Novel static composting method for bioremediation of olive mill waste Roberto Altieri a, * , Alessandro Esposito a , Tan Nair b a Institute for Agriculture and Forest Systems in the Mediterranean, Via Madonna Alta, 128, 06128 Perugia, Italy b Centre for Plants and Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia article info Article history: Received 6 April 2011 Received in revised form 10 May 2011 Accepted 10 May 2011 Keywords: Olive mill waste Bioremediation Static composting Humification Biological stability Respiration index abstract This paper presents results obtained on the evaluation of static composting process aimed at bioreme- diation of the hazardous solid olive mill waste (OMW). The static composting process carried out in gas- permeable polyethylene bags followed the fluctuating temperature and oxygen profiles similar to those seen in aerated composting systems. Static composting resulted in apparent increases and decreases in values for total nitrogen and C:N ratios respectively during the process. The amount of nitrogen (>3%) in the composting end product was in agreement with the Italian legislation (Decreto Legislativo 29 aprile 2010, n. 75) specification for nitrogen fertilizer. A gradual decrease in polyphenols during the storage of compost resulted in a non-phytotoxic composted organic matter high in humic substances. Different respirometric tests also stated high biological stability of the end compost product. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Solid and liquid wastes produced during olive oil extraction process pose significant environmental concerns. The hazardous olive mill wastes (OMW) contain high levels of BOD 5 , COD, high and low molecular weight polyphenols, short- and long-chain fatty acids and inorganic substances. The current practice of uncon- trolled spreading of OMW on farm lands creates environmental problems such as odour, ammonia and methane released into the atmosphere and leaching of organic pollutants into the ground water. Polyphenols in olive husk are well known to affect nitrifi- cation in the soil and have deleterious effect on soil microbial activity. High C:N ratio and low pH in the olive husk are also known to immobilize nitrogen in the soil (Benitez et al. 2004). Although several patented techniques for OMW management exist, most of them are too expensive, and therefore unsuited for commercial application (Niaounakis and Halvadakis 2006). Recycling OMW appears to be a cost-effective solution for managing an agro- industrial waste such as OMW (Morillo et al. 2009; Aviani et al. 2010; Fernández et al. 2010). Conversion of the solid OMW to humified organic matter (HOM) and the addition of HOM to soil appear to have several advantages. Amongst the advantages of the presence of humic substances in soil, increased nutrient availability and enhanced plant growth contribute most to sustainable farming practices. Alburquerque et al. (2007) reported an overall positive effect and an improve- ment of soil conditions by adding OMW-based compost. Altieri and Esposito (2008) observed that soil amended with OMW-based compost increased total organic carbon and humic substances without negatively affecting plant growth. Nair and Markham (2008) demonstrated the possibility of using OMW from 2- and 3-phase oil extraction processes as a major ingredient in the preparation of humified compost (HC) suitable for soil amend- ments; the bioremediation process converted OMW into a non- phytotoxic and value-added product. This paper presents results obtained on the evaluation of an innovative static composting system for the bioremediation of OMW. The novelty lies in the fact that composting has been con- ducted in gas-permeable bags characterized by a mass to surface ratio able to ensure adequate passive aeration and thermal inertia. The use of bags makes the OMW composting easier to carry out and more economically sustainable as no forced aeration nor watering of compost is required during the entire process. The main chem- ical parameters related to maturity and stability of the compost were analyzed during the process. 2. Materials and methods OMW used in this work was produced by a two-phase mill located at Cooperativa Nuova Cilento (San Mauro Cilento, Salerno, * Corresponding author. Tel.: þ39 075 5014540. E-mail address: r.altieri@iro.pg.cnr.it (R. Altieri). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2011.05.002 International Biodeterioration & Biodegradation 65 (2011) 786e789