Simultaneous Removal of Phosphate and Nitrate from Synthetic and Real Wastewater by Meretrix lusoria as an Efficient and Novel Material
2021
Daudzai, Zubaida | Dolphen, Rujira | Thiravetyan, Paitip
Phosphate (PO₄³⁻) and nitrate (NO₃⁻) contamination causes the threatening issue of eutrophication. A major waste from seafood industries of various seashells including Anadara inaequivalvis, Saccostrea commercialis, Perna viridis, Tegillarca granosa, Filopaludina martensi, Babylonai areolate and Meretrix lusoria was thermally modified and investigated for PO₄³⁻ and NO₃⁻ removal from synthetic and domestic wastewater. It was found that some raw seashells could remove ≥85% of PO₄³⁻, whereas their NO₃⁻ removal efficiency was poor. However, after calcination, among others, only M. lusoria pyrolysed at 800 °C (M. lusoria F800) was found as a novel adsorbent for both PO₄³⁻ and NO₃⁻ removal. An increase in temperature and increased Ca(OH)₂ content enhance the removal of PO₄³⁻ and NO₃⁻ by precipitating with calcium ions (Ca²⁺). M. lusoria F800 was the best for PO₄³⁻ and NO₃⁻ removal compared with commercial lime and other calcined seashells. The maximum adsorption capacity (Qₘₐₓ) of M. lusoria F800 for PO₄³⁻ and NO₃⁻ was 700 mg/g and 170 mg/g, respectively, which was higher than the Qₘₐₓ of PO₄³⁻ and NO₃⁻ by commercial lime Ca(OH)₂ which was about 465 mg/g and 18 mg/g, respectively. The crystals of calcium phosphate-hydroxide and calcium nitrate-hydroxide complexes were mainly found in M. lusoria F800 that adsorbed PO₄³⁻ and NO₃, respectively, as confirmed by X-ray diffractometer (XRD). Also, M. lusoria F800 could completely remove PO₄³⁻ and NO₃⁻ from domestic wastewater. Hence, easily handled and cost-effective M. lusoria F800 would increase the value of this waste material, increase water quality and mitigate eutrophication.
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