Study On The Treatment Of Composting Leachate With Two-stage Series Of Underwater Intermittent Aeration Reactor

Aerobic composting,one of the commonly employed and economically beneficial treatment in rural domestic waste disposal,generates a high concentration of organic wastewater-compost leachate.And the compost leachate is generaly characterized by large toxicity,complex composition and large variation of water quality and water quantity,which make the proper disposal of compost leachate become one of the urgent problem in the environmental protection of villages and towns.In this study,the activated sludge process was employed to treat the leachate produced by aerobic composting in WenQuan garbage disposal plant in Jimo City.In the activated sludge process,a two-stage series underwater intermittent aeration reactor(invention patent,application number: 201610504788.9)and self-sucking stirring type underwater aerator(invention patent,application number: 201510431817.9)which were designed and manufactured by the research group were investigated under the conditions of 1.0,1.5kgCOD/(m~3·d)to seek their optimal operating conditions for carbon and nitrogen removal operating in the mode of authomatic intermittent water and intermittent aeration.Then the optimum conditions of 1.0,1.5kgCOD/(m~3·d)were used to carry out the comparison experiment of aeration impeller.The final stage of experiment is to compare the effect of coagulation and biochemical combination process on carbon removal and denitrification under the optimum conditions of 1.0kgCOD/(m~3·d),and to seek better effect of composting leachate treatment.The whole study lasted for 6 months,the main conclusions are as follows:(1)The reactor was operated under the conditions of 1.0,1.5kgCOD/(m~3 · d)in three different working conditions,and the results were compared and analyzed,which showed that the optimum operating conditions in 1.5kgCOD/(m~3·d)is the best.And its operating parameters were as follows.HRT was controlled about 64 h,sludge recycle ratio was about 40%,the DO in the first and second aeration was about 2.2 and 1.3 mg/L,the periodicity was 4 times per day,the cycle time was 6h.In each cycle,the influent was started for 30 minutes,and the two-stage reactors began to aeration after the end of the influent.After aeration for 4h in the first-stage reactor,aeration cycle was carried out at intervals of 2h;after aeration for 2h in the second-stage reactor,the aeration cycle was carried out at intervals of 1h,and the two-stage reactor stopped aeration after 5h,and precipitated for 30 min.The total removal rate of COD and NH3-N were 83.75% and 95.2%.(2)In the contrast experiment of aeration impeller with different thickness,the aerator was replaced with the aeration impeller of different thickness running under the optimal working condition of 1.0,1.5kgCOD/(m~3·d).The following conclusions were drawn from comparing the results of the processing:The second aeration impeller(d=5mm)run effectivily under 1.5kgCOD/(m~3·d),whose removal rates of COD,NH3-N and TN were 98.15%,98.54%,97.3%.And the second impeller had lower speed,small energy consumption,better mixing and aeration ability.(3)In the experiment of coagulation and biochemical combination process,the coagulation and biochemical processes were combined to treat compost leachate under the condition of volume loading 1.0kg COD/(m~3·d).The results showed that the removal rates of COD and NH3-N were 99.1% and 98.8% respectively.And the COD and NH3-N concentration of effluent were 298mg/L and 12mg/L respectively.The combination process had the characteristics of low economic cost,simple operation,good removal effect and high automation degree.