Batch Test Evaluation of Four Organic Substrates Suitablefor Biological Groundwater Denitrification

Nitrates pollution represents nowadays a serious issue related to the quality of groundwater; continuousgrowth of industrial-scale agricultures lead to an increase of nitrates content in groundwater in the lastyears. Several technologies have been validated as capable to promote in situ biological nitratesremediation, such as permeable reactive barriers (PRB), biotrench, biobarriers etc. These technologies areall characterised by the use of organic substrate that act as a slow release carbon source. In freedissolved oxygen absence, such organic carbon is further oxidised, by heterotrophic bacteria naturallypresent in soil, in compliance to anoxic metabolism by using nitrates bound oxygen. Such dissimilatoryreaction converts nitrates in elemental nitrogen. Organic substrates capable to sustain this reaction arevarious and easily recoverable (e.g. sawdust, cotton, woodchips etc.); thus, several carbon source hasbeen already tested. The present paper reports the results of batch test carried out on four organicsubstrates used to promote biological denitrification; in details the organic matters tested were: sawdust,pine bark, cork and olive pomace. The first step of experimental study was focused to evaluate the organiccarbon release capability of each substrate; particularly, organic matter has been keep in contact with tapwater for almost 10 days; thus, samples of water has been periodically collected to measure Total OrganicCarbon (TOC). Further, microcosm batch test has been carried out to reproduce in situ biologicalgroundwater denitrification. In details, each batch reactor was prepared with a mixture of organic matterand agricultural soil, used to provide heterotrophic bacteria capable to promote biological denitrification,kept in contact with tap water artificially spiked at 60 mg NO3-N L-1. Batch test were realized in slowagitation condition, by using a vibratory plate, and were carried out for 12 days. All organic matters testedprovided good results, in terms of removal efficiency; further, specific denitrification rate has beencomputed and ranged from 0.06 (olive pomace) to 0.51 (sawdust) mg NO3-N L-1 d-1g-1sub. Column test areactually in progress to evaluate the biological denitrification in continuous.