Nutrient Removal at Wastewater Treatment Facilities. Nitrogen and Phosphorus. Gary M. Grey HydroQual, Inc X 7167

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1 Nutrient Removal at Wastewater Treatment Facilities Nitrogen and Phosphorus Gary M. Grey HydroQual, Inc X

2 Agenda Nitrification and Denitrification Fundamentals Processes Phosphorus Removal Enhanced Biological Phosphorus Removal Chemical Treatment 2

3 Nitrogen and Phosphorus Concentrations in Domestic Sewage Total Kjeldahl Nitrogen (25 to 50 mg/l) Ammonium Nitrogen (15 to 35 mg/l) Organic Nitrogen (10 to 20 mg/l) (Most organic nitrogen hydrolyzes to ammonia) Phosphorus (4 to 8 mg/l) Sludge handling streams can contain 100 to mg/l TKN and 10 to 100+ mg/l P 3

to 20 mg/l) (Most organic nitrogen hydrolyzes to ammonia) Phosphorus (4 to 8

4 Nitrogen Transformation in Biological Treatment Nitrification by Autotrophic Bacteria 4

5 Nitrogen Transformation in Biological Treatment Denitrification by Heterotrophic Bacteria NO 3 + BOD N 2 + CO 2 + H 2 O + OH - + CELLS Occurs under anoxic conditions. Required mixing and nitrate recycle. For 1 gram of NO 3 -N Denitrified: ~ 3.0 g BOD are consumed ~ 0.45 g new cells are produced 3.57 g of alkalinity are formed (~50% recovery of alkalinity consumed in nitrification) 5

Required mixing and nitrate recycle. For 1 gram of NO 3 -N Denitrified: ~ 3.

6 Nitrogen Transformations 6

7 Factors Affecting Biological Nitrification and Denitrification Kinetics Sludge Age ph Temperature Inhibition Parameter Effluent Ammonia Concentration Dissolved Oxygen (DO) Substrate Biodegradability Nitrification X X X X X X Denitrification X X X X 7

Effluent Ammonia Concentration Dissolved Oxygen (DO) Substrate

8 Original Nitrification/Denitrification Facilities Used Two or Three Sludge Processes Nitrification Denitrification with Methanol Addition CBOD Removal 8

9 Current Biological Nitrification / Denitrification Processes INFLUENT EFFLUENT ANOXIC AEROBIC RAS Ludzack-Ettinger Process WAS NITRATE RECYCLE (100 to 400% Q) INFLUENT EFFLUENT ANOXIC RAS AEROBIC WAS Modified Ludzack-Ettinger (MLE) Process 9

Process WAS NITRATE RECYCLE (100 to 400% Q) INFLUENT

10 BNR Retrofit Costs $100,000,000 Cost Factors Mixers Nitrate Recycle Piping and Pumps Tank Baffles Supplemental Carbon Plant Retrofit Costs ($/MGD) $10,000,000 $1,000,000 $100,000 $10,000 Source: Biological Nutrient Removal Processes and Costs, EPA-823-R , June 2007 <1 1 to 10 >10 Plant Flow (mgd) 10

$10,000,000 $1,000,000 $100,000 $10,000 Source: Biological Nutrient Removal

11 Nitrification/ Denitrification Summary Effluent Quality NH 3 -N N <<1 mg/l NO 3 -N N <1 to 5 mg/l depending on process, nitrate recycle and carbon availability. Organic nitrogen 1 to 2 mg/l (higher with industrial sources) Nitrification is more sensitive to toxic and inhibitory substances than CBOD removal. Denitrification provides alkalinity recovery and can reduce energy costs. Consider sludge handling return streams. Good process control needed for year-round round performance. 11

Organic nitrogen 1 to 2 mg/l (higher with industrial sources) Nitrification is more sensitive to toxic and inhibitory

12 Phosphorus Removal Enhanced Biological Phosphorus Removal (EBPR) Chemical Precipitation 12

13 What is Enhanced Biological Phosphorus Removal (EBPR)? Biological Process that promotes the growth of phosphorous accumulating ulating organisms (PAOs( PAOs) ) that are able to take up and store high concentrations of phosphorus Normally bacteria in activated sludge contain % P In the EBPR process, bacteria that store phosphorus are selectively ely retained in the biological process and they contain 20-30% P Need an anaerobic/aerobic process to select for these PAOs (phosphorus accumulating organisms) PAOs require readily biodegradable COD (rbcod( rbcod) ) as volatile fatty acids (VFAs) Denitrification bacteria out compete PAOs for rbcod.. Need anoxic zones for denitrification if nitrates are present. Supplemental carbon or fermentation may be needed of wastewater is carbon deficient. Phosphorus is removed by wasting PAOs. 13

14 Plant EBPR Retrofit Requirements Volume for anaerobic contact zone About 1 hour detention time A significant EBPR factor for achieving 1 mg/l is the BOD/P ratio. >40 may be able to achieve effluent P < 1 mg/l 25 to 35 will need chemical treatment for polishing <25 may require chemical treatment only. Most domestic wastewaters yield mg/l effluent phosphorus by EBPR unless supplemental carbon is provided. Low effluent phosphorus limits (<0.5 mg/l) will require effluent filtration. Minimize return loads containing phosphorus Anaerobic or aerobic sludge digestion (> 50 mg/l P) 14

>40 may be able to achieve effluent P < 1 mg/l 25 to 35 will need chemical treatment for polishing <25 may require chemical treatment only.

15 Biological Phosphorus Removal Processes INFLUENT EFFLUENT ANAEROBIC AEROBIC RAS A/O Process (no nitrates) WAS NITRATE RECYCLE (100 to 400% Q) INFLUENT EFFLUENT ANAEROBIC ANOXIC AEROBIC RAS A 2 O Process WAS 15

16 Biological Phosphorus Removal Processes NITRATE RECYCLE (100 to 400% Q) INFLUENT EFFLUENT ANOXIC AEROBIC ANOXIC AEROBIC RAS Bardenpho Process WAS NITRATE RECYCLE (100 to 400% Q) INFLUENT EFFLUENT ANAEROBIC ANOXIC AEROBIC RAS ANOXIC AEROBIC WAS Modified Bardenpho Process (phosphorus removal and fermentation) 16

NITRATE RECYCLE (100 to 400% Q) INFLUENT EFFLUENT ANAEROBIC ANOXIC AEROBIC

17 Chemical Treatment Phosphorus Removal Mechanism Metal salt precipitate at stoichiometric dose but.. For very low P concentration metal-hydroxide formed Al 2 (SO 4 ) 3 n18h 2 O+ 2H 3 (PO 4 ) => 2Al(PO 4 ) + 3H 2 SO H 2 O FeCl 3 + H 3 (PO 4 ) => Fe(PO 4 ) + 3HCl 3 Chemical treatment will deplete alkalinity, decrease ph and increase TDS 17

. For very low P concentration metal-hydroxide formed Al 2 (SO 4 ) 3 n18h 2 O+ 2H 3

18 Two Point Chemical Addition Example Chemical Addition #1 Chemical Addition #2 Influent Primary Clarifier Biological Treatment Process Secondary Clarifier Effluent Return Activated Sludge Waste Activated Sludge 18

Clarifier Biological Treatment Process Secondary

19 Al/P Or Fe/P Dose Is Function Of Effluent P Concentration Molar Al/P Ratio Project Target 0.2 to 0.4 mg/l Al/P = 1.5 to 2.0 Secondary Clarifiers Al/P = 1.0 to 1.2 Primary Treatment Soluble P, mg/l P o 19 19

0 Project Target 0.2 to 0.4 mg/l Al/P = 1.5 to 2.

20 Chemical Addition to Secondary Clarifiers 20

21 Escalation of Costs for Achieving <1 mg/l Phosphorus 7,000,000 PW Cost ($/MGD) 6,000,000 5,000,000 4,000,000 3,000,000 2,000,000 1,000,000 Par-Troy Mountain View Effluent Phosphorus (mg/l) 21 21

22 Phosphorus Removal Conclusions and Observations EBPR has higher capital costs and lower O&M costs, chemical treatment has lower capital costs and higher O&M costs. Costs increase dramatically for effluent limits <1 mg/l Wastewater characteristics must be determined to establish process requirements and effectiveness of EBPR. Standby chemical treatment should always be provided. For chemical treatment alone, two-point addition is the most cost effective. Sludge processing return streams must be characterized to assess their contribution of influent P load. Source control should be considered when P concentrations are above 6 to 8 mg/l or at low BOD/P ratios. 22

23 Questions? Gary M. Grey HydroQual, Inc X

Phosphorus Removal in Wastewater Treatment

RESEARCH & DEVELOPMENT REPORT NO. Phosphorus Removal in Wastewater Treatment (Final Report) Research and Development Section Electrical & Mechanical Projects Division Nov 2013 Final Report endorsed by