Effect of pyrolysis temperature on polycyclic aromatic hydrocarbons toxicity and sorption behaviour of biochars prepared by pyrolysis of paper mill effluent treatment plant sludge Parmila Devi, Anil K. Saroha ⇑ Department of Chemical Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India highlights  Paper mill sludge biochars were used for pentachlorophenol (PCP) removal.  Sorption behaviour of biochars was determined based on degree of carbonization.  Fractions of adsorption and partition in total PCP removal were determined.  Adsorption and partition parameters were correlated with biochar properties.  Risk assessment for 16 priority EPA PAHs in biochar matrix was performed. article info Article history: Received 6 April 2015 Received in revised form 22 May 2015 Accepted 23 May 2015 Available online 28 May 2015 Keywords: Biochar Pyrolysis Sludge Polycyclic aromatic hydrocarbons Adsorption abstract The polycyclic aromatic hydrocarbons (PAHs) toxicity and sorption behaviour of biochars prepared from pyrolysis of paper mill effluent treatment plant (ETP) sludge in temperature range 200–700 °C was stud- ied. The sorption behaviour was found to depend on the degree of carbonization where the fractions of carbonized and uncarbonized organic content in the biochar act as an adsorption media and partition media, respectively. The sorption and partition fractions were quantified by isotherm separation method and isotherm parameters were correlated with biochar properties (aromaticity, polarity, surface area, pore volume and ash content). The risk assessment for the 16 priority EPA PAHs present in the biochar matrix was performed and it was found that the concentrations of the PAHs in the biochar were within the permissible limits prescribed by US EPA (except BC400 and BC500 for high molecular weight PAHs). Ó 2015 Published by Elsevier Ltd. 1. Introduction The conversion of sludge into biochar is a promising method for the sludge management in comparison to traditional methods like landfilling and agricultural use. Most of the studies reported in lit- erature have used wood and agricultural waste as raw materials for biochar preparation. These biochar are rich in carbonaceous frac- tion with high surface area due to abundance of cellulose, hemicel- lulose and other organic compound in raw materials. Recently, large number of studies have been reported in the literature on the environmental benefits by use of sludge based biochar in var- ious applications like restoration of degraded land, increase in crop yield, adsorption of carbon dioxide and various contaminates from the environment (Tan et al., 2014; Devi and Saroha, 2014a). The usage of sludge based biochar as an adsorbent is emerging as an attractive option. Although the surface area and porosity of the sludge based biochar is much smaller than the commercial acti- vated carbon, the adsorption capacity of the biochar for organic contaminant removal is almost equal or higher than the commer- cial activated carbon due to presence of the mineral rich carbon phase in sludge based biochar (Wang and Xing, 2007; Luo et al., 2011). The sludge based biochar is abundant in metal oxides because the precursor sludge contains significant amount of min- erals, organic compounds and heavy metals. Several studies have been reported in literature on mobility and bioavailability of heavy metals in biochar to assess the environmental impact of usage of sludge based biochar. It has been reported that pyrolysis of paper mill sludge immobilize the heavy metals in biochar matrix result- ing in decrease in bioavailability and leaching potential of heavy metals (Devi and Saroha, 2014b). In order to use biochar as an adsorbent, it is significant to understand the key parameters that affect the physicochemical properties (surface area, porosity, moisture and ash content, http://dx.doi.org/10.1016/j.biortech.2015.05.084 0960-8524/Ó 2015 Published by Elsevier Ltd. ⇑ Corresponding author. Tel.: +91 1126591032; fax: +91 1126581020. E-mail address: aksaroha@chemical.iitd.ac.in (A.K. Saroha). Bioresource Technology 192 (2015) 312–320 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech