Study of Municipal Landfill Leachate: Recycling and. Treatment Using UASBR with post treatment by. Constructed Wetland. Submitted by: Rajesh Kumar Taneja.
SYNOPSIS
Study of Municipal Landfill Leachate: Recycling and Treatment Using UASBR with post treatment by Constructed Wetland Submitted by:
Rajesh Kumar Taneja (2005AMZ8133)
in fulfillment of the requirements of the degree of DOCTOR OF PHILOSPHY
AK Raghav Department of Applied Mechanics
AK Mittal Department of Civil Engineering
Department of Applied Mechanics Indian Institute of Technology Delhi New Delhi 110016 Jan. 2011
1.0 Introduction Delhi, with its urban and semi-urban population of 13.6 million (Census, 2001), is estimated to generate about 7000 tonnes of waste every day. As the amount of waste produced rapidly increases, space for permanent disposal becomes crucial. Since the production of solid waste is increasing much more rapidly than it degrades, land space for disposal has become more difficult and expensive to attain. There are several waste management options that can be used to reduce the amounts of waste requiring land disposal. Incineration of solid waste can be used but this is expensive and the emissions are of health concern. This is why landfills remain the major solid waste disposal option for most countries. All the collected solid waste is disposed off in lowlying areas at the landfill sites following conventional ways of dumping. Since the 1950s, over 12 large landfill sites have been packed with all sorts of non-biodegradable and toxic wastes. At present, there are three landfill sites – Bhalaswa, Gazipur, and Okhla. None of their bases is lined resulting in continuous groundwater contamination.
The waste dumped consists of mainly domestic garbage and inert materials. There is no proper leachate collection and treatment arrangement at the aforesaid sites and the leachate generated at these sites mostly percolate down the ground surface in absence of proper lining and the excess quantity of leachate gets collected in some low lying areas and some quantity of leachate also comes out of the premises of landfill and flows on the roads or into the nearby storm water drain which is a very dangerous situation from environment point of view. Leachate generated from the landfill site is highly toxic and responsible for the contamination of surrounding area, surface water and ground water. Solid waste in a landfill is degraded through aerobic and anaerobic processes. Stabilization of the wastes is a very complex and variable event due to the site-specific characteristics of each landfill. The degradation products generated from the stabilization process include leachate and gas. Landfill gas is generated due to the anaerobic biological degradation of organic material. Leachate is formed from the contact of water with refuse. The water, mainly from precipitation, dissolves soluble organics and inorganics including some toxic compounds if present in the landfill material. A leachate stream can be compared to a complex wastewater stream with varying characteristics. Leachate characteristics not only vary because of the different kinds of 1 | P a g e
waste present, but also vary according to the landfill age. Usually leachate from old landfills is rich in ammonia nitrogen due to the hydrolysis and fermentation of the nitrogenous fractions of the biodegradable wastes (Onay, 1998). Leachate from young landfills contains high dissolved solids content as well as high concentrations of organic matter compared to domestic wastewater (Reinhart, 1998). In present scenario the collection and treatment of the leachate is urgently required to avoid any possible future environmental hazards. A need is now being felt to take appropriate remedial actions to avoid further contamination of the environment. Landfill leachate in India has no systematic arrangement for its treatment causing serious risk of contamination of surface and underground water resources around the landfill. A number of processes including chemical, physico-chemical, advance oxidation, and biological have been reported in the literature. Both carbon and nitrogen content of leachate are high. Besides, it contains heavy metals, and recalcitrant organics. Recirculation of leachate may reduce organic content of the leachate to some extent. Anaerobic biological process based upon Upflow Anaerobic Sludge Slanket Reactor (UASBR) has been reported to treat leachate. India has largest number UASBR installations. However, these UASBRs in India are installed to treat domestic wastewater. But, this technology has been well stabilized and assimilated in the Indian system. So, UASBR seems to a viable solution under Indian conditions. Leachate treated by using UASB reactor is reported to reduce COD, but compliance with local environmental standards may not be met with UASBR based treatment. Therefore, there is need of some post-treatment. Identifying the nature of this treated effluent and current need and requirement to adopt an integrated sustainable approach towards this aspect, it was felt important to study and investigate an integrated treatment approach to give a wholesome treatment to landfill leachate. This combination may offer a sustainable technological solution and wastewater management strategy involving anaerobic and aerobic processes, particularly in developing countries having tropical climatic conditions like India.
This synopsis presents the summary of the research and outlines of the thesis. Topics that are discussed in detail in the thesis are briefly presented here. Other aspects of the research work like 2 | P a g e
monitoring, experimental data, graphs, figures, values, photographs, etc. are also given in the thesis. 2 Aim and Objectives of the Study
The aim of this study was to assess the suitability and applicability of recirculation of leachate, treating recirculated leachate by UASBR in combination with constructed wetland under ambient condition. Scope of the study are as follows: I.
Design and construction of the leachate re-circulation and treatment system at the Okhala landfill site and at the Environmental Engineering laboratory, Indian Institute of Technology Delhi (IITD).
II.
Rericulation of the collected leachate using different protocols through the recirculation column located at the Okhla landfill site.
III.
Use of the sewage from Okhla Sewage Treatment Plant (STP) to mix it with the leachate before treatment using UASBR at Okhla landfill and IITD.
IV.
Treating the diluted leacahte (leachate mixed with domestic sewage) using UASBR.
V.
Analysis of raw and single pass leachate for the various parameters like COD, pH, alkalinity, and heavy metals.
VI.
To study the efficacy of constructed wetland to polish the UASBR effluent
VII.
Efflect of type of vegetation and media characteristics on the treatability of UASB effluent.
3 Approach and Methodology The work was carried out at pilot scale level at Oklha landfill site and laboratory scale at the IITD. Pilot plant consisted of combination of landfill recirculation column and UASB reactor. One UASBR was operated at the IIT campus. One each recirculation column and UASB reactor were designed, fabricated and installed at Okhla landfill site, which is located in south Delhi. Raw municipal sewage was brought from Okhla sewage treatment plant, It was mixed with landfill leachate . For recirculation studies , fresh leachate collected from the Okhla landfill site was used. The effluent from the
UASBR at IIT campus was treated using three constructed
wetlands. Typha, cattail and phragmitis which are easily available in the study region were identified and used in the laboratory scale constructed wetlands. Influent and effluent samples were collected from each UASB reactor as per the monitoring schedule over a period of about 348 days. The parameters investigated during this study were mainly COD, pH and alkalinity 3 | P a g e
and heavy metals. All the analyses were carried out in accordance with the Standard Methods for Examination of Water and Wastewater (APHA, AWWA, 1992) in the Environmental Engineering Laboratory of IIT Delhi. Atomic Absorption Spectrophotometer was used for heavy metal analysis for fresh and multi-pass leachate through recirculation column in samples of influent and effluent from UASBR. Statistical analysis was performed using MINITAB Release 15 for Windows and included analysis of variance (ANOVA) and Paired-t test. Box plot for influent and
effluent
concentrations, percentile curves and time scale graphs were also plotted using this statistical tool.
4 Perspective and Significance of the Work There has been continuous increase in population leading to increase in waste generation and leachateproduction in indian cities .It has emerged as challenging task for community to mange it. The daily waste generation in city like Delhi is ranging from 6600 to 7500 tonnes. Due to lack of engineered landfill within city, the conventional way (open dumping) of solid waste disposal is still practiced making the scenario worse. These dumps generate the leachate, a highly dangerous and toxic liquid substance. Landfill leachate is a complex wastewater with considerable variation in both quality and quantity. In general, leachate is highly contaminated with organic contaminants measured chemical oxygen demand (COD) and biochemical oxygen demand (BOD), and also with high ammonium nitrogen concentration. Biological processes have been found ineffective for leachate from relatively old landfill. The monthly production of leachate in Delhi has been estimated to be 81.5 m3 (Kumar & Allapat, 2003). Actual production may be more than this which is not properly estimated. There is no treatment facility in place for leachate in Delhi. Recirculation is an attractive alternative for landfill operation as it is an inexpensive and offers the advantage of faster stabilization of waste in the landfill (Reinhart, 1996, Li et. al. 2004). This study investigates a integrated leachate treatment process using leachate recirculation and Upflow Anaerobic Sludge Blanket Reactor (UASBR) and subsequent post treatment by constructed wetland to meet the desired criteria for the disposal of the leachate from Okhla, New Delhi.
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5 Organization of the Thesis The thesis consists of five chapters including the Introduction, Chapter 1. This chapter gives the background information, description of the research objectives, scope of work, approach and methodology, perspective and significance of this study. Chapter 2 covers literature review on subjects of this study. This chapter gives detailed review of literature pertaining to this study. The materials and methods are described in Chapter 3, results and discussions in chapter 4, and finally the outcome of this research (conclusions) is given in Chapter 5. The list of references is provided at the end of thesis.
2.0 Literature Review A comprehensive review of the following aspects relevant to this study was carried out and a critical discussion is presented in the chapter on literature review of the thesis. However, some selected and brief description of this review is presented here. − Recirculation of landfill leachate − Factors affecting the leachate characteristics in landfill -
Leachate treatment by UASBR
-
Post-Treatment Issues after UASBR
− Use of constructed wetland for leachate treatment -
Role of Vegetation in Treatment Wetlands
− Performance of CWs for post treatment of leachate
2.1 Recirculation of landfill leachate During the recirculation the leachate is returned to a lined landfill for re-infiltration into the MSW. Many researchers (Lee et al, 2001) have reported leachate recirculation to enhance stabilization of fermentable organics in MSW. The rate of methane generation is controlled by the amount of moisture present in the waste. In the classical sanitary landfill where no attempt is made to restrict enhance of moisture, landfill gas formation typically takes place 30-50 years. If additional moisture is added to the waste the rate of methane formation increases. The process also benefits the landfill by increasing the moisture content there by increases the biological degradation in landfill, the biological stability and the rate of the methane recovery from the
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landfill. They reported that gas production essentially ceased when the percent moisture in waste is less than about 20% .The rate of gas production increased with moisture content up to the maximum moisture content evaluated about 60%.
2.3 Post-Treatment Issues after UASBR
UASB reactor is a well accepted anaerobic reactor type for treatment of sewage as well as low and high strength industrial wastewaters (Tare et al., 2003; Puspendu and Ghangrekar, 2008). In spite of their advantages, a review of literature suggests that UASB reactors have frequently not functioned efficiently for the removal of solids and organic materials (A´lvarez et al., 2008). Therefore, the effluents from UASB reactors usually require post-treatment as a means to adapt the treated effluent to the requirements of the environmental legislation and protect the receiving water bodies (Chernicharo, 2006). Unlike in conjunction with conventional systems, CWs have not been used at full scale with UASB to further polish the effluents. Some results from full-scale UASB with different post-treatment (except CWs) options are summarized in Table 1. Table 1: Average Effluent Quality from various UASB Post-Treatment Technologies Average Effluent Quality System
BOD
COD
TSS
Total
Nh3
Total P
>20
>4
FC
N >15
106-107
UASB Reactor
70-100
180-270
60-100
UASB +Activated Sludge
20-50
60-150
20-40
>20
>4
106-107
20-50
60-150
20-40
>20
>4
106-107
UASB +Trickling Filter
20-60
70-180
20-40
>15
>20
>4
106-107
UASB +Anaerobic Filter
40-80
100-200
30-60
>15
>20
>4
106-107
Process UASB +Submerged Aerated Biofilter
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UASB +Dissolved Air
>20
106-107
20-50
60-100
>20
UASB +Polishing Pond
40-70
100-180
50-80
15-20
15
>4
104-106
Floatation
(Source: Chernicharo, 2006 )
All parameters in mg/L except FC in MPN/100ml
2.4 Role of vegetation and treatment mechanism in CWs
CWs are one of the most conspicuous features of wetlands as it has several properties in relation to the treatment processes that make them an essential component of the wetland system. The role of vegetation is probably to act as “ecological engineers” (Edwards et al., 1993; Tanner, 2001). Brisson and Chazarenc (2008) states that Macrophytes provide a large surface area for attached microbial growth and supply reduced carbon and oxygen in the rhizosphere. They decrease current velocity, stabilize the surface of the bed, and insulate the surface against frost in winter. Plants in wetlands provides additional media where microorganisms can attach, help keep aerobic conditions at the bottom of the bed by transferring oxygen through their roots and rhizome systems, and control the growth of algae by restricting sunlight penetration (Abbas et al., 2003; Bezbaruah and Zhang, 2004).
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Figure 3.1 Schematic representation of mechanisms treatment by vegetation in CWs 3.0 MATERIALS & METHODS 3.1 Landfill site In Delhi, at present there are 3 active sanitary waste disposal sites viz: Gazipur, Bhalswa and Okhala, The field experimental set up has been installed at Okhla landfill site, which is situated about 10 Km north from the IIT Delhi. Okhla landfill is spread over an area of 56 acre out of which approximately 41 acre is filled up and remaining 15 acre is vacant land. This landfill is in operation since 1994. Waste fill height varies from 8 to 25 m. At this landfill, ground water table is 15 m below the ground level (Kumar and Alappat, 2003). The waste at this site consists of mainly domestic garbage and inert material comprising of demolition waste. There is no proper leachate collection and treatment arrangement at the aforesaid site. Leachate mostly percolates down the ground surface (in absence of proper lining) and the excess quantity gets collected in low lying areas. Sometimes, it also gets mixed up with the sewer and drainage systems. The final cover system consists of a layer of soil. The condition of landfill becomes worse in monsoon season.
3.2 Experimental set up at Okhla Landfill site Experimental set-up (Fig. 1) consists of a recirculation column and UASB Reactor. The UASB Reactor used in this study is made up of UV stabilized Linear Low Density Polyethylene (LLDPE). Reactor volume is 177.1 L with an internal diameter 23.75 cm, and a height as 100 cm. Three evenly distributed sampling ports are installed at 15, 55, and 65cm from the bottom sieve of the reactor. The port at 15 cm is also used for the purpose of removal of excess sludge. These sampling ports are plugged with valve to facilitate withdrawal of sample. The top portion of the reactor acts as gas liquid separator, with an internal diameter of 1.08 m and a height of 80 cm. One port is provided in this portion at a distance of 45 cm from the top. This port is connected with long tube to discharge the effluent in nearby drain. Leachate is diluted using domestic sewage obtained from the Okhala Sewage Treatment Plant, and is kept in separate container (500L LLDPE tank). The influent to the reactor is fed through a Peristaltic pump (Scientific India LTD). Bottom of the reactor is conical in shape. It has a 8 | P a g e
perforated sheet (1.5 mm thick having 2.0 mm size perforations) so as to distribute the flow evenly throughout the section of the reactor. The entire unit is erected above the ground level by iron stand having three legs, which are fixed on ground level with bolt and concrete. The recirculation column is also made up of UV stabilized Linear Low Density Polyethylene (LLDEP). The total height of the recirculation column is 2.6 m. It consists of two sieves of 1.0 m diameter. The lower sieve is of 6 mm thickness having perforations of 10 mm diameter. The upper sieve is of 3 mm thick having 5 mm diameter perforations. Distance between these two sieves is 1.17 m. This column is packed with the MSW in three layers having different densities. The bottom part of the recirculation column is conical in shape to facilitate the collection of the recirculated leachate. Its capacity is of 265 L. The volume of the top portion of the column above the upper sieve is 300 L, which could be used to store the leachate. 3.3 Excavation and characteristics of MSW from Landfill MSW was excavated in the month of December 2008 from Okhla landfill using an excavator from different depths and recirculation column was packed with this MSW in layers. Around 850 kg of waste was packed in the recirculation column. Waste was characterized for its physical composition. It was also analyzed for the heavy metal content. Characterization of the MSW was carried out by first drying the excavated MSW naturally in the laboratory. The larger non-biodegradable materials such as stones, glass bottles, plastic films (bags), rubber, etc were removed and weighed. For analysis, the finer fractions were broken into small pieces by hammer, ball mill, and grinder if necessary, until the particles were smaller than 2 mm. On occasion, large wooden pieces (such as used furniture) could be found in the samples in initial period after the MSW was placed. In this case, the wood was removed before weighing and drying. Culling of large wooden pieces was considered to be acceptable because they may be rarely encountered. 3.4 Simulated Landfill Reactor Loading Simulated landfill reactor (Fig. 1) was filled with nearly 850 kg of waste. Waste mainly comprises of biodegradable materials and household waste. For the better simulation, waste was taken from different depths having different densities. Re-circulation column was compacted 9 | P a g e
with in three layers with the help of hand rammer, each layer was separated by 3 cm thick soil layer. Density of waste in column was kept similar to the one in actual landfill, i.e., the densities of upper, middle and lower layers were 500Kg/m3, 700Kg/m3 and 900Kg/m3 respectively.
0. 0.0
0.37 m
1. 0.
^^ ^^ ^^
0.
0.
0.
0.
500 L Sintex
0.
2.
1 0.
1.75 m
0. 0.
1
1
0.
2
0.0
0.
0. 0.375 m
1
500
0.
2
1
Masonry Structure
or
0.
0.
2
0.02‐
2
0.
1. 2. 3. 4. 5. 6.
Leachate Container – 20 L glass bottle Pumps Re‐circulation Column – HDPE / Steel Bucket – 50 L Sewage Tank – (Sintex) – 500 L Mixing Chamber – 500 L (Bucket / Masonry Structure)
Fig. 3.2 Proposed setup for recirculation column and UASBR
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A
C
D
B
E
F
G
H
Figure 3.3 Schematic line diagram for integrated leachate treatment IIT campus (A. feed tank [raw leachate + municipal sewage] B. UASBR C. Water displacement bottle D. Water collection unit E. UASBR effluent feed for constructed wetland F. CWR unit-I G. CWR unit-II H. CWR unit-III)
3.5 Organic loading rate (OLR) After the first activity of start-up of the UASBR units, the reactors were stabilized using sucrose as substrate to increase the microbial activity inside the reactor. After the stabilization of reactors, organic loading rate (OLR) was observed from 0.50-0.67 Kg/m3/d during July to
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November at Okhla site and 0.75-3.0 Kg/m3/d was maintained in laboratory reactor at IIT Delhi during the entire study period of the reactor by varying the HRT from 48 h to 12 h. 3.6 Sampling and Analysis
UASBR were run from March 2009 to March 2010. After two months of continuous operation of the system, sampling was done on regular basis. However, data from the first period (one month after commissioning) have not been incorporated into result analysis as they do not truly reflect wetlands performance as that period represents the settling-in phase. Sampling ports provided in the beds were used for sample collection. Most of the time samples were collected between 9:30 - 11:30 hours. These samples after preservation were taken to the Environmental Engineering Laboratory, IIT Delhi in the ice box for further analysis. Samples were mostly analyzed the same day in the laboratory but for some of the parameters, it was done next day. However these samples were stored and preserved in accordance with guidelines prescribed in the Standard Methods for Water and Wastewater Examination (APHA, AWWA, 1989). The parameters monitored during this study were mainly COD, pH, alkalinity, VFA and heavy metals. 4.0 Results and Discussion 4.1 Waste characterization 4.1.1 Moisture Content of Landfill Refuge
Moisture content of landfill refuge is important parameter for the waste stabilization. For determination of moisture content wastes were collected from the different depth and a definite amount was taken randomly for analysis. After weighing, waste was kept for drying in oven till constant weight has been achieved. The moisture content at every depth was averaged to get final moisture content of landfill refuge. It was 30 to 35 %, which reveals that Indian wastes are high in moisture content, which makes it bulky, but transportation is very easy. 4.1.2 Composition of MSW The content of solid waste were analyzed by weight and were found to be 30.36% moisture content, 12% plastic films, bags, bottles and other products, 44% organic matter such as wood,
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and cooking wastes and about 34% inorganic matter such as stone, sand, coal ashes, and glass bottles. 4.1.3
Heavy metals analysis of MSW
The digested sample of the MSW was analyzed for the heavy metal content. Cd and Co could not be detected (Table 4.1). Table: 4.1 Heavy metals present in MSW Site
Zn
Mn
Cu
Ni
Okhla
0.066
0.030
0.550
0.096
Pb
Cr
Cd
0.0083
0.0044
Co
ND
ND
Landfill All concentrations are given in mg/g.(av. Values) 4.2 Leachate Characteristics of Okhla Landfill Heyer and Stegmann (1998) have reported the heavy metal content of the leachate. It is evident from Table 4.2 that all the heavy metals are quite high, which makes leachate from the Okhala landfill much polluted as compared to the leachate from other landfills. It warrants further investigations. Table: 4.2 Leachate characteristics of raw leachate Parameter
Heyer and Heyer and Stegmann Stegmann (1998), Site 1 (1998), Site 2
Present Study, Okhla Landfill
pH
7.5‐9.0
7.0‐8.3
7.29‐8.46
Alkalinity
‐
‐
13,220‐19578
COD
500‐4500
460‐8300
38,011‐54400
TDS
‐
‐
7200‐7400
TSS
‐
‐
23,000‐23400
TS
‐
‐
30,000‐31000
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NH3 – N
30‐3000
17‐1650
912‐992
TKN
40‐3425
250‐2000
2,715‐2952
Na
50‐4000
1‐6800
2,500‐2900
K
10‐2500
170‐1750
2,275‐2670
Ca
20‐600
50‐1100
8,908‐9592
Zn
0.1‐120
0.09‐3.5
1.5483
Mn
‐
‐
0.3647
Cu
0.004‐0.14
0.005‐0.56
0.5700
Cr
0.3‐1.6
0.002‐0.52
2.0881
Pb
0.008‐1.02
0.008‐0.40
0.2114
Ni
0.02‐2.05
0.01‐1.0
0.4672
All parameters are in mg/l except pH 4.3 Characteristics of Raw Sewage Used The raw sewage used for the dilution of leachate was collected from the Okhla Sewage Treatment Plant. The raw sewage was transported to the proposed unit by mechanical means. Sewage was collected after it passes through the screening unit. Raw sewage was allowed to settle before mixing with the leachate. Sewage was filtered through a fine cotton cloth so as to remove the fine suspended impurities. The average characteristics of raw sewage are given in Table 4.3. Average COD of sewage is 300mg/l which shows a medium strength wastewater.
Table: 4.3 Characteristics of raw sewage from Okhla STP Parameters
pH Total BOD5 COD TKN NH3- TS N Alkalinity
Concentration 7.4
400
200
300
60
35
1000
TSS TDS PO4-- Cl300
700
3.25
210
All concentration in mg/L except pH 14 | P a g e
4.4 Recirculation of leachate The recirculation column after compacting with solid waste was covered with 5 mm thick sieve. Leachate was applied (spreading technique) over the surface of the sieve manually. Leachate was poured over the sieve from nearby leachate collection system, which is an open area, so dilution of leachate varied due to mixing with the rain water. Leachate started coming out from the column first time after four days. Nearly 150 L leachate was applied for the first loading of the recirculation column. 4.5
Characteristics of leachate after single pass
In this study, leachate was introduced in recirculation column by simple pouring technique. Daily, approximately 20 L of leachate was poured in the recirculation column, which was collected from the leachate collection pond. The characteristics of leachate after one pass are given in table 4.5. Figure 4.1 presents the characteristics of the leachate before and after passing through
pH
it
the
10 9.5 9 8.5 8 7.5 7 6.5 6 5.5 5
re-circulation
pH fresh Leachate
0
10
20
Time,d
column.
pH One pass Leachate
30
40
Fig.4.1 Variation in pH of fresh and single pass leachate through RC
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mg/L
60000 55000 50000 45000 40000 35000 30000 25000 20000 15000 10000 5000 0
COD In(Fresh) COD Out(One pass)
0
10
20
30
40
TIME,d
Fig.4.2 Variation in COD of fresh and single pass leachate through Recirculation Column 6 A
7 E 5
3 D 2
1
4 B
2
2
C
2
Fig.4.3 Line diagram of recirculation and UASBR units installed at Okhla landfill 1. Leachate container
A. Sampling of Raw Leachate
2. Pump
B. Sampling of single pass Leachate
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3. Recirculating column
C. Sampling of Raw Domestic sewage
4. Mixing chamber (leachate and sewage)
D. Sampling of combined Influent
5. UASB Reactor
E. Sampling of treated effluent
6. Gas collection 7. Effluent disposal
4.6 Effect of recirculation on the heavy metal content
Fe (mg/L)
It is evident from the characteristics of the leachate that it contains Fe, Cu, Cr, Cd, Ni, Zn, Pb and Mn. Accordingly, heavy metals were determined before and after passing the leachate through the recirculation column. Heavy metal content decreased after recirculating the leachate, but it was varied. Figure 4.4 presents variation for Fe.
90 80 70 60 50 40 30 20 10 0 -10 0
Fresh Single Pass
5
10
15
20
25
30
Time (d)
Fig.4.4 Variation in Fe at Okhla landfill through Recirculation Column
4.6 Effect of recirculation on the heavy metal content: multi pass study Once recirculated leachate was repeatedly passed through the recirculation column. Data for the concentration of a number of heavy metals after each pass was collected. It is observed that heavy metal content does not follow any specific pattern. Results are discussed in detail in the thesis.
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4.7
Performance of the UASBR at Okhla
4.7.1 Temperature UASBR at Okhla is installed for operation under ambient temperature conditions. Variations in minimum and maximum temperatures show that it varied between 26.3 to 40.0 oC. Minimum temperature variation shown is 15 to 24.7 oC. The difference in maximum and minimum temperature is ranging between 11.3 to 15.3 oC 4.7.2
Organic Loading Rate
Organic load at the Okhla site UASB varied as per the organic strength of the leachate since the reactor was operated under ambient and field conditions. Organic strength of the sewage which was brought from the Okhla STP was also varied. COD removal was studied over a period of 180 days. Figure 4.5.
mg/L
6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0
COD In
0
50
100
Time, d
150
Fig.4.5 Variation in COD removal by the UASBR.at Okhla
4.8 Performance of the UASBR at IIT laboratory UASBR was operated at HRTs of 18 h, 24 h, 36 h, 48 h and 72 h. Volume of the UASBR was 36.5 L, having a height and diameter as 1.84 m and 15.90 cm respectively. Accordingly, upflow velocity in the reactor varied from 0.026 to 0.105 m/h. Performance was measured in terms of COD removal, VFA, pH and alkalinity. COD removal efficiency was measured using both fresh 18 | P a g e
and single pass leachate. With the use of single pass leachate, there was no appreciable change in COD removal efficiency. However, in absolute terms, total COD loading reduced substantially which will affect overall reactor size. Figure 4.6 presents COD removal for 36 h HRT. Detailed analysis for different HRTs shall be presented in the thesis. 3000 COD In
COD Out
2500
COD (mg/L)
2000 1500 1000 500 0 0
5
10
15
20
25
30 35 Time, d
40
45
50
55
60
Fig. 4.6 COD removal during start of UASBR at IIT at 24 h HRT
Alkalinity and pH were continually measured. Figs. 4.7 and 4.8 presents the variation of alkalinity and pH
Alkalinity (mg/L)
2500 2000 1500 1000 500 Alkalinity In
0 147
152
157
162 Time,Days
167
172
177
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Fig. 4.7 Alkalinity changes at UASBR (IITD) at an HRT of 32h.
8.4
pH In
8.2
pH Out
mg/L
8 7.8 7.6 7.4 7.2 7 147
152
157
162 Time, d
167
172
177
Fig. 4.8 pH variation at UASBR IIT at an HRT of 48 h. Effect of HRT on the COD removal was not very clear. Figure 4.9 presents the effect of HRT on the COD removal. 105.00 85.00
Acclimatization period
COD Removal (%)
65.00 45.00 25.00 36 L/d
5.00 -15.00 0
36
72
108
72 L/d
144
36 L/d
180
24 L/d
216
252
18 L/d
288
324
360
-35.00 -55.00
Time, d
Fig. 4.9 Effect of HRT on COD Removal Efficiency 4.9 Polishing of the UASBR treated effluent using Constructed Wetlands (CWs)
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Literature is available on the treatment of leachate by constructed wetlands (Vymazal, 2009). Size of these wetlands varied from 40 to 3600 m2. There is no study available from India where landfills are more of a dump containing MSW with greatly varying characteristics. Besides, no study has reported the use of constructed wetlands for the polishing of UASBR treated leachate. In the present study effect of HRT and type of plants, i.e. Typha, Phragmites and Canna. Results indicate that constructed wetlands could further polish the UASBR effluents. Performance of wetlands got affected during winter season. It shows the need to have a mix species of plants so that constructed wetland remains in operation throughout the year.
Conclusions In the present study, integrated comprehensive treatment of the leachate using leachate recycle, UASBR and constructed wetland has been studied. Following are the major findings of this study. 1. The pilot plant at the Okhla landfill site was successfully operated for over one year. It established the handling of varied leachate characteristics under field conditions. 2. A number of heavy metals like Pb, Cu, Cr, Zn, and Ni are present in municipal solid waste (MSW) at the Okhla site. Concentration of iron was the highest. Though, Cd and Co were below the detection limit. 3. The leachate at the Okhla Landfill is quite hazardous in nature. It is high in COD, Ammonia-N, with many heavy metals present in it. Notable heavy metals are Fe, Pb, Cu, Cr and Ni. 4. There is a potential of recirculating the leachate through the landfill which can result in substantial decrease in COD of the leachate. Recycling of leachate can bring down the organic load on the subsequent biological processes. However, no added advantage is obtained by increasing the number of cycles beyond 2. 5. UASBR is quite effective (85% -89%) in removing COD. 6
Recirculation did not improve the biodegradability of the leachate.
7. Trends of heavy metal removal by cyclic loading were obtained. 8. Constructed wetland could further remove COD by 30-50% 21 | P a g e
9. Hydraulics of wetlands plays important role in its efficiency. Improved inlet structure of a wetland could improve its efficiency. 10. Recirculation, UASBR and constructed wetland can be an effective alternative to treat the leachate.
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REFERENCES 1. Alvarez J.A., I. Ruı´z, M. Soto, 2008, “Anaerobic digesters as a pretreatment for constructed wetlands” Ecological Engineering, Vol.33. pp.54-67.
2. APHA, 1998, “Standard Methods for the examination of water and waste water, 20th ed., American Public Health Association, Washington. 3. Abbas Al-Omari and Manar Fayyad, 2003, “Treatment of domestic wastewater by subsurface flow Constructed wetlands in Jordan” Desalination, Vol.155. pp.27-39.
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6. Census 2001, “Census of Delhi 2001 Report”, Delhi Government, 2001 7. Chernicharo C. A. L. (2006) “Post-treatment options for the anaerobic treatment of domestic wastewater” Environmental Science and Bio-Technology, 5:73–92 pp. 335-343.
8. Debra, R. Reinhart, 1996, “Full-Scale Experiences With Leachate Recirculating Landfills: Case Studies”, Waste Management, 14, 347-365. 9. Debra, R. R. and Al-Yousfi, A. B., 1996, “The Impact of Leachate Recirculation on Municipal Solid Waste Landfill Operating Characteristics.” Waste Management. 14, 337346. 10. Edwards M E, Brinkmann K C and Watson J. T., 1993, “Growth of Soft-Stem Bulrush (Scirpus) plants in a gravel based sub-surface flow Constructed wetlands”. In: CWs for Water Quality Improvements. G A Moshiri Ed Lewis Publishers Boca Raton USA pp.415-425.
11. Heyer, K. U., and Stegmann, R. E. H. J., “Leachate Management: Generation, Collection, Treatment and Costs.” International Seminar. "Present and Future of MSW Landfilling", 24.-26. June 1998, Cittadella, Italia, Proceedings Edizioni Euro Waste. 12. Kumar D. and Alapatt, B. J., 2003, “A technique to quantify Landfill Leachate pollution” Ninth International Waste management and Labdfill Symposium, Cagliary, Italy.
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13. Lee, Kang-Kun, Suk, Heejun, Choi Sang-il, Lee, Chol Hyo, Chung, and sang-Young. (2001). “Numerical evaluation of Landfill stabilization by Leachate recirculation.” J. of Env. Engg. Vol.127 No.6, pp.555-563. 14. Onay T. T and Pohland F.G., 1998, “In Situ Nitrogen Mangament in controlled Boireactors landfills”, Wat. Res. No.5, pp.1383-1392. 15. Puspendu B, M.M. Ghangrekar (2008) “Analysis, evaluation, and optimization of kinetic parameters for performance appraisal and design of UASB reactors” Bioresource Technology, 99 pp.2132–2140.
16. Tanner, C. C., 2001, “Plants as ecosystem engineers in subsurface-flow treatment wetlands” Water Science & Technology, 44 (11-12), pp.9-17. 17. Tare, Vinod, Gupta, S. and Bose, Purnendu, 2003, “Case Studies on Biological Treatment of Tannery Effluents in India” Air and Waste Management Association, Vol.53, pp.976-982.
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Publications
Rajesh Taneja, Manish Kumar, Raghav A. K. and Mittal, Atul K (2009). On Site Integrated Landfill Leachate Treatment: Recirculation and Upflow Anaerobic Sludge Blanket Reactor (UASBR), Chemical, Biological and Environmental Engineering: Proceedings of the International Conference on Cbee 2009, Ed. Li Kai, World Scientific Publishing, Singapore, pp 163‐166.
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