Module 4: Fundamentals of Wastewater Treatment

Transcription

1 Wastewater Operatr Certificatin Training Mdule 4: Fundamentals f Wastewater Treatment Revised 2016 This curse includes cntent develped by the Pennsylvania Department f Envirnmental Prtectin (Pa. DEP) in cperatin with the fllwing cntractrs, subcntractrs, r grantees: The Pennsylvania State Assciatin f Twnship Supervisrs (PSATS) Gannett Fleming, Inc. Dering Cnsulting Grup Penn State Harrisburg Envirnmental Training Center

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3 MODULE 4: FUNDAMENTALS OF WASTEWATER TREATMENT Tpical Outline Unit 1 Preliminary Treatment: Screening, Degritting, Cmminutin & Pre-Aeratin I. General Overview II. III. IV. Screening A. General Overview B. Bar Screens and Racks Grit Remval A. General Overview B. Grit Remval Devices Cmminutin A. General Overview B. Cmminutrs V. Pre-Aeratin A. Purpses Unit 2 Primary Treatment: Sedimentatin and Fltatin I. Purpse f Primary Treatment A. Sedimentatin B. Fltatin C. Types f Units II. Principles f Operatin A. Clarifiers B. Fltatin C. Specialized Prcesses Bureau f Safe Drinking Water, Department f Envirnmental Prtectin Wastewater Treatment Plant Operatr Training i

4 MODULE 4: FUNDAMENTALS OF WASTEWATER TREATMENT Unit 3 General Overview f Bilgical Secndary Treatment I. Trickling Filters A. Prcess Descriptin B. Majr Cmpnents C. Classificatin f Filters D. Abnrmal Cnditins II. III. IV. Rtating Bilgical Cntactr A. Prcess Descriptin B. Principles f Operatin C. Abnrmal Cnditins Activated Sludge A. Activated Sludge Prcess B. Principles f Operatin C. Classificatin f Prcesses D. Aeratin Methds E. Abnrmal Cnditins Waste Treatment Pnds A. Prcess Descriptin B. Pnd Classificatins C. Abnrmal Cnditins Bureau f Safe Drinking Water, Department f Envirnmental Prtectin Wastewater Treatment Plant Operatr Training iii

5 Unit 1 Preliminary Treatment: Screening & Degritting Learning Objectives Explain the general purpse f the Preliminary Treatment Prcess. Explain the purpse f Screening, Grit Remval and Pre-aeratin. Indicate the differences between manually and mechanically cleaned racks and screens. Define differences between screening and cmminutin. Describe safe dispsal f screenings and grit. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-1 Wastewater Treatment Plant Operatr Training

6 SCREENING The Preliminary Treatment Prcesses Almst everything finds its way int sewers. Preliminary treatment is nrmally the first step in prcessing wastewater. It prtects pumps and ther equipment by remving harmful matter. Plants may r may nt utilize all f the preliminary equipment discussed in this sectin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-2 Wastewater Treatment Plant Operatr Training

7 SCREENING General Overview Screening is ne f the first methds f wastewater treatment. Remves r reduces size f slids which may interfere with dwnstream prcesses. Designed t remve flating material and larger suspended slids. Generates head lss. Bar Screens & Racks Manually Cleaned Vertical r inclined bars spaced at equal intervals acrss influent channel. Bar spacing ranges frm ½ t 1 ½, widely used. Usually incrprates hrizntal area at tp fr draining. Cleaned with a rake with tines that fit between bars. Debris raked t tp f rack. Placed in cntainer, fr prper dispsal, after draining. Requires frequent attentin. As debris cllects n bars it blcks channel. Figure 1.1 Manually cleaned bar screen 1 Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-3 Wastewater Treatment Plant Operatr Training

8 SCREENING Mechanically Cleaned Uses mechanically driven rake t traverse rack. Intermittent r cntinuus peratin. Requires less peratr attentin than thse manually cleaned. Screenings usually discharged directly t cntainer. Figure 1.2 Mechanically cleaned bar screen 2 Screenings Dispsal Screenings material is very ffensive. Stinks. Attracts vermin and flies. May cntain rganic material. Dispsal in accrdance with envirnmental regulatins r permit requirements. Generally landfilled. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-4 Wastewater Treatment Plant Operatr Training

9 GRIT REMOVAL Grit General Overview Grit is the heavier mineral matter fund in wastewater. Sand, cinders, eggshells, etc. Will nt decmpse. Causes excessive wear n pumps and ther mechanical equipment. Can clg pipes r accumulate in tanks and digesters. Shuld be remved as sn as pssible after reaching plant. Shuld remve grit but nly a minimum f rganic suspended slids. Grit Channels Grit Remval Devices Velcity cntrlled at apprximately 1.0 ft per secnd (fps) regardless f flw t allw grit t settle. Cleaning the grit frm the channel is imprtant t maintain grit remval efficiency. Cleaning the channel helps t keep the flw velcity f wastewater lw. As mre grit builds up, the velcity f wastewater increases and remval efficiency decreases. Velcity cntrl devices: Device usually lcated abve channel invert t prvide fr grit strage. Length f chamber sufficient t allw settlement f the smallest particle desired t be remved. Manually cleaned usually nly small plants r as a by-pass fr mechanically cleaned channel. Mechanically cleaned chain and flight scrapers. Grit remved n a daily basis. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-5 Wastewater Treatment Plant Operatr Training

10 GRIT REMOVAL Aerated Grit Chamber Tank with slping bttm and hpper. Injected air lwers specific gravity f fluid resulting in better grit settlement. Lighter rganic particles are suspended by the air and pass thrugh tank. Grit mves alng bttm t hpper by rlling actin created by air additin. Mst frequently fund at activated sludge plants where air is available. Figure 1.3 Aerated grit chamber 3 Cyclne Separatrs Cmmnly used fr grit washing. May be used as a grit remval device. Figure 1.4 Cyclne Separatr 4 Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-6 Wastewater Treatment Plant Operatr Training

11 GRIT REMOVAL Grit Washing Remves excess rganic material frm the grit and returns it t prcess stream. Grit remval generally by screw cnveyr t strage cntainer. Figure 1.5 Grit Washer 5 Grit Dispsal Dispsal in accrdance with envirnmental regulatins r permit requirements. Generally landfilled; hwever, ther ptins include incineratin and land applicatin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-7 Wastewater Treatment Plant Operatr Training

12 COMMINUTION General Overview During the Cmminutin Prcess Cuts and shreds retained material t apprximately ¼ size. Material nt remved frm flw. Material remved by sedimentatin later in the treatment prcess. Hard materials, such as wd and plastic, are nt shredded and must be remved peridically, either mechanically r manually. Rags, clth and ther fibrus material may clg the cmminutin device. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-8 Wastewater Treatment Plant Operatr Training

13 COMMINUTION Cmminutrs Cut and Shred Materials Cnsist f revlving cutter blades munted in a sltted screen. Slids t large t pass thrugh the screen slts are cut int pieces by rtating blades. Installed directly in flw channel. Usually prvided with by-pass barscreen. Figure 1.6 Cmminutr 6 Figure 1.7 Cmminutr with by-pass screen 7 Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-9 Wastewater Treatment Plant Operatr Training

14 COMMINUTION What is the purpse f preliminary treatment as it relates t screening and cmminutin? List at least tw differences between screening and cmminutin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-10 Wastewater Treatment Plant Operatr Training

15 PRE-AERATION Purpses Imprve grit remval efficiency. Freshen wastewater. Remve gases and add xygen. Prmte grease fltatin. Aid cagulatin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-11 Wastewater Treatment Plant Operatr Training

16 KEY POINTS AND REFERENCES Key Pints Preliminary treatment is nrmally the first step in prcessing wastewater and prtects pumps and ther equipment by remving harmful matter. Preliminary treatment includes screening/cmminutin, grit remval and pre-aeratin. Screening designed t remve flating material and larger suspended slids. Grit is the heavier mineral matter fund in wastewater. Grit channel velcity cntrlled at apprximately 1.0 ft per secnd (fps) regardless f flw t allw grit t settle. Screenings and grit are generally landfilled, hwever, grit may als be incinerated r land applied. Pre-aeratin tends t increase the verall efficiency f slids and BOD remval. References 1 Larry Bristw, Chapter 4: Racks, Screens, Cmminutrs and Grit Remval. In Operatin f Wastewater Treatment Plants Vlume I, (Sacrament, CA: Califrnia State University, Sacrament Fundatin, 1998), p Bristw, p Bristw, p Bristw, p Bristw, p Bristw, p Bristw, p.75 8 Bristw, p.81. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 1-12 Wastewater Treatment Plant Operatr Training

17 Unit 2 Primary Treatment: Sedimentatin and Fltatin Learning Objectives Explain sedimentatin and fltatin principles. List factrs that indicate when a clarifier is nt perfrming prperly. Use mathematical frmulas t slve fr detentin time, weir verflw, surface lading, and slids lading. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-1 Wastewater Treatment Plant Operatr Training

18 PURPOSE OF PRIMARY TREATMENT Sedimentatin Sedimentatin is the remval f heavier slids and grit. Fltatin Fltatin is the remval f lighter slids and grease. Types f Units There are Three Types f Units in the Primary Treatment Prcess Primary Clarifiers Fltatin units. Cmbined Sedimentatin-Digestin units. In yur wn wrds, define sedimentatin. In yur wn wrds, define fltatin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-2 Wastewater Treatment Plant Operatr Training

19 PRINCIPLES OF OPERATION Clarifiers Settling Characteristics Settling characteristics are dependent n three factrs: Specific Gravity. Weight f particle in relatin t weight f equal vlume f water. Particle size and shape. Relatinship f dwnward mvement f particle t frward flw velcity. Factrs Which Influence Settling Characteristics Temperature, detentin time, shrt circuits, weir verflw rate, surface settling rate, and slids lading rate all influence the settling characteristics f wastewater. Temperature. Water expands, r becmes less dense, as temperature increases (abve 4 C) and cntracts, r becmes denser, as temperature decreases. Oppsite is true belw 4 C. Generally, as water temperature increases settling rate increases; as temperature decreases s des settling rate. As water becmes denser, density differential between water and slid particles becmes less and particles settle slwer. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-3 Wastewater Treatment Plant Operatr Training

20 PRINCIPLES OF OPERATION Detentin Time. Wastewater must remain in sedimentatin basin lng enugh fr slid particles t fall t sludge layer. Generally 2 t 3 hurs. Detentin time calculatin based n flw and tank dimensins. If the flw is less than r exceeds that fr which the sedimentatin basin was designed, the basin will nt perfrm prperly. Frmulas Detentin Time, hr. = Tank Vlume, cu ft x 7.5 gal/cu ft x 24 hr/day Flw, gal/day Rectangular Tank Vlume, cu ft = Length, ft x Width, ft x Height (Depth), ft Area f Circle, ft 2 = (0.785) (Diameter 2 ) r (π) (Radius 2 ) Nte: π = 3.14 Circular Tank Vlume, cu ft = Area x Height (Depth), ft s, Circular Tank Vlume, cu ft = (0.785 x (Diameter, ft) 2 x Height (Depth), ft) r ((3.14) x (Radius, ft) 2 x Height (Depth), ft) Sample 2.1: What is the detentin time when the flw is 3.0 millin gallns per day (MGD), r 3,000,000 gal/day and Tank dimensins are 60 feet lng by 30 feet wide by 10 feet deep? Sample 2.2: What is the detentin time when the flw is 2.5 millin gallns per day (MGD), and Circular clarifier dimensins are 60 ft in diameter by 12 ft deep? Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-4 Wastewater Treatment Plant Operatr Training

21 PRINCIPLES OF OPERATION Shrt Circuits. Higher frward flw velcity in sme areas decreases detentin time in thse areas. Als caused by turbulence. Even dispersal f influent flw acrss entire tank crss sectin prmtes even flw velcity in all sectins f tank. Weir Overflw Rate. Prper WOR is necessary t prevent high velcities at discharge. Generally 10,000 t 20,000 gallns per day per ft f weir (gpd/ft). Calculatin is based n flw and length f the weir and is expressed as gallns per day per square ft as indicated in the frmula belw. Frmulas Weir Overflw, GPD/ft = Flw Rate, GPD Length f Weir, ft Length f Circular Weir = 3.14 x Weir Diameter, ft Prblem 2.1: Cmpute the weir verflw rate fr a circular clarifier with a 75 ft diameter verflw weir when 3.5 MGD is the flw rate int the unit. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-5 Wastewater Treatment Plant Operatr Training

22 PRINCIPLES OF OPERATION Surface Lading Rate (r Surface Settling Rate). Directly relates t slids remval efficiency. Generally 300 t 1200 gallns per day per tank surface area (gpd/sq ft). Calculatin based n flw and liquid surface area. Frmula Surface Lading Rate, GPD/sq ft = Flw Rate, GPD Area, sq ft Prblem 2.2: Cmpute the Surface Lading Rate when flw int a rectangular clarifier 40 feet wide by 110 feet lng by 12 feet deep is 5.0 MGD. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-6 Wastewater Treatment Plant Operatr Training

23 PRINCIPLES OF OPERATION Slids Lading. The amunt f slids, which can be remved fr each unit f clarifier surface area. Typical slids ladings: Primary clarifiers generally nt a cnsideratin. Secndary clarifiers 12 t 30 lbs/day/sq ft. Disslved air fltatin 5 t 40 lbs/day/sq ft. Sludge thickening 5 t 20 lbs/day/sq ft. Calculatin based n flw, suspended slids cncentratin, and liquid surface area. Frmulas Slids Applied, lbs/day = Flw, MGD x Cnc., mg/lx 8.34 lbs/gal Slids Lading, lbs/day/sq ft = Slids Applied, lbs/day Surface Area, sq ft Prblem 2.3: Cmpute the slids lading at which the clarifier is perating when a circular clarifier with a diameter f 125 feet is perating with a frward flw f 6.0 MGD and a return sludge flw f 2.0 MGD. The MLSS is mg/l. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-7 Wastewater Treatment Plant Operatr Training

24 PRINCIPLES OF OPERATION Indicatrs f Clarifier Operating Prblems Flating Sludge (Bulking). Black, drus septic wastewater entering clarifier. Black, drus septic wastewater leaving clarifier. Scum in clarifier effluent. Sludge hard t remve frm hpper. Lw sludge slids. Miscellaneus prblems: Surging flw. Slime grwth. Excessive crrsin. Mechanical prblems: Chain/drive prblems. Seal prblems. Bearing prblems There are several factrs that affect prper clarifier peratin. List as many as yu can belw. What are sme indicatrs f clarifier prblems? List several belw. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-8 Wastewater Treatment Plant Operatr Training

25 PRINCIPLES OF OPERATION Fltatin General Wastewater always cntains sme suspended slids that have neutral buyancy they neither settle nr flat. Particles can be flcculated with air r chemical cagulants and either settled (if heavy) r flated using small air bubbles. Vacuum Fltatin Aerated t saturatin with disslved air. Flws int vacuum chamber, which pulls ut the air in the frm f small bubbles. Pressure Fltatin Aerated under pressure. Pressure released disslved air released in the frm f small bubbles. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-9 Wastewater Treatment Plant Operatr Training

26 PRINCIPLES OF OPERATION Cmbined Sedimentatin-Digestin Units Specialized Prcesses Sedimentatin ccurs in upper unit. Slids (sludge) fall t lwer unit fr digestin. Septic Tanks Usually fr individual hmes r small cntributing ppulatin. Operatin similar t cmbined sedimentatin-digestin units. Slids must be remved peridically and dispsed f at a wastewater treatment plant r septage prcessing facility r land applied. Liquid effluent usually dispsed f undergrund by leaching thrugh sil. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-10 Wastewater Treatment Plant Operatr Training

27 KEY POINTS Key Pints Primary treatment cnsists f sedimentatin and fltatin. Sedimentatin is the remval f heavier slids (and any remaining grit nt previusly remved) and generally takes place in clarifiers r cmbined sedimentatin-digestin units. Fltatin is the remval f grease and ther lighter slids which will nt settle. The mst imprtant functin f a clarifier is t remve as much settleable and flatable material as pssible. Detentin time based n flw and tank vlume; generally 2 t 3 hurs. Mst cmmn factrs influencing settling characteristics are temperature, detentin time, shrt circuits, weir verflw rate, surface settling rate and slids lading. Indicatrs f clarifier perating prblems include bulking sludge, scum in the clarifier effluent, sludge hard t remve frm hpper and lw sludge slids just t name a few.. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 2-11 Wastewater Treatment Plant Operatr Training

28 Unit 3 General Overview f Bilgical Secndary Treatment Learning Objectives List fur bilgical secndary treatment prcesses. Explain the principles f the trickling filter prcess. Identify the different types f trickling filters. Explain the principles f the rtating bilgical cntactr (RBC) prcess. Explain the principles f the activated sludge prcess. List the three waste treatment pnd classificatins and explain the principles f each. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-1 Wastewater Treatment Plant Operatr Training

29 TRICKLING FILTERS Prcess Descriptin Bilgical Prcess - Fixed Film System (Trickling Filter) Wastewater sprinkled ver a fixed media prduces a slime (bilgical film) that cat media surface. Film cnsists f bacteria, prtza, and fungi that feed n waste rganics. Film requires cntinuus supply f disslved xygen. Adequate ventilatin required. Natural ventilatin. Frced air. Media vids must be kept pen. Flw is usually intermittent. Quantity f film prduced is cntrlled by the available fd. Increases as rganic lad increases until maximum effective thickness. During peratin, film will slugh ff. Effluent recirculatin increases treatment efficiency. Trickling Filter Prcess Raw Wastewater Preliminary Treatment Primary Clarifier Filter Pump Statin Wet Pit Distributr Trickling Filter Filter Underflw Secndary Clarifier Influent Primary Effluent Recirculatin Secndary Clarifier Chlrine Cntact Basin Plant Effluent Slids Handling Waste Slids TRICKLING FILTER PROCESS FLOW SCHEMATIC Figure 3.1 Trickling filter prcess flw schematic Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-2 Wastewater Treatment Plant Operatr Training

30 TRICKLING FILTERS Figure 3.2 Trickling filter 1 Majr Cmpnents Distributin system Distributes wastewater t tp f media. Fixed distributin system. Intermittent liquid dsing t prvide rest perids. Rtating distributr. Media Rck. Apprximately 35% vid space. Plastic media. Apprximately 95% vid space. Underdrain Cllects filtered water. Prvides ventilatin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-3 Wastewater Treatment Plant Operatr Training

31 TRICKLING FILTERS Classificatin f Filters Standard Rate Media. Usually rck media 6 t 8 ft depth. Hydraulic lading f 25 t 100 gal/day/sq ft. Organic lading f 5 t 25 lbs/day/1000 cu ft. High Rate Media. Rck 6 t 8 ft depth. Synthetic 15 t 30 ft depth. Hydraulic lading. Rck media t 1000 gal/day/sq ft. Synthetic media 350 t 2100 gal/day/sq ft. Organic lading. Rck Media - 25 t 100 lbs/day/1000 cu ft. Synthetic Media - 50 t 300 lbs/day/1000 cu ft. Generally all high rate trickling filters use recirculatin. Rughing Filters High rate filter with very high rganic lading. 100 t ver 300 lbs/day/1000 cu ft. Used t reduce rganic lading t subsequent xidatin prcesses. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-4 Wastewater Treatment Plant Operatr Training

32 TRICKLING FILTERS Abnrmal Cnditins Pnding Results frm a lss f pen area in media bed. Causes Excessive rganic lading. Lack f primary clarificatin. Imprper media selectin. Accumulated fibrus material filling media vids. Odrs Aerbic prcess n serius drs shuld exist. Ful drs indicate anaerbic cnditins. Filter Fly Tiny, gnat-sized fly (psychda). Mst frequently fund in lw-rate filters. Cntrl Increase recirculatin rate. Apply apprved insecticides. Fld filter. Results in pr effluent quality. Shuld be carefully mnitred. Apply chlrine dse. Slughing Excessive film lss is an indicatin that there are prblems with the bilgical activity within the filter media. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-5 Wastewater Treatment Plant Operatr Training

33 TRICKLING FILTERS What are the perating principles f the Trickling Filter Prcess? Explain them belw. Nte: Trickling Filters are discussed in further detail in Mdule 20. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-6 Wastewater Treatment Plant Operatr Training

34 ROTATING BIOLOGICAL CONTACTOR Figure 3.3 Rtating bilgical cntactr 2 Prcess Descriptin Bilgical Prcess - Fixed Film System (Rtating Bilgical Cntactr) A fixed film system similar t trickling filters. Media Media is mved thrugh wastewater. Rtating shaft surrunded by plastic discs called media. Slime grws n plastic media. As media drum rtates, media is alternately submerged in wastewater and expsed t air. Cvered Generally cvered fr reasns relating t weather cnditins. Prtect slime frm freezing. Prevent rain frm washing slime frm media. Avid expsure t sunlight Prevents grwth f algae. Prevents deteriratin f media. Prvides sme prtectin fr peratrs frm sun, rain, snw, wind, etc... during maintenance. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-7 Wastewater Treatment Plant Operatr Training

35 ROTATING BIOLOGICAL CONTACTOR Prcess Operating Cnditins Figure 3.4 Rtating bilgical cntactr prcess flw schematic Principles f Operatin Perfrmance is affected by hydraulic ladings and temperatures belw 55 F. Typical perating and perfrmance characteristics. Hydraulic lading. BOD remval 1.5 t 6 gpd/sq ft f media. Nitrgen remval t 1.8 gpd/sq ft f media. Organic lading. Sluble BOD 2.5 t 4 lbs BOD/day/1000 sq ft. BOD remval 80 t 95 percent. Effluent Ttal BOD 10 t 30 mg/l. Effluent Sluble BOD 5 t 15 mg/l. Effluent NH3-N 1 t 10 mg/l. Effluent NO3-N 2 t 7 mg/l. Pretreatment Requirements Usually prceeded by screening, grit remval, and primary settling. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-8 Wastewater Treatment Plant Operatr Training

36 ROTATING BIOLOGICAL CONTACTOR Abnrmal Cnditins Decreased Treatment Efficiency Pssible causes. Temperature belw 55 F. Large variatins in flw r BOD ladings. Unusually high r lw ph. Bimass Slughing Pssible causes. Influent cntaining txic r inhibitry substances. Unusual variatin in flw and/r rganic lading. Snails Nt a prblem in RBCs used fr BOD remval. Generally ccur in plants prviding nitrgen remval. Snail shells may clg pipes and pumps. Snail cntrl Chlrinatin. Increase ph t 10 kills snails withut harm t micrbial grwth. Nte: Rtating Bilgical Cntactrs (RBCs) are discussed in further detail in Mdule 21. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-9 Wastewater Treatment Plant Operatr Training

37 ACTIVATED SLUDGE Prcess Descriptin Activated Sludge Prcess Uses micrrganisms t speed up decmpsitin f wastes. Micrrganisms feed and grw n waste particles in the wastewater. As rganisms grw and reprduce, mre and mre waste is remved. Mass f rganisms needs a steady balance f fd and xygen. Principles f Operatin Prcess Descriptin Oxidatin and remval f sluble r finely divided suspended materials. Aerbic rganisms stabilize material by partial xidatin. Prcess frms carbn dixide, water, and sulfate and nitrate cmpunds. Remaining slids changed t a frm that can be settled and remved during sedimentatin. Prcess Objectives Cnversin f disslved and suspended material t settleable slids. Oxidatin f rganic waste. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-10 Wastewater Treatment Plant Operatr Training

38 ACTIVATED SLUDGE Classificatin f Prcesses Cmplete Mix Cntents f aeratin tank are cmpletely mixed. Organic lading. Mixed Liqur Suspended Slids (MLSS) 2000 t 5000 mg/l. Primary Effluent Raw Wastewater Preliminary Treatment Primary Clarifier Aeratin Tank r Reactr Secndary Clarifier Chlrine Cntact Basin Plant Effluent Return Activated Sludge Waste Slids Slids Handling Waste Activated Sludge CONVENTIONAL ACTIVATED SLUDGE SCHEMATIC (COMPLETE MIX) Figure 3.5 Cmplete Mix Activated Sludge Schematic Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-11 Wastewater Treatment Plant Operatr Training

39 ACTIVATED SLUDGE Cntact Stabilizatin Capture f waste material and digestin f that material is dne in different aeratin tanks. Organisms capture waste material in the cntact tank r reactr. Settled rganisms are returned t the reaeratin tank t digest the captured material. Organic lading. Mixed Liqur Suspended Slids (MLSS) 1500 t 2000 mg/l. Sludge wasted t maintain prper prcess cntrl. Raw Wastewater Preliminary Treatment Aeratin Cntact Tank r Reactr Secndary Clarifier Chlrine Cntact Basin Plant Effluent Waste Slids Slids Handling Waste Activated Sludge Reaeratin Tank r Reactr Return Activated Sludge CONTACT STABILIZATION ACTIVATED SLUDGE SCHEMATIC Figure 3.6 Cntact stabilizatin activated sludge schematic Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-12 Wastewater Treatment Plant Operatr Training

40 ACTIVATED SLUDGE Extended Aeratin Cnsists f aeratin and sedimentatin. Usually n primary settling. Organic lading. Mixed Liqur Suspended Slids (MLSS) t 5000 mg/l. Prduces less sludge than ther prcesses. Sludge wasting is still necessary t maintain prper prcess cntrl. Raw Wastewater Preliminary Treatment Aeratin Tank r Reactr Clarifier Chlrine Cntact Basin Plant Effluent Return Activated Sludge Waste Slids Slids Handling Waste Activated Sludge EXTENDED AERATION ACTIVATED SLUDGE SCHEMATIC Figure 3.7 Extended aeratin activated sludge schematic Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-13 Wastewater Treatment Plant Operatr Training

41 ACTIVATED SLUDGE Sequencing Batch Reactrs An activated sludge treatment arrangement where aeratin and secndary clarificatin are perfrmed in a single tank n the basis f time. Sequential cntrl stages. Fill wastewater is intrduced int the tank. Aeratin - the cntents f the tank are aerated. Settle the aeratin is discntinued and the tank cntents are allwed t settle. Draw the clarified supernatant is remved. Oxidatin Ditches Cntinuus channel extended aeratin prcess. Usually n primary settling. Mixing and aeratin prvided by brush rtr assemblies. Organic lading. Mixed Liqur Suspended Slids (MLSS) 2000 t 6000 mg/l. Rtr (Typ) Level Cntrl Weir Raw Wastewater Preliminary Treatment Oxidatin Ditch Final Clarifier Chlrine Cntact Basin Plant Effluent Return Sludge Return Sludge Pumping Waste Sludge Slids Handling Waste Slids OXIDATION DITCH SCHEMATIC Figure 3.8 Oxidatin ditch schematic Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-14 Wastewater Treatment Plant Operatr Training

42 ACTIVATED SLUDGE Aeratin Methds Mechanical Aeratin Mechanical aeratin devices agitate the water surface t cause spray and waves s that xygen can be absrbed frm the air. Types f mechanical aeratin devices Paddle wheels Mixers Rtating brushes Flating aeratrs Figure 3.9 Mechanical aeratin device 3 Diffused Aeratin Air frm a blwer system is discharged int the wastewater. Diffusers break up the air stream int fine bubbles. The smaller the bubbles the greater the xygen transfer. Figure 3.10 Air diffuser 4 Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-15 Wastewater Treatment Plant Operatr Training

43 ACTIVATED SLUDGE Abnrmal Cnditins Slids Carryver in Effluent Return sludge rate ut f balance with prcess requirements. Sludge nt settling in clarifier (bulking). Lw slids level. Lw disslved xygen. Strng, stale, septic influent. Clarifier sludge blanket level t high. Aeratin rate t high r t lw. Odrs Aeratin rate t lw. Return sludge rate t lw. Pr husekeeping. Faming/Frthing Faming usually caused by t lw a slids level. Frthing usually caused by t lng a slids retentin time. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-16 Wastewater Treatment Plant Operatr Training

44 ACTIVATED SLUDGE List 5 frms f the activated sludge treatment prcess. What tw aeratin methds are used t prvide xygen t the activated sludge treatment prcess? Why might slids be fund in the secndary clarifier effluent f an activated sludge treatment plant? Nte: Activated Sludge Prcesses are discussed in further detail in Mdules and 8. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-17 Wastewater Treatment Plant Operatr Training

45 PONDS AND LAGOONS Prcess Descriptin Pnds & Lagns Heavy slids settle. Decmpsed by bacteria. Lighter suspended material brken dwn by suspended bacteria. Disslved nutrient material (nitrgen and phsphrus) used by green algae. Sme wastewater liquid evaprated frm pnd surface. Advantages fr Smaller Systems Expensive equipment nt required. Ecnmical t cnstruct. Treatment is equal r superir t sme cnventinal prcesses. Adaptable t changing ladings. Cnsumes little energy. Serves as wildlife habitat. Pses few sludge handling and dispsal prblems. Mst truble-free f any treatment prcess prvided a cnsistently high quality effluent is nt required. Pnd Limitatins Odrs. Large land area required. Treatment efficiency is dependent n climatic cnditins. May cntaminate grundwater. High effluent suspended slids levels. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-18 Wastewater Treatment Plant Operatr Training

46 PONDS AND LAGOONS Pnd Classificatins Aerbic Have disslved xygen distributed thrughut the cntents practically all the time. Usually require supplemental xygen surce. Mechanical aeratin. Diffused aeratin. Anaerbic Withut disslved xygen. Treatment depends n fermentatin f sludge at the pnd bttm. Highly efficient in stabilizing rganic waste. Odr prblems. Facultative Mst cmmn type in use because it is almst impssible t maintain cmpletely aerbic r anaerbic cnditins thrughut the pnd all f the time. Upper prtin (supernatant) is aerbic. Bttm layer is anaerbic. Algae supply mst xygen t upper prtin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-19 Wastewater Treatment Plant Operatr Training

47 PONDS AND LAGOONS Abnrmal Cnditins Scum Cmmn characteristic f pnds. Usually greatest in spring. Water temperature warms. Bilgical activity resumes. Usually wind actin dissipates scum. In absence f wind r in sheltered areas, scum must be brken up by ther means. Hand rakes. Water jets. Outbard mtrs. If nt, will dry n tp and becme crusted. Reduces sunlight. Oxygen prductin by algae is reduced. Odr prblems result. Odrs Generally caused by verlading resulting in anaerbic cnditins. At times caused by prcess upsets. Remedy is t increase disslved xygen. Recirculatin frm aerbic units. Use f aeratrs. Chlrinatin. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-20 Wastewater Treatment Plant Operatr Training

48 PONDS AND LAGOONS Weeds and Insects Weed Cntrl Essential part f pnd husekeeping. Mdern herbicides and sil sterilants make task easier. Edge weeds prmte msquit breeding and scum accumulatin. Weed grwth hinders pnd circulatin. Weed Cntrl Methds Water depth greater than 3 feet. Remve first year grwth by hand. Drwn weeds by raising water level. Lwer water level and cut r burn weeds. Use riprap alng bank. Lime pnd. Use herbicides as last resrt. Insect Cntrl Types f insects: Msquites. Shrimp-like animals. Chirnmid midges. Cntrl with pesticide applicatins. What are the three types f waste treatment pnds? List them belw. Nte: Pnds and Lagns are discussed in further detail in Mdule 19. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-21 Wastewater Treatment Plant Operatr Training

49 KEY POINTS & REFERENCES Key Pints Fur bilgical secndary treatment prcesses include activated sludge, trickling filters, RBC s and Pnds and Lagns. Trickling filters and rtating bilgical cntactrs (RBCs) are fixed-film prcesses Activated sludge is a suspended grwth prcess Pnds and Lagns are classified as aerbic, anaerbic and facultative. Facultative pnds and lagns are the mst cmmn type in use due t the difficulty f maintaining cmpletely aerbic r anaerbic cnditins thrughut the pnd at all times. References 1 Larry Bristw, Chapter 6: Trickling Filters. In Operatrs f Wastewater Treatment Plants Vlume I, (Sacrament, CA: Califrnia State University, Sacrament Fundatin, 1998), p Richard Wick, Chapter 7: Rtating Bilgical Cntactrs. In Operatrs f Wastewater Treatment Plants Vlume I, (Sacrament, CA: Califrnia State University, Sacrament Fundatin, 1998) p Jhn Brady and Rss H. Gudgel, Chapter 8: Activated Sludge. In Operatrs f Wastewater Treatment Plants Vlume I, (Sacrament, CA: Califrnia State University, Sacrament Fundatin, 1998), p Brady, p.216. Bureau f Safe Drinking Water, Department f Envirnmental Prtectin 3-22 Wastewater Treatment Plant Operatr Training