Solids Separation, Laboratory, Bio-Solids/Sludges

Flashcards for the study guides of Wisconsin DNR Wastewater Operator Subclass B, C, and L

Clarification

Type of solids separation. Applies to primary, intermediate, and final.

Clarifier

A circular or rectangular tank with mechanical means to remove floatable and settleable solids in wastewater.

Coning in relation to sludge

What occurs when sludge is pumped too fast from the sludge hopper

Filamentous organisms

Group of thread-like organisms that can impair the settling of activated sludge and create bulking conditions.

Short-circuiting

uneven flow distribution in wastewater tank. Density currents occur in some parts and the detention time is less in other parts.

Weir

level control structure used to provide a uniform effluent flow

purpose of Primary treatment

settles solids and capture floatables, should remove 40-60% of overall suspended solids

purpose of intermediate treatment

settles secondary solids, usually attached-growth

purpose of final treatment

last clarifier in secondary treatment process, discharge clear effluent

purpose of tertiary treatmaent

provides advanced treatment beyond secondary. commonly consists of sand, mixed media, cloth, membranes, and others.

Headloss as it applies to granular filtration

the difference in the amount of pressure needed to force water through a clean vs dirty filter. Indicates present condition of bed, ability to remove solids, and backwash effectiveness. When water level rises, filter needs to be cleaned.

SLR

solids loading rate is relationship between solids entering clarifier and surface area of clarifier.

SOR

surface overflow rate, relationship of the flow into the clarifier to the surface area of the clarifier. 

WOR

weir overflow rate, flow in relation to weir length.

importance of even flow splitting

uneven flow will cause changes in detention times, WOR, sludge collection volumes, and primary effluent quality

Influent pipe

Conveys wastewater to clarifier

Drive unit

Moves sludge and scum arms

Torque limiting device

Protects drive unit (shear pins)

Sludge sump

Collects sludge from sludge scrapers

Clarifier baffle

Stops uneven detention time and keeps floating solids and grease from leaving tank

Flight and chain

What is moved along the bottom and top to collect settled and floating solids

Wear shoe

Prevents wear on flights

Sludge cross collecter

Drags sludge to deep end of sump for removal

types of pumps used to pump sludge

centrifugal

progressive cavity

diaphragm

rotary lobe

types of pumps used to recirculate sludge

centrifugal (most common)

progressive cavity

rotary lobe

Daily clarifier observations

Check for floating solids and bubbles

Weir obstructions

Arms and flights moving smoothly

Unobstructed scum beach/trough

Equipment has no leaks or strange noises

Sludge blanket depth

Check scum pit

Clean algae

significance of denitrification occurring in clarifier

in absence of oxygen, a thick sludge blanket can denitrify after a long detention time. Nitrates are converted to nitrogen gas. Release of N2 gas causes small bubbles that attach to sludge and solids rise to the surface

how to test for hindered settling

50% diluted settleability test (SVI)

Granular filtration

Wastewater treatment method using sand media

Granular filtration daily observations

Headloss

Effluent turbidity

Solids in effluent

Loss of media

Check all gauges and flowmeters

Influent qualities

Any floating solids

Steps to take a granular filter out of service

Thoroughly backwash

Chlorinate 5-15mg/L and let stand for 2-3 days

Thoroughly backwash again

Drain

Store filter wet ideally, if stored dry use proper startup procedure for dry filter

Every 3-6 months

How often to chemically clean disc filter cloth media

>95%

Solids removal efficiency of Dissolved Air Flotation systems

Membrane flux

Flow across the membranes (gpd/ft²)

Trans-membrane pressure

Pressure across membrane filter or headless through filter, (psi)

Permeability

Flux divided by trans-membrane pressure ((gpd/ft²)/psi)

Microfiltration

0.1 to 10 micrometers, bacteria, giardia, crypto, protozoan parasite cysts

Ultrafiltration

0.01 to 0.1 micrometers, DNA viruses and calloids

Nanofiltration

0.001 to 0.01 micrometers, large molecules like sugar and some salts

Reverse Osmosis

Less than 0.001 micrometers, ions and large atoms

Types of membrane elements and their components

Spiral wound

Plate and frame

Capillary fiber

Tubular

Membrane cleaning methods

Daily Air scouring

Relaxation

Backwash

Weekly or biweekly maintenance

Chemical Clean In Place (CIP) every 3-6 months

Breakthrough

When solids push through the granular filter media and out to the effluent. Occurs when a filter is run too long with insufficient backwashing.

Filter channeling

When portions of the filters get plugged and wastewater flows into effluent channels

Effluent turbidity and filter headloss

The two primary control measurements for granular filtration

10,000 mg/L = 1.0% solids

Relationship between mg/L in MLSS and percent solids

2-3 hours

Recommended clarifier detention time

negative consequences of leaving sludge sealed in a pipe

The bacteria generates gas, building pressure inside the pipe. Can also cause clogs

Hydrogen sulfide

Methane

Carbon monoxide

Chlorine

The 4 main toxic gases at a wastewater plant

Proper Chemical spill response

Report to DNR within 24 hrs, and to local emergency response agencies.

Filamentous organisms

Overly young sludge settling poorly

MLSS too high

Possible causes of high SVI

Saying for combining water and acid

Do what you otter, add acid to water.

MSDS

Material Safety Data Sheet

Grab sample guidelines

Well mixed area, center of stream, away from floor

Mixing

Most critical step of subsampling/split sampling

Sample collection info

Type, location, ID, time and date, preservation methods, sampler initials

Volumetric flasks

Always use this type of flask when making standards

Graduated cylinders

BOD and TSS when using 50ml or more of sample

Volumetric pipettes

Pipette used for Standard prep, classified as TD/EX, do not blow out, one specific volume

Wide-bore pipette

Pipette used for BOD and TSS sample

Best practice for pipet accuracy

A single larger volume is more accurate than multiple smaller volumes

Mohr pipette

Pipette used for color reagent, graduations stop well before tip, drain out

Serological pipette

Pipette used for BOD influent, preservation

Graduations continue to tip, can be drain out or blow out

BOD

Biochemical Oxygen Demand

cBOD

carbonaceous Biochemical Oxygen Demand, done by adding an inhibiting agent to prevent nitrification

60%

percentage of nitrogen that enters a WWTP as ammonia

1 pound

How much phosphorus a human body releases in a year

10:3

LOQ:LOD

Required documentation for corrective action

When, how, who, what, why

4 critical aspects of QC sample analysis

Parameter, frequency, criteria, corrective action

3 years

Minimum Amount of time laboratory records must be stored

Aerobic digestion

The biochemical decomposition of organic matter into CO2 and water in the presence of oxygen

Calcium Carbonate equivalent in mg/L

How alkalinity is measured in wastewater

Anaerobic digestion

The biochemical decomposition of organic matter into methane and CO2 in the absence of oxygen

Digester buffering capacity

Ability of an anaerobic digester to resist pH changes, indicated by alkalinity

Mesophilic bacteria

Bacteria that grow and thrive in temp range 85-100F, or 30-38C

Sludge conditioning

The treatment of liquid sludge before thickening/dewatering to separate by neutralizing electrical charges on fine particles. Clump small particles to form larger particles.

Sour digester

A digester that has become upset and is performing poorly. Low gas production, high VA to alkalinity ratio, and low pH. Often caused by excessive organic loading, can be affects by low temps and high toxicity.

Thermophilic bacteria

Bacteria that grow and thrive in 120-135F, or 49-57C

Vector attraction

The characteristics of sludge that draw rodents, flies, mosquitoes, and other organisms capable of spreading disease

Vector attraction reduction

The use of prescribed processes to reduce spread of pathogens by disease carriers when land applying sludge

550C

Temp to drive off volatile soids

Purpose of sludge treatment processes

To reduce organic content and pathogenic organisms to allow for reuse while protecting public health and the environment.

Qualities of treated, stable sludge.

Less odor to reduce vector attraction

Good dewatering properties

Publicly acceptable in odor and appearance

Process by which waste entering anaerobic digester is converted to methane, sludge, and water

Volatile solids in feed sludge are used as food by the bugs. The bugs break down the complex solids into soluble organic fatty acids, alcohols, CO2 and ammonia. Other bugs break down those products to acetic acid, propionic acid, H2, CO2, acetate, and methane.

Aerobic digestion process

Bugs use oxygen and volatiles to produce CO2, water, and nondegradable saccharides and cellulose compounds

Environmental factors that influence anaerobic digestion bugs

Food, temp, pH, volatile acid, alkalinity, toxicity

Environmental factors that influence aerobic digestion bugs

Food, DO, temp, pH, Toxicity

60-80%

Amount of volatile, organic solids in typical primary sludge

Siloxanes

Volatile organic chemicals containing silicon that are found in personal care products. When burned, creates abrasive silicon dioxide which is damaging. Can be removed by passing gas through activated carbon.

Rotary drum thickener

Type of thickener where sludge is fed into a horizontal drum that allows water to drain while solids stay inside and get discharged.

3-7% solids

Percent solid of sludge after DAF

Benefits associated with anaerobic digestion

Production of methane that can be utilized

Destroys volatile solids, reducing sludge mass

Less odorous sludge

Reduced pathogens

Key factors in anaerobic digestion

Organic loading rate (OLR)

Volatile acid/alkalinity ratio

Temp

Mixing/recirc

Solids retention time (SRT)

pH

Grit and scum blanket

Toxicity

15 days at 95-100F

Hydraulic retention time (HRT) needed in anaerobic digester to achieve adequate sludge treatment

Anaerobic digestion: methane

Typically 60-64% of anaerobic digester gas.

Anaerobic digestion: CO2

Typically 35-40% of gas produced in anaerobic digestion.

Hydrogen sulfide

Reacts with water to form corrosive, and potentially lethal, acids. Can be removed with an iron sponge.

7-12 ft³ per pound of volatile matter destroyed

Common range of gas production in digester

5-10 year interval

How often a digester should be completely taken down and totally cleaned