EVEG 3400 Water and Wastewater Treatment Flashcards

Metropolitan Board of Works - 1847

All houses ordered to close cesspits and connect to sewers which empty to the Thames River

Metropolitan Board of Works - 1858

The Great Stink; London sewage system authorized by Parliament to be led by Joseph Bazalgette; 81 miles of enclosed brick sewer mains, 1100 miles of street sewers, 4 pump stations and Northern and Southern outfall downstream of London

Metropolitan Board of Works - 1865

Project officially "opened"

Metropolitan Board of Works - 1875

Project completed

Water and Sanitation in Chicago - 1861-1866; 1872

tunnel built two miles out into Lake Michigan to collect drinking water; in 1872, capacity of the tunnel is too small for the growing population; sewage collecting ending up in epidemics of cholera and dysentery

Treatment objectives from 1900 to 1970

(1) remove suspended and floatable material (2) treat biodegradable organics (3) eliminate pathogens; ad hoc basis

Establishment of US EPA

December 2, 1970 after 1969 Cuyahoga River Fires and 1962 Silent Spring by Rachel Carson

The Clean Water Act, 1972

Federal Water Pollution Control Act Amendments, to restore and maintain chemical, physical, and biological integrity of the nation's waters; establishes NPDES (National Pollution Discharge Elimination System)

Minimum Standards for Secondary Treatment: three major effluent parameters

(1) biodegradable organics (measured as biological oxygen demand, BOD), (2) total suspended solids (TSS), (3) hydrogen ion concentration (pH)

Water Quality Act 1987

strengthens federal water quality regulations, adds substantial penalties for violators, amends solids control program to emphasize identification and regulation of toxic pollutants in sewage sludge, funds state and US EPA studies for defining point and non-point sources of pollution, establishes new deadlines for compliance

Biosolids Regulation

1993, 40 CFR Part 503; regulates use and disposal of biosolids from wastewater treatment plants (limitations on metals, pathogens, vector attraction); development of clean sludge

Total Maximum Daily Load (TMDL)

the maximum amount of a pollutant a water body can receive and still meet water quality standards (mass balance)

2000, Section 303 (d) of the CWA (took effect in 2002)

Designed to protect ambient water quality, watershed-based water quality management plan (point and non-point sources of pollution); shift focus from tech-based to preservation

Sources of wastewater

domestic, industrial, infiltration/inflow (I/I), stormwater

Sources of wastewater-domestic

discharged from residences and from commercial, institutional, and public facilities; primary objective of domestic wastewater treatment is the reduction of BOD

Sources of wastewater-industrial

discharged from industrial processes; usually permitted via pre-treatment programs

Sources of wastewater-infiltration/inflow

water that infiltrates into the collection system through cracks and leaks

Sources of wastewater-stormwater

runoff from stormwater and snowmelt; can cause combined sewer overflow (CSO)

Domestic Wastewater

combo of feces, urine, and graywater (showers, dishwashers...)

Physical properties: color, odor, solids (total and suspended)

Chemical constituents: organic and inorganic

Biological constituents: bacteria, viruses, helminths, protozoa

Organic matter in wastewater

determines degree of biological treatment necessary; 40-60% proteins, 25-50% carbohydrates, 8-12% oils and fats, also urea; measured in aggregate

3 tests of organic matter

biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC)

Biological oxygen demand (BOD)

amount of dissolved oxygen consumed by microorganisms during the biochemical oxidation of organic (carbonaceous BOD) and inorganic (ammonia) substrate

Empirical BOD-5 test

measure of the amount of oxygen consumed by a mixed population of heterotrophic bacteria in the dark and 20 degrees Celsius over 5 days

BOD (mg/L) = (Do-D5)/P

when seeding not needed; Do=initial dissolved oxygen (mg/L); D5=DO at day 5 (mg/L); P=decimal volumetric faction of wastewater utilized (ratio of volume of wastewater to total volume of water incubated (wastewater + dilution water))

If the dilution water is seeded with an inoculum, we have to account for BOD of seeded material BOD (mg/L) = [(Do-D5)-(Bo-B5)f]/P

Bo=initial DO of seed control (mg/L)

B5=final DO of seed control (mg/L)

f=ratio of seed in sample to seed in control (% seed in D1/%seed in B1)

Carbonaceous BOD

if nitrification is inhibited, measured BOD is carbonaceous BOD; measure of oxygen demand exerted by oxidizable carbon in sample

Limitations of BOD

(1) high concentration of active, acclimated seed bacteria required (2) pretreatment may be required for toxic water samples (3) only biodegradable organics are measured (4) doesn't have stoichiometric validity (strictly empirical) (5) long period of time required to perform tests

Uses of BOD

(1) determine quantity of oxygen required to treat organic matter present (2) determine appropriate sizing of wastewater treatment facilities (3) measure efficiency of treatment process (4) determine compliance with NPDES permits

Chemical Oxygen Demand (COD)

amount of oxygen required to completely oxidize to CO2 the organic material in wastewater using potassium dichromate in an acid solution; BOD slightly lower than COD because some organic matter cannot be degraded biologically, test done in about 2.5 hours

Total Organic Carbon (TOC)

measured by oxidation of organic matter with heat and oxygen followed by measurement of CO2 produced with an infrared analyzer; takes 5-10 minutes to complete

Typical BOD/COD for untreated municipal WW:

0.3-0.8

Total solids (TS)

residue remaining after a wastewater sample has been evaporated and dried at a specified temperature (103-105 C)

Total suspended solids (TSS)

portion of the TS retained on a filter with a specified pore size, measured after being dried at a specific temperature (105 C); most commonly used filter has a nominal pore size of 1.58 mirometers

Total Dissolved Solids (TDS) (TS-TSS)

solids that pass through TSS filter and then evaporated and dried at a specified temperature; TDS is comprised of colloidal and dissolved solids

Colloidal solids

particles small enough to remain suspended in liquid due to thermal motion (0.01-1 micrometer)

Settleable solids

measured by standard test using Imhoff cone; volume of solids in millimeters that settle after a specified time period (~1 hr); 60% solids are settleable

Turbidity

measure of the light scattering properties of a solution containing suspended and colloidal particles; often used as a rapid method for measuring TSS

Inorganic nonmetallic constituents-pH

hydrogen ion concentration is an important water quality parameter for both natural and wastewaters; typically 6-9

Inorganic nonmetallic constituents- chlorides

various sources, human excrement ~6g/person/day

Inorganic nonmetallic constituents- alkalinity

"buffering" capacity; ability to resist changes in pH; hydroxides, carbonates, bicarbonates (calcium and magnesium); measured by titration

Inorganic nonmetallic constituents-other

nitrogen, phosphorus, sulfur

Inorganic nonmetallic constituents- gases

oxygen, H2S, methane, odors

Nitrogen

essential building block for protein synthesis and biomass, reduction of nitrogen to control algal growth in receiving waters is often necessary

Total nitrogen

composed of organic nitrogen, ammonia, nitrite, nitrate

Organic nitrogen

content measured using Kjeldahl method (boiling and digestion); total Kjeldahl nitrogen is same besides boiling (ammonia kept and included)

Phosphorus

essential for growth of algae, crops, other bio organisms; fractions exist in particulate and dissolved

Orthophosphates

available for biological metabolism

Polyphosphates

can undergo hydrolysis to orthophosphates but this process is slow

Metallic constituents

trace quantities can be found from industrial and domestic sources; cadmium, chromium, copper, iron, lead, manganese, mercury, nickel, zinc (many are priority pollutants and can be toxic)

Other compounds of concern in wastewater

disinfection byproducts, pesticides and agricultural compounds, antibiotics and personal care products

Biological wastewater constituents

bacteria, archaea, fungi/yeast, protozoa, helminths, rotifers, algae, viruses, infectious agents, human pathogens

Levels of wastewater treatment

preliminary, primary, secondary, tertiary

Preliminary wastewater treatment

removal of large solids such as sticks, floatables, grit, and grease that may damage downstream equipment

Primary wastewater treatment

removal of a portion of the suspended solids (settleable solids) and organic matter

Secondary wastewater treatment

removal of biodegradable organic matter (biological treatment, activated sludge); can also include nutrient removal (nitrogen, phosphorus)

Tertiary wastewater treatment

removal of residual suspended solids after secondary (filtration) and typically includes disinfection

Preliminary Treatment: screening

first unit process; goes from coarse to fine screening, have to be cleaned

Preliminary treatment: grit removal

removal to protect downstream equipment; separation accomplished in separate grit chambers designed to physically separate heavier particles from lighter ones; three types: horizontal-flow, aerated, vortex grit chambers

Primary treatment: primary sedimentation

remove readily settleable solids, reduce suspended solids content; occurs in primary clarifier with quiescent flow conditions to allow suspended solids to settle to the bottom, clean and remove settle solids

Secondary treatment: biological treatment goals

(1) oxidize dissolved and particulate biodegradable constituents into acceptable end products (2) incorporate suspended and colloidal solids into a biological floc (biomass) (3) transform or remove nutrients (4) remove specific trace organic constituents

Role of microorganisms in secondary treatment

(primarily bacteria) remove dissolved and particulate CBOD via oxidation

Activated sludge

aerobic, suspended growth process, CBOD removal and nitrification, adding oxygen to the WW activities

3 components of activated sludge process

(1) reactor in which microorganisms are kept in suspension and aerated (2) liquid solid separation unit (secondary clarifier) after biological treatment to remove biological floc from suspension by settling (3) recycle system for returning settled solids from (2) to (1)

Return activated sludge (RAS)

allows separation of hydraulic retention time and solids retention time; provides independently controlled feed of biomass into aeration basin for biological treatment and shrink footprint of WW facilities

Important factors for design and control of RAS

type of process and reactor configuration, relevant kinetic relationships, SRT and loading, sludge production rate, oxygen and nutrient input required, sludge settling characteristics, effluent characteristics

Loading: food to microorganism ratio F/M = (QSo)/(VX)

Q=flow rate into the reactor

So=substrate concentration in the input flow

V=volume of reactor

X=biomass concentration in reactor

Biological nitrogen removal (denitrification)

required before discharge, anoxic and suspended growth process, classified by location of anoxic reactor relative to nitrification step (preanoxic, post anoxic, two stage and Bardenpho process)

Key considerations of denitrification

primary substrate source and nitrate reduction kinetics

Enhanced biological phosphorus removal (Phoredox process)

provide anaerobic zone prior to aeration to give phosphate accumulating organisms (can use volatile fatty acids as a substrate more efficiently than heterotrophs) a competitive advantage and allow their biomass to increase for uptake of phosphorus under aerobic conditions

Liquid solid separation with secondary clarifier

(1) gravity settling to remove 99.5% of the mixed liquor TSS from treated effluent (2) thickening of the settled sludge to reduce volume; critical to performance of activated sludge process

Membrane bioreactor (MBR)

located at end of aeration basin; separate solids and liquids instead of a secondary clarifier

Tertiary treatment goals

further removal of organic and inorganic suspended solids, colloidal particulate matter, dissolved organic compounds, dissolved inorganic compounds, biological elements using (1) mass transfer separation or (2) chemical and biological transformation

Mass transfer techniques in tertiary treatment

absorption, adsorption, distillation, filtration, reverse osmosis, etc.

Depth filtration

sand filter supported by gravel layer; further reduces suspended solids and conditions effluent for disinfection

Disinfection

chemical and biological transformation using oxidant (reduction of potentially harmful pathogens); chlorine and ozone primarily used

Key design considerations of disinfection

turbidity and CT value required for log reduction

Sludge from typical treatment train: preliminary treatment

screenings and grit; typically disposed of in landfill

Sludge from typical treatment train: primary treatment

primary sludge from primary clarifier to digestion

Sludge from typical treatment train: secondary treatment

waste activated sludge from secondary clarifier to digestion

Anaerobic digestion

biological wastewater treatment with redox reactions involving the use of electron acceptor other than oxygen

Anaerobic digestion uses

digestion of waste sludge; often used for pretreatment of high strength organic wastes prior to discharge to municipal wastewater collection system

Anaerobic digestion: fermenters

hydrolysis and acidogenesis (breakdown complex organics in short-chain volatile fatty acids)

Anaerobic digestion: acetogenesis

creation of acetate

Anaerobic digestion: methanogens

creation of methane (CH4)

Advantages of anaerobic digestion:

can be net energy producers (methane can be used to produce power), energetics lead to biomass production 6-8 times lower than activated sludge, less nutrients required due to low biomass production, higher volumetric organic loading rates than aerobic processes

Disadvantages of anaerobic digestion:

longer startup time, sensitivity to toxic compounds, operational stability, odors and corrosive off gases, need to add alkalinity to maintain pH in correct range

Anaerobic digestion considerations

characteristics of wastewater, variation, wastewater strength and temperature, alkalinity, nutrients, inorganic and toxic organic compounds, gas production

Anaerobic digestion gas production:

methane from organic carbon, CO2 from organic carbon, ammonia from nitrogen, hydrogen sulfide from sulfer

Biosolids

sludge that has been stabilized to meet criteria of US EPA 40 CFR 503 and can be used beneficially

Sludge content

organic carbon, nutrients, pathogens, metals, toxic organics

Class A sludge

safe for use by general public; <100 MPN fecal coliforms/g total dry solids of <3 MPN salmonella spp./4g total dry solids

Class B sludge

agricultural land or solid waste disposal

Surface disposition

limits established for pollutants based on distance of disposition site from property line

Preliminary sludge processing

grinding, screening, degritting, blending, storage

Preliminary sludge processing: grinding

large material cut or sheared into small particles (protect equipment)

Preliminary sludge processing: screening

alternative to grinding

Preliminary sludge processing: degritting

further grit removal may be required

Preliminary sludge processing: blending

blend primary, secondary sludge to produce uniform feed

Preliminary sludge processing: storage

uniform feed flow rate

Thickening

procedure to increase solids content of sludge by removing some of the liquid portion