Phosphogypsum biotransformation in cultures of sulphate reducing bacteria in whey Dorota Wolicka a, * , Andrzej Borkowski b a Institute of Mineralogy, Geochemistry and Petrology, Al. _ Zwirki i Wigury 93, 02-089 Warsaw, Poland b Institute of Agricultural Microbiology, Department of Soil Sciences, Faculty of Agriculture and Biology, Warsaw Agricultural University, Nowoursynowska 159, 02-776 Warsaw, Poland article info Article history: Received 16 June 2008 Received in revised form 11 September 2008 Accepted 18 September 2008 Available online 31 January 2009 Keywords: Sulphate reducing bacteria Phosphogypsum Biotransformation Whey abstract Assemblages of anaerobic sulphidogenic microorganisms were isolated from soil polluted by oil-derived products and grown using the microcosms method. The cultures were grown in minimal and Postgate media with phosphogypsum (PG) as the sole electron acceptor and with lactate, casein or lactose as the sole carbon source. The most effective was the assemblage in Postgate medium with lactose as the sole carbon source. A reduction of 980 mg COD l 1 (reduction of about 40%) and 790 mg SO 4 2 l 1 (reduction of 53% of phosphogypsum introduced to the medium) was noted in the culture. The lowest activity was observed for minimal medium with lactose as sole carbon source (reduction of 4.4% COD and 40% PG). The selected assemblage became an inoculum for a culture in Postgate, minimal and/or distilled water medium with PG (6 g l 1 ) and cheese whey (2.5 and 4.5 g l 1 ). A percentage reduction of COD and SO 4 2 of PG was observed in all cultures. After growth, the residues were weighed and in all cases a distinct mass reduction of PG was observed in comparison to the 6 g l 1 introduced to the medium. Diffractometric studies of the residues confirmed the presence of calcite and apatite. The presence of these mineral phases in the residues allows their application as agricultural fertilisers. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Phosphogypsum (PG) belongs to industrial wastes formed during the production of phosphoric fertilisers by treating apatites or phosphorites with sulphuric acid according to the reaction: 3CaO 3 P 2 O 5 D 3H 2 SO 4 D 6H 2 O / 3CaSO 4 $2H 2 O D 2H 3 PO 4 Production of 1 ton of phosphoric acid results in the formation of about 5 ton of this waste (Baena et al., 1998). On a global scale this amounts every year to 220–280 million tons of PG, of which 14% is subject to further processing, 28% is introduced into surface waters, and as much as 58% is stored in dumps (van Kauwenbergh, 1997; Davister, 1998). In Poland PG dumps comprise as much as 35 million tons. PG is composed of gypsum CaSO 4 $2H 2 O and bassanite CaSO 4 $ 1/ 2H 2 O, which means that 50% of the PG mass comprises sulphates that can be used in the process of dissimilative reduction of sulphates by sulphate reducing bacteria (SRB) as the final electron acceptor (Wolicka and Kowalski, 2005, 2006). The preferred carbon source for SRB is compounds characterised by low molecular weight, which are intermediate products of the fermentation process. These include organic acids, e.g., acetic acid, and alcohols, e.g., ethanol. Most SRB strains prefer sodium lactate as the optimal carbon source (Postgate, 1984). However, its applica- tion in technological processes as the sole electron donor is economically unprofitable. Therefore, it was essential to search for other carbon sources for SRB, i.e. representing the main pollutants of various organic liquid wastes. An example of such wastes is whey which contains about 72% lactose, 10% protein, 0.5% fat and mineral soils and vitamins (Chartrain and Zeikus, 1996; Vela et al., 2002). Whey is developed during the production of cheese or casein. In terms of volume, one part of produced cheese results in the formation of almost 10 parts of whey, this being a major problem in the cheese-making industry. SRB are used in anaerobic conditions in all types of sewage treatment bioreactors (Blonskaja and Vaalau, 2006) where they compete for available organic compounds with various groups of bacteria at all decomposition levels except hydrolysis, because SRB do not produce hydrolytic enzymes. The number of papers devoted to high-sulphide sewage treat- ment by sulphidogenesis has significantly increased in recent years (Lens et al., 2002; Sliva et al., 2002). Some papers have focused on * Corresponding author. Tel.: þ48 22 5540321. E-mail address: d.wolicka@uw.edu.pl (D. Wolicka). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2008.09.011 International Biodeterioration & Biodegradation 63 (2009) 322–327