Abstract
In this work, a sand filtration-activated carbon adsorption system was evaluated to remove the fungicide content of a biologically treated effluent. The purification process was mainly carried out in the activated carbon column, while sand filtration slightly contributed to the improvement of the pollutant parameters. The tertiary treatment system, which operated under the batch mode for 25 bed volumes, resulted in total and soluble COD removal efficiencies of 76.5 ± 1.5% and 88.2 ± 1.3%, respectively, detecting total COD concentrations below 50 mg/L in the permeate of the activated carbon column. A significant pH increase and a respective electrical conductivity (EC) decrease also occurred after activated carbon adsorption. The total and ammonium nitrogen significantly decreased, with determined concentrations of 2.44 ± 0.02 mg/L and 0.93 ± 0.19 mg/L, respectively, in the activated carbon permeate. Despite that, the initial imazalil concentration was greater than that of the fludioxonil in the biologically treated effluent (i.e., 41.26 ± 0.04 mg/L versus 7.35 ± 0.43 mg/L, respectively). The imazalil was completely removed after activated carbon adsorption, while a residual concentration of fludioxonil was detected. Activated carbon treatment significantly detoxified the biologically treated fungicide-containing effluent, increasing the germination index by 47% in the undiluted wastewater or by 68% after 1:1 v/v dilution.
Highlights
Tertiary treatment systems are based on the application of a wide range of physical and chemical methods to completely remove various recalcitrant pollutants from activated sludge secondary effluents [1,2]
Regarding the removal of organic matter, the total chemical oxygen demand (COD) was significantly reduced from 209 ± 4.3 mg/L in the biologically treated fungicide-containing wastewater to 177 ± 2.1 mg/L and 49.1 ± 2.1 mg/L in the permeate of the sand filter and activated carbon column, respectively (Figure 2)
The soluble COD was significantly decreased from 181 ± 5.64 mg/L in the biologically treated effluent to 151 ± 2.1 mg/L in the sand filtrate, whereas the respective value in the permeate of the activated carbon absorbent was extremely low (21.3 ± 2.1 mg/L (Figure 2))
Summary
Tertiary treatment systems are based on the application of a wide range of physical and chemical methods to completely remove various recalcitrant pollutants from activated sludge secondary effluents [1,2]. Sand filtration and activated carbon adsorption are considered eco-friendly approaches, since no chemicals are required to remove the pollutants. Sand filtration has been recognized as one of the most widely used physical methods in tertiary wastewater treatment, resulting in high suspended solids removal at a low cost [6]. Previous studies have shown that treatment of secondary effluents with a slow sand filtration process results in reduced suspended solids compared with the rapid filtration process [1,8]. The low capital and operating cost as well as the easiness and simplicity of handling and maintenance are the main advantages of slow sand filtration [1]
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