Mitigation of Soil Degradation, and Ground Water Pollution caused by on-landdisposal of Vegetable Oil mill Effluents
Prof Andrei Rozanov, Department of Soil Science, Faculty of AgriSciences,Stellenbosch University.
Vegetable-oil mill effluents are wastewaters generated from oil mills (such as olive-oil mill wastewaters and palm-oil mill effluents) during the extraction of oil. These effluents are produced in such large quantities that their disposal is causing great environmental pollution and is of serious concern to researchers. Research has revealed that these effluents are composed of heterogeneous (metabolisable carbon-source and toxininhibiting) compounds. Their nutrients are good enough for restoring degraded soils and enhancing crop yield but the complex organic pollutants in them contradict their potential.
Their polluting effects are felt in the soil years after their application because of their slow biodegradable rate, for example, and they have the potential to affect groundwater. These effluents are also very good sources for fertilisers, biofuel and bio-energy. At high rates of application, however, they not only inhibit or reduce crop yield but also contaminate soil with
organotoxins and pollute groundwater, resulting in large-scale land degradation. The effluents contain 3.5 to 15% organic matter, 0.5 to 2% mineral salts, 83 to 95% water and 11.5% phenols. Unfortunately, the phenols in oil fruits all go to the effluents during the extraction process and then cause problems in the soil; only 1% is retained in the oil extracted.
The main objective of this research is to understand the complexity of the interaction between effluent and soil and to explore both in situ and ex situ options for pollution prevention and the remediation of polluted land. In exploring these options for the treatment of these effluents, many researchers have used mechanisms to destroy the phenol and other organic pollutants (such as oil, fat and grease), while others have tried to eliminate them from the effluent, although none have been efficient. This research focuses on using a column experiment to identify physical (solute transport, adsorption rates, soil-pore clogging) and chemical (dissolved organic carbon, electrical conductivity, ionic substitution, cations and anions in the solution) degradation caused by the effluents. The filtration of the effluents using sandy soil, ultisol, biochar, and biochar mixed with ultisol is also a strategy to reduce contaminants in the effluents. The study intends to explore a biochar amendment strategy to restore polluted soil. Biochar was selected because it has a recalcitrant effect on soil and on the effluents. The effluents have the ability to degrade soil for a considerable period but biochar will outlast this in remediating the soil. One of the most generated waste products in oil-mill industries is the palm-kernel shell. This is one of the materials that is intended to be used for the biochar preparations. Its other potential uses are not many and it can therefore be reused; it is also readily available to local farmers. The intention is furthermore to use pinewood biochar for olive-oil wastewater treatment. The anaerobic-digestion option of treating wastewater will also be explored. Local farmers will be advised on the quantity of effluent and biochar that should be used for a particular type of soil for sustained agricultural production using vegetable-mill effluent.
BSc Soil Science, University of Nsukka, Nigeria; MSc Soil Science,
University of Nsukka, Nigeria
Faculty of AgriSciences, Department of Soil Science, SU (2013)
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