A screening guide for efficient dye adsorbents under continuous flow conditions: a review

In general, the pollutants can be sequestrated from wastewater by adsorption technology under batch or continuous flow conditions. Although there are a good number of reviews on pollutants uptake under batch conditions and related operational factors affecting the process, reviews on pollutants uptake under column conditions are relatively few. Hence, the importance of this review comes as it evaluated the performance of many adsorbents under continuous flow conditions, which is considered more practical than batch process. Based on this aim, many synthetic and non-conventional adsorbents were examined which utilized for dyes uptake under batch and continuous flow conditions. It is necessary to assess the performance of the examined adsorbents using both processes to determine the most appropriate one, taking into account the high production cost of synthetic adsorbents. The performance of sixty nine adsorbents for removing different classes of dyes using batch and column type processes are examined in this review. The results are collected under the following criteria: (a) The adsorbent should have maximum uptake capacity higher than 100 mg g⁻¹; (b) Column saturation capacity, operational factors and service time for dye uptake are reported; (c) Adsorbent recycling under dynamic conditions is reported. Based on the earlier criteria a screening guide was proposed for the most efficient dye adsorbent under column conditions: (a) column saturation capacity > 184 mg g⁻¹; (b) column service time < 10 h; (c) the adsorbent should be used up to 5 cycles after regeneration with a green solvent. The most efficient synthetic adsorbent is vinylpyridine-methacrylic acid cryogel toward Basic Blue 9 with column capacity 388 mg g⁻¹, service time 0.8 h and used for 4 cycles with 100% efficiency. For non-conventional adsorbents, modified-chitosan is outstanding toward Basic Blue 9 with column capacity 379 mg g⁻¹, service time 3.4 h and used for 5 cycles with a final efficiency 93%.

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