Preparation of porous biochar by urine assisted pyrolysis of sewage sludge and their application for Eriochrome Black T adsorption

Urine, which is composed of water, urea and mineral substance, has been treated as a kind of wastewater for a long time. In this work, urine was used as a novel activator for sludge activation and porous carbon preparation. The pyrolysis was implemented for urine transformation and sludge carbonization. It was found that urine was firstly converted to pore template g-C3N4 at 550℃ and g-C3N4 was in situ decomposed to form pores at 650℃ in the 2nd stage. The influence of pyrolysis temperature in each stage and urine to sludge ratio on properties of carbon was systematically investigated by using thermogravimetric analysis, N2 adsorption-desorption technique and transmission electron microscope. The maximum specific surface area of the produced carbon was 253 m2 g−1, which was equivalent to the carbon prepared by traditional H3PO4 activation. The carbon also had higher adsorption capacity (19.1 mg g−1) to a typical dye Eriochrome Black T (EBT) and meanwhile showed strong stability and reusability in the repeated adsorption cycles. The implementation of using urine as bio-waste activator for porous carbon preparation would have important implications for waste recycle and reutilization.