Integrated treatment of olive oil mill effluents: effect of chemical and physical pretreatment on anaerobic treatability

Abstract

Difficulties met in the anaerobic treatment of olive oil mill effluents (OME) suggest the use of a chemico-physical pretreatment for the removal of biorecalcitrant and/or inhibiting substances (essentially lipids and polyphenols) as selectively as possible before anaerobic digestion. Laboratory scale experiments were carried out in order to identify pretreatment type and conditions capable of optimizing OME anaerobic digestion in terms both of kinetics and methane yield. Ultrafiltration, even if it allowed very high removals of lipids and polyphenols, was affected by poor selectivity (indeed, large amounts of biodegradable COD were also removed). Centrifugation turned out to be preferable to sedimentation owing to smaller volumes of separated phase. Results of great significance were obtained by adding Ca(OH)2 (up to pH 6.5) and 15 g/l of bentonite, and then feeding the mixture to the biological treatment without providing an intermediate phase separation. Indeed, the biodegradable matter adsorbed on the surface of bentonite was gradually released during the biotreatability test, thus allowing the same methane yield (referred to the total COD contained in untreated OME) both in scarsely diluted (1 : 1.5) pretreated OME and in very diluted (1 : 12) untreated OME. Application of a continuous process combining pretreatment (with Ca(OH)2 and bentonite) and anaerobic digestion without intermediate phase separation is suggested.

Energy production from anaerobic co-digestion processing of cow slurry, olive pomace and apple pulp

“…Just after day 4 the P4 mixture became less productive than the P3 mixture, and the total biogas volume produced was 1655 l (40% less compared to the P3 series). The reasons of this big difference in biogas production could be explained by an accumulation of lipids and polyphenols that were difficult to degrade and may have inhibited certain microbial groups [15].…”

Treatment of olive mill effluents by coagulation–flocculation–hydrogen peroxide oxidation and effect on phytotoxicity

“…In further runs (5)(6)(7)(8)(9)(10)(11)(12), Fenton reagents were coupled with K1; in this series of experiments, the flocculant concentration was kept constant at 230 mg/L since this concentration was found to be sufficient to yield complete solids separation. For all runs but 9 and 10, addition of Fe(II) was followed by H 2 O 2 addition and the mixture was left to react for 8 h prior to the addition of K1.…”

“…Coagulation with materials such as lime, alum, ferric chloride and ferrous sulphate has also been employed in OME treatment. Jaouani et al [6] recently demonstrated a two-stage process comprising aerobic degradation followed by lime coagulation, while Beccari et al [7] proposed a process comprising OME pre-treatment by means of lime coagulation and adsorption on bentonite followed by anaerobic digestion; they reported that pre-treatment was capable of enhancing considerably the anaerobic treatability of the original effluent. The effect of several OME pre-treatments such as lime or ammonium iron sulphate coagulation, resin adsorption and H 2 O 2 oxidation on subsequent anaerobic degradability was investigated by Zouari [8] who found that the pre-treated effluent was always more readily amenable to biodegradation than the original un-treated effluent.…”

Olive pulp and its effluents suitability for soil amendment

“…OP has the highest content of total LMWP: 2.37 g kg −1 d.m., whereas EH 2 and ECH 4 contain respectively 1.22 and 0.96 g kg −1 d.m. Table 2 Chemical characteristics of olive pulp (OP) and effluents derived from its anaerobic digestions for the production of hydrogen (EH 2 ) and methane (ECH 4 ( Fig. 1, sum of LMWP).…”

“…It separates the oil from an aqueous phase (olive mill wastewater) and a solid phase (olive husk) in a continuous process. The main inconvenience of this system is a large production of wastewaters characterised by a heavy pollutant load [2][3][4][5]. Numerous attempts have been made in order to reduce their environmental impact, such as treating them physically, chemically and biologically or applying them directly to soils; nevertheless the disposal of wastewaters continues to be a very difficult process [4].…”