M1U1: Principles of Environmental Engineering Flashcards
Leads to the development of sludge deposits and anaerobic conditions
Suspended Solids
Biological destabilization can lead to the depletion of natural oxygen resources and the development of septic conditions
Biodegradable Organics
Communicable diseases can be transmitted by pathogenic microorganisms
Pathogens
Can lead to algal growth and pollution of groundwater when discharged on land
Nutrients
Organic and inorganic compounds selected on the basis of their known or suspected carcinogeniticy, mutagenicity, teratogenicity or high acute toxicity
Priority Pollutants
Resist conventional methods of WW treatment. Low value of BOD: COD
Refractory Organics
May cause poisoning; need to be removed when wastewater is to be reused
Heavy Metals
Constituents such as Ca2+, Na+ and SOx added during water usage
Dissolved Organics
Wastewater Treatment Methods
Preliminary
Primary
Secondary
Tertiary
Sludge Treatment
Processes in Preliminary Treatment
Screening
Comminution
Grit Removal
Oil and Grease Removal
abrasive in nature and will cause accelerated wear on pumps and sludge handling equipment with which it comes in contact with.
Grit
Most common device use for Grit removal
Parshall Flumes and Palmer-Bowlus flumes
dependable and cheap way to remove oil, grease and other hydrocarbons from water.
Skimmers
Processes in Primary Treatment
Settling and Sedimentation
to produce a clarified effluent simultaneous with production of concentrated sludge that can easily be handled and treated.
sedimentation
Processes in Secondary/Biological Treatment
activated sludge
fixed-film reactors
lagoons
pond
systems
They use the organics in wastewater as food supply and convert them into biological cells or biomass.
Microorganisms
Types of Biological Culture
Suspended Growth
Attached Growth
suspended in the wastewater as single cells or clusters (flocs)
Suspended Growth
the biological mass formed when air is continuously injected into the wastewater.
As the microorganisms grow and are mixed by the agitation of the air, the individual organisms flocculate to form an active mass of microbes
(biologic floc) called
activated sludge
This is the name given by Barnard (1975) to represent any anaerobic/aerobic sequence to promote BPR. A version of this process with multiple stages is patented as A/O ™ (anaerobic/aerobic).
Phoredox
This is a proprietary modification of the A/O ™ process that provides internal recycle and an anoxic zone for denitrification
A2/O™
This modification of the four-stage process provides for both denitrification and phosphorus removal. Uses a longer SRT thus increases the carbon oxidation capability.
Bardenpho (5 stage)
It is similar to the A2/O ™ process with two exceptions. The return sludge is recycled to the anoxic stage instead of the aeration stage, and the internal recycle is from the anoxic stage to the anaerobic stage.
University of Cape Town (UCT)
The six operational steps of the SBR denitrification process are retained, but the conditions are modified
Sequencing Batch Reactor (SBR)
stabilization pond, oxidation pond or sewage lagoon; shallow earthen basin where wastewater is retained long enough for natural purification processes to provide treatment
Ponds
distinguished from ponds in that oxygen is provided by artificial aeration
lagoons
ponds, in which both aerobic and anaerobic zones exist, may be used as the total treatment system for municipal wastewater. They are assumed to be completely mixed reactors without biomass recycle.
Facultative ponds and lagoons
used in plug flow where compressed air is injected
air diffusers
larger surface area per volume of air; 2 – 2.5mm bubble diameter
fine bubble diffuser
less maintenance but poorer oxygen transfer; upto 25mm diameter
Coarse bubble diffuser
used in completely mixed reactors employing high-speed impellers
mechanical aerators
organisms attach themselves to the medium and grow into dense films of a viscous, jelly-like nature.
attached growth
uses randomly packed solid medium where wastewater is passed over the biofilm in intermittent doses;
trickling filter
uses modular synthetic media of high porosity and low weight such as light weight flat PVC sheets in alternating patterns/deep trickling filters
biotowers
uses rotating disks partially submerged in the wastewater. The medium moves the biofilm alternately through water and air thus also maintains aerobic condition.
Rotating biological contactors (rbc)
these processes were called “advanced wastewater treatment” because they employed techniques that were more advanced than secondary treatment methods.
tertiary treatment
processes involved in tertiary treatment
nutrient removal
organic material removal
ion exchange
reverse osmosis
present in precipitation resulting from soluble and particulate nitrogen forms that are scrubbed from the atmosphere;
nitrogen
effects of discharges
*Eutrophication leading to depletion of DO from nitrification and bio-stimulation
* Ammonia toxicity to aquatic life
* Reduction in the suitability of water for re-use
biological oxidation of ammonium by chemoautotrophic bacteria
nitrification
microorganism used in nitrification
nitrobacter
biological reduction of nitrate to nitrogen gas by heterotrophic bacteria
denitrification
from phosphate-rich rocks and organic decomposition
phosphorus
Phosphorus removal process
chemical precipitation
biological removal
primary microorganisms responsible for P removal. They utilize volatile fatty acids (VFA) in the influent wastewater under anaerobic conditions by releasing stored P.
acinetobacter
microorganism starvation (stressed state)
anoxic/anaerobic
storage of P exceeding their normal need (luxury uptake)
aerobic
processes in sludge treatment and disposal
stabilization
dewatering
basic processes of sludge treatment
preliminary operations
thickening
stabilization
conditioning
dewatering
reduction
sludge processing
conditioning
thickening
stabilization
disinfection
sludge dewatering
solids reduction
beneficial use system
biosolids disposal
removes soluble compounds
elutriation
releases bound water and destroys biological cells
thermal conditioning
generally restricted to biological solids; achieved by extended aeration, maintaining the m.o. in the endogenous respiration
aerobic digestion
for primary sludge
anaerobic digestion
consist of facultative and anaerobic bacteria. They ferment soluble organic solids to acids and alcohols of low molecular weights
acid formers
consist of strict anaerobic bacteria that convert acid and alcohols along with H and CO2 to CH4
methane formers
addition of Ca(OH)2 or CaO to sludge to raise pH to about 11 or above
lime stabilization
aerobic to a certain degree and takes 30-40 days
composting
use of belt filter, vacuum filter, plate and frame filter press
filtration
dewatering by evaporation or percolation through the sludge bed or underlying media.
drying in drying beds
this is common in industrial plants with available land
sludge lagoons
for cold climates
sludge freezing beds
combination of thermal cracking & condensation reactions; oil from sludge (OFS) and gasification
pyrolysis
vitrified sludge can be used as material for floorings.
vitrification
