Abstract
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.
Highlights
According to the famous Redfield ratio, the molecular ratio of carbon, nitrogen and phosphorus in phytoplankton is C:N:P = 106:16:1 (Liang 2007)
Equilibrium time was determined by varying the contact time from 0 to 120 min and allowing 100 mL test solution containing 19.3 mg/L orthophosphate and 5.14 mg/L NO3-N to be adsorbed onto 20 g solid waste residue (SWR) dose via shaking the mixture in the 250-mL plastic bottle at 150 rpm
90 min was considered as equilibrium time, and this result agrees with the previous report (Baraka et al 2012; Kamiyango et al 2009)
Summary
Discharge of wastewater containing excess nitrogen and/or phosphorus species is a serious environmental problem worldwide, as these nutrients cause eutrophication of surface water bodies (Khelifi et al 2002; Painting et al 2007; Tiemeyer et al 2009; Wei et al 2008). Nutrient removal from wastewater is imperative to deter eutrophication of water bodies and various techniques, such as chemical precipitation (Huang et al 2017), adsorption (Fink et al 2016), reverse osmosis (Luo et al 2017), biological removal (Chiu et al 2015), electrodialysis (Guedes et al 2016) and constructed wetlands (Wu et al 2015) widely employed to remove nutrients from wastewaters (Zeng et al 2004). Physical methods have been proved to be either too expensive, as in the case of electrodialysis and
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