Degradation of landfill leachate using transpiring-wall supercritical water oxidation (SCWO) reactor

Oxidation of landfill leachate wastewater was studied in a transpiring-wall SCWO reactor, operated under varied temperature and pressure 320–430 °C, 18–30 MPa. Effect of temperature and pressure on COD and BOD removal efficiency was investigated. COD and BOD removal efficiency being 99.23%, 98.06% were achieved at 430 °C, 30 MPa, which increased with temperature and pressure. The modified pseudo first-order rate model was regressed from experimental data, taking into account the induction time (t_ind) effect. The resulting pre-exponential factor A and activation energy E_a were 34.86 s^?1 and 32.1 kJ mol^?1, respectively, assuming that the reaction order for feed wastewater (based on COD) and oxidant were first order and zero order, respectively.     

Application of response surface methodology to the advanced treatment of biologically stabilized landfill leachate using Fenton’s reagent

A Fenton process that uses FeCl₂ as the alternative catalyst was employed to deal with the biologically treated landfill leachate. Data obtained revealed that this Fenton process can provide an equivalent pollutant removal as the Fenton process that uses FeSO₄ as catalyst. Central composite design (CCD) and response surface methodology (RSM) were applied to evaluate and optimize the four key factors, namely initial pH, Fe(II) dosage ([Fe²⁺]), H₂O₂/Fe(II) mole ratio ([H₂O₂]/[Fe²⁺] ratio) and reaction time, which affect the performance of the Fenton treatment. Chemical oxygen demand (COD) and color were selected as response variables. This approach provided statistically significant quadratic models, which were adequate to predict responses and to carry out optimization under the conditions studied. It was demonstrated that the interaction between initial pH and [H₂O₂]/[Fe²⁺] ratio has a significant effect on the COD removal, while the interaction between [H₂O₂]/[Fe²⁺] ratio and reaction time shows a large impact on color removal. The optimal conditions were found to be initial pH 5.9, [Fe²⁺] = 9.60 mmol/L, [H₂O₂]/[Fe²⁺] ratio = 2.38, reaction time = 5.52 h. Under this optimal scheme, the COD and color in the effluent were reduced to 159 mg/L and 25°, respectively, with an increase of BOD₅/COD ratio from 0.05 to 0.21.     

Pilot study on the advanced treatment of landfill leachate using a combined coagulation,fenton oxidation and biological aerated filter process

Mature landfill leachate is typically non-biodegradable. A combination process was developed that includes coagulation, Fenton oxidation, and biological aerated filtering to treat biologically-produced effluent. In this process, coagulation and Fenton oxidation were applied in order to reduce chemical oxygen demand (COD) organic load, and enhance biodegradability. Poly-ferric sulfate (PFS) at 600 mg l^?1 was found to be a suitable dosage for coagulation. For Fenton oxidation, an initial pH of 5, a total reaction time of 3 h, and an H₂O₂ dosage of 5.4 mmol l^?1, with a (H₂O₂)/n(Fe²⁺) ratio of 1.2 and two-step dosing were selected to achieve optimal oxidation. Under these optimal coagulation and Fenton oxidation conditions, the COD removal ratios were found to be 66.67% and 56%, respectively. Following pretreatment with coagulation and Fenton oxidation, the landfill leachate was further treated using a biological aerated filter (BAF). Our results show that COD was reduced to 75 mg l^?1, and the color was less than 10 degrees.     

Non-biodegradable landfill leachate treatment by combined process of agitation,coagulation, SBR and filtration

This study describes the complete treatment of non-biodegradable landfill leachate by combined treatment processes. The processes consist of agitation as a novel stripping method used to overcome the ammonia toxicity regarding aerobic microorganisms. The NH₃-N removal ratio was 93.9% obtained at pH 11.5 and a gradient velocity (G) 150 s^?1 within a five-hour agitation time. By poly ferric sulphate (PFS) coagulation followed the agitation process; chemical oxygen demand (COD) and biological oxygen demand (BOD₅) were removed at 70.6% and 49.4%, respectively at an optimum dose of 1200 mg L^?1 at pH 5.0. The biodegradable ratio BOD₅/COD was improved from 0.18 to 0.31 during pretreatment step by agitation and PFS coagulation. Thereafter, the effluent was diluted with sewage at a different ratio before it was subjected to sequencing batch reactor (SBR) treatment. Up to 93.3% BOD₅, 95.5% COD and 98.1% NH₃-N removal were achieved by SBR operated under anoxic–aerobic–anoxic conditions. The filtration process was carried out using sand and carbon as a dual filter media as polishing process. The final effluent concentration of COD, BOD₅, suspended solid (SS), NH₃-N and total organic carbon (TOC) were 72.4 mg L^?1, 22.8 mg L^?1, 24.2 mg L^?1, 18.4 mg L^?1 and 50.8 mg L^?1 respectively, which met the discharge standard. The results indicated that a combined process of agitation-coagulation-SBR and filtration effectively eliminated pollutant loading from landfill leachate.     

Application of hydration reaction on the removal of recalcitrant contaminants in leachate after biological treatment

Leachate contains amounts of non-biodegradable matters with COD range of 400–1500 mg/L after the biological treatment, and should be removed further to attain the Chinese discharge standards. Hydration reaction has the potential to combine and solidify some recalcitrant substances, and thus could be applied as the advanced leachate treatment process. It was found that COD and NH₃N decreased from 485 to <250 mg/L and 91 to 10 mg/L, with the removal rate over 50% and 90% in the first 6 d, respectively, and COD and NH₃N removal capacity were around 23.7 and 9.2 mg/g under the test conditions. The percentage of the substances with low Mn range of <1000 decreased from 32.9% to 3.2% in leachate after hydration reaction. Tricalcium aluminate, tricalcium silicate and dicalcium silicate were the most activity compounds successively for the pollutant removal in leachate, and hydration reaction could be the option for the advanced wastewater treatment process thereafter.     

Treatment of mature landfill leachate by biofilters and Fenton oxidation

A series of processes by biofilter and Fenton oxidation to treat mature landfill leachate has been devised. At a hydraulic loading rate of 20 l m^?3 d^?1, a biofilter packed with aged refuse is found to remove 80% of chemical oxygen demand (COD), 89% of ammonia nitrogen and 96% of total phosphorus (TP). Particularly, TP levels dropped below 1 mg l^?1. The optimal condition for Fenton oxidation was selected to be an initial pH of 5, a dosage of 0.01 and 0.02 mol l^?1 of FeSO₄ and H₂O₂, respectively, and a duration of 3 h, where COD removal efficiency reaches 58.6%, and BOD₅/COD ratio is raised from 0.05 to 0.20. Subsequent treatment by a biofilter packed with slag reduces COD, ammonia nitrogen levels to less than 100, 25 mg l^?1, respectively. A pilot scale experiment conducted in situ demonstrates that this series of processes exhibits a high efficiency in removing pollutants from mature landfill leachate and it is viable for application.     

Physico-chemical and biological treatment of MSW landfill leachate

This paper analyses the evolution of the physico-chemical characteristics of the leachate from the Central Landfill of Asturias (Spain), which has been operating since 1986, as well as different treatment options. The organic pollutant load of the leachate, expressed as chemical oxygen demand (COD), reached maximum values during the first year of operation of the landfill (around 80,000 mg/L), gradually decreasing over subsequent years to less than 5000 mg/L. The concentration of ammonium, however, has not decreased, presenting values of up to 2000 mg/L. When feasible, recirculation can greatly decrease the organic matter content of the leachate to values of 1500–1600 mg COD/L. Applying anaerobic treatment to leachates with a COD between 11,000 and 16,000 mg/L, removal efficiencies of 80–88% were obtained for organic loading rates of 7 kg COD/m³ d. For leachates with lower COD (4000–6000 mg/L), the efficiency decreased to around 60% for organic loading rates of 1 kg COD/m³ d.Applying coagulation–flocculation with iron trichloride or with aluminium polychloride, it was possible to reduce the non-biodegradable organic matter by 73–62% when treating old landfill leachate (COD: 4800 mg/L, BOD₅: 670 mg/L), also reducing turbidity and colour by more than 97%. It is likewise possible to reduce the non-biodegradable organic matter that remains after biological treatment by adsorption with activated carbon, although adsorption capacities are usually low (from 15 to 150 mg COD/g adsorbent). As regards ammonium nitrogen, this can be reduced to final effluent values of 5 mg/L by means of nitrification/denitrification and to values of 126 mg/L by stripping at pH 12 and 48 h of stirring.     

Evaluation of landfill leachate treatment by advanced oxidative process by Fenton’s reagent combined with membrane separation system

A high content of refractory organic matter, ammonia and toxic compounds is characteristic of landfill leachate. Advanced oxidative processes (AOPs) are an attractive alternative for landfill leachate treatment. However, when applied as a unique process treatment, they do not provide a complete solution for the effluent treatment. Combining AOP with a membrane separation process (MSP) presents a number of benefits and provides an adequate solution for this problem. With this in mind, the present work aims to evaluate, using a bench scale, leachate treatability through AOP by Fenton’s reagent (AOP/Fenton) combined with microfiltration (MF) and nanofiltration (NF). A high efficient removal of COD (63%), true color (76%) and humic substances (50%) was observed during AOP/Fenton under optimized conditions (1.7 g H₂O₂/g COD_{raw leachate}; FeSO₄·7H₂O:H₂O₂ = 1:5.3; pH = 3.8; reaction conditions = 115 rpm/28 min). According to the evaluated parameters, MSP presented an efficient complementary treatment, in which the integrity of the stages was sufficient for reaching regulatory levels in the effluent (Deliberação Normativa Conjunta COPAM/CERH-MG N^o. 1, May 5, 2008).     

Treatment of municipal landfill leachate using a combined anaerobic digester and activated sludge system

The main objective of this study was to assess the feasibility of treating sanitary landfill leachate using a combined anaerobic and activated sludge system. A high-strength leachate from Shiraz municipal landfill site was treated using this system. A two-stage laboratory-scale anaerobic digester under mesophilic conditions and an activated sludge unit were used. Landfill leachate composition and characteristics varied considerably during 8 months experiment (COD concentrations of 48,552–62,150 mg/L). It was found that the system could reduce the COD of the leachate by 94% at a loading rate of 2.25 g COD/L/d and 93% at loading rate of 3.37 g COD/L/d. The anaerobic digester treatment was quite effective in removing Fe, Cu, Mn, and Ni. However, in the case of Zn, removal efficiency was about 50%. For the rest of the HMs the removal efficiencies were in the range 88.8–99.9%. Ammonia reduction did not occur in anaerobic digesters. Anaerobic reactors increased alkalinity about 3.2–4.8% in the 1st digester and 1.8–7.9% in the 2nd digester. In activated sludge unit, alkalinity and ammonia removal efficiency were 49–60% and 48.6–64.7%, respectively. Methane production rate was in the range of 0.02–0.04, 0.04–0.07, and 0.02–0.04 L/g COD_rem for the 1st digester, the 2nd digester, and combination of both digesters, respectively; the methane content of the biogas varied between 60% and 63%.     

Full-scale blending treatment of fresh MSWI leachate with municipal wastewater in a wastewater treatment plant

Fresh leachate, generated in municipal solid waste incineration (MSWI) plants, contains various pollutants with extremely high strength organics, which usually requires expensive and complex treatment processes. This study investigated the feasibility of blending treatment of MSWI leachate with municipal wastewater. Fresh MSWI leachate was pretreated by coagulation–flocculation with FeCl₃ 2 g/L and CaO 25 g/L, plate-and-frame filter press, followed by ammonia stripping at pH above 12. After that, blending treatment was carried out in a full-scale municipal wastewater treatment plant (WWTP) for approximately 3 months. Different operational modes consisting of different pretreated leachate and methanol addition levels were tested, and their performances were evaluated. Results showed that throughout the experimental period, monitored parameters in the WWTP effluent, including COD (<60 mg/L), BOD₅ (<20 mg/L), ammonium (<8 mg/L), phosphorus (<1.5 mg/L) and heavy metals, generally complied with the Chinese sewage discharged standard. Under the experimental conditions, a certain amount of methanol was needed to fulfill TN removal. An estimation of the operation cost revealed that the expenditure of blending treatment was much lower than the total costs of respective treatment of MSWI leachate and municipal wastewater. The outcomes indicated that blending treatment could not only improve the treatability of the MSWI leachate, but also reduce the treatment cost of the two different wastewaters.     

Combined processes of two-stage Fenton-biological anaerobic filter–biological aerated filter for advanced treatment of landfill leachate

There are numerous non-biodegradable organic materials in the mature landfill leachate. To meet the new discharge standard of China, additional advanced treatment is needed for the effluent from the biological treatment processes of leachate. In this study, a combined process including two stages of “Fenton-biological anaerobic filter (BANF)–biological aerated filter (BAF)” was evaluated to address the advanced treatment need. The Fenton oxidation was applied to reduce chemical oxygen demand (COD) and enhance biodegradability of refractory organics, and the BANF–BAF process was then applied to remove the total nitrogen (TN). The treatment achieved effluent concentrations of COD < 70 mg/L, TN < 40 mg/L and NH₃–N < 10 mg/L. The removal efficiency of COD and TN were 96.1% and 95.9%, respectively. The effluent quality met the new discharge standard for Pollution Control on the Landfill Site of Municipal Solid of PR China (GB16889-2008). The operation cost of these processes was about 36.1 CHY/t (5.70 USD/t).     

N2O emission from a combined ex-situ nitrification and in-situ denitrification bioreactor landfill

A combined process comprised of ex-situ nitrification in an aged refuse bioreactor (designated as A bioreactor) and in-situ denitrification in a fresh refuse bioreactor (designated as F bioreactor) was constructed for investigating N₂O emission during the stabilization of municipal solid waste (MSW). The results showed that N₂O concentration in the F bioreactor varied from undetectable to about 130 ppm, while it was much higher in the A bioreactor with the concentration varying from undetectable to about 900 ppm. The greatly differences of continuous monitoring of N₂O emission after leachate cross recirculation in each period were primarily attributed to the stabilization degree of MSW. Moreover, the variation of N₂O concentration was closely related to the leachate quality in both bioreactors and it was mainly affected by the COD and COD/TN ratio of leachate from the F bioreactor, as well as the DO, ORP, and NO₃^?-N of leachate from the A bioreactor.     

High solids co-digestion of food and landscape waste and the potential for ammonia toxicity

A pilot-scale study was completed to determine the feasibility of high-solids anaerobic digestion (HSAD) of a mixture of food and landscape wastes at a university in central Pennsylvania (USA). HSAD was stable at low loadings (2 g COD/L-day), but developed inhibitory ammonia concentrations at high loadings (15 g COD/L-day). At low loadings, methane yields were 232 L CH₄/kg COD fed and 229 L CH₄/kg VS fed, and at high loadings yields were 211 L CH₄/kg COD fed and 272 L CH₄/kg VS fed. Based on characterization and biodegradability studies, food waste appears to be a good candidate for HSAD at low organic loading rates; however, the development of ammonia inhibition at high loading rates suggests that the C:N ratio is too low for use as a single substrate. The relatively low biodegradability of landscape waste as reported herein made it an unsuitable substrate to increase the C:N ratio. Codigestion of food waste with a substrate high in bioavailable carbon is recommended to increase the C:N ratio sufficiently to allow HSAD at loading rates of 15 g COD/L-day.     

Response surface analysis of effects of hydraulic retention time and influent feed concentration on performance of an UASFF bioreactor

The interactive effects of hydraulic retention time (HRT) and influent chemical oxygen demand (COD_in) on the performance of an up-flow anaerobic sludge fixed film (UASFF) bioreactor treating palm oil mill effluent (POME) was studied. Anaerobic digestion of POME was modeled and analyzed with two variables i.e. HRT and COD_in. Experiments were conducted based on a general factorial design and analyzed using response surface methodology (RSM). The region of exploration for digestion of POME was taken as the area enclosed by HRT (1–6 days) and COD_in (5260–34,725 mg/l) boundaries. Eight dependent parameters were either directly measured or calculated as response. Increase in the variables resulted in decrease in COD removal efficiency, solid retention time (SRT) and sludge retention factor (SRF) and increase of COD removal rate, volatile fatty acid to alkalinity ratio (VFA/Alk), CO₂ percentage in biogas and methane production rate. The value of the maximum specific microbial growth rate (μ_m) determined through the equation that correlated organic loading rate (OLR) and μ (calculated by quadratic model for SRF) was found to be 0.153 d^?1. This value was close to that obtained using Chen and Hashimoto kinetic equation (0.207 d^?1) in a previous study. The present study provides valuable information about interrelations of quality and process parameters in POME digestion using a UASFF bioreactor.     

Greenhouse gas emissions from landfill leachate treatment plants: A comparison of young and aged landfill

With limited assessment, leachate treatment of a specified landfill is considered to be a significant source of greenhouse gas (GHG) emissions. In our study, the cumulative GHG emitted from the storage ponds and process configurations that manage fresh or aged landfill leachate were investigated. Our results showed that strong CH₄ emissions were observed from the fresh leachate storage pond, with the fluxes values (2219–26,489 mg C m^?2 h^?1) extremely higher than those of N₂O (0.028–0.41 mg N m^?2 h^?1). In contrast, the emission values for both CH₄ and N₂O were low for the aged leachate tank. N₂O emissions became dominant once the leachate entered the treatment plants of both systems, accounting for 8–12% of the removal of N-species gases. Per capita, the N₂O emission based on both leachate treatment systems was estimated to be 7.99 g N₂O–N capita^?1 yr^?1. An increase of 80% in N₂O emissions was observed when the bioreactor pH decreased by approximately 1 pH unit. The vast majority of carbon was removed in the form of CO₂, with a small portion as CH₄ (<0.3%) during both treatment processes. The cumulative GHG emissions for fresh leachate storage ponds, fresh leachate treatment system and aged leachate treatment system were 19.10, 10.62 and 3.63 Gg CO₂ eq yr^?1, respectively, for a total that could be transformed to 9.09 kg CO₂ eq capita^?1 yr^?1.     

Enhancement of the anaerobic hydrolysis and fermentation of municipal solid waste in leachbed reactors by varying flow direction during water addition and leachate recycle

Poor performance of leachbed reactors (LBRs) is attributed to channelling, compaction from waste loading, unidirectional water addition and leachate flow causing reduced hydraulic conductivity and leachate flow blockage. Performance enhancement was evaluated in three LBRs M, D and U at 22 ± 3 °C using three water addition and leachate recycle strategies; water addition was downflow in D throughout, intermittently upflow and downflow in M and U with 77% volume downflow in M, 54% volume downflow in U while the rest were upflow. Leachate recycle was downflow in D, alternately downflow and upflow in M and upflow in U. The strategy adopted in U led to more water addition (30.3%), leachate production (33%) and chemical oxygen demand (COD) solubilisation (33%; 1609 g against 1210 g) compared to D (control). The total and volatile solids (TS and VS) reductions were similar but the highest COD yield (g-COD/g-TS and g-COD/g-VS removed) was in U (1.6 and 1.9); the values were 1.33 and 1.57 for M, and 1.18 and 1.41 for D respectively. The strategy adopted in U showed superior performance with more COD and leachate production compared to reactors M and D.     

The performance of Electro-Fenton oxidation in the removal of coliform bacteria from landfill leachate

Leachate pollution is one of the main problems in landfilling. Researchers have yet to find an effective solution to this problem. The technology that can be used may differ based on the type of leachate produced. Coliform bacteria were recently reported as one of the most problematic pollutants in semi-aerobic (stabilized) leachate. In the present study, the performance of the Electro-Fenton process in removing coliform from leachate was investigated. The study focused on two types of leachate: Palau Borung landfill leachate with low Coliform content (200 MPN/100 m/L) and Ampang Jajar landfill leachate with high coliform content (>24 × 10⁴ MPN/100 m/L). Optimal conditions for the Electro-Fenton treatment process were applied on both types of leachate. Then, the coliform was examined before and after treatment using the Most Probable Number (MPN) technique. Accordingly, 100% removal of coliform was obtained at low initial coliform content, whereas 99.9% removal was obtained at high initial coliform content. The study revealed that Electro-Fenton is an efficient process in removing high concentrations of pathogenic microorganisms from stabilized leachate.     

Investigation of the effect of culture type on biological hydrogen production from sugar industry wastes

The bio-hydrogen generation potential of sugar industry wastes was investigated. In the first part of the study, acidogenic anaerobic culture was enriched from the mixed anaerobic culture (MAC) through acidification of glucose. In the second part of the study, glucose acclimated acidogenic seed was used, along with the indigenous microorganisms, MAC, 2-bromoethanesulfonate treated MAC and heat treated MAC. Two different COD levels (4.5 and 30 g/L COD) were investigated for each culture type. Reactors with initial COD concentration of 4.5 g/L had higher H₂ yields (20.3–87.7 mL H₂/g COD) than the reactors with initial COD concentration of 30 g/L (0.9–16.6 mL H₂/g COD). The 2-bromoethanesulfonate and heat treatment of MAC inhibited the methanogenic activity, but did not increase the H₂ production yield. The maximum H₂ production (87.7 mL H₂/g COD) and minimum methanogenic activity were observed in the unseeded reactor with 4.5 g/L of initial COD.     

Membrane bioreactor technology: A novel approach to the treatment of compost leachate

Compost leachate forms during the composting process of organic material. It is rich in oxidizable organics, ammonia and metals, which pose a risk to the environment if released without proper treatment. An innovative method based on the membrane bioreactor (MBR) technology was developed to treat compost leachate over 39 days. Water quality parameters, such as pH, dissolved oxygen, ammonia, nitrate, nitrite and chemical oxygen demand (COD) were measured daily. Concentrations of caffeine and metals were measured over the course of the experiment using gas chromatography – mass spectrometry (GC/MS) and inductively coupled plasma – mass spectrometry (ICP–MS) respectively. A decrease of more than 99% was achieved for a COD of 116 g/L in the initial leachate. Ammonia was decreased from 2720 mg/L to 0.046 mg/L, while the nitrate concentration in the effluent rose to 710 mg/L. The bacteria in the MBR system adjusted to the presence of the leachate, and increased 4 orders of magnitude. Heavy metals were removed by at least 82.7% except copper. These successful results demonstrated the membrane bioreactor technology is feasible, efficient method for the treatment of compost leachate.     

Anaerobic treatment of effluents from an industrial polymers synthesis plant

The feasibility of the anaerobic treatment of an industrial polymer synthesis plant effluent was evaluated. The composition of the wastewater includes acrylates, styrene, detergents, a minor amount of silicates and a significant amount of ferric chloride. The average chemical oxygen demand (COD) corresponding is about 2000 mg/l. The anaerobic biodegradability of the effluent is shown and the toxicity effect on the populations of anaerobic bacteria is evaluated. The results of the anaerobic biodegradation assays show that 62% of the wastewater compounds, measured as COD, could be consumed. An upflow anaerobic sludge blanket (UASB) reactor was used in the evaluation, it has a diameter–height ratio of 1:7, and 4-liter volume. The inoculum was obtained from a UASB pilot plant that treats brewery wastewaters. At the beginning of the operation, the biomass showed an anaerobic activity of 0.58 gCOD/(gVSS×d), it decreased only 2.5% in the subsequent 4 months. After 35 days of continuous operation, the reactor was operated at different steady states for 140 days. The COD was maintained at 2200 mg/l in the feed. The results were: organic loading rate (OLR): 4.3 kg COD/(m³×d), hydraulic retention time: 12 h, superficial velocity: 1 m/h, average biogas productivity: 290 L CH₄/kg COD fed, biogas composition: 70–75% methane and a COD removal percentage >75%. ©