Soil Quality And The Potential Improvement With Green Waste Biochar For Spongy Urban Of Shenzhen Municipality

With the global urbanization,massive land area has been hardened losing ecological functions,including water permeability.In order to prevent waterlogging on the impervious surface by storm events,the strategy to develop sponge city requires the function of permeation and water retention of urban soil.However,the urban soil has weakened or lost its ability to absorb rainwater due to human activities;Greening area has continued to rise,and garden waste has also become a burden for municipal disposal.Existing disposal technologies(composting,incineration and power generation,etc.)are constrained by various factors,and biomass carbonization as a green and safe disposal technology is suitable for construction in cities,and garden biomass carbon has high specific surface area,high adsorption,water retention,etc.The characteristics are consistent with the concept of sponge city construction.If the biomass carbonization technology is applied to the disposal of urban garden waste,and the use of garden waste biochar for urban soil improvement and upgrading,it can not only improve the water absorption function of the soil,but also dispose of urban gardens.Waste.Therefore,in this study,a typical city-Shenzhen was used as an example to carry out urban soil quality surveys and garden waste recycling pattern surveys.Using garden waste biochar pyrolysis at a temperature of 800℃ as the material,the gardening of the LID facility filler layer was carried out.The experiment on indoor improvement of garden waste biochar and the experiment on the promotion of garden waste biochar in green soils were used to determine the improved sponge material pollutant interception function and water retention and permeability performance,which provided a scientific basis for the disposal of urban garden waste and played a role in the construction of sponge cities.The function of the natural underlying surface provides new ideas.The main research results of this article are as follows:(1)The overall quality of the garden soils in Shenzhen is poor.The garden soil in the built-up area is weakly alkaline and the soil layer is relatively thin.The organic matter content of the whole soil is only about 6.79g·kg-1.The overall variability of other physical and chemical indicators is strong,and the differences between types are not significant.The average bulk density of the garden soils in the built-up area is as high as 1.6 g·cm-3,and the saturated water content is smaller than 25%.It has serious compaction,poor water retention capacity,and poor sponge function.(2)The daily production volume of garden waste in Shenzhen is more than 300,000 tons.The resource utilization is mainly composting and incineration power generation.The quality loss in daily and emergency disposal processes exceeds 65%.The resource utilization is insufficient and the economic value of the product is low.The daily disposal cost is between 130-175 CNY/ton,and the government should grant 35 million CNY of relevant subsidies to enterprises to ensure the sustainable development of this environmental service industry.At the same time,the government needs to pay attention to the professional companies engaged in the emergency treatment of garden waste in order to improve the efficiency of emergency treatment and the level of resource utilization.(3)The filter system of the filler layer added with biochar has significantly improved the effect of water infiltration and retention.The deamination effect is very significant,and the amount of garden waste biochar increases linearly.It may also be due to the electronic acceptor of biochar.Function,the biomass carbon filler layer also has a denitration(NO3-)effect.However,the removal effect of chemical oxygen consumption(COD)and total phosphorus needs to be improved.(4)Artificially prepared sponge soil has good infiltration and water holding capacity.It can effectively alleviate the occurrence of runoff for longer than 20 min during heavy rain level rainfall events,and can effectively retain moisture.After rain,it can slow the temperature rise to the soil.Evaporation of water,and can effectively reduce the concentration of runoff pollutants COD,TP,NO3-during heavy rain events,and it has a good slowing effect at the beginning of runoff,and can effectively increase the biomass of Taiwan grass and increase the chlorophyll content,and also significantly enhanced the ability of Taiwan grass to resist stress.