Preparation And Carbon Release Performance Of Constructed Wetlands Stable Release Solid Carbon Source Based On Agricultural Waste

In view of the low nitrogen removal efficiency of constructed wetlands caused by insufficient carbon sources,agricultural wastes(reed straw and poplar sawdust)were selected as the sustained release carbon source after pretreatment to improve the nitrogen removal efficiency of the system.The carbon source release of agricultural waste was simulated in the laboratory.The optimal carbon source and pretreatment method were selected.In order to achieve the stable release of carbon source,the selected carbon source was physically blended with biodegradable polycaprolactone(PCL)with different molecular weights.As a solid carbon source for denitrification,the carbon release efficiency was studied in shaking flask experiment,which provided theoretical support for enhancing the selection of nitrogen removal plus carbon sources in constructed wetlands.1.Carbon source pretreatment(simple treatment,ultrasonic treatment,alkali washing treatment and acid washing treatment)experiments showed that the content of cellulose in reed straw increased significantly after alkali treatment.The maximum release of carbon source was 33.62 mg/g in the early stage of the experiment,and could be maintained at about 2.2 mg/g in the later stage.The total release of carbon was 185.74mg/g in 22 days,with an average release rate of 8.44 mg/(g·d),and the release of TN and TP was dimension-dependent.At a low level,it can be used as an additional carbon source for further research.2.Because of the different proportion of alkali-straw blends and the molecular weight of PCL,the release rule of carbon source was also different.The results showed that the average diameter of the 12 new solid carbon sources prepared is about 3.7 mm,and height is about 4 mm,the grain weight is about 0.023 g,and the hardness is suitable.Under the same molecular weight PCL,with the increase of alkali-straw blending ratio,the carbon release from the new solid carbon source showed an increasing trend;under the same addition ratio,with the decrease of the molecular weight of the blended PCL,the stable carbon release of the new solid carbon source increased,especially when the molecular weight of PCL was 5000 and the addition ratio was the lowest,it reached the maximum value of 3.1 mg/g.3.Through the experiment,the results showed that the new solid carbon source D3(PCL with molecular weight 5000/alkali-straw blended)has strong organic matter release performance.The total carbon release in 22 days is 271.14 mg/g,and the final stable carbon release is 3.1 mg/g.The specific surface area of D3 was the largest,reaching24.968 cm~2/g,and the dissolution rate was 30.11%.TN and TP are less released and have less impact on water quality,so they are more suitable as additional carbon sources for constructed wetlands.4.To sum up,the new solid carbon source of D3(PCL with molecular weight5000/alkali-straw blended)meets the requirements of nitrogen in constructed wetland,and can be selected as additional carbon source in constructed wetland.