Simultaneous removal of nitrate and phosphate from wastewater using solid waste from factory

Phosphorous and nitrogen concentration, respectively, between 20–100 and 500–1000 μg/L can cause eutrophication. Thus, developing efficient low-cost removal method is important to protect the aquatic environment. The aim of this study is to investigate simultaneous nitrate and phosphate adsorption capacity of solid waste residue (SWR) generated from Awash Melkassa Aluminium Sulphate and Sulphuric Acid Factory. Batch adsorption experiments were conducted to evaluate the effect of various parameters on the simultaneous removal of nitrate and phosphate ions. The experimental results show that the equilibrium time was attained within 90 min, while the optimum pH and adsorbent dose were found to be 7 and 20 g/L, respectively. The pseudo-second-order equation with R2 values 0.99 and 1, respectively, fits to the adsorption kinetics of nitrate and phosphate. Moreover, isotherm analysis shows that adsorption of nitrate and phosphate was better modeled with Freundlich and Langmuir isotherms with R2 0.99 and 0.98 for phosphate and 0.99 and 0.96 for nitrate, respectively. Results of regeneration of the spent adsorbent show nearly 50% of the adsorbed phosphate can be desorbed with NaOH, while that of nitrate is 99.75%. Under optimum conditions, SWR can potentially remove phosphate from wastewater. However, the adsorbent is not suitable to remove nitrate ion from wastewater.