Constructed Wetlands

22.04.2010_Fabio Masi

When we talk about wastewater should understand it’s composition: we are talking basically of WATER and other ELEMENTS that can be considered misplaced, if we can get them back in the right place we could use them for many good things.

The wastewater characterization is based on:
PHYSICAL PARAMETERS (temperature, electrical conductivity, solids, colour, odour)
CHEMICAL PARAMETERS (PH, alkalinity, O2 demand COD-BOD-TOD, TOC total organic component, nitrogen, phosphorus, oils and fats, mineral oils, surfactants, toxic substances, dissolved oxygen)
BIOLOGICAL PARAMETERS (total coliforms, fecal coliforms, fecal streptococcus, Escherichia coli as pathogen indicator, salmonella)

Wastewater treatment has to be a primary target, and we have to consider the best technology for our necessities. We have three treatment levels:
PRIMARY, it is the first line of defence and consists in screening, grit removal and primary sedimentation
SECONDARY, it is the minimum level of municipal and industrial treatment before discharge, it gets rid of additional solids and of the pollutants that are solved in water, with microbial uptake and growth
TERTIARY, after secondary treatment water can still we full of bacteria, so this advanced phase works on processes of nitrification, denitrification and phosphorus removal


Natural wetlands are areas of land whose soil is saturated with moisture and can be partially or completely covered with water, they are considered one of the most biologically diverse ecosystems, due to the richness of it’s components: plants, soil and water. The high biological activity can transform many of the common pollutants contained in wastewaters into harmless by-products or essential nutrients that can be recycled for additional biological activity.
This transformation is obtained with a low utilisation of external energy due to the natural environmental energies at work (sun, wind, soil, plants and animals).

Constructed wetlands are man-made systems designed to emphasize specific characteristics of wetland ecosystems to improve the treatment capacities, they can be defined as engineered water saturated areas in which the natural removal for the water pollutants is reproduced, enhanced and controlled in order to optimize the purification performances.

We have three types of constructed wetlands:
FREE WATER SURFACE (FWS): they are areas of open water and are similar in appearance to natural wetlands.

HORIZONTAL SUBSURFACE FLOW (HSSF): they typically employ a gravel bed planted with wetland plants; the water, kept below the surface of the bed, flows horizontally from the inlet to the outlet.

VERTICAL FLOW (VF): water is distributed across the surface of a sand or gravel bed planted with wetland plants; the water is treated as it percolates through the plant root zone.

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