Phosphate can be reduced by maintaining the phosphate level

removal from waste effluent using improved fly ash



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In this research,
activity of fly ash was improved towards phosphate removal by giving treatment of
sulphuric acid. Obtained improved fly ash was useful for the phosphate removal
from water effluent up to 99 %. Important and required parameter like contact
time was varied from zero to 60 min, adsorbent dose from 5gm /l to 30 gm /l and
initial phosphate concentration was changes from 50 ppm to 80 ppm. After completing
all the experimental work 20 min contact time, improved fly ash dose of 15 gm/l
and 60 ppm initial concentration emerged as an optimum and desired conditions
for the phosphate removal up to 99 %. Temperature of 30 o c, 8 pH and
sufficient stirring was more favorable for above optimum condition. Improved
fly ash as an adsorbent worked well and removed more quantity of phosphate from
taken water effluent.


Phosphate present in the
waste water creates problem to the surface water. Present phosphate in lakes
and rivers responsible for the water pollution. Excess amount of phosphate
increases extra growth of aquatic algae and plants. This excess growth
responsible for reduction of oxygen present in the water 1-3. Reduced oxygen
is again harmful to aquatic life present in the water. Phosphate is always
limiting factor for Eutrofication of algae present in water 4. Excess
phosphate when discharge in water will contribute Eutrofication. Water effluent
from fertilizer plants and municipal waste is the major source of phosphate.
Range of 0.5-1.0 mg/l is the standard limit recommended for the phosphate in
water. Higher level of phosphate in water increases excess growth of algae.
This excess growth is consuming more oxygen from water. Reduced oxygen may destroy
aquatic life. Fertilizer industries are also responsible for excessive
discharge of phosphate in the water. Use of fertilizer in agricultural field is
increases tremendously. Excessive use of fertilizer by the farmers leads runoff
of fertilizer from farms to rivers and nearby water steams. Eutrofication of
algae and other plants can be reduced by maintaining the phosphate level in
0.5-1.0 mg/l. Fly ash which is available as a waste in thermal power plant can
be effectively and economically used for the removal of phosphate from water
5-8. Adsorption is the tools that can be used for the removal of phosphate
from stagnant water. Fly ash should be improved with acid (Suphuric acid)
treatment to increase rate of adsorption 9-10. Fly ash has sufficient calcium
content which will react with phosphate. This work Represent how improved fly
ash is responsible for the effective removal of phosphate from water effluent using
adsorption by varying different parameter like fly ash dose, temperature,
initial phosphate concentration and contact time. 

Material and Methods

2.1.   Improved Fly ash

Fly ash was collected
from local thermal power plant. Collected fly ash washed with distilled water
and was dried at 100 o C for two hour in drier. The size of fly ash
is between 0.120 mm to 0.078 mm. Improvement of fly ash completed by giving
treatment of Sulphuric acid. Treated fly ash again dried at 100 oC
for 2-3 hour. Sulphuric acid of 0.5 ml was used for 5gm of fly ash.
Characteristic of fly ash and improved fly ash (IFA) was carried out using XRD
(Philips, PW 1140/90) method, shown in fig 1.   


M= mullite
(Al1.27Si0.73O4.86), Q= quartz (SiO2),
H= hematite (Fe2O3), L= lime (CaO)

A.       Fly ash (Before improvement)

(Al1.27Si0.73O4.86), Q=quartz (SiO2),H=hematite
(Fe2O3),L=lime (CaO),
(CaSO4.2H2O), A= millosevichite (Al2(SO4)3),F=
paracoquimbite (Fe2(SO4)3.9H2O)

B.       Improved fly ash (IFA)


X-Ray diffraction (XRD) analysis
of adsorbent


2.2.  Phosphate

Potassium Di-hydrogen
ortho phosphate (KH2PO4) was taken as an artificial
source of phosphate which was acted as waste water. A stock solution of 1000
ml/lit was prepared for the experimental work.

2.3.  Analytical

Phosphate removal was
measured using UV-visible spectrophotometer (Elico, SL-159). A wavelength of
648 nm was set for the determination of amount of phosphate available in
samples. All the experiments were carried out incubator with sufficient shaking
facility. pH meter (Hanna, HI 22091) was used for the determination pH. Adjustment
in pH was carried out using H2SO4 and NaOH.

Result and Discussion

3.1.  Effect of
contact time

Effective contact time
for the adsorbent and solution plays important role in adsorption of phosphate.
IFA given rapid adsorption of phosphate and equilibrium was reached in 10-20
min. Increasing contact time beyond 20 min was not able to favor for more
adsorption of phosphate from water. Phosphate removal was carried out by
precipitation reaction and this formed insoluble precipitate can be separated
easily from main water sample. Effect of contact time on phosphate removal from
water samples was carried out at adsorption dose of 10 gm/l, 8 pH, and initial
phosphate concentration of 50 mg/l (50 ppm) at 30 o C with
sufficient agitation. Conducted experimental result was plotted and is shown in
fig 2. Contact time of 20 min was evolved as an optimum for above mentioned
parameter and this optimum contact was considered for further experimental

Fig. 2. Effect of contact time on phosphate removal

3.2.  Effect of
adsorbent dose

Adsorbent dose (IFA
dose) was varied from 5 gm/l to 30 gm/l for phosphate removal at pH of 8,
contact time 20 min and initial concentration of 50 mg/l (50 ppm). Obtained
experimental result were plotted and shown in fig 3. Adsorbent dose of 15 gm/l
was found optimum for maximum phosphate removal. Increasing IFA dose beyond 15 gm/l
shown no change on phosphate removal. IFA worked as an adsorbent able to
removed 98% of phosphate from given water samples. Therefore 15 gm/l adsorbent
dose proved itself as an optimum quantity for better phosphate removal.

Fig. 3. Effect of adsorbent dose on phosphate

3.3.  Effect of
Phosphate concentration

Effect of contact time
and adsorbent dose was carried out at 50 ppm at defined conditions. Phosphate
removal was conducted in changing initial phosphate concentration from 50 ppm
to 80 ppm. This experimental work was completed at pH of 8, adsorbent dose 15
gm/l and contact time of 20 min at 30 o C with sufficient stirring.
Phosphate removal was achieved up to 99% at 60 ppm. When solute (phosphate)
concentration was increased beyond 60 ppm, adsorbent sites gets saturates and
no more adsorption was possible. Formed gypsum in IFA gets react with phosphate
and formed brushite (CaHPO4.2H2O), remaining phosphate react
with metal ions present on adsorbent and form soluble precipitate which is then soluble in water. Obtained XRD result
is shown in fig 4 and effect of phosphate concentration shown in fig 5.

M=mullite (Al1.27Si0.73O4.86), Q=
quartz (SiO2), B=brushite (CaHPO4.2H2O)


4. X-Ray diffraction (XRD) analysis
of IFA after adsorption at 60
ppm initial phosphate concentration, adsorbent dose 15 gm/l and contact time of
20 min

5. Effect of phosphate concentration on phosphate removal


Outcomes of this
completed experimental work proved that improved fly ash can be used
effectively and economically for the phosphate removal from water effluent. Improved
fly ash has more affinity for the phosphate hence it can be use as a low cost
adsorbent. Phosphate removal up to 99% is achieved on considering emerged
optimum conditions from different experimental work. Varying operating
conditions like contact time, adsorbent dose and initial phosphate
concentration was useful to find out optimum condition for phosphate removed. Obtained
optimum parameter is useful to carry out phosphate removal operation
commercially on large scale.




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