Method for systematically controlling rapid proliferation of cyanobacteria cells in lakes in spring

Abstract

A method for systematically controlling rapid proliferation of cyanobacteria cells in lakes in spring is described. The method applies physical, biological and chemical methods in an integrated and synergistic manner and includes using flexible enclosures to close a control water area and using modified soil to adsorb and settle algal cells; coupling four technologies including algae control by fish, algae control by biological floating islands, algae inhibition by plants and algae control by microorganisms; and using H.sub.2O.sub.2 to kW algae and using 40% FeCl.sub.3+CaCO.sub.3 and 50% Ca(NO.sub.3).sub.2 to treat sediment. The method establishes a complete system for physical, chemical and biological control of algae, forms joint control of exogenous contaminants, endogenous contaminants and cyanobacteria, integrates physical, biological and chemical methods and optimizes systematic methods that are used synergistically.

Claims

1. A method for systematically controlling rapid proliferation of cyanobacteria cells in lakes in spring, comprising: determining an algae control water area and using flexible enclosures to close the control water area; using FeCl.sub.3, CaCO.sub.3 and Ca(NO.sub.3).sub.2 to treat sediment; using H.sub.2O.sub.2 to kill the algae and then using modified soil to adsorb and settle the algal cells; arranging an ecological floating island comprising floating plant beds, aquaculture net cages and biofilms in a closed water area; arranging the aquaculture net cages under the floating plant beds to breed filtering-feeding fish and shellfish; and hanging the biofilms at the lower ends of the aquaculture net cages for natural growth of periphyton; and deploying snails to the lakebed of the algae control water area.

2. The method according to claim 1, wherein the structure of the flexible enclosures comprises floats, aprons and clump weights; the upper end of each apron is connected to a float and the lower end is connected to a clump weight to form the flexible enclosures to close the control water area to be protected; and the clump weights are stone cages or sand cages and are buried in bottom sediment.

3. The method according to claim 1, wherein 40% FeCl.sub.3+CaCO.sub.3 is injected into the surface sediment at first to make Fe.sup.3+ reach about 300 g/m.sup.2 and then 50% Ca(NO.sub.3).sub.2 is injected into the surface sediment to make NO.sub.3—N reach 10-12 g/m.sup.2 to control phosphorus release of the bottom sediment.

4. The method according to claim 1, wherein 10-15 mg/L H.sub.2O.sub.2 is used to kill algal cells first and then 15-30 mg/L chitosan modified soil is deployed into the water body to adsorb and settle the algal cells.

5. The method according to claim 1, wherein the floating plant beds are made from a combination community of Alternanthera philoxeroides, Paspalum vaginatum swartz and Lolium perenne in which Alternanthera philoxeroides is an edificator, and Paspalum vaginatum swartz and Lolium perenne are planted as supplements at a ratio of 6:2:2.

6. The method according to claim 1, wherein the dimensions of the aquaculture net cages are 0.6-1 m high, 5-8 m long and 3-4 m wide and the aquaculture net cages are connected to floating plant beds through polyethylene ropes.

7. The method according to claim 1, wherein filtering-feeding fish and shellfish are bred inside the aquaculture net cages; the filtering-feeding fish is sliver carp and the breeding density is controlled at 100-150 g/m.sup.3; and the filtering-feeding shellfish is Sinanodonta woodiana, Cristaria plicata, or Hyriopsis cumingii and the breeding density is controlled at 300-400 g/m.sup.2.

8. The method according to claim 5, wherein filtering-feeding fish and shellfish are bred inside the aquaculture net cages; the filtering-feeding fish is sliver carp and the breeding density is controlled at 100-150 g/m.sup.3; and the filtering-feeding shellfish is Sinanodonta woodiana, Cristaria plicata, or Hyriopsis cumingii and the breeding density is controlled at 300-400 g/m.sup.2.

9. The method according to claim 1, wherein the lower ends of the aquaculture net cages use plastic nets or combined packing/elastic packing or tree branches/bamboo branches to construct and hang biofilms; when plastic nets are used to hang biofilms, the distance between the plastic nets is 15-20 cm; when combined packing or elastic packing is used to hang biofilms, the packing density is 25-35 pcs/m.sup.2; when tree branches/bamboo branches are used to hang biofilms, they can be fully filled; and the biofilms are hung to the water bottom.

10. The method according to claim 1, wherein the ecological floating island covers 30%-50% of the water area.

11. The method according to claim 1, wherein the deployment density of snails to the lake bottom is 200-300 g/m.sup.2.

12. The method according to claim 1, wherein the snails are cipangopaludina.

13. The method according to claim 12, wherein the snails are cipangopaludina.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow diagram of a method provided by the present invention.

DETAILED DESCRIPTION

(2) Below the technical solution of the present invention is further described in detail by referring to embodiments.

Embodiment 1

(3) From March to June 2017, the area within a semi-closed weir in the west half of the Chaohu Lake was selected to carry out a demonstration of algae control technology for the rapid growth period of cyanobacteria.

(4) Flexible enclosures were used to close three control water areas, each with an area of 600 m.sup.2, 1800 m.sup.2 in total.

(5) After completion of the closure of the control water areas, algae control measures were taken for the rapid growth period of cyanobacteria; environmentally friendly chemicals were used first, 40% FeCl.sub.3+CaCO.sub.3 was injected into the surface sediment to make Fe.sup.3+ reach about 300 g/m.sup.2 and then 50% Ca(NO.sub.3).sub.2 was injected into the surface sediment to make NO.sub.3—N reach 10 g/m.sup.2 to control the release of phosphorus in the bottom sediment and promote the denitrification process on the sediment surface;

(6) After completion of the above measures, 10 mg/L H.sub.2O.sub.2 was used to kill algae cells and then 20 mg/L chitosan modified soil was added to the water body to adsorb the settled algal cells;

(7) 3 m wide and 5 m long floating plant beds were arranged in the control water areas and made from a combination community of Alternanthera philoxeroides, Paspalum vaginatum swartz and Lolium perenne in which Alternanthera philoxeroides is an edificator, and Paspalum vaginatum swartz and Lolium perenne were planted as supplements at a ratio of 6:2:2;

(8) After the floating plant beds were made, the combined aquaculture net cages were installed under the floating plant beds. 250-500 g/tail silver carp and Sinanodonta woodiana were bred to control algae. The 1 m high, 5 m long and 3 m wide aquaculture net cages were used to filter the algae in the water body, the breeding density of silver carp was controlled at 100-150 g/m.sup.3 and the density of Sinanodonta woodiana was controlled at 300-400 g/m.sup.2;

(9) Biofilms were hung at the lower ends of aquaculture net cages and composite packing or elastic packing was used to naturally grow periphyton (algae, protozoa, fungi, bacteria, etc.), so that they naturally form films. The density of composite packing or elastic packing was 25-35 pcs/m.sup.2;

(10) The combined ecological floating island comprising floating plant beds, aquaculture net cages and biofilms for purification and algae control covered nearly 40% of the water areas.

(11) Lastly, cipangopaludina was deployed to the control water areas to eat the settled cyanobacteria debris and fish manure. The deployment density was 250 g/m.sup.2.

(12) The monitoring results from April to June show that compared with the water body outside the control areas, the algae density and biomass in the control areas decreased by more than 60% and 80% respectively and no cyanobacterial bloom occurred in the control areas during the testing stage; the water transparency reached 1 m or more (the transparency outside the control areas was only about 30 cm), the concentrations of TN, TP and COD.sub.Mn in the water body decreased by 28%-35%, 32%-48% and 55%-60% respectively and the effect was significant.

Embodiment 2

(13) From March to June 2015, the experimental enclosure ecosystem of the Taihu Station, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences was selected to carry out a demonstration of algae control technology for the rapid growth period of cyanobacteria. The control effect was observed until August.

(14) Flexible enclosures were used to close three control water areas, each with an area of 100 m.sup.2, 300 m.sup.2 in total.

(15) After completion of the closure of the control water areas, algae control measures were taken for the rapid growth period of cyanobacteria; environmentally friendly chemicals were used first, 40% FeCl.sub.3+CaCO.sub.3 was injected into the surface sediment to make Fe.sup.3+ reach about 300 g/m.sup.2 and then 50% Ca(NO.sub.3).sub.2 was injected into the surface sediment to make NO.sub.3—N reach 12 g/m.sup.2 to control the release of phosphorus in the bottom sediment and promote the denitrification process on the sediment surface;

(16) After completion of the above measures, 15 mg/L H.sub.2O.sub.2 was used to kill algae cells and then 15 mg/L chitosan modified soil was added to the water body to adsorb the settled algal cells;

(17) 4 m wide and 6 m long floating plant beds were arranged in the control water areas and made from a combination community of Alternanthera philoxeroides, Paspalum vaginatum swartz and Lolium perenne in which Alternanthera philoxeroides is an edificator, and Paspalum vaginatum swartz and Lolium perenne were planted as supplements at a ratio of 6:2:2;

(18) After the floating plant beds were made, the combined aquaculture net cages were installed under the floating plant beds. 250-500 g/tail silver carp and Sinanodonta woodiana were bred to control algae. The 0.6 m high, 6 m long and 4 m wide aquaculture net cages were used to filter the algae in the water body, the breeding density of silver carp was controlled at 100-150 g/m.sup.3 and the density of Sinanodonta woodiana was controlled at 300-400 g/m.sup.2;

(19) Biofilms were hung at the lower ends of the aquaculture net cages and plastic nets were used for natural growth of periphyton (algae, protozoa, fungi, bacteria, etc.) to naturally form membranoid substances. The distance between plastic nets for hanging biofilms was 15-20 cm;

(20) The combined ecological floating island comprising floating plant beds, aquaculture net cages and biofilms for purification and algae control covered about 50% of the water areas.

(21) Lastly, cipangopaludina was deployed to the control water areas to eat the settled cyanobacteria debris and fish manure. The deployment density was 200 g/m.sup.2.

(22) The monitoring results from April to August show that compared with the water body outside the control areas, the algae density and biomass in the control areas decreased by more than 76% and 65% respectively and no cyanobacterial bloom occurred in the control areas during the testing stage; the water transparency reached 1.2 m or more (the transparency outside the control areas was only about 25 cm), the concentrations of TN, TP and COD.sub.Mn in the water body decreased by 30%-37%, 40%-51% and 35%-43% respectively and the effect was significant.

Embodiment 3

(23) From March to June 2016, the estuary water area of the Nanfei River into the Chaohu Lake was selected to carry out a demonstration of algae control technology for the rapid growth period of cyanobacteria.

(24) Flexible enclosures were used to close a control water area, with an area of 10,000 m.sup.2. The control effect was observed until September.

(25) After completion of the closure of the control water area, algae control measures were taken for the rapid growth period of cyanobacteria; environmentally friendly chemicals were used first, 40% FeCl.sub.3+CaCO.sub.3 was injected into the surface sediment to make Fe.sup.3+ reach about 300 g/m.sup.2 and then 50% Ca(NO.sub.3).sub.2 was injected into the surface sediment to make NO.sub.3—N reach 11 g/m.sup.2 to control the release of phosphorus in the bottom sediment and promote the denitrification process on the sediment surface; After completion of the above measures, 12 mg/L H.sub.2O.sub.2 was used to kill algae cells and then 30 mg/L chitosan modified soil was added to the water body to adsorb the settled algal cells;

(26) 96 3.5 m wide and 8 m long floating plant beds were arranged in the control water area and made from a combination community of Alternanthera philoxeroides, Paspalum vaginatum swartz and Lolium perenne in which Alternanthera philoxeroides is an edificator, and Paspalum vaginatum swartz and Lolium perenne were planted as supplements at a ratio of 6:2:2;

(27) After the floating plant beds were made, the combined aquaculture net cages were installed under the floating plant beds. 250-500 g/tail silver carp and Sinanodonta woodiana were bred to control algae. The 0.8 m high, 8 m long and 3.5 m wide aquaculture net cages were used to filter the algae in the water body, the breeding density of silver carp was controlled at 100-150 g/m.sup.3 and the density of Sinanodonta woodiana was controlled at 300-400 g/m.sup.2;

(28) Biofilms were hung at the lower ends of the aquaculture net cages and tree branches/bamboo branches were used for natural growth of periphyton (algae, protozoa, fungi, bacteria, etc.) to naturally form membranoid substances. The tree branches/bamboo branches were fully filled when biofilms were hung;

(29) The combined ecological floating island comprising floating plant beds, aquaculture net cages and biofilms for purification and algae control covered nearly 30% of the water area.

(30) Lastly, cipangopaludina was deployed to the control water area to eat the settled cyanobacteria debris and fish manure. The deployment density was 300 g/m.sup.2.

(31) The monitoring results from April to September show that compared with the water body outside the control area, the algae density and biomass in the control area decreased by more than 63% and 55% respectively and no cyanobacterial bloom occurred in the control area during the testing stage; the water transparency reached 0.8 m or more (the transparency outside the control area was only about 30 cm), the concentrations of TN, TP and COD.sub.Mn in the water body decreased by 26%-34%, 34%-43% and 42%-55% respectively and the effect was significant.