Wastewater 101 Agenda. What is wastewater? Classroom. Field Trip. Wastewater characteristics Wastewater treatment processes. CUC treatment plants

Transcription

1 Introduction to Wastewater Treatment For Water Operators August 11, 2010 CNMI Division of Environmental Quality Wastewater 101 Agenda Classroom Wastewater characteristics Wastewater treatment processes Solids treatment and disposal CUC treatment plants Field Trip & Commonwealth Utilities Corporation Water used for any purposes picks up contaminants and requires disposal. What is wastewater? Sources of wastewater: Domestic Sources of wastewater: Industrial 1

2 Sources of wastewater: stormwater Why do we treat wastewater? Prevent the spread of disease Protect the environment and down stream users For our purposes: WASTEWATER CONTAMINANTS: 5 categories: Stuff that sinks Stuff that floats Stuff that is dissolved Stuff that is suspended Pathogenic microorganisms Useful microorganisms Pathogenic organisms Microorganisms Microorganisms Useful microorganisms Bacteria Protozoa Algae higher life forms BACTERIA: our workhorses 3 types, based on Oxygen use: Aerobic Need oxygen Fast, good for wastewater treatment Low odor Anaerobic No oxygen Slow, not as good for wastewater treatment, good for digestion of sludge (septic tanks) Stinky! Facultative Can live with or without oxygen Used in wastewater lagoons 2

3 OXYGEN: a crucial parameter Strength of wastewater is measured by BIOCHEMICAL OXYGEN DEMAND Septic sewage: No oxygen. Black in color Rotten egg odor: hydrogen sulfide Corrodes steel, dissolves concrete Very difficult to treat Keeping sewage fresh: Quick delivery Aeration (O 2 ) OXYGEN Source: Milton Village, UK Biological Oxygen Demand (BOD) The quantity of oxygen used in the biological oxidation of organic matter 5 days 20 C Ranges: Raw domestic sewage: mg/l Primary effluent: mg/l Secondary effluent: mg/l Wastewater treatment 3 basic treatment processes: Physical treatment Preliminary treatment PRIMARY treatment Biological treatment SECONDARY treatment ADVANCED SECONDARY and TERTIARY treatment Chemical Treatment Disinfection Wastewater treatment Effluent HEAVY DUTY Influent Ancillary processes: Solids treatment stabilization dewatering 3

4 Wastewater Treatment Preliminary treatment: The process of grinding material that can clog equipment, removing rags with screens, and the removal of grit. Premilinary treatment is commonly a part of primary treatment. Primary treatment: The first major (sometimes only) treatment in a sewage treatment works. This process takes place in a rectangular or circular tank and allows those substances in wastewater that readily settle or float to be separated from the water being treated. Wastewater Treatment Secondary treatment: A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. Usually a biological treatment process. Tertiary treatment: Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical processes include chemical treatment and pressure filtration. Headworks Preliminary Treatment Grinding comminutors Preliminary Treatment Source: Muffin Monster channel grinders Source: Grinding barminutors Preliminary Treatment Preliminary Treatment Grit Channel Muffin Monster Chain & Rake Monster Source: Source: Indiana University of Pennsylvania 4

5 Preliminary Treatment Aerated Grit Chamber Flow Measurement Parshall Flumes (with ultrasonic height measurements no stilling wells) Source: T.L.M. Engineers (G.S.H.) Ltd Source: Indiana University of Pennsylvania Primary Treatment: Primary Treatment Comes after preliminary treatment Circular or rectangular tanks Removes settleable & floatable solids Also known as sedimentation or clarification Many small plants do not use primary treatment, or use microscreens as equivalent Primary Treatment Theory of settling: Settled particle size depends on detention time Longer time = smaller (& more) particles removed Detention time depends on size of clarifier and flow INFLUENT ZONE SETTLING ZONE SLUDGE EFFLUENT ZONE Primary Treatment Rectangular Clarifiers Primary Treatment Rectangular Clarifiers Source: Source: 5

6 Primary Treatment Rectangular Clarifiers Circular Clarifiers Primary Treatment MECHANICAL DRIVE Source: Source: Circular Clarifiers Primary Treatment On-Site Treatment Systems Septic Tank SCUM BOX BAFFLE HYDRAULIC SLUDGE REMOVAL Source: EFFLUENT WEIR Source: Clearford Industries Inc. Source: On-Site Treatment Systems Septic Systems may achieve secondary treatment quality: Septic System in limestone: SEPTIC SYSTEM WELL Both physical and biological treatment Anaerobic digestion of solids in tank Solids require removal every 3 years or more Biological treatment of dissolved and suspended contaminants in soil L I M E S T O N E G R O U N D W A T E R CNMI Division of Environmental Quality 2005 BGB 6

7 REVIEW Types of Secondary Treatment Processes Primary Treatment Plants: Grinding, grit removal, primary sedimentation Secondary Treatment Plants: Primary plus biological treatment Uses aerobic bacteria to reduce the organics and develop a sludge that can be settled easily Sludge = biomass Fixed Film Media Lagoons & Wetlands Activated Sludge Trickling Filters Trickling Filters Process: Fixed Film Media Aerobic biological slime does the work Media: River rock (usually 10 feet or less in depth) Crushed stone Synthetic media (20 feet or more in depth) Malakal Wastewater Treatment Plant - Palau Source: CNMI DEQ Malakal Wastewater Treatment Plant - Palau Source: CNMI DEQ 7

8 Zoogleal film Trickling Filters Malakal Wastewater Treatment Plant - Palau Source: CNMI DEQ Trickling Filters Theory Removes nonsettleable suspended & dissolved organic matter Biological slime on filter media consumes organics Produces a settleable sludge Zoogleal film Bacteria, protozoa, fungi, algae Trickling Filters Piping & Recirculation RBCs Rotating Biological Contactors Same treatment method as trickling filter Popular small plant option RBCs Rotating Biological Contactors Multiple Contactors Source: 8

9 Lagoons Ponds or Lagoons Ponds or Lagoons Treatment Process Symbiotic relationship between bacteria and algae Night time: Bacteria use D.O. made during day; emit CO2 Good to check D.O. before sunrise if too low, supplemental air may be required Ponds or Lagoons Operating zones (Facultative pond) Anaerobic bottom 20% Facultative Aerobic top 80% Ponds or Lagoons Classification of ponds Ponds or Lagoons Classification of ponds (continued) Aerobic Ponds Shallow (< 4 feet deep) D.O. throughout depth of pond Usually requires additional air Surface aerators or diffusers Facultative Ponds Most common type 4 to 6 feet deep Aerated Facultative Ponds Used when not enough land available, or high BOD wastes Reduces stabilization time from 8-12 weeks, to 1-3 weeks Can accept wastes with 10x organic loading than regular ponds Anaerobic Ponds 12 feet deep or more Very odorous Can be effective, especially with some industrial wastes 9

10 Constructed Wetlands Free water surface (FWS) wetland: Two types: Free water surface (FWS) wetlands Easier to construct & operate Requires most land Attracts birds (bad near airport) Breeds mosquitos Vegetated Submerged Bed (VSB) Higher removal efficiencies Requires less land Fewer mosquito & bird problems Malakal Wastewater Treatment Plant, Palau Vegetated Submerged Bed (VSB) wetland: Vegetated Submerged Bed (VSB) wetland: Source: EPA Marpi Landfill Facility, Saipan, CNMI Activated Sludge - Description Activated Sludge - Description A suspended film, aerobic, secondary, biological treatment process Favorable conditions maintained to create an active biological mass called activated sludge Consists of one or more tanks called aeration basins, followed by secondary clarifier Contents of aeration basins called mixed liquor measured by mixed liquor suspended solids - MLSS Activated sludge process Air Influent Aeration Tank Clarifier Effluent Return Activated Sludge Waste Activated Sludge 10

11 Activated Sludge - Description Activated Sludge - Process Balancing food & microorganisms Operator must achieve balance between incoming waste ( food ) and sludge mass (microorganisms) Imbalance can cause sludge that will not settle properly The basic cycle: Microorganisms pick up food in aeration tank Microorganisms digest food in clarifier & rest Microorganisms returned to aeration basin to eat again Activated Sludge - Process As bacteria grow: They secrete a slime layer that contains polymers Polymers help food stick to bacteria Also helps bacteria stick together in clumps of food & bacteria agglomeration Activated Sludge Process Control Efficiency of process depends on high quality sludge Settles well microorganisms allowed to digest & rest before return Sludge age = time sludge is in the system Source: University of California at Los Angeles Activated Sludge - Process Young Sludge under the microscope: Increase in number of ciliates & stalked ciliate protozoa, feeding on bacteria Activated Sludge - Process Young Sludge & Settling Does not settle easily bulking sludge Tends to fill clarifier & go over weirs straggle floc Source: University of California at Los Angeles 11

12 Activated Sludge - Process Normal growth phase Bacterial energy more evenly divided between reproduction & movement Slime layer decreases in size, contains more polymer Under microscope: An abundance of free swimming & stalked ciliates, a few rotifers Activated Sludge - Process Normal sludge appearance Light to dark brown Small amount of crisp, white foam Source: Environmental Leverage, Inc. Activated Sludge - Process Normal Sludge & Settling Agglomerates immediately upon discharge to clarifier Settles evenly Forms a discrete interface near the top Activated Sludge - Process Old sludge Under microscope: Very little protozoa activity Maybe some rotifers & worms Releases clear water as it settles, like a sponge Source: Environmental Leverage, Inc. Activated Sludge - Process Old Sludge: settling Settles quickly but does not agglomerate well Small particles remain & are carried over into effluent pin floc Activated Sludge - Process Old Sludge: denitrification rising sludge Source: Environmental Leverage, Inc. Source: Environmental Leverage, Inc. 12

13 Activated Sludge Process Control Settleometer & sludge age Activated Sludge Process Control Controlling the activated Sludge Process The operator has control of: Rate of sludge wasting Sludge age Rate of return sludge MLSS Dissolved Oxygen in aeration basin Not much control equipment limited Just keep above 1 mg/l Activated Sludge - Aeration Systems Purpose of aeration: Provides dissolved oxygen for microorganisms Mixes mixed liquor Activated Sludge - Aeration Systems Diffusers: on bottom of tank Fine Bubble Diffusers: Two types of aeration systems: Diffused air Mechanical aeration systems Activated Sludge - Aeration Systems Coarse Bubble Diffusers: Activated Sludge - Aeration Systems Blowers 2 types: lobe (most common) centrifugal Source: Aerzen USA Corp. 13

14 Activated Sludge - Aeration Systems Mechanical Aeration Systems At surface of tank Turbine Aerator: Activated Sludge - Aeration Systems Aspirator Aerator Four types of mechanical aeration systems: Propeller Aspirator Turbine Jets Source: MAOF Madan Source: Environmental Expert.com Activated Sludge - Aeration Systems Jet Aerator Activated Sludge - Aeration Systems Brush Aerator Used in oxidation ditch plants Source: Mixing Systems, Inc. Source: CST Wastewater Solutions Race Track configuration Source: Mixing Systems, Inc. Secondary Clarifiers Very similar to primary clarifiers, with a few changes: Rectangular box trough used in center of tank to increase weir length (reduce weir loading) Or, larger diameter tank Sludge removal mechanisms different, depending on treatment process Activated Sludge Varieties Extended Aeration Contact Stabilization Nitrification/Denitrification Sequencing Batch Reactors Sequencing Batch Reactors Package Plants Membrane Bio Reactors (MBRs) Source: 14

15 Membrane Biological Reactors (MBR) Membrane Biological Reactors (MBR) Activated Sludge system NOT an R/O system Microfilter replaces secondary clarifier: VACUUM PUMP 1 3 psi Source: Zenon Technologies Source: Hitachi Plant Technologies Ltd. Source: King County, WA Membrane Biological Reactors (MBR) Membrane Biological Reactors (MBR) Advantages Significantly smaller than other systems Tolerant of higher MLSS: 15,000 to 25,000 mg/l (8,000 to 10,000 most cost effective) Higher hydraulic loadings (shorter detention time) Longer MCRT = less sludge production Can operate with low D.O Nitrification/Denitrification a common addition High quality effluent Turbidity Bacteria TSS BOD Source: Wastewater Engineering Metcalf & Eddy, 2003 Disadvantages Expensive Limited Membrane life Replacement every 3 years Complicated operation Often automated Need to control membrane fouling Source: Wastewater Engineering Metcalf & Eddy, 2003 Disinfection GOAL OF DISINFECTION: To destroy all disease causing organisms in order to protect downstream users of the water HOW DO WE MEASURE EFFECTIVENESS: Fecal Coliform bacteria Methods of Disinfection Lime Kills pathogens by raising ph to 11.5 or higher Most commonly used for: screening waste Digested sludge Honeybucket waste Sewage spills 15

16 Ozone O 3 disinfection Petro Stopping Center on-site wastewater treatment system, Kingman, AZ: Methods of Disinfection Ultraviolet (UV) disinfection Rota Resort wastewater treatment & reuse plant: Methods of Disinfection Photo: Ozone Water Systems, Inc. Photo: CNMI DEQ Methods of Disinfection Chlorine Most common in U.S. Most commonly used for: Drinking water systems Wastewater disinfection Swimming pools Contact Chamber Maximize contact time Minimize turbulence Plug flow minutes needed Chlorine Facilities Available as gas, liquid, or powder Chlorine Facilities Dechlorination Why dechlorinate? Chlorine is deadly to fish & other aquatic life Can kill small fish at 6 µg/l (parts per billion) 2 common dechlorination processes: Sulfur dioxide Gas; same equipment as standard gas chlorine system Sodium bisulfate Liquid; same equipment as hypochlorite system standard chemical feed pump Photo: City of Denver, CO 16

17 Other Uses of Chlorine Odor reduction Prevention of corrosion by hydrogen sulfide Control of undesirable bacteria at plant Prevent sewage from becoming septic Sludge Treatment & Disposal Sludge treatment & disposal = solids handling 3 Steps: Stabilization to reduce pathogens & organic content Conditioning & Dewatering to reduce volume Disposal to prevent contamination Five basic groups: Primary sludge Biological sludges Scum Screenings Lagoon sludge Types of Sludge STABILIZATION: Aerobic Digestion Occurs in open, aerated tank called digester Common part of activated sludge plant Stabilization accomplished by aerobic microorganisms Best for secondary sludges requires about 30 days 1 to 3% solids Aerobic Digestion Aerobic Digestion Continuous operation Illustrtion: Kimon Zentz, ARC Publications Illustrtion: Kimon Zentz, ARC Publications 17

18 Anaerobic Digestion Occurs in airtight tank called digester Tank is heated Stabilization accomplished by anaerobic microorganisms Produces methane gas can be used for heating tank, generating electricity Works for both secondary and primary sludges, and scum requires about days 3 to 4% solids Anaerobic Digestion Digester: Photo: City of Santa Fe, NM Anaerobic Digestion Boilers: Anaerobic Digestion Gas flare: Heat exchangers: Photo: City of Santa Fe, NM Photo: City of Santa Fe, NM Lime Stabilization Solids Conditioning & Dewatering Lime stabilization tank: Dewatering: Purpose: Remove water from sludge Reduce handling costs Photo: City of Santa Fe, NM 18

19 Solids Conditioning & Dewatering Drying Beds Solids Conditioning & Dewatering Drying Beds FILL TO 18 INCHES Illustrtion: Kimon Zentz, ARC Publications Photo: Humboldt University Solids Conditioning & Dewatering Vacuum Filter Solids Conditioning & Dewatering Solid-Bowl Type Centrifuge installation Photo: pollutionsolitions-online.com Solids Conditioning & Dewatering Screw Press Solids Conditioning & Dewatering Belt Filter Press Photos: Goble-Samspon Associates Inc. Photos: Andritz AG 19

20 Sludge disposal Sludge disposal Photo: City of Columbia, MO Dedicated land disposal site: Subsurface injection equipment: Photo: City of Santa Fe, NM Photo: City of Santa Fe, NM Photo: Region of Huronia Environmental Services, Ltd. Sludge disposal Sludge disposal Disposal in Landfills: Liquids restriction in federal solid waste regulations minimum 10% solids No Free Liquids measured by paint filter test Sludge placed into conical paint filter PASS: no drained liquid after 5 minutes FAIL: any free liquid in container below filter Paint Filter free liquids test EPA SW-846 method 9095 Sludge disposal Other disposal methods: Sludge lagoons Provides some further treatment, but disposal still required Incinerators Expensive Permitting & monitoring a serious challenge Ash disposal a problem - metals Sludge disposal Other disposal methods: Composting Can provide a useful product Soil amendment, not fertilizer Must be carefully monitored & controlled to meet regulatory requirements 131 F (55 C) for 3 consecutive days to kill pathogens Requires mixing with a carbon source Wood chips, shredded paper, etc. 20

21 Sludge disposal Regulatory Agencies Composting Palau EQPB USEPA Permits Clean Water Act NPDES Permits National Pollutant Discharge Elimination System Inspection & enforcement DEQ Permits Water Quality Standards Section 401 Water Quality Certification Inspection & enforcement Operator certification Operator Certification: All OWTS under responsible charge of operator with proper level cert. All personnel making process control / system integrity decisions Must be available for each operating shift High school diploma Operator Certification Table 1 - Years of Experience Required for Certification at each Classification Level Classification OIT* Class 1 Class 2 Class 3 Class 4 Level Wastewater Treatment Wastewater Collection *OIT means Operator-In-Training. An operator certified at the OIT level is a certified operator, but can not be the supervising operator having responsible charge over an OWTS because the certification level is not at the classification level of the OWTS. Photo: 21