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Tratamiento físico-químico: coagulación y floculación

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Purpose

Principle

Fine suspended solids and colloidal pollutants are stable in water and settle at best very slowly, which means a clarifier or lamella separator is not sufficient for their removal from wastewater. The coagulation-flocculation process overcomes this problem by forming well separable flocks from this fine particulate matter. The process consists of three steps, namely coagulation, neutralization and flocculation.

  • Adding a coagulant such as iron trichloride (FeCl3) or aluminiumsulphate (AlSO4) to wastewater neutralizes the surface charge of fine particles and helps them clog together to form small flocks.
  • The coagulation process works optimally at a neutral pH. To realize this a neutralization step is often needed after the coagulation step.
  • A last step is the enlargement of the flocks by dosing a polymer. Afterwards the flocks are separated from the purified water by settling or flotation.

Scheme

Applications

There are lots of applications for the coagulation flocculation process. A few examples:

  • The preparation of processwater and drinking water from surfacewater.
  • The physicochemical treatment of wastewater. This often goes together with phosphoros removal and/or the removal of heavy metals. Typical industries:
    • Automotive industry, surface treatment of metals
    • Storage of scrap metal or raw materials
  • Pretreatment of wastewater which contains high concentrations of fats or suspended solids, preceding a biological wastewater treatment plant. Among which:
    • Tankcleaning, waste processing
    • Food industries ( slaughterhouses, meat processing, dairy, baking, oils,…)

Example of a realization

Mobile physico-chemical WWTP

Operational costs

Besides the investment in the purification equipment there are also operational costs during the physicochemical removal of heavy metals from wastewater. The main operational costs in this case are the consumption of chemicals and the removal of the physicochemical sludge.

Approach Trevi

Trevi always checks whether the costs for physicochemical wastewater treatment could be optimized by at-source measures or by side-stream treatment of certain wastewaters. The most efficient choice and dose of chemicals is determined based on jar tests, keeping a minimal chemicals consumption and sludge production in mind.