role of protozoa and algae in waste water treatment plant
TRANSCRIPT
Protozoa and Algae in
Waste water treatment plantShafiqa Shahzadi
Roll no. 03
M.phil-I
Protozoa
Several types of protozoa such as: amoebae, ciliates, and flagellates are
found present throughout the entire sewage water treatment process.
The importance of protozoa in wastewater treatment is to maintain a slime
layer within trickling filter systems. They play a predatory role in
removing bacteria, other protozoa, and several small particles.
Protozoa have multiple feeding
mechanisms:
• Filter feeders
• Raptorial feeders
Filter feeders
• Filter feeders consume during the trickling filter phase
• when water is passed through the filter.
Raptorial feeder
• such as flagellates and amoebae, feed on different types of bacteria
• Larger forms of amoebae eat ciliates and flagellates as well as smaller amoebae feed primarily on bacteria
Protozoan parasites
They can contribute to
human morbidity and mortality
Giardia lamblia Cryptosporidum
Giardia lamblia
G. lamblia enters the water supply through
contamination by fecal matter. It is a protozoan parasite located in the
small intestines.
It causes giardiasis. Cysts formed by the protozoan
can be ingested by drinking contaminated
water
CryptosporidumIt causes
cryptosporidiosis which is acquired through
tainted drinking water.
It is removed from sewage water by
dissolved-air floatation or by dual-media filtration.
Amoebae
• Rarely predominant except for start-up conditions and conditions that mimic start-up such as over-wasting, recovery from toxicity, washout, and organic overloading
Flagellates, plant-like
• Dominant under high organic loading, dispersion of floc particles, such as through chlorination, and start-up conditions or conditions that mimic start-up. Also may dominate in the presence of excess soluble phosphorus.
Flagellates, animal-like
• Except for the presence of excess soluble phosphorus, these are dominant for operational conditions listed for plant-like flagellates and usually follow plant-like flagellates as the dominant group.
Free-swimming ciliates
• Transition group that dominates between healthy and unhealthy conditions and proliferates when large numbers of free-swimming bacteria are present.
Crawling ciliates
• Dominant in the presence of mature floc particles and low BOD in the bulk solution. Alternate with stalked ciliates as the dominant group.
Stalked ciliates
• Dominant in the presence of mature floc particles and low BOD in the bulk solution. Alternate with crawling ciliates as the dominant group.
In terms of biomass, protozoa represent between 0.17 and 0.44% ofthe sludge during the colonization phase but can represent up to 9% atsteady state (Madoni, 1994a).
These protozoa have an important role in maintaining a good balance in thebiological ecosystem: they eliminate the excess bacteria and stimulate theirgrowth and they promote flocculation (Gerardi et al., 1995).
By consuming the free bacteria, they help to decrease the turbidity of theeffluent as well as its BOD and its suspended matter content (Curds et al.,1968).
Protozoa are known to be an important indicator of the efficiency ofwastewater treatment plant. Segmentation of the protozoa from the sludgeflocs is a key step. Identification is based on size and shape descriptors of theprotozoa silhouette.
The protozoa are characterized by their size (projected surface, A, and length,L, given by the maximal Feret diameter, Fmax) and shape descriptors(elongation, FS, circularity, C, and eccentricity, E, calculated from the second-order moments (M2x, M2y and M2xy))
FS = Fmax / Fmin
C = P2 / (4π A)
where P is the perimeter of the silhouette
E = (4π)2 (M2x-M2y)2 + 4M22xy / A2
The presence of a flagellum or a stalk is helpful in the identification step, but itis not always possible to obtain complete protozoa (with flagella or stalk).
Wastewaters are excellent algal growth media,with CO2 addition
• 2,400 acres of large WW ponds operate in No.Calif.
A 10-fold increase is reasonable statewide.
Harvesting & nutrient removal: Cal Poly research
WWT helps in energy balance & costs of biofuel
Wastewater algae biofuel is rapid path to market
Algae
Algae for Wastewater Treatment
ProsProduce oxygen
with
low energy input
Remove soluble N
and P
CO2 fixed
Biomass produced
Cons
Rarely settle well
Failure to meet
suspended solids limits (~45 mg/L)
Interfere with
disinfection
Biomass produced
Algae Harvesting Options
Chemical Coagulation +
FlotationNatural Settling
Chemical Coagulation & Dissolved Air Flotation
Metal Salts & Petroleum-based Polymers– Create algae flocs
– $300 to $600 per MG chemical costs
vs. $1000 per MG total O&M cost avg.
(AMSA 2002)
• Dissolved Air Flotation– Mechanical floc removal
– Pressurized air and water
Conventional vs. High Rate Ponds
Conventional Ponds• Little mechanical mixing
• 20 – 100s days residence times
• C-limited
High Rate Ponds
• Paddle wheel mixing
• 4 – 10 day residence times
• C-limited with wastewater
Mechanical Systems
Drawbacks
• High Energy Consumption
• especially for nutrient
removal
• High Cost
• $20 billion investment
needed in next decade -
ASCE
Ponds (deep or C-limited)
Drawbacks
• Methane Emissions
• Poor Nutrient Removal
• Land Requirement
• Costly Chemical Coagulation
A New Approach
CO2-Enhanced Wastewater Ponds
Add CO2 to Balance C:N:P
Algae: C : N : P = 50 : 8 : 1
Wastewater: C : N : P = 20 : 8 : 1
Add CO2
CO2-Enhanced High Rate Ponds
• Improved and accelerated treatment
• Biomass fuel provides greenhouse gas abatement
• WWT savings: ~$6 per gallon oil produced
– Marginal oil cost is only extraction/processing
• Energy used in WW treatment decreases:
15 kWh saved per gallon oil produced
• Fuel production residual becomes fertilizer
CO2-Enhanced Algae Cultures
Research Results
• Low nutrient levels achieved
• Algae production accelerated
• Harvesting costs decrease due to
bioflocculation
• Lipids produced
– 30% lipid content, current maximum
– 1500 gallons per acre per year (best
est.)
NEXT STEPS
• CO2 addition at pilot scale
• C:N:P ratio flexibility studies to
improve range of
applications
• Full-scale demonstration