The use of alum, ferric chloride and ferrous sulphate as coagulants in removing suspended solids, colour and COD from semi-aerobic landfill leachate at controlled pH.

Suspended solids, colour and chemical oxygen demand (COD) are among the main pollutants in landfill leachate. Application of physical or biological processes alone is normally not sufficient to remove these constituents, especially for leachate with a lower biochemical oxygen demand (BOD)/ COD ratio. The main objective of this research was to investigate the efficiency of coagulation and flocculation processes for removing suspended solids, colour and COD from leachate produced in a semi-aerobic landfill in Penang, Malaysia. A 12-month characterization study of the leachate indicated that it had a mean annual BOD/COD ratio of 0.15 and was partially stabilized, with little further biological degradation likely to occur. Particle size analysis of the raw leachate indicated that its 50th percentile (d50) was 11.68 microm. Three types of coagulants were examined in bench scale jar test studies: aluminium sulphate (alum), ferric chloride (FeCl3) and ferrous sulphate (FeSO4). The effects of agitation speed, settling time, pH, coagulant dosages and temperature were examined. At 300 rpm of rapid mixing, 50 rpm of slow mixing, and 60 min settling time, higher removals of suspended solids (over 95%), colour (90%) and COD (43%) were achieved at pH 4 and 12. FeCl3 was found to be superior to other coagulants tested. At pH 4 and 12, fair removal of suspended solids was observed at a reasonably low coagulant dose, i.e., 600 mg L(-1); hHowever, about 2500 mg L(-1) of coagulant was required to achieve good removals at pH 6. Better removals were achieved at higher temperature. The d50 of sludge after coagulation at pH 4 with a 2500 mg L(-1) FeCl3 dose was 60.16 microm, which indicated that the particles had been removed effectively from the leachate. The results indicate that coagulation and flocculation processes can be used effectively in integrated semi-aerobic leachate treatment systems, especially for removing suspended solids, colour and COD.     

Different treatment strategies for highly polluted landfill leachate in developing countries

The aim of this research was to determine appropriate treatment technique for effective treatment of heavily polluted landfill leachate. We accomplished several treatment experiments: (i) aerobic biological treatment, (ii) chemical coagulation, (iii) advanced oxidation process (AOP) and (iv) several combined treatment strategies. Efficiency of these treatment procedures were monitored by analysing COD and colour removal. Leachate used for this study was taken from Matuail landfill site at Dhaka city. With extended aeration process which is currently used in Matuail landfill site for leachate treatment, maximum COD and colour removal of 36% and 20%, respectively could be achieved with optimum retention period of 7days. With optimum aluminium sulphate dose of 15,000mg/L and pH value of 7.0, maximum COD and colour removals of 34% and 66%, respectively were observed by using chemical coagulation. With optimum pH of 5.0 and optimum dosages of reagents having H(2)O(2)/Fe(2+) molar ratio of 1.3 the highest removal of COD and colour were found 68% and 87%, respectively with sludge production of 55%. Fenton treatment which is an advanced oxidation process was the most successful between these three separate treatment procedures. Among the combined treatment options performed, extended aeration followed by Fenton method was the most suitable one.     

Use of zeolitised coal fly ash for landfill leachate treatment: a pilot plant study

Treatment of municipal solid waste (MSW) landfill leachate generally results in low percentages of nutrient removal due to the high concentration and accumulation of refractory compounds. For this reason, individual physical, chemical and biological processes have been used for the treatment of raw landfill leachate and sometimes for the mixture of domestic wastewater and landfill leachate. In this work, the possibility of treating landfill leachate was tested in a bench-scale pilot plant by a two-step method combining adsorption and coagulation-flocculation. Zeolite synthesized from coal fly ash, a by-product of coal-fired power stations, was used in this study both as a decantation aid reagent and as an adsorbent of COD and NH4-N. The coagulation-flocculation step was performed by the use of aluminium sulphate and a polyelectrolyte (ACTIPOL A-401). The leachate was collected directly from a storage unit of the organic fraction of MSW, before it was composted. For this reason the raw leachate was diluted before treatment. The sludge was recirculated to enhance the removal efficiency of nutrients as well as to optimize flocculant saving and to decrease sludge production. The results showed that it is possible to remove 43%, 53% and 82% of COD, NH4-N, and suspended solids, respectively. Therefore, this method may be an alternative for ammonium removal, as well as a suitable pre- or post-treatment step, in combination with other processes in order to meet regulatory limits.     

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.     

New treatment of stabilized leachate by ozone/Fenton in the advanced oxidation process

Ozonation, combined with the Fenton process (O(3)/H(2)O(2)/Fe(2+)), was used to treat matured landfill leachate. The effectiveness of the Fenton molar ratio, Fenton concentration, pH variance, and reaction time were evaluated under optimum operational conditions. The optimum removal values of chemical oxygen demand (COD), color, and NH(3)-N were found to be 65%, 98%, and 12%, respectively, for 90 min of ozonation using a Fenton molar ratio of 1 at a Fenton concentration of 0.05 mol L(-1) (1700 mg/L) H(2)O(2) and 0.05 mol L(-1) (2800 mg/L) Fe(2+) at pH 7. The maximum removal of NH(3)-N was 19% at 150 min. The ozone consumption for COD removal was 0.63 kg O(3)/kg COD. To evaluate the effectiveness, the results obtained in the treatment of stabilized leachate were compared with those obtained from other treatment processes, such as ozone alone, Fenton reaction alone, as well as combined Fenton and ozone. The combined method (i.e., O(3)/H(2)O(2)/Fe(2+)) achieved higher removal efficiencies for COD, color, and NH(3)-N compared with other studied applications.     

Report: anaerobic digestion of a sulphate-rich high-strength landfill leachate: the effect of differential dosing with FeCl3.

The effect of different dose concentrations of FeCl3 on the performance of a mesophilic anaerobic digester treating a highly alkaline, high-strength and sulphate-rich landfill leachate was tested. The results indicated that sulphate reduction was the predominant reaction and methanogenic processes were entirely inhibited in the reactor without FeCl3 addition. Adding FeCl3 into the reactor restored some methanogenic activity and also improved the rates of sulphate reduction. A combination of sulphate reduction and methanogenic activity resulted in up to 75% chemical oxygen demand (COD) removal and 85% sulphate removal. Sulphate reduction remained the principle mechanism by which COD removal took place with a methane yield of only between 0.14 and 0.18 m3 CH4 kg(-1) COD removed being achieved. The process was, however, stable and offered advantages for the further treatment or conveyance of the anaerobically treated leachate.     

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%.     

Use of Sphagnum peat moss and crushed mollusk shells in fixed-bed columns for the treatment of synthetic landfill leachate

A laboratory bench-scale fixed-bed column study operated as a down-flow configuration was conducted to evaluate Sphagnum peat moss and crushed mollusk shells as natural low-cost adsorbents for the removal of heavy metals from aerated and unaerated synthetic landfill leachate. Columns were packed with 15 cm of prepared peat moss, or 15 cm adsorbent mixtures made up of peat moss and crushed mollusk shells (4.0–4.75 mm) from Lake Ontario at different bed depth ratios. Peat was found to have the best adsorption capacities in columns treating aerated synthetic leachate for cadmium and nickel with 78.6% and 83.8% removal efficiencies, respectively. The removal of chemical oxygen demand (COD) and total nitrogen from the synthetic leachate was also monitored to evaluate the potential effects of biological activity on heavy metal adsorption. Columns receiving unaerated raw synthetic leachates did not show any significant removal of COD and total nitrogen, whereas some reduction in COD and total nitrogen was noted in the columns treating aerated synthetic landfill leachate. The results suggested that biological activity and biofilm growth could positively contribute to heavy metal retention within the fixed-media biosorption columns.     

Removal of dissolved organic matter and phthalic acid esters from landfill leachate through a complexation-flocculation process

Dissolved organic macromolecules (DOM) and micropollutants, such as phthalic acid esters (PAEs), are often enriched in landfill leachate. PAEs were detected in 10 leachate samples from three landfills in Hubei province, central China. In particular, di-(2-ethyhexyl) phthalate (DEHP) concentration was higher than 70microgL(-1) in most samples, and the highest DEHP concentration was in the colloid fraction (1000Da-0.45microm). Use of flocculants may result in flocculation and precipitation of colloids and associated contaminants, such as DEHP. Biodegradation is not effective for long chain PAEs or the landfill leachate, given the low ratio of BOD5/COD (less than 0.2) and deficient phosphorus content. Complexation-flocculation is therefore proposed as an alternative process for removing DOM and PAEs. Jar-test experiments were employed to investigate the mechanism and feasibility of the process. Among tested coagulants (ferric chloride, aluminum sulfate and poly aluminum chloride (PAC)), PAC was the most efficient. Hydrophobic contaminants with log KOC greater than 4 and DOM in wastewater can be removed simultaneously through the complexation-flocculation process.     

Landfill leachate treatment by electrochemical oxidation

This study investigated the electrochemical oxidation of stabilized leachate from Pulau Burung semi-aerobic sanitary landfill by conducting laboratory experiments with sodium sulfate Na₂SO₄ (as electrolyte) and graphite carbon electrodes. The control parameters were influent COD, current density and reaction time, while the responses were BOD removal, COD removal, BOD:COD ratio, color and pH. Na₂SO₄ concentration was 1 g/L. Experiments were conducted based on a three-level factorial design and response surface methodology (RSM) was used to analyze the results. The optimum conditions were obtained as 1414 mg/L influent COD concentration, 79.9 mA/cm² current density and 4 h reaction time. This resulted in 70% BOD removal, 68% COD removal, 84% color removal, 0.04 BOD/COD ratio and 9.1 pH. Electrochemical treatment using graphite carbon electrode was found to be effective in BOD, COD and color removal but was not effective in increasing the BOD/COD ratio or enhancing biodegradability of the leachate. The color intensity of the treated samples increased at low influent COD and high current density due to corrosion of electrode material.     

Organic and nitrogen removal from landfill leachate in aerobic granular sludge sequencing batch reactors

Granule sequencing batch reactors (GSBR) were established for landfill leachate treatment, and the COD removal was analyzed kinetically using a modified model. Results showed that COD removal rate decreased as influent ammonium concentration increasing. Characteristics of nitrogen removal at different influent ammonium levels were also studied. When the ammonium concentration in the landfill leachate was 366 mg L⁻¹, the dominant nitrogen removal process in the GSBR was simultaneous nitrification and denitrification (SND). Under the ammonium concentration of 788 mg L⁻¹, nitrite accumulation occurred and the accumulated nitrite was reduced to nitrogen gas by the shortcut denitrification process. When the influent ammonium increased to a higher level of 1105 mg L⁻¹, accumulation of nitrite and nitrate lasted in the whole cycle, and the removal efficiencies of total nitrogen and ammonium decreased to only 35.0% and 39.3%, respectively. Results also showed that DO was a useful process controlling parameter for the organics and nitrogen removal at low ammonium input.     

Application of quadratic regression model for Fenton treatment of municipal landfill leachate

The effectiveness of Fenton process in municipal landfill leachate treatment, as a pre- or post-treatment approach, has been demonstrated. However, no general recommendations of universal validity could be made in the term of optimized conditions affecting Fenton process. At the first stage of this study, collected leachate samples from Aradkooh site, Tehran, Iran, were investigated using one-factor-at-a-time method to find out optimum coagulation pH and flocculation time values. Subsequently, the obtained results in addition to data issued previously by the authors were employed to develop a predictive model of the true response surface, namely chemical oxygen demand (COD) removal efficiency. Finally, the main parameters of Fenton procedure, i.e. initial pH, [H(2)O(2)]/[Fe(2+)] molar ratio, Fe(2+) dosage, and coagulation pH were optimized taking advantage of the above-mentioned quadratic model. The derived second-order model included both significant linear and quadratic terms and seemed to be adequate in predicting responses (R(2)=0.9896 and prediction R(2)=0.6954). It was found that the interaction between initial pH and Fe(2+) dosage has a significant effect on COD removal. While, the optimal [H(2)O(2)]/[Fe(2+)] molar ratio was independent of ferrous ion dosage. The optimum conditions for the maximum COD removal of 50.76% for the parameters of initial pH, [H(2)O(2)]/[Fe(2+)] molar ratio, Fe(2+) dosage, and coagulation pH were found to be 5.8, 8.0, 22,500mg/L, and 8.7 respectively.     

Landfill leachate treatment using a rotating biological contactor and an upward-flow anaerobic sludge bed reactor

This paper describes the feasibility of an aerobic system (rotating biological contactor, RBC) and a biological anaerobic system (upward-flow anaerobic sludge bed reactor) at small scale for the treatment of a landfill leachate. In the first phase of the aerobic system study, a cyclic-batch RBC system was used to select perforated acetate discs among three different acetate disc configurations. These discs were chosen on the basis of high COD removal (65%) and biological stability. In the second phase, the RBC system (using four stages) was operated continuously at different hydraulic retention times (HRT), at different rotational speeds, and with varying organic concentrations of the influent leachate (2500-9000mgL(-1)). Forty percent of the total surface area of each perforated disc was submerged in the leachate. A COD removal of about 52% was obtained at an HRT of 24h and a rotational speed of 6rpm. For the anaerobic system, the reactor was evaluated with a volumetric organic load of 3273g-COD m(-3) day(-1) at an HRT of 54, 44, 39, 24 and 17h. At these conditions, the system reached COD removal efficiencies of 62%, 61%, 59%, 44% and 24%, respectively.     

Advanced physico-chemical treatment experiences on young municipal landfill leachates

In this study, Membrane Filtration (UF+RO), Struvite (MAP) precipitation and ammonia stripping alternatives were studied on biologically pre-treated Landfill Leachate. The results indicated that the system including the Upflow Anaerobic Sludge Blanket Reactor (UASBR) and Membrane Reactors (UF+RO) has been offered as an appropriate treatment alternative for young landfill leachates. This system provided high removals of COD, colour and conductivity (>98-99%). For ammonia removal, struvite precipitation was applied at the stoichiometric ratio (Mg:NH4:PO4=1:1:1) to anaerobically pre-treated raw landfill leachate effluent having an influent ammonium concentration of 2240 mg/l. Maximum ammonium nitrogen removal was observed as 85% at pH of 9.2. In ammonia stripping following 2 h of aeration, the removal was 72% at pH=12 while the removals were around 20% at pH=10 and pH=11. When membrane reactor, and struvite precipitation or ammonia stripping was applied to anaerobically pre-treated effluents, the results indicated that each system could be used as an appropriate post-treatment option for young landfill leachates. In economic aspect, ammonia stripping was found as the cheapest alternative with high ammonium removal. However, when both high COD and ammonium removals were to be achieved membrane technology such as UF+RO (SW) could be considered as the most appropriate system due to the fact that COD removal could be obtained very low by ammonia stripping.     

Fungal and enzymatic treatment of mature municipal landfill leachate

The aim of our study was to evaluate biotreatability of mature municipal landfill leachate by using white rot fungus and its extracellular enzymes. Leachates were collected in one active and one closed regional municipal landfill. Both chosen landfills were operating for many years and the leachates generated there were polluted by organic and inorganic compounds. The white rot fungus Dichomitus squalens was able to grow in the mature leachate from the closed landfill and as it utilizes present organic matter as a source of carbon, the results were showing 60% of DOC and COD removal and decreased toxicity to the bacterium Aliivibrio fischeri. On the other hand, growth of the fungus was inhibited in the presence of the leachate from the active landfill. However, when the leachate was introduced to a crude enzyme filtrate containing extracellular ligninolytic enzymes, removal levels of COD and DOC reached 61% and 44%, respectively. Furthermore, the treatment led to detoxification of the leachate to the bacterium Aliivibrio fischeri and to reduction of toxicity (42%) to the plant Sinapis alba. Fungal and enzymatic treatment seems to be a promising biological approach for treatment of mature landfill leachates and their application should be further investigated.     

Treatment of a high-strength sulphate-rich alkaline leachate using an anaerobic filter

The research looks at the feasibility of treating an alkaline sulphate-rich leachate arising from the co-disposal of municipal solid waste with cement kiln dust by means of an anaerobic filter (AF). This type of leachate with a high sulphate concentration is commonly prohibited for discharge to sewer and requires an on-site treatment solution. The AF used had a working volume of 4l and contained reticulated polyurethane foam as the biomass support material. The filters were operated over a 152 day experimental period during which the COD loading onto the filter was increased from 0.76 to 7.63kgCODm(-3)d(-1). In the early stages of operation at low loading, soluble sulphides accumulated that inhibited methanogenic activity. This was restored by dosing FeCl(3) to the reactor. The continued dosing allowed efficient COD removal of between 75% and 90% until the nominal retention time in the reactor was 3 days, at which point reactor performance declined significantly. The main mechanism for COD removal was by sulphate-reducing bacteria, which also resulted in up to 88% sulphate removal from the leachate. The average methane generation rate was 0.10lg(-1) COD removed. The results indicate the potential for using this approach as a pre-treatment that could significantly reduce the COD load to a second stage treatment process, but problems associated with the implementation of the technology at a larger scale have been identified.     

Bench-scale evaluation of treatment schemes incorporating struvite precipitation for young landfill leachate

In this study, landfill leachate treatment technologies alternative to anaerobic treatment were experimentally investigated. The emphasis was placed upon nitrogen removal through the use of struvite precipitation. Treatment technologies studied included struvite precipitation, low pH (acidic) air stripping, and activated sludge. Dilution of landfill leachate was used as a means to obtain appropriate quality for feeding the activated sludge process in some instances. Five main treatment combinations were applied. The first and second schemes were struvite precipitation followed by activated sludge process which was fed on undiluted and diluted (1:5) effluents. The third scheme was dilution, activated sludge and struvite precipitation. The fourth alternative was acidic air stripping, struvite precipitation and activated sludge process. The fifth scheme was acidic air stripping, activated sludge and struvite precipitation. All treatment schemes provided comparable COD and ammonia removals, all being around 90%. The treatment schemes incorporating the acidic air stripping, however, was found to be the most advantageous in terms of both efficiency and volume and aeration requirements of the activated sludge process since over 80% COD could be removed in the stripping step. Of the fourth and fifth alternative schemes, the fourth was the most efficient, providing 95% removal of both COD and ammonia. Initial dilution of the leachate at a 1:5 ratio was the least effective one, yielding 90% or lower removals for COD and ammonia. The first scheme, namely application of struvite precipitation to raw leachate followed by activated sludge with or without dilution, proved to be a practical system, providing over 85% COD and 99% ammonia removals. High organic loading up to 0.8 g COD/g VSS day was found to be applicable within this scheme.     

Trends in the use of Fenton,electro-Fenton and photo-Fenton for the treatment of landfill leachate

Advanced oxidation processes (AOPs) such as Fenton, electro-Fenton and photo-Fenton have been applied effectively to remove refractory organics from landfill leachate. The Fenton reaction is based on the addition of hydrogen peroxide to the wastewater or leachate in the presence of ferrous salt as a catalyst. The use of this technique has proved to be one of the best compromises for landfill leachate treatment because of its environmental and economical advantages. Fenton process has been used successfully to mineralize wide range of organic constituents present in landfill leachate particularly those recalcitrant to biological degradation. The present study reviews the use of Fenton and related processes in terms of their increased application to landfill leachate. The effects of various operating parameters and their optimum ranges for maximum COD and color removal are reviewed with the conclusion that the Fenton and related processes are effective and competitive with other technologies for degradation of both raw and pre-treated landfill leachate.     

Impacts of temperature and liquid/solid ratio on anaerobic degradation of municipal solid waste: an emission investigation of landfill simulation reactors

Management of landfill emissions, i.e., landfill gas (LFG) and landfill leachate, is an important and resource-intensive task. A long-term demonstration pilot, consisting of landfill simulation reactors (LSRs), was used to study the impact of temperature and the applied liquid/solid ratio (L/S ratio) on landfill emissions, characteristics, and trends. This pilot has already run for more than 1000 days since the end of 2004 and will continue to run for some time. The degradation of waste at different temperatures has impacts on the overall degradation degree and on the length of post-closure care required. Higher temperatures accelerated the degradation, but also resulted in higher leachate chemical oxygen demand (COD) and ammonia concentrations, which prolong the aftercare period. Meanwhile, at a given stabilization degree [e.g., 70 l gas/kg waste (dry)], the total leached nitrogen under psychrophilic conditions was 3.5 times that under mesophilic/thermophilic conditions, which resulted in a higher required effort for leachate treatment. The impact of L/S ratio or simulated annual L/S rates was also evaluated. The results show the significance of efficiently obtaining the targeted L/S ratio in order to achieve low landfill emission potential.     

Characterization and tropical seasonal variation of leachate: Results from landfill lysimeter studied

This study aims to characterize the leachate and to investigate the tropical climatic influence on leachate characteristics of lysimeter studies under different seasonal variations at KUET campus, Bangladesh. Three different situations of landfill were considered here as well as both the open dump lysimeter-A having a base liner and sanitary landfill lysimeter-B and C at two different types of cap liner were simulated. The leachate characteristics, leachate generation and climatic influence parameter had been continually monitored since June 2008 to May 2010, these periods cover both the dry and rainy season. The leachate generation had followed the rainfall pattern and the open dump lysimeter-A without top cover was recorded to have highest leachate generation. Moreover, the open dump lysimeter-A had lower total kjeldahl nitrogen (TKN), ammonia nitrogen (NH(4)-N) and TKN load, while both the COD concentration and load was higher compared with sanitary landfill lysimeter-B and C. In addition, sanitary landfill lysimeter-B, not only had lowest leachate generation, but also produces reasonable low COD concentration and load compared with open dump lysimeter-A. Result reveals that lysimeter operational mode had direct effect on leachate quality. Finally, it can be concluded that the knowledge of leachate quality will be useful in planning and providing remedial measures of proper liner system in sanitary landfill design and leachate treatment.