Nutrient Removal Objective: To understand the fundamental principles of nutrient removal using chemical and biological methods To know examples of the major wastewater treatment processes for nutrient removal. –Reference: “Operation of municipal wastewater treatment plants. Manual of Practice 11, Vol2 (1996). Water Environment Federation “ – see section ‘CIV912’; user and password both cassie

Nutrient Removal Introduction Chemical Methods Principle of Biological Nitrogen Removal Biological Nitrogen Removal Processes Principle of Biological Phosphorus Removal Biological Phosphorus Removal Processes Combined Biological N & P Removal Processes

Pretreatment Sed Tank Aerobic Biological Process Sed Tank Final Effluent Influent BOD 300 SS 300 TKN 50 PO 4 15 BOD <20 SS <30 TKN >20 PO 4 >10 Primary Sludge Secondary Sludge Nutrient levels in a Conventional Aerobic Treatment Plant

Nutrient Cycles Eutrophication potential –Nutrient balance C:N:P (100:5:1) 10,000 pe x 200 l/d x 15mgN/l  500kg algae/d 10,000 pe x 200 l/d x 5mgP/l  1200kg algae/d

Nutrient Removal - Standards - UWWT Directive (1991): Pop >10,000 N<15mg/l P<2mg/l Pop >100,000 N<10mg/l P<1mg/l or 80% removal of Total P % removal of Total N (The above applies to “sensitive waters”)

Chemical Methods Nitrogen –Ammonia stripping at high pH (Lime, CaO) NH OH - NH 3  + H 2 O Phosphorus –Precipitation by metal ions Ca(OH) 2 + HPO 4 2- Ca 5 (OH)(PO 4 ) 3 Al 2 (SO 4 ) 3 + PO 4 3- AlPO 4 + SO 4 2-

Biological Nutrient Removal Assimilation –C, N, P, S etc uptake for synthesis of new cells Dissimilation –C, N, S, oxidized/reduced to provide energy Aerobic (oxic) –in the presence of molecular oxygen (O 2 ) Anoxic –very low concentration of molecular oxygen (O 2 ) –significant levels of electron acceptors (NO 3 -, SO 4 - ) Anaerobic –no oxygen, lack of electron acceptors (only CO 2 )

Biological Nitrogen Removal Wastewaters contain: Org-N, ammonia, (nitrate) Dissimilatory metabolism Nitrification 1.NH O 2 NO H + + H 2 O Nitrosomonas 2.NO O 2 NO 3 - (nitrified effluent) Nitrobacter Denitrification NO CH 2 + H + N 2  + CO 2 + H 2 O denitrifying bacteria (many)

Anoxic (denitrification) Aerobic Influent Effluent N2N2 Basic Nitrogen Removal System (Ludzak-Ettinger Process) Sedimentation Tank RAS QRQR Modified L-E Process has recycle (Q R )

Aerobic + Nitrification Anoxic (denitrification) Aerobic Methanol Influent Effluent N2N2 Re-aeration for Excess Methanol Removal Alternative Nitrogen Removal System Sedimentation Tank RAS

Biological Phosphorus Removal Selection of Bacteria in Sludge –Luxury uptake of Phosphorus (Acinetobacter, Pseudomonas) –Cyclic Environmental Conditions High BOD when anaerobic Low BOD when aerobic Sidestream –P is stripped from sludge in separate unit process Mainstream –P is concentrated to high levels in the sludge (biomass)

Selection of Bacteria Aerobic Low BOD Carbon Oxidation (PHA oxidised to CO 2, releases energy) Phosphate uptake (Luxury) (PO4  polyP) * Anaerobic High BOD Carbon uptake (fatty acids stored as poly hydroxy alkanoates PHA) * Phosphate released from cells (polyP  PO 4, energy released) * These processes need energy to drive them

Aeration Tank Sed. Tank Waste Chemical Sludge ( P ) Lime RAS Phosphorus Stripped Sludge Supernatant Return Waste Sludge Influent Effluent Primary Effluent (BOD, Elutriation) PhoStrip  Process (Sidestream) Anaerobic Stripper PP

Aeration BOD Rem Nitrific -ation PhoStrip Denitrification Final Effluent Waste Chemical Sludge (P) RAS Phosphorus Free Sludge Methanol Aerobic Anoxic Anaerobic Sedimentation Combined N & P Removal N2N2 PP

NH 3 to NO 3 HRT= 3-6 h HRT= h HRT= h Anaerobic Anoxic Aerobic Settling Tank Nitrified Re-cycle ( %Q) RAS (50-100%Q) (= 6% P) Anoxic Re-cycle (100%Q) Q Combined N & P Removal (Mainstream) ( UNIVERSITY OF CAPE TOWN PROCESS, UCT) WAS (P) N2N2

Operational Considerations Maintain discrete environments –excess recycle rate gives completely mixed system Limitations –Combined System optimized for N (denitrification), biological P removal non-optimized (requires chemical supplementation) Efficiency –denitrification re-uses Oxygen bound in the nitrate Contingency –provide P removal by chemical means (when biological process fails)