Scholarly article on topic 'Comparison of Photo ElectroFenton Process(PEF) and combination of PEF Process and Membrane Bioreactor in the treatment of Landfill Leachate'

Comparison of Photo ElectroFenton Process(PEF) and combination of PEF Process and Membrane Bioreactor in the treatment of Landfill Leachate Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — T.K. Nivya, T. Minimol Pieus

Abstract Landfill leachate treatment is an integral part of municipal solid waste management. The conventional biological treatment of landfill leachate is limited because of the presence of toxic contaminants and recalcitrant organics. Among Advanced Oxidation processes(AOPs), Photo Electro Fenton Process(PEF) can be used effectively for the treatment of highly contaminated water. In the treatment of leachate by biological methods, Membrane Bioreactor(MBR) is efficient while considering the effluent quality. So a combination of PEF followed by MBR treatment is adopted in this study. The percentage removal of pollutants -TSS, BOD,COD, Ammonia Nitrogen, Phosphate, Sulphate, Sulphide and Chloride from landfill leachate after PEF process is 89.3,71.9,83.6,100,58,92.3,65 and 65 respectively. The percentage removal of the same pollutant parameters after combined treatment of PEF followed by MBR is 95.5,90.2,96.2,100,82.7,93.3,88.2 and 88.3. The pollutant removal efficiency is increased by adopting combined treatment –PEF followed by MBR.

Academic research paper on topic "Comparison of Photo ElectroFenton Process(PEF) and combination of PEF Process and Membrane Bioreactor in the treatment of Landfill Leachate"

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Procedía Technology 24 (2016)224 -231

Procedía

Technology

Comparison of Photo ElectroFenton Process(PEF) and combination of PEF Process and Membrane Bioreactor in the treatment of Landfill Leachate

Nivya T Ka, Minimol Pieus Tb

aPG Student, Dept. of Civil Engineering, GEC Thrissur,680009, India bAssociate Professor, Dept. of Civil Engineering, GEC Thrissur, 680009, India

Abstract

Landfill leachate treatment is an integral part of municipal solid waste management. The conventional biological treatment of landfill leachate is limited because of the presence of toxic contaminants and recalcitrant organics. Among Advanced Oxidation processes(AOPs), Photo Electro Fenton Process(PEF) can be used effectively for the treatment of highly contaminated water. In the treatment of leachate by biological methods, Membrane Bioreactor(MBR) is efficient while considering the effluent quality. So a combination of PEF followed by MBR treatment is adopted in this study.The percentage removal of pollutants -TSS, BOD,COD, Ammonia Nitrogen, Phosphate, Sulphate, Sulphide and Chloride from landfill leachate after PEF process is 89.3,71.9,83.6,100,58,92.3,65 and 65 respectively. The percentage removal of the same pollutant parameters after combined treatment of PEF followed by MBR is 95.5,90.2,96.2,100,82.7,93.3,88.2 and 88.3. The pollutant removal efficiency is increased by adopting combined treatment -PEF followed by MBR.

© 2016 The Authors.Publishedby ElsevierLtd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICETEST - 2015

Keywords: Landfill leachate Advanced Oxidation Processes; Photo Electro Fenton process, ;Membrane Bio Reactor.

1. Introduction

Municipal solid waste keeps growing as a result of increasingly wealthy lifestyles and continuing industrial and commercial development in many countries around the world. Landfilling method is the most frequently employed worldwide of all available dumping options under the solid waste management

* Corresponding author. Tel.:0 9447731946 E-mail address:tk.nivya@gmail.com

2212-0173 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICETEST - 2015 doi:10.1016/j.protcy.2016.05.030

system. Leachate gereration is a major problem for for municipal solid waste(MSW) landfills.

Treatment of landfill leachate has become a main concern in managing the environmental impact due to landfill. Leachate may contain large amounts of organic matter (Biodegradable and refractory to Biodegradation). It also contains ammonia nitrogen, heavy metals, chlorinated organic and inorganic salts. The landfill leachate characteristics can be represented by parameters such as COD , BOD, the ratio of BOD / COD, pH, Suspended solids (SS) and ammonium nitrogen (NH3-N) [1,2]. The landfill leachate can be treated in two ways - Biological or Physicochemical methods . As age of leachate increases, it matures and non bio-degradable or recalcitrant substances become predominant. Conventional biological treatment methods are inadequate in the case of matured landfill leac hates.. They cannot completely remove all pollutants in the leachate . After biodegradation leachate contains pollutants such as heavy metals and some persistent organic compounds. Advanced Oxidation Processes (AOPs) are promising methods to treat effectively the recalcitrant substances present in landfill leachate [ 3]. 1.1.Advanced OxidatioProcesses(AOPs)

Advanced Oxidation Processes (AOPs) are successfully used as pretreatment method for reducing concentration of toxic organic compounds in wastewater . In AOPs toxic organic contaminants oxidizes primarily by reacting with hydroxyl radicals. During AOPs oxidation occurs in two stages - (1) the formation of strong oxidants (hydroxyl radicals) which are highly reactive and (2) the reaction of these oxidants with organic contaminants in water. Hydroxyl radicals (»OH) are effective in destroying organic chemicals because they are reactive electrophiles (electron preferring) that react rapidly and non selectively with nearly all electron-rich organic compounds. Once generated, the hydroxyl radicals can attack organic chemicals by radical addition, hydrogen abstraction and electron transfer. Thus AOPs are effective in decomposing many toxic and bio-resistant organic pollutants without producing additional hazardous by-products or sludge which requires further handling. Many methods are classified under the broad definition of AOPs. Most of these methods utilize a combination of strong oxidizing agents (e.g H2O2, O3) with catalysts (e.g. transition metal ions) and irradiation (e.g. ultraviolet, visible). Fenton's reactions are considered to be the most popular technologies for wastewater treatment.

Fenton's reagent is a mixture of ferrous iron FeSO4.7H2O (Catalyst) & hydrogen peroxide (H2O2 ) (oxidising agent). The oxidation power of »OH radical (produced from hydrogen peroxide by adding Fe2+ as catalyst) is better on certain organic contaminants. When it is necessary to remove recalcitrant compounds , Fenton process is frequently used because of its simplicity. Fenton process can oxidize and mineralize almost all the organic carbons to CO2 & H2O. The reactions that takes place during Fenton process can be expressed as given below.

Fe2+ + H2O2 ^ Fe3+ + OH- +»OH (1)

Fe2+ + »OH ^ Fe3+ + »OH (2)

•OH + RH ^ H2O + R» (3)

R» + Fe3+ ^ R+ + Fe2+ (4)

Fenton reaction can be efficiently enhanced in photoelectro assisted Fenton process.The reason being Fe may form complex with certain target compounds or byproducts, produced by UVA light and current. During photo-reduction and reduction in the cathode the ferric complexes reduce to ferrous ion .This assist in efficient Fenton chain reaction [4].Fenton pre treatment of landfill leachate will improve biological treatability

1.2 Electro Fenton Process (EF)

Electrically assisted Fenton reaction is called Electro Fenton process The more OH» radicals produced will enhance the oxidation of the organics to CO2 . There are two different methods in Electro-Fenton(EF) process - 1) the Fe 2+ and H2O2 are added to the reactor from outside and inert electrodes having high catalytic activity are used as anode material. 2) H2O2 is added from outside and Fe2+ is provided from sacrificial cast iron anodes. EF method has the advantage of allowing a better control of hydroxyl radical production. In electro-fenton process, soluble Fe3+ can be cathodically reduced to Fe2+. The fast generation of Fe2+ accelerates the production of »OH.The mechanism of EF process is represented in equations as below [6]. At anode:

Fe (s) ^ Fe2+ (aq) +2e- (5) Fe2+ (aq) + 2 OH- (aq) ^ Fe(OH)2

At cathode: (6)

H2O (l) + 2e- ^ H2(g) + 2OH-(aq) (7) Overall:

Fe (s) + 2 H2O (l) ^ Fe(OH)2 + H2(g) (8)

Higher electro regeneration of ferrous ion from ferric ion with increasing current increases the efficiency of EF process.

1.3. Photo Electro Fenton Process (PEF)

The degradation of organic compounds is accelerated when EF process is irradiated by means of ultraviolet light. The ferric complexes reduce to ferrous ion by photo-reduction and by reduction in the cathode. Fe3+ ions generated are photo chemically transformed to Fe2+ ions. When the system is irradiated with UVA light (X = 320-400 nm), Fe2+ ions generation is improved. In PEF process, the acceleration of degradation of organic compounds occurs by two principal pathways: a) the photolysis of Fe3+ -oxidation products complexes, and b) improving the Fe2+ regeneration from the photoreduction of Fe3+ ions according to the equation [ 7]. Fe(OH)2+ + hu ^ Fe2+ + «OH (9)

1.4. Membrane Bioreactor (MBR)

When the leachate is young, the membrane bioreactors can be effectively used as a treatment method. MBR consists of a combination of conventional activated sludge (CAS) system and advanced membrane separation system. It enables independent control of sludge retention time (SRT) and hydraulic retention time (HRT). It also retains a high concentration of sludge biomass in the reactors. Compared with CAS processes, the advantages of MBR process are - 1)It has a smaller footprint 2) less sludge production 3) better effluent quality 4) can be operated at very long sludge ages and 5) can extend greatly in the field of application of biological processes for concentrated streams, such as leachate. The combination of membrane separation technology and bioreactors has led to a new focus on wastewater treatment [8]. 2. Materials and method

. The landfill leachate samples were collected from Municipal Solid Waste Disposal Facility at

Brahmapuram, Kochi. The various parameters (BOD, COD, chloride, sulphide, sulphate, phosphate, TSS, Ammonium nitrogen) were anlaysed as per standard procedure. The characteristics of original sample obtained are given in Table 1. The BOD/COD ratio of original sample is 0.18.

Table 1 Characteristics of original sample

Parameter Concentration

pH 6.0- 8 .1

TDS (mg/L) 11020 -32760

TSS (mg/L) 110 - 498

COD (mg/L) 19800 - 24000

BOD (mg/L) 4250 - 5100

Sulphate (mg/L) 446 - 2597

Phosphate (mg/L) 184.8 8 - 268

Sulphide (mg/L) 4.75- 186

Chloride (mg/L) 2660 - 6700

Ammonia nitrogen (mg/L) 1530 - 4000

Leachate characteristics showed daily and seasonal variations. So for the experimental studies conducted, synthetic waste water (SWW) was used. SWW was prepared based on the physico-chemical parameters obtained for the original sample. The composition of synthetic sample was obtained by trial & error method so that reasonable match with the original leachate sample could be obtained. The chemicals used for the preparation of synthetic wastewater is given in Table 2. The chemicals are added in to one litre of distilled water and mixed well.

Table 2 Composition of synthetic sample

Chemicals Added Quantity (g)

Ammonium chloride 1.7

Sodium sulphide 0.3

Sodium chloride 0.75

Calcium carbonate 0.095

Dipotassium hydrogen 0.2

ortho phosphate

Ferrous sulphate 0.054

Magnesium sulphate 0.06

D- Glucose 30

The charactreistics of synthetic wastewater is given in Table 3. The BOD/COD ratio of synthetic sample is 0.19.

Table 3 Characteristics of Synthetic Sample

Parameters Concentration

pH 8.08

TDS(mg/L) 3160

TSS(mg/L) 112

COD(mg/L) 23200

BOD(mg/L) 4630

Sulphate (mg/L) 510

Phosphate(mg/L) 181

Sulphide(mg/L) 20.8

Chloride(mg/L) 2601

Ammonia 2196

Nitrogen(mg/L)

2.1. Photo Electro- Fenton (PEF) Process

The reactor used for photo electro- fenton (PEF) process was a 1000ml borosil glass beaker. 800 ml synthetic leachate sample was used for batch studies. The reaction mixture was continuously stirred by a magnetic stirrer. Experiments were carried out at room temperature. The cast iron electrodes (12 cm x 6.5 cm x 0.1 cm) were placed vertically inside the reactor. The distance between two electrodes was fixed 2.5 cm. The cast iron plates acted as the source of Fe2+ ions also. The connections were made. The EF reactor was irradiated with UV light with 8W capacity. It was placed top of the glass beaker. It was covered with aluminium foil. The UV lamp was turned on. Reaction mixture is continuously stirred by a magnetic stirrer. The reaction mixture had H2O2 dosage 57.6 % ,the current density 140.5 A/m2 ,reaction time 45 min. and pH 2.9. After 45 minutes treated samples were allowed to settle for 2 hours and the supernatant was used for analysing the parameters.Fig.1 shows the experimental setup of PEF process.

Fig. 1 Photo Electro Fenton process(UV light) experimental setup

2.2 Membrane Bio Reactor

A acrylic container of 6L capacity was used as the Bioreactor and membrane arrangement was used for the evaluation of external membrane bioreactor. The reactor of size 28.5cm x 15.1cm x15.1cm was made of acrylic sheet. The reactor was supplied with oxygen by aerator. The membrane arrangement consists of hollow fibre membrane module having pore size of 0.1 ^m, pump and DC adapter were connected in series (Fig.2). This is provided for enhancing treatment efficiency. In the running of reactor aeration rate of 5L/min was provided .

2.3 Combination of PEFfollowed by MBR

The SWW is primarily treated by PEF process .The effluent after PEF process is collected and added in to the bioreactor (3L)

Fig.2 Hollow fiber Membrane arrangement Fig. 3 Bioreactor

which contains 1L of biosludge. After 6 days of HRT the supernatant from the bioreactor is collected in a collection beaker after the settling process. Then it is passed through hollow fibre membrane module and the effluent is collected and analysed.

Bio-sludge collected from sedimentation tank of MILMA DAIRY Ramavarmapuram was used as the inoculums for the bioreactor systems after being acclimatized with leachate for 1 month. External membrane bioreactor(Fig.3) consists of bioreactor and membrane filtration. The reactor was operated in batch mode. Bioreactor is the reactor which was filled with 1 L sludge and 3L of synthetic waste water. Aeration is provided from the bottom of the reactor. After the reaction time, the mixed liquor was allowed to settle. The supernatant from the bioreactor was transferred into a collection beaker and passed through the hollow fibre membrane module using a pump. The treated effluent was collected and analysed.This process was repeated for different HRTs. The optimum HRT is selected by analysing the pollutant removal efficiency of MBR arrangement in different HRTs. The HRT obtained was 6 days.

3. Results and discussions

3.1. Treatment of Synthetic Wastewater by Photo Electro Fenton Process

EF reactor was irradiated with UV light.The effluent is analysed and result is given in Table 4. In PEF method, H2O2 in presence of Fe2+ as catalyst (EF conditions) and UV irradiation of the solution, mineralizes the pollutants[9]. The action of this irradiation is complex and can be described by: (a) the increase in the production of hydroxyl radical from photoreduction of Fe(OH)2+ and (b) the predominant Fe3+ species in acid medium and the photolysis of complexes of Fe(III) with generated carboxylic acids. Biodegradability in terms of BOD/COD ratio of synthetic wastewater improved to 0.34. The pollutant removal efficiency of EF process is increased by irradiating the EF reactor by using UV light.The biodegradability of the landfill leachate is increased after AOP treatment. So the effluent is treated biologically using MBR. In this study the BOD/COD ratio obtained after PEF treatment is between 0.3 and 0.6. Therefore seeding is required for biological treatment [10].

3.2. MBR Treatment of Pretreated Synthetic wastewater

The SWW is pretreated by PEF process and the effluent is treated using MBR with an optimum HRT of 6days.The results are tabulated in Table 4. In Biological nitrification ammonia is converted to nitrite (NO2) and then to nitrate (NO3) by oxic process. After this anoxic denitrification takes place in which nitrogen is removed from wastewater by reducing nitrate to nitrogen gas (N2). Table 4 Percentage removal of Synthetic wastewater after PEF treatment and PEF followed by MBR

Initial After PEF % Final

Parameter characteristics treatment Removal effluent % Total

of synthetic after PEF characteristic Removal remova

wastewater treatment followed by by MBR %

(mg/L) MBR) mg/L

TSS 112 12 89.3 5 62 95.5

BOD 4630 1300 71.9 455 65 90.2

COD 23200 3800 83.6 880 76.7 96.2

Phosphate 181 BDL 100 BDL 100 100

Sulphate 510 215 58 88 59 82.7

Sulphide 20.8 1.6 92.3 1.4 60.1 93.3

Chloride 2601 910 65 307 66.3 88.2

Ammonia Nitrogen 2196 559 65 257 54 88.3

While considering the performance of biological nitrogen removal, nitrification is generally a rate-limiting step .This is due to the low growth rate and poor cell Yield of nitrifying bacteria. For nitrification to occur, it is important that the net rate of accumulation of biomass (and hence the net rate of withdrawal of biomass from the system) should be less than the growth rate of nitrifying bacteria. MBR is a highly viable wastewater treatment technology regarding nitrification-denitrification.

PERCENTAGE REMOVAL Vs WASTEWATER PARAMETERS FOR SYNTHETIC WASTEWATER AFTER PEF AND PEF FOLLOWED BY MBR

inn inn

TSS BOD COD AmmoniaPhosphate Sulphate Sulphide Chloride Nitrogen PARAMETERS ■ AFTER PEF AFTER PEF FOLLOWED BY MBR

Fig. 4 Comparison of PEF and PEF followed by MBR treatment of Synthetic wastewater High Biomass concentration in combination with filtration effect increases the actual concentration of substrate in the bioreactor. This in effect increases their bioavailability, and therefore biodegradation is accelerated. The permeate quality is improved due to implementation of a biological stage [11]. At low F/M ration and high sludge age,the MBR performance is explained by the presence of dispersed bacteria that are advantageous in the overall population competition. Flocs in a bioreactor were found to be smaller which can be explain by enhanced mass transfer for both oxygen and carbon. This increases the removal rate and more adaptability to changes in the influent quality and quantity.

4.Conclusion

Percentage pollutant removal efficiencies of synthetic landfill leachate pollutants -TSS,BOD,COD,Ammonia Nitrogen, Phosphate, Sulphate, Sulphide and Chloride are 89.3,71.9,83.6,65,100,58,92.3 and 65 in PEF process. The biodegradability in terms of BOD/COD ratio of synthetic wastewater is increased from 0.19 to 0.34. So the effluent is biologically treated using MBR. After MBR treatment the percentage removal efficiencies of pollutants- TSS ,BOD,COD, Ammonia Nitrogen, Phosphate, Sulphate, Sulphide and Chloride are increased to 95.5, 90.2, 96.2,88.3, 100, 82.7, 93.3 and 88.2. From this study it is proved that in the case of landfill leachate treatment, by utilizing MBR as a post treatment after PEF increased the pollutant removal efficiency.

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