Wyoming Department of Environmental Quality Division Lagoon Aeration – Theory & Design Tuesday, February 28, 2012 Kevin Rood, P.E., BCEE

Overview 1)Lagoons in general 2)Decision process to determine if the aerated lagoons are the right answer 3)Facultative lagoons 4)Partially mixed aerated lagoons 5)Mixed aerated lagoons completely 6)Equipment 7)Questions (at any time)

Community Goals 1)Meet treatment requirements 2)Lowest possible capital costs 3)Lowest possible operating costs 4)Be trouble-free

LagoonsLagoons Surface Water Discharge Land Application ContinuousContinuousIntermittentIntermittent DischargingDischarging Non Discharging Non Discharging Lagoon Systems are a Combination of these Process Types StorageStorageFacilitativeFacilitativeAerobicAerobicAnaerobicAnaerobic

Community Needs Population Flows Loads Type of waste Water quality issues Available land

Size of lagoons Separation distances Available stream Discharge requirement Distance from the community Topography Geology LagoonsLagoons Mechanical Plant Available Land Community Needs NOYES NO

AdequateAdequate Non Discharge NPDES Permit Required LagoonsLagoons Mechanical Plant Available Land Community Needs NO YES NO DischargeDischarge NO YES YES ContinuousIntermittent Land Application EvaporationRetention

Retention 1.Storage = Water Gain – Weight Loss 2.Water Gain = Water Loss – Hydraulics problem – Evaluation organic loading – Construction controlled by geology – Design controlled by topography and other physical constraints – Weather AdequateAdequate Non Discharge NPDES Permit LagoonsLagoons Mechanical Plant Available Land Community Needs NO YES NO DischargeDischarge NO YES YES ContinuousIntermittent Required Land Application EvaporationRetention

Industrial Manufacturing Mining Fracking Agricultural Grain Crops Livestock Food Silviculture Wetlands AdequateAdequate Non Discharge NPDES Permit LagoonsLagoons Mechanical Plant Available Land Community Needs NO YES NO DischargeDischarge NO YES YES ContinuousIntermittent Required Land Application EvaporationRetention

Intermittent Discharge to Surface Water Regulatory issues Effluent quality Down stream issues Sizing control / by influent water Sampling and monitoring AdequateAdequate Non Discharge NPDES Permit LagoonsLagoons Mechanical Plant Available Land Community Needs NO YES NO DischargeDischarge NO YES YES ContinuousIntermittent Required Land Application EvaporationRetention

Continuous Discharge Sizing control by water quality in and out Most treatment Sampling and monitoring AdequateAdequate Non Discharge NPDES Permit LagoonsLagoons Mechanical Plant Available Land Community Needs NO YES NO DischargeDischarge NO YES YES ContinuousIntermittent Required Land Application EvaporationRetention

Anaerobic Without oxygen High strength waste Energy recovery Odor issues

Aerobic With oxygen Physically smaller More equipment Completely mixed Highest quality effluent

FacilitativeAnoxic Anaerobic Aerobic

Facultative Preliminary Treatment Treatment Cell #1 Treatment Cell #2 Treatment Cell #2 Storage Cell Polishing Cell Stream * Optional * * Wyoming Requirement Max Loading 40 lbs/Acre/Day 180 HDT Outfall

The Operation of the Facultative Pond o2o2o2o2 o2o2o2o2 During daylight hours Co2Co2Co2Co2 C o 2 + NH 3 + H 2 S + CH 4 Bottom sludge Organic wastes Organic acids alcohols H 2 S H 2 S0 4 Algae Dead Cells Bacteria Wastewater Reaeration Sunlight o2o2o2o2 Wind C0 2 H2SH2SH2SH2S New Cells Nutrients

Design Considerations Solids loading rate to primary cells Hydraulic detention time Temperature Minimize short circuiting Predominant wind direction

Solids Loading Models can be used to predict loading rates Regulatory agency usual sets max. rate Wyoming Regulations = Max 40 lbs/pc/day

Hydraulic Detention Time BOD reduction and Coliform reduction are generally modeled as 1 st order kinetic BOD BOD (eff) = BOD (Inf) 1 + K e (T) T = Time (days) K e = K 20 THETA (t-20) K 20 = per day THETA = 1.07 range (1.05 – 1.09)

Coliform N e = N i 1 + K t (T) N i = Influent Coliforms N e = Effluent Coliforms K t = removal constant per day T = time days K t = 2.6 (1.19) (t-20) t = Temperature C Hydraulic Detention times range days Wyoming regulation = 180 days

Treatment Cell No. 1 Treatment Cell No. 2 Storage Cell Polishing Cell 2’2’2’2’ Facultative Lagoon

Seepage – Wyoming limits - 1/8-inch day max – Common 2.6x10 -9 cm/sec/ft depth - approx. 0.1 inch/day – Common - no seepage, use impervious liner Compacted Soil 95% Standard Proctor, MR O, + 3% 1 ft select cover material Erosion Control (RIP RAP) Impervious Liner Leak Detection System

Partial Mixed Aerated Lagoon Satisfy oxygen requirement but not mixing requirements Wyoming requirements loading for treatment Cells less than 2 lbs/1000 cft Minimum D.O. = 2 mg/l HDT = 7 day for treatment Storage to provide 30 days overall HDT * Optional Stream Outfall Preliminary Treatment ***** * * * Aerated Cell No. 1 Aerated Cell No. 2 Storage Cell Polishing Cell * *

Partial Mixed Aerated Lagoon Upgrade of overloaded lagoons Reduce the footprint of lagoon to fit specific location Good for BOD removal less effective in other areas Add oxygen to shorten treatment time

Mixing and Oxygenation How much is the question Complete mix is considered Hp/MG Partial mix is considered 5-15 Hp/MG Complete mix with air scfm/sft fine bubble Complete mix with air scfm/sft course bubble BOD lb needs lbs of oxygen Lb Ammonia to nitrate needs 4.6 lbs of oxygen Mechanical aerators lbs of O 2 /hp-hour Diffused aeration lbs O 2 /hp-hour

Oxygen 1.Flow (mgd) x BOD (mgll) x 8.34 lbs/gal = lbs BOD/Day 2.Flow (mgd) x TKN (mgll) x 8.34 lbs/gal = lbs TKN/Day Oxygen (lbs/day) = 1.5 (lbs BOD/Day) (lbs TKN/Day) at 20 C & 1 ATM Air contains approximately 21% oxygen and weighs approximately lbs/cft

Oxygen (cont) Standard oxygen required equal lbs of oxygen to meet the applied load Actual oxygen required accounts for temperature, wastewater characteristic, and dissolved oxygen residual AOR = Alpha (SOR (beta x C sw – C) (t-20) Cs alpha = oxygen-transfer correction factor alpha = (surface aerator) alpha = (diffused aerator) Beta = salinity correction factor B = Typical C SW = Oxygen saturation for water at temperature & elevation Cs = oxygen saturation at 20 C and sea level (9.17 mg/l) C = residual dissolved oxygen t = temperature in Degrees C Elev. Cheyenne Wyoming ~ 6,100 ft elevation

Oxygen (cont) Use corrected lbs of oxygen to mechanical Use corrected lbs of oxygen to convert to cubic feet of air per minute at standard condition SCFM Size blowers based on SCFM corrected for – Temperature – Elevation – Humidity – Corrected conditions call ICFM or inlet cubic feet per minute

Oxygen (cont) Wyoming requirements – Surface aerator intervals 200 ft or less – Minimum of two aerators – Transfer oxygen needed with larger unit out of service – Diffused aerator minimum of two blowers – Transfer oxygen needed with largest blower out of service

Treatment Cell No. 1 Treatment Cell No. 2 Storage Cell Polishing Cell Partially Mixed Aerated Lagoon

Complete Mixed Aerated Lagoon Preliminary Treatment ***** * * * Wyoming requirements Max loading treatment cell No lbs/ BOD /1000 cft HDT = 1.5 days Max loading treatment cell No. 2 2lbs BOD/1000 cft HDT-7days DO level 2.0 mg/l minimum Increase storage to 30 days overall Treatment Cell No. 1 Treatment Cell No. 2 Storage Cell Polishing Cell Out Fall

Complete Mix Lagoons Almost activated sludge Significant amount of equipment If we would add a clarifier and return it, it would be activated sludge Requires frequent solids removal depending upon the size of the storage cell Higher loading Same oxygen calculations a partial mixing

Complete Mix Lagoon No sedimentation in process basin Mixing = 30 – 50 hp/mg = 0.15 – 0.3 scfm/ft 2 fine bubble = 0.5 – 1.0 scfm/ft 2 course bubble Wyoming Requirement — Surface aerator interval 200 ft or less (much less) — Minimum two aerators — Transfer oxygen needed with largest aerator out of service — Diffused aeration minimum of two blowers — Transfer oxygen needed with largest blower out of service

Treatment Cell No. 1 Treatment Cell No. 2 Storage Cell Polishing Cell Complete Mixed Aerated Lagoon

EQUIPMENT

Aeration Equipment Broadly classified into two categories based on location of operation: – Surface Aerators – Sub-surface Aerators Parameters used to measure system performance – OTR – Oxygen Transfer Rate, lb O2/h – SOTR – Standard Oxygen Transfer Rate STP*), lb O2/h – OTE – Oxygen Transfer Efficiency, % – SOTE – Standard Oxygen Transfer Efficiency STP), % – SAE – Standard Aeration Efficiency STP), lb O2/KW.h STP – Standard Temperature & Pressure of 70 ⁰ F & 1 atm

Surface Aerators Surface aerators, as the name indicates, are stationed (floating or fixed) and operate at the water surface Types include: – Floating Mechanical Aerators – Aspirators – Reel Type/Paddle Wheel Aerators Aerators operating on renewable sources are further classified as: – Solar powered Aerators – Wind powered Aerators Surface aerators usually tend to have moderate OTRs and low SAEs Oxygen transfers rates of 1.5 to 3 lbs O 2 / Hp-hr

Floating Mechanical Aerators Uses the principle of agitation and turbulence Uses electrical energy to create turbulence Can be moored in different ways to suit needs

Floating Mechanical Aerators

Aspirators Utilizes both air injection and mechanical mixing Units can be operated to suit the needs: – Angle of mixing and air injection can be changed – Dentrification mode – only mechanical mixing – Nitrification mode– Both mechanical mixing and air injection No additional blower(s) required for operation Can operate effectively during winter

Aspirators Installation at Moorhead, MN

Aspirators

Paddle Wheel Aerators Installation at Austin, TX Utilizes paddle wheels to agitate the surface of the water Typically operates at lower speeds compared to other aerators Induces more horizontal mixing than vertical Can be installed as floating or fixed units

Paddle Wheel Aerators

Solar Powered Aerators/ Mixers Utilizes solar power Water is drawn from the depths and circulated at the surface For very deep waters (>10ft), multiple pipes/draft tubes may be used Installation at Richmond, CA Installation at Guatemala

Solar Powered Aerators

Wind Powered Aerators/ Mixers Utilizes wind power Can operate at wind speeds as low as 5 mph Backup motors can be used during low wind speeds Installation at Holkham, UK

Wind Powered Aerators

Subsurface Aerators/ Mixers Subsurface aerators are installed below the water surface and they operate by forcing/diffusing air bubbles through the water. Types of subsurface aerators are: – Coarse Bubble Systems – Fine Bubble Systems – Submersible Mechanical Aerators With the exception of subsurface mechanical aerators, all subsurface aerators require air blowers, air blowers are further classified into: – Centrifugal blowers – Positive displacement blowers

Coarse Bubble Systems Coarse bubble systems use pores/orifices to release air bubbles in the order of 50 mm (50,000 micron) in size Offers high OTR and low SAE (2 to 5.5 Kg O 2 /KWh) Considered low maintenance Types of coarse bubble systems are: – Air spargers – Broadband diffusers (chicken feeders) – Static tube aerators – Snap cap/permacap aerators – Non-clog diffusers

Coarse Bubble Systems Static Tube Aerators Permacap Diffusers BroadbandDiffusers

Coarse Bubble Systems Air Sparger System Tideflex Diffusers

Coarse Bubble Systems

Fine bubbles are created by passing compressed air through a porous material (diffusers)or by mechanically shearing (e.g. Jet Aeration) large air bubbles into smaller ones – Jet aerators usually have lower SAEs, in the order of 2.6 – 4 lb O2 /Hp-hr – Fine pore diffusers have higher SAEs, in the order of 8 – 11 lb O2 /Hp-hr – Fine pore diffusers require periodic cleaning Based on diffuser geometry, fine bubble diffusers can be classified into: – Tube Diffusers – Membrane Diffusers – Ceramic Diffusers Fine Bubble Systems Biolac® process utilizes fine bubble diffusion

Fine Bubble Systems Fine Bubble Tube Diffuser Jet Aeration Fine Bubble Ceramic Diffuser Fine Bubble Diffuser Video

Biolac® Process Activated sludge process invented by Parkson co Required mixing and suspension achieved at 4 CFM/1000 Cu.Ft Diffusers are suspended above the floor by means of hanging chains Biolac ® Process

Submersible Mechanical Aerators Self aspirating Blower assistance can be provided for deeper installations Installation at Groveland, FL Installation at Lake City, TN

Submersible Mechanical Aerators – Video

Blowers All sub surface aerators (except submersible aerators) require blowers Blowers are compressors that operate at low pressures Offer limited “turn up” or “turn down” and are energy hungry Classified into: – Positive Displacement (PD) Blowers - constant flow, variable pressure – Centrifugal Blowers – constant pressure, variable flow Smaller plants use PD blowers or centrifugal blowers Larger plants use centrifugal blowers

Centrifugal Blowers Newer centrifugal blowers can be throttled using variable inlet guide vanes and variable outlet diffusers Have an optimum range and outside of it their efficiency drops Single Stage Centrifugal Blower Multi Stage Centrifugal Blower

PD Blowers Due to mode of operation, PD compression is not as efficient as centrifugal blowers, but achieve higher pressures for same air flow Variable Freq. Drives (VFDs) can be used to vary the flow With VFDs, flow is proportional to blower rpm Positive Displacement Blower

QUESTIONS

Thank You Kevin Rood, P.E., BCEE