Treating landfill leachate using passive aeration trickling filters; effects of leachate characteristics and temperature on rates and process dynamics

Biological ammoniacal-nitrogen (NH₄⁺-N) and organic carbon (TOC) treatment was investigated in replicated mesoscale attached microbial film trickling filters, treating strong and weak strength landfill leachates in batch mode at temperatures of 3, 10, 15 and 30 °C. Comparing leachates, rates of NH₄⁺-N reduction (0.126-0.159 g m^− 2 d^− 1) were predominantly unaffected by leachate characteristics; there were significant differences in TOC rates (0.072-0.194 g m^− 2 d^− 1) but no trend relating to leachate strength. Rates of total oxidised nitrogen (TON) accumulation (0.012-0.144 g m^− 2 d^− 1) were slower for strong leachates. Comparing temperatures, treatment rates varied between 0.029-0.319 g NH₄⁺-N m^− 2 d^− 1 and 0.033-0.251 g C m^− 2 d^− 1 generally increasing with rising temperatures; rates at 3 °C were 9 and 13% of those at 30 °C for NH₄⁺-N and TOC respectively. For the weak leachates (NH₄⁺-N < 140 mg l^− 1) complete oxidation of NH₄⁺-N was achieved. For the strong leachates (NH₄⁺-N 883-1150 mg l^− 1) a biphasic treatment response resulted in NH₄⁺-N removal efficiencies of between 68 and 88% and for one leachate no direct transformation of NH₄⁺-N to TON in bulk leachate. The temporal decoupling of NH₄⁺-N oxidation and TON accumulation in this leachate could not be fully explained by denitrification, volatilisation or anammox, suggesting temporary storage of N within the treatment system. This study demonstrates that passive aeration trickling filters can treat well-buffered high NH₄⁺-N strength landfill leachates under a range of temperatures and that leachate strength has no effect on initial NH₄⁺-N treatment rates. Whether this approach is a practicable option depends on a range of site specific factors.     

Adsorption of ammonium to activated sludge

The adsorption of ammonium (NH₄⁺) to the sludge floc matrix has been investigated in two activated sludge treatment plants. When activated sludge was extracted in 1 N KCl the extractable amounts were between 0.5 and 1.3 mg NH₄⁺-N/l higher than the dissolved ammonium concentration at dissolved ammonium concentrations between 1 and 6 mg NH₄⁺-N/l. The difference between the extractable and the dissolved ammonium, the exchangeable ammonium, thus represented 18–30% of the dissolved ammonium concentration. A part of this, around 0.5–0.6 mg NH₄⁺-N/l was not exchangeable under the actual operational conditions in the treatment plants due to a slow desorption kinetics, but seemed to be accessible for nitrification under prolonged aeration. The highest observed amount of adsorbed ammonium corresponded to 0.4–0.5 mg NH₄⁺-N/gSS. Adsorption of ammonium should be investigated in more details and included in models for nitrogen mass balances for activated sludge.     

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH₄⁺-N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.     

Hydraulic and physicochemical properties of dense thin bentonite layers permeated with variably mixed alkaline solutions of KOH and CaCl2 at various temperatures (25–75 °C) for 3 years

Hydraulic conductivity tests were performed using mixed alkaline solutions of KOH and CaCl₂ (pH ～12) on thin Na-bentonite layers under various temperature conditions (25–75 °C) for 3 years. For dense thin Na-bentonite (dry density of 1.12 Mg/m³) in a mixed alkaline solution of 0.03 M KOH and 0.03 M CaCl₂, the hydraulic conductivities at 50 °C and 75 °C were approximately 10 times higher than that at 25 °C. The bentonite samples permeated with the mixed solution at 50 °C and 75 °C achieved almost complete cation exchange of Na ions by Ca and K ions. However, only slight cation exchange occurred in the bentonite specimens permeated at 25 °C, regardless of the type of permeant. The free swell index of the reacted bentonite permeated with a mixed solution of 0.03 M KOH and 0.03 M CaCl₂ significantly decreased at 50 °C and 75 °C compared with that at 25 °C. X-ray diffraction analysis revealed that the decreases in the relative intensities of the peaks of accessory minerals, such as opal-cristobalite/tridymite, quartz, and feldspar, were enhanced at 50 °C and 75 °C.     

Coupled effects of saline solutions and temperature on the swelling deformation property of GMZ bentonite-sand mixtures

Based on the results of one-dimensional free swelling tests, the coupled effects of NaCl-Na₂SO₄ solutions and temperature on the swelling deformation property of compacted GMZ bentonite-sand mixtures were analyzed. The concentrations of the NaCl-Na₂SO₄ solutions were 0, 0.008, 0.04, 0.08 and 0.16 mol/L, the temperatures were 20 °C, 40 °C, 60 °C, 80 °C and 90 °C and the sand contents were 0, 30 and 50%. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were also performed to find the influences of the temperature, solution concentration and sand content on the mineral composition and microstructure. The results showed that the maximum swelling strain of the specimens increased with an elevated temperature, while it decreased with increases in the solution concentration and sand content. The swelling process was accelerated by the rising temperature. The XRD tests indicated that the combined effect of a high temperature and a high solution concentration may have caused more Na⁺ from the saline solutions to enter the interlayer, partly displacing the divalent cations. The MIP tests demonstrated that adding sand to the bentonite could reduce the amount of inter-granular pores and increase the intra-aggregate pores. These findings are advantageous to the transfer of heat and pour fluid in the specimens; and thus, the swelling deformation capacity of the bentonite-sand mixtures was higher than that of pure bentonite under the same conditions.     

Performance of a CO2 sorbent for indoor air cleaning applications: Effects of environmental conditions,sorbent aging,and adsorption of co-occurring formaldehyde

Indoor air cleaning systems that incorporate CO₂ sorbent materials enable HVAC load shifting and efficiency improvements. This study developed a bench-scale experimental system to evaluate the performance of a sorbent under controlled operation conditions. A thermostatic holder containing 3.15 g sorbent was connected to a manifold that delivered CO₂-enriched air at a known temperature and relative humidity (RH). The air stream was also enriched with 0.8-2.1 ppm formaldehyde. The CO₂ concentration was monitored in real-time upstream and downstream of the sorbent, and integrated formaldehyde samples were collected at different times using DNPH-coated silica cartridges. Sorbent regeneration was carried out by circulating clean air in countercurrent. Almost 200 loading/regeneration cycles were performed in the span of 17 months, from which 104 were carried out at reference test conditions defined by loading with air at 25°C, 38% RH, and 1000 ppm CO₂, and regenerating with air at 80°C, 3% RH and 400 ppm CO₂. The working capacity decreased slightly from 43-44 mg CO₂ per g sorbent to 39-40 mg per g over the 17 months. The capacity increased with lower loading temperature (in the range 15-35°C) and higher regeneration temperature, between 40 and 80°C. The CO₂ capacity was not sensitive to the moisture content in the range 6-9 g/m³, and decreased slightly when dry air was used. Loading isothermal breakthrough curves were fitted to three simple adsorption models, verifying that pseudo-first-order kinetics appropriately describes the adsorption process. The model predicted that equilibrium capacities decreased with increasing temperature from 15 to 35°C, while adsorption rate constants slightly increased. The formaldehyde adsorption efficiency was 80%-99% in different cycles, corresponding to an average capacity of 86 ± 36 µg/g. Formaldehyde was not quantitatively released during regeneration, but its accumulation on the sorbent did not affect CO₂ adsorption.     

Effect of ammonium on the hydraulic conductivity of geosynthetic clay liners

Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH₄OAc) solutions to investigate how NH₄⁺ accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the Na-B was 27.7 mL/2 g in 5 mM NH₄⁺ solution and decreased to 5.0 mL/2 g in 1000 mM NH₄⁺ solution, whereas the swell index of Na-B in DI water was 28.0 mL/2 g. Hydraulic conductivity of the Na-B GCL to 5, 50, and 100 mM NH₄⁺ was low, ranging from 1.6–5.9 × 10^?11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 × 10^?11 m/s). Hydraulic conductivities of the Na-B GCL permeated with 500 and 1000 mM NH₄⁺ solutions were much higher (e.g., 1.6–5.2 × 10^?6 m/s) due to suppression of osmotic swelling. NH₄⁺ replaced native Na⁺, K⁺, Ca²⁺, and Mg²⁺ in the exchange complex of the Na-B during permeation with all NH₄⁺ solutions, with the NH₄⁺ fraction in the exchange complex increasing from 0.24 to 0.83 as the NH₄⁺ concentration increased from 5 to 1000 mM. A Na-B GCL specimen permeated with 1000 mM NH₄⁺ solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH₄⁺ converted the Na-B to “NH₄-bentonite” with more than 80% of the exchange complex occupied by NH₄⁺. Hydraulic conductivity of this GCL specimen decreased from 5.9 × 10^?6 m/s to 2.9 × 10^?11 m/s during permeation with DI water, indicating that “NH₄-bentonite” can swell and have low hydraulic conductivity, and that the impact of more concentrated NH₄⁺ solutions on swelling and hydraulic conductivity is reversible.     

Coupling effect of landfill leachate and temperature on the microstructure of stabilized clay

This paper studies the microstructure of stabilized clay polluted by landfill leachate at different temperatures. For this purpose, dynamic corrosion-stabilized clay was used to prepare mercury intrusion porosimetry and scanning electron microscopy samples by lyophilization. The results showed that a rise in temperature affects the pore structure of corrosion-stabilized clay. Macropores are easily produced when the temperature ranges from 40 to 60 °C, while cryptopores and ultramicropores appear in significant numbers if the temperature reaches 80 °C. The corresponding micrographs show a dispersed structure at temperatures of 40 to 60 °C and a clearly flower-like structure at 80 °C. Landfill leachate has obvious effects on the microstructure of stabilized clay. After corrosion processes, pore size is reduced while average pore radius is increased. Macropores increase and span a wider range. The peak of the pore size distribution curve shifts from the middle to both ends; porosity initially decreases and then increases. From the chemical point of view, this corrosion mechanism is mainly due to the growth of new material such as calcium chloro-aluminates, ettringite or dihydrate gypsum that were generated by the reaction between landfill leachate and stabilized clay.

     

Adsorption of Cu(II) from industrial liquid waste on Na-bentonite and Al-PILC following a full factorial design

The paper reports a study of the performance of Maghnia bentonite in a purified and modified state for the removal of Cu(II) from industrial liquid waste in the region of Oran (North West Algeria). Bentonite was firstly treated to produce a Na-bentonite, then modified with an aluminum solution containing molar ratio OH/Al of 1.8 and finally calcined at 450 °C. The polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ formed in solution was adsorbed by surface complexation on the bentonite, which is known to have a high capacity to fix metal cations. The prepared materials were characterized by DRX, BET and EDX. In order to find the optimum conditions, a full factorial design of 2⁴ allowed us to determine the main effects and interactions of the factors studied: pH, mass of materials, contact time and temperature. The results obtained show that the best rate of adsorption of copper requires a pH = 10, a mass = 0.8 g, a stirring time = 80 min, and a temperature = 25 °C. The adsorption capacity of treated bentonite increased considerably from 4.147 mg/g for Na-bentonite to 7.173 mg/g for pillared aluminum bentonite. This shows the strong adsorption of copper compared with Na-bentonite, caused by its high surface area.     

Simultaneous nitrification and denitrification in a CEM (cation exchange membrane)-bounded two chamber system

A novel process was developed to induce a simultaneous oxidation of ammonia and denitrification in a single system consisting of two chambers separated by a cation exchange membrane. One was an anoxic chamber and the other was an aerobic chamber. The maximum mass flux via the membrane was calculated as 0.83 mg NH₄⁺-N/m² s in a batch test when the initial concentration of NH₄⁺ was 700 mg N/L. And it was observed that NO₃⁻ and NO₂⁻ moved via the membrane in a reverse direction when NH₄⁺ was transported. When the system was operated in a continuous mode by feeding a wastewater containing glucose and NH₄⁺, it was observed that soluble chemical oxygen demand and NH₄⁺ were simultaneously removed showing 99% and 71  86% of efficiency, respectively. Denitrification occurred in the anoxic chamber and nitrification was carried out in the aerobic chamber.     

Interaction between temperature and ammonia in mesophilic digesters for animal waste treatment

Four anaerobic sequencing batch reactors (ASBRs) were operated during a period of 988 days to evaluate the effect of temperature, ammonia, and their interconnectivity on the methane yield of anaerobic processes for animal waste treatment. During period 1 (day 0-378), the methane yield was 0.31 L CH₄/g volatile solids (VS) for all digesters (with no statistical differences among them) at a temperature and total ammonium-N levels of 25 °C and ∼1200 mg NH₄⁺-N/L, respectively. During period 2 (day 379-745), the methane yield at 25 °C decreased by 45% when total ammonium-N and ammonia-N were increased in two of the four ASBRs to levels >4000 mg NH₄⁺-N/L and >80 mg NH₃-N/L, respectively. During period 3 (day 746-988), this relative inhibition was reduced from 45% to 13% compared to the low-ammonia control reactors when the operating temperature was increased from 25 °C to 35 °C (while the free ammonia levels increased from ∼100 to ∼250 mg NH₃-N/L). The 10 °C increase in temperature doubled the rate constant for methanogenesis, which overwhelmed the elevated toxicity effects caused by the increasing concentration of free ammonia. Thus, the farmer/operator may alleviate ammonia toxicity by increasing the operating temperature within the mesophilic range. We extrapolated our data to correlate temperature, ammonia, and methane yield and to hypothesize that the difference between high- and low-ammonia reactors is negligible at the optimum mesophilic temperature of 38 °C.     

Membrane behavior of bentonite-amended compacted clay

The performance of landfill liners can be enhanced if they exhibit a semipermeable membrane behavior, which restricts the migration of contaminants. Consequently, enhancing the membrane property of clays used for liners is becoming increasingly important. As bentonite has already proven to be an excellent additive for improving the membrane behavior of clay, the hydraulic conductivities and membrane behaviors of a locally available clay, known as Fukakusa clay, amended with different amounts of dry bentonite (5%, 10%, 15%, and 20%) were herein evaluated. The chemico-osmotic efficiency coefficient, ω, was obtained under different concentration differences of KCl solution (0.5, 1, 5, 10, and 50 mM) for specimens in rigid-wall cells. The test results show that the ω of unamended clay is very low and can be ignored unless amended with bentonite, and that hydraulic conductivity k is suitably low (1.58×10⁻⁹ m/s). Additionally, ω decreased as the KCl concentration increased, which is consistent with the theory that increasing concentration causes progressively greater shrinkage of the diffuse-double layers of the clay particles. Furthermore, the mechanisms that influence the membrane behavior are discussed from the viewpoints of the diffuse-double layer and the interparticle pore size with the assistance of SEM.     

Utilisation de la clinoptilolite en potabilisation des eaux—elimination de l'ion NH4

The objective of this study is to develop a technique to remove ammonium ion from water intended for potable purposes. An ion exchange method is used with a selective ion exchanger, a natural cation zeolite, clinoptilolite. Glass columns (Fig. 1) are used for laboratory experiments. These experiments show that the NH₄⁺ exchange capacity is very small compared to its total capacity 2.17 meq g⁻¹; its value depends essentially on the NH₄⁺ initial concentration and less on the Ca²⁺ concentration in the influent water. Figure 3 illustrates the practical exchange capacity relative to the initial concentration of ammonium ion for a soft water (Ca²⁺ = 35–50 mg l⁻¹). We were particularly interested in waters weak in ammonium ion concentration (NH₄⁺ = 1–3 mg l⁻¹). In this case and for 1 and 2 mg l⁻¹ NH₄⁺ concentration in water, the practical capacity is only 0.06 and 0.108 meq g⁻¹ respectively. The leakage is smaller than the ECC limit (European Community Council) for drinking waters (NH₄⁺ 0.5 mg l⁻¹) and the treated volume of water to breakthrough, defined at 0.5 mg l⁻¹ of NH₄⁺, is 720 BV (BV = bed volume) in both cases.In another way Fig. 6 shows that hard waters (due to Ca²⁺ ions) are more difficult to treat than soft waters. The practical capacity is smaller than before and the NH₄⁺-leakage is greater. To lessen NH₄⁺-leakage to less than 0.5 mg l⁻¹ for soft waters down-flow and up-flow, regeneration is used. Figure 7 shows that up-flow regeneration is more attractive than down-flow regeneration.Cycle reproducibility (Figs 4 and 5) shows that the regeneration conditions satisfied our requirements: in this case, the salt consumption is 180 eq of salt per eq of NH₄⁺ eliminated. This prompted us to try to reuse the regenerant (with NH₄⁺ ion). An increase of NH₄⁺-leakage is noticed in the presence of an NH₄⁺-residual in the regenerant. This increase is more significant with down-flow regeneration.After these laboratory experiments, we carried out a semi-industrial pilot-plant. Our objective was first to verify the laboratory results and secondly to study clinoptilolite behaviour relative to the time it was used. Two plexiglass columns comprise the pilot-plant shown in Fig. 9; soft water is used for these experiments. The first column is regenerated with fresh salt solution. The cycles obtained, considering their initial NH₄⁺-concentration, are reproduced in Fig. 10. For 2 mg l⁻¹ NH₄⁺ in the influent water, the leakage is about 0.2 mg l⁻¹ and the treated volume to breakthrough (0.5 mg l⁻¹ of NH₄⁺) is about 750 BV. The second column is regenerated with a recycled solution. The quality of the cycles decreases with the number of reuse of the regenerant as shown in Fig. 11. Nevertheless, it is interesting to note that after 3 reuses, the performance decrease is only 25% and the leakage, although it increases is smaller than 0.5 mg l⁻¹.Pilot results allowed us to propose a treatment of 30,000 m³ day⁻¹; the cost per cubic meter water treated, relative to NH₄⁺-removal, is about 0.165 FF (0.033 US $) for a plant and 0.77 FF (0.014 US $) for the same plant at the seaside. Using two serial columns decreased the cost by about 40–50%.     

Adsorption effect on the degradation of 4,6-o-dinitrocresol and p-nitrophenol in a montmorillonite clay slurry by AFT

The adsorption and degradation of 4,6-o-dinitrocresol (DNOC) and p-nitrophenol (PNP) in SWy-2 montmorillonite clay slurry were investigated. The pH and type of cation of the slurry were varied. Results showed that adsorption of DNOC and PNP increased at lower pH values, and when pH < pK_a (4.4) of DNOC, DNOC was almost completely adsorbed on the clay under given experimental conditions. The specific cation also had a significant effect on adsorption, which was dramatically enhanced in the presence of K⁺ and NH₄⁺, compared with the presence of Na⁺ or Ca²⁺. Anodic Fenton treatment (AFT) degradation of DNOC and PNP in the clay slurry was studied, and it was found that DNOC degradation rates were greatly affected by the initial pH and the types of electrolytes. Due to the higher adsorption, the degradation rate substantially decreased in the clay slurry system in the presence of K⁺ and low pH, with a large amount of DNOC residue remaining after 60 min treatment. AFT degradation of PNP was completed within 30 min treatment. Based on LC-MS data, a DNOC degradation pathway was proposed. Overall, the results showed the inhibition effect of adsorption on the degradation of nitroaromatic compounds in montmorillonite clay slurry by AFT, providing important implications for water and soil remediation.     

Experimental investigation on methane advection and diffusion in geosynthetic clay liners

Geosynthetic clay liners (GCLs) are widely used in landfill and heap-leach facility cover system for mitigating rainfall infiltration and gas migration into atmosphere. Laboratory tests were conducted to investigate methane diffusion and advection through GCLs. Gas permeability coefficient of GCL for the case with moisture content = 47.5% is one and two orders of magnitude greater than the cases with moisture content = 68.5% and 80.9%, respectively, when 20 kPa vertical stress was applied. The batch adsorption tests indicated that adsorption of methane onto bentonite is negligible. The concentration variation for the adsorption of methane onto bentonite can be neglected. However, methane concentration decreased by 14.2% for the test of methane adsorption onto GCL during the first 2–3 days. This is because methane was adsorbed by the geotextiles rather than by the bentonite in GCL. The large porosity and surface area of geotextiles provide lots of micropores for methane adsorption. Analytical model was then developed to analyze the performance of GCL-based liners system with respect to methane transport. The results indicate that methane emission fluxes for the case with SL + GCL are 7.8 and 5.1 times less than the cases with SL + CCL when the moisture contents were 25.9% and 35.1%, respectively. The methane emission fluxes for both of the SL + GCL and SL + CCL can be neglected when they are fully saturated. GCL is recommended to be used in arid and semi-arid regions rather than CCL. GCL is recommended to be used in arid and semi-arid areas rather than CCL. Advection plays a more important role in methane migration through SL + GCL and SL + CCL than that of diffusion. With moisture contents = 25.9% and 32%, methane emission flux attributed to advection accounts for more than 90% of the total emission flux for both cases of SL + GCL and SL + CCL. With the increase of moisture content of SL, the effectiveness of SL in reducing methane emission increases. The saved space for using GCL + SL composite cover compared with using a single SL cover is 0.7 m when the moisture content equals 25.9%, which is 0.5 m greater than the case when moisture content equals 32%. GMB plays a dominant role in inhibiting methane migration and reducing methane emission flux. When moisture content equals 25.9%, the methane emission fluxes for SL + GMB + GCL and SL + GMB + CCL are 343 times and 2643 times less than the cases with SL + GCL and SL + CCL, respectively.     

Migration behavior of landfill leachate contaminants through alternative composite liners

Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540 days to investigate and to simulate the migration behaviors of phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and heavy metals (Pb, Cu, Zn, Cr, Cd, Ni) from landfill leachate to the groundwater. Alternative landfill liners of four reactors consist of R1: Compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R2: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R3: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + bentonite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn), and R4: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + zeolite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn). Wastes representing Istanbul municipal solid wastes were disposed in the reactors. To represent bioreactor landfills, reactors were operated by leachate recirculation. To monitor and control anaerobic degradation in the reactors, variations of conventional parameters (pH, alkalinity, chloride, conductivity, COD, TOC, TKN, ammonia and alcaly metals) were also investigated in landfill leachate samples. The results of this study showed that about 35-50% of migration of organic contaminants (phenolic compounds) and 55-100% of migration of inorganic contaminants (heavy metals) to the model groundwater could be effectively reduced with the use of bentonite and zeolite materials in landfill liner systems. Although leachate contaminants can reach to the groundwater in trace concentrations, findings of this study concluded that the release of these compounds from landfill leachate to the groundwater may potentially be of an important environmental concern based on the experimental findings.     

Impact of a synthetic leachate on permittivity of GCLs measured by filter press and oedopermeameter tests

Geosynthetic clay liners (GCLs) are used in landfill liner applications due primarily to their low hydraulic conductivity to water. The low hydraulic conductivity of GCLs comes from the structure of the clay in the bentonite. However, the interaction between clay and aggressive liquids may alter the structure of the clay and, thus, result in an increase in the hydraulic conductivity of the GCL. This paper presents the results of a project aimed at evaluating the impact of a synthetic leachate on the structure of four different bentonites used in the manufacturing of GCLs. The preparation of bentonite dispersions increased the interaction between the bentonites and the various liquids. The hydraulic properties of the dispersions also were tested using filter press tests to obtain flow curves. Results of these tests were correlated with the cationic concentration, electrical conductivity and pH of the dispersions, swell indexes of the bentonite extracted from the GCLs, and permittivities of the intact GCLs determined in oedopermeameter tests. The results showed that one bentonite was more sensitive to the synthetic leachate than the other bentonites. For example, the permittivities of the more sensitive bentonite based on the oedopermeameter tests and filter press tests were respectively 2.11 × 10⁻⁸ s⁻¹ and 5.6 × 10⁻⁸ s⁻¹, whereas the permittivities for other bentonites, including a natural sodium bentonite and two sodium-activated calcium bentonites, were respectively 5.7 to 6.5 × 10⁻⁹ s⁻¹ and 3.2 to 3.5 × 10⁻⁸ s⁻¹. The filter press test served as a quick and easy-to-use test to compare the performance of the various bentonites in containing a given liquid. However, the oedopermeameter test or direct permeation test is preferable to filter press tests or fluid loss tests for evaluating the long-term impact of a liquid on a bentonite.     

Releasing behavior of zinc in recirculated bioreactor landfill

The purpose of this research was to determine the releasing behavior of zinc in municipal solid waste (MSW) in landfill site 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. Results showed that the content of zinc in MSW could amount to 591.29 ± 31.33-632.14 ± 18.98 µg g ^− 1 dry weight ^− 1 (DW ^− 1). It exceeded the set standard for “Environmental quality standard for soil” (≤ 500 µg g ^− 1 DW ^− 1) and had high potential environmental risk. The releasing behavior of zinc in refuse mainly experienced speciation of solid-Zn, Zn²⁺, ZnHCO₃⁺, ZnCO₃, Zn(OH)⁺, Zn(OH)₂, Zn(NH₃)₄²⁺, ZnS, etc. Zinc in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of refuse in bioreactor landfill. The Zn²⁺ concentration in leachate, which varied correspondingly with releasing behavior of zinc in refuse, were 0.75 mg L ^− 1 to 3.13 mg L ^− 1 and had no great difference in landfill with different operation modes (CL and RL). However, the amount of Zn²⁺ leached out from refuse, which accounted for 28.70 mg and 130.67 mg after 320 day's operation, respectively. More attention should be paid to the inseparable system including refuse and leachate together.     

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH₄-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH₄-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.     

Nitrification in porous media during rapid,unsaturated water flow

A substantial nitrification in rapid infiltration (RI) systems for wastewater treatment is a prerequisite for obtaining good N removal by denitrification. The purpose of this study is to investigate nitrification in porous media at conditions corresponding to RI treatment systems. Nitrification in six 50-cm porous media columns (98% weathered granite or sand and 2% field soil) during unsaturated leaching at constant flow rates of synthetic wastewater was investigated. Concentrations of NH₄-N between 20 and 60 mg l⁻¹ were applied and vertical concentration profiles of NO₃-N, NO₂-N and NH₄-N were measured for 54 d at 30°C (three columns) and for 140 d at 10°C (three columns). A time lag in nitrification of 20 d was found at 10°C. Complete nitrification was obtained after 3–5 at 30°C and after approximately 50 d at 10°C. Assuming first-order nitrification at steady-state, the corresponding first order reaction rate coefficients (k₁) for NO₃ production in the columns were estimated to be between 0.4 and 1 h⁻¹ at 10°C and between 6 and 9 h⁻¹ at 30°C. Steady-state NO₃ profiles were obtained between 1.5 and up to 9 weeks after the experiments were started. At the actual soil-air contents (0.10 cm³ air phase cm⁻³ soil), oxygen limitations were not observed during the experiments. Nitrogen loadings (water flow times N concentration) above 100 mg N 1⁻¹ cm h⁻¹ (1 g N m⁻² h⁻¹) caused NH₄ accumulation in the columns at 10°C and should probably be avoided during operation of RI system.