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

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  • Biological 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)

  • Wastewater Treatment

  • Environmental EffectsReuse ImplicationsPotableIndustrialRegulatory Requirements

  • Types of Pollutants

  • 1) Suspended Solids 2) Dissolved Solids 3) Colloidal Solids

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

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

  • Metcalf & EddyTS = TVS + TFSTS = organic + inorganicTS = TSS + TDSTSS=VSS+FSSTDS=VDS+FDS

  • Dissolved Oxygen (DO)Biochemical oxygen demand (BOD)Chemical oxygen demand (COD)Total organic carbon (TOC)

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

    Low oxygen conditions may kill fish and other organisms

  • 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.

  • 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 measuredCan be assessed in 5 to 10 minutesTheoretical > Measured

  • Methods of 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

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


    microbes with the ability to degrade the waste organics contact time with the organics favorable conditions for growth

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

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

  • Microorganisms

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

    Basic unit of life = cell

  • animal cellvirusbacterial cell

  • Coccispherical cells, often in chains or tetrads

    Rods most common shapevary in shape & size

    Spiral Rod curved rods

  • Growth = cell division one cell divides to produce two equal daughter cells

    Generation time length of time required for bacterial population to double

  • single cellcell elongates cell produces cell walltwo daughter cells producedThe cell replicates all its components, reorganizes it into two cells, forms a cell wall, and separates.

  • log phasestationary phasedeath phaselag phasecell count time

  • Percentage by weightCarbon50Oxygen20Nitrogen14Hydrogen 8Phosphorus 3Sulfur 1 Potassium1 Sodium1 Calcium0.5 Magnesium0.5 Iron0.2 All other elements0.3

  • NutritionalCarbon source (waste to be degraded )N & P(100:5:1;C:N:P)Trace mineralsEnvironmentalOxygen (terminal electron acceptor)TemperatureWater pHNon-toxic

  • 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

  • Aerobic - oxygen

    Anoxic - nitrate

    Anaerobic - strict and facultative

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

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

  • Activated Sludge Process

  • There are two phases to biological treatment

    Mineralization of the waste organics producing CO2 + H2O + microbes Separation of the microbes and water

  • W (WAS)R(RAS)Q(IN)Q-W(OUT)Aeration basin ClarifierQ+R(MLSS)Clarifier

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

  • 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

  • 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

  • *Activated Sludge Process*

    Activated Sludge Process

  • 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)*Activated Sludge Process*

    Activated Sludge Process

  • 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

    *Activated Sludge Process*

    Activated Sludge Process

  • 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.

    *Activated Sludge Process*

    Activated Sludge Process

  • 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*Activated Sludge Process*

    Activated Sludge Process

  • 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