Optimization And Operation Mechanisms Of Aged-refuse-based Reactor For The Treatment Of Landfill Leachate

The objectives of this research were to perfect the removal performance and explain the removal mechanisms of the aged-refuse-based reactor in treating landfill leachate. The optimization and operation mechanisms of the aged-refuse-based reactor for the treatment of landfill leachate were mainly investigated, including the determination of the optimized parameters from the operation of the bench-scale, pilot-scale and full-scale stratified reactors; the improvement of the aged-refiise-based reactor in treating landfill leachate by addition of inducing materials such as waste iron scraps,steel slag,mushroom residual and straw individual; the best hybrids of the iron-scraps-fixed reactor and the aged-refuse-based reactor; the feasibility of enhanced coagulation in polishing effluent from the aged-refuse-based reactor; the transformation mechanisms of ammonium and phosphrous in the reactor and the molecular microbial community profile during the operation of the reactor.The influences of operating parameters including the volume ratio of aged refuse and influent, the influent COD concentration and the operating cycles on the removal performance of the landfill leachates treatment with the stratified aged-refuse-based reactor were investigated by the Orthogonal Test. The results indicated that the volume ratio of aged refuse and influent was crucial for the operation of the reactor at ambient temperature of 10-37℃. The optimized operational parameters were the volume ratio of aged refuse and influent greater than 50, the influent COD of less than 8000 mg/L and the operation cycle of below 3 h. The pilot-scale experiments showed that under the operating temperature of 10-37℃and the hydraulic load of 0.267-0.444 m~3/ m~3.d, the COD and ammonium of the effluent could conform to the requirements of Second Grade National Discharge Standard generally. The relatively low biomass in the aged refuse and the poor biodegrability of the leachate used in the full-scale reactor could be mainly responsible for its unsatisfactory performances.The improvement of aged-refuse-based reactor in treating landfill leachate was tested by addition of inducing materials such as waste iron scraps, steel slag, mushroom residual and straw individually. The experiments were conducted with the volume ratio of the aged refuse and the influent of 100, the operating cycle of 3 h and the hydraulic load of 0.08 m~3/m~3.d . The results indicated that waste iron scraps could notably improve the removal performance of the aged-refuse-based reactor in terms of COD and color; the addition of the steel slag could facilitate the removal of COD,color and total phosphrous, while lower the removal capacity of the reactor in ammonium and total nitrogen; The enhanced removal of COD and color by the mushroom residual could not be attained until long time operation of the reactor; likewise, the increased removal of COD,color, ammonium,total nitrogen and total phosphrous by straw could not be achieved until its termination of self-degradation. Therefore, waste iron scrap was considered a kind of proper inducing material in terms of engineering application.The optimized hybrids of the iron-scraps-fixed reactor and the aged-refuse-based reactor were investigated. The results showed that the preceding iron-scraps-fixed reactor and the intermittent aeration-sedimentation could improve the removal performance of the aged-refuse-based reactor in terms of COD and ammonium; the COD and ammonium concentration in the effluent were 150mg/L and 5mg/L, respectively. The posterior iron-scraps-fixed reactor and the intermittent aeration-sedimentation could not enhance the removal capacity of the stratified aged-refuse-based reactor, which could be explained by the fact that the COD removal pathway of iron scraps was discontinued due to the rising potential from high-level nitrate and the refractory soluble COD in the effluent. With the gradual improvement in the iron-scrap-fixed reactor, the preceding iron-scraps-fixed reactor and the intermittent aeration-sedimentation could be considered a promising way in bettering the removal performance of the aged-refuse-based reactor.The feasibility of enhanced coagulation in polishing the effluent from the aged-refuse-based reactor was tested regarding polymer aluminum chloride (PAC), ferric chloride and aluminum sulfate. The results demonstrated that the enhanced coagulation of ferric chloride was the best and that of aluminum sulfate was the worst for polishing the effluent. The optimal coagulation condition of ferric chloride was pH4.5, ferric chloride dose of 1500 mg/L, PAM dose of 15 mg/L. sulfonic-group compound dose of 5 mg/L and diatomite dose of 1500 mg/L. The maximum COD removal of 60.9% was obtained by the ferric chloride enhanced coagulation. The best COD removal of PAC and aluminum sulfate were 50%-53% and 34.4%, respectively.The adsorption and desorption tests showed that the adsorption of ammonium by aged refuse occurred instantly and the adsorbed ammonium was stable and less exchangeable. The Freundlich isotherms could fit the adsorption trend of ammonium by aged refuse. The value of n was 0.1-0.5, indicating the adsorption of ammonium occurred easily. The synergistic transformations of ammonium within aged-refuse-based reactor indicated that the cation exchange sites only provided temporary storage of ammonium prior to subsequent nitrification. The nitrification process could be considered the predominant restoration pathway of ammonium adsorption capacity of the reactor. The wetting cycle allows ammonium to be adsorbed onto aged refuse. During the subsequent drying cycle, the oxygen infiltrates in the reactor and ammonium is mostly converted to nitrate via nitrification. Hence, it could be concluded that there was no expire for the aged-refuse-based reactor in terms of ammonium removal. The low removal of total nitrogen could be mainly attributed to poor denitrification and anaerobic ammonium oxidation (anammox).A modified Hedley phosphorus (P) fractionation method was used to investigate the quantities and proportions of P fractions in aged refuse. The results indicated that the moderately available P (sum of hydroxide and dilute acid fractions) was the predominant forms and accounted for 74.9% of total P in aged refuse, indicating that the phosphorus in aged refuse had the potential of high-efficacy utilization. The temporal and spatial distributions of different P speciations in the stratified aged-refuse-based reactor showed that the phosphrous was accumulated in the reactor during the treatment of landfill leachate. The increase of phosphrous was in form of Dil.acid-P and NaOH-P. The accumulated P was mainly occurred in the upper part of the reactor. Therefore, the conclusion could be drawn that the phosphrous was removed mostly by adsorption and transformation into the precipitated combound of hydroxyl apatite. The activation effects of chicken manure (high P content) and straw (low P content) on different P forms indicated the chicken manure and straw had significant activation effects on the phosphorus in aged refuse, and the chicken manure was superior to straw in P-activation. It was found that NaOH-P, Dil.acid-P and Conc.acid-P were main sources of activitable P in aged refuse.In order to develop and validate a method for isolation of PCR-amplifiable DNA from the aged refuse samples, the orthogonal experiment was conducted to evaluate systematically the effects of various steps within each method in terms of DNA yield, purity, fragment size, humic substances contamination, PCR amplifiability using universal eubacterial and archaea 16S rDNA prime pair, and genetic diversity estimate from denaturing gradient gel electrophoresis (DGGE). The combined method of TENP buffer/PBS buffer-Bead beating/Proteinase K/SDS- Sephadex G-200 spin column was recommended.The molecular analyses of microbial community under different operation of the reactor were performed. An interesting phenomenon was discovered that the aged refuse was the carrier of extremophiles, including halophilic, alkaliphilic, thermophilic and psychrotrophic microorganism. The strong pollutant removal capacity of aged refuse could result from the high content of extremophiles, which were of the facultative metabolic pathways and the strong adaptive capacity. The predominant eubacteria within the reactor consisted of bacillus sp., proteobacterium and planococcus sp., and the chief archaea included methanosarcinales and crenarchaeote. During the optimized operation of the stratified reactor, the main eubacteria consisted of bacillus sp., microbacterium sp., actinobacteria, planococcus sp.,γ-proteobacterium and one kind of undefined N-transformation bacteria,the predominant archaea were euryarchaeote, methanomicrobia, methane-producing archaea, meihano thermophiles and one unnamed archaea. The self-immobilization of extremophiles by the carrier of aged-refuse makes it possible to treat the refractory industrial wastewater of hypersalinity and hyperalkalinity by biological pathway.In the finality, further studies were discussed in terms of the development of high-performance bioreactor, the improvement of the total nitrogen removal and the comprehensive molecular analyses of microbial community in the aged refuse.