Common names used to refer to algae include "seaweed" and "pond scum."



Algae are distinguished from animals, fungi, and protozoans by their ability to make their own food through photosynthesis and are distinguished from plants by their relative simplicity of structure.  All algae contain the green pigment chlorophyll and the organelles chloroplasts, both of which are essential for photosynthesis. 

Algae may be either unicellular (in which case they are known as phytoplankton) or multicellular.  The algae which are important to water treatment are generally unicellular.  All algae contain a rigid cell wall and some also have sheaths (or thin gelatinous coatings) outside the cell wall.  Algae may be non-motile, but many are able to move using a flagella, in which case they are known as flagellates (a term based on morphology rather than taxonomy.)




Most algae are aquatic, living in salt or fresh water, though a few live in soil or on the bark of tres.  In natural waters, algae are an important source of food for other organisms.  They also produce oxygen during photosynthesis, adding to the dissolved oxygen content of the water during the day. 

Since algae require light for growth, they are restricted mostly to the top surfaces of trickling filters and ponds.  They are seldom found in large numbers except in tertiary treatment units, such as clear wells, and usually are not important for water treatment.  However, in oxidation ponds, the algae may represent a substantial portion of the microorganism population and may play a significant role in treatment.



Algae Bloom

Algae bloom.


Algae can be problematic in nutrient-rich waters, especially those containing phosphorus, in which case they often reproduce rapidly and produce colored water and mats of algae known as algae blooms.  In natural waters or treatment plants, algae blooms are problematic because they can change many water characteristics. 

One of the primary factors which algae blooms influence is the dissolved oxygen content of the water.  During the day, the masses of algae produce so much oxygen that the water becomes supersaturated.  Then, at night, the algae actually use up oxygen in the water and can cause such extremely low dissolved oxygen levels that fish kills may result. 

Algae blooms can also cause elevated pH levels in the water.  They may raise the pH levels as high as 9.5, which will influence many of the natural processes occurring in the water.

In some cases, an algae bloom will consume itself.  As the algae grow and reproduce, they use up nutrients in the water.  Eventually, the nutrient levels will drop so low that the algae will have no nutrients and will die back.  In this case, the dead algae bodies will often promote a bacterial bloom as the bacteria respond to the abundance of food.  This overabundance of bacteria can cause yet more problems, depleting the dissolved oxygen levels in the water and causing the system to become anaerobic. 

The best method of dealing with algae blooms is prevention.  




Cellular properties, the nature of the cell wall, and the arrangement of flagella all influence the classification of algae species.  However, the most important factor in algae classification is the types of photosynthetic pigments present in the cell.  Although all algae contain chlorophyll, some species also contain xanthophylls (which are yellow) or carotenoids (which are orange.)  The three phyla of algae which are commonly found in fresh water are described below. 


Phylum Chlorophyta consists of green algae which typically do not contain pigments other than chlorophyll.  Chlamydomonas, shown in the picture above, is a typical green alga.  Notice that this species has two flagella, and is thus able to swim freely through the water.  (When looking through a microscope, you should be aware that the algae's flagella are only visible under extremely high magnification.  Also note that some species in phylum Chlorophyta do not contain flagella and are not mobile.)  Each Chlamydomonas cell contains a single, large chloroplast which fills up most of the cell.  It also contains an eyespot which is a light-sensitive organelle which helps the Chlamydomonas know how to swim toward the light.  


Phylum Euglenophyta contains green or colorless flagellates commonly known as euglenoid algae.  Some scientists consider euglenoid algae to be protozoans because of the species which do not contain chloroplasts and which are able to feed on organic matter and other microorganisms in the water.  A typical euglenoid is Euglena, shown above.  Euglenoids usually have a single flagellum and several chloroplasts. 


Phylum Chrysophyta contains golden-brown algae which contain carotenoids as a major pigment.  Although there are several different kinds of algae in phylum Chrysophyta, one group - the diatoms - is especially important in water treatment.  Diatoms are algae which form a variety of intricate shapes and which contain silicon in their cell walls.  Although other algae in the phylum Chrysophyta have flagella, diatoms are either nonmobile or glide slowly along surfaces.   

In addition to the types of algae mentioned above, there are several other phyla which are found primarily in salt water.  Phylum Pyrrhophyta contains algae known as dinoflagellates, phylum Phaeophyta contains brown algae, phylum Rhodophyta contains red algae, and phylum Cryptophyta contains blue and red flagellates. 




Reservoir Management


Water Storage


Water Uses




Goals of water treatment:



Water Quality Problems

Algae blooms:


How will an algae bloom change water quality?

How does this change the cost of treatment?








Taste and Odor:



Shortened Filter Runs:


Changes in pH:


Changes in Dissolved Oxygen:


Organic Loading:



What Can the Operator Do?



Chemical Control of Algae



Use of Copper Sulfate




Effectiveness of Copper Sulfate


Dosage of Copper Sulfate

Condition 1:


Condition 2:


Maximum Dosage:



Application of Copper Sulfate



Problems with Copper Sulfate



Other Methods for Algae Control