The furrow irrigation tests were done to estimated the efficiency of the HRT(Hydraulic Retention Time) and landfill leachat collected from Dalian Maoyimgzi Municipal Solid Waste Landfill, which contained high level of COD (Chemical Oxygen Demand, 3.8 × 10 4 mg·L –1), TOC (total carbon, 4.8 × 10 3 mg·L –1), TN(total nitrogen, 2.9 × 10 3 mg·L –1) and SS (Suspended Solids, 6.5 × 10 2 mg·L –1), using the reed (phragmites) cultivated onland located in south area of Dalian Jiaotong University. The results showed that: 1) The TN concentration was decreased from 9.8 × 10 2 mg·L –1 in the landfill leachate to 7.6 × 10 2 mg·L –1 in the soil water, and the 22.4% of the removal rate; 2) The TOC concentration was decreased from 4.8 × 10 3 mg·L –1 in the landfill leachate to 1.0 × 10 3 mg·L –1 in the soil water, and the 79.2% of re- moved rate; 3) The water concentration in the soil was no significant difference of irrigation between the water and the landfill leachate; 4) ΔHRT was 2.1 hours in irrigation 39 L of the water and landfill leachate and 1.3 hours in the 9 L.
There are many project cases and researches on treating the landfill leachate with constructed wetland around the world. For example, Ithaca Landfill in New York in the USA started to treat the landfill leachate with constructed wetland in 1989 [
Cultivated onland treatment of landfill leachate is a relatively new wastewater treatment technology, and was attention and gradually applied in recent decades [10-16]. Landfill leachate has a large concentration of pollutants, black, dark green and chocolate color, and complex components, so it’s hard to treat by tradition ways. As investigation that the main treatment of landfill leachate in China is reverse osmosis, and it has good treatment effect, but there are running unstable, expensive, consume large and some other shortcomings [17-22]. In addition, there is no effective disposal traditional way for the production of concentrated solution, and any mistake will cause secondary pollution. Therefore, research on cultivated onland treatment of landfill leachate is of great significance. the applicable criteria that follow.
The landfill leachate was collected from Dalian Maoyingzi Municipal Solid Waste Landfill, which contained high level TN (9.8 × 102 mg·L–1) and TOC (4.8 × 103 mg·L–1). Its color was dark brown and smelled bad. The cultivated onland located in the South Area of Dalian Jiaotong University. The main onland plant was reed (Phragmites) with a spacing of 0.5 m, and the roots extended about 30 cm depth under the onland surface. Preparing instruments and medicines used for analyzing the TN and TOC by international standard methods, and Marriott Bottles, polyethylene plastic films, collecting basins, tape measure, shovel, pickaxe, scraper knife, adhesive tapes, sieve, bezel and some other equipment and tools.
The schematic diagram of experiment ground can be seen from Figures. Digging the soil in between the reed of 2 ridges with long (1 m), wide (0.34 m) and depth (0.25 m), and became the furrow, and dripping the landfill leachate (
of the water and the landfill leachate was 39 L and 9 L, respectively. The experiment was 4 times of repeats. While the water and the landfill leachate had permeated the ground, having been taken 1 kg of the soil nearby 5 cm of the furrow were 12 samples, and N, C and water concentrations in the samples were measured by semimicro-Kjeldahl azotometer, external heating potassium dichromate and drying and weighing method.
Total nitrogen in the 48 L of the landfill leachate is 47.14 g, and the soil (valume 1.00 × 0.25 × 0.34 m, density 2.65 g/cm3 and background value 0.58 g/kg) is 130.65 g. It is 177.79 g of both in the landfill leachate and the soil. The total nitrogen content in the soil might be 0.79 g/kg as the theory. In 1 day after treatment, the 0.76 g/kg its content was measured (
The total carbon of 48 L of the landfill leachate is 228.77 g, and the soil (valume 1.00 × 0.25 × 0.34 m, density 2.65 g/cm3 and background value 4.67 g/kg) is 1051.92 g. It is 1280.69 g of both in the landfill leathate and the soil. The total carbon content might be 5.69 g/kg as the theory. In 1 day after treatment, the 10.01 g/kg of its content was measured (
In the 1 day after the treatments, the average water contents of the background value, the deionized water and
the landfill leathate in the soil were 9.51%, 17.23% and 17.18%, respectively. It ranged from 7.41% to 10.71% in the soil of the background value, from 12.50% to 20.00% in soil of the deionized water and from 15.79% to 18.52% in the soil of the landfill leathate. It was no significant difference (P > 0.05) of irrigation between the water and the landfill leachate, and background value. First time, HRT of irrigating 39 L the deionized water was 15 hours and it of the landfill leathate was 12.9 hours; then it of the 9 L of the deionized water was 8.3 hours and the landfill leathate was 7.0 hours. ΔHRT was 2.1 hours in irrigation 39 L of the water and landfill leachate and 1.3 hours in the 9 L. To some extent, the landfill leathate increased the leakage of water and solute loss, and reduced the HRT of pollutants in soil. It was in accordance with Chen et al. [
In 1 day after the treatment of furrow irrigation the landfill leathate, total nitrogen and total carbon remove 22.4 and 79.2% of efficiency rate from 9.8 × 102 and 4.8 × 103 mg·L–1 in the landfill leachate to 7.6 × 102 and 1.0 × 103 mg·L–1 in the soil water, respectively. Hydraulic load in the landfill leathate of 1.70 × 103 m3/(ha·d) was 16.9% higher than it in the water of 1.45 × 103 m3/(ha·d). As time goes by, the removal efficiency will be very higher than the 1 day. Furrow irrigating the landfill leathate in growing Reed onland may be a better method of treating the landfill leathate, which more and more will have being permeated by city solid waste.