Wastewater Flashcards
Total Solids
all matter remains after evaporation by oven 105 deg C for 24h
Volatile Solids
Amount that of total solids that evaporates after being put in the muffle for 4h at 550 deg C
Organic Solids
Fixed solid
amount of total solid that remains after being put in the muffle for 4h at 550 deg c. INORGANIC
Total Suspended Solids
Solids that don’t pass through 0.45 microm filter (measured after drying)
60% of them are settleable
75% are organics
Total Dissolved Solids
Amount that pass through a filter of 0.01-1micro (measured after drying)
40% are organics
Settleable Solids
Solids that settles in a 1L imhoff cone after 30 min - 1 hr due to gravity. unit is mL/L
Odors
from gasses produced during degradation process
Temperature
Optimal for microbial activity is 25-20 deg C
Electrical Conductivity
Measures ability of water to conduct electrical current due to the presence of ion.
Indirect measure of TDS
Colors
From organic and inorganic compounds
Turbidity
Measure of light scattering properties due to the presence of suspended and colloidal particles. It is proportional to TSS Concentration
Total Organic Carbon
The total amount of carbon in organic compounds in a water sample.
Mw C x mole C
Theoretical Oxygen Demand
Indirect measurement of organics. How much O2 needed to oxidize to CO2
COD
O2 equivalent of organic (bio and non bio) that can be chemically oxidized
measurement usually using dichromate
TOC/COD Ratio
Oxidation state, the higher the ratio, the higher the oxidation state, the less O2 needed to oxidize compound
Theoretical COD
ThCOD=ThOD
COD Classification factsz
- Check particulate of soluble: Filtration
- Check if Organic or not: BOD
- Check if inert or not: SRT, if longer than SRT to degrade than it is inert
- Soluble Inert COD go in go out WW as is
- Particulate inert COD go out as sludge
- bCOD= biodegradable particulate (xs) + biodegradable soluble (Ss)
- Xs need more time to degrade because it needs to be hydrolyse to Ss first, and the time to hydrolyse is SRT or Sludge Age
BOD
Oxygen equivalent of organic that can be oxidized by M/O
Indirect measurement of biodegradable organic (bioCOD estimate)
BOD measurement conditions
must add O2, sufficient m/o, sufficient nutrients, no toxic compounds, no nitrification
What is the meaning of BOD5/BODtot ratio
BOD5: amount of dissolved oxygen consumed by microorganisms while decomposing organic matter over a 5-day period.
UBOD: total amount of oxygen required to completely decompose all the biodegradable organic matter
BOD5/UBOD Ratio: A high BOD5/BODtot ratio (closer to 1) indicates that most of the organic matter is readily biodegradable.
BOD effects of Nitrification
Nitrification normally starts after 8-10 days. If initial presence is high, need to inhibit. Or else the BOD inflates. Because nitrification also needs oxygen so higher o2 consumption –> BOD inflates
BOD Limitation
- Takes 5 days
- Result varies due to inocculum acclimitazation
- Does not include Non-biodegradable organics
4.
BOD/COD ratio?
How much COD is actually biodegradable.
Usually, 0.5
If very low meaning not ideal to use biological units.
Alkalinity
Capacity of a buffer to resist pH changes
Mainly come from OH-, CO32-,HCO3-, Ammonia, Phosphates
Mass Equivalent of CaCO3
50 g CaCO3/ eq
What is typical value of alkalinity in Domestic WW
3-7 eq/m3 or 150-350 mgcaco3/l
What is Organic and Inorganic Nitrogen?
Organic: Mainly proteins
Inorganic: Ammonia (from hydrolysis of org matter), Ammonia oxide –> Nitrate (NO3-) and NItrite (NO2-)
What is TKN
Total reduced form of N
Organic Nitrogen + Ammonia
Estimation of Total Nitrogen at incoming WW because not yet oxidized and change form to nitrite and nitrate (Ammonia oxide)
What is Ammonia Nitrogen?
NH3 (Volatile Gas) + NH4+ (Ion)
usually 50-80% in WW
Concentration depends on pH higher pH usually more Ammonia Gas portion. but at pH 9.25 the % is the same
Total Nitrogen
TKN+Ammonia oxide
Ammonia N + N org, Nitrate + Nitrite
Pseudomonas role
Reduce NO3 to N, biological nitrate removal
Acinetobacter Role
store large amount of phosphate under aerobic and release under anaerobic conditions
nitrosomonas
transform NH4 to NO2-
Nitrobacter
Transform NO2- to NO3-
Coliform Bacteria Role
E-coli indicator for pathogens
Hydraulic and BOD PE
Hydraulic PE: 200 L/cap/day
BOD PE: 60g BOD/cap/day
QAverage and Q Peak
QAve: Consumption/cap/day x population x WW generation coefficient (0.7-0.9)
Q Peak: Qave x K
K= peaking factor
Why is below contaminants of concerns?
Suspended Solids, Biodegradable org, pathogens, Nutrients, Heavy Metals
Suspended Solids: Sludge deposits and anaerobic conditions
Biodegradable org: O2 depletion –> Septic
Pathogens: Health disease
Nutrients: Groeth of indesirable aquatic life
Heavy Metals: Toxicity, Bioaccumulation
Scheme of WWT General
Screening
Grit Sed. or Floatation
Eq. Tank
Primary Settling
Aerobic treatment
Secondary Settling
Filtration
Disinfection
Additional units: Nitrification, denitrification, phosphorus removal, Filtration, coagulation and flocculation, adsorption
Role of Preliminary Treatment and which are removed by screenings, grit sedimentation, and floatation
Removal of coarse solids that may cause operational & maintenance Problems
Screening: Remove coarse solids and avoid damages
Grit Sedimentation: eliminate sand, gravel, cinders, and other heavy solid particles
Floatation: remove particles that are too light to settle by gravity, such as oils, grease, and fine suspended solids. By gas bubbles, remove suspended matters.
Role of Secondary Treatment
Remove biodegradable organic compounds (particulate and soluble COD) by bacterial growth and conversion into CO2 energy and biomass
High org content should choose Anaerobic
Role of Tertiary Treatment
Chemical & Physical process to enhance WW Quality.
Removal of residual solids, Nutrients, pathogens
e.g: Filtration, precipitation, membrane treatment, disinfection, adsorption
Sludge Management
Stabilize sludge, thickening & dewatering, Anerobic or aerobic digestion, drying, composting
What does steady state mean
Rate of accumulation is zero
Mass flow in - Mass flow out +- Reaction = 0
What is HRT & SRT
HRT (Hydraulic Retention Time): The average time wastewater remains in a treatment tank or system. It ensures adequate contact time for treatment processes.
SRT (Solids Retention Time): The average time biological solids remain in the treatment system. It ensures the maintenance of an effective microbial population for treatment processes.
SRT=total mass of solids in the system/flow of solids leaving the system= Vx/QwXr
Types of screens
Coarse screen for >6 mm
could be manually and mechanically cleaned (e.g: belt screen, vertical bar screen, arch screen)
Fine Screen 0.5 mm to 6 mm
possible substitute for primary sedimentation (catch COD)
Grit chamber types
Horizontal Flow Grit Chamber (oldest)
Aerated Grit Chamber (done properly 100% grit removal)
Vortex Type Grit Chamber (small size) use a turbine
Types of Floatation
Dispersed-Air Floatation or Induced air Floatation (IAF)
Air is directly sparged into tank, usually for high vol industrial WW.
Pros: Compact size, low capital cost
Cons: High power req, strict hydraulic control, less flocculation flexibility
Dissolved Air floatation (DAF)
Air is pressurised instead of injected, thus very fine bubbles, main design parameter is Air to Solid Ratio, have higher removal efficiency than sedimentation but more high capital cost.
Whar are the 3 types of settling, and where it used
Discrete particle settling: settle as individual, no interaction, Grit and Sand removal
Flocculent Settling: floc together and settle, primary sedimentation
Hindered or zone settling: fixed position particles and settle as unit (secondary sedimentation)
A/S design in DAF is based on what
TSS in effluent goals NOT TSS Removed
Equalisation Tank
Dampen fluctuations in Flow, concentration or both and avoid shock loading
Pros and Cons of Equalisation Tank
Pros: Overcome potential problems caused by flowrate fluctuations (shock loadings), improve downstream performance (constant loading, better feed control), Reduce size and cost of downstream facilities
Cons: large areas needed
what are the 2 arrangements of equalisation tank
Inline: All flow pass through after grit removal
Offline: only flow above specified flow limit is diverted to the tank
What is the principle settling of primary sedimentation?
Gravity settling: type 2 –> flocculent sedimentation
What are the shape of primary sedimentation tank?
rectangular and circular
Can we add chemicals during primary sedimentation? if yes what?
yes to increase efficiency thus reducing surface area
