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Olive mill industrial wastewater treatment

By 15 September 2016case, food, pcf

The production of olive oil generates two kind of waste waters:

  • RINSING WATERS: the quantity is subject to change. It can be re-circulated, after the settling to remove the solids, or discharged directly.
  • SLUDGE: vegetation water with additional water, whose quantity is subject to change. In case of traditional oil mills, the hot additional water flows to the inlet of the centrifuge. Part of the vegetation water remains in the sludge.

The first water basically contains suspended solids and comes from the olive washing. The second one shows a high pollution charge and it has a great environmental impact.

Average composition of the olives:

  • Water = 50%
  • Oil = 22%
  • Sugar = 19,1%
  • Cellulose = 5,8%
  • Proteins = 1,6%
  • Ash = 1,5%

Average characteristics of the produced sludge (traditional olive mill – presses):

  • Humidity = 25%
  • Greases = 6,0%

Type of olive mills

Type % average of produced sludge Factor
Traditional – Presses 15 – 20% 0.18
Continuous – three phases 40 – 70% 0.55

Estimation of the quantity of sludge to treat
C = Annual consume of oil
D = Duration of the campaign in days (including Sundays and holidays)
f = Factor
A = Daily quantity of sludge to treat
Formula: A = (C x f) / D

The Process
The vegetation water is stored in a tank, where the settling occurs, and then sucked by the evaporator that produces a concentrate (20-25%) and a distillate (75-80%). The distillate will have characteristics which allow its recycle in the washing step or, after the pH correction, the direct discharge.
The concentrate can be made inert with quicklime and used as fertilizer or sent directly to the olive mill for the further extraction of the oil.

The Solution provided
Evaporation is a thermal treatment that can be applied directly to waste waters with little or no pre-treatment, and allows separation of the water from the waste because of the different volatility of the compounds contained within the water.
Evaporation provides advantages over traditional water treatment techniques, such as full automation, very low chemical consumption and high tolerance of variability to concentrations of pollutants. The low temperature of boiling in a vacuum (around 35°C) leads to low energy requirements. The waste water is sucked via a filter into the boiling chamber by the vacuum. The circulation pump sends the water through the primary heat exchanger where it is supplied with the heat necessary for boiling. Once heated, the water goes back to the boiling chamber, where it immediately boils (flash evaporation). The vapour rises through the demister in order to damp any droplets and is condensed against the U tube heat exchanger. The distillate is then sent to the storage tank. The concentrate is discharged automatically according to settings determined at the commissioning stage.

Characteristics of the vegetation water before the evaporation and its distillate

Parameter UM Vegetation water Distillate
pH 4,4 3,3
Density g/ml 1,007 1,000
COD mg/l 14.700 1.800
Total phosporous mg/l 71 < 0,1
Fats and greases mg/l 1290 2
Phenols mg/l 1 0,5
Aldehydes mg/l 24,5 0,1