FLOTATING MACROPHYTES FILTER TECNOLOGY

WATER TREATMENT USING MACROPHYTE SYSTEMS

Systems that use aquatic macrophytes are based on single-crop or multi-crop farming of macrophytes in shallow ponds, tanks, or canals. Although they are usually used for tertiary water treatment, they are suitable for certain types of secondary water treatment. The plants supply oxygen to the treatment process, which develops in the root system. Plants degrade, absorb and assimilate pollutants in their tissues and they provide a large surface area on which bacteria can grow and solid elements are treated.

The different treatment systems that use aquatic macrophytes are classified as:

1. EMERGENT SUPERFICIAL-FLOW MACROPHYTE SYSTEM

This system and the next one make use of rooted plants. The leaves of these plant species (Phragmites, Scirpus, or Typha) dry out in winter and sprout in spring. In the superficial-flow systems, contaminants are eliminated through reactions that take place in the water and upper zone of contact. Little wastewater circulates through the roots, which limits their water treatment capacity.

2. EMERGENT SUBSUPERFICIAL-FLOW MACROPHYTE SYSTEM

As in the previous system, water circulates by gravity through a layer of gravel or soil. The most important drawback of the system is rapid clogging up of the terrain over time with roots, rhizomes, and sediment solids. When the system gets clogged up, it has to be destroyed to eliminate contaminants.

3. FLOATING MACROPHYTE SYSTEM

These systems use species that float naturally, such as Lemma, Wolffia, Spirodella, Azolla, or Eichomia. The advantage of these systems is that the contact between roots and wastewater is complete and a large surface area is exposed. However, these species are small and their biomass production is limited, which reduces their absolute water treatment value, although they absorb large quantities of nitrogen and phosphorus. They are very effective for low concentrations of organic matter and diluted solids.

4. FLOTATING MACROPHYTES FILTER (FLOATING MACROPHYTE FILTER) SYSTEM

This LIFE project proposes to use floating macrophyte filter systems and has arranged for the construction of different prototypes in Lorca.

This system is based on emergent macrophytes that naturally root to the soil, but in this case are converted into artificially floating macrophytes. It is an innovative method that has the combined advantages of floating and emergent macrophyte systems, while eliminating or reducing their drawbacks. It was developed by the Polytechnical University of Madrid and is exemplified by three experimental treatment plants in the Madrid-Barajas, Reus, and Alicante airports.

This system is suitable for the tertiary treatment of secondary effluents from conventional treatment systems, eliminating eutrophicising elements, particularly phosphorus and nitrogen. Secondary treatment processes occur in the system because microorganisms attached to the roots of the plants decompose organic matter. Finally, the system also reduces diluted solids, which are retained by roots. Some species of emergent plants can absorb large quantities of heavy metals and decompose phenols, which makes the system suitable for treating industrial effluents.

The system is based on a floating mat of plants that occupies the entire surface of the pond or canals through which water circulates. Their depth ranges from 25 to 75 cm. Plants should be native species whenever possible and arrayed in such a way that their roots, rhizomes and part of the stem are submerged. Until now, the plants that have been used are Phragmites sp., Sparganium sp., Scirpus, Schoenus, Iris pseudocorus and Typha sp. Typha species have shown the best results, with high growth and treatment rates.

Since these plants are grown floating, they form a dense mat of roots and rhizomes that occupy the entire collector volume (pond or canal), thus forcing all the water to circulate through the matted vegetation, which supports microorganisms that degrade organic matter. Leaves pump oxygen to the roots, thus favouring the process of contaminant degradation.

Advantages of the FLOTATING MACROPHYTES FILTER system

- Economical and easy installation.
- Greater effectiveness than other systems, because the entire volume of the effluent circulates through the treatment mesh.
- Easy harvest of the biomass, above and below the water surface. Harvesting does not destroy the system, as occurs with rooted-plant systems.

In addition, once the system is stabilised, it produces a large amount of biomass, which must be removed periodically. The system produces annually 2.23 kg/m2 of dry material above water in the case of cattails (Typha latifolia L.), which can be used as livestock feed or as an energy source (a square metre of canal has the same caloric value as a litre of oil).

WATER POLICY

WATER FRAMEWORK DIRECTIVE OF THE EUROPEAN UNION

The Water Framework Directive was adopted, after a long debate in the European Parliament and European Commission, on 22 December 2000. This initiative entailed an important challenge for water management and comprises all the former directives about this matter. It is considered to be one of the best water legislations in the world, and its correct implementation should improve the ecological situation of rivers, for example, before 2015.

The main principles of this Framework Directive are:

1. The river basin as a management unit that is equivalent to the natural operating unit of the hydrological cycle.
2. Environmental externalities are to be included in the price of water.
3. Achievement of a “good ecological state” (biological, hydromorphological, and physical-chemical) of water and aquatic ecosystems is the best proof of water quantity and quality (making it an ecological approach to the sustainable use of water).
4. The main tools of this initiative are pollution control, elimination of dangerous substances, restoration of ecosystems, tax policy, water basin management planning, efficient water use, prevention of the degradation of aquatic ecosystems, public participation, and the designation of protected areas.

These principles are vital for the conservation of aquatic ecosystems in relation to water conservation and sustainable use of this resource. This directive was transposed in 2003 and entails commitments that must be met by Member States according to a strict calendar.

Available:

- A complete version of the Directive in Spanish.
- Calendar for application.
- A document in English about the principles of the Directive.

WATER TREATMENT IN SPAIN

Traditionally, there have been two main water-related problems in Spain. The first problem is that water is a scarce resource that is even more difficult to obtain in periods of prolonged draught. The second problem is the deterioration of water quality in some parts of our hydrographic network due to effluents from urban areas.

Wastewater from Spanish urban areas (some of them with thousands of inhabitants) is dumped into river basins and the sea. Years ago, polluting agents were diluted by the volume of water, but now, the increase in the load of contaminants and the reduction in water flow make solutions exclusively based on the self-treatment capacity of the hydrographic system ineffective. This has raised the need for treating wastewater before releasing it into the water network.

Spanish legislation includes various regulations designed to guarantee the quality of our continental and maritime waters. Act 46/1999 of 13 December, on the modification of Act 29/1985 (now repealed), of 2 August, on Water; the revised text of the Water Law, approved by Royal Decree 1/2001, and Act 22/988, on the Coasts, establish, among other measures, the need for previous authorisation for activities that can cause pollution of public water resources or maritime and terrestrial waters, especially the discharge of effluents. There are many other dispositions and regulations related with water quality and with the obligation to treat effluents in suitable plants.

In 1991, the European Union, acknowledging the need to ensure water quality in Member States, began their journey on the path that Spanish authorities had taken when drafting the legislation cited, with Directive 91/271/EEC. Member States were asked to install water treatment plants for urban effluents in all population centres with more than 2000 inhabitants before 2005, so that the necessary measures would be taken to ensure the correct collection and treatment of urban wastewater before discharge.

Fourteen years have passed by since the Directive was adopted and at the beginning of 2004, one year from the deadline for fulfilling the commitments with the European Union, it is noteworthy how well work has progressed in Spain as a continuation of the work that had been under way: from the transposition of the Directive into Spanish legislation to the preparation of a National Treatment Plan and execution of most of the planned infrastructures. It is estimated that the investment required to meet the demands of the European Union was almost 2 billion pesetas (about 12,000 million euros).

According to agreements with Autonomous Communities, the total participation of Central Government in financing the Plan was about 3000 million euros during its period of execution up to 2005. For example, since the creation of the Ministry of Environment in 1996, the General Administration contracted about 721 million euros worth of infrastructure development, which indicates the strong support given to the Plan. To that amount must be added calls for tenders through participation in the European Funds for Autonomous Communities.

In 1998, almost 48% of the Spanish population lived in areas with treatment systems that fulfilled satisfactorily the requirements established by the European Union and it was expected that an additional 16% lived in areas where water treatment plants were soon to be developed.

A document available on the website of the Spanish Ministry of the Environment presents in a systematic way a summary of the Spanish National Treatment Plant and its development and evolution since Directive 91/271/EEC was prepared until its adoption and entry into force, describing the works executed and results obtained. Another aim of the document is to disseminate the action lines currently being developed.

From this perspective, this document starts with an abstract about European legislation related to this issue and the Spanish legal provisions that have allowed its transposition and application (contained in Annex III).

After this abstract, the document briefly describes the main characteristics of the Spanish Water Treatment Plan adopted in 1995 and in the following sections it describes the advances made up to 2000.