Phosporus Removal● Removal of Phosphorus

○ Get it into a solid and then remove the solid○ Types of solids

■ Biological (microorganisms)■ Chemical (precipitates)

○ When treating the solids, avoid phosphorus release and recycle back to liquid treatment scheme

● Phosphorus Removal Technology Selection Criteria○ Capital and operating costs○ Effluent phosphorus limits○ Feasibility of EBPR (BOD / P ratio; VFA’s)○ Method and cost of sludge disposal○ Influent phosphorus concentration○ Availability and cost of chemicals○ Acceptability of use of chemicals

● Advantages of removal methods

----------------------------------------------------------------------------------------------------------------------------● Enhanced Biological Phosphorus Removal (EBPR)

○ PAOs (Phosphate accumulating organisms)■ Store orthophosphate in excess of growth requirements■ Need favorable operational conditions■ Anaerobic selector■ Facultative Heterotrophs

● Organic carbon for growth● Oxygen for energy generation● But can grow in the absence of oxygen● Require anaerobic zone● Influent to secondary system● No electron acceptors present

■ In Anaerobic Zone● PAOs do not grow● PAOs convert organics to PHAs

○ Polyhydroxyalkanotes○ Consume energy

■ Break cellular high energy P bonds as energy source

■ Releasing P to the wastewater○ Breakdown glycogen

■ In Aerobic Zone● PAOs grow

○ Oxidize stored PHAs for energy○ Use DO as electron acceptor

● Restore P energy reserves○ Rebuild high P energy bonds○ Take up excess P

■ Accumulate 125% of P released in anaerobic zone● Low effluent P

○ Summary of EBPR Biology (U = Used, R= Released, S = Stored, O = Oxidized)

○ Phosphorus Removal from System■ P removed via waste activated sludge (WAS)■ P content of WAS

● Without EBPR—1.5 - 2.0% of volatiles● With EBPR— up to 5% of volatiles

■ Building “FAT P” BUGS○ Requirements for EBPR

■ Readily biodegradable BOD / COD (VFAs)■ Relatively high BOD / TP Ratio (>20:1)■ Correctly sized anaerobic selector■ Sufficient cations - Mg & K

○ Temperature Impacts

■ EPBR tends to perform better at lower temps■ EBPR performance diminishes with warmer temperatures

○ EBPR Interference■ Insufficient VFA■ Glycogen Accumulating Organisms (GAO)

● compete for VFA under anaerobic conditions■ GAO favored over PAO■ Avoid GAO Interference By:

● Operate at lowest SRT that provides nitrification● Minimize unaerated zones

○ Avoid anoxic zones larger than req’d for denit● Add VFAs when req’d● Maintain adequate pH

○ Variability in EBPR Performance■ Changes in influent sewage characteristics

● Flow● P● BOD● Minimum BOD/TP >20● VFA concentrations

■ Chemical precipitation improves control and minimizes effluent variability○ Biological Phosphorus Removal Advantages

■ Lower operating cost■ “No chemical sludge produced

● No deterioration in sludge dewaterability■ No increase in effluent TDS/salinity■ Can add touch-up chemical dose to achieve very low P concentrations

○ Biological Phosphorus Removal Disadvantages■ Higher capital cost

● Unless existing tankage available■ More land required■ Potential for P release during sludge treatment■ Greater dependence on sewage quality■ Less stable■ Requires complex bio-reactor configuration■ Increased operational knowledge

● Conclusion○ Works, but has variability○ Avoid anaerobic conditions in solids handling○ VFA addition capability reduces variability○ Best used in conjunction with chemicals○ Reduces chemical consumption○ Reduces sludge production○ Usually not cost effective to build new tankage (anaerobic zones)

----------------------------------------------------------------------------------------------------------------------------● Chemical Precipitation

○ Aluminum, iron, and calcium compounds are used for phosphorus removal.○ Selection of chemicals depends on several factors:

■ Effectiveness■ Cost■ Availability■ Ease of handling■ Effect on metals in effluent

● Copper removal● Increase in aluminum

○ Chemical Caution: UV Disinfection and ferric addition may not mix○ Large dosages are needed to reach low concentrations○ Chemical precipitation increases sludge production○ Effluent filters lower effluent P and provide greater reliability○ Tertiary clarification ahead of filtration provides low phosphorus concentrations.○ Membranes can also be used○ Optimization of Chemical P Removal

■ Automate chemical feed controls■ Reduce recycle P■ Provide rapid mix / flocculation■ Evaluate different chemicals and doses■ Multiple point chemical addition

Biological Nitrogen Removal● Too often measured as “Ammonia”● Forms of nitrogen in wastewater:

○ Organic○ Ammonia○ Nitrite○ Nitrate

● Total Kjeldahl Nitrogen (TKN) is organic plus ammonia● Inorganic Nitrogen is ammonia plus nitrate plus nitrite● Biological Nitrogen Removal

○ Two Step Process1. Nitrification (NH3 to NO2 then NO2 to NO3)2. Denitrification (nitrate reduced to nitrogen gas)

○ Nitrification/Denitrification:■ Design for N removal must be based on influent TKN

○ Nitrification:■ Nitrifiers are very slow growers

● Only grow on ammonia and nitrite● Only grow in presence of dissolved oxygen

■ Substantial consumption of DO and destruction of alkalinity○ Denitrification

■ Nitrate converted to nitrogen gas■ Denitrification very easy to do if given:

● Anoxic conditions● Nitrate● Carbon source

■ Denitrification rates:● Increase with higher F/M● Decrease with temperature

■ Carbon sources for denitrification:● Raw wastewater (free carbon source)● External carbon (typically methanol)● Endogenous (biomass decay and release)

■ Denitrification Rates are a function of carbon source■ Supplemental Carbon Addition

● Methanol● Ethanol● Micro-C● Glycerin● On-site sources (primary sludge fermentation & WAS lysis)

○ N Removal via MLE■ MLE works as a “dilution” process■ Sensitive to TKN/BOD ratio

■ Higher removals with no primary treatment■ Lower influent TKN/BOD ratio yields lower effluent N concentrations■ Primary treatment increases influent TKN/BOD ratio

○ Alternative Processes■ Membrane Bioreactor (MBR) Process

● Much more energy intensive● No clarification● Membrane tank highly aerated

Aeration● History of Wastewater Aeration

○ First experiments England 1882○ Air initially introduced through open tubes or perforations○ English patent issued in 1904 for metal plate diffuser○ In 1915 Jones & Atwood of England introduced porous plate concrete diffuser○ US Carborundum, Ferro Corp, Norton Co. offered porous plate diffusers in US○ Clogging problem from onset

■ Gradually led to coarser media■ Air filtration introduced■ Mechanical aeration

● 1916-Archimedean screw type aerator introduced in Sheffield, England

● 1919-Bury, England installed up-flow surface aerator■ 1950-coarse bubble diffusers

● Sacrificed substantial transfer efficiency● Inability to transfer sufficient oxygen to front of aeration basins led

to development of step feed patterns○ 1970s-US Clean Water Act require secondary treatment, resulting in demand for

more efficient aeration■ US turned to European technology■ Fine bubble regained popularity

● Properties of Air○ Composition of earth’s atmosphere -AIR – is more or less constant for about

300,000 ft■ By volume (78% Nitrogen &21% Oxygen)■ By weight (23.2 % Oxygen)

○ Density of air varies with Temperature and pressure (ie altitude)○ Standard Air defined as: 68 F, 14.7 psia (sea level) and 36% relative humidity

● Types of Aeration:○ Classified into mechanical and diffused○ Mechanical (surface or submerged)

■ Transfer O2 by entraining air from atmosphere into mixed liquor by pumping or agitating the wastewater

○ Diffused■ Compressed air from blowers introduced through diffusers located in the

aeration basin, usually near the bottom● Air Requirements

○ Air required to provide oxygen for biological oxidation of carbonaceous & nitrogenous matter and to maintain solids mixed within the wastewater.

○ To be used in biological oxidation, oxygen present in air must be transferred to dissolved oxygen within the wastewater.

○ Mixing required in influent channels if wastewater and RAS are mixed ahead of aeration.

○ Mixing required within aeration basins.

○ Mixing desirable in effluent channels. Aeration can be used to provide mixing.○ Mixing: Aeration devices must provide energy to keep contents mixed. Oxygen

transfer is not a factor.● Biological Oxidation

○ Dissolved oxygen required for:■ oxidation of carbonaceous BOD■ oxidation of ammonia (and organic N going to ammonia) to nitrate

● Oxygen for Nitrification:○ Common practice is to use Influent Ammonia as the basis of design. YOU

MUST USE TKN which is ammonia plus organic nitrogen. Organic nitrogen is converted to ammonia during BOD oxidation.

● Oxygen demand:○ varies hourly and daily ○ varies within aeration tank

● Advantages of diffused air systems:○ Turndown (with proper design) = maximization of energy efficiency○ Ability to move air where you want it without varying tanks in service

● Oxygen transfer○ Aeration performance tested and reported as “Standard Oxygen Transfer Rate”

(SOTR) or “Standard Oxygen Transfer Efficiency” (SOTE)○ Transfer Efficiency of mechanical aerators is reported as “Standard Aeration

Efficiency” (SAE)

Organic Carbon● Removal of organic carbon

○ Biological removal of:■ Soluble organic matter ■ Insoluble matter too small for physical removal (BOD) ■ Removal using suspended growth and/or attached growth systems■ Removal achieved by:

● conversion of BOD to CO2 + H2O● new cell growth (biomass)

■ Biomass removed with physical sedimentation process (ie clarifiers)● Suspended Growth Biology

○ Electron acceptors for biological reactions■ Oxygen■ Inorganic compounds■ Organic compounds

○ Biological environments■ Aerobic: dissolved oxygen (DO) present■ Anaerobic: absence of oxygen (CO2, sulfate and organic compound serve

as electron acceptors)■ Anoxic: No DO; oxygen present in nitrate (NO3) which serves as electron

acceptor○ Growth Rate:

■ Aerobic > anoxic > anaerobic○ Suspended growth reactors

■ Completely mixed● Concentrations uniform throughout the reactor ● concentrations in effluent equal to concentrations in reactor ● biomass is in constant, average growth regime. ● Complete mix reactors … :

○ no longer common for municipal suspended growth systems

○ advantageous for wastes prone to biological toxicity■ Plug flow

● Flow moves through reactor in the order it entered● No longitudinal mixing. ● Growth conditions vary length of the reactor

■ Batch● Influent loaded as a batch● Biological reaction occurs without additional influent.● Batch reactors are true plug flow based on time (not flow)

○ Heterotrophs: Use organic compounds as electron donor and as carbon source for cell synthesis.

○ Autotrophs:■ Use inorganic compounds as electron donor and carbon dioxide carbon

source. ■ Most important are nitrifiers.

○ Obligate aerobes■ Use only oxygen as the electron acceptor■ Most significant are nitrifiers

○ Obligate anaerobes ■ Function in absence of molecular oxygen

○ Facultative■ Use oxygen as the electron acceptor when it is available■ Shift to alternate acceptor in the absence of oxygen. ■ Tend to predominate in biochemical operations ■ Organisms function in condition that is most efficient for growth ■ Aerobic conditions more efficient than anaerobic.

● Fermentation: use organic compounds as terminal electron acceptor in absence of oxygen - create reduced organic end products

● Anaerobic respiration: absence of oxygen - inorganic compound serves as the terminal electron acceptor

○ Floc formation■ necessary for effective sedimentation of biomass ■ Single bacteria are 0.5-1.0 μm

● too small for individual gravity separation ■ Under proper growth conditions, bacteria grow in clumps or biofloc 0.05-

1.0 mm.○ Nuisance bacteria

■ Need to be aware of these organisms and their growth characteristics ■ Design (and operate) to discourage or prevent growth.■ Foam formers:

● Copious quantities of surface foam in aeration tanks● can completely cover aeration tanks and clarifier

■ Filaments: ● Very small number strengthen floc● Excessive numbers ⇒BULKING

○ significantly reduce settling rates, overload clarifiers● Conditions favoring filamentous growth

○ low DO○ high SRT○ completely mixed reactor○ nutrient defiency○ low pH

○ Fungi■ Can compete with bacteria for soluble organic matter ■ Seldom competitive in suspended growth environments. ■ Can predominant causing problems similar to filaments with DO or

nutrient deficiencies or low pH○ Protozoa

■ Important in suspended growth treatment■ “Graze” on colloidal organic matter and dispersed bacteria

● reduce effluent turbidity ● increasing bioflocculation (and thus settling rates)

■ Indicators of healthy process■ Tolerate very little changes in environment■ Consume large amount of viable bacteria. ■ Swing in dominant protozoa with start up of activated sludge system

(replaced by ciliates)■ Primary benefit from protozoa

● predation on free-living bacteria ○ reduction in the bacterial population in the clarifier effluent○ reduction in turbidity and non-settleable solids

● no direct metabolism of dissolved substrate by ciliated protozoa; flagellates metabolize dissolved organics

○ Rotifiers and nematodes ■ Present in suspended growth systems■ Feed on protozoa and bacteria flocs■ Indicative of a well-stabilized/high-quality effluent

○ Activated Sludge■ Two components: aeration tanks and clarifiers■ Designers must provide system with enough operational flexibility to

allow continual compliance with required levels of treatment under constantly varying conditions

○ Basics of Activated Sludge-Aeration Tank■ Aeration tank (AT) provides a controlled environment for the growth of

the activated sludge and resultant removal of organic matter ■ Think of AT as “a bug house”

● Growth and reactions of the MLSS controlled via ○ AT configuration ○ SRT

■ Air addition● Keeps the MLSS contents mixed● Provide oxygen as the terminal electron acceptor in the oxidation

of the organic matter. ● Environment of AT directly impacts the settleability characteristics

of the MLSS in the subsequent clarifiers.○ Yield

■ The net or apparent yield can be determined directly from treatment plant operations data and incorporates microbial growth kinetics directly (growth and decay rates).

■ Correct kinetic parameters, determined from the waste in question, must be applied when modeling and in nondomestic wastes.

■ For municipal designs the net yield can be directly applied● Existing plant data● From literature

○ Solids Retention Times (SRT)■ Equal to time in days that the biomass is held in the AT. ■ Is critical parameter in setting system effluent quality.

○ Selectors■ Used to control settleability of mixed liquor

● Selector provides conditions favoring growth of bugs that settle well

● Smaller clarifiers provided with designs incorporating selectors■ Provided at influent to AT (part of AT) as 3-stage volumes■ Three types

● Aerobic● Anaerobic● Anoxic● AT volume increased to accommodate anaerobic and anoxic

selectors○ Total AT volume = volume req’d for aeration + volume for

selectors● AT volume not increased for aerobic selectors

○ Basics of Activated Sludge-Clarifier■ AT effluent MLSS is introduced to the top of the secondary clarifiers and

allowed to settle. ■ Settled flow discharged over clarifier weirs■ Settled solids collected on the bottom of the clarifier

● Recycled back to AT. ● Portion of settled solids wasted ● To maintain the desired AT MLSS level● To maintain desired system SRT.

■ Upper regions of the clarifier function in a zone or hindered settling mode (Type III Settling).

■ Lower levels function in a compression mode (Type IV Settling).■ Required clarifier surface area directly related to:

● downward settling rate of the zone settling region ● solids flux rate in the compression zone

○ Return Activated Sludge (RAS)■ RAS is the solids which are settled and collected in the secondary clarifier

and returned to AT ■ RAS solids are described in terms of lbs per day and the concentration in

mg/L.● This material is also referred to as “underflow”

Alternative Filtration Systems● Major components of a drinking water treatment system

● Pretreatment Options○ RiverBank Filtration○ RiverBed Filtration○ Plain Sedimentation○ Tilted Plate Sedimentation○ Dynamic Bed Filtration○ Roughing Filtration

● Processes taking place at an RBF site

● Viable Water Treatment Options for Small System○ Packaged Coagulation Treatment Systems○ Pressure Filtration Systems

■ Granular Media● Diatomaceous Earth/Precoat● Ceramic Media

■ Membrances○ Biological Filtration Systems

■ Riverbank Filtration■ Slow Sand Filtration

● Conventional Treatment: Rapid Sand Filtration = Chemical Clarification Treatment

● Basic Filtration Equation: Rate of Flow = Driving Head (Filter Resistance - Filter Deposition)

● Typical Rapid Sand Filter

● Purpose of Body Feed○ Create Permeable Cake○ Increase Dirt-Holding Capacity○ Provide Longer Filter Cycles

● Proven modifications to enhance slow sand filter performance

Concern Modification

Increase raw water applicability Roughing filtersMicrostrainers

Minimize filter downtimes and ripening periods

Filter harrowing

Improve organic precursor PreozonationGranular media amendments

● Selected “Multi-stage” Prefabricated Treatment System