Olive oil mill wastewaters before and after treatment: a critical review from the ecotoxicological point of view

Abstract

The olive oil mill wastewater (OMW) is a problematic and polluting effluent which may degrade the soil and water quality, with critical negative impacts on ecosystems functions and services provided. The main purpose of this review paper is presenting the state of the art of OMW treatments focusing on their efficiency to reduce OMW toxicity, and emphasizing the role of ecotoxicological tests on the evaluation of such efficiency before the up-scale of treatment methodologies being considered. In the majority of research works, the reduction of OMW toxicity is related to the degradation of phenolic compounds (considered as the main responsible for the toxic effects of OMW on seed germination, on bacteria, and on different species of soil and aquatic invertebrates) or the decrease of chemical oxygen demand content, which is not scientifically sound. Batteries of ecotoxicological tests are not applied before and after OMW treatments as they should be, thus leading to knowledge gaps in terms of accurate and real assessment of OMW toxicity. Although the toxicity of OMW is usually high, the evaluation of effects on sub-lethal endpoints, on individual and multispecies test systems, are currently lacking, and the real impacts yielded by its dilution, in freshwater trophic chains of receiving systems can not be assessed. As far as the terrestrial compartment is considered, ecotoxicological data available include tests only with plants and the evaluation of soil microbial parameters, reflecting concerns with the impacts on crops when using OMW for irrigation purposes. The evaluation of its ecotoxicity to other edaphic species were not performed giving rise to a completely lack of knowledge about the consequences of such practice on other soil functions. OMW production is a great environmental problem in Mediterranean countries; hence, engineers, chemists and ecotoxicologists should face this problem together to find an ecologically friend solution.

Constructed wetlands with light expanded clay aggregates for agricultural wastewater treatment

“…These pollutants may contaminate surface waters from point sources typically associated with concentrated farming activities or from diffuse or non-point sources associated with surface runoff (which may be potentially more problematic due to the difficulty to intercept and treat those pollution sources). Examples of insidiously challenging cases of agricultural pollution sources are the wastewaters resulting from the production of livestock such as piggeries, or food industries such as olive oil production, and situations of water contamination with pesticides after runoff events (Cronk, 1996;Fiorentino et al, 2003;Justino et al, 2012;Matamoros et al, 2012b).…”

“…In Mediterranean countries where olive tree culture is well established and available water resources are scarce, an important source of river contamination is olive mill wastewater (OMW) (Fiorentino et al, 2003;Justino et al, 2012). The environmental impact of OMW is mainly due to its high contents of organic matter, total suspended solids, a significant content of phytotoxic and antibacterial phenolic compounds, acidic pH, dark colour and unpleasant smell (Fiorentino et al, 2003;Greco et al, 2006;Azaizeh et al, 2012;Justino et al, 2012).…”

“…The environmental impact of OMW is mainly due to its high contents of organic matter, total suspended solids, a significant content of phytotoxic and antibacterial phenolic compounds, acidic pH, dark colour and unpleasant smell (Fiorentino et al, 2003;Greco et al, 2006;Azaizeh et al, 2012;Justino et al, 2012). Another characteristic of OMW (which is common to some other agricultural wastewaters such as those from wineries and sugarcane processing) is its seasonality, associated with the period of fruit harvesting.…”

“…For some types of wastewater (e.g. OMW) advanced technologies such as advanced oxidative processes have been proposed but these are characterized by high operational costs and frequently require complex maintenance and availability of experienced personnel (Justino et al, 2012).…”

“…In recent years, the use of constructed wetlands (CWs) for the treatment of agricultural wastewaters, including those produced by food-processing industries and by livestock farms, has been gaining popularity due to their relatively low construction costs and maintenance requirements (Cronk, 1996;Knight et al, 2000;Del Bubba et al, 2004;Carty et al, 2008;Harrington and McInnes, 2009;Yalcuk et al, 2010;Herouvim et al, 2011;Yalcuk, 2011;Harrington et al, 2012;Kapellakis et al, 2012;Justino et al, 2012). Their use as buffer zones to provide effective protection of water bodies from agricultural runoff events, namely for the containment of associated pesticide contamination hazards, has also been studied and applied (Gregoire et al, 2009;Warsaw et al, 2012;Matamoros et al, 2012b).…”