Generalities
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1.2.2. Wastewater treatment
1.2.2.1 .Wastewater treatment processes
The main aim of treatment is to reduce and eliminate suspended solids, biodegradable organic
matter, pathogens and toxic compounds present in wastewater, so that the water finally
discharged into the natural environment does not degrade it. This process involves obtaining
purified water that complies with the discharge standards set by legislation, while preserving
public health and the environment (Martonen, 2017).
1.2.2.1.1. Pre-treatment
Pretreatment or preliminary treatment is the first stage of treatment, which consists of removing
the coarsest materials from the effluent, as well as elements likely to interfere with subsequent
stages of treatment. (Grosclaude, 1999). This treatment removes around 35% of pollutants
(Moulin et al., 2013). Pre-treatment stages include screening, grit removal, oil removal and
degreasing.
 Screening
This involves separating the most voluminous solid debris from the raw water, by passing the
inlet effluent through a screen with bars spaced at varying distances to remove the most
voluminous matter. The spacing of the bars is determined by the nature of the solids to be
removed as well as the requirements of the treatment system (Merair & Salmi, 2014).
 Grit removal
Grit removal is a step carried out by reducing the flow speed to allow sedimentation of
particles: sand, gravel and more or less fine mineral particles present in wastewater to eliminate
them so as to avoid deposits in channels and pipes, thus protecting pumps and other equipment
against abrasion and avoiding overloading subsequent treatment steps (Merair &Salmi, 2014).
N𝑂3 -
<1mg/l
PO4
32mg/l