Rimozione Solidi Sospesi Totali nel Trattamento Acque

Removal of Total Suspended Solids from Wastewater.

Total suspended solids (TSS) are solid particles of different sizes and origins found suspended in wastewater. Removal of these solids improves the yield of the purification process and reduces the risk of contamination of surface and groundwater. The most common methods used: sedimentation, filtration, coagulation.

Total suspended solids: what they are

This term refers to solid particles, of any nature and of even very different sizes, which are the most obvious cause of wastewater pollution. Suspended solids can be of organic or inorganic origin, a few microns in size or clearly visible to the human eye.

The amount of total suspended solids can also be very different: they are usually measured in milligrams per liter (mg/l), and values can range from a few dozen to several thousand mg/l, depending on the origin of the effluent and the treatments to which the sewage has been subjected.

Rimozione Solidi Sospesi Totali nel Trattamento Acque

Total suspended solids removal: methods and processes

The removal of total suspended solids involves different methods, depending on the size and characteristics of the particles in the wastewater.

  • Gravity sedimentation. This is the simplest and most widely used method, as it takes advantage of the higher specific gravity of the solid relative to the aqueous medium, with the former tending to settle to the bottom of a specially prepared basin. Lamellar pack sedimenters exploit this simple and effective principle, but occupy an area that is a fraction of that required by conventional sedimentation processes. It is a method that lends itself very well to treating water particularly laden with solids.
  • Filtration. This is a system used primarily as a refinement, and thus downstream of other treatments such as sedimentation. Filtration intercepts residual solid particles and temporarily accumulates them on/in the filter itself, until a limit is reached beyond which an automatic cleaning system is activated. Options include sand filters and free-fiber cloth filters, one of the most compact and efficient technologies.
  • Coagulation and flocculation. We talk about processes by which fine particles of suspended solids are aggregated into larger particles, changing some of their chemical and physical properties, and then a conventional or lamellar-pack sedimentation process is operated.
  • Mechanical separation. Includes a wide variety of mechanical solutions (such as grates and sieves) that are suitable for intercepting coarser bodies.

The main processes used for the removal of suspended solids are listed below.

  • Screening. Grates used for wastewater treatment capture coarser solids, usually with an equivalent diameter greater than half a centimeter, that could clog downstream treatment machinery.
  • Sieving. Fine-weave mechanical sieves, which can be pushed down to half a millimeter of passage clearance, are used here.
  • Primary and secondary sedimentation. This category can include gravity sedimentation tanks, as well as tanks equipped with lamellar packs. Primary sedimentation is aimed at removing solids in sewage, while secondary sedimentation is an integral part of biological treatment processes using activated sludge.
  • Advanced technologies. These are coagulation-flocculation processes, and filters of various kinds, useful for colloidal particles, very fine suspended solids, and situations where the required treatment performance is particularly demanding.

MITA technologies for the removal of total suspended solids

MITA Water Technologies’ solutions remove suspended solids in different plant sections and can be integrated upstream and downstream of existing treatments in plants already in operation.

  • Lamella-pack oil separators and decanters. The lamellar pack system is, usable for both solid particles and oils and greases.
  • Dissolved air flotation units. They remove light suspended solids as well as oils and greases by the formation of micro-bubbles of air that, as they rise to the surface, entrain solid pollutants.
  • Continuous sand filters. Classic and simple mechanical technology that operates through sand as the filter media. MITA Water Technologies offers an exclusive backwash system as a plus.
  • Cloth filtration systems. Very high efficiency free-fiber cloth filters for the finishing stage. They guarantee an effluent with a few tens of mg/l of total suspended solids. Their cleanliness is automatically controlled, ensuring consistent performance over time.
  • Biocombi compact plants. They combine biological treatment, by aerobic bacteria, with filtration of a matter now at the final stage of treatment. Ideal for effluent from small communities or particular industrial applications.
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Case studies for SST removal

Biodiscs and Sand Filters for Coastal Depots of Esso

MITA Water Technologies provided ESSO Italiana with wastewater treatment solutions at the coastal depots in Naples and Palermo. Through the use of continuous regeneration sand filters and Biorulli(r) biodiscs, significant results were achieved, such as reduced energy consumption and maintenance costs, plant modularity, and compliance with current regulations.

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