WEFTEC 2003 PROCESS OPTIMIZATION RESULTS IN COST EFFECTIVE BNR UPGRADE Sam Jeyanayagam, Ph.D., P.E., DEE Associate Malcolm Pirnie, inc. 1900 Polaris Parkway, Suite 200 Columbus, OH 43240 Harry Housholder Operations Manager Hillsborough County, FL Roy Neal Supervising Operator Hillsborough County, FL Edward Balchon, P.E. Senior Associate Malcolm Pimie, Inc. ABSTRACT The Valrico Advanced Wastewater Treatment Plant (AWTP) is owned and operated by Hillsborough County, FL. The A WTP is rated for an Average Annual Daily Flow (AADF) of 4 mgd. The permit effluent limits are 5.0 ppm BODs; 5.0 ppm TSS; 3.0 ppm TN; and 1.0 ppm TP. In order to accommodate the anticipated growth in the service area, the existing biological system was optimized to realize a 50 percent increase (4 to 6 mgd) in BNR capability without the addition of new aeration basin. Process optimization entailed (i) Implementation of tight DO control using on-line nutrient and DO analyzers to maximize simultaneous nitrification/denitrification, and (ii) Examination of the behavior of the clarification processes under various operating scenarios using the State Point approach. The opinion of probable cost and construction cost were $5 and $4.2 million, respectively. The upgraded facility was commissioned in June 2002, on schedule and under budget. Construction change orders were limited to less than 2 percent. KEWWORDS BNR, oxidation ditch, simultaneous nitrification denitrification, state point analysis, on-line nutrient analyzer INTRODUCTION The Valrico Advanced Wastewater Treatment Plant (A WTP) is owned and operated by Hillsborough County, FL. The AWTP is rated for an Average Annual Daily Flow (AADF) of 4 mgd. The treatment train consists of screens, grit removal, anaerobic selectors, oxidation Copyright 2003 Water Environment Federation. All Rights Reserved.

WEFTEC 2003 and chlorination/dechlorination. Treated plant has the add a OBJECTIVES The project objectives are:.. the year 5.0 parts per (ppm) Biochemical Suspended Solids 3.0-ppm Total (TN) Minimize treatment structures the optimization of the "'A'"'''''''' process... need for vw~lulvu.l" to meet permit limits ALTERNATIVE EVALUATION the the upgrade were.. present mode of.. biological system to This entails use nutrient and DO nitrification/denitrification (SND).. Convert to a proprietary Final Since the...prtnrn'l ofthe clarifier impacts that of the biological and vice versa, the state point was used to link of the clarifiers to operating conditions in the activated state point analysis the following three variables:.. Solids flux curve developed based on settling tests plant operators.. Overflow the clarifier influent clarifier surface area. It is.. Underflow rate is sludge withdrawal determined by dividing the clarifier underflow rate clarifier surface area. As shown in Figure 1, continuing the present of operation (Option 1) lead to critically loaded Due to reduced Option 2 will result in clarifier operation (Figure Copyright 2003 Water Environment Federation. All Rights Reserved.

WEFTEC 2003 Figure 1: Option 1 Clarifier Behavior 5.0~----------------------,---------------------~ ------------~ MLSS :: 5.850 rrgj\. 4. 0 +-~-..J.~---="""",=:----~:------+-----------::7"''''------------1 ~~r:a =C~~~lf~: :c "E ~ 3.0~-+----------~~~~~~~~-----1 <5 K, ii: 2. 0 '6'" ~ 1. 0 5850 mg/l MLSS, 3 Clarifiers Sludge Concentration, X (kg/ml) 1 0 11 12 13 14 15 - So lid s Flu )( -MLS S -Ove rflow -Underflow -Unde rflow (70) Figure 2: Option 2 Clarifier Behavior 5.0 4.0 :c "E E 3.0 <5 i ii: 2.0 '6 '" (; (I) 1.0 4,000 mg/l MLSS 3 Clarifiers 0.0 Sludge Concentration, X (k g/ml) I- SO lids Flux - M LSS - O verflow - Underflow I 1 0 1 1 12 13 14 15 ALTERNATIVE SELECTION Based on economic and non-economic factors, Option 2 was selected for plant upgrade to 6 mgd. This resulted in a 50 percent increase in treatment capacity without the addition of new basins or chemicals, and realized a cost saving of $800,000, the amount originally budgeted for new anaerobic selector tanks. Key plant modifications include new bar screen, final clarifier, effluent filter with denitrification capability, variable speed drive on aerators, on- Copyright 2003 Water Environment Federation. All Rights Reserved.

WEFTE~2003 VAluaC1VU ditch 15,112 1 1 21,157 16,068 1 3,J 540 Selectors Number, d HRT at peak h Mixers Number HP each Oxidation Ditches (Existing) Number Volume, HR T at month, h Mechanical aerators Number ditch HP each Clarifiers Number Dimension Overflow gpdlsf 20 30 4000 to 4500 75 9 15 2 (existing) 0.32 2.1 2 15 2 125 2 + 1 100 ft. dia., 15 SWD Ibsldlsf Peak 916 Copyright 2003 Water Environment Federation. All Reserved.

WEFTEC 2003 NU1rient Analysis SlImple Puint:; (;(~~:~:;'d).0. [~ --0-1 Prelimin"y 1--'-1 11 tw1 ~, ~ I Treatment I ----. AERATION/ ~ C5--- ---- -== SCREENING GRIT REMOVAL SELECTOR OXIDATION DITCHES FLOW SPLITTING CLARIFIERS INTERMEDIATE PUMP STATION B~0 --;---l Sllrfacc To - )...---, -,:l _I Water. REA ERAnON Cf RECLAIM WATER EFFLUENT TANK STORAGE PUMP STATION UJ tt. c",""", 1-'1'-1 CONTACT (ifrc(1uin;tl) SPRAY IRRIGATION Valrico Adlianced Wastewater Treatment Plant PROCESS FLOW SCHEMATIC I FIGURE 3 The PID process (Option 3) was associated with lowest energy cost and may become the option of choice for the 12 mgd expansion slated for 2007. Implementation of Option 2 at this time will not preclude the County from considering Option 3 in the future. On-Line Nutrient Analyzer A special feature of the selected alternative is the use of on-line nutrient analyzer for automatic DO. Control. The nutrient analyzer control schematic and sampling locations are shown in Figure 4. Figure 5 is a plot of the on-line analyzer output (effluent nitrate-n concentration), the corresponding aerator speed response, and DO change over a 24-hour period. As the effluent nitrate level increases, the aerator speed is decreased resulting in an immediate drop in DO. This increases denitrification leading to a decrease in the effluent nitrate level. While this presentation will cover the initial process evaluation and selection, the following will also be covered: Factors that contributed to the excellent change order record Operations review using over a year of operating data Performance assessment and O&M requirements ofthe on-line nutrient analyzer Lessons learned during design, construction, and operation Copyright 2003 Water Environment Federation_ All Rights Reserved.

WEFTEC 2003 Oxidation Ditch I l I #2 W i Samples From.--- Sample Pump 1 Oxidation -t;- ~~J).----*.----------------- Ditch #1 ~L--:---:---:-:.:--~: :' :' ~ Sample :'., " Excess Chern Scan I Pump., Valve I Filter Control :' Control Process System ":, Sequence :'., i Clear Sample :1 :1 ChemScan.1 :1 Analyzer Process Analyzer :1., Sample Waste System :' Analyzer Control :," i Signals l: Chern Scan :'..... L., Process Sample..,......-..._...--_...--. Sample to Sequencer Sample # I: NHJ-N & TP. Output Signal to Plant Control Samples #2 & 3: NHJ-N, NOx. Otho-P... System to Control Aerator on/off Speed Valrico Advanced Wastewater Treatment Plant ON-LINE NUTRIENT ANALYZER SCHEMATIC FIGURE 4 Figure 5 On-Line Nutrient Analyzer Trending & Control Copyright 2003 Water Environment Federation. All Rights Reserved.

WEFTEC 2003 COST AND SCHEDULE of probable cost was million, The construction bids were the of $4,2 to $6.6 Million. The upgraded was in June 2002, on schedule and under budget. Construction VU'.U",v orders were limited to less 2 percent. CONCLUSION presentation outlines how one facility has been able to a 50 "'Ar'r-p.rn capability process and implementing a systems approach coupled behavior biological clarification processes, It is a can use to develop reliable and cost treatment VIJ'.lV1IC) with increased plant loadings while continuing to meet nutrient limits. Copyright 2003 Water Environment Federation, All Reserved,