Integrated method for clearance, collection and capture of internal pollutants and algae in a surface layer of the lake bottom

Abstract

An integrated method for clearance, collection and capture of internal pollutants and algae at the bottom of a lake include the following steps: selecting areas where the pollution level is high, and organic or inorganic particulate matter is prone to accumulation and carrying out trenching operations at the bottom of the lake to form a plurality of traps; and removing the sludge and algae inside the traps and clearing the sediment inside the traps, for subsequent internal pollution control when the surface-layer sludge on both sides of the traps almost fills up the traps. This method makes use of the hydrodynamic disturbances of waves formed by natural wind energy and lake currents to continuously transport sludge with a high pollution level and a small specific gravity and algae in the surface layer of the lake bottom, which are rich in organic debris, to artificially built traps.

Claims

1. An integrated method for clearance, collection and capture of organic or inorganic particulate matter pollutants and algae in a surface layer of a bottom of a lake having a main body, wherein the method comprises the following steps: (1) selecting accumulation-prone areas where the pollutants are prone to accumulation and building a plurality of deep concave traps at the bottom of the lake in the accumulation-prone areas to collect pollutants and algae at the bottom of the lake; and (2) removing the pollutants and the algae inside the traps for pollution control when the pollutants on both sides of the traps fills up the traps; wherein the accumulation-prone areas at the step (1) are convergence areas of lake currents at the bottom of the lake or peripheral areas of an estuary; wherein in each of the accumulation-prone areas at the step (1), there are a plurality of high-frequency convergence points and the trap is a straight line or a curve connecting the plurality of high-frequency convergence points, wherein the high-frequency convergence points are determined through the following steps: (1.1) collecting data including wind speed, wind direction, river mouth positions entering or leaving the lake, discharge, water depth, current direction and shear stress at the lake bottom; (1.2) according to the collected data, using a three-dimensional hydraulic model to calculate a lake flow field and wind wave for a year, analyzing calculation results of a daily average or hourly average lake current at the bottom of the lake and determining the frequency and distribution of convergence points, among which the convergence points with an annual frequency of more than 25% are high-frequency convergence points; wherein each of the traps vertically extend into the main body establishing an upper boundary and a lower boundary, along with an inner section and an outer section, wherein the inner section is configured to collect the pollutants, wherein the outer section adjoins to the main body of the lake on one side, forming a contiguous boundary with the lake, and the outer section is bordered by water on another side; and the depth of the trap itself from the upper boundary to the lower boundary of the trap is more than 1 meter; and wherein the vertical extension of the trap is designed to interact with waves and hydrodynamic action to guide the pollutants into the inner section.

2. The method according to claim 1, wherein the step (1) further comprises protecting edges of the traps.

3. The method according to claim 2, wherein an edge protection material is concrete, metal plate or engineering plastic plate.

4. The method according to claim 1, wherein the depth of the lake is less than 6 meters at a normal water level.

5. The method according to claim 1, each of the traps having a length and a width, the width of the traps is 4 to 20 meters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is schematic diagram of the present invention.

(2) FIG. 2 is schematic diagram of the present invention.

DETAILED DESCRIPTION

(3) Embodiment 1

(4) In the Zhushan Lake area where sludge pollutants and algae of the Taihu Lake are prone to accumulation and precipitation, the zones that conform to

(5) $\frac{?u}{?x}+\frac{?v}{?y}<0$
are selected as convergence zones, the wind velocity, wind direction, lake current flow direction and lake bottom shear stress of the zones are investigated, the lake flow field and wave value in a typical year are calculated using a three-dimensional hydrodynamic model according to the method in the prior art (reference: Hu, W., Jorgensen, S. E., Zhang, F., 2006. A vertical-compressed three-dimensional ecological model in Lake Taihu, China. Ecol. Model. 190(3), 367-398.) and the calculation results of daily average or hourly average bottom-layer flow field are analyzed to determine the frequency and distribution of convergence points of the bottom-layer flow field and determine that the convergence points with an annual frequency of above 25% are high-frequency convergence points.

(6) Trenching operations are conducted at the bottom of the lake to form a plurality of traps at the bottom of the lake. The traps randomly connect a plurality of high-frequency convergence points and are 4 m wide, 2 m deep and 0.6-0.9 time as long as the convergence zones. The water depth of the trap bottom is 7 m (more than half of wavelength of highest one-tenth wave in the typical year).

(7) Meanwhile, engineering plastic plates are used to protect the edges of the traps.

(8) 12 months later, after the polluted sludge and algae in the water settle in the traps through water current action, the sludge and algae inside the traps are collected and removed using shipborne dredging equipment.

(9) After this technology is used, the total nitrogen and total phosphorus contents in the surface layer of the sediment are reduced by 40% and the content of chlorophyll a is reduced by 50%.