Recycling of groundwater treatment sludge to prepare nano-rod erdite particles for tetracycline adsorption

Abstract

Groundwater treatment sludge was a ferrihydrite-rich solid waste and abundantly generated for potable water production in groundwater treatment plant. Here we demonstrated an alternative strategy to reuse the sludge for preparing nano-rod erdite particles (EPs) via a facile hydrothermal method with only adding Na2S. The produced EPs were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The SEM results showed that with the molar ratio of N2S to Fe in the sludge increasing from 1 to 2, the product EPs grew long from 0.5-1 μm to 1–4 μm. The product EP-0.2, prepared at the molar ratio of 0.2, was amorphous aggregates with dotted distribution of hexahedral pyrite. With the molar ratio increasing to 2, the product EP-2 was in the form of nanorod, and exhibited high TC adsorption capacity of 1960.8 mg/g, approximately 15 times of that of EP-0.2. By adding 0.02g EP-2, the removal rate of TC was 92.5% at the initial TC concentration of 1000 mg/L, higher than that of active carbon, diatomite, polyaluminium chloride and polyferric sulfate, and nearly 100% TC and 51.5% total organic carbon were removed from pharmaceutical wastewater. EP-2 was completely hydrolyzed to yield Fe oxyhydroxide in TC-containing solution, which exhibited adequate hydroxyl groups to link the –NH2 group at the side chain of TC molecules, resulting in high TC adsorption. This is the first report of recycling groundwater treatment sludge for preparing nano-rod erdite particles, which can be serve as low-cost materials in wastewater treatment.