Lecture 10 Flashcards
how does wastewater treatment depend on effluent discharge?
- Ocean
- Inland stream
- Environmentally sensitive lakes, streams, estuaries
- Groundwater
what is preliminary treatment?
pumping, screening, grit removal
what is primary treatment
Sedimentation – a portion of suspended solids and organic matter removed (~30 % BOD, ~60% TSS)
what is secondary treatment?
- Further treatment of effluent from primary treatment for residual organic matter and suspended solids removal (~ 90% BOD and TSS)
- Typically biological reactors (i.e. activated sludge process, trickling filter
what is advanced (teriary) wastewater treatment?
Effluent from secondary treatment may be further treated to reduce
specific chemical constituents in wastewater (i.e. phosphorous, nitrogen) if discharging to environmentally sensitive estuaries
what is wastewater treatment process?
SPGRTSS
what is the suspended growth process?
In suspended growth process, active biological solids are mixed with the wastewater and held in suspension by aeration. The suspended biological solids are subsequently separated from the treated wastewater and returned to aeration process as needed.
what is one of the most common suspended growth processes?
Activated Sludge process. Others are aerated lagoon, oxidation pond and membrane bioreactor.
how does activated sludge process work?
air is injected into the wastewater and mixed thoroughly with the organic matters present.
how to microbes grow?
By the agitation of air and having organic matters as food, microbes will grow in number and clump together (flocs) to form an active mass of microbe called ‘activated sludge’
where does the name activated sludge come from?
The name activated sludge comes from the fact that the microorganisms have high activity in the sludge.
explain how a typical wastewater treatment plant can be designed/operated sustainably from a resource recovery perspective?
- enabling municipalities to capture heat from sewer pipes and use it to heat nearby buildings
- turning gas from treatment processes into electricity and heat for use in treatment plants (co-generation)
- using biosolids as an ingredient in landscaping soils, to reclaim mines and gravel pits, and other uses
how does the formation of flocs happen in activated sludge?
- The formation of the flocs happens due to secretion of extracellular polymer from bacteria(which have a binding property) that have reached the end of the ‘stationary phase’ of their life cycle [recall the log phase, growth phase, stationary phase and death phase].
- Organisms other than bacteria (protozoa, rotifers, fungi etc) live in or on the flocs but do not ordinarily occur in large numbers. Protozoa and rotifers feed on free swimming bacteria and therefore, known as polishers and help in reducing turbidity in the effluent.
what is assimilative respiration?
- takes up BOD
- makes new cells (new biomass)
what is endogenous respiration
- food depletion
- biomass start to “die” due to starvation
- Rate of production of new cells or biomass LESS THAN rate of decline
what is an attached growth system? (i.e. trickling filter)
- It consists of a rotating distributing arm that sprays the feed wastewater over a circular bed of plastic packing or other coarse materials.
- Plastic material is preferred due to low cost, ability to build taller structures, and option to have larger surface area for microbial growth per volume of filter.
- The space between the packing allow air to circulate easily.
- The name filter is a misnomer as no filtering takes place. Instead, the media bed is covered with bacteria slime that adsorbs and consumes the wastes trickling through the
bed. Slime mainly consists of bacteria, but may include algae, fungi, protozoa etc. - Accumulating slime periodically sloughed off and transferred to secondary clarifier to be removed.
- Sometimes some effluent from the filter is sent back to the incoming flow to enable more effluent organic removal and to keep the biological slimes from drying out then dying during low flow conditions.
what is the process of utilization of substrate?
- Adsorption of soluble and colloidal substrate on floc surface
o Cell produces enzyme that hydrolyzes (adding water) the colloidal organic matter and breaks them into smaller parts to let them enter through the cell wall. - Transport of substrate into the cell
- Metabolism in cell
-Energy will be generated due to metabolism and new cells will be formed. - Solid liquid separation process
- Agglomeration of bacteria by biopolymers.
what is the food to mass ratio (F/M)
- F/M ratio defines the operation of the system
- Excess microorganisms (biomass) in returned sludge used to maintain proper balance of F/M ratio
what is a result of a high f/m
- poor BOD removal
- Poor settling characteristics
what is a result of a low f/m
microbes compete for food
efficient BOD removal
good settling characteristics
typ. f/m approx. 0.2->0.5
what is mixed liquor?
mixture of wastewater and suspended culture/bacterial mass
what is mixed liquor suspended solids (MLSS)
actual bacterial (biomass) concentration in aeration tank
what does MLSS testing measure?
the total concentration of mixed liquor suspended (non-soluble) solids in the aeration basin of an activated sludge system.
why is MLSS data critical?
critical in determining the operational behavior and solids inventory of the system and it is used to determine when to waste and/or
recycle sludge.
