Summer Seminar Emerging Issues in the Water/Wastewater Industry Austin s Full-Scale Step-BNR Demonstration Rajendra P. Bhattarai, P.E., DEE Austin Water Utility, City of Austin 625 East 10 th Street, Suite 300 Austin, Texas 78701 Phone: 512-972-0075, Fax: 512-974-3504 Raj.Bhattarai@austintexas.gov San Antonio, Texas July 24, 2015
Presentation Outline Background Step-Feed Biological Nutrient Removal (BNR) System Used Operating Characteristics Results Lessons Learned
Background Austin s wastewater treatment plants discharge to the Colorado River Waterbody of exceptional quality Nutrient removal required in future Need for demonstration of N & P removal Goal: TP < 1mg/L; TN < 10 mg/l Full-Scale Step-Feed BNR operated at South Austin Regional (SAR) WWTP for two years: January 1996 - December 1997
Activated Sludge Influent Aerobic Effluent RAS WAS
Activated Sludge For 25% increase in treatment capacity 12.5 MGD MLSS = 3,750 mg/l 10 MGD MLSS = 3,000 mg/l High MLSS can overload secondary clarifier Influent Aerobic Effluent RAS WAS
Step-Feed Primary Effluent 40% 30% 20% 10% 4,900 MLSS 3,800 MLSS 3,300 MLSS 3,000 MLSS Final Clarifier Aerobic Average MLSS = 3,750 mg/l RAS WAS
Advantages of Step-Feed Operational Flexibility Higher MLSS results in higher capacity without increasing solids loading to secondary clarifiers Maximize use of existing facilities Better handling of peak flows Robust and stable operation
Virginia Initiative Plant (VIP) Process Anoxic Recycle, 1-2Q (ARCY) Nitrate Recycle, 1-2Q (NRCY) Q Q Anaerobic Anoxic Aerobic RAS WAS A staged reactor configuration is provided by using at least two complete-mix cells in series for each zone of the biological reactor.
Step-Feed Primary Effluent 40% 30% 20% 10% 4,900 MLSS 3,800 MLSS 3,300 MLSS 3,000 MLSS Final Clarifier Aerobic RAS WAS
BNR demonstration system at SAR used the Step-Feed BNR Process -- combination of VIP and Step-Feed PE ARCY PE ARCY ANR ANX AER ANR ANX AER AER RAS NRCY
SOUTH AUSTIN REGIONAL WASTEWATER TREATMENT PLANT LIFT STATIONS INFLUENT BAR SCREENS GRIT BASINS SCREENINGS AND GRIT TO LANDFILL PRIMARY CLARIFIERS PRIMARY SLUDGE FLOW EQUALIZATION DIVERSION BOX ACTIVATED SLUDGE AERATION BASINS SECONDARY CLARIFIERS RETURN ACTIVATED SLUDGE FILTER BACKWASH CHLORINATION EFFLUENT FILTERS TO GOLF COURSE IRRIGATION SUPERNATANT GRAVITY THICKENER SLUDGE BLENDING WASTE ACTIVATED SLUDGE REUSE PUMPS SLUDGE PUMPS TO HORNSBY BEND BIOSOLIDS MANAGEMENT PLANT DECHLORINATION EFFLUENT DISCHARGE TO THE COLORADO RIVER
Train B Train A Control BNR South Austin Regional Wastewater Treatment Plant
Activated Primary for VFA Generation Raw Wastewater Primary Effluent containing VFAs Return Primary Sludge (Elutriates Sludge) Waste Primary Sludge (To Thickening)
Original Aeration Basin Flow Path Effluent Channel RAS Channel Influent Channel (RAS and PE mix) Flow Diversion Box Primary Effluent
Aeration Basin Step-BNR Modified Flow Path Effluent Channel RAS (Alt) AER AER Pass 4 ANR ANR ANX ANX AER Pass 3 AER AER Pass 2 ANR ANR ANX ANX AER Pass 1 RAS Channel Indicates Internal Recycle ANX ANX ANR ANR AER ANX ANX ANR ANR AER Influent Channel Primary Effluent 48 Bypass Flow Diversion Box Normal Input of Secondary Influent
Baffles added to Existing Aeration Basins to form Anaerobic, Anoxic and Aerobic Zones Volume, million gallons Step- BNR Control Total 2.6 2.6 Anaerobic 0.4 0 Anoxic 0.4 0 Aerobic 1.8 2.6
Baffles for Anaerobic, Anoxic and Aerobic Zones
Aeration Basin on the Control side Activated Sludge No persistent foam Only air bubbles
BNR Basins: Aerobic Zone in the foreground; Anoxic and Anaerobic Zones in the background. Comparatively more foam and scum than control
BNR Basins: Anaerobic Zone in the foreground; Anoxic and Aerobic Zones in the background
Close-up view of the Anaerobic Zone
Wastewater Temperature: 19 o - 30 o C 32 30 o C Influent Temperature, 28 26 24 22 20 18 Operating Periods: 1 2 3 4 5 6 7 16 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
Test flows were 6 to 20 MGD 20 Primary Effluent Flow, MGD 18 16 14 12 10 8 6 4 2 0 1-Mar CONTROL Operating Periods: BNR 1 2 3 4 5 6 7 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
Flow and Temperature Defined Operating Periods Startup Period 1 Period 2 Period 3 Period 4 Period 5 Period 6 Period 7 Steady 8 MGD; ~22 o C Steady 8 MGD; ~27 o C 10-13 MGD; ~27 o C (Construction Outage) 9-20 MGD; ~22 o C 12 MGD; ~28 o C Improved APC, Steady 6 MGD; ~22 o C Jan-96 Mar-96 Jun-96 Sep-96 Dec-96 Mar-97 Jun-97 Sep-97 Dec-97
Activated Primary Clarifier 80 70 worked well at times 1 2 3 4 5 6 7 Net TSCOD Produced, mg/l 60 50 40 30 20 10 0 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
MCRT lower than in Control 25 Aerobic MCRT, days 20 15 10 5 CONTROL BNR 0 1 2 3 4 5 6 7 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
SVI for BNR was higher 180 Sludge Volume Index (SVI), ml/g 160 140 120 100 80 60 40 20 0 1-Mar 12-Apr BNR 24-May 5-Jul 16-Aug 27-Sep Control 8-Nov 20-Dec 31-Jan 14-Mar Excessive Foaming 1 2 3 4 5 6 7 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
Excessive Foaming in BNR Basins due to Nocardia Growth and poor hydraulics
Both systems nitrified well 10.00 Trend lines are seven day moving averages Effluent NH 3 -N, mg/l 1.00 0.10 CONTROL BNR 0.01 1 2 3 4 5 6 7 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
Nitrogen removal was good 35 30 CONTROL Effluent NO 3 -N, mg/l 25 20 15 10 BNR 5 0 1 2 3 4 5 6 7 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
BNR Ortho-P Profile 3/13/96 to 4/8/96 12 PASS-1 PASS-2 PASS-3 PASS-4 Ortho-P, mg / L 10 8 6 4 2 PRI1B ANR1W ANR1E ANX1E ANX1W AER1S ANR2W ANR2E ANX2E ANX2W AER2N ANR3W ANR3E ANX3E ANX3W AER3S AER4S ZONES
P removal was variable Effluent Ortho- P, mg/l 7 6 5 4 3 2 1 2 3 4 5 6 7 CONTROL BNR 1 0 1-Mar 12-Apr 24-May 5-Jul 16-Aug 27-Sep 8-Nov 20-Dec 31-Jan 14-Mar 25-Apr 6-Jun 18-Jul 29-Aug 10-Oct 21-Nov 2-Jan
Lessons Learned BNR systems not that different from other treatment systems But they do require some understanding and familiarity BNR systems need more operational attention than conventional activated sludge
Lessons Learned (continued) Volatile Fatty Acids crucial for BNR - especially for phosphorus removal VFA production depends on Activated Primary Clarifier operation BNR systems more prone to foaming than conventional activated sludge Foaming can be controlled using polymers, water sprays and chlorine
Lessons Learned (continued) Allow sufficient hydraulic head between different zones for easy removal of scum and foam Provide free-flow path at water surface through all zones to secondary clarifiers for scum removal Good hydraulics for flow split critical for Step-feed
Lessons Learned (continued) Nitrogen removal depends on F/M in anoxic zones Phosphorus removal depends on F/M in anaerobic zones (especially VFAs) Phosphorus removal is directly proportional to the amount of phosphorus released in the anaerobic zones
Questions, Comments?
Train B Train A Train C BNR Control South Austin Regional Wastewater Treatment Plant