Superior visible-light photocatalytic activity of biocarbon derived from sewage sludge in the absence of active phase for hydrogen production

Sewage sludge, a bioproduct generated in surplus amount from the domestic wastewater treatment has always been a chief environmental concern. Thermochemical and biological conversion of Sewage sludge into the valuable products can be an effective and efficient alternative strategy than conventional disposal method. Herein, Sewage sludge was pyrolyzed at highest treatment temperature of 700 °C in rotary kiln pilot-scale pyrolysis unit (Stage III) at the UKBRC, University of Edinburgh to obtain biochar, bio-oil and biogas. Basic utility properties of Sewage sludge biochar (SS700) such as CHNS, functional group, crystalline structure, electric conductivity, Polycyclic Aromatic Hydrocarbons, Dioxin/Furan and Polychlorinated Biphenyls were determined and then SS700 was utilized for photocatalytic hydrogen generation. Photocatalytic H2 production of SS700 was studied under visible-light irradiation. The H2 yield was 3331 µmol/g which is higher than its conventional carbon-based competitors (i.e. Graphene, CNTs and C3N4). In order to justification of superior activity of SS700, photocurrent measurements were carried out and ultraviolet-visible (UV-vis) diffuse reflectance spectra were recorded. The superior activity is attributed to its aromatic carbon structure, high surface area, inorganic materials, electron-conductive nature and hydrophilic surface functional group. This work introduces SS700 as a low-cost, stable, environmentally friendly, and sustainable method which can be a great leap forward toward the more sustainable energy development.