REDUCTION OF THE AMMONIACAL-N CONCENTRATION OF THE LANDFILL LEACHATE BY OVERLAND FLOW SYSTEM

Silsoe College

Department of Agricultural Water Management

MSc. Part II Environmental Water Management

1994-1995

REDUCTION OF THE AMMONIACAL-N CONCENTRATION OF THE LANDFILL LEACHATE BY OVERLAND FLOW SYSTEM

ON CLAY AND SANDY LOAM SOILS

CRISTOBAL PINCHE - LAURRE

Supervisor: Sean Tyrrel

This paper is submitted in partial fulfilment of the requirements for the degree of Master of Science

ACKNOWLEDGEMENTS

I would like to thank Silsoe College, especially Sean Tyrrel for his guidance and his suggestions to complete this research project, and Simon Medaney for his support in the edition of this thesis.

My especial gratitude to my wife Loren Ruiz Garcia who supported my MSc. studies and help me with this project.

Finally, I also thank the British Council for granting me with a scholarship to get my MSc. degree at Silsoe College.

REDUCTION OF THE AMMONIACAL-N CONCENTRATION OF THE LANDFILL LEACHATE BY OVERLAND FLOW SYSTEM

ON CLAY AND SANDY LOAM SOILS

Cristobal Pinche-Laurre, MSc Environmental Water Management,

Silsoe College, 1995

_____________________________________________________________________

ABSTRACT

Landfill leachate had been researched previously to achieve permissible level of contaminants. This study focuses in ammonium removal by overland flow system in the clay and the sandy loam soils. This was carried out by daily recirculation of leachate on a pilot-scale overland flow. The result showed good performance (70.65% in Sandy Loam and 94.94% in Clay soils) in mass ammonium removal, and reduction of leachate volume in the clay soil. There was no effect of the soil type during the first 5 days of experiment. After that, ammonium removal in the clay soil was higher than in the sandy loam soil. Nitrate production was not significantly different between the two soil types. The research shows that the CEC is an important factor in ammonium removal.

TABLE OF CONTENTS

1. INTRODUCTION....................................................................................... 2

1.1. Landfill leachate treated by Overland flow.................................................... 3

1.2. Ammonium removal processes in Landfill leachate treatment......................... 7

1.3. Overland Flow treatment on ammonium removal.......................................... 9

1.4. Soil Type and Ammonium removal..............................................................10

2. AIM AND OBJECTIVE..............................................................................14

3. MATERIALS AND METHODOLOGY......................................................15

3.1. Leachate characteristics................................................................................15

3.2. Grass Plots...................................................................................................15

3.3. Operation of the overland flow plot...............................................................16

3.4. Determination of ammonium and nitrate........................................................17

4. RESULTS.....................................................................................................18

4.1. Ammonium removal by overland flow system in Sandy loam

and Clay soils...............................................................................................18

4.2. Nitrate Concentration and Total Mass in Sandy loam and Clay soils.................22

4.3. Grass condition and Volume reduction of leachate during

overland flow treatment.................................................................................25

5. DISCUSSION................................................................................................26

5.1. Ammonium removal......................................................................................26

5.2. Nitrate reduction............................................................................................26

5.3. Permeability effect.........................................................................................27

6. CONCLUSIONS............................................................................................28

7. REFERENCES..............................................................................................29

1. INTRODUCTION

Landfill represents more than 65 % of the waste disposal in UK. It has increased in the last 20 years, because it is the cheapest way to dispose of more than 90 % of domestic waste and over 80 % of hazardous waste (Croner Publication, 1995).

Landfill gas and leachate are the main landfill residues which can endanger the environment. Landfill gas is mainly composed of methane and carbon dioxide. They are generated by the microbiological processes known as anaerobic digestion in which organic matter is degraded in the absence of oxygen (Hooker, 1993). Landfill gas can be managed by landfill gas control.

Leachate is formed by the action of water (precipitation) passing through a landfill, becoming contaminated with various organic and inorganic pollutants produced by the biodegradation of waste material (Crawford and Smith 1985). Leachate (Table 1), due to its high concentration of ammoniacal-N, requires efficient management techniques to prevent the contamination of surface fresh water and groundwater .

Leachate can be treated by off-site treatment and disposal or by on-site treatment. The former refers to a transfer of leachate to sewage works. The latter refers to a low technology treatment system (Crawford and Smith 1985).

A common and effective mean of leachate treatment is land treatment, specifically overland flow. This relies on processes in the soil-plant system to reduce the high level of ammoniacal-N.

Table 1. Typical composition of leachate from recent and aged domestic waste

(All results in mg/l except pH value)

PARAMETER AGE OF REFUSE

< 2 years old > 10 years old

pH 5-6.5 6.5-7.5

BOD 4000-30000 < 100

COD 10000-60000 50-500

TOC 1000-20000 < 100

Total solids 8000-50000 1000-3000

TSS 200-2000 100-500

N (NH3-N or Org-N) 100-1000 < 100

Phosphate 5-100 < 5

Chloride 500-200 100-500

Sulphate 50-1000 < 10

Iron 500-3000 10-400

Sodium 200-1000 < 200

Potassium 500-2500 50-400

Calcium 100-400

After Crawford and Smith, 1985

1.1. Landfill Leachate treated by Overland Flow

Land application is based on the interaction of waste and the soil-plant system. The assimilative capacity of land depends on the contact and the processes which take place in the upper zone of this system, which include adsorption, immobilisation dispersion and chemical and biological decomposition (Bache and MacAskill, 1984).

For liquid waste there are three major types of land treatment: slow rate (irrigation), overland flow and rapid infiltration. This classification depends largely on the soil permeability (Figure 1). In the UK, a number of overland flow system are in use for leachate treatment.

Overland flow is a biological treatment technique which consists of applying water at the top of a slope of a relatively impermeable soil and allowing the flow to go through vegetation to runoff collection ditches. A well-known land treatment system incorporating overland flow has been in operation at Werribee Farm, treating waste-water from Melbourne, Australia since 1905 (Bache and MacAskill, 1984).

Grass is well suited to overland flow system because they allow very little erosion. Table 2 indicates that vegetation plays a significant role in the removal of nitrogen, phosphorus and the major anions and cations but it is generally less effective than in slow infiltration (Bache and MacAskill, 1984).

The design of overland flow suggested by Metcalf & Eddy (1991), Gray (1989) and Crawford and Smith (1985) comprises: an irrigation or application rate of between 50 l/m2.d and 80 l/m2.d, a slight slope (2°-8°) and a soil with low permeability such as clay or clay loam. This encourages more contact between leachate, soil surface particles and the root zone in the soil surface.

1.2. Ammonium Removal Processes in Landfill Leachate Treatment

Leachate treatment mechanisms, specifically ammonium removal, may be broadly classified as chemical and biological processes, but in many instances they are interdependent.

- CHEMICAL PROCESSES

The chemical processes which account for most of the retention are adsorption and precipitation. Overland flow is concerned with adsorption which refers to the attachment of ammonium to the soil.

Adsorption manifested as ion exchange and specific adsorption depends on the bond strengths. In this case, ammonium removal deals with ion exchange.

In general, the soil surface carries a net negative charge associated with clay and humic particles. This implies the retention of ammonium ions. Cation exchange takes place when one of the soil solution

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