Pilot process of arsenic-containing groundwater purification by iron-based granular adsorbent fixed bed column

Arsenic (As) pollution in groundwater has become an important environmental issue in China. In order to purify the arsenic-contaminated groundwater in rural areas, an iron-based granular adsorbent (FMGA) capable of synchronously removing As(Ⅲ) and As(Ⅴ) from water was developed and packed into an adsorption fixed bed. A pilot-scale water treatment system was designed and established with a fixed bed as the core unit, which had a good capability for the treatment of As-contaminated groundwater. The results showed that during the continuous operation of 33 days, the residual As concentration in the effluent of the pilot-scale system was continuously below the limit of Standards for Drinking Water Quality (GB 5749-2022 ) (10 μg/L). The breakthrough time of the fixed bed reached 786 h in the first cycle. After the in-situ regeneration using 0.2 mol/L NaOH solution, the breakthrough time of the fixed bed for reuse could still reach 750 h, and the recovery rate of its arsenic adsorption capacity was close to 91%. The turbidity of the effluent for the pilot-scale system was close to zero, and the concentrations of iron and manganese ions were both lower than the limits of the sanitary standard (Fe<0.3 mg/L, Mn<0.1 mg/L). FMGA could be efficiently regenerated and reused without secondary pollution. The adsorption kinetics indicated that the adsorption process of As by FMGA was consistent with the quasi-second-order kinetic model, and As could be removed by chemisorption. The adsorption isotherm showed that the theoretical maximum adsorption capacity of FMGA for As was 74.94 mg/g (pH=7.0). According to the surface characterization results, the maximum load of FMGA was 89.39 N, indicating an excellent mechanical strength.