Treatment Of Rural Domestic Refuse In Sequencing Batch Bioreactor At Pilot Scale

In this paper,rural domestic refuse in Shi village of Fu Yang city was investigated,and two sets of bioreactor systems named R1(sequencing batch bioreactor)and R2(leachate recirculated directly bioreactor)were designed.A study of biological treatment of rural domestic refuse at pilot scale was conducted for about 70 days,and a follow-up experiment of leachate absorption,desorption and purification by soil was carried out in laboratory.The main results of this research were summarized as follows:(1)On the whole,the trends of fresh refuse reduction in R1 and R2 were similar during operation.In the end,reduction rate of R1 and R2 were up to 57%and 53%, respectively.(2)Fresh refuse organic matter content and BDM in upper and lower layers of R1 and R2 decreased throughout the pilot process,and finally became stable.During operation,refuse organic matter content and BDM in R1 declined significantly faster than R2.In the end,refuse organic matter content in upper and lower layers of R1 dropped to 221.2 g/kg and 223.5 g/kg,and R2 for the corresponding 250.2 g/kg and 264.4 g/kg,respectively.BDM in upper and lower layers of R1 dropped to 19.1%and 18.3%,and R2 for the corresponding 20.2%and 21.1%.(3)After running for about 70 days,refuse almost didn't produce leachate any longer.In the end,leachate amount of R1 and R2 was almost the same,each of which accumulating to a total of 440L,respectively.(4)Leachate pH value of R1 rised slowly from the third day of 4.78,and then was basically neutral,ranged from 6.00 to 8.00.During the whole pilot,the leachate pH value of R2 had been acid,basically around 5.20.(5)The change of leachate COD and VFA concentration of R1 and R2 was greatly different.Leachate COD and VFA concentration of R1 rised slowly from 14800.2 mg/L and 5689.3 mg/L to the peak of 24770.5 mg/L and 17932.4 mg/L,then decreased rapidly compared with R2.In the end,leachate COD and VFA concentrations were 10113.1 mg/L and 1502.3 mg/L.On the contrary,leachate COD and VFA concentration of R2 rised rapidly from the third day of 15098.0 mg/L and 6510.3 mg/L to the peak of 41328.4.mg/L and 34688.0 mg/L.Then,leachate COD and VFA concentration of R2 decreased slowly,maintaining at a high level.In the end, leachate COD and VFA concentrations of R2 were 35300.9 mg/L and 23723.4 mg/L, which were 3.49 and 15.79 times R1,respectively.(6)Leachate TN and NH₄⁺-N concentration of R1 and R2 changed same,firstly increased and then gradually stabilized,but the increased speed and the final accumulated value were different.Leachate TN and NH₄⁺-N concentration of R1 rised slowly from 502.9 mg/L and 410.2 mg/L to the end of 822.3 mg/L and 765.5 mg/L. On the contrary,leachate TN and NH₄⁺-N concentration of R2 rised rapidly from 567.1 mg/L and 432.6 mg/L to the end of 2790.6 mg/L and 2309.1 mg/L,which was 3.39 and 3.02 times R1,respectively.(7)During operation,there was little reduction of aged refuse.Ruling out the reduction caused by no compaction,reduction rate of aged refuse was only 2%in the end,indicated that aged refuse was basically stable.(8)Aged-refuse-based bioreactor had a buffer capacity and degradation performance of organic matter for leachate.Leachate effluent was basically neutral, and COD removal efficiency increased from the start of 7.4%gradually to a maximum value of 39.2%,and then dropped,basically stable at around 10.0%.(9)The adsorption equation of leachate COD and NH₄⁺-N in the soil was consistent with Langmuir isothermal adsorption equation,and the adsorption of leachate COD and NH₄⁺-N by the soil increased by their concentration.Because adsorption was a exothermic reaction,adsorption of COD and NH₄⁺-N decreased by temperature,saturated adsorption of the order was in 10℃,20℃and 30℃.The desorption of leachate COD and NH₄⁺-N increased by their adsorption amount,but desorbed little from the soil.(10)Temperature had a great impact on the purifying effect of leachate COD by the soil.At 20℃and 30℃,with the extension of culture time,the exudation of leachate COD was on a significant downward trend.For three days,the COD exudation of leachate(A)decreased rapidly from the beginning of 1984.8 mg/kg to the third day of 52.0 mg/kg and 54.2 mg/kg.The COD exudation of leachate(B) decreased rapidly from the beginning of 768.0 mg/kg to the third day of 54.18 mg/kg and 50.98 mg/kg.And then,the COD exudation of both leachate changed very little. At low temperature of 10℃,the exudation of leachate COD declined slowly.After a week,the COD exudation of leachate(A)was still up to 714.0 mg/kg.As leachate(B) contained little pollutants,the purifying effect was not particularly evident compared with 20℃,30℃,and gradually narrow with the extension of time.The COD exudation of leachate(B)was 98.0 mg/kg after a week.(11)Temperature had a great impact on the purifying effect of leachate NH₄⁺-N by the soil..At 20℃and 30℃,With the extension of culture time,the exudation of leachate NH₄⁺-N was on a significant downward trend.For 5 days,the NH₄⁺-N exudation of leachate(A)decreased rapidly from the beginning of 105.32 mg/kg to the fifth day of 4.36 mg/kg and 4.34 mg/kg.The NH₄⁺-N exudation of leachate(B) decreased rapidly from the beginning of 106.38 mg/kg to the fifth day of 4.38 mg/kg and 4.34 mg/kg.And then,the NH₄⁺-N exudation of both leachate changed very little, and the NH₄⁺-N concentration was very low.At low temperature of 10℃,the exudation of leachate NH₄⁺-N declined slowly.After a week,the NH₄⁺-N exudation of leachate(A)and leachate(B)were 33.44 mg/kg and 33.58 mg/kg,respectively.(12)When the rural domestic refuse in Shi village was disposed by sequencing batch bioreactor,total leachate amount was 10000L one year.Therefore,it need a soil of 396.8m² and five days treatment to reach a low COD and NH₄⁺-N exudation.As each set of bioreactor apparatus discharged leachate once in 70 days,that is,the 396.8m² soil treated leachate only once in a year,leachate COD and NH₄⁺-N adsorbed by the soil could be degradated well.(13)After leachate running in sequencing batch bioreactor for 70 days was purified by the soil once,Cu incremental content in soil was 0.2 mg/kg,Zn incremental content was 0.5 mg/kg.As the soil treated leachate only once in a year,so heavy metal had little pollution to the soil.