The suitability of the substrates to carry out denitrification was assessed based on the carbon content and the ratio of carbon to nitrogen in the substrate. 100 Table 4.3-15: Output characterization results of cell 2 + CGRraw + batch test with treated leachate at different times.
INTRODUCTION
- Motivation
- Research Question(s)
- Aims & Objectives
- Methodological Approach
- Thesis Layout
The purpose of the study is to determine the viability of pretreated general waste at different degrees of stability (8 and 16 weeks composted) as a carbon source for in-situ bio-denitrification in landfills. At the end of the chapter, a case study of the Bisasar Road landfill is presented.
LITERATURE REVIEW
Chapter Overview
Landfilling
- D EFINITION OF LANDFILLING
- L ANDFILL WASTE DISPOSAL MANAGEMENT
- L ANDFILL DECOMPOSITION STAGES
Enzymatic catalysis quickly/accelerates the hydrolysis process, this is done by the oxygen in the waste (landfill mass) causing the breakdown/decomposition of the organic matter/waste via a process called aerobic biological processes (Pisano, 2007) and this process provides stable hydrocarbons, heat, carbon dioxide and water (Hester & Harrison, 2003). The aerobic decomposition and hydrolysis, which is the first stage of waste decomposition, uses up all the oxygen present in the waste mass and anaerobic condition is created.
Landfill Leachate
- D EFINITION OF LANDFILL LEACHATE
- L EACHATE CHARACTERISTICS
- L EACHATE P RODUCTION
- L EACHATE COMPOSITION AND Q UALITY
- F ACTORS AFFECTING THE LEACHATE COMPOSITION
The level of decomposition in which the landfill is located can be determined by the age of the landfill. The concentration of leachate can be influenced by the way the landfill is designed and managed.
Methods of Landfill Leachate Treatment
- P HYSICO - CHEMICAL T REATMENT M ETHOD
- Leachate transfer (Channeling)
- B IOLOGICAL T REATMENT M ETHOD
- Wetlands
- Suspended growth process
According to Ceçen et al. 2004) this method can reduce the treatment efficiency and increase the concentration in the wastewater. A number of mechanisms can be used to remove organic nitrogen contained in suspended solids.
Nitrogen Cycle
- O VERVIEW ON NITROGEN
- F IXATION OF N ITROGEN GAS
Nitrogen input to landfills can also be through precipitation or surface runoff from agricultural land. According to Harrison (2003), when nitrogen is added to organic matter, it can be converted back to the inorganic state by decay.
Nitrification and Denitrification
- N ITRIFICATION
- Microbiology
- Factors influencing nitrification
- D ENITRIFICATION
- Factors influencing denitrification
For the process of denitrification to occur, heterotrophic bacteria require a carbon source which will act as food to live (Metcalf & Eddy, 2003). The following organisms are necessary for the denitrification process to occur diazotrophic, phototrophic, organotrophic and lithotrophic. Oxygen availability: Dissolved oxygen prevents the enzymes required for electron transfer, but acts as a strong inhibitor in the denitrification process (Karnaros and Hyberatos, 1998).
An increase in pH is expected during the denitrification process, but the extent of the increase depends on the buffering capacity of the wastewater (Christensen and Harremoes, 1997, cited in Nadioo, 1999). Organic carbon substrate: The availability of organic carbon (biodegradable substrates) strongly influences the rate of denitrification.
B IOLOGICAL D ENITRIFICATION P ROCESS AND T ECHNOLOGY
- Attached growth process
Temperature: Temperature is an important factor in the denitrification process as researchers have found that the denitrification rate doubles to triples with a 10-30oC increase in soil temperature. The denitrification rate is optimal at a temperature between 28-60oC, but in thermophic conditions (50-60oC) the nitrate removal rate is approximately 50% greater than that under mesophilic conditions of 35oC (Henze et al, 1997). In general, a temperature increase of up to 50-60oC increases the denitrification rate; any further increase above 60oC reduces the denitrification rate (Abufayed and Schroeder, 1986).
However, in a pH range of 6.0 and 8.0, denitrification rates are high and an optimal denitrification rate is reached at a pH of 7.5 (Plug et al, 2010). The selection of the treatment process is based on many factors such as the age of the drain, installation and operating cost, including the requirement for qualified personnel.
Case Study
As the truck enters the landfill, it is weighed by waste and is also weighed upon departure so that the weight of waste entering the landfill can be monitored. According to Trois et al, 2010a, the SBR must treat up to 50m3 of leachate daily. The operational treatment of leachate at Mariannhill is as follows, the raw leachate is fed into the SBR tank where it is treated for ammonia-nitrogen after treatment is achieved. The treated waste water from the SBR is led into the balance tank.
The cell number, the type of waste entered in each cell and the waste volume including the waste mass are shown in the table. Treated leachate was collected from the SBR balance tank at the Mariannhill landfill in Durban. The treatment of the leachate was carried out using small-scale batch tests.
METHODOLOGY AND MATERIALS
Introduction
Materials
- S UBSTRATES
Fresh Commercial Garden Refuse (CGRraw) and Commercial Garden Refuse (CGR10) The Fresh Commercial Garden Refuse (CGRraw) consists of organic deposits mainly from branches and plant clippings from parks and green municipal areas, this organic waste is reduced in about 4 - 5 cm long by sending them (CGRraw) through a shredder to reduce the size as shown in Figure 3.2-4. The Commercial Garden Refuse (CGR10) consists of the same organic waste, the CGRraw the organic waste was mainly branches of plant finishing and green municipal areas. Leachate samples used were collected from the Sequencing Batch Reactor (SBR) at the Mariannhill landfill.
The treated leachate from the SBR was diluted with distilled water to obtain a concentration of 500 mg/l NO3. As a way of comparison, cell 1 was mixed with other substrate such as CGRraw and CGR10 respectively using a 1:1 ratio, both batches were performed in the presence of treated leachate.
Sampling
- S OLID S AMPLING
- E LUATE S AMPLES
- L EACHATE S AMPLE
To obtain a representative sample size, each batch (Cell 1, Cell 2, CGRraw and CGR10) of substrates was quartered using the standard method (Pisano, 2007). The untreated leachate (mixed liquor) was collected from the sequencing batch reactor (SBR) before being treated (Figure 3.3-5), while the treated leachate sample was collected in the SBR balance tank before entering the wetland. The untreated leachate was collected to inoculate the treated leachate to provide some bacteria to facilitate denitrification.
A ratio of 1:100 between untreated leachate and treated leachate was used as the untreated leachate has a high ammonia content. The untreated leachate from the SBR contained a high amount of ammonia as the process of nitrification takes place in the SBR tank (Metcalf and Eddy, 2003).
Characterization Test
- M OISTURE C ONTENT (MC)
- T OTAL S OLIDS (TS) AND V OLATILE S OLIDS (VS)
- R ESPIRATION I NDEX AT 7 D AYS (RI 7 )
- T OTAL C ARBON (TC), T OTAL N ITROGEN (TN) AND C/N R ATIO
- P H
- T OTAL S OLID (TS)
- V OLATILE S OLID (VS)
- C HEMICAL O XYGEN D EMAND (COD)
- B IOCHEMICAL O XYGEN D EMAND (BOD)
- A MMONIA (NH 3 )
After cooling the sample to obtain the mass of the dry sample, the cooled sample is weighed again. A thimble was placed on the neck of the flask and 10 drops of KRH were added. After the crucibles had cooled, they were weighed again to determine the mass of the dried solid residue.
Wvs = Mass of the volatile residue (ash) remaining after baking (grams). Mass of the residue + Mass of the crucibles before ignition) – (Mass of the residue + Mass of the crucibles after ignition). COD is defined as the measurement of the amount of oxygen required for the chemical oxidation of organic matter in a sample (Metcalf and Eddy, 2003).
Batch Test
- B ATCH S ETUP
- S AMPLE E XTRACTION AND N ITRATE C ONCENTRATION T ESTING
- S AMPLE A NALYSIS
- pH
- Nitrates and Nitrites
A known amount of substrate was mixed with the effluent using a 10:1 (liquid-solid) ratio and the total liquid volume was 750 mℓ. The sample was then placed on a shaker operated at 150 rpm to ensure continuous and complete contact of the solid with the liquid as shown in Figure 3.5-1. The color changes on the nitrate test stick depending on the concentration of nitrate at that time.
At the end of the batch test, the eluate solution was analyzed for pH, nitrate and nitrite concentration, ammonia and COD. Although the kinetics of the denitrification process was mainly focused on the Tend, other results were also evaluated to increase accuracy and also better understand the population dynamics of the bacteria responsible for denitrification at different critical moments.
RESULTS AND DISCUSSIONS
Introduction
Characterization Test Results
- S OLID
- E LUATE
- L EACHATE
The results in Table 4.2-2 show that the pH is closer to neutrality in all substrates used. The results in Table 4.2-2 show that there is a high NH3-N content in all substrates, especially in cell 2, which allows the NH3-N to leach from the substrate into the wastewater to be treated, causing an increase in the nitrate content through a process known as bioleaching. From Table 4.2-1 it can be seen that Cell 1 + CGRra and Cell 2 are above the range, while Cell 2 + CGR10 are below that range.
A substrate with a low BOD5 : COD ratio, as shown in Table 4.2-2, indicates that the substrate has been extensively biodegraded. Table 4.2-3 shows that the leachate is characterized by a low ammonia content, except for the mixed leachate, as it was sampled from the SBR tank, where the untreated leachate is treated for ammonia.
Batch Tests Results
- C ELL 1 B ATCH T EST
- N ITRATE C ONCENTRATION E VOLUTION OF C ELL 1 B ATCH T ESTS A ND T HEIR K INETIC
- N ITRATE C ONCENTRATION E VOLUTION OF C ELL 2 BATCH T ESTS AND T HEIR K INETIC
The results presented in Table 4.3-9 and Figure 4.3-4 show that complete denitrification cannot be achieved. The results in Table 4.3-5 show an increase in valve pH from the initial eluate input of 7.03 to 7.43 of the batch eluate output. The increase in the level of COD according to Table 4.3-11 is an indicator of the process of biological cleaning of carbon from solids in the eluate of the batch test.
After the batch test was completed, the endpoint (Tend) was characterized and the summary of results is presented in Table 4.3-14. After the batch test was completed, the endpoint (Tend) effluent (solids and eluate) was characterized and the results are presented in Table 4.3-16.
Comparing the Different Substrates Used
The temperature range throughout the study was between 19oC and 24oC as shown in the appendices, which is within the 60oC range considered suitable for denitrification according to Henze et al (1997). It was observed that the batch consisting only of treated general waste without mixing with other substrate did not have good contact with the liquid as it consists of fine particles which settle on the bottom of the batch bottle thus reducing the contact between solid and liquid. It was observed that the effluent samples from the batch test had a brown color as they contained the fine particles that have been washed from the fine pretreated waste.
The acclimation phase is not evident in cell 1 substrates, this may be due to the presence of readily biodegradable carbon. For batch 2 cells, the initial plateau is the acclimation phase at the beginning of the batch test as suggested by Trois et al (2010). This phase involves buffering of pH levels as well as competition between nitrifiers and denitrifiers, and occurs until the batch environment is more stable for denitrification to occur.
CONCLUSION AND RECOMMENDATIONS
Efficiency and Performance of Substrates
The kinetics of the substrates
Recommendation for Further Research
Choi, (2002). Advanced treatment of leachate from landfills using an integrated membrane process. 2007) Practice review of five bioreactor landfills. Investigating the denitrification of high strength landfill leachate using pine bark and raw and composted commercial garden waste as a carbon source: Column studies. Master's thesis in Civil Engineering: Microbiological investigation of the biological denitrification of non-hazardous landfill leachate using garden waste compost and pine bark as a carbon source.
2010b) Effect of compost and pine bark on the biological denitrification process of non-hazardous landfill leachate: focus on microbiology. 2007). 2009). Nitrogen removal from landfill leachate via ex situ nitrification and sequential in situ denitrification. Waste management.
