In situ nitrogen removal in phase-separate bioreactor landfill

The feasibility of in situ nitrogen removal in phase-separate bioreactor landfill was investigated. In the experiment, two sets of bioreactor landfill systems, namely conventional two-phase and in situ nitrogen removal bioreactor landfills, were operated. The in situ nitrogen removal bioreactor landfill (NBL) was comprised of a fresh-refuse filled reactor (NBLF), a methanogenic reactor (NBLM) and a nitrifying reactor (NBLN), while the two-phase bioreactor landfill (BL) used as control was comprised of a fresh-refuse filled reactor (BLF) and a methanogenic reactor (BLM). Furthermore, the methanogenic and nitrifying reactors used aged refuse as bulk agents. The results showed that in situ nitrogen removal was viable by phase-separation in the bioreactor landfill. In total 75.8 and 47.5 g of nitrogen were, respectively, removed from the NBL and the BL throughout the experiment. The methanogenic reactor used the aged refuse as medium was highly effective in removing organic matter from the fresh leachate. Furthermore, the aged refuse was also suitable to use as in situ nitrification medium. The degradation of fresh refuse was accelerated by denitrification in the initial stage (namely the initial hydrolyzing stage) despite being delayed by denitrification in a long-term operation.     

Performance and bacterial compositions of aged refuse reactors treating mature landfill leachate

Aged landfill leachates become more refractory over time and difficulty to treat. Recently, aged refuse bioreactors show great promise in treating leachates. In this study, aged refuse bioreactors were constructed to simulate landfill leachate degradation process. The characteristics of leachate were: COD_cr, ∼2200 mg/L; BOD₅, ∼280 mg/L; total nitrogen, ∼2030 mg/L; and ammonia, ∼1900 mg/L. Results showed that bioreactor could remove leachate pollutants effectively at hydraulic loading of 20 L/m³ d. The removal rate reduced when hydraulic loading doubled or temperature lowered. Effluent recirculation could alleviate the temperature effect. Combining aged refuse and slag biofilters could treat leachate more efficiently. Pyrosequencing analysis indicated that bacteria from Pseudomonas, Lysobacter, Bacillus and δ-proteobacter, Flexibacteraceae were more abundant in the samples. The Shannon index decreased at lower temperature, while evenness and equitability increased with recirculation. We suggest that filter medium and temperature may be the main factors for shaping bacterial community structure.     

Novel engineering controls to increase leachate contaminant degradation by refuse: From lab test to in situ engineering application

Here we provide direct evidence through a series laboratory and field-scale experiments using different age refuse to treat landfill leachate that aged refuse exhibits increased leachate contaminants removal ability with refuse stabilization time addition. Ten-years aged refuse showed best contaminant removal in a laboratory-scale test, removing 70.0% (8340.0-2540.0 mg/L) chemical oxygen demand (COD) and 75.0% (910.0-215.0 mg/L) ammonium-N, as well as removing 61.5-67.0% COD and 50.4-58.1% ammonium-N with variable COD (9948.0-12286.0 mg/L) and NH₃-N (780.0-1184.0 mg/L) in a field-scale test, respectively. When the 10-years aged refuse was disinfected by 20% NaClO (wt%), COD, biochemical oxygen demand (BOD₅), total nitrogen (TN), and ammonium-N removal showed a dramatic decrease throughout operation time from 84.4-86.2% to 15.2-34.5%, 94.4-99.8% to 26.2-54.4%, 31.2-33.9% to 2.1-10.1%, and 88.5-90.1% to 1.5-14.5%, respectively, suggesting biodegradation is the dominant contaminant removal. Based on this finding, a 3-stages (8 years) age refuse bioreactor (ARB) was constructed to treat leachate and ARB efficiently reduced chemical oxygen demand (COD) from 5478.0-10842.0 mg/L to 261.0-1020 mg/L (87.8-96.2% removal), ammonium-N from 811.4-1582.0 mg/L to 8.5-43.3 mg/L (96.9-99.4%), respectively, in 18 months running. In summary, the present studies suggest that increased leachate contaminant biodegradation ability of aged refuse could be used directly to create an engineering approach to treat leachate with operational and economic advantages.     

Nitrogen removal through different pathways in an aged refuse bioreactor treating mature landfill leachate

In this study, an aged refuse bioreactor was constructed to remove nitrogen in a mature landfill leachate. The nitrogen removal efficiency and the microbial community composition in the bioreactor were investigated. The results showed that the aged refuse bioreactor removed more than 90 % of total nitrogen in the leachate under the nitrogen loading rate (NLR) of 0.74 g/kg (vs) day, and the total nitrogen removal rate decreased to 62.2 % when NLR increased up to 2.03 g/kg (vs) day. Quantitative polymerase chain reaction results showed that the average cell number of ammonia-oxidizing bacteria in the bioreactor was 1.58?×?10⁸ cells/g, which accounted for 0.41 % of total bacteria. The number of anammox bacteria in the reactor was 1.09?×?10⁸ cells/g, which accounted for 0.27 % of total bacteria. Isotopic ¹⁵N tracing experiments showed that nearly 10 % of nitrogen was removed by anammox. High-throughout 454 pyrosequencing revealed that the predominant bacteria in the bioreactor were Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and Gemmatimonadetes, including various nitrifiers and denitrifiers with diverse heterotrophic and autotrophic metabolic pathways, supporting that nitrogen was removed through different pathways in this aged refuse bioreactor.     

生物反应器填埋场系统渗滤液的脱氮性能

利用填埋场垂直分布的好氧-缺氧-厌氧的独特生态环境,并采用填埋垃圾上层间歇曝气充氧的方式,研究了生物反应器填埋场系统渗滤液的脱N性能.结果表明,填埋垃圾上层间歇曝气充氧,促进了填埋垃圾层硝化细菌和反硝化细菌的生长,且可使反硝化细菌的数量比普通的填埋垃圾层高4～13个数量级,硝化细菌的最大数量可达到10⁹个·g^-1;营建了填埋场内硝化、反硝化等脱N反应的生物环境,有利于回流渗滤液含N化合物的去除.试验结束时,其渗滤液NH₄⁺-N和TN浓度分别为186和289 mg·L^-1,仅为对照的18%和26％.此外,填埋垃圾上层间歇曝气充氧也有利于填埋垃圾的降解,提高垃圾的稳定化效果.     

Effects of in situ nitrogen removal on degradation/stabilization of MSW in bioreactor landfill

The effects of in situ nitrogen removal on degradation of municipal solid waste (MSW) in bioreactor landfill system were investigated. The in situ nitrogen removal bioreactor landfill (NBL) consisted of fresh-refuse filled, methanogenic and nitrifying reactors was operated. The two-phase bioreactor landfill (BL) comprised of fresh-refuse filled and methanogenic reactors was used as control. The methanogenic and nitrifying reactors were all loaded with aged refuse whose placement time was 6-7 yr. Furthermore, the nitrifying reactor was in situ aerated. The results showed that the degradation of fresh-refuse was delayed and CH4 production also was reduced in the in situ nitrogen removal bioreactor landfill. It was feasible to perform in situ ammonia nitrification in aged refuse. Moreover, the efficiency of oxygen utility was high during the in situ nitrification because of the porous characteristic of aged refuse. Supplementing only 8.5mg O2 mg(-1)Nd(-1) to aged refuse could make ammonia removed completely. However, aeration did not accelerate the further stabilization of aged refuse.     

In situ simultaneous organics and nitrogen removal from recycled landfill leachate using an anaerobic-aerobic process

An anaerobic-aerobic process including a fresh refuse landfill reactor as denitrifying reactor, a well-decomposed refuse reactor as methanogenesis reactor and an aerobic activated sludge reactor as nitrifying reactor was operated by leachate recirculation to remove organic and nitrogen simultaneously. The results indicated that denitrification and methanogenesis were carried out successfully in the fresh refuse and well-decomposed landfill reactors, respectively, while the nitrification of NH(4)(+)-N was performed in the aerobic reactor. The maximum organic removal rate was 1.78 kg COD/m(3)d in the well-decomposed refuse landfill reactor while the NH(4)(+)-N removal rate was 0.18 kg NH(4)(+)-N/m(3)d in the aerobic reactor. The biogas from fresh refuse reactors and well-decomposed refuse landfill reactors were consisted of mainly carbon dioxide and methane, respectively. The volume fraction of N(2) increased with the increase of NO(3)(-)-N concentration and decreased with the drop of NO(3)(-)-N concentration. The denitrifying bacteria mustered mainly in middle layer and the denitrifying bacteria population had a good correlation with NO(3)(-)-N concentration.     

Behavior of dimethyl phthalate (DMP) in simulated landfill bioreactors with different operation modes

The behavior of dimethyl phthalate (DMP) from municipal solid waste (MSW) in the leachate and refuse of two simulated landfill bioreactors was compared. In one reactor, the leachate was circulated between a landfill and a methanogenic reactor, while the other reactor was operated using direct recirculation of the leachate. The results revealed that the original concentration of DMP in the refuse was approximately 3.3 μg g⁻¹, and the concentration decreased greatly during decomposition of the waste in both reactors. The major loss of DMP from the landfill occurred in an active methanogenic environment in the later period, while the environment was acidic due to a high concentration of chemical oxygen demand (COD), volatile fatty acids (VFA), and contained a large volume of biologically degradable material (BDM) during the early stage. In addition, a high correlation was found between the residual DMP concentrations and the BDM of the refuse in both systems. Circulating the leachate between the landfill and a methanogenic reactor resulted in an increase in the biodegradability of MSW and the degree of waste stabilization. Furthermore, the removal of DMP was enhanced 14% in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill in which there was direct leachate recirculation.     

Biological degradation of MSW in a methanogenic reactor using treated leachate recirculation

With a methanogenic reactor using treated leachate recirculation, the effects of 12 effective microorganisms (EMs), isolated from Hangzhou Tianzhiling landfill, on the degradation of municipal solid waste (MSW) were investigated. The preliminary experiment indicated that the EMs increased the biodegradability of MSW, enhanced 24% of organic mass effluent from the landfill reactor, and shortened methane production period to about 91 days in the bioreactor landfill system. The total gas production volumes for the landfill only with leachate recirculation, the bioreactor landfill system with and without EMs inoculation were 65.7, 620.9 and 518.6 l, respectively, after 105 days operation. The average methane concentration of the gas formed in the bioreactor landfill system was above 70%. These showed that a combination of EMs and methanogenic reactors using treated leachate recirculation might be a good way to increase the degree of MSW stabilization, and enhance the rate and quality of gas production for energy recovery.     

Nitrogen transformation in the hybrid bioreactor landfill

The hybrid bioreactor landfill was promising in solid waste management. In the work, the nitrogen removal and nitrogen transformation in hybrid bioreactor landfill with sequencing of facultative anaerobic and aerobic conditions was explored. The result showed that the combination of facultative anaerobic and aerobic conditions in the hybrid bioreactor landfill was indeed effective in eliminating ammonia both from the leachate and the refuse thoroughly. About 72% of nitrogen was reduced from the landfilled fresh refuse through the operation of 357 days. At the end of the experiment, the concentrations of COD, ammonia, nitrate and TN in the leachate decreased to 399.2 mg l^?1, 20.6 mg N l^?1, 3.7 mg N l^?1 and 25.3 mg N l^?1, respectively.     

Fermentative hydrogen production from fresh leachate in batch and continuous bioreactors

This research for the first time investigated hydrogen production from the fresh leachate originated from municipal solid wastes. We found that fermentation of the leachate generated H₂ and was very much enhanced in the presence of extra phosphate in the batch reactor. The continuous expanded granular sludge bed (EGSB) reactor started to generate H₂ at day 20 and continued to 176 days with 120 mg/l of extra phosphate present. The highest chemical oxygen demand (COD) removal efficiency (66.9%) was achieved at liquid up-flow velocity of 3.7 m/h and hydraulic retention time of 12 h. Under proposed optimal operation conditions, the mean H₂ production rate reached up to 2155 ml/(l day). We also found that over 80% liquid metabolites were acetic acid and ethanol, suggesting the ethanol-type fermentation was dominant in the bioreactor. These findings indicate that the fresh leachate can be used as the source for continuous hydrogen production.     

Releasing behavior of copper in recirculated bioreactor landfill

The purpose of this study was to determine the releasing behavior of copper in municipal solid waste (MSW) in landfill with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Copper in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of landfill obviously. The significant different amounts of Cu²⁺ leached out from refuse into leachate of two landfills were 24.74 mg and 118.53 mg after 320 days’ operation, respectively. It also reflected the releasing behavior of copper in landfill refuse at different stage accordingly. The results confirmed that the refuse in landfill had high potential of secondary pollution after closure.     

Cascade bioreactor with submerged biofilm for aerobic treatment of Tunisian landfill leachate

A bioreactor cascade with a submerged biofilm is proposed to treat young landfill leachate of jbel chakir landfill site south west from capital Tunis, Tunisia. The prototype was run under different organic loading charges varying from 0.6 to 16.3 kg TOC m⁻³ day⁻¹. Without initial pH adjustment total organic carbon (TOC) removal rate varied between 65% and 97%. The total reduction of COD reached 92% at a hydraulic retention time of 36 h. However, the removal of total kjeldahl nitrogen for loading charges of 0.5 kg N m⁻³ day⁻¹ reached 75%. The adjustment of pH to 7.5 improved nitrogen removal to a rate of 85% for loading charge of 1 kg N m⁻³ day⁻¹. The main bacterial groups responsible for a simultaneous removal of organic carbon and nitrogen belonged to Bacillus, Actinomyces, Pseudomonas and Burkholderia genera. These selected isolates showed a great capacity of degradation at different leachate concentrations of total organic carbon.     

Stability and efficiency of biofilms for landfill leachate treatment

The objective of this work was to assess the feasibility of a fixed-film biological aerated filtration process for the treatment of the leachate produced at Harnhill landfill site (South Gloucestershire, UK). The laboratory scale plant consisted of four identical biological aerated filters (a triplicate and a “control” column) packed with small brick fragments. Biofilm formed within 24 h of immersion of the support material in the reactor, and had a high resistance to antibiotics and other toxic agents. The plant maintained a stable operation in the 20–45 °C temperature range, showing the best results (35.4 ± 6.6% COD removal and 73.9 ± 5.5% BOD₅ reduction) at 40 °C. The lowest COD and BOD₅ values obtained at the outlet of the columns were 7067 mg/L and 1050 mg/L, respectively.     

Effect of enzyme additions on methane production and lignin degradation of landfilled sample of municipal solid waste

Operation of waste cells as landfill bioreactors with leachate recirculation is known to accelerate waste degradation and landfill gas generation. However, waste degradation rates in landfill bioreactors decrease with time, with the accumulation of difficult to degrade materials, such as lignin-rich waste. Although, potential exists to modify the leachate quality to promote further degradation of such waste, very little information is available in literature. The objective of this study was to determine the viability of augmenting leachate with enzymes to increase the rate of degradation of lignin-rich waste materials. Among the enzymes evaluated MnP enzyme showed the best performance in terms of methane yield and substrate (lignin) utilization. Methane production of 200 mL CH₄/g VS was observed for the MnP amended reactor as compared to 5.7 mL CH₄/g VS for the control reactor. The lignin reduction in the MnP amended reactor and control reactor was 68.4% and 6.2%, respectively.     

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.     

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents.The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m³ per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m³ per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.     

The effect of calcium on the treatment of fresh leachate in an expanded granular sludge bed bioreactor

This research investigated the calcium effect on the anaerobic treatment of fresh leachate in an expanded granular sludge bed (EGSB) bioreactor under mesophilic conditions. The observations show that the bioreactor, inoculated with anaerobic granular sludge, can be started up only in about 40 days for the treatment of calcium-containing fresh leachate with chemical oxygen demand (COD) removal efficiency above 90% and organic loading rate up to 72.84 kg COD/m³ day. The calcium accumulation onto the granules was monotonically related to the calcium concentration, accounting for 17-18 wt.% of Ca in the suspended solid in the form of calcium carbonate, phosphates/phosphonates and carboxylates. The mineral formation significantly increased the granule settling velocity (by ∼50%) and the suspended solid concentration (by ∼100%). However, the effect of calcium precipitation on the specific methanogenic activity and the CH₄ production rate was complex, first positive during the start-up but later on negative.     

Consuming un-captured methane from landfill using aged refuse bio-cover

A novel simulated bio-cover was developed to facilitate the biological methane oxidation process using aged refuse and aged sludge from landfill. It was found that 78.7% and 66.9% of CH₄ could be removed, with the aged refuse: aged sludge (w/w%) ratio of 7:3 and 6:4 in bio-cover system, respectively. The maximum CH₄ removal rate could reach 100%, when the aged refuse with the disposal time more than 14 years were applied in bio-cover. Some controlled factors for the methanotrophic activity, i.e. moisture, Eh and organic matter content, were also investigated. It was found that CH₄ oxidation rate increased greatly, when the moisture content and organic matter were increased from 6.0%, 4.8% to 8.0%, 9.5%, respectively. The optimum conditions for this bio-cover system was found to be as follows: aged refuse: aged sludge ratio of 7:3, the moisture content of 8-9%, Eh of 104-108 mV and organic matter of 9.5%.     

垃圾渗滤液在土壤中的生物降解动态

通过室内好氧、厌氧2种培养,研究了3种不同填埋年限垃圾渗滤液在红壤和潮土中的生物降解动态.鲜样、天井洼样、水阁样垃圾渗滤液分别为填埋0年、4～5年和12年的垃圾渗滤液.结果表明,垃圾渗滤液在前7 d降解相对较快.在好氧培养条件下,红壤鲜样、天井洼样、水阁样渗滤液在前7 d的表观降解率为88.9%、60.5%、25.0%;潮土中的表观降解率更大,分别为96.6%、80.4%和65.0%;7 d后下降趋势均趋于平缓.在相同土壤中,填埋龄越短的垃圾渗滤液的表观降解率越大,在厌氧培养条件下的情况与此类似,但降解率不如好氧条件下高.在没有土壤介质参与的条件下(如低洼处积存的渗滤液),3种垃圾渗滤液自身降解速率均符合一级动力学方程.鲜样垃圾渗滤液降解的半衰期为12～16 d,其余垃圾渗滤液降解的半衰期为20～30 d.垃圾渗滤液一旦进入土壤环境,降解速率会大大加快.土壤处理垃圾渗滤液有一定的功效.