Production of composite adsorbents using clay and activated sludge together and investigation of applications for the treatment of various pollutants in industrial wastewaters

In this study, the adsorption of Remazol Black B (in anionic form in its aqueous solutions), phenol (in molecular form in its aqueous solutions) and cadmium(II) ions (in cationic form in its aqueous solutions), which are frequently found in industrial wastewaters, onto activates sludge, clay and activated sludge-clay composite adsorbent which is chemically modified with polyethylenimine, respectively was investigated in a batch stirred system and onto the composite adsorbent packed in a continuous column. The effects of initial pH and initial pollutant concentration on the adsorption for each pollutant and for each adsorbent were searched in a batch stirred system while the effect of feed flow rate for RBB and the effect of feed concentration for all pollutants on the composite adsorbent filled in a continuous column were studied. At the first part of studies, the production of composite adsorbent with high mechanical strength and structural stability, and with high adsorption capacity, including activated sludge and clay at 47/53 (w:w) ratio and chemically modified with polyethylenimine was performed. In the batch system adsorption studies, the optimum initial pH values for Remazol Black B, phenol and cadmium(II) ions were determined as 2.0, 2.0, 6.0 for activated sludge adsorption, respectively, as 2.0, 2.0, 6.0 for clay adsorption, respectively and 7.0 for all pollutants for composite adsorbent adsorption. It was stated that adsorption capacity increased and adsorption yield decreased with increasing initial pollutant concentration up to 500 mg/L for each pollutantadsorbent system. Maximum adsorption capacities of activated sludge, clay and activated sludge-clay composite adsorbents for Remazol Black B, phenol and cadmium(II) adsorptions were found as 131,17 mg RBB/g dried activated sludge, 78,92 mg phenol/g dried activated sludge and 67,13 mg cadmium(II)/g dried activated sludge, respectively; 34,77 mg RBB/g clay, 27,23 mg phenol/g clay and 21,77 mg cadmium(II)/g clay, respectively, and 142,64 mg RBB/g composite adsorbent, 104,30 mg phenol/g composite adsorbent and 87,90 mg cadmium(II)/g composite adsorbent, respectively. In the batch system, to define the adsorption equilibrium mathematically, Langmuir and Freundlich adsorption models were used and it was seen that the Langmuir model fitted better to equilibrium data for each pollutant-adsorbent system. The suitability of the adsorption kinetics to the first and second degree kinetics models for each contaminant-adsorbent system was also investigated, and it was found that the second degree kinetics model defined the adsorption kinetics much better. In RBB adsorption onto the activated sludge-clay composite adsorbent modified with polyethylenimine in the continuous packed bed column, the effect of the feed flow rate was studied in the range of 1.2-3.5 mL/min and it was observed that the highest column capacity and column performance values were reached at the lowest flow rate. All other column studies were carried out at this flow rate. In the column, the effect of the feed pollutant concentration between 25-200 mg/L on the adsorption of RBB, phenol and cadmium(II) ions onto the activated sludge-clay composite adsorbent modified with polyethylenimine and it was seen that as the feed concentration increased for each pollutant, the amount of adsorbed pollutant increased and the column yield decreased. In the adsorption of RBB, phenol and cadmium(II) ions, the highest column adsorption capacity values were found as 49.62 mg RBB/g composite adsorbent, 46.24 mg phenol/g composite adsorbent and 39.05 mg cadmium(II)/g composite adsorbent, respectively. Experimental breakthrough curves were also obtained for each pollutant in the continuous packed column. By applying Adams-Bohart (or Wolborska), Thomas and Yoon-Nelson models to column breakthrough curve data, kinetic constants of the column were determined, theoretical breakthrough curves were found using these constants and it was found that Thomas and Yoon-Nelson models predicted the experimental breakthrough curves better.