Oils and greases are present in most industrial effluents. Their removal is necessary prior to discharge due to the negative aesthetic effects that they produce when discharged to a body of surface water and due to the damage caused to flora and fauna. Furthermore, their removal is also necessary as a pre-treatment prior to any other treatment phase, in that they create problems for the development of the biological treatment processes. In the case of service stations, vehicle washes and parking areas, the oils and greases are essentially mineral type and non-biodegradable, including in the long-term. Consequently, the discharge of these substances into the sewerage system has an even greater negative effect, not only due to the risk causing blockages in the sewerage system but also because they cannot be degraded at all during the subsequent treatment process. In order to remove these types of pollutants, use is made of oil separators which, depending on the treatment system adopted, are divided into two classes: Gravity separation and Coalescing filter separation.
GRAVITY OIL SEPARATORS
TECHNICAL CHARACTERI STICS
Static oil separator tanks are stilling tanks sized for a retention time of at least 15 minutes at maximum discharge flow. These oil separators are defined as class II according to UNI-EN 858-1 and consist of a sedimentation zone in which the lighter liquid (volumetric mass not exceeding 0,95 g/cm3) is separated from the inert materials: sludge, sand/grit and silt. Each model is designed with a light liquid storage capacity. The oil separators are sized according to a defined nominal flow, i.e. the maximum treatable flow according to the project specifications. This value is defined to allow a sufficient retention time of the treated effluent and on the basis of performance trials carried out on water and diesel oil mixes. The sizing of light liquid separators must take into account the nature and flow of the substances to treat, as well as any stormwater flows that
could reach the plant, the volumetric mass of the light liquid and the presence of substances that could obstruct the separation, such as, for example, detergents. The design flow is calculated for light liquids of density less than 0,85 g/cm3 (diesel, petrol), in the absence of detergents and for surface runoff only.
USE AND MAINTENANCE
An excessive accumulation of floating material causes a reduction in the volume available for separation. This risk worsens in the presence of considerable quantities of sedimentable substances that settle at the bottom of the plant. To prevent the escape of solids and mineral oils that could compromise the quality of the discharged effluent, it advisable to carry out frequent inspections and removal of the accumulated pollutants every 6-8 months. These operations should be more frequent if the plant receives effluent from vehicle workshops, oil storage areas or vehicle washes. The deposits must be removed by specialised personnel and subjected to the appropriate treatment.
OIL SEPARATORS WITH COALESCING FILTER
TECHNICAL CHARACTERI STICS
Oil separators with coalescing filters allow improved performance to be obtained in removing light substances. The system makes use of a polyurethane sponge support on which the oil and hydrocarbon particles collect until their dimensions are such that enable them to settle away from the effluent by gravity. This treatment is recommended in the presence of particularly severe limitations on the discharged concentrations of mineral oils and hydrocarbons. It is advisable to install a grit separator upstream of the oil separator in order to prevent solid particles from clogging the filter meshes.
USE AND MAINTENANCE
As far as maintenance of the coalescing filter oil separators is concerned, in addition to the normal emptying, it is also advisable to remove the sponge support and wash it thoroughly upstream of the plant.
GRAVI TY OIL SEPARA TORS
Separation treatment for surface runoff from impermeable areas with minor presence of mineral oils, hydrocarbons and heavy sediments coming from vehicules parks, workshops and garages, in polyethylene (PE) one-piece structure, manufactured in ISO 9001/2008 company, in accordance with Legislative Decree n°152/2006 for the discharge in public sewer, sized in accordance with UNI-EN 858-1 norm, for underground installation, fitted with: sedimentation chamber, inlet pipe with n°2 90° elbows in PVC with watertight gasket in NBR rubber for the dampening and distibution of the flow, outlet pipe with deflector T in PVC with watertight gasket in NBR rubber, biogas vent, threaded covers in polypropylene (PP) for inspection, emptying and cleaning purposes; optional threaded extensions.
OIL SEPARATOR WITH COALESCING FILTER
Separation treatment for surface runoff from impermeable areas with presence of mineral oils, hydrocarbons and heavy sediments coming from vehicules parks, workshops and garages, in polyethylene (PE) one-piece structure, manufactured in ISO 9001/2008 company, in accordance with Legislative Decree n°152/2006 for the discharge to surface watercourse, sized in accordance with UNI-EN 858-1 norm, for underground installation, fitted with: inlet pipe with 90° elbows in PVC with watertight gasket in NBR rubber for the dampening and distibution of the flow, outlet pipe in PVC with a coalescing filter made of polyurethane sponge, put in an inox steel pull-out basket, for the separation of hydrocarbons drops and suspended mineral oils, with watertight gasket in NBR rubber, fitted also with biogas vent, threaded covers in polypropylene (PP) for inspection, emptying and cleaning purposes; optional threaded extensions; installation downstream a grit separator.