Biological process of phosphorous removal

1. BIOLOGICAL PHOSPHORUS REMOVAL
Prepared by. Sandy

2. Introduction
• Presence of nutrient like nitrogen & phosphorous in waste water effluents and their impacts on natural
water bodies are major concern.
• Anthropogenic phosphorous (originating in human activity) addition in microorganism in milligram per liter
level can trigger algal growth.
• Chemical and biological means are adopted to remove.
• Biological phosphorous removal has advantage of simplicity, economy and various environmental benefits.
• Process relies on enhancing ability of organisms to uptake more phosphorous into cell.
• C:N:P ratio in municipal wastewater is about 100:20:5.
PHOSPHORUS IS A NUTRIENT
100:5:1(C:N:P)
Increase Plant Growth
Good for Food Crop
Not Good for Aquatic Systems
Individual nutrients in wastewater correspond to needs of bacteria in activated sludge (aerobic wastewater
treatment). Balanced relationship between C, N and P .

3. Source of Phosphorous in Waste Water
 Max from human waste .
 Industrial process wastewater and food soils are significant
sources as well.
 Multiple sources, such as water treatment ,household
cleaners and even toothpaste.
 Most phosphorous in wastewater occurs as :
 Orthophosphate-Simplest form (individual molecules of
phosphate).
 Polyphosphate-Large molecules containing many
individual molecules of orthophosphate.
 Organic phosphate-Phosphate combined with an organic
compound such as human waste.
 During biological treatment , most polyphosphates and
organic phosphate is converted to orthophosphate ,a form
that is readily assimilated by microorganism.

4. Control of Eutrophication
Essential Nutrient
Not easily replaced in nature
P removal is practical
Phosphorus
The Phosphorus Cycle

5. Rate of Eutrophication is increased by human activities
(Cultural Eutrophication)
Wastewater Discharges
WWTP
On-Site Systems
Combined Sewer Overflow
Stormwater Run-Off
Development
Agriculture
Eutrophication
Water Body overly Enriched with Nutrients.
Plentiful Growth of Simple Plant Life.
Excessive Growth (Or Bloom) of Algae And Plankton.
 Secondary treatment remove 1-2 mg/l, so
large excess of phosphorous discharged
.
 New legislation. Maximum concentration
of P discharges into sensitive water of 2
mg/l.

6. Forms and Sources of Phosphorus
Organic Phosphorus
•Complex organic compounds
•Soluble or particulate
•Decomposes to Ortho-P
•Phytin, phospholipids, and nucleic acids.
Polyphosphate (condensed phosphate)
•Chained molecules
•Soluble
•Home, industrial detergents
•Potable water treatment
• Decomposes to Ortho-P
Orthophosphate
• Simple Phosphate, PO4
• Soluble
• Household cleaning agents
• Industrial cleaners
• Phosphoric acid
•Conversion of organic and poly phosphate
Phosphorus load in inflow of a wastewater treatment plant . Made
up of orthophosphate-phosphorus (PO4-P), polyphosphates, and
organic phosphorus compounds. Together, give sum parameter
‘total phosphorus’ (Ptot).
Triphosphoric acid (also tripolyphosphoric acid),
H5P3O10

7. Anaerobic Metabolism of Phosphorus in Phosphate Accumulating Bacteria
 Anaerobic phases considered as stress conditions
for PAOs.
 Take up carbon sources and store them to cope
with a potentially long-term absence of oxygen .
 In wastewater, acetate is main carbon source
 Converted into acetyl-coa.
 Required energy provided by the hydrolysis of
ATP, leading to ADP and release of P in medium.
 Acetyl-coa is next metabolized into
Polyhydroxyalkanoates (PHAs), which are carbon
storage compounds.
 pyruvate, conjugate base, ch3cocoo−

8. Aerobic Metabolism of Phosphorus in Phosphate Accumulating Bacteria
 PHAs (Poly hydroxyalkanoates) used for cell growth
and reconstitution of the Poly-P reserves.
 PHAs degraded, leads to synthesis of Acetyl-CoA,
processed through the TCA cycle.
 TCA cycle produces energy from oxidation and carbon
for new cell growth.
 Energy is used to take up soluble P from environment
and incorporate it into Poly-P.
 Another part of carbon and energy used to regenerate
glycogen .

9. Volatile Fatty Acids
VFAs can be affected by recycle flows.
 RAS return high in NO3 to anaerobic zone
 Interfere with fermentation ,reducing amount of VFAs.
 Recycle from sludge handling contain high quantities of nitrogen and
phosphorous .
 Using air lift pumps to return activated sludge produces aeration and
introduce oxygen into anaerobic zone.
 Although you have no control over formation of VFAs in the collection
system, ways to maximize VFA formation in primary clarifier.
 Keep a higher blanket (storing sludge longer in primary clarifier
promote fermentation and produce more VFAs)
 Turbulence of water being added to anaerobic zone will add oxygen
and impair process.
Fermentation is a metabolic process produces chemical changes in organic
substrates through the action of enzymes. In biochemistry defined as the
extraction of energy from carbohydrates in the absence of oxygen

10. Phosphorus Removal
• Removal of Settleable Solids
Provides
• Some Phosphorus Removal
• Primary Sedimentation 5 - 15 %
P
P
Primary
Clarifier Aeration
Tank
Secondary
Clarifier
P
P
Removal of Ortho-P may Occur Through:
.Chemical Precipitation
.Enhanced Biological Uptake

11. Biological P Removal
Candidatus Accumulibacter phosphatis (Accumulibacter) is widely used PAO.
Acinetobacter species, were reported to be the organisms primarily responsible for EBPR.

12. Minimum Requirements Needed In Anaerobic Zone
 BOD5 to total phosphorous (TP) ratio ratio of 20:1
 Hydraulic detention time (HDT) in the anaerobic zone of
about one hour ( Do not run out of VFAs for the bio -P bugs.
 Secondary release of phosphorous occurs when PAOs are
under anaerobic conditions in absence of a source of VFA.
 Energy stored as polyphosphate for cell maintenance and
phosphorous released to liquid phase.
 Upon reaeration, no stored food to supply energy for uptake
of phosphorous.
 A solids retention time (SRT) in anaerobic zone of about one
and a half to two days (allow just enough time for the
enhanced biological phosphorous removal reactions to take
place).
 Characteristics of wastewater entering anaerobic zone
determine effluent phosphorous concentration is possible.

13. PAOs in Anaerobic Conditions
 To perform biological P removal , you must ensure:
 Sufficient organic carbon and phosphorous in secondary
influent.
 Anaerobic zone is sized correctly.
 Sufficient cations (magnesium and potassium) to facilitate
phosphorous release and uptake.
PAO Able to store soluble organics as Polyhydroxybutyrate (PHB).
PAO Break Energy-Rich Poly-P Bonds To Produce Energy Needed for the
Production of PHB.
Ortho-P is Released Into Solution .

14. PAOs in Aerobic Conditions
 PAOs take up orthophosphate using energy from oxidation of
organic matter by nitrate or dissolved oxygen.
 Convert it to polyphosphate stored in cell.
 PAOs take up more orthophosphate than released under
anaerobic conditions.
 Called luxury uptake.
 Phosphorous removed from system through waste activated
sludge.
 Cycling of wastewater through anaerobic and aerobic zones
favors the growth of PAOs.
Rapid Aerobic Metabolism of Stored Food
(PHB)Producing New Cells
PO4 Used in Cell Production
Excess Stored as Polyphosphate
(“Luxury Uptake”)

15. Microbiology of A/O Process

16. Mechanism of Biological phosphorus Removal
Under Anaerobic Conditions
 PAOs use stored polyphosphate as a source of energy
for taking up and storing food.
 Polyphosphate split apart into molecules of
orthophosphate.
 Molecules can not cross cell membrane by
themselves because they are negatively charged
(anions).
 Bond with magnesium and potassium, which are
positively charged (cations).
 During bonding , charges are neutralized.
 Cross cell membrane and pass into wastewater .
 Process ,called phosphorous releases ,also releases
magnesium and potassium into wastewater.
Magnesium and potassium cations are in sufficient
quantities to allow bonding to take place.

17. Conditions for Good Biological P Removal
 Available VFAs in anaerobic zone .
 A BOD5 of TP ratio of 20:1 .
 7-10 mg/l of VFAa per mg of phosphorous removed by Bio-P.
 Waste biomass when MLSS is aerobic and phosphorous stored in cell mass.
 Avoid secondary release of phosphorous.
 Anaerobic zones have hydraulic detention time of about one hour.
 Concentration and a solids retention time (SRT)of 1.5 -2 days.
 Monitor sludge blanket in secondary clarifier so it does not go anaerobic and release phosphorous.
 Take care in managing recycle streams . Recycle from sludge handling may contain high quantities of nitrogen and
phosphorous.
 Minimize dissolved oxygen and nitrate will interfere with fermentation.
 Avoid producing aeration through pumping and turbulence between tanks.

18. Biological process. Promotes growth of phosphorous accumulating organisms(PAOs).
Store high concentration of phosphorous.
Bacteria in activated sludge contain 1-1.5% P.
Bacteria contains 20-30 % P.
Need an anaerobic/aerobic process to select PAOs.
PAOs require readily biodegradable COD(rbCOD) as volatile fatty acids (VFAs).
Supplemental carbon or fermentation may be needed of wastewater is carbon deficient.
Phosphorous is removed by wasting PAOs.
What is Enhanced Biological Phosphorus Removal
Anaerobic /oxic (A/O) configuration

19. Enhanced Biological Phosphorus Removal Design Configurations
Anaerobic/anoxic/Oxic (A2 O) Configuration
Modified Bardenpho Configuration University of Cape Town Configuration Johannesburg (JHB) configuration