Abstract

Sewage sludge was used as precursor to develop a potential inexpensive adsorbent by both simple drying and pyrolysis. The resulting materials were evaluated as adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solution. The dried biosolids showed a BET surface area lower than 3m2/g, which yield a maximum adsorption capacity of 0.73mmol 4-CP/g at pH 5.0 and 15°C. The carbonization of biosolids under relatively mild conditions allowed obtaining materials with BET surface area up to 45m2/g, which led to a significant increase of the maximum adsorption capacity (1.36mmol 4-CP/g). The high ash content of the starting material (23%, d.b.) limits the development of porosity on a total dry-weight basis. Adsorption data were well fitted to the Redlich–Peterson isotherm equation whereas the most commonly used Langmuir and Freundlich equations were less satisfactory probably because of the occurrence of summative adsorption phenomenon. A thermodynamic study of the adsorption showed the spontaneous and exothermic nature of the process. Thus, simple drying and carbonization provide two ways of valorization of sewage sludge through its conversion into inexpensive low-rank adsorbents potentially useful for the removal of some hazardous water pollutants, like chlorophenols and related compounds.

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