Industrial and agricultural wastes as a potential biofilter media for groundwater nitrate remediation

Abstract

Legislative measures like the Waste Framework Directive enforce the European Union member countries to increase the re-use of waste and/or the extraction of secondary raw materials. The Nitrate Directive requires the implementation of relevant measures to decrease groundwater nitrate concentration. This study evaluated the potential use of two dominant organic wastes in Turkey, tea factory waste and hazelnut husk, as potential carbon sources to stimulate nitrate removal in low cost permeable reactive barrier (PRB) systems. Leaching and batch experiments were carried out to determine the dissolution level and the degree of the heterotrophic denitrification process. Both organic substrates and inherent microbial communities supported the reduction of nitrate (NO 3-) to nitrogen (N) gases. However, the percentage of organic substrate played an important role in the removal of nitrogenous compounds. The highest nitrate removal efficiencies were observed in flasks with 40% tea factory waste and 100% hazelnut husk, which were 64% and 97%, respectively. The corresponding zero-order reaction rates and half-lives were 3.03 mg N L-1 d(-1) and 6 d(-1) for tea factory waste and 5.17mg N L-1 d(-1) and 4.4 d(-1) for hazelnut husk. Of particular note, both wastes supported the denitrifying populations at such an excellent level that 99% of the nitrate was removed in the column study for a duration of 51 d under low and high flow rate conditions. Thus, the release of nitrate, ammonium and total organic carbon from wastes was not limiting its suitability in PRB systems.