Study On The Modularization Of Substrate In Constructed Wetlands

The substrate clogging is the most serious problem of constructed wetland in the actual operation, that is, after a period of operation time, constructed wetland can not be used continuously, or must be changed the operating mode because of the substrate clogging which has attracted widespread attention because its deadly hazards to the operation of constructed wetland. Based on the comprehensive analysis of the causes and the characteristics of substrate clogging, combining the characteristics and the application status of porous pervios concrete, we raise a new idea to restore the constructed wetland function rapidly and effectively through rapid replacement of the clogging modular substrate.This study successfully prepares the modular substrate using the weight mix proportioning, four-step mixing procedure and pound molding process. By orthogonal test, we mainly discuss the influences of the water-cement ratio, the aggregate grade, and the design objective porosity to the permeability coefficient and the compressive strength of modular substrate. After statistical analysis of the experiment data, we find that the aggregate grade and the design objective porosity are the main factors influencing the characteristics of the modular substrate. Based on the permeability coefficient, compressive strength and the cost of the modular substrate, the optimal mix proportioning of the modular substrate is: aggregate grade 5 to 10 mm; design objectives porosity 30%; water-cement ratio 0.3 and water-reducing agent 0%.We conduct the water distribution performance and clogging performance, and compare the clogging time of six modular substrates, which have different design objective porosity, different aggregate size, and different substrate thickness. It can be considered qualitatively that modular substrate is better than the bulk substrate in water distribution. Modular substrates with bigger aggregate size, the greater effective porosity have the longer clogging time. In practical engineering applications, the priority should be given to the selection of bigger aggregate size and greater effective porosity, but it must be balanced by the compressive strength of modular substrate. After nine-day's natural dried, the porosity of modular substrate can be restored to their original value of 88.3%.Finally, base on the comprehensive technical and economic analysis of the application feasibility of modular substrate in the constructed wetlands, we successfully applied the modular substrate to the constructed wetland of Chongming Chenjiazhen Yu'an community wastewater treatment plant. Although the initial investment of the modular substrate wetland is slightly higher than that of conventional constructed wetland, but in the follow-up operation, the maintenance costs of the modular substrate wetland is significantly lower than that of conventional constructed wetland, and when modular substrate must be replaced because of clogging, it has obvious advantages in time and cost.