Wastewater Operator

Certification Information

Terms CWA – Clean Water Act passed in 1972 NPDES – National Pollutant Discharge

Elimination System – permit good for 5 years (must reapply 180 day prior to expiration date)

PE – Population Equivalency – how plants are designed – design for 20 years future growth

PE, capita = (Flow, MGD)(BOD, mg/L)(8.34lb/gal) 0.17 lbs/BOD/capita/day

* An operator should be present during construction to become familiar with the plant, including the equipment, machinery and the operation of it. Provides you with the opportunity to relate your plant to the drawings.

Overview Collection Systems Rain Water I & I Wastewater Flow Preliminary Treatment Secondary Treatment Solids Handling Tertiary Treatment Laboratory Safety

Rain Water Inflow and Infiltration (I&I)

Enters collection system through cracks and holes in pipes, open cleanouts, cross connections, manholes, #1 cause – leaking pipe joints

Can cause hydraulic overload at WPCF, decreased capacity due to sand and grit accumulation, lift station pump failures and overflows, increased operating costs

Accounts for 30% of wastewater flow

Liftstations Must maintain a velocity of 2ft per

second to stop solids from settling and H2S from forming, when unable to reach that velocity build a lift station – lift flow to a higher elevation where it can again flow by gravity

Has forced ventilation to prevent toxic gas fume build-up

Most common is air-lift pump

Wastewater Contents Domestic waste is 99.9% water Contains pathogenic (disease causing)

bacteria, viruses, cysts that can cause Typhoid, Cholera, Dysentery, Polio and Hepatitis

Floatable – floats to surface (scum & grease) Settleable – settles to bottom Suspended – won’t float or settle (same weight

as water) Dissolved – such as food dye Colloidal – finely dissolved that remains in

suspension causing turbidity (cloudiness) due to its size and electrical charge

Raw Wastewater Solids Composition

Wastewater is 99.9% water

Dissolved solids makes up the highest percent of

solids

Dissolved and Suspended Solids make

up Total Solids

Preliminary Treatment To remove material that can damage or plug

up equipment – grit, rags, plastics, sticks, etc. Flow Equalization / Surge Basins Bars Screens / Bar Racks Moving or Rotating Screens Shredding / Grinding Grit Chambers / Channels Odor Control Pumps (not considered treatment, but located

in head works of plant)

Pumps

Cavitation The formation of partial vacuums in a

liquid by a swiftly moving solid body (as a propeller) or by high-intensity sound waves

The pitting and wearing away of solid surfaces (as of metal or concrete) as a result of the collapse of these vacuums in surrounding liquid

Impeller vane damage

Sedimentation and Floatation

Sedimentation and Floatation happens in both Primary and Secondary (or final) clarifiers

Purpose – to remove settleable and floatable solids from raw ww– Organic solids have high oxygen demand

(BOD) Primary Clarifiers follows grit removal

– Velocity 1.0 to 2.0 feet per minute Secondary Clarifier follows any

biological treatment

Primary VS Secondary Sludge

Primary is denser (heavier)

Primary is darker in color (dark chocolate)

Effluent (liquid on top) is gray in color

Secondary is lighter is color (milk chocolate)

Secondary is mainly microorganisms (lighter)

Effluent is clear

Rotating Biological Contactor (RBC)

Mechanical or air operated drive units rotate the media through wastewater

Biomass is attached to the moving media (attached growth)

40% of the media is immersed in wwCovered

RBCs

Sequencing Batch Reactors (SBR)

Treatment is carried out in a single tank through sequencing stages

Handles periodic flows or batch dumps with ease

Especially well suited for industries– Automatic control through Programmable Logic

Control (PLC)– Stable due to high sludge age and long

retention time– Less costly to build – no need for sludge

handling – can be sent directly to drying beds or composting process

BOD/N/P The ratio of biochemical oxygen demand to

nitrogen to phosphorus should be 100/5/1. If the organic loading rate increases the appropriate N & P need to be added at a point where the incoming wastewater is highly mixed to provide nutrients needed by the microbes. The pounds of N & P required per day will be about 10% of the organic solids (dry weight) produced every day. The P required will be one-fifth of the N requirement. The amount of P & N added daily are equal to the difference between the quantity required and the quantity in the waste. Aqueous ammonia or anhydrous ammonia may be added to provide the nitrogen. Phosphate fertilizers or phosphoric acid from a waste acid facility may be used to provide P.

Conventional Activated Sludge

Detention time – 4 to 8 hours (6 hrs) Sludge Age – 3.5 to 7 days MLSS – 1,000 to 3,000 mg/L DO – 2 to 4 mg/L or ppm

– High (>5.0) shear floc, waste energy– Low (<0.5) lead to bulking, poor effluent

Mixing– Distributes oxygen evenly– Brings food in contact with microorganisms– Prevents septic conditions on bottom of tank

Nitrification CycleHeterotrophic Bacteria – Carbonaceous Stage Get energy from the oxidation of organic materials Common bacteria in wastewater This bacteria is responsible for denitrification Form floc – fast growing

Autotrophic Bacteria – Nitrogenous Stage Get energy from inorganic materials or from the

sunlight (some are algae) Are the nitrifiers Sulfide oxidizing organisms Do not form floc – slow growing

Sludge Floc

Floc under electron microscope

Good floc

Young – weak lacy

Old – dark and falling apart

Notice the large thing running through this –

that is a filament. The small rice shaped objects

are the floc forming bacteria (heterotrophic).

You can clearly make out each floc particle and see pretty clear liquid outside of the floc. There is very

little filament outside of the floc and the

floc is “roundish” in shape.

Floc looks like a lace doily, almost no clear water between the

floc particles, not way for this to settle. Acts more like a

parachute.

Floc is almost see through, very fragile

looking. Sharp edges in comparison to the Good

Floc. Filaments are starting to reach outside

the floc particles.

Ponds

Primary Pond or Lagoon

Secondary or Two

Stage Pond

Tertiary or Three Stage

Pond

This is how it works

Feed the Primary Digester with Primary or Secondary (WAS)

Sludge

Heat and Mix the Primary Digester –

called primary because it is the first

digester – creates gas

Sludge is transferred

(pumped) from the Primary Digester to

the Secondary Digester

No Heating or Mixing – allow solids to settle and liquids (supernatant) to float to the top – some

gas production

Chemical Stabilization

Lime– Addition of lime adds to the overall

quantity of solids that must be disposed

– High costs Chlorine

– pH will drop <3.5 (acidic)– Lime may be added before dewatering

Sludge Incineration Use dewatered sludge Converts dewatered sludge by

combustion to carbon dioxide and water vapor

Reduce volume up to 90% Most common is MHF (multiple

hearth furnace) Temperature 1,300 – 1,700°F

Only use the chlorine wrench when opening or closing cylinders –

open 100%, close then reopen ¼ turn only

Fusible plug – center is lead – will

melt at 158 to 165ºF to release

gas instead of liquid or explosion

Trunions – used to turn ton cylinders so the valves are straight vertically

when opening

Train cargo cars (Class C)

Ton (2,000 lb) cyliners (Class B)

Biological Treatment Luxury Uptake of Phosphorous –

modification of activated sludge Definitions

– Aerobic (oxic): free DO is present – Anoxic: oxygen is deficient or

present as combined oxygen in Nitrate (NO3) and Sulfate (SO4)

Anaerobic: No oxygen

Safety

Top three injuries in wastewater in order:– Back– Leg– Hand

Lockout/Tagout– Everyone who is working on

that piece of equipment must sign/date/add lock

Lab Miscellaneous

Meniscus (commonly found in pipettes) – read at the bottom of the curve or the top of the curve

You can preserve a metals sample for 6 months

BOD solution water make-up – phosphate buffer, magnesium sulfate, calcium chloride, ferric chloride

A bottle containing only dilution water is called a blank

Pretreatment

Total toxic organics (TTO) refers to the sum of the masses or concentrations of certain toxic organic pollutants found in the regulated discharge at a concentration greater than 0.01 mg/L

Inspection – minimum of once per year or as needed

Sampling – Significant Industrial User (SIU) at least annually and self monitored semi-annually