Total costs, including system amortization, operation and maintenance.
Minimum energy consumption.
Minimum maintenance and need for specialized technical personnel.
Systems that support major seasonal variations in flow rate.
Minimum visual impact and maximum integration into the natural environment.
Quality of the effluent obtained, complying with riverbed discharge parameters and contemplating the possibility of its reuse for irrigation.
Minimizing the management costs of the sludge, considering the possibility of recovery of the biosolids obtained as fertilizer.
Complete in-situ treatment of the influent, avoiding transport and dependence on external managers that generate a higher operating cost and environmental impact.
Based on these criteria, the selected WETWINE treatment system consists of a water treatment line and a sludge treatment line. It is composed of the following main units:
- Primary treatment through an HUSB anaerobic digester
- A secondary treatment stage of constructed wetlands, combining vertical and horizontal subsurface flow wetlands, which will be called the water treatment line.
- A sludge treatment stage using sludge treatment wetlands, which will be called the sludge treatment line.
1. HUSB (Hydrolytic UpFlow Sludge Bed) Digester
The pre-treatment will consist of a hydrolytic upflow digester (HUSB), whose main functions will be the retention of solids and the hydrolysis of compounds that are difficult to biodegrade into simpler ones.
After this pre-treatment phase, two phases will be separated:, a liquid that will be treated in the constructed vertical and horizontal wetlands and the sludge that will be treated in the sludge wetlands.
In this reactor, the main aim is to retain suspended solids. The main physical processes that take place in a HUSB reactor are sedimentation, filtration and absorption.
2. Water treatment line: vertical and horizontal subsurface flow wetlands
Artificial wetlands are passive treatment systems designed to enhance the decomposition of the degradable materials contained in wastewater with mechanisms that occur spontaneously in nature, at both the physical-chemical and biological levels. Decontamination processes take place in these systems through the interaction between water, solid substrate, microorganisms, vegetation and even wildlife.
The wetlands proposed in the WETWINE system are subsurface flow wetlands, in which water circulates underground through a granular medium, in contact with the roots and rhizomes of plants. The biofilm that grows attached to the granular medium, as well as to the roots and rhizomes of plants, plays a fundamental role in the processes of water decontamination.
The two types of wetland considered in the WETWINE system are distinguished by the type of circulating flow, being divided between vertical and horizontal subsurface flow wetlands.
2.a-Vertical subsurface flow wetlands
Vertical wetlands are fundamentally aerobic and can take higher pollutant loads. This is why it will be placed at the head of the secondary treatment, to receive the heaviest wastewater at the exit from the HUSB digester pre-treatment.
This type of wetland was originally developed as an alternative to horizontal wetlands to produce nitrified effluents. Vertical systems are generally combined with horizontal ones so that nitrification and denitrification processes take place gradually, thereby eliminating the nitrogen.
Vertical and pulse-loaded water flow, so that the granular medium is not permanently flooded. Vertical systems have a higher treatment capacity than horizontal systems.
2.b-Horizontal subsurface flow wetlands
A horizontal flow wetland system,, with aerobic and anaerobic zones, is installed afterwards so that a greater number of pollutants are degraded, through the combination of both environments. This horizontal wetland will take over the treatment of the effluent from the vertical wetlands, which will already be partially purified and oxygenated.
In this type of system the water circulates horizontally through the granular medium and the rhizomes and roots of the plants. The water depth is between 0.3 and 0.9 m and the wetlands are characterized by operating in a permanently flooded state.
3.- Sludge treatment line: sludge wetlands
Sludge treatment wetlands are a type of vertical wetland developed to treat sludge which comes from the HUSB digester. These systems consist of several cells into which the homogenised sludge is pumped intermittently and sequentially, alternating between periods of feeding and rest.
Rest periods will depend on design and climate conditions, but intervals between feeding should be sufficient to allow the water contained in the sludge to drain. As the sludge accumulates and the layer grows, plant rhizomes develop and penetrate the sludge layer, increasing dehydration through an evapotranspiration process.
Once the sludge storage capacity is reached in the wetlands, and after the physical (drying) and biological (mineralisation) processes that allow its stabilization, a final biosolid is obtained with a dry matter content greater than 25% and suitable for direct reuse as fertilizer.
This WETWINE web tool allows an approach to the dimensioning of the different stages that make up the WETWINE system, it being possible in this way and through the introduction of a series of parameters specific to each winery to pre-dimension the necessary plant.