Closed cycle of recycling of waste activated sludge Marina Vlasova a,⇑ , Abigail Parra Parra a , Pedro Antonio Márquez Aguilar a , Ariadna Trujillo Estrada a , Veronica González Molina a , Mykola Kakazey a , Tamara Tomila b , Virginia Gómez-Vidales c a Center of Investigation in Engineering and Applied Sciences of the Autonomous University of the State of Morelos (CIICAp-UAEMor), Av. Universidad, 1001 Cuernavaca, Mexico b Institute for Problems of Materials Science, National Academy of Sciences of Ukraine,3, Krzhyzhanovsky St., Kiev 252680, Ukraine c Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior C.U., 04510 Cd. México, Mexico article info Article history: Received 6 March 2017 Revised 24 October 2017 Accepted 31 October 2017 Available online xxxx Keywords: Waste activated sludge Carbonization Adsorption Porous bricks abstract The recycling of waste activated sludge (WAS) formed in the process of biological purification of sewage is an urgent ecological problem. In the present work, two ways of recycling of WAS containing from 8 to 30% free water, namely, the synthesis of a carbon-containing component and synthesis of porous building ceramics (bricks) with the use of WAS and waste carbonizate, have been considered. For the preparation of a carbon adsorbent, the carbonization of WAS has been carried out in an argon atmosphere. For the synthesis of ceramics, clay–cullet–tezontle–WAS mixtures with different contents of the components have been used. Sintering has been performed in air. It has been established that, in treatment of WAS at 600 °C for 30 min, better adsorption properties are obtained due to the presence of free carbon bonds. The efficiency of water purification from dyes (methy- lene blue) depends on the standard conditions: the methylene blue concentration, cabonizate-to-solution ratio, and exposure time of the carbonizate in solution. The use of wet WAS makes it possible to exclude the addition of water from the traditional scheme of preparation of a plastic semiproduct, i.e., realize a water-saving technology. The introduction of low-melting cullet, basalt, and WAS powders into red clay makes enables us to reduce substantially the sintering time of porous bricks (down to 8 h) and vary their strength properties. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction At present, the biological method with the use of activated sludge is extensively employed for the final purification of sewage, as indicated in (Asano et al., 2007; van Haandel and van der Lubbe, 2007; Chan et al., 2009; Tilley, 2011; Activated Sludge Process, 2012). The biopurification process is based on the ability of microorganisms to utilize organic and inorganic substances for nutrition in the process of their vital activity (organic substances are carbon sources for microorganisms). Contacting with them, microorganisms partially destruct them into ecologically neutral compounds, transforming aromatic and aliphatic hydrocarbons into innocuous carbon dioxide, water, nitrite ions, sulfate ions, etc. The other part of the substance is consumed on the formation of biomass. Activated sludge consists of suspended particles that were not arrested in primary settling tanks and adsorbable colloid substances with microorganisms reproduced on them. The compo- sition of activated sludge depends on the composition of sewage, contents of salts and oxygen in it, temperature, pH, etc. In terms of a dry substance, activated sludge contains 70–90% organic substances and 10–30% inorganic substances. The treatment and recycling of waste activated sludge (WAS) removed from the sys- tem, as a rule, turn to be a much more laborious problem than the sewage purification process because these waste have different composition, high moisture, and large volume and contain a num- ber of dangerous elements. This is why the recycling of such waste is an important environmental conservation problem of the industry. There exist a number of methods of recycling of WAS. A promis- ing method of recycling of waste activated sludge that includes neutralization of heavy metals is obtaining pyrolysis products and activated coal on the base of them, as described in (Tilley, 2011; Activated Sludge Process, 2012; Ma et al., 2017; Ruiz-Gómez et al., 2017, Maroušek et al., 2017). Depending on the pyrolysis regime, adsorbents that remove pollutants of differ- ent type from water are obtained. As a rule, the solid residue (car- bonizate) is activated by different methods to increase the porosity (of the surface) of the material, as was shown in (Fasoli and Genon, 1976; Jeyaseelan and Lu, 1999; Ahmedna et al., 2000; Rozada et al., https://doi.org/10.1016/j.wasman.2017.10.051 0956-053X/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: vlasovamarina@inbox.ru (M. Vlasova). Waste Management xxx (2017) xxx–xxx Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman Please cite this article in press as: Vlasova, M., et al. Closed cycle of recycling of waste activated sludge. Waste Management (2017), https://doi.org/ 10.1016/j.wasman.2017.10.051