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