4th lecture wastewater engineering

secondary treatment

the biological treatment of wastewater in order to continue to remove biodegradable waste.

Public law 92-500

In __________ the US, the congress required municipalities and industries to provide secondary treatment before discharging wastewater into natural water bodies

>85%

Average removal shall not be ______

CBOD5

BOD5 must be substituted by ______ at the option of the permitting authority

Suspended growth reactor

The organism and wastewater are mixed together

Attached growth reactors

Also known as fixed film system in which the media provides a large area for smile growth as well as for ventilation

Activated sludge process

It is the most common biological treatment system

activated sludge

aerated sewage containing aerobic microorganisms that help to break it down

May 3, 1914

Activated sludge was developed in england in ___________

adern and lockett

Activated sludge process was developed by

Lawrence experiment station

First experiment with aeration were performed at the ___________

Dr. Gilbert john fowler

Is the initiator of thefirst activated sludge studies in england

Arden and lockett

____________ set up a series of tests in which they would aerate a sample of waste for some days, settle outthe sludge solid, decant the liquid off the top and refill the container with new wastewater

Synthesis

the process wherein microorganisms derive energy from crbonaceous orhanic matter in aerated wastewater for the production of new cells

Respiration

The process by which cells break down simple food molecules to release the energy they contain.

Nitrification

ammonia is converted to nitrate ions (NO3-).

aeration tank

Where the biological reactions occur

Aeration source

Maybe provided by pure oxygen, compressed air or mechanical aeration that provides oxygen and mixing

secondary clarifier

In activated sludge sewage treatment, the tank where organisms and other particles settle out after the aeration tank.

Return activated sludge

Must be collected from the secondary clarifierss and pumped back to the aeration tank before dissolved oxygen is depleted

Waste Activated Sludge

Activated sludge containing an overabundance of microorganisms must br removed or waste with the use of pump

Mixed Liquor

The mixture of activated sludge and the wastewater in the aeration tank

Mixed liqour suspended solids

Concentration of suspended solids

Mixed liqour volatile suspended solids

Fraction of suspended solids in activated sludge mixed liqour that can be driven off by combustion at 550°C

60-80%

________ of MLSS is MVLSS

jet aeration

Oxygen tranfer efficiency is accoplished by mixing pressured air and with water with lin a jet nozzle and then discharging the air liquid into the tank. Oxygen tranfer efficiency is high as 25%

Machanical aeretors

Eithe rsurface or submerged

Surface Aerators

Oxygen is entrained from the atm

submerged aerator

Oxygen is entrained both from atm and from air or pure oxygen introduced at the bottom of the tank

diffuse

Designed to produce fine, medium or course bubbles

coarse bubble diffusers

OTE range 4 to 8%

Medium bubble diffuser

OTE range 6 to 15%

Fine bubble diffuser

OTE range 10 to 30%

activated sludge

Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in aeration tanks in the presence of dissolved oxygen. the term "activated" comes from the fact that the particles are teeming with bacteria, fungi, and protozoa. It is different from primary sludge in that the sludge particles contain many living organisms which can feed on the incoming wastewater.

activated sludge process

A biological wastewater treatment process which speeds up the decomposition of wastes in the wastewater being treated. Activated Sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated. After some time in the aeration tank, the activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused (returned to the aeration tank) as needed, the remaining wastewater then undergoes more treatment.

Aerobic

A condition where oxygen is present

BOD

biological oxygen demand, amount of dissolved oxygen needed by aerobic decomposers to break down organic materials

Bulking

Sludge the forms clouds in the secondary clarifier when the sludge does not settle properly usually caused by filamentous bacteria

Carbonaceous BOD removal

Biological conversion of the carbonaceous organic matter in wastewater to cell tissue and various gaseous end products. In this conversion, it is assumed that the nitrogen present in various compound is converted to ammonia

F:M

Food to Microorganism Ratio

Floc

Clumps of bacteria and particulate impurities that have come together and formed a cluster. Found in flocculation tanks and settling or sedimentation basins.

Flocculation

Igitating wastewater to intoducethe small, suspended particles to bunch together into heavier particles and settle out

Mean Cell Residence Time

Also called solids retention time, is the average amount of time that microorganisms are kept in the system,. Also called sludge age

Loading

A quantity of materials added to the process at one time

Package Plant

Pre manufactured treatment facility small communities or indivual properties use to treat wastewater

sludge

The solids that settle out during the process

Substrate

The term use to denote the organic matter or nutrients that are converted during biological treatment or that may be limiting in biological treatment.

Supernatant

The liquid that is removed for settled sludge, it commonly refer to the liquid between the sludge on the bottom and the scum on the surface

wasting

Removing excess microorganism from the system

Obligate aerobes

Are microorganisms that must have oxygen as the terminal electron acceptor.

obligate anaerobes

organisms that cannot live where molecular oxygen is present

facultative anaerobes

can live with or without oxygen

Anoxic microorganisms

A group of facultative anaerobes called denitrifiers utilizes niritite and nitrates as terminal electron acceptor

Anoxic denotrification

The process whereine nitrite nitrogen is converted to nitrogen gas in the absence of oxygen

Phototrophs

Are able to use light as energy sources, they can be either autotrophic or heterotrophic

Chemotrophs

Chemical reactions as energy source

Chemoautotrophs

obtain energy directly from inorganic molecules

Chemoheterotrophs

obtain energy from organic compounds and carbon from organic compounds as well

Metabolism

Refer to all the chemical reactions occuring within a cell. The reactions are referred as metabolic reactions

Catabolism

Reactions involve the breaking of bonds

Anabolism

reactions involve the creation of bond

Biochemical pathways

a series of reactions in which the product of one reaction becomes the substrate for the next reaction

Respiratory metabolism

Orgamism that regenerate enrgy by enzyme mediated alectron transport to an external electron acceptor

aerobic respirtation

When oxygen is used for the acceptor the reaction is aerobic

Fermentive metabolism

Internal electron acceptor is used and it is less efficient energy yeilding process compared to respiration,

anoxic

The use of NO2 or NO3 for electron acceptors under anaerobic conditionsc. Under this condition the reaction is biological denitrification

Facultative aerobic

When they can use O2 or NO2/NO3 as electron acceptor when O2 is not available

facultative anaerobes

Organisms that can grow with or without oxygen

True facultative anaerobes

Can shift from fermentive to aerobic respiration metabolism

aerotolerant anaerobes

Have a strictly fermentive metabolism but are relatively insensitive to the presence of molecular oxygen

Extracellular

Conversion of substrate that can be transported into the cell

intracellular

Involve in synthesis and energy reactions within the cell

Hydraulic load

This refer to the amount of water entering the aeration tank. As the hydraulic load or flow increase, the concentration of organic may decrease

Hydraulic detention time

This refer to the duration or time a wastewater is retained in a reactor

Return sludge requirement

To maintain a sufficient concentration of activated sludge

Sludge Blanket

Is the accumulation of settled sludge in the clarifier, ideally it should be in the lower quarter of clarifier

filamentous bacteria

Can affect activated sludge floc structure in postive and negative way

10°C

The rate of microorganism growth double every______increase in temp up to a limiting temp

10° to 40°C

Most microorg do best at moderate temp such as found in the aeration tank

Sternothermophiles

Grow best above 60°C

-2 to 20

Cryophilic

20 to 45

Mesophilic

45 to 75

Thermophilic

6.5 to 8.5

Most microorg do well at a PH of

8 to 9

Optimum PH for the growth of nitrifying bacteria is in the _______ range, with PH lvl below 7 causing a substantial reduction in nitrifying activity

BOD5:N:P:Fe=100:5:1:0.5

The weight ratio for industrial wastewater treatment plants should be maintained as follows

Rotifer and nematodes

Aremost frequently found in system with long aeration period

Amoeboids

Predominate in young sludges

Flagellates

Are free swimmers and predominate in light mixed liqour

Free swimming ciliates

Predominate as the F:M ratio decreases

Conventional plug flow activated sludge

Air application is uniform throughout the tank lenght

Tapered Aeration

-A modification of conventional plug flow process

-match the quantity of air supplied

-diffuser are spaced close together to achieve a high oxygenation rate

step aeration

Or step feed aeration is also modification of conventional plug flow

modified aeration

-Identical with conventional or tapered aeration, but short aeration time(1.5-4 hrs) and higher F/M ratio are used

-BOD removal efficiency is lower than otgrt activated sludge processes

85 to 95

Conventional BOD removal efficiency %

85 to 95

Tapered BOD removal efficiency %

85 to 95

CFST BOD removal efficiency %

85 to 95

Step aeration BOD removal efficiency %

60 to 75

Modified aeration BOD removal efficiency %

filamentous bacteria

Can cause the sludge not to settle properly