Lecture 6 Flashcards
(25 cards)
Legal definition of waste?
“any substance or object which the holder discards or intends or is required to discard.”
What are six waste sources?
Mining, Agricultural, Industrial, Construction, Municipal. and Waste treatment
What is COD?
Chemical Oxygen Demand.
Used to measure organic matter.
COD is amount of O2 required to fully oxidise the organic carbon to CO2 and H2O.
How is COD measured in a lab?
use strong chemical oxidising agent in an acidic medium (3 hours)
CaHbOc + Cr2O7-2 +H+ -> Cr3+ + CO2 + H2O
How is ThCOD calculated?
Mass of O2 needed divided by mass of carbonaceous compound.
Why might ThCOD differ from COD?
ThCOD estimates maximum oxygen demand if compound is fully oxidised under ideal conditions.
Measured COD might differ due to incomplete oxidation, presence of inert materials, or other oxidisable materials.
What is total COD made of?
Soluble organics, Particulate organics, Biodegradable organics, and Unbiodegradable organics
What is BOD?
Biological Oxygen Demand.
Amount of dissolved oxygen (DO) used by microorganisms in biochemical oxidation/degradation of organic or inorganic matter.
How is BOD measured in a lab?
Water sample in closed bottle is incubated in the dark at a temperature of 20 for 5 days.
Difference in DO concentration is taken as BOD5.
Equation for L0?
LO = Yt/1-exp(-kt)
Why might COD be higher than BOD?
COD measures both biodegradable and non biodegredable organics.
BOD only measures oxygen demand for biodegredable organics.
How can wastewater be classified?
S = soluble, dissolved in water.
C = collodial, microscopically dispersed particles, does not settle.
X = particulate, tiny separate solid phase particles.
What are wastewater constituents?
Organic matter, expressed in COD.
Particulate COD is expressed in VSS
1g VSS= 1.48 g COD.
What are Total Solids (TS)
Residue after drying at 105 degrees.
What are Total Suspended Solids (TSS)
Collection of particulate matter after filtration.
Then dried at 105.
Contains both suspended inorganics (ISS) and organics (VSS)
What are Volatile Suspended Solids (VSS)?
TSS dried and ashed at 600-650.
VSS = TSS - ISS
Represents organic matter present in particulate form.
What are Inert Suspended Solids (ISS)?
Particulate inorganic matter.
Steps for wastewater treatment.
Before treatment screen out large particles and remove grit.
Primary treatment is the first process to remove a significant fraction of organic particulate matter (Suspended Solids). These solids contribute to BOD5 demand of water, removal also reduces this, reducing oxygen demand. Also removes scum and inert particulate matter.
Principal form is sedimentation.
Controlling parameter is settling velocity of the particles.
Heavier solids sink and form a sludge, fats rises to top and form crust which is colonised by aerobic bacteria.
Liquid between two layers is drained and secondary treatment is performed which involves removing the removal of small organic matter that did not float or settle in primary tank. Secondary treatment includes aerobic biological treatment which is introduction of oxygen and aerobic bacteria break down organic material remaining.
The effluent then transfers to final settlement tank, where sludge is removed for further treatment.
Tertiary treatment involves a further aerobic stage, followed by an oxygen depleted stage, reducing nitrogen and phosphorous.
Activated sludge process.
Conversion of organics into CO2 and biomass.
Main mixing regimes.
Completely mixed: influent is instantly and thoroughly mixed with contents. Effluent has same concentration to reactor content. Reactor effluent passes to a settling tank. Overflow is treated waste stream, underflow is concentrated sludge recycled back to reactor.
Plug flow: Reactor is long channel type basin. Influent is introduced at one end, flow is mixed along the basin.
Sludge Retention Time
Mass of sludge in reactor/ Mass leaving per day.
If directly removed from biological reactor SRT = Vr/Qw
Oxygen requirements
Oxygen uptake rate is oxygen usage/ time in min.
SOUR is amount of oxygen consumed by 1g of activated sludge per hour.
Hydraulic Retention Time
Average time liquid stays in reactor tank under steady flow conditions.
HRT= Vr/Qi
Sludge Loading Rate
Amount of substrate given to bacteria to metabolise each day.
Bx = Qs0/VX
