Abstract:
Nitrogen and Phosphorous are limiting nutrients for plant growth. Contrary to this, phosphorous
between 20 to 100 µg/L and nitrogen between 500 to 1000 µg/L can cause eutrophication in most
aquatic systems. Therefore, developing low cost and efficient method of removing these
nutrients to protect the aquatic environment is mandatory. The objective of this study was to
investigate simultaneous nitrate and phosphate adsorption capacity of solid waste residue
collected from Awash Melkassa Aluminium Sulphate and Sulphuric Acid Factory. Batch
adsorption experiments were conducted to evaluate the effect of contact time, initial solution pH,
initial nitrate and phosphate ion concentration, adsorbent dose and effect of coexisting ions on
simultaneous removal of nitrate and phosphate ions. Besides, adsorption isotherms and kinetics
were analysed to determine the mechanism and rate determining steps during the adsorption
process. After conducting batch experiment, the equilibrium time was achieved within 90
minutes while the optimum pH and adsorbent dose were found to be 7 and 20 gm/L respectively.
The adsorption kinetics of nitrate and phosphate ions best fitted to the pseudo-second order
equation with R2
values 0.992 and 1 respectively. Moreover, isotherm studies showed adsorption
of nitrate and phosphate fitted better to Freundlich isotherm and Langmuir isotherm with R2
0.988 and 0.984 for phosphate and 0.991 and 0.955 for nitrate respectively. Studies on
reusability of the spent adsorbent showed nearly 50% the adsorbed phosphate can be desorbed
with 0.1M NaOH while that of nitrate is 99.75% showing there is a possibility of reusing. Last
but not least, application on wastewater showed promising result though there is decrease in
percent removal. At the optimums found during the batch experiment, AW residue collected
from Awash Melkassa Aluminium sulphate and Sulphuric acid factory can potentially remove
phosphate from wastewater. But, the untreated AW was not suitable to remove nitrate ion from
wastewater since its percent removal was from 27-30%.
