By:Heba Numan Harara

Samar khuzundar

Submitted to:Dr. Thaer AbuShbak

2014

The effects of leachate recirculation with supplemental water addition on methane production and waste decomposition in a

simulated tropical landfill

What do we do with all this garbage?

Landfills• A landfill, also

known as a dump, is a site for the disposal of waste materials by burial and is the oldest form of waste treatment. Historically, landfills have been the most common methods of organized waste disposal and remain so in many places around the world.

Classification of landfill

Three general categories:

1.Open dumps 2.Controlled dumps 3.Sanitary landfills

LANDFILL LEACHATE During landfill siteoperation, a liquid known asleachate is produced.

It is a mixture of organicdegradation products, liquidwaste and rain water.

It has high organic carboncontent, high concentrationsof nitrogen and is usuallyslightly acidic.

Landfill Leachate ConstituentsConstituent Typical Ranges1

Landfill Leachate ConstituentsConstituent Typical Ranges1

Leachate effects the pipes become weakened by chemical attack (acids,

solvents, oxidizing agents, or corrosion) and may then be crushed by the tons of garbage piled on them.

Leachate contains a host of toxic and carcinogenic chemicals, which may cause harm to both humans and environment.

leachate-contaminated groundwater can adversely affect industrial and agricultural activities that depend on well water.

The use of contaminated water for irrigation can decrease soil productivity, contaminate crops, and move possibly toxic pollutants up the food chain as animals and humans

Gasses found in landfills:The typical constituents of gases produced by a municipal solid waste

landfill:

• Component Percent (dry volume basis)Methane 40-60%Carbon Dioxide 40-60%Nitrogen 2-5%Ammonia 0.1-1.0%

Methane : It is often flammable and sometimes even explosive.

• Carbon Dioxide: Non harmful to the environment

• Nitrogen: Non harmful to the environment

• Ammonia: Ammonia in air is an irritant and causes burning of the eyes, nose, throat and lungs.

Leachate collection and treatment:

Leachate collection systems are installed above the liner and consist of a perforated piping system which collects and carries the leachate to a storage tank.

Periodically, leachate removed from the storage tank and treated or disposed of.

Most common leachate management methods are: discharge to wastewater treatment plant, on-site treatment and recirculation back into the landfill.

Leachate recirculation

the practice of retraining leachate to landfill from which it has been abstracted.

This technology could be more cost-effective than other treatment systems.

Benefits of leachate recirculation

-reduction in leachate treatment and disposal cost.- Accelerated decomposition and

settlement of waste.- Acceleration in gas production.- Accelerating stabilization of organic

waste.- Potential reduction in cost and

environmental impact after closure.

After weighing these advantages and disadvantages, federal regulators in the US decided to allow leachate recirculation only at landfills that have a composite liner and a leachate collection system that meets specified performance requirements.

An example of the electrical generation equipment in one of the Michigan CogenerationSystem Plants. These engines burn only landfill gas as a fuel andoperate 24 hours a day. Each engine produces 750 kw of electricity

Bioreactor Defined“……a sanitary landfill operated for the purpose of transforming and stabilizing organic waste constituents by purposeful control to enhance microbiological processes.

Why Operate a Landfill as a Bioreactor?

to increase potential for waste to energy conversion,

to store and/or treat leachate,

to recover air space,

to ensure sustainability.

Objective of study:

to determine the effects of leachate recirculation and supplemental water addition on municipal solid waste decomposition and methane production in three anaerobic digestion reactors.

The effects of leachate recirculation with supplemental water addition on methane production and waste decomposition in a

simulated tropical landfill

Used Techniques for improving methane production

• Bioreactor technology is becoming more widely accepted in landfill design and operation methodology.

• This technique enhances waste decomposition rates and methane production.

• An increase in moisture content in a landfill enhances the anaerobic degradation processes by facilitating the redistribution of substrates and nutrients and the spreading of microorganisms between the micro environments in the landfill, leading to an increase in the methane production rate

overviewThe most common problem associated with

landfill operations is the generation of leachate and gases.

The results from this investigationsmight not be applicable to landfills in Thailand due to the differences in waste type and composition.

In tropical landfills, where high temperature and high evaporation lead to insufficient moisture content in the cell.

However, during the dry season, leachate recirculation may be insufficient to maintain the moisture content, and supplemental water addition into the cell is then necessary to stabilize moisture levels as well as stimulate biological activity.

leachate recirculation not only helps to increase the moisture content but also to circulate organic matter back into the cell.

Reactor preparation

The study was conducted by constructing three simulated landfill reactors from opaque PVC.

Material and methods

These reactors had a diameter and height of 0.30 and 1.25m,respectively

PVC leachate collection pipe with a diameter of 1.8 cm was installed at the center of the bottom of the reactor.

Leachate was collected in a transparent container

• A leachate sampling port was installed in the collection pipe.

• A tap-water addition port was installed at the top of the reactor.

• A distribution pipe was installed at the top of the

reactor to add liquid to the waste mass.

• A 1.8cm diameterPVC pipe was used to construct a gas-sampling port

The concept of using a gas meter to calculate gas production is based on the liquid displacement by gas in the fixed volume chamber which causes a chamber turnover.

All connections (ports and the lid) were checked for leakages by using a soap solution before waste loading.

Soil preparation

The soil, which was taken from BangkhuntienCampus,was sampled and sent to the Department of Soil Science, Faculty of Agriculture, KasetsartUniversity for texture analysis.

The result showed that the soil, consisting of 45%sand, 16% silt and 39% clay, had a sand-clay (SC) texture and had acceptablecharacteristics for use as soilcovering in sanitary landfills

MSW preparation

The MSW was collected from Nongkham transfer station, Bangkok, Thailand.

Bulky wastes and recyclable materials (glass, metal and non-metal materials) were removed.

Large plastic and paper materials were torn into 1–2 cm size pieces.

The sample was then mixed with abackhoe to maximize the homogeneity of wastes.

Approximately 1000 kg of MSW moisture content of the MSW was 70.28% on a

wet basis and the C/N ratio was 21.79.

Solid wastes loading Before the reactors were filled with waste, an

8 cm thick layer of 2.5 cm diameter gravel was placed at the bottom of each reactor.

A circular nylon screen with 1-mm diameter holes was placed over the gravel layer to prevent clogging of the reactor drainage system.

During loading, the MSW was manually compacted and then covered with a 3 cm thickness of soil every 30 cm for the bottom and medium layers and a 6 cm thickness of final cover soil.

In this investigation, the waste was compacted to a density of 600 kg/m3.

The soil was compacted to 1300 kg/m3.

to ensure anaerobic conditions in the reactors, a rubber gasket was placed between an acrylic flange and the top lid.

After the reactor was closed, the top lid was screwed down and sealed with the silicone rubber to make the reactor gas tight.

The quantities of MSW andsoil used in each reactor are presented in Table

Experimental design and operation

One reactor was operated as a control .without leachate recirculation (RC)

while the other two served as experimental reactors, one with leachate recirculation (R1)

and the other with leachate recirculation and supplemental water addition (R2).

the buffer capacity (proportion of TVA and alkalinity) for all reactors was controlled to not exceed more than 0.8 by adding sodium bicarbonatec(NaHCO3) to the water before introduction into the reactors on day 200,

except R2 which had a high pH and buffer capacity.

The total amounts of NaHCO3 added to RC and R1 were 877 and 858 g, respectively.

it was difficult to recirculate at the same rate for both reactors because of the variation of leachate quantity circulating from the reactors.

Laboratory analysis

Gas volume in the reactor was measured by a gas meter.

the gas composition was analyzed by gas chromatography and a Thermal Conductivity Detector (TCD).

The leachate volume collected at the bottom of each reactor was quantified and sampled.

Leachate was analyzed for pH, alkalinity,TVA and COD by standard methods

RC :control reactor Without LEACTAH RECRIULATION

RC provide 9.02 l/kg dry weight at a rate of0.10 l/kg dry weight/d, and reached the stabilization phase on day 270.

R1 : WITH LEACTAH RECRIULATION leachate recirculation reactor provided 17.04 l/kg dry weight at a rateof 0.14 l/kg dry weight/d and reached the stabilization phase on day 290

The effects of leachate recirculation

• waste decomposition was in the acid phase approximately 210 days after loading as indicated by the high concentration of TVA (8.13 gAA/l from RC and 7.91 gAA/l from R1) in the leachate,

• low leachate alkalinity (5.12 gCaCO3/l from RC and 5.31 gCaCO3/l from R1) and a subsequent.

• drop in leachate pH to approximately 5.7. • The natural buffering capacity of the waste was

insufficient to overcome the effects of the TVA accumulation.

• The acidic environment resulted in the inhibition of methanogenesis as indicated by the continued high COD concentration(21.59 g/l from RC and 22.61 g/l from R1)

• no methane was produced before recirculation commenced.

• The addition of a buffer compound (NaHCO3) on day 200 provided the environment required for methanogens to utilize substrates and methane composition and productionrapidly increased.

• The remaining COD concentrations of RC and R1 on day 330 were 1.26 and 5.99 g/l, respectively,

• while the remaining TVA concentrations were 0.73 and 3.11 gAA/l, respectively.

• The steady remaining values of COD and TVA concentrations in the leachate indicated that the reactors entered into the stabilization phase.

• the control reactor (RC) reached the stabilization phase more quickly than the leachate recirculation reactor (R1) (day 270 for RC and day 290 for R1).

• This was unexpected and was attributed to the exhaustion of the substrates for methanogens due to leachate washout.

• However, leachate recirculation with buffer addition (R1) provided a greater methane production rate (0.10 l/kg dry weight/d from RC and 0.14 l/kg dry weight/d from R1)

• and greater cumulative methane production than the control reactor (RC) (9.02 l/kg dry weight and 17.04 l/kg dry weight from RC and R1, respectively).

• Therefore, it can beconcluded that leachate recirculation with buffer addition accelerates waste stabilization and enhances methane production.

R2 :with leachate recirculation an supplemental water additions

accumulated methane production of 54.87 l/kg dry weight of MSW at an average rate of 0.58 l/kg dryweight/d and reached the stabilization phase on day 180.

• supplemental water addition in the early acid phase helped to dilute inhibitory substances and negated the need for buffer addition to vercomethe acid phase.

• In addition, R2 entered the methanogenesisphase on day 75, which was 135 days earlier than RC and R1.

• The results show similar methane production rates from both reactors from day 75 to 140.

• The average methane production rate of R1 was 0.10 l/kg dry weight/d while that of R2 was 0.11 l/kg dry weight/d.

The effects of leachate recirculation with supplemental water addition

• However, it was observed that R1 was in an acid phase while R2 was in a methanogenesis phase, as indicated by the increasing methane content and leachate pH and decreasing leachate concentrations of e.g. COD and TVA.

• This meant that supplemental water addition in the early acid phase helped accelerate waste decomposition but did not result in higher methane yield rates

• methane production was found to gradually increase.

• In RC, the substrates and essential nutrients for methanogens were removed by leachate drainage whereas in the R2 reactor the substrates for methanogens were captured, reapplied and utilized by the microbes.

• This also increased contact opportunity between the nutrients and microbes.

• Recirculation into R2 was started on day 203, which was after the waste had nearly reached the stabilization phase (day 180), whereas leachate recirculation into R1 was started on day 203, which was before the waste had reached the stabilization phase(day 290).

• This result shows that when the leachate recirculation is started after the waste has reached the stabilization phase, a much higher methane production can be produced than when the recirculation is started before the waste has reached the stabilization phase.

The effects of leachate recirculation with increasing organic loading rate

The results during the stabilization phase for all reactorsrevealed that higher OLR led to a higher CH4 productionrate, CH4 composition and COD removal.

This reveals that a reactor that has entered into thestabilization phase not only enhances methane productionthrough leachate recirculation, but can also help to increase

the OLR in the circulated leachate.

Conclusion: -The leachate recirculation reactor provided a greater degree of stabilization than the single pass leachate recirculation reactor.-the effect of leachate recirculation along with buffer addition could enhance methane production and reduce the stabilization time. -Supplemental water addition increase dilution of inhibitory substances and reduce leachatestrength resulting in favorable conditions for methanogens.

Conclusion-Supplemental water addition in acid phase can be used as an effective operational strategy to accelerate the methanogenesis

.Phase-Starting to recirculate leachate after the waste had reached the stabilization phase produced much more methane than when starting recirculation before the waste had reached the stabilization phase.