Effects of different types of carbon based filter materials on purification of livestock wastewater by earthworm bioengineering bed

Earthworm is a soil residence animal, which can effectively enrich and remove nutrients in the environment, and its role in the field of ecological environment has gained more and more attention.Earthworm bioengineering bed can efficiently purify various sewages. In such bioengineering, the filter is an important part, and carbon material is the core material of the filler.In order to determine the impact of the carbon types on the earthworm bioengineering bed, in this study, rice straw and biochar were used as carbon source filler, and livestock wastewater was added to the bioengineering bed at different time interval.The inlet and outlet water quality parameters were continuously monitored for 22 d.Results showed that bioengineering bed of rice straw as filler could significantly reduce various pollutants in livestock wastewater.The pollutant reduction was 67.2% of nitrate nitrogen, 81.4% of ammonium nitrogen, 79.5% of total nitrogen, 29.9% of phosphate, 35.2% of total phosphorus, 21.4% of COD (chemical oxygen demand) and 77.8% of EC (electric conductivity) value.The bioengineering bed of rice straw filler changed the pollutant reduction in the addition of earthworms.The increase of average reduction was 11.1% of ammonium nitrogen, 10.4% of total nitrogen, 17.8% of phosphate, 73.9% of total phosphorus and 27.3% of COD, and the average reduction was 10.3% of nitrate nitrogen and 3.4% of EC value.Bioengineering bed of biochar as filler could significantly reduce various pollutants in livestock wastewater, and pollutant reduction was 36.8 % of nitrate nitrogen, 86.2% of ammonium nitrogen, 53.4% of total nitrogen, 21.2% of phosphate, 33.3% of total phosphorus, 33.3% of COD and 51.7% of EC value.The bioengineering bed of biochar filler increased the pollutant reduction in the addition of earthworms, and the increase of average reduction was 0.4% of nitrate nitrogen, 1.4% of ammonium nitrogen, 10.6% of total nitrogen, 26.0% of phosphate, 29.5% of total phosphorus, 39.2% of COD and 0.7% of EC value.After bioengineering bed treatment, average increase of pH value of outlet water was 3.1% for rice straw as filler, and 7.7% for biochar as filler.The average decline rate of pH value of the outlet water in adding earthworms was 0.1% and 7.7%.In summary, the type of carbon and earthworm activity significantly influenced the effect of livestock wastewater purification for the earthworm bioengineering bed.The straw filler was beneficial to the reduction of nitrate nitrogen, total nitrogen, phosphate, total phosphorus and EC of the livestock wastewater.Biochar filler was conducive to the reduction of ammonium nitrogen and COD in livestock wastewater, and significantly increased the pH of outlet water.The removal rate of ammonium nitrogen, total nitrogen, phosphate, total phosphorus and COD was significantly improved after adding earthworm into bioengineering bed, but it was not conducive to the removal of nitrate nitrogen.It was the most conducive to the removal of pollutants in livestock wastewater that adding earthworm into the bioengineering bed filler which was made by the biochar and straw in a certain proportion.