Simultaneous organic and nitrogen removal from municipal landfill leachate using an anaerobic-aerobic system

An anaerobic-aerobic system including simultaneous methanogenesis and denitrification was introduced to treat organic and nitrogen compounds in immature leachate from a landfill site. Denitrification and methanogenesis were successfully carried out in the anaerobic reactor while the organic removal and nitrification of NH4+,-N were carried out in the aerobic reactor when rich organic substrate was supplied with appropriate hydraulic retention time. The maximum organic removal rate was 15.2 kg COD/m3 d in the anaerobic reactor while the maximum NH4+-N removal rate and maximum nitrification rate were 0.84kg NH4+-N/m3/d and 0.50kg NO3--N/m3/d, respectively, in the aerobic reactor. The pH range for proper nitrification was 6-8.8 in the aerobic reactor. The organic compounds inhibited nitrification so that the organic removal in the anaerobic reactor could enhance the nitrification rate in the following aerobic reactor. The gas production rate was 0.33 m3/kg COD and the biogas compositions of CH4, CO2, and N2 were kept relatively constant, 66-75, 22-32, and 2-3%, respectively.     

Organic removal by denitritation and methanogenesis and nitrogen removal by nitritation from landfill leachate

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180 d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5 kgCODm(-3)d(-1) in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80-92% and about 99%, respectively. Without controlling temperature (17-30 degrees C) and dissolved oxygen (0.5-4.0 mgL(-1)), the maximum NH4+-N removal rate was 0.68 kg NH4+-Nm(-3)d(-1), and about 99% of NH4+-N removal was obtained by nearly complete nitritation. The 81-93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of "ammonia valley" on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5.     

The effect of decreased ambient temperature on the biological nitrification and denitrification of a high ammonia landfill leachate

This research investigated the nitrogen removal capabilities of a pre- and post-denitrification process, when treating sanitary landfill leachate containing an ammonia concentration of over 2200 mg N/L, at operating temperatures down to 10 degrees C. The treatment system employed is generally known as a 4-Stage Bardenpho process. Two parallel systems were operated throughout the study; each system had an aerobic solids retention time of 20 days and an external recycle ratio (return activated sludge) of about 3:1. During the entire experimental period, one system used an internal recycle ratio of about 4:1, while the other system used one of 3:1. Methanol was used as supplementary carbon source for denitrification. When operating temperature was decreased from 20 to 17 degrees C, an approximate 15% decrease in denitrification was immediately experienced within both systems, with no noticeable affect on nitrification. This was an unexpected result. Subsequently, the temperature was further decreased to 14 degrees C, and finally to 10 degrees C. With the temperature at 14 degrees C, aerobic wasting was also stopped and methanol loading was progressively decreased to match actual denitrification requirements. At 10 degrees C, both systems suffered major nitrification and denitrification inhibition. Changes in operating parameters, such as a decrease in influent ammonia and methanol loading, as well as an increase in ambient temperatures, from 10 to 15 degrees C, did not significantly improve overall system performance, within a reasonable time frame. Both denitrification and nitrification problems were mainly attributed to decreased ambient temperature, although other possible factors were noted; at project completion, about 50% of the incoming ammonia was being removed across the system.     

Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor, allowing for simultaneous removal of carbon (at the anode) and nitrogen (at the cathode). In this study, we supplemented the cathodic process with in situ nitrification through specific aeration, and thus obtained simultaneous nitrification and denitrification (SND) in the one half-cell. Synthetic wastewater containing acetate and ammonium was supplied to the anode; the effluent was subsequently directed to the cathode. The influence of oxygen levels and carbon/nitrogen concentrations and ratios on the system performances was investigated. Denitrification occurred simultaneously with nitrification at the cathode, producing an effluent with levels of nitrate and ammonium as low as 1.0 ± 0.5 mg N L⁻¹ and 2.13 ± 0.05 mg N L⁻¹, respectively, resulting in a nitrogen removal efficiency of 94.1 ± 0.9%. The integration of the nitrification process into the cathode solves the drawback of ammonium losses due to diffusion between compartments in the MFC, as previously reported in a system operating with external nitrification stage. This work represents the first successful attempt to combine SND and organics oxidation while producing electricity in an MFC.     

PAEs and BPA removal in landfill leachate with Fenton process and its relationship with leachate DOM composition

An increasing attention has been paid to the trace endocrine disrupting compounds (EDCs) in landfill leachate. In this paper, the removal of EDCs including phthalic acid esters (PAEs) and bisphenol A (BPA) from the fresh and mature landfill leachate by Fenton treatment was studied. More than 40% of PAEs and about 62% of BPA were removed from the raw mature leachate while only 20% of PAEs and 37% of BPA in the raw fresh leachate were reduced, respectively. After the fresh and mature leachates were spiked with PAEs to 1.5 mg L^− 1 and BPA to 0.08 mg L^− 1, the removal efficiencies of BPA and PAEs increased to more than 88%. The results indicated that the removing efficiencies of the EDCs in the leachate had a relationship with their concentrations, and that the trace levels of EDCs in leachate challenged the treatment capacity of the Fenton process. Most of the EDCs in the enriched leachate were removed by oxidation, which had no clear correlation with the hydrophobicity of the EDCs. The flocculation played an important role in the removal of di-(2-ethylhexyl) phthalate that could not be completely oxidized in the Fenton process, in that the EDCs with high n-octanol/water partition coefficient inclined to precipitate after the Fenton process. The dissolved organic matter (DOM) in the fresh leachate inhibited the EDCs removal more than the DOM in the mature leachate did. Both the composition of the leachate DOM and the characteristics of the EDCs determined the removing efficiencies of the EDCs in the Fenton process.     

Removal of refractory organics and nitrogen from landfill leachate by the microorganism-attached activated carbon fluidized bed process

The microorganism-attached activated carbon fluidized bed (MAACFB) process was applied to treat a real landfill leachate containing refractory organics and a high concentration of ammonium nitrogen. The MAACFB process consisted of two fluidized bed reactors in series: anaerobic and aerobic.The MAACFB process was found to be effective in treating the landfill leachate. The MAACFB process removed about 60 and 70% of refractory organics and nitrogen, respectively, from the landfill leachate simultaneously and steadily over more than 700 days of the operation period. A mass balance of the organics around the MAACFB process revealed that most of the removed organics may be biodegraded.     

Effect of heat recovery from raw wastewater on nitrification and nitrogen removal in activated sludge plants

By recovery of heat from the raw wastewater in the sewer system, the influent temperature of a wastewater treatment plant (WWTP) is reduced. This can have a negative effect on nitrification in the WWTP, since this process strongly depends on temperature. The analysis of the temperature regime in the WWTP of Zurich, Switzerland, revealed that in the cold season, the effluent temperature is about 0.7 degrees C higher than the influent temperature and that nitrification is not affected by a decrease of the influent wastewater temperature lasting for a couple of hours only, but is significantly affected by a longer lasting temperature decrease. Three diagrams were developed with a steady-state model, from which the consequences of a permanent temperature decrease on the nitrification safety factor, aerobic sludge retention time and total nitrogen removal can be evaluated. Using simulations with a dynamic model, calibrated for the Zurich WWTP, a quantitative relationship between the wastewater temperature and the ammonium effluent concentration was established. This relationship can, in combination with measured effluent concentrations of an existing WWTP, be used to predict the increase of the ammonium effluent concentration in this plant resulting from a permanent decrease of the wastewater influent temperature.     

城市污水脱氮除磷技术与展望

介绍了国内外城市污水的脱氮除磷现状,探讨了城市污水脱氮除磷技术的发展趋势,同时提出较为高效、经济且资源化的城市污水脱氮除磷工艺,对城市污水脱氮除磷技术的发展进行了展望。     

The impact of temperature and gas-phase oxygen on kinetics of in situ ammonia removal in bioreactor landfill leachate

Microcosm experiments aimed at defining a rate equation that describes how different environmental conditions (i.e., gas-phase oxygen concentrations, temperature and ammonia concentration) may impact in situ ammonia removal were conducted. Results indicate that ammonia removal can readily occur at various gas-phase oxygen levels (between 0.7% and 100%) and over a range of temperatures (22, 35 and 45 degrees C). Slowest rates occurred with lower gas-phase oxygen concentrations. All rate data, except at 45 degrees C and 5% oxygen, fit well (r2=0.75) to a multiplicative Monod equation with terms describing the impact of oxygen, pH, temperature and ammonia concentration. All ammonia half-saturation values are relatively high when compared to those generally found in wastewater treatment, suggesting that the rate may be affected by the mass transfer of oxygen and/or ammonia. Additionally, as the temperature increases, the ammonia half-saturation value also increases. The multiplicative Monod model developed can be used to aid in designing and operating field-scale studies.     

Experimental results and mathematical modelling of an autotrophic and heterotrophic biofilm in a sand filter treating landfill leachate and municipal wastewater

A better understanding of wastewater treatment with soil filters is important to optimise plant operation and reduce the risk of clogging. The article presents results of a treatment concept which uses a combination of SBR and vertical-flow sand filter technology. The SBR was mainly used for denitrification and sedimentation of substances in particulate form. Efficient nitrification was achieved by the planted sand filter. Degradation rates of 10gNH(4)-N/(m(2)xd) were measured for periods with peak loadings. The two-dimensional dynamic model reproduces the biofilm growth and decay of heterotrophic and autotrophic biomass. It is capable of describing the clogging of the sand filter by combining a biochemical and a geometric model. After calibration, the model was used for the calculation of maximum nitrogen degradation performances. Maximum degradation rates of 12gNH(4)-N/(m(2)xd) can be achieved if the COD/TKN ratio is reduced before to a level lower than that of municipal wastewater. The COD was further degraded in the filter than we expected comparing it with activated sludge plants. Within the soil filter a biofilm thickness of up to 110mum is simulated depending on the embankment of gravel and grains of sand. Sensitivity analysis of model parameters showed the high impact of the maximum autotrophic growth rate, the autotrophic yield, the diffusion coefficient for oxygen and the number of contact points of the single grains of sand.     

Characteristics and fate of organic nitrogen in municipal biological nutrient removal wastewater treatment plants

The aim of this study was to investigate the occurrence and fate of colloidal and dissolved organic nitrogen (CON and DON) across biological nutrient removal (BNR) activated sludge bioreactors. Primary and secondary effluent total nitrogen (TN) measurements and component fractionation, CON and DON concentration profiles across BNR bioreactors, and laboratory batch experiments with the process mixed liquor were carried out at several full-scale BNR plants in northern Poland. The organic nitrogen (ON) components were divided into high CON, low CON, and DON based on sequential filtration through 1.2, 0.45 and 0.1 μm pore-size filters. The average influent DON_0.1μm (<0.1 μm) concentrations ranged from 1.1 g N/m³ to 3.9 g N/m³ and accounted for only 4-13% of total organic nitrogen. In the effluents, however, this contribution increased to 12-45% (the DON_0.1μm concentrations varied in a narrow range of 0.5-1.3 g N/m³). Conversions of ON inside the bioreactors were investigated in more detail in two largest plants, i.e. Gdansk (565,000 PE) and Gdynia (516,000 PE). Inside the two studied bioreactors, the largest reductions of the colloidal fraction were found to occur in the anaerobic and anoxic compartments, whereas an increase of DON_0.1μm concentrations was observed under aerobic conditions in the last compartment. Batch experiments with the process mixed liquor confirmed that DON_0.1μm was explicitly produced in the aerobic phase and significant amounts of ON were converted in the anoxic phase of the experiments.     

Non-steady state simulation of BOM removal in drinking water biofilters: applications and full-scale validation

A biofilter model called "BIOFILT" was used to simulate the removal of biodegradable organic matter (BOM) in full-scale biofilters subjected to a wide range of operating conditions. Parameters that were varied included BOM composition, water temperature (3.0-22.5 degrees C), and biomass removal during backwashing (0-100%). Results from biofilter simulations suggest a strong dependence of BOM removal on BOM composition. BOM with a greater diffusivity or with faster degradation kinetics was removed to a greater extent and also contributed to shorter biofilter start-up times. In addition, in simulations involving mixtures of BOM (i.e. readily degradable and slowly degradable components), the presence of readily degradable substrate significantly enhanced the removal of slowly degradable material primarily due to the ability to maintain greater biomass levels in the biofilters. Declines in pseudo-steady state BOM removal were observed as temperature was decreased from 22.5 to 3 degrees C and the magnitude of the change was significantly affected by BOM composition. However, significant removals of BOM are possible at low temperatures (3-6 degrees C). Concerning the impact of backwashing on biofilter performance, BOM removal was not affected by backwash resulting in biomass removals of 60% or less. This suggests that periodic backwashing should not significantly impact biofilter performance as observed biomass removals from full-scale biofilters were negligible. In general, the simulation results were in good qualitative and quantitative agreement with experimental results obtained from full-scale biofilters.     

Phosphorus and nitrogen removal with minimal COD requirement by integration of denitrifying dephosphatation and nitrification in a two-sludge system

Denitrifying dephosphatation enables the removal of phosphorus and nitrogen with minimal use of COD, minimal oxygen consumption and minimal surplus sludge production. Moreover it would make aeration only necessary for nitrification. Therefore we have studied an anaerobic-anoxic (A₂) sequencing batch reactor (SBR) coupled to a nitrification SBR. Denitrifying phosphorus removing bacteria (DPB) and nitrifiers were completely separated in two sludges in these two SBRs. The nitrified supernatant was recirculated from the nitrification SBR to the A₂ SBR where nitrate was utilized by DPB as an electron acceptor for phosphorus removal. The technical feasibility for simultaneous phosphorus and nitrogen removal in the proposed two-sludge system was evaluated. The benefits of two-sludge systems over single-sludge systems were also discussed. It could be concluded that the separation of the nitrification step leads to an optimal process design for the application of denitrifying dephosphatation. The two-sludge system showed stable phosphorus and nitrogen removal, and enabled the removal of 15 mg-P/1 and 105 mg N/1 at the expense of only 400 mg-COD/1 acetic acid. Stoichiometric calculations showed that, in the two-sludge system the required COD can be up to 50% less than for conventional aerobic phosphorus and nitrogen removal systems. Moreover oxygen requirements and sludge production can be decreased in significant amounts of about 30 and 50%, respectively.     

Advances in enhanced biological phosphorus removal: from micro to macro scale

The enhanced biological phosphorus removal (EBPR) process has been implemented in many wastewater treatment plants worldwide. While the EBPR process is indeed capable of efficient phosphorus (P) removal performance, disturbances and prolonged periods of insufficient P removal have been observed at full-scale plants on numerous occasions under conditions that are seemingly favourable for EBPR. Recent studies in this field have utilised a wide range of approaches to address this problem, from studying the microorganisms that are primarily responsible for or detrimental to this process, to determining their biochemical pathways and developing mathematical models that facilitate better prediction of process performance. The overall goal of each of these studies is to obtain a more detailed insight into how the EBPR process works, where the best way of achieving this objective is through linking together the information obtained using these different approaches. This review paper critically assesses the recent advances that have been achieved in this field, particularly relating to the areas of EBPR microbiology, biochemistry, process operation and process modelling. Potential areas for future research are also proposed. Although previous research in this field has undoubtedly improved our level of understanding, it is clear that much remains to be learned about the process, as many unanswered questions still remain. One of the challenges appears to be the integration of the existing and growing scientific knowledge base with the observations and applications in practice, which this paper hopes to partially achieve.     

Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofilms of the Douro River estuary, Portugal

The regulatory effects of salinity and inorganic nitrogen compounds on nitrification and denitrification were studied in intertidal sandy sediments and rocky biofilms in the Douro River estuary, Portugal, over a 12-month period. Nitrification and denitrification rates were measured in slurries of field samples and enrichment experiments using the difluoromethane and the acetylene inhibition techniques, respectively. Salinity did not regulate denitrification in either environment, suggesting that halotolerant bacteria dominated the denitrifier communities. However, nitrification rates were stimulated when salinity increased from 0 to 15 practical salinity units. NO3- addition experiments revealed that NO3- availability stimulates denitrification rates in sandy sediments, but not in rocky biofilms; however, in rocky biofilms a positive and linear relationship was observed between denitrification rates and water column NO3- concentrations (r=0.92) during the monthly surveys. The N2O:N2 ratios increased rapidly when NO3- increased from 63 to 363 microM; however, results from monthly surveys showed that environmental parameters other than NO3- availability may be important in controlling the variation in N2O production via denitrification. Ammonium additions to sandy sediments stimulated nitrification rates by 35% for the 20 microM NH4+ addition, but NH4+ appeared to inhibit nitrification at high concentration addition (200 microM NH4+). In contrast, rocky biofilm nitrification was stimulated by 65% when 200 microM NH4+ was added.     

Biological nitrogen and phosphorus removal and changes in microbial community structure in a membrane bioreactor: effect of different carbon sources

Bacterial community structures in four sequencing anoxic/anaerobic-aerobic membrane bioreactors (SAMs) that were fed with synthetic medium composed of different organic compounds in substrate as carbon source; acetate-dominant (acetate/propionate = 4/1), propionate-dominant (acetate/propionate = 1/4), glucose-dominant (glucose/acetate = 4/1) and methanol-dominant (methanol/acetate/propionate = 6/3/1) were analyzed by respiratory quinone profile and fluorescent in situ hybridization (FISH) techniques. The SAMs were operated at controlled pH range 7-8.5 and at constant temperature 25 degrees C. Total nitrogen (TN), total phosphorus (TP) and COD removal performances were also evaluated and compared. In addition, trans-membrane pressure was monitored to observe the impact of substrate composition on membrane fouling. The dominance of the mole fraction of ubiquinone (UQ-8) in the SAMs indicated dominance of the beta-subclass of Proteobacteria; however, its population comparatively decreased when the substrate was glucose dominant or methanol dominant. A relatively higher and stable enhanced biological phosphorus removal performance was observed when methanol-dominant substrate was used concurrently with an increase in the gamma-subclass of Proteobacteria. The population of the alpha-subclass of Proteobacteria slightly increased along with a decrease in phosphate removal activity when the substrate was glucose-dominant. Results from FISH analysis also supported the findings of the quinone profile. The trans-membrane pressure variation in the SAMs indicated that fouling was relatively rapid when propionate-dominant or methanol-dominant substrate was used and most stable when glucose-dominant substrate was used. A combination of methanol and acetate would be a better choice as an external carbon source when nutrients removals, as well as fouling, are considered in the membrane bioreactor- (MBR-) coupled biological nutrients removing (BNR) process.     

Evaluation on speciation and removal efficiencies of mercury from municipal solid waste incinerators in Taiwan

Two large-scale municipal solid waste incinerators (MWIs) located in Taiwan were selected for conducting flue gas sampling to determine the chemical speciation of mercury by both USEPA Method 29 and Ontario Hydro Method (OHM). In addition, the emission characteristics and removal efficiencies of mercury were evaluated via isokinetic sampling of flue gas upstream and downstream of APCDs. Results indicated that the average removal efficiencies of Hg for MWI-A and MWI-B were 29.56 and 44.70%, respectively. In terms of mercury speciation by USEPA Method 29 and Ontario Hydro Method (OHM), oxidized mercury (Hg2+), in the flue gas was predominant at the inlet of APCD for both incinerators. Less than 30% of mercury in the flue gas existed in the elemental form (Hg0) at APCD inlet. Mercury emitted from the stack also predominated as a form of Hg2+ in MWI-A. Approximately 90% of total mercury emission from the stack existed in the form of Hg2+ for MWI-A. Due to the higher removal efficiency of soluble mercury (Hg2+) in wet scrubber, less total Hg was actually emitted from MWI-B than MWI-A. Regarding the removal efficiency of Hg0 in the flue gas, the APCDs of MWI-A (DSI + FF) had a higher removal efficiency than that of MWI-B (ESP + WS) possibly due to the reduction of Hg2+ which occurred in the wet scrubber.     

Biological manganese removal from acid mine drainage in constructed wetlands and prototype bioreactors

Mine drainage waters vary considerably in the range and concentration of heavy metals they contain. Besides iron, manganese is frequently present at elevated concentrations in waters draining both coal and metal mines. Passive treatment systems (aerobic wetlands and compost bioreactors) are designed to remove iron by biologically induced oxidation/precipitation. Manganese, however, is problematic as it does not readily form sulfidic minerals and requires elevated pH (>8) for abiotic oxidation of Mn (II) to insoluble Mn (IV). As a result, manganese removal in passive remediation systems is often less effective than removal of iron. This was found to be the case at the pilot passive treatment plant (PPTP) constructed to treat water draining the former Wheal Jane tin mine in Cornwall, UK, where effective removal of manganese occurred only in one of the three rock filter components of the composite systems over a 1-year period of monitoring. Water in the two rock filter systems where manganese removal was relatively poor was generally 相似文献