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This study reveals the optimization of ultrasonic-Fenton process for the treatment of sludge taken from a local municipal wastewater treatment plant after anaerobic digestion. Box-Behnken design (BBD), a common approach of response surface methodology (RSM), was applied to evaluate and optimize the individual and interactive effects of three process variables, namely Fe dose, HO amount and sonication time for Fenton-ultrasonication method. Five dependent parameters including total organic carbon (TOC), extracellular polymeric substances (EPS), as LB-EPS and TB-EPS, and metals such as Zn and Cu were considered as the responses to investigate. According to the results of analysis of variances (ANOVA), five modelling equations are proposed that can be used to operate the design space with high regression coefficient R. Modelling results suggest that Fenton parameters, such as: HO and Fe dosage had the significant effects on the overall removal of TOC; whereas, sonication improved the metal removal from the sludge sample. Based on response surface methodology, best performance is achievable under the following conditions: 36 mM of Fe, 320 mM HO with 30 min of sonication respectively for all of the responses.

a b s t r a c tDate palm fiber (DPF) was demonstrated in the present issue as a potential low cost adsorbent for the removal of hexavalent chromium [Cr(VI)] from aqueous solution. A series of batch tests were conducted and the influence of initial metal ion concentration, contact time, pH of the solution and adsorbent dosage was investigated. The adsorbent was characterized by Fourier Transformed Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) to confirm the surface properties of the DPF adsorbent. The adsorption process was found to be strongly pH dependent. The adsorption isotherm data were fitted with Langmuir equation and the adsorption process was found to be followed pseudo-second-order rate kinetics. Chromium showed peculiar activities in aqueous solution due to its transition properties and the mechanism of Cr(VI) adsorption onto the DPF solid surface exhibited physisorption due to intermolecular bonding. Therefore, DPF can be employed as an efficient cost-effective adsorbent for the removal of Cr(VI) as a model component for heavy metals present in industrial wastewater.