Civil Wastewater Treatment Stages

Stages of civil wastewater treatment in sewage treatment plants

In contrast to the industrial sphere, civil wastewater treatment respects a precise sequence of steps: from roughing up to reintroduction into a community’s water cycle, passing through precise mechanical and biological treatments. Indeed, one must consider that civil wastewater treatment plants serve the needs of even vast communities, ranging from hundreds to millions of population equivalents (PEs): wastewater that is very heterogeneous in terms of quantity and quality of pollutants is collected and treated.

The aim, of course, is to make the treated water safe to be returned to the environment or, in some cases, suitable for irrigation reuse.

Three phases of civil wastewater treatment can be enucleated.

1. Primary Treatment. We start with a series of mechanical processes to remove the coarser solids and impurities present. Some processes: screening, sieving, desanding, de-oiling. The related technologies: mechanical screens, sand and oil separators.
2. Secondary Treatment or Biological Treatment. Involves biological processes in which microorganisms (bacteria) decompose organic matter in wastewater, transforming complex organic substances into simpler, easily removed materials. Technologies used: aeration tanks, moving biological bed (MBBR) systems, biological membrane (MBR) systems, rotating biological contactors also called “biodiscs” (RBCs).
3. Tertiary Treatment. This is a “finishing” stage of wastewater, which is further purified to remove residual contaminants and pathogenic bacteria. It also involves disinfection, to kill or inactivate remaining pathogenic bacteria and allow the water to be potable. Examples of technologies: sand filters, cloth filters for surface and depth filtration, reverse osmosis membranes, chlorination, UV irradiation, ozonation.

Civil wastewater treatment: technical needs

But what are the specific technical requirements of wastewater treatment? Here are them at a glance below.

• Removal of suspended solids. These are organic and inorganic solid particles of different sizes found suspended in wastewater.
• Phosphorus removal. A plant nutrient that, if present in excess, can cause water eutrophication, thus with excessive growth of algae and aquatic plants.
• Nitrogen removal. The presence of this element, if in excess, can also cause eutrophication. This can pose health hazards to animals and humans.
• BOD and COD removal. These are two measures of water quality. They stand for “Biochemical Oxygen Demand” and “Chemical Oxygen Demand”, respectively.
• Removal of oils and fats. A useful step, among other things, to prevent clogging of pipes operated by very water pollutants.

For a more in-depth discussion, you can read this page on our website.

MITA technologies for civil wastewater treatment

MITA Water Technologies provides for all stages of civil wastewater treatment some of the simplest and most effective solutions on the market: they can be integrated into any new or existing sewage treatment plant, ensuring proper disposal of the pollutant load and facilitating subsequent stages.

• Lamellar-pack decanters and de-oilers (primary treatment). They separate suspended solid particles and oils in wastewater.
• Dissolved air flotation units (DAF, primary treatment). They are used to flotate oils and fats in a roughing stage of the wastewater.
• Biorulli® biological oxidation (RBC) systems (secondary treatment or biological treatment). They act on COD, BOD and Nitrogen: disc structure of various sizes depending on the input load to be abated.
  Continuous sand filters (tertiary treatment). Systems for wastewater filtration using self-cleaning sand for fine removal of suspended solids.
• Free-fiber cloth filters (tertiary treatment). Systems with filter fabric with 5- or 10-micron threads, for final removal of suspended solids, with limited footprint.
• Biocombi compact systems (secondary and tertiary treatment). Combination of Biorulli and cloth filters: removal of BOD, nitrogen and removal of total suspended solids.