A metallic phenolic network-enhanced bentonite for ammonical nitrogen removal from black-odorous water

A black colouration and strong odours of highly polluted water are often associated with high levels of ammonical nitrogen (NH4+-N), which is a priority for pollution control. Treatment technology needs to be cost-effective and the natural mineral, bentonite (Be) is widely used in water treatment, but without activation performs poorly in NH4+-N removal. We report on a new adsorbent (denoted as Be-TA-Fe) prepared by the coupling of bentonite and a metallic phenolic network, ferric tannate (Fe-TA). Advanced characterisation techniques and batch adsorption tests were used to determine its structural features and adsorption behavior for NH4+-N. After modification by Fe-TA, the bentonite showed a larger BET surface area up to 75.842 m2/g. The optimal conditions for the preparation of Be-Fe-TA which resulted in the highest removal of NH4+-N were a mass ratio of bentonite to Fe-TA (mBe/mFe-TA) of 8:1, with 8% w/w starch and 8% w/w polyvinyl alcohol (PVA). As expected, lower adsorbent doses produced higher adsorption capacity. The main mechanisms for the removal of NH4+-N by Be-Fe-TA were through electrostatic adsorption, ion exchange and ionic bonding. The novel sorbent performed well in a weak acid and neutral environment, and some parameters, such as dissolved oxygen and microorganisms, did not affect the removal significantly. For example, the removal efficiency could reach 92.85% removal of NH4+-N at 13.5 mg/L and pH 6.8 with 25 g/L of Be-TA-Fe. Overall, Be-TA-Fe shows significant promise as a method of treatment for contaminated by ammonical nitrogen.