxygen 2020 NitrogenNitrogen 1414 HydrogenHydrogen 8 8 Phosphorus Phosphorus 3 3 Sulfur Sulfur 1 1

Potassium 1 Sodium 1 Calcium 0.5 Magnesium 0.5 Iron 0.2 All other elements 0.3

Page 27: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

NutritionalNutritional• Carbon source (waste to be degraded )Carbon source (waste to be degraded )• N & PN & P (100:5:1;C:N:P)(100:5:1;C:N:P)• Trace mineralsTrace minerals

EnvironmentalEnvironmental• Oxygen (terminal electron acceptor)Oxygen (terminal electron acceptor)• TemperatureTemperature• Water Water • pHpH• Non-toxicNon-toxic

Page 28: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Classification: Heterotrophic- obtain energy from oxidation of

organic matter (organic Carbon)

Autotrophic- obtain energy from oxidation of inorganic matter (CO2, NH4, H+ )

Phototrophic- obtain energy from sunlight

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Aerobic - oxygen Aerobic - oxygen

Anoxic - nitrateAnoxic - nitrate

Anaerobic - strict and facultativeAnaerobic - strict and facultative

Page 30: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

In the case of domestic wastewater treatment, the objective of biological treatment is:

To stabilize the organic content To remove nutrients such as nitrogen and phosphorus

Types:

Aerobic ProcessesAnoxic ProcessesAnaerobic ProcessesCombined Aerobic-Anoxic-Anaerobic Processes

Pond Processes

Attached GrowthSuspended Growth Combined Systems

Aerobic MaturationFacultativeAnaerobic

Page 31: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Activated Sludge Activated Sludge ProcessProcess

Page 32: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

There are two phases to biological treatment There are two phases to biological treatment

• ““Mineralization” of the waste organics Mineralization” of the waste organics producing COproducing CO22 + H + H22O + microbes O + microbes • Separation of the microbes and water Separation of the microbes and water

Page 33: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

W (WAS)

R(RAS)

Q(IN)

Q-W(OUT)Aeration basin

Clarifier

Q+R(MLSS)

Clarifier

Page 34: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

MLSS / MLVSS ( active microbes )F / M ( food to mass )RAS / WAS ( recycle & waste )MCRT ( sludge age )

Page 35: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Recycle converts once-through system into Activated Sludge

Clarifier separates solids (biomass), thickens and allows return of microorganisms (RAS)

Recycle or clarifier underflow influences thickening and mass balances

Retention Time of Biomass no longer limited by Hydraulic Retention time

Page 36: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Biomass is created as the microorganisms grow = Sludge Yield (kg/kg-deltaBOD)

Sludge Yield varies by type of waste and operating conditions (e.g. growth rate)

For Equilibrium conditions, Yield, or Excess Sludge must be removed or Wasted

Excess sludge can involve significant influent inert TSS

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Page 39: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

activated sludge: sludge particles produced by the growth of microorganisms in aerated tanks as a part of the activated sludge process to treat wastewater

aeration: exposing to circulating air; adds oxygen to the wastewater and allows other gases trapped in the wastewater to escape (the first step in secondary treatment via activated sludge process)

biochemical oxygen demand (BOD): a laboratory measurement of wastewater that is one of the main indicators of the quantity of pollutants present; a parameter used to measure the amount of oxygen that will be consumed by microorganisms during the biological reaction of oxygen with organic material

biosolids: sludge that is intended for beneficial use. Biosolids must meet certain government specified criteria depending on its use (e.g., fertilizer or soil amendment) Apr

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decomposition: the process of breaking down into constituent parts or elements

domestic wastewater: wastewater that comes primarily from individuals, and does not generally include industrial or agricultural wastewater

effluent: treated wastewater, flowing from a lagoon, tank, treatment process, or treatment plant

grit chamber: a chamber or tank used in primary treatment where wastewater slows down and heavy, large solids (grit) settle out and are removed

influent: wastewater flowing into a treatment plant Apr 21, 2023Activated Sludge Process

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Page 41: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

lagoons (oxidation ponds or stabilization ponds): a wastewater treatment method that uses ponds to treat wastewater. Algae grow within the lagoons and utilize sunlight to produce oxygen, which is in turn used by microorganisms in the lagoon to break down organic material in the wastewater. Wastewater solids settle in the lagoon, resulting in effluent that is relatively well treated, although it does contain algaemunicipal: of or relating to a municipality (city, town, etc.). Municipal wastewater is primarily domestic wastewater.primary treatment: the first stage of wastewater treatment that removes settleable or floating solids only; generally removes 40% of the suspended solids and 30-40% of the BOD in the wastewatersecondary treatment: a type of wastewater treatment used to convert dissolved and suspended pollutants into a form that can be removed, producing a relatively highly treated effluent. Secondary treatment normally utilizes biological treatment processes (activated sludge, trickling filters, etc.) followed by settling tanks and will remove approximately 85% of the BOD and TSS in wastewater. Secondary treatment for municipal wastewater is the minimum level of treatment required by the EPA.

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sedimentation: the process used in both primary and secondary wastewater treatment, that takes place when gravity pulls particles to the bottom of a tank (also called settling).

settling tank (sedimentation tank or clarifier): a vessel in which solids settle out of water by gravity during wastewater or drinking water treatment processes.

sludge: any solid, semisolid, or liquid waste that settles to the bottom of sedimentation tanks (in wastewater treatment plants or drinking water treatment plants) or septic tanks

tertiary treatment: any level of treatment beyond secondary treatment, which could include filtration, nutrient removal (removal of nitrogen and phosphorus) and removal of toxic chemicals or metals; also called “advanced treatment” when nutrient removal is included

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Page 43: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

total suspended solids (TSS): a laboratory measurement of the quantity of suspended solids present in wastewater that is one of the main indicators of the quantity of pollutants present

trickling filter process: a biological treatment process that uses coarse media (usually rock or plastic) contained in a tank that serves as a surface on which microbiological growth occurs. Wastewater trickles over the media and microorganisms remove the pollutants (BOD and TSS). Trickling filters are followed by settling tanks to remove microorganisms that wash off or pass through the trickling filter media.

turbidity: the cloudy or muddy appearance of a naturally clear liquid caused by the suspension of particulate matter

wastewater: water that has been used for domestic or industrial purposes

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Mixed Liquor Suspended Solids

Waste Activated Sludge

Returned Activated Sludge

Page 45: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

The most common suspended growth process used for municipal wastewater treatment is the activated sludge process

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Page 46: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Activated sludge plant involveswastewater aeration in the presence of a microbial suspensionsolid-liquid separation following aerationdischarge of clarified effluentwasting of excess biomassreturn of remaining biomass to the aeration tank

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Page 47: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Activated Sludge serves two purposes1.Reducing organic matter in wastewater by using a complex biological community in the presence of oxygen and converting the organic matter to new cell mass, carbon dioxide and energy2.Producing solids capable of bio-flocculating and settling out in the clarifier to produce and effluent low in Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS)

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Page 48: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

In activated sludge process wastewater containing organic matter is aerated in an aeration basin in which micro-organisms metabolize the suspended and soluble organic matter.

Part of organic matter is synthesized into new cells and part is oxidized to CO2 and water to derive energy.

In activated sludge systems the new cells formed in the reaction are removed from the liquid stream in the form of a flocculent sludge in settling tanks.

A part of this settled biomass, described as activated sludge is returned to the aeration tank and the remaining forms waste or excess sludge

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The growth curve has five distinct phases

These are:

1. Adaptation (Lag) Phase – This portion of the curve represents the time required for the organisms to acclimate themselves to the organic material present in the wastewater. The numbers of bacteria are not increasing, however, a shift in the population of the different species of bacteria in the wastewater is occurring so that the bacteria that can best utilize these organic materials become predominate.

2. Log Growth Phase – Once the bacteria have “adapted”, only the number of organisms present limit the rate of growth. Because bacterial cells reproduce by binary fission (i.e., cell division – one cell divides and becomes two, these two divide and become four, then eight, sixteen … ), this is known as

logarithmic growth. Food is not a limiting factor for growth in this phase, that is, for each cell formed enough food is present to allow it to grow and divide.

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Page 52: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

3. Declining Growth Phase – In this phase food becomes a limiting factor to the growth of the bacterial cell mass because not every bacterium that is formed has the food required to grow.

4. Maximum Stationary Phase – Here the available food is just sufficient to keep the cell mass at a constant level with a rate of growth equal to zero.

5. Endogenous (Cell Death) Phase – When the supply of food becomes insufficient to maintain the bacterial mass at a constant level, the microorganisms are forced to metabolize their own protoplasm.

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Page 53: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

The basic activated sludge process has several interrelated components. These components are1. aeration tank2. aeration source3. clarifier4. recycle 5. waste

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Page 54: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Aeration tank. A single tank or multiple tanks designed generally for either complete mix or plug flow with a detention time of as little as 2 hours and up to over 24 hours. The contents of the aeration tank are referred to as mixed liquor.

Aeration source. Generally either diffused air or surface mechanical aeration used to supply oxygen and mix the aeration tank contents.

Clarifier. A settling tank where the mixed liquor solids are separated from the treated wastewater. Most treatment plants employ several secondary clarifiers.

Recycle. Solids that settle in the clarifier and are returned to the aeration tank.

Waste. Excess solids that must be removed from the system.Apr 21, 2023Activated Sludge Process

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Page 55: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

A typical activated sludge plant identifies the three major control mechanism for the activated sludge treatment process1. aeration rate2. return sludge rate3. waste sludge rate

Control of three variables in addition to providing the proper environment (physical, chemical, biological and nutritional requirements) all lead to good sludge quality Apr

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Page 56: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

The combination of raw sewage and biological mass is commonly known as Mixed Liquor.

In all activated sludge plants, once the sewage (or industrial wastewater) has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated supernatant is run off to undergo further treatment before discharge.

Part of the settled material, the sludge (RAS), is returned to the head of the aeration system to re-seed the new sewage entering the tank.

Mixed Liquor is a mixture of raw or settled wastewater and activated sludge within an aeration tank in the activated sludge process

Mixed Liquor Suspended Solids (MLSS) is the concentration of suspended solids in the mixed liquor, usually expressed in milligrams per litre (mg/l)

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Page 57: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

If MLSS content is too high◦ The process is prone to bulking and the treatment

system becomes overloaded◦ This can cause the dissolved oxygen content to

drop with the effect that organic matters are not fully degraded and biological 'die off‘

◦ Excessive aeration required which wastes electricity If MLSS content is too low

◦ The process is not operating efficiently and is wasting energy

Typcial Control band◦ 2,000 to 4,000 mg/l

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Page 58: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

A proportion of the floc is called Return Activated Sludge (R.A.S.) and is used to re-seed the process.

Measuring the solids concentration of RAS allows the return volume to be adjusted to keep the solids level in the aeration basin within the control parameters

Excess sludge which eventually accumulates beyond that returned is defined as Surplus or Waste Activated Sludge (SAS/WAS)

This is removed from the treatment process to keep the ratio of biomass to food supplied (sewage or wastewater) in balance

Typical Range

◦ 4,000 to 6,000 mg/l Apr 21, 2023Activated Sludge Process

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Page 59: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Stabilization ponds: The stabilization ponds are open flow through basins specifically designed and constructed to treat sewage and biodegradable industrial wastes. They provide long detention periods extending from a few to several days.

Aerated lagoons: Pond systems, in which oxygen is provided through mechanical aeration rather than algal photosynthesis are called aerated lagoons.

Oxidation ditch: The oxidation ditch is a modified form of "extended aeration" of activated sludge process. The ditch consists of a long continuous channel oval in shape with two surface rotors placed across the channel. Apr

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Page 60: Biological Wastewater Treatment.  Wastewater treatment Importance  Type of Pollutants  Methods of Treatment  Biological process as Wastewater Treatment

Dredging is an excavation activity or operation usually carried out at least partly underwater, in shallow seas or fresh water areas with the purpose of gathering up bottom sediments and disposing of them at a different location.

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