Research article Influence of process parameters on sorption capacity of microwave activated biosorbents for urea recovery from human urine: a comparative study M. Ganesapillai, 1,2 * A. Venugopal, 2 V. Ananthkrishna 2 and N. Tapankrishna 2 1 Chemical Engineering Department, Faculty of Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 2 Mass Transfer Laboratory, Chemical Engineering Division, School of Mechanical and Building Sciences (SMBS), VIT University, Vellore 632014, Tamil Nadu, India Received 10 September 2014; Revised 10 February 2015; Accepted 12 March 2015 ABSTRACT: The present investigation elicits a comparative study for recovering urea from human urea via adsorption onto three biosorbents: Microwave Activated Carbonized Bamboo Shoots (MACBS), Walnut Shells (MACWS) and Coconut Shells (MACCS). The rate of sorption was investigated under different process parameters including initial sorbate concentration, amount of sorbent, temperature and agitation speed, and further, sorption capacity of MACBS, MACWS and MACCS was compared. Batch results indicated that urea uptake capacity increased with an increase in sorbate concentration and a decrease in sorbent loading and temperature. The experimental data were tested against the Langmuir, Freundlich, Tempkin, Flory–Huggins and Dubinin–Radushkevich (D-R) isotherms with the D-R model being a good fit for MACBS and MACCS and the Freundlich model for MACWS. Kinetic studies were performed to understand the order and rate of the sorption process. While pseudo-second-order kinetic model fits best for MACBS and MACWS, pseudo- first order was followed by MACCS. Based on the urea sorption capacity, the following order of suitability of precursors for activated carbon preparation was established: MACBS > MACCS > MACWS. This study illustrates the suitability of biomass-based precursors for activated carbon preparation and nutrient recovery from wastewater streams like human urine for subsequent use as fertilizers on agricultural land. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. KEYWORDS: human urine; activated carbon; microwave activation; coconut; bamboo; nutrient recovery INTRODUCTION Organic agriculture is a perspective way of farming with a positive impact on the environment. It addresses a variety of socio-economic aspects by contributing to the sustainable development of rural areas as well as protecting all components of the environment. [1] Over the past few decades, organic agriculture has gained scientific attention and has become popular among people, as there is a widespread belief that organic agricultural systems are friendlier to the environment and the consumer. [2] Although organic agriculture has been promoted as more sustainable than traditional farming, both approaches may be falling too short and are drawing criticism for different reasons. While agricultural biomass production for energy generation possesses a new threat to the sustainability of land-use systems, organic farming extensively depends on fossil fuels. [3] Hence, an integrated perspective of organic and recommended dose of chemical fertilizers might benefit efforts to meet current global challenges. [4] Human urine, a liquid waste product of the human body, is one such kind of organic source, available plenty in nature at little to no cost. In human urine, about 75–90% of nitrogen excreted is through urea and the leftover is in the form of creatinine, amino acids and uric acid. The application of human urine for agricultural practices has gained popularity as a fertilizer in a few countries. [5] Fresh human urine with and without the addition of supplements were tested on a wide variety of common crops like cress, spinach, tintel, mustard, green pea, black gram, tomato, cabbage and banana. [6–9] Most of the nitrogen fractions in urine were taken up by these plants similar to commercial urea or ammonium fertilizer. [10] Even though the necessity to recover urea from human urine is well-known, the urine-blindness associated with ethical and prejudice issues is a major setback for its popularity. [1] Although extensive research *Correspondence to: Mahesh Ganesapillai, Department of Chemical Engineering, Faculty of Engineering, Aristotle University of Thessaloniki, II Floor, D Building, Un. Box 455, P.C. 54124, University Campus, 54006 Thessaloniki, Greece. E-mail: maheshgpillai@vit.ac.in; drmaheshgpillai@gmail.com © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. Curtin University is a trademark of Curtin University of Technology ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING Asia-Pac. J. Chem. Eng. (2015) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/apj.1888