WO2009154539A1

WO2009154539A1 - A floating plant bed for biological water treatment

Info

Publication number: WO2009154539A1
Application number: PCT/SE2009/000311
Authority: WO
Inventors: Stanislaw Lazarek; Wlodzimierz Lawacz; Lars-Erik Einevik
Original assignee: Phytohydrology Europe Ab
Priority date: 2008-06-18
Filing date: 2009-06-18
Publication date: 2009-12-23

Abstract

The invention regards a biological bed (10) mimicking a structure of a natural community of aquatic and terrestrial plants with inhabiting invertebrates. It comprises a prefabricated extendable flat tubular net blanket structure, and a tube (12) in the flat net structure containing a pre-designed fine-mesh netting (14) inside, to support and secure development of plant roots, while offering a large extended surface for biofilm development.

Description

Title

A floating plant bed for biological water treatment

Technical field

The present invention pertains to a biological bed consisting of a balanced community of autotrophic and heterotrophic organisms forming a functional system mimicking structures and functions of natural communities of aquatic and terrestrial plants with associated invertebrates.

Background art Vegetation in most cases does not need soil for growth. The indispensable elements of growth are water and nutrients. This fact is practically applied in hydroponic cultivations of plants that are normally terrestrial. It appears that the growth rates and the biomass of hydroponically cultivated plants exceeded considerably traditional soil-based cultivations. In Nature, there are also hydroponic varieties of terrestrial plants. In many surface waters there are communities of aquatic and terrestrial plants forming floating islands known as "plaur". Such communities are known from wetlands and aquatic ecosystems as for instance the estuary of Danube and Lake Titicaca.

Biological wastewater treatment in most conventional plants is carried out by application of activated sludge. This is in a form of suspended fine particles with high concentration of heterotrophic microbial communities. It means that their growth js sustained by continuous supply of organic compounds (sewage) and oxygen. In order to ensure that microbial degradation processes in sewage run properly, activated sludge must be pontinuously agitated. High continuous production of activated sludge also brings a necessity for continuous evacuation of "excessive sludge". The most commonly used technological process is based on aeration of wastewater and activated sludge in chambers equipped with compressed air diffusers. Vertical movement of air bubbles from the bottom up to the surface also causes vertical movement of liquid from the bottom up to the surface of an aeration chamber and back down to the bottom. This simple and efficient method of simultaneous mixing and aeration of the activated sludge has a serious drawback: air bubbles migrating through the sewage release back oxygen and in the same time, due to a concentration difference, pick up volatile organic compounds from the sewage.

These compounds, e.g. mercaptans are responsible for sometimes intensive odors. Bubbles breaking at the agitated wastewater surface "shoot" to the atmosphere water molecules known as aerosol as well as microorganisms within it. This constant export to the atmosphere not only causes unpleasant odors around treatment plants. It also brings potential health hazard to people working or living in the vicinity of treatment plants. Aerosols from treatment plants are transported by wind on considerable distance and they contribute substantially to spreading of the extracellular genetic material e.g. prions. One of the fundamental laws of Nature and the foundation of economics of life on Earth is that heterotrophic and autotrophic processes occur simultaneously and that they are interdependent. This interdependence is described by a simple equation of photosynthesis and respiration. Summary of the invention

The present invention pertains to new type of biological bed, Green Blanket ™ that mimics structure of natural community of aquatic and terrestrial plants with inhabiting invertebrates. The structure and processes within Green Blanket ™ find application in improvement of efficiency of aeration chambers in conventional wastewater treatment plants and in restoration of heavily polluted surface waters. The simplicity in construction, low investment and operation costs combined with apparently high efficiency of water purification, offers worldwide commercial application of the Green Blanket ™ in upgrading of all types of conventional biological wastewater treatment.

Hence, the present invention sets forth a biological bed mimicking a structure of a natural community of aquatic and terrestrial plants with inhabiting invertebrates. The invention comprises: a prefabricated extendable blanket of tubular net structures with a predesigned mechanism for support and development of plant roots (rhizosphere) and floaters for additional positive buoyancy, while offering a large extended surface for bio-film development.

One embodiment comprises the net is extended through joints assembling the structure and forming a monolithic flat structure covering the surface of an aeration chamber.

Another embodiment comprises that the tubular netting is creating a biological bed consisting of a rhisosphere and a bio-film when in operation. Furthermore, the present invention sets forth a system adapted to an aeration chamber, which is containing a biological bed mimicking a structure of a natural community of aquatic and terrestrial plants with inhabiting invertebrates. The present invention system thus comprises: a prefabricated extendable flat tubular net blanket structure; a tube in the flat net structure containing a pre-designed mechanism for to support and secure development of plant roots, while offering a large extended surface for bio-film development, and the aeration chamber being equipped with an air diffusing system imposing a vertical flow of liquid from the bottom up and down again, the blanket positioned on the surface of the aeration chamber continuously being supplied by activated sludge, partly becoming incorporated into bio-film covering the surface of root and the tubular netting system; and the bed being supplied with oxygen supporting aerobic processes. An embodiment of the present invention system comprises that the rhisosphere is continuously supplied with nutrients and warm water sustaining biological activity of the blanket also during the winter.

A further embodiment comprises that there is a continuous process of sludge flotation towards the surface of the aeration chamber which parallels the sedimentation process of fractions of the sludge and the incorporation of another part of sludge into the rhisosphere.

Still a further embodiment provides that roots of aquatic plants release biologically active substances, among them the coagulating compounds which have a positive effect on transformation of pollutants from a dissolved phase into a suspended phase. Yet another embodiment provides a continuous compacting and densification process of suspended matter in the structure of the blanket which is self-regulated by comprising the processes: of sedimentation, including the more suspended matter which becomes retained in the blanket, the higher probability that transformed particles return to the bottom of the aeration chamber; and grazing by invertebrates due to ideal life conditions in the blanket supplied by heat, oxygen, and nutrients resulting in a massive growth of invertebrates grazing on sludge particles.

Brief description of the drawings Henceforth reference is had to the attached figures in the accompanying text of the description for a better understanding of the present invention with its embodiments and given examples, wherein:

Fig. 1 schematically illustrates a cross sectional view of a flat tubular net blanket structure in accordance with an embodiment of the present invention; and Fig. 2 illustrates a part of a prefabricated tubular net in accordance with the present invention.

Detailed description of preferred embodiments

The present invention benefits from practical experience in applications of constructed wetlands for wastewater treatment and knowledge of eco-physiology of aquatic and terrestrial vegetation in relation to nutrient loading and hydraulics. Introducing autotrophic elements organized in form of "plaur" to the heterotrophic system based on activated sludge will in a natural way and in accordance with Nature's laws restore equilibrium between respiration (activated sludge) and photosynthesis (green vegetation).

With reference to Fig. 1 schematically illustrating a cross sectional view of a flat tubular net blanket structure in accordance with an embodiment of the present invention as a biological bed 10. In Fig. 1 vertical arrows depict convection of heat, oxygen and flotation of particles applied. Functions of the Green Blanket are depicted by Zones 10.

Fig. 2 illustrates a part of a prefabricated tubular net in accordance with the present invention. It depicts a prefabricated tubular 12 net assembled by a mechanical clamp device for instance placed where X points in Fig. 2. In the direction of Y floaters provide additional positive buoyancy.

A basic construction of Green Blanket ™ mimics and follows organization of naturally occurring "plaur". It's a construction that allows for stabile setting of green plants, macrophytes on the surface of a liquid in such a way that the roots and rhizosphere have free room for growth and expansion in a continuous contact with liquid environment. To accomplish this, a prefabricated tubular net construction is applied put together using designed clamps X (Fig. 2) in form of panels in dimensions: 100 x 100 x 20 cm. Actual measures are not intended to limit the invention to those. They are given as examples of a possible embodiment. Any amount of panels is than put together by for instance click-joints forming a monolithic flat structure covering the surface of an aeration chamber. Every tube 12 in this flat structure contains a special fine-mesh netting 14 inside in order to support and secure development of plant roots while offering a large extended surface for bio-film development.

As a root system develops, together with tubular 12 netting 14 it creates a new type of integrated biological bed (bio-bed) consisting of a rhisosphere and a bio-film making up a bio-bed 10. The bio-bed 10 becomes inhabited by numerous water invertebrate species that consume organic material accumulated in the bio-bed 10.

The aeration chambers equipped with air diffusing systems are characterized by vertical flow of liquid from the bottom up and down again. In consequence of such process, the Green Blanket ™ positioned on the surface of the aeration chamber is continuously supplied by activated sludge, part of which becomes incorporated into bio-film covering the surface of the root and tubular netting system. The bio-bed 10 is also supplied with oxygen which prevents anaerobic processes. Warm water and continuous supply of nutrients do the rhisospere also sustain biological activity of the Green Blanket™ during the winter. Continuous flotation of sludge particles towards the surface parallels the sedimentation process of some fractions of sludge as well as incorporation of another part of sludge into the rhisosphere.

Roots of aquatic plants release many biologically active substances. Some of the organic substances are dissolved coagulating compounds which can have a positive effect on transformation of pollutants from a dissolved phase into a suspended phase. Continuous compacting and densification process of suspended matter in the structure of Green Blanket is self-regulated by two processes: Process of sedimentation - the more suspended matter becomes retained in the Green Blanket the higher probability that transformed particles return to the bottom of the aeration chamber.

Grazing by invertebrates - ideal life conditions in the Green Blanket (heat, oxygen, nutrients) result in a massive growth of invertebrates grazing on ideal food - sludge- bacterial aggregates. As a result, the Green Blanket zone converts into the missing link in the natural food chain or trophic pyramid where the simplified microbial heterotrophic system (activated sludge) is complemented by new, substantially richer trophic pyramid consisting of hundreds of invertebrate species that are integrated with autotrophic plant community of high biological diversity.

It is estimated that biomass of the activated sludge in aeration chambers is in the range of 3 to 5 kilograms of dry weight in one cubic meter. Assuming the depth of an aeration chamber to be 5 meters, the liquid column of one square meter would contain between 15 to 25 kilograms of sludge. By introducing the Green Blanket ™ to such conditions would in 2-3 months growth, result in a biomass density of one square meter of Green Blanket ™ close to 100 kilograms and it will still be on the ascending curve. Such high biomass consists of the above water vegetation (5 - 10 kg) and a "hydrosoif - concentrated activated sludge incorporated in rhizomes and roots of plants with associated very high biomass of invertebrates. At this stage of the present invention, it's difficult to differentiate contributions of various components of the biomass to the total weight due to the fact that the system is of a dynamic nature that follows seasonal and spatial changes. It is however assumed that the biomass of Green Blanket will oscillate around 100 kg of dry matter per one square meter. Such a considerable share of the new dynamic component in aeration chambers will have important and measurable influence on efficiency of their processes. The efficiency will be considerably upgraded without an economic investment that would normally be required for alternative equally efficient technical measures. It can be expected a considerably improved microstructure of activated sludge particles due to the above-mentioned enrichment with coagulating organic compounds released by macrophyte root system. Prolonged trophic chains resulting from introduction of many sludge consumers will inevitably reduce the amount of excessive sludge but in the same time it will modify the microstructure of organic particles so that the process of final dewatering of excessive sludge would be more energy efficient and economically less expensive. Appropriate selection of macrophyte species to be used in construction of Green Blanket ™ bio-bed will effectively reduce or eliminate spreading of aerosols and odors. This particular bio-filtering function of the Green Blanket ™ is achieved by selecting macrophyte species that create floors in the canopy of vegetation so that the temperature, humidity and movement of air within the canopy can be controlled. For this purpose a lower floor of macrophyte consists of plants type Mimulus and Veronica. The higher floor of macrophyte consists of plants type Cyperus and Carex. A completely new and visually attractive element, the Green Blanket offers to concrete structures of conventional wastewater treatment plants an aesthetic greenery which will have a positive effect on the surrounding environment and people. The present invention is not limited to given examples and embodiments, but to what a person skilled in the art can derive from the attached set of claims.

Claims

1. A biological bed (10) mimicking a structure of a natural community of aquatic and terrestrial plants with inhabiting invertebrates, characterized by comprising: a prefabricated extendable flat tubular net (14) blanket structure with floaters for additional positive buoyancy and a tube (12) in said flat net structure containing a pre-designed fine-mesh netting (14) inside, to support and secure development of plant roots, while offering a large extended surface for biofilm development.

2. A bed according to claim 1 , wherein said net is extended through joints assembling said structure and forming a monolithic flat structure covering the surface of an aeration chamber.

3. A bed according to claim 1 , wherein said tubular netting is creating a biological bed consisting of a rhisosphaere and a biofilm when in operation.

4. A system adapted to an aeration chamber, which is containing a biological bed (10) mimicking a structure of a natural community of aquatic and terrestrial plants with inhabiting invertebrates, characterized by comprising: a prefabricated extendable flat tubular net blanket structure; a tube (12) in said flat net structure containing a pre-designed fine-mesh netting (14) inside, to support and secure plant roots, while offering a large extended surface for biofilm development, and said aeration chamber being equipped with an air diffusing system imposing a vertical flow of liquid from the bottom up and down again, said blanket positioned on the surface of said aeration chamber continuously being supplied by activated sludge, part becoming incorporated into bio-film covering the surface of root and said tubular netting system; and said bed being supplied with oxygen preventing anaerobic processes.

5. A system according to claim 4, wherein the rhisospere is continuously supplied with nutrients and warm water sustaining biological activity of the blanket during winter conditions.

6. A system according to claim 4, wherein a continuous flotation of sludge particles towards the surface of said aeration chamber correlates with the sedimentation process of fractions of sludge as well as incorporation of another part of sludge into the rhisosphere.

7. A system according to claim 4, wherein roots of aquatic plants release biologically active substances, whereby organic substances are dissolved coagulating compounds which have a positive effect on transformation of pollutants from a dissolved phase into a suspended phase.

8. A system according to claim 4, wherein a continuous compacting and densification process of suspended matter in the structure of said blanket is self-regulated by comprising the processes: of sedimentation, including the more suspended matter which becomes retained in said blanket, the higher probability that transformed particles return to the bottom of said aeration chamber; and ideal life conditions in said blanket supplied with heat, oxygen, and nutrients resulting in a massive growth of invertebrates grazing on activated sludge and sludge-bacterial aggregates.