Ang, Brian Yee Hoong (2021) Removal Of Nitrate And Phosphate From Water By Adsorption Using Food Wastederived Biosorbents And Biochars. Master dissertation/thesis, UTAR.
Abstract
Due to inappropriate residential and industrial effluent dumping, eutrophication caused by nitrate and phosphate pollution disturbs the local aquatic ecosystem, as well as health conditions of humans consuming contaminated water. However, conventional nitrate and phosphate treatment methods have been proven with possible inefficacy and lack of durability. This has prompted the demand for ecofriendly and cost-effective contingency such as food wastes, which could be accessible adsorbents containing specific functional sites for nitrate and phosphate. This research investigated the application of six biosorbent candidates, namely rambutan peel (RP), passion fruit peel (PFP), longan seeds (LS), chia seeds (CS), papaya seeds (PS), and luffa (L) in the nitrate and phosphate removal from water using shake flask study after acid treatment and heat treatment. Preliminary results showed that acid-treated passion fruit peel biochar (PFPBC) and longan seeds (LS) were the most eligible for nitrate and phosphate biosorption, respectively. The nitrate and phosphate biosorption were predominantly affected by the relatively higher porosity and wider pore size range in biochars than biosorbents. Besides, they highly depended on the introduction of protonated surface functional groups as ionexchange sites through acid treatment. From the interaction effect study, the maximum adsorption uptakes were found at relatively low pH and biosorbent particle size, relatively high initial concentration, and moderate levels of biosorbent dosage. The nitrate and phosphate biosorption fitted pseudo-second-order kinetic model and Langmuir isotherm, suggesting that the biosorption followed homogenous, monolayer chemisorption mechanism. The competitive adsorption study had demonstrated that acid-treated PFPBC had higher selectivity towards nitrate (uptake for both) while acid-treated LS favoured towards phosphate (uptake for both). The effect of phosphate ions on competitive biosorption was more significant than nitrate ions. The adsorption uptake of acid-treated PFPBC towards nitrate was also more significant than that of nitrate ions on the adsorption uptake of acid-treated LS towards phosphate. This was due to the higher ionic charge and binding strength of phosphate ions than nitrate ions, besides higher specificity of binding sites for phosphate ions than nitrate ions. The desorption rate of nitrate approached almost 100 %, whereas that of phosphate exceeded 40 %. Acid-treated PFPBC and acid-treated LS were found with good reusability.
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