Environmental Impacts

Effects on soil

The uncontrolled disposal of OMWW on the land produces toxicity on plants and soil microorganisms. Thus, in some countries (Italy and France) doses of OMWW higher than 200 m3/ha are forbidden. However a controlled application rate of these wastes can improve, as soil amendment, the physical, chemical and biological properties of the soil.

Effects on soil physical properties:

  • Reduction of soil porosity attributed to the combined effect of the suspended and soluble organic matter and salts in OMWW. Doses higher than 200 m3/ha can cause structural damage accompanied by a decrease of the porosity
  • Aggregation: The application of OMWW contributes to the stabilization of the soil aggregates by the binding action of polysaccharides. o Effects on soil chemical properties.
  • Acidity: The application of OMWW or TPOMW at a moderate dose does not affect the acidity of the soil.
  • Salinity: OMWW contains many acids, mineral and organics that could destroy the cation exchange capacity of the soil. The application of a moderate dose of this waste does not affect the salinity of the soil.
  • Inorganic compounds. The application of OMWW decreased N-NO3- and N-NH4+. TPOMW causes great nutritional imbalances since it modifies the nitrogen cycle in soil due to its high C/N ratio. However OMWW and TPOMW has been used as soil amendment considering its high potassium concentration. Researchers reported significant increases of levels of TOC, TN, available P and K, and aggregate stability after the yearly application of oiled and de-oiled TPOMW to an olive grove soil for five years.
  • Organic compounds. OMWW contains phenols that are assumed to be responsible for phytotoxicity and their biotransformation is very important for humic synthesis. The high lignin content of TPOMW complicate its biodegradation
  • Element mobilization. The discharge of OMWW in soils causes the release of heavy metals retained by them.
  • Pesticide sorption, degradation and mobilization. OMWM amendment produces an increase of the residence time of herbicides in the immobile water phase, enhancing diffusion, sorption and degradation processes, thus retarding its mobility

Effect on soil biological properties

  • Microorganisms. A greater development of free-living N-fixer in soils treated with OMWW has been observed (Paredes et al., 1987. In general the controlled disposal of this kind of wastes can have a beneficial influence on soil microbial populations.
  • Plants/Crops. Soil application of OMWW inhibits the germination of various seeds and early plant growth of several vegetable species. The phytotoxicity of OMWW is attributed to its phenolic content and some organic acids such as acetic and formic acids. While the herbaceous plants are sensitive to the phytotoxic effect of OMWW or TPOMW no such effect were observed on olive trees with a controlled use of TPOMW as soil amendment.Beneficial effect of foliar fertilization of TPOMW on the productivity and quality of maize crops was also observed.

Effects on water

The principal effects of OMWW discharges on water bodies are related to their concentration, composition, and to their seasonal production.




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