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Application of Response Surface Methodology (RSM) for Optimization of Semi-Aerobic Landfill Leachate Treatment Using Ozone

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... The major reason could be that during the adsorption reaction, the adsorption sites remain unsaturated, whereas increasing the adsorbent dosage increases the number of sites available for adsorption. The agglomeration of the adsorbent can also be a reason for the lack of increase in phenol removal capacity at the high concentrations of the adsorbent (Salem et al. 2014). This means that the higher values of phenol adsorption are obtained by increase in the pH. ...
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Background Optimization of adsorption processes using statistical methods of experiment for the removal of pollutants from wastewater, in an effort to curb the global problem of water pollution, is increasingly being adopted because it is cost-effective and time-saving. In most cases, standard central composite designs (CCDs) are often employed for the optimization processes, where the experimental variables are often randomized completely. However, most experiments especially within the industries often involve factors with some hard-to-change (HTC) levels and some with easy-to-change (ETC) levels, in which case the HTC factor cannot be completely randomized, and this challenge can only be overcome by the use of a split-plot CCD. However, there is scarcity of literature on the use of split-plot CCD for the optimization of adsorption processes, and hence in this study, the prime conditions for the removal of phenol onto BiFeO 3 from synthetic wastewater were studied. The effect of three adsorption variables (pH, adsorbent dosage, and shaking time) was investigated using split-plot CCD. pH was considered as the HTC factor due to the amount of time, acid and/or base required to change it, while the adsorbent dosage and contact time were the ETC factors. Quadratic model was developed for the phenol percentage removal. Results The optimum adsorption conditions obtained from the study were adsorbent dosage of 0.60 g, pH of 7 as well as contact time of 167 min with desirability of 1. The predicted and experimental values obtained were 89.73 and 89.21%, showing good agreement between the experimental value and those predicted by the quadratic model. Langmuir isotherm model was found to be the best fit for the equilibrium adsorption data giving rise to monolayer adsorption capacity of 106.50 mg/g. The pseudo-second-order kinetic model’s correlation coefficient ( R ² ) was higher than that of the pseudo-second-order kinetic suggesting the applicability of the model to the adsorption of phenol. Conclusions The synthesized BiFeO 3 could be considered as a viable alternative to the expensive commercial activated carbon for the removal of phenols in wastewater, and the use of split-plot CCD model makes the experiment much easier to run and save time and/or cost due to fewer number of runs and restriction in the randomization of HTC factors.
... Nevertheless, leachate generated from old landfill site is more complex as compared to that generated from new landfill site as it is practically impossible to be effectively treated via biological processes (Abu Amr et al., 2013; Mohajeri et al., 2010). Various methods, such as precipitation, adsorption, oxidation, evaporation, reverse osmosis and ion exchange have been exercised to remove diverse pollutants originated from old landfill leachate (Bashir et al., 2012Bashir et al., , 2013 Abu Amr et al., 2014). Adsorption process is one of the most effective methods used for the treatment of broad range of wastewaters (Halim et al., 2012; Bashir et al., 2014; Azmi et al., 2015). ...
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The removal of nitrate from a mature landfill leachate with high nitrate load in a lab-scale anoxic rotating biological contactor (RBC) was studied. Under a phosphorus-phosphate concentration of 10 mg P-PO43− L−1 and nitrogen-nitrate concentrations above 530 mg N-NO3− L−1 the reactor achieved nitrogen-nitrate removal efficiencies close to 100%, without nitrite or nitrous oxide accumulation. Although the reactor presented a very good denitrification performance, the effluent carbon concentration was still above the legal discharge value. In order to increase the biodegradability of the leachate recalcitrant carbon load, a pre-ozonation was further investigated. The pre-ozonation led to a total organic carbon (TOC) removal of 28%. The sequence of treatments, leachate ozonation followed by RBC denitrification did not affect the denitrification efficiency. In fact, it was possible to attain a denitrification rate of 123 mg N-NO3− L−1 h−1. The moderate decrease in the carbon load of the final effluent indicated that some recalcitrant compounds were still present after ozonation. The anoxic RBC showed to be a promising technology for removing nitrate from landfill leachate.
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The performance of a multilayer tungsten carbide tool was described using response surface methodology (RSM) when turning AISI 1045 steel. Cutting tests were performed with constant depth of cut and under dry cutting conditions. The factors investigated were cutting speed, feed and the side cutting edge angle (SCEA) of the cutting edge. The main cutting force, i.e. the tangential force and surface roughness were the response variables investigated. The experimental plan was based on the face centred, central composite design (CCD). The experimental results indicate that the proposed mathematical models suggested could adequately describe the performance indicators within the limits of the factors that are being investigated. The feed is the most significant factor that influences the surface roughness and the tangential force. However, there are other factors that provide secondary contributions to the performance indicators. In the case of surface roughness, the SCEA2 and the interaction of feed and SCEA provides these contributions whilst for tangential force, the SCEA2, the interaction of feed and SCEA; and the cutting speed provides them.
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Municipal solid waste (MSW) landfills worldwide are experiencing the consequences of conventional landfilling techniques, whereby anaerobic conditions are created within the landfilled waste. Under anaerobic conditions within a landfill site slow stabilization of the waste mass occurs, producing methane, (an explosive ‘green house’ gas) and leachate (which can pollute groundwater) over long periods of time. As a potential solution, it was demonstrated that the aerobic degradation of MSW within a landfill can significantly increase the rate of waste decomposition and settlement, decrease the methane production and leachate leaving the system, and potentially increase the operational life of the site. Readily integrated into the existing landfill infrastructure, this approach can safely and cost-effectively convert a MSW landfill from anaerobic to aerobic degradation processes, thereby effectively composting much of the organic portions (one of the potentially polluting elements in a conventional landfill site) of the waste. This paper summarizes the successful results of two separate aerobic landfill projects located in Georgia (USA) and discusses the potential, economic and environmental impacts to worldwide solid waste management practices.
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The literature has been critically reviewed in order to assess the attenuation processes governing contaminants in leachate affected aquifers. Attenuation here refers to dilution, sorption, ion exchange, precipitation, redox reactions and degradation processes. With respect to contaminants, focus is on dissolved organic matter, xenobiotic organic compounds, inorganic macrocomponents as anions and cations, and heavy metals. Laboratory as well as field investigations are included. This review is an up-date of an earlier comprehensive review. The review shows that most leachate contamination plumes are relatively narrow and do not in terms of width exceed the width of the landfill. The concept of redox zones being present in the plume has been confirmed by the reported composition of the leachate contaminated groundwater at several landfills and constitutes an important framework for understanding the behavior of the contaminants in the plume as the leachate migrates away from the landfill. Diverse microbial communities have been identified in leachate plumes and are believed to be responsible for the redox processes. Dissolved organic C in the leachate, although it appears to be only slowly degradable when the volatile organic acids are gone, apparently acts as substrate for the microbial redox processes. Several xenobiotic organic compounds have been found to be degradable in leachate contaminated groundwater, but degradation rates under anaerobic redox conditions have only been determined in a few cases. Apparently, observations in actual plumes indicate more extensive degradation than has been documented in the laboratory. The behavior of cations in leachate plumes is strongly influenced by exchange with the sediment, although the sediment often is very coarse and sandy. Ammonium seems to be subject to anaerobic oxidation, but the mechanisms are not yet understood. Heavy metals do not seem to constitute a significant pollution problem at landfills, partly because the heavy metal concentrations in the leachate often are low, and partly because of strong attenuation by sorption and precipitation. Although complexation of heavy metals with dissolved organic matter is significant, the heavy metals are in most cases still strongly attenuated in leachate-polluted aquifers. The information available on attenuation processes has increased dramatically during the last 15 a, but the number of well-documented full scale leachate plumes are still few and primarily from sandy aquifers. Thus, the diversity of attenuation processes in leachate plumes is probably not yet fully understood. Apparently, the attenuation processes in leachate plumes may for many contaminants provide significant natural remediation, limiting the effects of the leachate on the groundwater to an area usually not exceeding 1000 m from the landfill.
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Two new applications for sequence treatment of mature (stabilized) landfill leachate, that is, cationic resin followed by anionic resin (cationic/anionic) and anionic resin followed by cationic resin (anionic/cationic), are employed and documented for the first time in the literature. Response surface methodology (RSM) concerning central composite design (CCD) is used to optimize each treatment process, as well as evaluate the individual and interactive effects of operational cationic resin dosage and anionic resin dosage on the effectiveness of each application in terms of color, chemical oxygen demand (COD), and NH(3)-N removal efficiency. A statistically significant model for color, COD, and NH(3)-N removal was obtained with high coefficient of determination values (R(2)>0.8). Under optimum operational conditions, the removal efficiency levels for color, COD, and NH(3)-N are 96.8%, 87.9%, and 93.8% via cationic/anionic sequence, and 91.6%, 72.3%, and 92.5% via anionic/cationic sequence, respectively. The experimental results and the model predictions agree well with each other.
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Municipal landfill leachate is a high strength wastewater characterized by high concentrations of organics and ammonia and potentially containing toxic materials. The paper reports the results of a laboratory scale investigation aimed at evaluating the effectiveness of mature municipal landfill leachate treatment by a biological stage (used SBBR as a biological treatment) to study the nitrogen removal capabilities for treatment of sanitary landfill leachate containing high ammonia concentration. The monitored sample taken from the Chang Sheng bridge landfill site in Chongqing city-China, has its concentrations of COD, BOD5 and NH3-N about 1650, 75 and 1100 mg Lˉ1 respectively. The results showed that after two months long period of domestication and one month period of stability, the ammonia nitrogen removal efficiency reached to 99% in the SBBR reactor, at nitrogen loading rate 0.51 kg TN mˉ3 per day and HRT was 9 hrs, met to Chinese standards for discharge.
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An assessment of potential methods suitable for degradation and/or reduction of refractory organics was performed on landfill leachate from SYSAV AB, Malmö, Sweden. Pretreatment of the leachate was performed in a sequence batch reactor designed for nitrification in activated sludge. Oxidation of the leachate was then O3, O3/pH adjustment (pH 9 and 10), H2O2, O3/H2O2 and performic acid in lab-scale reactors. The degradation of organic material was followed with chemical oxygen demand (COD) measurements for all experiments except for the performic acid treatment for which total organic carbon (TOC) measurements were used. The potential degradation of refractory organics into biodegradable organic material was analysed by subsequent oxygen uptake rate (OUR) measurements in laboratory batch reactors. Ozonation of biologically pre-treated leachate increased reduction of the organic material. The most biodegradable organic material was produced after oxidation with only ozone and ozonation at pH 9. Performic acid did not reduce the content of organic material in the leachate. However, a combination of biological pretreatment, chemical oxidation with O3/H2O2 and a subsequent biological process resulted in the most efficient oxidation method for the tested leachate.
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A two case study of industrial wastewater treatment is reported in order to prove the suitability of ozonation for biorefractory COD removal. The ozone application as an end treatment is shown to provide an excellent oxidation yield of organic matter in a landfill leachate. The combination of ozonation and fixed bed biofilm process appears quite effective for the post-treatment of two biological effluents from paper industry.
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Landfill leachate is a complex wastewater which the composition and concentration of contaminants are influenced by the type of waste deposited and the age of landfill. In the last years, several processes or process combinations were developed and tested to reach requirements for the discharge of leachate. Among the new processes, membrane processes are considered as promising: reverse osmosis is one of the most widely used treatment in the Northwestern European countries and nanofiltration is gained in popularity during the last 5 years. Successful application of membrane technology for the treatment of landfill leachates, requires efficient control of membrane fouling. Two organic membranes of nanofiltration were used for pilot-scale testing. Leachates were subject to several pretreatments (pH modification, prefiltration and coagulation with FeCl3) to remove potential foulants including dissolved organic and inorganic substances, colloidal and suspended particles. These pretreatments do not enhance the performances (retention and permeation flux) of membranes because the pH range and the presence of Fe3+ ions contribute greatly to change the characteristics of organic matter and the surface charges of membranes. However, the results show that nanofiltration is sufficient to eliminate refractory COD, the permeates have a COD lower than the requirements for discharge.
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Biological treatment is widely preferred by many landfill owners to remove the bulk of the pollutants in leachate. Specific problems due to toxicity and nutrient deficiencies are however frequently reported. This study investigates the possibility of pre-treating leachate to decrease its toxicity and increase its biodegradability, using ozonation. Lab-scale and pilot testing has shown that nitrification toxicity was minimised by ozone pre-treatment. A decrease of the COD/BOD-ratio from 16 to 6 was achieved, making the pre-treated leachate co-treatable in municipal sewage treatment. The operational cost for the pre-treatment was estimated at 1.34 Euro/kg COD.
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Ozone has been used as a pre-oxidation step for the treatment of stabilized leachates. Given the refractory nature of this type of effluents, the conversion of some wastewater quality parameters has been moderate after 1 h of ozonation (i.e. 30% chemical oxygen demand (COD) depletion). Ozone uptake was calculated in the interval 1.3-1.5 g of ozone per gram of COD degraded. An optimum dose of ozone has been experienced in terms of biodegradability of the processed effluent (60 min of treatment, 1 x 10(-3) mol L(-1) ozone inlet feeding concentration and 50 L h(-1) gas flow-rate). pH and other typical hydroxyl radical generator systems exerted no influence on the efficiency of the process, suggesting the negligible role played by the indirect route of oxidation (generation of hydroxyl radicals). The ozonated effluent was thereafter treated in a second adsorption stage by using a commercial activated carbon. Removal levels up to 90% of COD in approximately 120 h were experienced for adsorbent dosages of 30 g L(-1). Both steps, the single ozonation and the adsorption stage have been modelled by using different pseudoempirical models.
Article
In this study, laboratory experiments are conducted to compare the efficacy using several ozone-based advanced oxidation processes (AOPs), such as O3, O3/H2O2, and O3/UV, to treat landfill leachate. Raw leachate was initially coagulated by ferric chloride (FeCl3) at the experimental-determined optimal dosage of 900 mgl(-1), and the ozone-based AOPs were subsequently applied. Results indicate that all AOPs would result in a significant increase on the ratio of BOD5/COD from 0.06 to 0.5 at the applied ozone dosage of 1.2 gl(-1). The increase on biodegradability for ozonated leachate indicates that these AOPs would be beneficial to the subsequent biological treatment process. To better explain the alteration of high organic molecules after oxidation, ultrafiltration was used to separate the leachate by several molecular weight cutoffs (MWCO). The COD distribution for coagulated leachate is 34% for MWCO>10 kDa, 7% for MWCO between 5 and 10 kDa, 22% for MWCO between 1 and 5 kDa, and 37% for MWCO<1 kDa. Following ozonation or AOPs, the predominant distribution of COD would be obviously shifted to the MWCO less than 1000 gmol(-1) (72-85%) over the other MWCO ranges. In addition, Gel Permeation Chromatograph (GPC) analysis has showed a substantial agreement on the cleavage of larger organic compounds into smaller ones. O3/UV was found to be the most effective approach among these ozone-based AOPs to enhancing the biodegradability and eliminating the color of leachate.
Article
In this work, activated carbons (ACs) were modified by ozone treatment to enhance the efficiency of removal of ammonia gas over the ACs. Surface properties of the ACs were confirmed by X-ray photoelectron spectroscopy (XPS) analysis and N2 adsorption isotherms at 77 K were investigated by BET and D-A methods to characterize the specific surface area, total pore volume, and micropore volume. The ammonia removal efficiency was confirmed by the gas-detecting tube technique. The results showed that the specific surface area and micropore volume of ACs were slightly destroyed as the ozone treatment time increased. However, the ozone treatment led to an increase in ammonia removal efficiency of ACs, mainly due to an increase of acid functional groups, such as carbonyl and ether groups, on carbon surfaces. It was revealed that the improvement of ammonia removal efficiency of ACs was greatly affected by the interfacial acid-base interactions between modified ACs and basic ammonia adsorbate.
Article
A study was conducted to investigate the efficiency of coagulation and flocculation processes for removing colour from a semi-aerobic landfill leachate from one of the landfill sites in Malaysia. Four types of coagulant namely aluminium (III) sulphate (alum), ferric (III) chloride, ferrous (II) sulphate and ferric (III) sulphate were studied using standard jar test apparatus. Results indicated that ferric chloride was superior to the other coagulants and removed 94% of colour at an optimum dose of 800 mg/l at pH 4. The effect of coagulant dosages on colour removal showed similar trend as for COD, turbidity and suspended solids. This suggested that colour in landfill leachate was mainly contributed by organic matters with some insoluble forms that exhibited turbidity and suspended solids readings. The results from this study suggested that ferric chloride could be a viable coagulant in managing colour problems associated with landfill leachate.
Article
In the search for an efficient and economical method to treat a leachate generated from a controlled municipal solid waste landfill site (Jebel Chakir) in the region of greater Tunis in Tunisia, ozone alone and ozone combined with hydrogen peroxide were studied. The leachate was characterised by high COD, low biodegradability and intense dark colour. A purpose-built reactor, to avoid foaming, was used for the study. It was found that ozone efficacy was almost doubled when combined with hydrogen peroxide at 2g/L but higher H(2)O(2) concentrations gave lower performances. Enhancement in the leachate biodegradability from about 0.1 to about 0.7 was achieved by the O(3)/H(2)O(2) system. Insignificant changes in pH that may due to buffering effect of bicarbonate was found. A small decrease in sulphate concentrations were also observed. In contrast, chloride concentration declined at the beginning of the experiment then increased to reach its initial value. Estimates of the operating costs were made for comparison purposes and it was found that the O(3)/H(2)O(2) system at 2g/L H(2)O(2) gave the lowest cost of about 3.1TND( approximately 2.3USD)/kgCOD removed.
New treatment of stabilized leachate by ozone/ Fenton in the advanced oxidation process
  • Abu Amr
  • S S Aziz
Abu Amr SS, Aziz HA (2012) New treatment of stabilized leachate by ozone/ Fenton in the advanced oxidation process. Waste Manag. doi:10. 1016/ j. wasman. 2012. 04. 009
Experience with landfill leachate treatment in Germany
  • S U Geissen
Geissen SU (2005) Experience with landfill leachate treatment in Germany. In: Workshop on landfill leachate: state of the art and new opportunities, INRST, Borj Cedria, Tunis, Tunisia
Oxidation of aged raw landfill leachate with O3 only and O3/H2O2 and molecular size distribution analysis
  • F Wang
  • D W Smith
  • M G El-Din
Wang F, Smith DW, El-Din MG (2003) Oxidation of aged raw landfill leachate with O3 only and O3/H2O2 and molecular size distribution analysis. In: Proceedings of the 16th World Congress of the International Ozone Association, IOA, Las Vegas, USA, pp 1-21
Priority pollutants: a perspective view
  • L H Keith
  • W A Teliard