Abstract:
The reconstruction of small wetland systems through on-site utilization of vegetable land may be an effective way to realize on-site absorption and resource utilization of domestic sewage. The combination of vegetable garden soil and adsorption materials is directly related to the removal of nitrogen and phosphorus in water. In this study, zeolite, grain husk, activated carbon, ceramsite and local vegetable garden soil were selected as test materials, and were characterized by the BET specific surface area aperture analyzer, scanning electron microscope and X-ray diffraction (EDX), and adsorption tests. Zeolite and ceramsite with better adsorption effect on nitrogen and phosphorus were screened out, Setting up a vegetable garden soil: ceramsite: zeolite mass proportional combination: F1 (10:0:0), F2 (6:2:2), F3 (8:1:1), F4 (8:2:0), (8:0:2) F5, F6 (dry cattle excrement) and F7 (6:3:1). Finally, under low, medium and high concentrations of nitrogen and phosphorus, the matrix combination with the best removal effect was selected through adsorption kinetic test. The results showed that: (1) The specific surface area (35.72, 33.23 m
2/g) and micropore volume (2.20×10
−1, 8.25×10
−2 cm
2/g) of activated carbon and ceramsite were larger in the five single substrates. The surface of zeolite and ceramsite has rough porous structure. (2) The adsorption of nitrogen and phosphorus by the substrates conformed to the Freundlich and Langmuir models. The nitrogen adsorption capacity of the five substrates was in the order of zeolite (2.00 mg/L) > ceramsite (1.47 mg/L) > vegetable garden soil (1.17 mg/L) > activated carbon (0.99 mg/L) > grain hull (0.21 mg/L), and the phosphorus adsorption capacity of substrates followed the order of ceramsite (1.28 mg/L)> activated carbon (1.25 mg/L)> zeolite (1.16 mg/L)> grain hull (0.80 mg/L)> vegetable garden soil (0.50 mg/L). (3) The adsorption kinetics of the seven substrate combinations for nitrogen and phosphorus were similar, and could be well fitted by the Elovich equation, double constant equation and first order kinetic equation under three different pollution loads. (4) The adsorption rates of nitrogen and phosphorus by substrate combinations increased at first and then slowed down, and finally stabilized at 12-48 h. The study shows that F2, F4 and F7 matrix combinations have good removal effects on nitrogen and phosphorus, but considering the simplicity and operability of vegetable field transformation, F4 was the best matrix combination, and its adsorption capacity of nitrogen and phosphorus was 0.36-0.68 mg/L and 0.10-0.39 mg/L, respectively under 3 different nitrogen and phosphorus concentrations.