Abstract: Aluminum sulfate reacts with phosphates to create
aluminum phosphate and a sulfate. The conversion of the phosphate
to aluminum phosphate is very important because this allows the
phosphate to be easily extracted. This manipulation is used today
in industrial waste treatment sights. The removal of phosphates is
very important for if phosphates are not removed, they plague
bodies of water by feeding algae which clog the surface waters and
eventually effect every living and nonliving thing in that
environment.
Chemical Process: The reactions which occur are the following:
Aluminum sulfate(alum) in combination with wastewater can
flocculate phosphorus. The Flocculation that happens with aluminum
sulfate addition is the formation of aluminum phosphate particles
that attach themselves to one another and become heavy and settle
to the bottom of a clarifier. The aluminum sulfate and phosphorus
mixture can then be withdrawn, thereby removing the phosphate or
phosphorus from the wastewater flow.
Industrial Applications: The application of this reaction to the
industrial world consists of a set of processes to filter out the
phosphate. The setup is the following:
Purpose: Restrict phosphates to aluminum phosphates for easier
disposal of phosphorus.
The first step in phosphorus removal is the Rapid Mix. In
this stage, alum and waste or water runoff(known as effluent) is
blended together as rapidly as possible with the use of a high-
speed mixer called a “flash mixer.” After this instant mixing, a
slower moving process called coagulation and flocculation follows
to allow the formation of a floc. These processes occur in a
Flocculation Chamber. This floc consists of suspended and colloidal
matter, mainly including the aluminum phosphate. Next, the
effluent travels to a clarifier in which sedimentation occurs. The
heavier aluminum phosphate settles to the bottom then pumps at the
bottom of the clarifier pump out the aluminum phosphate via pipes.
This aluminum phosphate is then disposed. Currently, there are no
economical uses for aluminum phosphate.
Also, this chemical process is similar to the process used by
laundry detergents. Many detergents contain synthetic phosphates,
called tripolyphosphates(TTPs). These chemicals cling to grease
and dirt particles(alum in the previous example), keeping them in
suspension until the wash water is flushed out of the washing
machine.
Impact on Society: This reduction in phosphorus is very important.
This added phosphorus disrupts the natural cycle of phosphorus. One
result of this is an algal blooms, or exponential growth in algae.
When algal blooms occur, the surface of a freshwater lake is
clouded with an almost finite amount of bacteria because of an
increase in a nutrient. In this case an increase in phosphate, a
favorite for algae. This deprives the bottom of the lake by
cutting off light. A dense mat of algae choke off the lake. Also,
phosphates are nutrients for plantlife. When fall approaches, or
when phosphate levels are decreased, the algae die and fall to the
bottom, changing the bottom from a silt, sand and clay bottom to a
sand gravel and rock bottom. When the plants die, they are
degraded by aerobic bacteria, which can deplete dissolved oxygen,
killing aquatic organisms. As oxygen levels drop, anaerobic
bacteria resume the breakdown and produce noxious products. All of
this impairs navigation, fishing, swimming and recreational
boating.
Total phosphorus removal through filters after using alum as
a filtering aid achieves 70 to 95 percent efficiency. Phosphates
must be filtered out before the water or wastes are dumped back
into bodies of water.
Glossary
Flocculation: The gathering together of fine particles to form
larger particles.
Effluent: Wastewater or other liquid — raw, partially or
completely treated — flowing from a basin, treatment process, or
treatment plant.
Coagulation: The use of chemicals that cause very fine particles
to clump together into larger particles. This makes it easier to
separate the solids from the liquids by setting, skimming, draining
or filtering.
Floc: Groups or clumps of bacteria and particles or coagulants and
impurities that have come together and formed a cluster.
Colloidal: Very small and finely divided. Referring to solids.
Does not dissolve and remains dispersed in a liquid for a long time
due to small size.
Algal blooms: Rapid growth of algae in surface waters due to
increase in inorganic nutrients.
Bibliography
Kerri, Kenneth D. Advanced Waste Treatment. Sacramento, Ca.: CSU,
Sacramento, 1987.
Adams, Melinda. Environmental Science. Redwood City, Ca.: The
Benjamin/Cummings Publishing Company, Inc., 1991.
