Research On The Purification Of Fe, Mn-contaminated Wastewater By Constructed Wetland With Bamboo Biochar Mixed Matrix

As an important source of water for China's water supply,groundwater has become increasingly polluted with iron and manganese.Especially in rural areas where water use conditions are limited,the health of residents is seriously endangered by groundwater containing high concentration of iron and manganese.The constructed wetland technology with many advantages has a broad prospect in rural areas.The use of bamboo biochar to improve the matrix of constructed wetlands can provide a new idea for the removal of groundwater iron and manganese,also a cost-effective method for the reuse of the bamboo waste.In this paper,bamboo-biochar mixed quartz sand was used as the matrix of constructed wetland to treat simulated ground water containing iron and manganese.Under different concentration and hydraulic retention time,four corresponding control groups?quartz sand constructed wetland CW-S,biochar mixed matrix constructed wetland CW-BS,the quartz sand matrix calamus constructed wetland CW-SP,and the bio-carbon mixed matrix constructed wetland CW-BPS?were constructed to evaluate its'purification effect of Fe,Mn-contaminated wastewater.The main conclusions are as follows:?1?Biochar had a well-developed pore structure with a dense microporous structure.The micropore volume accounted for 51.16%of the total volume and the specific surface area reached 141.3 m²/g.At the same time,its surface featured rich functional group,high polarity and reduction,pH value of 7.21.These characteristics contributed to good bamboo biochar adsorption performance,increased the microbial load of bamboo biochar and made it an improved wetland matrix for iron and manganese contaminated simulated ground water treatment.?2?Through the fitting of absorption isotherm,it was found that the adsorption process of Fe²⁺and Mn²⁺in bamboo biochar was mainly physical adsorption and the adsorption capacity of bamboo biochar to Fe²⁺was better than that of Mn²⁺and there was a significant ion replacement in Fe-Mn competitive adsorption.The competitive ability of Fe²⁺was stronger than that of Mn²⁺.In the experimental concentration range,when the initial concentration of competitive adsorption was Fe²⁺:1.2 meq/L,and Mn²⁺:0.8 meq/L,the total adsorption amount of the two reached a maximum of 0.78 meq/g.?3?In the experiment of treating single pollution in constructed wetlands,for iron-contaminated simulated ground water,the best purification effect for each concentration is the bamboo biochar mixed matrix constructed wetland;the removal rates of CW-BS and CW-BSP reached the highest under the HRT of 36h while running low-concentration Fe²⁺?15 mg/L?,which were 99.35%and 99.52%,respectively.For manganese-containing simulated ground water,the best purification effect at each concentration is the bamboo biochar mixed matrix calamus constructed wetland;the bamboo biochar mixed matrix calamus constructed Wetland CW-BSP under the HRT of 36h while running low-concentration Mn²⁺?10 mg/L?,the removal rate reached the highest?99.42%?.Comparing the removal rates of different HRTs under different concentrations,the purification effect of constructed wetlands was greatly reduced when HRT was 12h,and the removal rates of bamboo biochar mixed matrix constructed wetlands were similar under the HRT of 24h and 36h,all reached 90%.So that when the HRT is 24h,the constructed wetland has the best removal efficiency.Under the combined pollution of iron and manganese,the total removal rate in the CW-SP was 89.51%;the total removal rate in the CW-BSP was 92.40%,indicating that the bamboo biochar can effectively improve the purification performance of the wetland treatment for combined pollution.?4?The effective purification of iron-containing simulated ground water from constructed wetlands relied on the action of bamboo biochar matrix;the purification of manganese-containing simulated ground water relied mainly on plants.The calamus in this experiment showed good resistance and can be used as a selection plant for wastewater containing Mn and Fe.The underground part enjoyed significantly higher heavy metal enrichment capacity than the aboveground and higher enrichment capacity towards manganese than iron.The iron removal capacity of the biochar mixed matrix is greater than the manganese removal capacity.Comparing biochar characterization before and after wastewater treatment,biochar was found to remove heavy metals through surface precipitation and chemical adsorption.?5?Using high-throughput sequencing techniques to compare the biological diversity and community composition before and after the operation of the quartz sand matrix constructed wetland and biochar mixed wetland,it was proved that the biomass carbon can keep the diversity of the microbial community well,maintain the stability of the dominant flora,thereby contributing to the treatment of sewage and the development of bacterial colony populations.