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ioE 411 and AE/CE/BRT 511 Wastewater treatment
BioE 411 and AE/CE/BRT 511
Wastewater treatment
Attached growth systems: sewage farms
Morestead sewage farm
Berlin sewage farm layout
Sewage farm
Overland flow designs
Improved attached growth:early biobed
Large-scale wastewater treatment
Rotating disc arrangement
Leach field after septic tank
Suspended growth systemsSo far, we have studied systems where treatment is effected by bacteria, and other organisms, which are attached to a solid medium, i.e. soil, rocks, etc. There are also systems where the microbial growth occurs in suspension. The bacteria then aggregate into flocs, which are barely visible to the naked eye, but each consists of millions of bacteria and often protozoa attached to the floc.
Systems range from the simple facultative lagoon or pond, with no aeration, to aerated ponds and to sophisticated activated sludge systems, where the biomass is separated from the effluent and recycled to treatment and excess production treated separately.
The simple lagoon or pond systems purify the water quite well, but since there is no provision to separate the biomass production, the effluent is quite turbid and still contains much organic material, but stabilized to a non-smelling and not rapidly degrading form.
Facultative lagoonsFacultative lagoons or stabilization ponds use only natural phenomena and almost no mechanical action. Oxygenation for bacterial oxidation of organics comes from photosynthesis by algae and a bit from wind. CO2 released by bacteria is used by the algae. Excess biomass and other settleables are treated by anaerobic bacteria at the bottom.
Facultative lagoon interactions
http://www2.bren.ucsb.edu/~keller/courses/esm223/esm223_15.pdf
Design approaches to pond treatment systems
Ponds usually require lengthy treatment periods, weeks for facultative systems and days for aerated systems. Although facultative systems have very little mixing other than inflow, gas bubbles and wind effects, the long retention periods ensures some homogeneity except with respect to depth, as there is much stratification.
As in any mixed system, the contents have the same concentration as the overflow. This means that the organisms in the pond continuously experience a low level of substrate to feed on, which slows down the treatment considerably, as the typical first-order reactions are directly proportional to the BOD. Therefore, significant improvement in treatment rate can be achieved by approaching a channel (tube) flow, or using multiple ponds.
Multiple pond system analysis can be performed by assuming that each is a completely mixed system, operating on a first-order degradation and a mass balance around each provides one equation. Intermediate values can be eliminated as of no interest, so the solution will provide final effluent quality for given retention times, or more importantly, retention times to achieve a necessary effluent quality.
Activated sludge process
Activated sludge flocs
Note filamentous bacteria
Note Vorticella and other protozoa
Activated sludge model
LL0
L
L
L
L
Activated sludge plants
Hyperion, Playa del Rey, CA)
Primary aeration tank
Oxygenated systems
Cryogenic air separation facility, Hyperion, Playa del Rey, CA)
Settling tanks
Secondary settling tank, Hyperion, Playa del Rey, CA)
Aerobic suspended systems – activated sludge
Volumetric loading = QL0/V
QL0
Nitrogen removal Nitrification (Nitrosomonas and Nitrobacter)
NH3 + O2 NO2- NO3
-
Denitrification
NO3- + organics CO2 + N2
Process adaptations
Anoxic Aerobic
Air
Phosphate removal BNR plants
Discarding phosphate anaerobically
Luxury aerobic uptake of P in aerobic stage
Process adaptations for N and P removal
Anaerobic Anoxic Aerobic
AirWastewater
Excess biomass disposal Production
Separation
Further biological treatment – (an)aerobic
Dewatering
Drying – solar or gas heated
Disposal/ beneficial use – soil amender/fertilizeror fuel
The cost of biomass disposal amount to about half the cost of wastewater treatment. Aeration, if used, almost up to half of the rest of the cost. If no aeration, the capital cost , including the cost of land, could be very high.
Typical steps in modern wastewater treatment
How are living beings classified?
Linnaeus(1735)
2 kingdoms
Haeckel(1866)
3 kingdoms
Chatton(1925)
2 groups
Copeland(1938)
4 kingdoms
Whittaker (1969)
5 kingdoms
Woese(1977,1990)3 domains
Animalia Animalia
Eukaryote
Animalia Animalia
EukaryaVegetabilia PlantaePlantae Plantae
ProtoctistaFungi
Protista
(not treated) Protista
Procaryote Monera MoneraArchaea
Bacteria
Historic development of classification
How are living beings classified? Two super- .kingdoms
Three domains
Six kingdoms
Mineralia non-life
Biota/ Vitaelife
Acytota / Aphanobionta (Viruses, Viroids, Prions?, ...) non-cellular life
Cytotacellular life
Prokaryota / Procarya
(Monera)
Bacteria Eubacteria
Archaea Archaebacteria
Eukaryota / Eucarya
ProtistaFungiPlantaeAnimalia
Carl Woese’s Tree of Life
