CH715708B1 - Process for backfilling a constructed wetland based on biomass circulation - Google Patents

Abstract

The present invention relates to a method for filling a plant-based sewage treatment plant based on biomass circulation, which is filled with a layer of activated carbon, the activated carbon of which is produced by carbonizing plant remains and/or animal remains from the plant-based sewage treatment plant. The recovery of withered wetland plants and rotting animal remains from the constructed wetland to produce activated charcoal and the decay of the produced activated charcoal into the constructed wetland can on the one hand solve the problem that biomass such as plant remains, animal remains and the like easily lead to clogging of the fillers in the constructed wetland and thus the Decrease the constructed wetland's ability to treat organic wastewater, thereby improving the constructed wetland's utilization efficiency. On the other hand, it can solve the problem that biomass such as plant and animal residues generate numerous pollutants in the putrefaction and decomposition process and cause secondary pollution of organic waste water. Thirdly, the activated carbon is filled into the constructed wetland so that a stronger adsorption effect for the pollutants to be treated is achieved compared to activated carbon from other sources.

Description

FIELD OF THE INVENTION

The present invention belongs to the field of waste water treatment, resource utilization and water pollution control and relates in particular to a method for backfilling a constructed wetland based on biomass circulation.

STATE OF THE ART

A constructed wetland is an ecological treatment technology that excels in beautifying the landscape, maintaining the ecological balance, and being easy to manage. Constructed wetland technology has outstanding application advantages in the control of watershed pollution worldwide, especially in developing regions, and is widely applied to the treatment of various types of wastewater such as polluted river water, tail water from municipal sewage treatment plants, scattered domestic sewage, etc. As the main component of constructed wetland, wetland plants are mostly annual. The conventional sewage treatment technology for constructed wetland has problems such as weed degradation and putrefaction. Wetland animals show good adsorption and degradation effects for pollutants in constructed wetlands. However, the generation of animal remains such as shrimp and crab shells and fish scales and their rotting and rancidity lead to water body degradation and secondary pollution. The problems of clogging of the fillers and the release of pollutants due to withered wetland plants, decaying animal remains and other biomass, as well as the problem of low economic added value of using wetland plants, which is often encountered in the operation of constructed wetland projects, severely limit their spread and application.

[0003] In constructed wetlands, a large amount of wetland straw is generated, and so far there has been no good treatment and utilization method. The most common treatment method is natural degradation or incineration, causing environmental pollution in addition to taking up space and wasting resources. To date, no effective treatment method for wetland animal remains is available. Therefore, it is very important to realize comprehensive use of wetland straw and treatment and disposal of animal remains to improve the sustainable use of constructed wetlands.

A variety of studies have shown that the adsorption method is an effective technology for treating waste water polluted by organic matter. However, conventional adsorbents are expensive and difficult to recycle. The corresponding task can no longer be fulfilled when the adsorbents are saturated. Thus, the cost of treating organic waste water by constructed wetlands is increased, and it is difficult to maintain the efficiency of treating organic waste water by constructed wetlands.

DISCLOSURE OF THE INVENTION

To solve the above problems in the prior art, the present invention is based on the object of providing a method for backfilling a constructed wetland system based on biomass circulation. In constructed wetland, plant straw, animal remains and other biomass are carbonized to produce activated carbon, which is filled in the constructed wetland substrates to realize biomass circulation and improve the removal of pollutants in wastewater.

According to the present invention, the object is achieved by a method for backfilling a plant-based sewage treatment plant based on biomass circulation, which comprises the following steps: Recovery of plant remains and/or animal remains from the constructed wetland, carbonizing the plant residues and/or animal residues to produce activated charcoal and Filling the activated carbon into the bottom sludge or the filler of the constructed wetland.

[0007] By recovering withered wetland plants and rotting animal remains from the constructed wetland for the production of activated charcoal and filling the activated charcoal produced into the constructed wetland, charcoal is produced and covered with the biomass from the constructed wetland, which means that the disposal of plant and animal remains from the constructed wetland is realized. On the other hand, this solves the problem that biomass such as plant residues, animal residues and the like easily clog the fillers in the constructed wetland and thus reduce the ability of the constructed wetland to treat organic waste water, thereby improving the utilization efficiency of the constructed wetland. Third, it can solve the problem that biomass such as plant and animal residues generate numerous pollutants in the process of putrefaction and degradation, and cause secondary pollution of organic waste water.

It is preferably provided that in an open water constructed wetland system, the backfilling methods of the activated carbon layer include the direct mixing and addition method, the modular method and the floating ball method, while in an underground constructed wetland system with horizontal flow, the backfilling methods of the activated carbon layer include the modular method and the floating ball method include.

Furthermore, it is preferably provided that in the direct mixing and addition method, the respective activated carbon is filled with a soil sludge after mixing in order to obtain a mixed layer of activated carbon and soil sludge, with a top layer above the mixed layer and a top layer below the mixed layer a bottom mud layer is provided. Cladding the activated carbon after mixing it with bottom mud increases the stability of the activated carbon and largely prevents it from floating or dispersing.

Still further, it is preferably provided that the thickness of the top layer is 4 to 8 cm, the thickness of the mixed layer is 25 to 40 cm and the height of the water layer is 30 to 50 cm, with the thickness of the top layer preferably being 5 to 6 cm, the thickness of the mixed layer is 26-35 cm and the height of the water layer is 35-45 cm.

Due to the low density, the activated carbon floats in the bottom sludge when filling. The top layer is laid flat on top of the mixed layer to cover it and prevent the activated carbon from floating out. In order to prevent the adsorption effect from being impaired, the thickness of the cover layer is limited to 4 to 8 cm. If the thickness/height of the top layer, the mixed layer and the water layer are adjusted like this, the activated carbon in the mixed layer has a better treatment effect for organic waste water in the water layer.

Still further, it is preferably provided that the mass ratio of the activated carbon to the bottom sludge in the mixed layer is 1:0.8-1.2.

Still further, it is preferably provided that the substance in the top layer is bottom sludge.

Furthermore, it is preferably provided that with the modular method, a tank body filled with activated carbon is buried in a soil mud or filler, with the activated carbon in the tank body being divided into two layers, with the upper layer being lumpy activated carbon with a grain size of 7 to 8 cm and the bottom layer contains activated carbon with a grain size of 10-20 mesh, with both the perimeter and the bottom of the tank body drilled evenly.

The small-grain activated carbon easily floats in the bottom sludge or in the filler. By covering the small-grain activated carbon with lump activated carbon, on the one hand, the small-grain activated carbon can be pressed to avoid floating, on the other hand, it can fulfill the task of supporting and widen the flow channel of the sewage, so that the surface flow sewage can quickly reach the lower small-grain activated carbon area and thus the Adsorption treatment effect is improved with the same residence time and the treatment effect of organic waste water is increased. Third, the upper lumpy activated carbon can block and filter out solid impurities in the organic waste water to avoid blocking the small-grain activated carbon layer and extend the life of the activated carbon.

When the activated carbon in the tank body reaches the adsorption upper limit, the tank body can be taken out as a whole to facilitate the recovery and replacement of the activated carbon.

Still further, it is preferably provided that the distance between the top of the tank body and the top of the bottom mud or filler is 4 to 20 cm. There are roots of aquatic plants here, and the organic matter near the roots promotes attachment and growth of microorganisms on the surface of the activated carbon and improves the adsorption treatment ability of the activated carbon.

Still further, it is preferably provided that the diameter of the bore on the tank body is smaller than the particle diameter of the small-grain activated carbon. This prevents the small-grain activated carbon from escaping from the tank body.

Still further, it is preferably provided that the thickness of the upper layer of granular activated carbon is 7 to 8 cm and the thickness of the lower layer of small-grain activated carbon is 8 to 10 cm.

Furthermore, it is preferably provided that in the floating ball method filled with activated carbon hollow spheres buried in a soil mud or filler and the hollow spheres are connected to each other and fixed by ropes, wherein a plurality of through holes are formed on each of the hollow spheres.

Still further, it is preferably provided that the diameter of the activated carbon in the hollow spheres is 5 to 8 cm in the vicinity of a water inlet of the constructed wetland, while the diameter of the activated carbon gradually decreases from the water inlet to the water outlet of the constructed wetland.

Organic waste water enters from the water inlet, flows out from the water outlet, thereby sequentially flowing through activated carbon with gradually decreasing grain size. The adsorption effect of the activated carbon is gradually enhanced. In addition, clogging in the vicinity of the water inlet can be avoided, which has a beneficial effect on improving the treatment result.

When the activated carbon reaches the upper limit of air flotation, the hollow spheres are pulled out to facilitate the recovery and replacement of the activated carbon.

Still further, it is preferably provided that the diameter of the hollow sphere is 10 to 15 cm and the diameter of the through hole is 1 to 2 cm.

The subject matter of the invention is also a coupling system which comprises a constructed wetland filled as described above and a microbial fuel cell, the microbial fuel cell comprising an anode, a cathode and a conducting wire, the anode being buried in the activated carbon layer and the cathode being in a oxygen-dissolving portion of a water layer of the constructed wetland, and wherein the anode and the cathode are connected to each other by the lead wire.

Preferably, the animal remains are shrimp and crab shells or fish scales.

Preferably, the plant residues are harvested during a non-growth period of the plants and converted to activated charcoal using the hydrothermal carbonization technique in combination with a novel activating agent.

The present invention achieves the following advantageous effects: 1) Compared with the conventional sewage treatment technology for constructed wetlands, biomass as a filler is recycled and backfilled into the constructed wetlands to realize material recycling, avoid secondary pollution and at the same time avoid clogging of constructed wetlands to prevent. 2) The recovery of the activated carbon can be realized by using a tank and floating balls or the like as carriers for the addition of activated carbon. 3) By adding the biomass activated carbon to the coupling system of a constructed wetland and a microbial fuel cell, electricity generation is increased in addition to reduced costs.

Presentation of the invention

The accompanying drawings, which form a part of the application, are included for a better understanding of the present application. The exemplary embodiments of the present application and the description thereof are intended to illustrate the application without unduly limiting the invention. Therein FIG 1 shows an open water constructed sewage treatment plant based on biomass circulation and an associated method for increased removal of pollutants according to the present invention in a device drawing, FIG 2 shows the tank in the open water constructed sewage treatment plant based on biomass circulation and the associated method for increased removal of pollutants according to the present invention a device drawing, FIG 3 shows the floating ball in the open water constructed wetland system based on biomass circulation and the associated method for increased removal of pollutants according to the present invention in a device drawing, FIG 4 shows a horizontal flow underground constructed wetland system based on biomass circulation and an associated method for increased removal of pollutants according to the present invention in a modular device drawing, FIG 5 shows the floating ball in the underground constructed wetland system based on biomass circulation with horizontal flow and the associated method for increased removal of pollutants according to the present invention in a device drawing, FIG 6 shows the use of the constructed wetland system based on biomass circulation according to the present invention Combination with a microbial fuel cell in a device drawing.

1 for bottom mud layer, 2 for mixed layer of activated carbon and bottom mud, 3 for top layer, 4 for water layer, 5 for hydrilla, 6 for water outlet, 7 for water inlet, 8 for myriophyllum, 9 for tank body, 10 for activated carbon, 11 for Ceratophyllum demersum, 12 for bottom needle, 13 for Typha orientalis, 14 for rope, 15 for floating ball, 16 for coarse substrate layer, 17 for fine substrate layer, 18 for gravel layer, 19 for filler ball, 20 for reed, 21 for surface soil layer, 22 for anode, 23 for cathode, 24 for titanium wire and 25 for external resistance.

Concrete embodiments

It is to be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein are intended to have the same meanings as commonly understood by those of ordinary skill in the art.

It should be noted that the terms used here only serve to describe specific embodiments without limiting the exemplary embodiments according to the present application. Unless expressly stated otherwise in the context, references to the singular form are intended to include the plural form as well, it also being understood that the term "comprise" and/or "contain" as used in the specification refers to features, steps, acts, elements , component and/or their combinations.

First embodiment

As can be seen from FIG. 1, the open water constructed sewage treatment plant includes, from bottom to top, a bottom sludge layer 1, a mixed layer of activated carbon and bottom sludge 2, a top layer 3, a water layer 4, Hydrilla 5 and Myriophyllum 8. The constructed wetland flows through intermittently and the hydraulic residence time is 3 days. The bottom mud layer 1 is formed by blanket laying of bottom mud taken from a depth of about 10 cm below the surface of the bottom mud layer and a distance of about 5 m from the shore, and filtered through a 200-mesh sieve to remove impurities. The thickness of this layer is about 25 cm. The activated carbon is made from a mixture of hydrilla and shrimp, after grinding to powder, mixed with the bottom mud in a ratio of 1:1 and laid out flat on the bottom mud layer 1. The thickness of this layer is about 30 cm. The covering layer 3 has the same composition as the bottom mud layer 1 and is laid flat on and thus covers the mixed layer 2 of activated carbon and bottom mud to prevent the activated carbon from floating out and thereby deteriorating the adsorption effect. The thickness of this layer is about 5 cm. The water layer 4 is polluted by pollutants and has a height of about 40 cm. As submerged plants, Hydrilla 5 and Myriophyllum 8 are alternately planted in a 1:1 ratio. For Hydrilla 5, well-growing plants about 30 cm long are chosen, which are inserted by the cutting method with roots in a substrate, with the main body of the plant being in the water. For Myriophyllum 8, plants with a length of 7 to 10 cm are selected and planted in the bottom mud layer 1 by the cutting method.

Second embodiment

As can be seen from FIG 2, the simplest structure is used for the open water sewage treatment plant, which consists of a bottom sludge layer 1, a water layer 4 and Ceratophyllum demersum 11. The constructed wetland is flowed through intermittently and the hydraulic residence time is 3 days. The bottom mud layer consists of bottom mud taken from a depth of about 10 cm below the surface of the bottom mud layer and a distance of about 5 m from the shore, filtered through a 200-mesh sieve to remove impurities and coarse particles, and flattened to the lowest layer is laid out. The thickness of this layer is about 25 cm. The activated charcoal is made from a mixture of Ceratophyllum demersum and crab shells. Ceratophyllum demersum is planted in the bottom mud by the cuttings method.

In particular, there are two ways to add activated carbon in this embodiment. One possibility is the modular method. There is a module of a PVC tank body 9, which is drilled evenly both on the circumference and on the bottom. Small-grain activated carbon with a grain size of 10 to 20 mesh is laid out on the lower layer, and the upper layer is covered with lump activated carbon (grain size: 7 to 8 cm). The tank body 9 is located about 5 cm below the surface of the bottom mud layer 1 where the roots of Ceratophyllum demersum 11 are located. The organic matter near the roots promotes the attachment and growth of microorganisms on the surface of the activated carbon and enhances the adsorption treatment ability. The upper layer of granular activated carbon allows the surface flow wastewater to quickly enter the small-grain activated carbon area in the lower part, thereby improving the adsorption treatment effect and reducing the problem of clogging of the surface layer of the open water constructed wetlands. When the activated carbon reaches an adsorption limit, the whole tank is removed and replaced, providing convenient operation.

FIG. 3 shows another addition method, namely the floating ball method. A polyethylene floating ball 15 with a diameter of about 12 cm is used. The ball is uniformly drilled with holes about 1.5 cm in diameter, and small activated carbon particles with a grain size of 10 to 20 mesh are placed in the floating ball. The floating balls 15 are connected to each other by ropes 14 and are arranged about 5 cm below the surface of the bottom layer 1 of mud. The number of activated carbon floating balls to be added can be flexibly selected depending on the concentration of pollutants and the area of the constructed wetland. The beginning end and the tail end of the entire set of floating balls are connected by ropes 14 to the ground spikes 12, which ground spikes 12 are fixed to the bank of the constructed wetland. When the activated carbon reaches the adsorption limit, it can be taken out and replaced as a whole. As plants, Ceratophyllum demersum 11 and Typha orientalis 13 are planted evenly in a 1:1 ratio. For semi-natural wetlands resembling open-water constructed wetlands, the same addition method can be used.

Third embodiment

As shown in FIG 4, there is a flow-through underground constructed wetlands from a coarse substrate layer 16, a fine substrate layer 17 and Typha orientalis 13. The activated carbon is made from a mixture of Typha orientalis and earthworm. The activated carbon is added modularly. Both the perimeter and the bottom of the stainless steel tank body 9 are drilled evenly. Pieces of activated carbon are filled in at the front end and small particles with a grain size of 10 to 20 mesh are filled in at the rear end. The tank body 9 is located about 15 cm away from the surface filler.

The waste water flows in via the water inlet, first flows through the plants, which are used for filtration and adsorption, and then through the lumpy activated carbon area at the front end. Large lump activated carbon can not only adsorb and treat pollutants, but also quickly pass the sewage to avoid front-end clogging. Small-grain activated carbon at the back end enhances the adsorption effect. In other embodiments, the number of modules to be added can be flexibly selected according to the area of the constructed wetland and the pollutant concentration. The activated carbon can be replaced as a whole when the adsorption limit is reached.

Fourth embodiment

As shown in FIG 5, there is a flow-through underground constructed wetlands from a gravel layer 18, a surface soil layer 21 and reed 20. The activated carbon is made from a mixture of reed and fish scales. The activated carbon is introduced into a filler ball 19 with a diameter of about 12 cm. The floating ball is evenly drilled with a diameter of about 1.5 cm. The filler balls 19 are placed directly in the interstices of the gravel and at a distance of about 15 cm from the surface of the fillers and are connected to each other by cables 14. Both ends of the infill ball 19 are fastened with ropes to soil nails 12 fixed to the bank of the constructed wetland. In the filler ball 19 in the vicinity of the water inlet 7, the activated carbon is lumpy and about 6 cm long. The grain size of the activated carbon in the filler ball 19 decreases as the distance from the water outlet decreases. Wastewater enters through the water inlet and exits from the water outlets 6, and flows through smaller and smaller activated carbon in turn, gradually enhancing the adsorption effect and avoiding clogging at the front end. When the adsorption limit is reached, the activated carbon is pulled out directly for replacement.

Fifth embodiment

As can be seen from FIG 6, the open water sewage treatment plant consists of a bottom sludge layer 1, a layer of water 4 and Hydrilla 5. The sewage treatment plant is flowed through intermittently and the hydraulic residence time is 3 days. The bottom mud layer consists of Xiaomei River bottom mud, which is collected from a depth of about 10 cm below the surface and a distance of about 5 m from the bank, and filtered through a 200-mesh sieve to remove impurities and coarse particles. The thickness is about 25 cm. The activated charcoal is made from a mixture of hydrilla and earthworm and mixed with the bottom mud in a 1:1 ratio. The water layer 4 is polluted by pollutants and has a height of about 40 cm. As the submerged plants, Hydrilla is used, and well-growing plants about 30 cm long are selected, which are inserted by the cutting method with roots in the soil mud, with the main body of the plant being in the water.

Microbial fuel cells are introduced and both the anode 22 and the cathode 23 are made of carbon felt. The anode 22 is embedded in the mixed layer 2 of activated carbon and bottom mud. The cathode 23 floats in water. The cathode 23 and the anode 22 are connected to one another via a titanium wire 24 and connected to an external resistor 25 . The resistance of the external resistor 25 is approximately 1000 ¿. The addition of the activated carbon can effectively improve the pollutant removal effect from two points of view. First, the adsorption effect is enhanced to remove pollutants through adsorption. Second, the addition of the activated carbon improves the conductivity of the bottom mud and increases the power production of the entire system. Thus, the anode can decompose more pollutants to achieve better removal effect.

Waste water flows into the constructed wetland and the pollutants contained therein are first removed in a small proportion by plants and animals in the constructed wetland through absorption and metabolism. The wastewater then penetrates into the bottom sludge. The bottom sludge has a stronger adsorption effect for pollutants, and a large amount of pollutants exist in water in pores of the bottom sludge. Plant and animal residues are used to produce activated carbon, which is filled into soil sludge to adsorb pollutants in the pore water of the soil sludge, thus realizing biomass circulation. In addition, the pollutants in the pore water are used by the electro-generating microorganisms on the anode surface, which release protons and electrons. Electrons reach the cathode through an external circuit and protons reach the cathode through the bottom mud. At the cathode, protons, electrons and oxygen are reduced to create the electrical circuit of the microbial fuel cell. The two processes are carried out simultaneously, which greatly improves the pollutant removal rate. At the same time, electricity can be generated and energy saved.

So far, only preferred exemplary embodiments of the present application have been explained, which in no way serve to restrict the application. Various modifications and changes to the present application are possible for those skilled in the art. Any modifications, equivalent substitutions, and improvements within the spirit and principles of the present application are intended to be included within the scope of the application.

Claims (6)

1. A method for backfilling a constructed wetland based on biomass circulation, characterized in that it comprises the following steps: ¿ recovery of plant remains and/or animal remains from the constructed wetland, ¿ carbonization of plant remains and/or animal remains to produce activated charcoal and ¿ Filling of the activated carbon into the bottom sludge or the filler of the constructed wetland. 2. The method according to claim 1, characterized in that: ¿ in an open water constructed wetland, the backfilling methods of the activated carbon layer include a direct mix and add method, a modular method and a floating ball method, ¿ while in the case of a horizontal flow underground constructed wetland, the backfilling methods of the activated carbon layer include the modular method and the floating ball method, whereby: ¿ in the direct mixing and addition method, the respective activated carbon (10) is filled with a bottom mud after mixing to obtain a mixed layer (2) of activated carbon (10) and bottom mud and a water layer (4), with above the mixed layer ( 2) a top layer (3) and a bottom mud layer (1) under the mixed layer, preferably the thickness of the top layer (3) is 4 to 8 cm, the thickness of the mixed layer (2) is 25 to 40 cm and the height of the water layer (4) is 30 to 50 cm, preferably the thickness of the top layer (3) is 5 to 6 cm, the thickness of the mixed layer (2) is 26 to 35 cm and the height of the water layer (4) is 35 to 45 cm, preferably wherein the mass ratio of the activated carbon (10) to the bottom sludge in the mixed layer (2) is 1: 0.8-1.2, and preferably wherein the top layer (3) consists of bottom sludge; ¿ in the modular method, a tank body filled with activated charcoal (10) is buried in a bottom mud or filler, with the activated charcoal (10) in the tank body being divided into two layers, with the top layer being lump activated charcoal (10) with a grain size of 7 to 8 cm, the circumference of the tank body are drilled evenly, preferably the distance between the top of the tank body and the top of the soil mud or filler is 4 to 20 cm, preferably the diameter of the hole on the tank body is smaller than the particle diameter the activated carbon (10) of the lower layer and preferably wherein the thickness of the upper layer of granular activated carbon (10) is 7 to 8 cm and the thickness of the lower layer of activated carbon (10) is 8 to 10 cm, and ¿ in the floating sphere method, hollow spheres filled with activated carbon are buried in a bottom mud or filler, and the hollow spheres are connected and fixed to each other by ropes, with a plurality of through holes formed on each of the hollow spheres. 3. The method according to claim 2, characterized in that the diameter of the activated carbon in the hollow spheres in the vicinity of a water inlet (7) of the constructed wetland is 5 to 8 cm, while the diameter of the activated carbon from the water inlet (7) to the water outlet (6 ) decreases towards the constructed wetland. 4. The method according to claim 3, characterized in that the diameter of the hollow spheres is 10 to 15 cm and the diameter of the through hole is 1 to 2 cm. 5. The method according to claim one of claims 1 to 4, characterized in that the animal remains are shrimp and crab shells or fish scales, preferably wherein the plant residues are harvested during a non-growth period of the plants and converted to activated charcoal using the hydrothermal carbonization technique in combination with a novel activating agent. 6. Coupling system, characterized in that it comprises a constructed wetland system filled according to one of claims 1 to 5 and a microbial fuel cell, the microbial fuel cell comprising an anode, a cathode and a conducting wire, the anode being buried in the activated carbon layer and the cathode being in one oxygen-dissolving portion of a water layer of the constructed wetland, and wherein the anode and the cathode are connected to each other by the lead wire.