Page 221 - Materials Chemistry, Second Edition

202 Life Cycle Assessment of Wastewater Treatment

which were modified in 1965, removing the demerits of biodegradable detergents
(Devey and Harkness, 1973) with the development of soluble mono-calcium and
ammonium phosphates. The sodium salt of triphosphoric acid plays a main role in
detergents by sequestering the magnesium and calcium ions and working as a soft-
ening agent in water. But the problem with the modified detergents lay in their non-
biodegradable nature and large quantity of phosphorus, which when released into
the water system, stimulated enormous blooming of algae. Additionally, excessive
phosphates cause a deadly threat to the coral reef ecosystem (Pastorok and Bilyard,
1985). Phosphorus is also used as a dispersing agent for clays in oil well drilling and
cement technology, as a fertilizer, and as a flame retardant (Valsami-Jones, 2004).
It has wide applications in the production of baking powder, food additives, match-
sticks, and toothpastes. Phosphorus is also used in industries as corrosion inhibitors
for protection of metal surfaces. (Corbridge, 2013). Hence, the effluents from these
industries contain phosphorus.
Inorganic phosphates act as key substrates in the metabolism and biosynthesis of
nucleic acids (Mudd et al., 1958). They also assist in the formation of bones and per-
form as a buffer during blood purification. Organic phosphorus in the form of esters
is involved in enzymatic action in biochemical reactions as coenzymes. A slight
increase or decrease in phosphorus affects the functioning of the body to a great
extent and can be lethal (Takeda et al., 2004). Phosphorus is found in milk products
and meat. Intake of phosphorus beyond the permissible limit (1.3 g per day) leads to
a shortage of calcium in the body, causing hypocalcemia (Simesen et al., 1970) and
digestive problems (Kumar and Puri, 2012). The World Health Organization recom-
−1
mends a maximal discharge limit of 0.5–1.0 mg L . Moreover, it is known that an
−1
increase in phosphorus in nature of even 1 mg L leads to excessive eutrophication,
which detrimentally affects the quality of water reservoirs.
Thus, it becomes essential to design effective methods for the treatment of phos-
phorus-containing wastewater to maintain an optimal balance. Several methods,
such as biological treatment, chemical precipitation, ion exchange, membrane filtra-
tion, and adsorption have been effectively explored to date for this purpose.

10.2 AVAILABLE TECHNOLOGIES FOR PHOSPHORUS REMOVAL
Phosphorus in water is present in dissolved and particulate forms. Different methods
have been adopted for the removal of phosphorus from wastewater, such as sedimen-
tation, chemical precipitation, ion exchange, membrane filtration, reverse osmosis,
electro-dialysis, and biological methods.
A sedimentation method followed by filtration, or membrane technology, is
required to convert soluble phosphorus into particulate matter (Painter Omoike, 1999).
Chemical precipitation using alum, lime, or iron salts has been widely employed for
the removal of orthophosphate. It requires a large amount of chemicals and results
in excessive production of chemical sludge (Clark et al., 1997). The ion exchange
method encounters a decrease in removal ability after regeneration. The membrane
filtration method undergoes fouling and hence, is uneconomical (Blaney et al.,
2007). Physical processes such as reverse osmosis (Bohdziewicz and Sroka, 2005)
and electro-dialysis (Simons, 1979) suffer from the drawback of high cost, whereas