Transcript WASTEWATER TREATMENT
BioE 411 and AE/CE/BRT 511
Attached growth systems: sewage farms
Morestead sewage farm
Berlin sewage farm layout
Overland flow designs
Improved attached growth:
Large-scale wastewater treatment
Rotating disc arrangement
Simple treatment: septic tank
Leach field after septic tank
Suspended growth systems
So 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 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
Design approaches to pond
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
Activated sludge model
Activated sludge plants
Hyperion, Playa del Rey, CA)
Primary aeration tank
Cryogenic air separation facility, Hyperion, Playa del Rey, CA)
Secondary settling tank, Hyperion, Playa del Rey, CA)
Aerobic suspended systems –
Volumetric loading = QL0/V
Nitrification (Nitrosomonas and Nitrobacter)
NH3 + O2 NO2- NO3 Denitrification
NO3- + organics CO2 + N2
Discarding phosphate anaerobically
Luxury aerobic uptake of P in aerobic stage
Process adaptations for N and P removal
Excess biomass disposal
Further biological treatment – (an)aerobic
Drying – solar or gas heated
Disposal/ beneficial use – soil amender/fertilizer
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?
Historic development of classification
2 kingdoms 3 kingdoms
4 kingdoms 5 kingdoms 3 domains
How are living beings classified?
Three domains Six kingdoms
Acytota / Aphanobionta
(Viruses, Viroids, Prions?, ...)
Eukaryota / Eucarya
Carl Woese’s Tree of Life