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.     

Comparison of cellulose solubilisation rates in rumen and landfill leachate inoculated reactors

The aim of this study was to conduct a number of controlled digestions to obtain easily comparable cellulose solubilisation rates and to compare these rates to those found in the literature to see which operational differences were significant in affecting cellulose degradation during anaerobic digestion. The results suggested that differences in volumetric cellulose solubilisation rates were not indicative of the true performance of cellulose digestion systems. When cellulose solubilisation rates were normalised by the mass of cellulose in the reactor at each time step, the comparison of the rates became more meaningful. Cellulose solubilisation was surface area limited. Therefore, changes in the loading rate of cellulose to the reactor altered the volumetric solubilisation rate without changing the mass normalised rate. Comparison of mass normalised solubilisation rates from this study and the literature demonstrated that differences in reactor configuration and operational conditions did not significantly impact on the solubilisation rate whereas the difference in composition of the microbial communities showed a marked effect. This work highlights the importance of using appropriately normalised data when making comparisons between systems with differing operational conditions.     

Nitrogen mass balance and microbial analysis of constructed wetlands treating municipal landfill leachate

Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen and bacterial contents. Under a tropical condition (temperature of about 30 degrees C), the constructed wetland units operating at the hydraulic retention time of 8d yielded the best treatment efficiencies with BOD(5), TN and fecal coliforms removal of 91%, 96% and more than 99%, respectively. Cadmium removal in the SFCW bed was 99.7%. Mass balance analysis, based on total nitrogen contents of the plant biomass and dissolved oxygen and oxidation-reduction potential values, suggested that 88% of the input total nitrogen were uptaken by the plant biomass. Fluorescence in situ hybridization results revealed the predominance of bacteria, including heterotrophic and autotrophic, responsible for BOD(5) removal. Nitrifying bacteria was not present in the constructed wetland beds.     

Temperature-induced changes in treatment efficiency and microbial structure of aerobic granules treating landfill leachate

This paper investigates the effect of temperature on nitrogen and carbon removal by aerobic granules from landfill leachate with a high ammonium concentration and low concentration of biodegradable organics. The study was conducted in three stages; firstly the operating temperature of the batch reactor with aerobic granules was maintained at 29 °C, then at 25 °C, and finally at 20 °C. It was found that a gradual decrease in operational temperature allowed the nitrogen-converting community in the granules to acclimate, ensuring efficient nitrification even at ambient temperature (20 °C). Ammonium was fully removed from leachate regardless of the temperature, but higher operational temperatures resulted in higher ammonium removal rates [up to 44.2 mg/(L h) at 29 °C]. Lowering the operational temperature from 29 to 20 °C decreased nitrite accumulation in the GSBR cycle. The highest efficiency of total nitrogen removal was achieved at 25 °C (36.8 ± 10.9 %). The COD removal efficiency did not exceed 50 %. Granules constituted 77, 80 and 83 % of the biomass at 29, 25 and 20 °C, respectively. Ammonium was oxidized by both aerobic and anaerobic ammonium-oxidizing bacteria. Accumulibacter sp., Thauera sp., cultured Tetrasphaera PAO and Azoarcus–Thauera cluster occurred in granules independent of the temperature. Lower temperatures favored the occurrence of denitrifiers of Zooglea lineage (not Z. resiniphila), bacteria related to Comamonadaceae, Curvibacter sp., Azoarcus cluster, Rhodobacter sp., Roseobacter sp. and Acidovorax spp. At lower temperatures, the increased abundance of denitrifiers compensated for the lowered enzymatic activity of the biomass and ensured that nitrogen removal at 20 °C was similar to that at 25 °C and significantly higher than removal at 29 °C.     

Influence of phenol additions on the efficiency of an anaerobic hybrid digester treating landfill leachate

Summary A hybrid digester with leachate as substrate was used to determine the influence of the addition of phenol. The phenol was increased stepwise from 2 to 25 mg/l and then to 30, 40, 50 and 60 mg/l leachate. Within 24 h the addition caused a significant decrease in the COD removal and biogas production while the methane content increased. Phenol loading was characterised by the accumulation of volatile fatty acids. With the continuous addition of phenol, a recovery time of 28 d was required for the performance to reach the control values. As the concentration was increased, the recovery time shortened to 8 d at 20 mg/l. At higher concentrations (>50 mg/l) the recovery time was found to increase to >60 d.     

Screening and degradation performances of dominant strains in high-salinity landfill leachate

In order to enhance the removal efficiency of chemical oxygen demand (COD) in the high-salinity landfill leachate, the dominant strains were isolated from high-salinity landfill leachate. The dominant strains and bacteria consortium were screened for COD treatment potential using an aerobic COD concentration decrease test. Ten strains, TJ01–TJ10, were isolated, of which six strains TJ02, TJ03, TJ05, TJ06, TJ07, and TJ09 were found to have higher COD removal when the single bacteria were added, all more than 20%. The most effective combination was TJ06 + TJ09; the COD removal efficiency reached 45.57%. 16S rDNA gene sequence analysis revealed that TJ06 and TJ09 belonged to the genus Bacillus. The effects of the dominant bacteria consortium on the high-salinity landfill leachate varied with pH value and the volume fraction of leachate. The COD removal efficiencies maintained higher when the pH value was 6–8 and the volume fractions of leachate were less than 80%. The result also suggested that there is little effect on the growth of TJ06 and TJ09 when the range of Cl⁻ concentration is 0–30,000 mg/L.     

Eukaryotic diversity in an anaerobic aquifer polluted with landfill leachate

Eukaryotes may influence pollutant degradation processes in groundwater ecosystems by activities such as predation on bacteria and recycling of nutrients. Culture-independent community profiling and phylogenetic analysis of 18S rRNA gene fragments, as well as culturing, were employed to obtain insight into the sediment-associated eukaryotic community composition in an anaerobic sandy aquifer polluted with landfill leachate (Banisveld, The Netherlands). The microeukaryotic community at a depth of 1 to 5 m below the surface along a transect downgradient (21 to 68 m) from the landfill and at a clean reference location was diverse. Fungal sequences dominated most clone libraries. The fungal diversity was high, and most sequences were sequences of yeasts of the Basidiomycota. Sequences of green algae (Chlorophyta) were detected in parts of the aquifer close (<30 m) to the landfill. The bacterium-predating nanoflagellate Heteromita globosa (Cercozoa) was retrieved in enrichments, and its sequences dominated the clone library derived from the polluted aquifer at a depth of 5 m at a location 21 m downgradient from the landfill. The number of culturable eukaryotes ranged from 10(2) to 10(3) cells/g sediment. Culture-independent quantification revealed slightly higher numbers. Groundwater mesofauna was not detected. We concluded that the food chain in this polluted aquifer is short and consists of prokaryotes and fungi as decomposers of organic matter and protists as primary consumers of the prokaryotes.     

Electricity from landfill leachate using microbial fuel cells: Comparison with a biological aerated filter

Four experimental columns were employed in this study to investigate their performance under wastewater treatment conditions. One column was set-up as a biological aerated filter and the remaining three were set-up as microbial fuel cells (MFCs), two of which were connected to an external load whereas the third was left open circuit. The performance of the columns under several flow rates and leachate strengths was studied in terms of BOD₅ removal efficiencies and electricity generation, when a fixed resistive load was connected. Results obtained demonstrated that it is possible to generate electricity and simultaneously treat landfill leachate in MFC columns. Energy generation in MFC columns improved with increasing flow rates from 24 to 192 mL/h, while BOD₅ removal efficiency levels reached a maximum at 48 mL/h and dropped to relatively low values at higher flow rates. The maximum removal efficiencies were obtained at a loading rate of 0.81 kg BOD₅/m³ d for columns C1, C2 and C4 and 1.81 kg BOD₅/m³ d for column C3. Electrical output levels and BOD₅ concentrations at the MFC columns showed a linear relationship, which allows the system to be used as a BOD₅ sensor. Part of the BOD removal was not associated with power generation and was attributed to the presence of alternative end terminal electron acceptors and volatilisation. The MFC columns could reach the same or even higher removal efficiencies than those from the biological aerated filter with the advantage of producing energy and saving cost of aeration. To the best of the authors’ knowledge, this is the first study that compares the MFC technology with other conventional treatment systems for removing pollutants from wastewater.     

Membrane fouling and micro-pollutant removal of membrane bioreactor treating landfill leachate

Reviews in Environmental Science and Bio/Technology - The characteristics of landfill leachate from solid waste disposal vary, depending on waste composition, waste age, and landfilling technique....     

渗滤液覆盖层灌溉处理对夹竹桃的生理生态效应

以夹竹桃（Nerium indicum Mill．）作为填埋场覆盖层封场植被材料,历时1a现场研究了有无渗滤液灌溉下夹竹桃生长及其生理生化反应。结果表明,10mm／d渗滤液灌溉下夹竹桃持续生长,生长的快慢呈季节性,且生长较对照组略快;渗滤液灌溉组和对照组夹竹桃丙二醛（MDA）、脯氨酸（Pro）含量的动态变化同气温变化规律相似,超氧化物岐化酶（SOD）、过氧化物酶（POD）活性和抗坏皿酸（AsA）、还原型谷胱甘肽（GSH）含量基本呈季节性波动。盛夏（6—8月份）和秋冬（10-4月份）SOD、POD活性明显提高,AsA、GSH积累显著;1a中渗滤液灌溉组各生理生化指标均较对照组变化辐度大,但两组间差异基本不显著;表明有无渗滤液灌溉下,夹竹桃生理生态反应主要受气候的季节性变化调控,渗滤液灌溉处理不会显著加大对夹竹桃胁迫。     

Influence of environmental conditions on methanogenic compositions in anaerobic biogas reactors

The influence of environmental parameters on the diversity of methanogenic communities in 15 full-scale biogas plants operating under different conditions with either manure or sludge as feedstock was studied. Fluorescence in situ hybridization was used to identify dominant methanogenic members of the Archaea in the reactor samples; enriched and pure cultures were used to support the in situ identification. Dominance could be identified by a positive response by more than 90% of the total members of the Archaea to a specific group- or order-level probe. There was a clear dichotomy between the manure digesters and the sludge digesters. The manure digesters contained high levels of ammonia and of volatile fatty acids (VFA) and were dominated by members of the Methanosarcinaceae, while the sludge digesters contained low levels of ammonia and of VFA and were dominated by members of the Methanosaetaceae. The methanogenic diversity was greater in reactors operating under mesophilic temperatures. The impact of the original inoculum used for the reactor start-up was also investigated by assessment of the present population in the reactor. The inoculum population appeared to have no influence on the eventual population.     

In situ microbial treatment of landfill leachate using aerated lagoons

The aim of this study was to assess the efficiency of leachate treatment by microbial oxidation in four connected on-site aerated lagoons at a landfill site. The landfill site was found to be in an ageing methanogenic state, producing leachate with relatively low COD (mean value 1740 mg l⁻¹) and relatively high ammonium concentrations (mean value 1241 mg l⁻¹). Removal of COD averaged 75%, with retention times varying from 11 to 254 days. Overall 80% of the N load was removed within the plant, some by volatilisation of ammonium. Microbial community profiling of the water from each lagoon showed a divergent community profile, presumably a reflection of the nutrient status in each lagoon. In municipal solid waste landfills under similar conditions, leachate treatment through a facultative aerobic system in which sequential aerobic and anaerobic microbial oxidations occurred can readily be achieved using a simple two-lagoon system, suggesting this technology can be economic to install and simple to run.     

The performance of peat-filled subsurface flow filters treating landfill leachate and municipal wastewater

The main objective of this study was to determine the treatment capacity of well-mineralized peat in vertical and horizontal flow filters designed to reduce phosphorus, nitrogen and organic matter in municipal wastewater from the town of Tapa and landfill leachate in Väätsa, Estonia. Two identically designed onsite experiments were conducted using the following filter systems: (a) a vertical flow (VF) peat filter, (b) a vertical flow peat/ash sediment filter (both materials in equal volumes) followed by a horizontal flow (HF) peat filter. Sphagnum peat and hydrated oil-shale ash (ash sediment) was used. In our experiments, one treated municipal wastewater over 6 months and another treated landfill leachate over 12 months. In both cases, effluent from a conventional treatment (aerated activated sludge treatment) plant was used. The median value of total phosphorus (TP) concentration in Väätsa landfill leachate was 3.4 mg P L^?1 and in municipal wastewater from Tapa 4.9 mg P L^?1. The reduction of TP in VF peat filters during the first 6 months was 58% and 63%, and in peat/ash sediment filters 94% and 67% for the Tapa experiment and the Väätsa experiment, respectively. Both experiments demonstrated that the P-removal efficiency in VF peat filters begins to decrease after 6 months of operation. The purification efficiency in HF filters fluctuated, and no significant removal of TP was found. In the removal of organic matter (BOD, COD values) and nitrogen, the best results were obtained in VF peat filters.     

Modeling the final phase of landfill gas generation from long-term observations

For waste management, methane emissions from landfills and their effect on climate change are of serious concern. Current models for biogas generation that focus on the economic use of the landfill gas are usually based on first order chemical reactions (exponential decay), underestimating the long-term emissions of landfills. The presented study concentrated on the curve fitting and the quantification of the gas generation during the final degradation phase under optimal anaerobic conditions. For this purpose the long-term gas generation (240–1,830 days) of different mechanically biologically treated (MBT) waste materials was measured. In this study the late gas generation was modeled by a log–normal distribution curve to gather the maximum gas generation potential. According to the log–normal model the observed gas sum curve leads to higher values than commonly used exponential decay models. The prediction of the final phase of landfill gas generation by a fitting model provides a basis for CO₂ balances in waste management and some information to which extent landfills serve as carbon sink.     

Treatment of leachate from a solid waste landfill site using a two-stage anaerobic filter

Raw leachate was treated using a two-stage upflow anaerobic filter process. Leachate from a solid waste landfill site, which received both municipal and industrial wastes, contained high organic matter (17-21 g/L COD, 13-14 g/L BOD, and 3.5-4.6 g/L volatile acids), and low metal (Zn and Fe) concentrations. Depending on sampling time, leachate composition and characteristics varied considerably. At an organic loading up to 4 g COD/day(2) media area, the BOD and COD removal percentages were 98 and 91%, respectively. The biofilters were also effective for metal removal. However, the filter effluent contained a high concentration of ammonia. System overloading was characterized by the accumulation of large quantities of volatile acids and by a now ratio of alkalinity/volatile acids, resulting in low COD removal and reduced gas production. Once the first filter was upset, the second stage could only partially respond to the volatile acids accumulated in the effluent of first filter.     

Comparison of horizontal and vertical constructed wetland systems for landfill leachate treatment

The main purpose of this study was to treat organic pollution, ammonia and heavy metals present in landfill leachate by the use of constructed wetland systems and to quantify the effect of feeding mode. The effect of different bedding material (gravel and zeolite surface) was also investigated. A pilot-scale study was conducted on subsurface flow constructed wetland systems operated in vertical and horizontal mode. Two vertical systems differed from each other with their bedding material. The systems were planted with cattail (Typha latifolia) and operated identically at a flow rate of 10 l/day and hydraulic retention times of 11.8 and 12.5 day in vertical 1, vertical 2 and horizontal systems, respectively. Concentration based average removal efficiencies for VF1, VF2 and HF were NH₄–N, 62.3%, 48.9% and 38.3%; COD, 27.3%, 30.6% and 35.7%; PO₄–P, 52.6%, 51.9% and 46.7%; Fe(III), 21%, 40% and 17%, respectively. Better NH₄–N removal performance was observed in the vertical system with zeolite layer than that of the vertical 2 and horizontal system. In contrast, horizontal system was more effective in COD removal.     

Granulation in anaerobic sludge bed reactors treating food industry wastes

Three parallel laboratory reactors, R1, R2 and R3, received food industry wastewater: R1 unadulterated; R2 supplemented with calcium and phosphate; R3 supplemented with ferric chloride and traces of nickel and cobalt. Reactors were packed with active granular sludge from a large scale pilot reactor treating the same wastewater. Addition of calcium and phosphate was found to be detrimental to the granule formation at naturally established reactor pH = 6·9–7·4 in R2 while iron promoted granulation in R3. Conditions of upflow velocities of 1·5–6 m h⁻¹, rapid increase of loads up to 15 kg COD m⁻³ day⁻¹ and ratios of recycle to raw waste feed of 20:1–80:1 were imposed on all reactors. The granules in R1 and R2 disintegrated, from 70–100 g liter⁻¹ VSS to a flocculant sludge at 1·5–3 g liter⁻¹. In spite of such severe washout, reactors R1 and R2 were able to maintain a steady COD removal of over 90% at a load of 10kg m⁻³ day⁻¹. R3 retained a VSS concentration around 100 g liter⁻¹ and maintained COD removal at over 95%. R3 exhibited a more stable performance and was less vulnerable to the shock treatment to which all reactors were subjected.     

Biomass retention and performance of anaerobic fixed-film reactors treating acetic acid wastewater

An acetic-acid-based synthetic wastewater of different organic concentrations was successfully treated at 35 degrees C in anaerobic downflow fixed-film reactors operated at high organic loading rates and short hydraulic retention times (HRTs). Substrate removal and methane production rates close to theoretical values of complete volumetric chemical oxygen demand (COD) removal and maximum methane conversion were obtained. A high concentration of biofilm biomass was retained in the reactor. Steady-state biofilm concentration increased with increased organic loading rate and decreased HRTs, reaching a maximum of 8.3 kg VFS/m(3) at a loading rate of 17 kg COD/m(3) day. Biofilm substrate utilization rates of up to 1.6 kg COD/kg VFS day were achieved. Soluble COD utilization rates at various COD concentrations can be described by half-order reaction kinetics.