© by PSP Volume 23 – No 6. 2014 Fresenius Environmental Bulletin 1433 EVALUATING THE SUITABILITY OF THE TESTING PROCEDURES FOR ALTERNATIVE ADSORBING MATERIALS IN WASTEWATER TREATMENT Hamid Reza Zafarani 1 , Nadège Gactha-Bandjun 2 , Cornelius Tsamo 2,3 , Mohammad Ebrahim Bahrololoom 1 , Chicgoua Noubactep 4,5, * and Javad Tashkhourian 6 1 Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran 2 Department of Chemistry, Higher Teachers Training College, University of Maroua, P.O. Box 55 Maroua, Cameroon 3 Department of Applied Chemistry, National School of Agro-industrial Sciences, University of Ngaoundéré, P.O. Box 455 Ngaoundéré, Cameroon 4 Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, Göttingen, Germany 5 Kultur und Nachhaltige Entwicklung CDD e.V., Postfach 1502, D-37005 Göttingen, Germany 6 Department of Chemistry, College of Sciences, Shiraz University, Shiraz, 71454, Iran. ABSTRACT Over the years, researchers have been developing low- cost bio-adsorbents as alternative materials to conventional activated carbons for water treatment. New materials are used either ‘as is’ or slightly chemically or physically modified. Their efficiency is mostly characterized in batch experiments with parameters like (i) adsorption capacity (mg/g), (ii) fitting of adsorption isotherms (e.g. Langmuir) and/or kinetics (e.g. first order models), (iii) optimal ex- perimental conditions (e.g. pH value, duration), (iv) reaction mechanism (e.g. adsorption vs. bioreduction), and (v) re- moval efficiency (%). The suitability of this approach is questioned in this communication using green walnut shell as adsorbent and Cr VI as a model contaminant. It is shown that results from such experiments are highly qualitative and not comparable with each other. The two main reasons are (i) the lack of a reference material and (ii) the lack of a standard experimental procedure. Based on the Bernoulli's principle, tools for more comparable results are discussed. The Bernoulli's principle suggests that batch experiments should be designed at constant solution pressure on adsorb- ing particles. KEYWORDS: Adsorption process, Bernoulli's principle, green walnut shell; low-cost biomass, water treatment. 1. INTRODUCTION Water treatment with adsorption processes is an on- going research area [1-5]. Tested adsorbing materials include activated carbon, biosorbents, carbon nanotubes, chitosan, clays, fly ash, food waste, metal oxides, natural minerals, peat moss, polymers, silica gel, zeolites and zero-valent metals [4-11]. Chromium has been one of the * Corresponding author most common model contaminants for testing the suitabil- ity of conventional and alternative water treatment ad- sorbents [7, 12-16]. Biosorbents from walnut (e.g. hull, shell) are gaining increasing importance [11, 17-20]. These materials are used as raw materials for the manufac- ture of activated carbons as well [8]. The present commu- nication is focused on characterization methods for biosor- bents in wastewater treatment. Biosorbents are biologically dead masses in which lignin and cellulose are of key importance for the adsorption of heavy metals. 1.1 The problem Activated carbons (ACs) are considered to be the standard adsorbing materials for water treatment. The efficiency of alternative materials should be compared to that of ACs. A conventional approach for the characteri- zation of ACs is the determination of their surface area and pore size distribution via adsorption capacities for various standard species (e.g. iodine, methylene blue, N 2 ). Long years of experience with such parameters has cumu- lated in the selection of ACs for special application based on one or two parameters (e.g. iodine number, phenol number or methylene blue adsorption capacity). For exam- ple, an AC for wastewater treatment should exhibit a methylene blue removal capacity ≥ 200 mg/g [21]. For alternative adsorbing materials, including biosorbents, no such parameters are yet available. For example, Sartape et al. [7] summarized the effi- ciency of various biosorbents for Cr VI as follows: (i) dried roots of water hyacinth revealed a very high degree of removal efficiency (almost 100 %) (statement 1), (ii) beech sawdust had shown 100 % as maximum adsorption effi- ciency at pH 1 (statement 2), (iii) the Cr VI adsorption capacities of walnut, hazelnut and almond were 8.01, 8.28 and 3.40 mg/g, and percentage removals were 85.32, 88.46 and 55.00 %, respectively (statement 3). Rigorously, statements 1-3 are highly qualitative and only valid for the specific experimental conditions of individual studies.