WO2001077027A1

WO2001077027A1 - Leachate treatment and disposal process and apparatus

Info

Publication number: WO2001077027A1
Application number: PCT/AU2001/000368
Authority: WO
Inventors: Anand Thakur; Ned Sardelic
Original assignee: Waste Recycling And Processing Services Nsw.
Priority date: 2000-04-05
Filing date: 2001-04-03
Publication date: 2001-10-18
Also published as: AUPQ670200A0

Abstract

The present invention relates to a process for the treatment and disposal of leachate and an apparatus for carrying out such a process. A leachate treatment process according to the present invention comprises the steps of: (i) filtering a raw leachate to produce a leachate filtrate; and (ii) atomising the leachate filtrate to produce a leachate mist; characterised in that the leachate mist has an average particle size of less than 20 microns in diameter and in that the leachate mist is substantially completely evaporated through exposure to atmospheric conditions.

Description

LEACHATE TREATMENT AND DISPOSAL PROCESS AND APPARATUS.

Field of the Invention

The present invention relates to a process for the treatment and disposal of leachate and an apparatus for carrying out such a process. In particular, the invention relates to a process and apparatus for the removal of ammonia from leachates from waste material landfills.

Background and Description of the Prior Art

Various approaches have been adopted in the treatment of contaminated water and waste water. Solid materials are typically removed by settling or filtration or a combination of both. Dissolving contaminants of impurities may be removed by a variety of stripping or volatilisation techniques. The composition of waste or contaminated water from different sources varies considerably and thus the treatment method used is generally specific to the nature of the water to be treated.

By definition, leachate is any liquid that percolates through a medium. In the waste management industry, leachate refers to a contaminated liquid which is a by-product of waste material landfills. Leachate is generated in landfills primarily by two processes, (i) by rainwater infiltrating into the landfill and washing out soluble contaminants, and (ii) by biodegradation of waste within the landfill itself. Large volumes of leachate may be produced.

Leachates usually contain high levels of contaminants such as ammonia, biochemical oxygen demand ("BOD") and heavy metals and suspended solids. Leachate typically contains in the order of 500 - 1000 mg/L of ammonia whereas household effluent typically contains of the order of 100 - 150 mg/L of ammonia. Traditionally, leachate has been managed through a combination of irrigation and reinjection into the landfill or disposal into water streams that are subsequently treated in conventional waste water treatment plants. However, the efficient and effective disposal of leachate remains a problem.

Australian Patent No. 628380 (N. A. Salmond and P. J. Wotton) discloses an effluent processing apparatus and a method for processing effluent, both of which are directed to the treatment of domestic effluent emanating from a domestic septic tank. The treatment method comprises the steps of filtering the effluent, chemically treating the effluent to sterilise and deodorise the effluent and pumping the effluent through a spray means into an air stream to disperse the effluent. The apparatus and method are designed for the treatment of domestic waste and to operate on a domestic scale. No reference is made to the removal of or otherwise of ammonia, neither is there any reference to the treatment of leachates, nor operating parameters of the apparatus / method.

US Patent No. 5,635,077 (The Dow Chemical Company) discloses a method for stripping ammonia from sludge obtained from the treatment of waste water. The sludge is applied to a surface as a film which travels downwards with respect to the surface. A stripping gas travelling in the opposite direction to the film is then passed over the film to strip the ammonia. This technique is restricted to the treatment of waste water sludges which may be suitably applied to a surface as a film.

US Patent No. 3,966,633 (Cogas Development Company) discloses a two step waste water treatment process wherein hydrogen sulphide and a substantial proportion of any ammonia present in the waste water is removed in a steam-stripping step after which the remaining waste is flashed into a stream of superheated steam to decompose remaining impurities. Sufficient ammonia to keep the pH of the waste at between 8.5 and 10.5 is retained after the first step. US Patent No. 5,726,405 (J. A. White) discloses a waste water treatment method and apparatus for treatment of domestic and industrial effluent. Claimed is a method of conversion of soluble phosphates from the waste water comprising atomising the waste water under selected atmospheric conditions to achieve substantially complete phase change of the waste water to ice crystals causing release of carbon dioxide and ammonia and consequently causing an increase in pH which causes phosphate ions to combine with alkaline cations and precipitate as insoluble phosphate salts. The primary action is the production of ice crystals, which are characterised by complete freeze through, which fall to the ground. This process suffers from the draw backs that complete freeze through of the ice crystals, formed by atomisation and nucleation, is essential and that the process can only be carried out when atmospheric conditions are appropriate. US 5,726,405 indicates that the atomisation process is best carried out using a multiple nozzle assembly as employed in artificial snow production and disclosed in US Patent No. 5,135,167 (J. A. White & Associates Ltd.). US 5,135,167 does not provide any indication of the size of the water droplets / particles which are produced although various operational parameters are discussed.

Despite the existence of various waste water treatment process and apparatus as indicated in the above discussion, there remains a need for an efficient and effective method for disposing of ammonia in waste water, and in particular leachates, before such water can be safely discharged into the environment. It is an object of the present invention to provide such a method.

It is another object of the present invention to provide a process and apparatus for the treatment of leachate.

It is a further object of the present invention to provide a process and apparatus for the treatment of leachate in an environmentally less harming manner than achieved through use of conventional waste water treatment plants.

These objects are met by the leachate treatment process and apparatus of the present invention.

Brief Description of the Invention

A leachate treatment process according to the present invention comprises the steps of: (i) filtering a raw leachate to produce a leachate filtrate, and (ii) atomising the leachate filtrate to produce a leachate mist; characterised in that the leachate mist thus produced has an average particle size of less than 20 microns in diameter and in that the leachate mist is substantially completely evaporated through exposure to atmospheric conditions.

The process of the invention achieves effective removal of ammonia from the raw leachate and disperses part of it in a suitable form into the environment. The pH of the leachate typically lies in the range of from 7 to 8.5 and the temperature of the liquid is generally between 15 and 22°C. Under these conditions the ammonia in the leachate is estimated to be approximately 90 % ammonium ion and 10 % ammonia gas. When this liquid is evaporated ammonium ions combine with chloride, sulphate, carbonate, phosphate or similar anions in the leachate to form salts. These salts are produced on the basis that ammonium ions will first combine with the least soluble anions to form the least soluble salt and then with other less soluble anions and so on until the maximum possible amount of ammonium ions have been removed. When the pH of the leachate is within the range specified above, the ammonia gas released during evaporation is typically about 10 % of the total ammoniacal nitrogen in the leachate. The process of the invention may be operated in a wide range of atmospheric conditions, as discussed in more detail below, and is not restricted to conditions of near or below 0°C. b

Preferably, the step of filtering the raw leachate to produce a leachate filtrate comprises a primary filtration step of passing the leachate through a sand filter to produce a primary filtrate and a secondary filtration step of subsequently passing the primary filtrate through at least one secondary filter to produce a secondary filtrate, the secondary filtrate being the leachate filtrate which is subsequently atomised.

Preferably, the step of filtering the raw leachate to produce a leachate filtrate reduces the size of any suspended solids remaining to about 1 micron.

The sand filter may operate under the force of gravity or may have a pump for pumping the leachate through the filter. The sand filter serves to remove suspended solids, colloidal clays and other paniculate impurities from the raw leachate, eliminating particles which are greater than about 30 microns in diameter.

The filter or filters used in the secondary filtration step may be of the cartridge filter type, typically filtering out particles of greater than about 1 micron in diameter.

Preferably, the atomisation step comprises expelling the leachate filtrate under high pressure through one or more nozzles having a predetermined orifice size thus producing a leachate mist.

Preferably, the leachate mist is expelled into an air stream created using one or more fans.

A leachate treatment apparatus according to the present invention for treating raw leachate collected in a leachate collection pond comprises at least one filter for producing a leachate filtrate, an atomisation arrangement for atomising the leachate filtrate and a pump for pumping the leachate filtrate from the filter to the atomisation arrangement, characterised in that the atomisation arrangement has at least one nozzle which, in operation, causes the leachate filtrate to be converted into a leachate mist having a particle size of less than 20 microns in diameter.

The apparatus of the present invention achieves effective separation of ammonia from raw leachate and further serves to disperse the filtered leachate in a safe and effective manner. As described in more detail below, the apparatus of the invention has the further advantage of being capable of processing large volumes of leachate effectively. Under optimum operation conditions the present invention can be used to process any volume of liquid depending on specific site constraints, with maximum through put being achieved under optimum meteorological conditions. Generally, volumes which are beyond the capability of many of the prior art systems may be processed.

In one embodiment, the atomisation arrangement comprises a plurality of nozzles mounted on a series of concentric ring pipes that are located within a cylindrical or hyperbolic tower housing that surrounds one or more fan propellers. One or more of such nozzle / fan arrangements may be employed. In order to achieve desirable performance levels, each nozzle is preferably capable of evaporating 5 L of liquid per hour.

Description of the Drawings

The invention is described in more detail below with reference to the accompanying drawings, in which:

Figure 1 is a schematic flow diagram of a leachate treatment apparatus according to the present invention; and

Figure 2 is a plan view of the fan nozzle distribution arrangement according to one embodiment of the invention. Detailed Description of the Invention

A preferred embodiment of the process and apparatus according to the invention is now described with reference to the accompanying drawing, Figure 1. The process and apparatus are designed for the treatment of leachate typically produced from landfill sites used for disposing of solid waste from various sources. The process and apparatus are particularly for use in the treatment of waste water from a variety of sources which contains ammonia and other similar volatile components. The leachate, typically produced by the mechanisms referred to in the prior art description, is collected in one or more collection ponds or other means (not shown in Figure 1 ). Raw leachate from the collection ponds is transferred, via a pump (not shown) if necessary, to a filtering arrangement indicated generally at 2 in Figure 1. The embodiment represented in Figure 1 has a sand filter 3 for the primary filtration of raw leachate. Primary filtration removes suspended solids, colloidal clays and any impurities down to a particle size of approximately 30 microns. Indicated by the label 1 , raw leachate is fed into the sand filter 3 and percolates through the filter under the force of gravity. The capacity of the sand filter 3 may be greater than that of the down stream components in which case any excess filtrate from the primary filtration step may be recycled as indicated by cycle 4.

Cleaning of the sand filter, which is an optional feature of the invention, may be carried out as follows: sand is channeled into a washing receptacle (not shown) using compressed air, or some other means, where any excess filtrate is used to wash the sand. The cleaned sand is then fed via a screw conveyor (not shown), or other means, back into the top of the sand filter 3. Reject water collected after the cleaning process is filtered, for example through a 10 micron bag filter 5, the residue being disposed of in the landfill and the filtrate returned to the leachate input 1. The cleaning process may be carried out as a continual cyclical process. The continuous removal of a quantity of sand from the sand filter 3, washing and return of the washed sand ensures that the o

sand in the sand filter is maintained in a clean condition, resulting in constant filtration efficiency of the primary filtration step involving the sand filter 3.

After the primary filtration step the primary filtrate thus produced is pumped by means of a pump 6 to one or more secondary filters 7. Optionally there may be a balance tank (not shown) between the sand filter 3 and the secondary filters 7. The secondary filters 7 may be cartridge filters or the like. While only one cartridge filter 7 is shown in Figure 1 , a series of such filters may be used. For example a series containing 20, 15, 10 5, 2 and 1 micron filters would be suitable. Secondary filtrate produced by passing the primary filtrate through the cartridge filter 7 is fed into the atomiser arrangement, indicated generally at 8. Any excess secondary filtrate is returned to the balance tank (not shown) or redirected to the input 1.

The atomiser arrangement 8 consists of a number of atomising units 9 that are arranged to flash vaporise liquid that is expelled at high pressure therefrom, preferably more one dispersion fan 10 per atomising unit 9 and at least one high pressure pump (not shown) arranged to enable high pressure discharge of liquid from the atomising units 9 of arrangement 8.

Each of the atomising units 9 and the associated dispersion fans 10, which include a multi-blade fan rotor and a drive motor, are mounted within an open top cylindrical or double-hyperbolic housing tower 11. In the embodiment shown in Figure 2, each dispersion fan 10 consists of a number of substantially concentric ring pipes 12 that are connected to a common supply pipe 13. As shown in Figure 2, the ring pipes 12 may be integral with, or a continuation of, the supply pipe 13. The supply pipes 13 of all fans 10 form part of a manifold pipeline system having appropriately located regulation and shut off valves that enable selected distribution of leachate filtrate from an outlet pipe of the secondary filters to individual ones of the atomisation units. The ring pipes 12 are suitably mounted on a support grill within housing tower 11. Each ring pipe 12 is provided with a plurality of adjustable fluid discharge nozzles 14 located equidistantly along each pipe. The nozzles 14 are mounted so as to allow adjustable discharge orientation of the leachate filtrate fluid expelled there through towards the open top of housing tower 1 1. Alternatively, the entire tower is mounted such as to allow directional adjustment of its longitudinal axis and therefore of the discharge orientation of its open top.

The nozzles are designed to achieve high emission velocity with a low flow rate. This facilitates atomisation of liquids into aerosol particles of micron size that are dispersed into the atmosphere through out the working pressure range. Better atomisation facilitates evaporation of the material passing through the nozzle even under climatic conditions of relatively high humidity.

The nozzles incorporate one or more orifices of a size and geometric configuration that ensure that the filtrate which is being discharged there through at high pressure is atomised into droplets of about 2 to 20 microns in diameter, preferably 10 microns.

Typically the nozzles will produce a conical spray pattern. Depending on the pressure of the leachate pumped through the nozzles it has been found that spray angles of 55 - 70 degrees may be obtained with a 0.20 mm nozzle diameter while a 80 degree spray angle may be obtained with 0.50 mm nozzle. In general a higher proportion of sub-50 micron droplets are produced at higher pressure ranges. Depending on the size of the nozzles the minimum operating pressure through the nozzles will be in the range of from about 20 kg/cm to about 1 kg/cm.

For optimum performance the minimum pressure is adjusted to achieve the following spray pattern: Median Particle Diameter Percentage

(microns)

0.75 0.05

1.5 0.2

2.75 1.81

4.25 9.78

6.25 24.66

8.75 30.18

12.5 28.83

15 4.49

Table 1

A high pressure pump (or individual pumps, one per atomising unit) of sufficient capacity to pump the leachate filtrate through the atomising units 10 at the pressure required to achieve the desired level of flash vaporisation of the leachate filtrate is typically employed. The line pressure close or at the discharge nozzles should preferably range from about 56 atmospheres (800 psi) to about 70 atmospheres (1200 psi) where discharge nozzles with orifice size of about 186 microns are employed. The high pressure pump (or its suction line) incorporates a dump valve which facilitates collection of any excess leachate filtrate, for return to the balance tank or re-introduction input stream. As the leachate filtrate is expelled through the atomiser unit nozzles, a very fine leachate mist is created, with mist particle size of the order of about 2 to 10 microns in diameter. The air stream generated by the dispersion fan(s) disperses the mist and increase the distance between individual droplets, thereby promoting vaporisation further. Due to the proportionally large surface area of the leachate mist droplets, once they leave the nozzles and are dispersed in air, the rate of evaporation is increased dramatically resulting in the efficient disposal of treated leachate in the atmosphere in a safe manner.

High pressure discharge of the leachate filtrate through the nozzles of the atomising units into the air stream enables efficient stripping of all volatile components contained in the atomiser filtrate, thus releasing most of the ammonia content of the raw leachate. The discharge pressure is chosen such that at the atmospheric conditions given at the time of operation of the plant, i.e. ambient temperature, barometric pressure and humidity, the water content of the leachate is fully vaporised and dispersed. The discharge pressure level will also ensure that the ammonia contents will be released into the atmosphere in gaseous form, where some part of the ammonia will react with atmospheric gases and other vaporised or otherwise released chemical compounds contained in the leachate filtrate.

It is expected that of the total ammonia present in a leachate only about 10 % of it will be present as ammonia gas, the remainder being present in ionic form. During the process of the present invention the ammonia gas is stripped during the evaporation process and is subsequently diluted in the atmosphere (rather than reacting with other atmospheric gases). The ammonium ions present in the leachate react with various anions also present in the leachate (typically for example, chloride, sulphate, phosphate and carbonate ions) and fall out of solution in the form of ammonium salts.

It is evident, that the plant will incorporate suitable surveillance and control devices to monitor and control the quantity of leachate entering and exiting the system, as well as monitor the environmental conditions during operation of the plant thereby to ensure optimal performance.

Overall operation of the apparatus may be controlled manually or alternatively may be fully automated and controlled via a central control unit which may optionally contain a PLC (Programmable Logic Controller). Such a central control system may typically incorporate checks for leaks, which may be indicated by pressure losses, and/or safety features such an automatic shut down facility in the event of a serious fault being detected.

The process and apparatus of the present invention may be effective in conditions of up to about 93 % relative humidity. An automatic shut down sensor may be provided to terminate operation in the event of rain. In the event of an overall shut down, any leachate in the atomiser plant 9 may be returned to the leachate pond for treatment at a later time.

Ammonia sensors are provided, for example at regular intervals and around the perimeter of the plant, e.g. at a distance of 50 m from the atomiser plant 9 to monitor ammonia levels and thus evaluate performance of the process.

An apparatus according to the invention was built and tested at an atomiser arrangement (plant) output level of 160 litres of leachate per hour with no detrimental impact on air quality. The leachate content prior to treatment is summarised in Table 2.

Test Parameter Quantity (mg/L)

Suspended solids 20 - 500

Total Organic Carbon 600 - 1700

BOD 90 - 720

Ammonia - N 500 - 1950

Nitrate - N 0.001 - 3.0

Nitrite - N 0.001 - 2.5

Total Nitrogen Content 600 - 2000

Chloride 900 - 2600

Sulphate 2 - 25 Total Phosphate as P 0.01 - 14.0

Fluoride 0.1 - 2.0

Arsenic <0.146

Barium <1.4

Cadmium <0.003

Cobalt <0.135

Chromium <0.350

Copper <0.4

Manganese <1.73

Molybdenum <0.025

Nickel <0.384

Lead <0.08

Antimony <0.03

Selenium <0.1

Tin <0.3

Zinc <1.66

Mercury <0.0006

Ethylbenzene <0.022

Naphthalene <0.017

Toluene <0.036 ,2,4-Trimethylbenzene <0.024 ,3,5-Trimethylbenzene <0.008

Ortho-Xylene <0.023

Meta & Para Xylene <0.041

Para-lsopropyltoluene <0.081

1 ,4-Dichlorobenzene <0.007

2-Butanon (MEK) <0.06

Phenol <0.09

2-Methylphenol <0.03

4-Methylphenol <0.16

3-Methylphenol <0.16 2,4-Dimethylphenol <0.02

Bis(2- <0.33 ethylhexyl)phthalate

Table 2 The data appearing in Table 2 was collated from measurements taken over an extended period of time, thus some values appear as ranges observed. Values preceded by a < sign showed no significant variation and are presented as "less than" values to indicate a maximum observed level.

(Leachate pH was recorded as 7.2 - 8.6)

Using the AUSPLUME modeling system ("AUSPLUME Gaussian Plume Dispersion Model - Technical User Manual", Victorian EPA, Publication 671 , December 1999) the following conclusions were reached:

(a) ambient concentrations of C0₂, CH₄, and TOC (total organic carbon) did not vary significantly from background during the leachate treatment process; (b) total suspended particle concentrations measured 45 m from the atomiser arrangement were below levels recommended as safe by the National Health and WHO;

(c) CO concentrations were below ambient air guidelines;

(d) Ammonia levels beyond 45 m of discharge were within ambient air guidelines;

(e) Predicted ammonia ground level concentrations did not exceed the 3 minute guideline established by the Victorian Environment Protection Agency (EPA);

(f) Microbiological air sampling did not indicate any significant increase in concentrations of airborne organisms above background levels;

(g) Concentrations of volatile contaminants were below their respective odour thresholds. 01/77027 _. _c PCT/AUOl/00368

T

It was found that none of the predicted onsite airborne chemical agents exceeded their respective Worksafe standard levels and the predicted offsite airborne chemical agents were all below the residential risk-based acceptance criteria set by the ANZECC/NHMRC (Australia and New Zealand Environment and Conservation Council / National Health and Medical Research Council) USEPA (United States Environment Protection Agency) and Worksafe.

"Comprises / comprising" or grammatical variations thereof, when used in this specification, is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A leachate treatment process comprising the steps of:

(i) filtering a raw leachate to produce a leachate filtrate, and

(ii) atomising the leachate filtrate to produce a leachate mist; characterised in that, the atomising step produces a leachate mist having an average particle size of less than about 20 microns in diameter, and in that, the filtrate mist is substantially completely evaporated through exposure to atmospheric conditions.

2. A leachate treatment process according to claim 1 wherein step (i) comprises passing the raw leachate through a sand filter and subsequently passing the output from the sand filter through a secondary filter.

3. A leachate treatment process according to either claim 1 or claim 2 wherein the raw leachate is filtered to remove substantially all suspended solids having an average diameter of greater than about 1 micron.

4. A leachate treatment process according to either claim 2 or claim 3 wherein the secondary filter comprises one or more cartridge filters.

5. A leachate treatment process according to any one of the preceding claims wherein step (ii) comprises expelling the leachate filtrate under high pressure through one or more nozzles producing a leachate mist.

6. A leachate treatment process according to claim 5 wherein the leachate mist is expelled into an air stream created using one or more fans.

7. A leachate treatment apparatus for the treatment of raw leachate comprising at least one filter for producing a leachate filtrate, an atomisation arrangement for atomising the leachate filtrate, and a pump for pumping the leachate filtrate from the filter to the atomisation arrangement; characterised in that, the atomisation arrangement has at least one nozzle, which in operation, causes the leachate filtrate to be converted into a leachate mist having an average particle size of less that about 20 microns in diameter.

8. A leachate treatment apparatus according to claim 7 further comprising one or more fans for producing an air stream into which the leachate mist may be introduced.

9. A leachate treatment apparatus according to claim 9 wherein each fan has a fan housing and wherein the atomisation arrangement comprises a plurality of nozzles mounted on a series of concentric ring pipes associated with each fan housing.