ISO 24297:2022
(Main)Guidelines for treatment and reuse of leachate from municipal solid waste (MSW) incineration plants
Guidelines for treatment and reuse of leachate from municipal solid waste (MSW) incineration plants
This document provides guidelines for the treatment and reuse of MSW leachate. It is applicable to personnel involved in the design, management, operation and supervision of the treatment and reuse of MSW leachate and environmental authorities engaged in regulation.
Lignes directrices pour le traitement et la réutilisation du lixiviat provenant des installations d'incinération des déchets ménagers
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 24297
First edition
2022-07
Guidelines for treatment and reuse of
leachate from municipal solid waste
(MSW) incineration plants
Lignes directrices pour le traitement et la réutilisation du lixiviat
provenant des installations d'incinération des déchets ménagers
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 General principles . 3
5.1 General . 3
5.2 Safety. 3
5.3 Reliability . 4
5.4 Stability . 4
5.5 Economic sustainability . 4
5.6 Environment . 4
6 Quantity and quality of the MSW leachate . 4
6.1 Quantity . 4
6.2 Quality . 5
6.3 Influencing factors and considerations . 6
7 Treatment system design for the MSW leachate . 6
7.1 Treatment process . 6
7.2 Treatment system . 7
7.2.1 Preliminary treatment . 7
7.2.2 Biological treatment . 8
7.2.3 Advanced treatment for reuse . 9
7.3 M onitoring system . 10
7.4 Auxiliary treatment . 11
7.4.1 General . 11
7.4.2 Sludge . 11
7.4.3 Concentrate . 11
7.4.4 Biogas .12
7.4.5 Odour .12
7.4.6 Foam . 12
7.4.7 Noise .12
8 Reuse of treated leachate .12
8.1 Reuse application considerations .12
8.2 Reclaimed water quality considerations .12
9 Environmental and occupational health and safety .13
9.1 Identification of health and safety risks . 13
9.2 Establishment of health and safety programmes . 13
9.3 Safety considerations in system design . 13
9.4 Implementation of health and safety equipment . 14
9.5 Training . 14
9.6 Management of incidents and emergencies . 14
Annex A (informative) Process parameters for leachate treatment system design .15
Annex B (informative) Quantity generation of MSW leachate .17
Annex C (informative) Potential treatment options for MSW leachate .18
Annex D (informative) Overview of MSW composition and treatment .19
Bibliography .28
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 2,
Water reuse in urban areas.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Commonly used methods for disposal of municipal solid waste (MSW) include landfilling, incineration
and composting (Annex D), and each of these methods generates leachate. Leachate is a kind of
wastewater containing highly concentrated organic contaminants that can pose a high risk to the
environment. It is necessary for leachate to have proper treatment before being discharged or reused
to avoid adverse impacts on the environment. Due to the differences in duration of waste stacking and
fermenting, leachate from different MSW disposal methods varies significantly in the concentration and
biodegradability of organic matter, which requires tailored treatment processes. Leachate generated
from MSW incineration plants has a higher concentration of biodegradable organic pollutants, and
thus degrades more easily than leachate from landfills and composting plants. Due to higher quality
requirements for water reuse in MSW incineration plants, this document focuses on leachate treatment
and reuse in MSW incineration plants.
In MSW incineration plants the MSW first enters the unloading platform and then goes to the MSW
pit, where stacking and fermentation occurs. The stacking and fermenting process aims to reduce
moisture content of the MSW before incineration. The MSW leachate has a strong odour and high
concentrations of organic and inorganic compounds; it includes stacking and fermenting wastewater
and unloading platform flushing water. Many kinds of wastewater, such as municipal wastewater,
industrial wastewater and stormwater, are used as sources of reclaimed water to address worldwide
water shortages caused by economic growth, increasing populations, climate change and other factors.
The quality and quantity of MSW leachate can vary based on climate, residents’ living habits,
composition of waste and waste collection and separation systems. Therefore, leachate treatment can
be more challenging than other kinds of wastewater treatment. Due to the complex composition of
leachate and the high concentrations of pollutants, a combined treatment process is usually necessary
for leachate treatment to meet environmental requirements and intended reuse applications. The
essential components of the leachate treatment and reuse system include pretreatment, biological
treatment and advanced treatment.
In consideration of the problems in the treatment of MSW leachate and the absence of relevant
International Standards, an integrated standard is needed to guide the treatment and reuse of MSW
leachate.
This document aims to provide design and operation principles and advice for MSW leachate treatment
and reuse in MSW incineration plants. It considers and addresses the critical issues and factors in the
design and operation of treatment and reuse systems and is intended to assist engineers, authorities,
decision-makers and stakeholders in providing a clear structure and feasible approach for safe and
reliable treatment and reuse of MSW leachate.
v
INTERNATIONAL STANDARD ISO 24297:2022(E)
Guidelines for treatment and reuse of leachate from
municipal solid waste (MSW) incineration plants
1 Scope
This document provides guidelines for the treatment and reuse of MSW leachate.
It is applicable to personnel involved in the design, management, operation and supervision of the
treatment and reuse of MSW leachate and environmental authorities engaged in regulation.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 20670, Water reuse — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
municipal solid waste
MSW
waste stream consisting of end-of-life-materials
[SOURCE: ISO 16559:2022, 3.135, modified — Notes to entry removed.]
3.2
MSW leachate
mixture of flushing water from the waste unloading platform and wastewater generated during the
stacking and fermenting (3.3) process
3.3
stacking and fermenting
process to reduce moisture content of MSW and to degrade the organic materials in a MSW pit, during
which leachate is generated
3.4
leachate treatment system
treatment units that receive and treat municipal solid waste leachate
Note 1 to entry: Leachate treatment systems include those for preliminary treatment, biological treatment,
advanced treatment, disposal of sludge and concentrate and odour control.
3.5
aerobic biological treatment
biological treatment in the presence of oxygen
[SOURCE: ISO 11074:2015, 6.4.1]
3.6
anoxic biological treatment
biological treatment process in which nitrate and/or nitrite are reduced by microbes in the absence of,
or with minimal, dissolved oxygen concentration with molecular nitrogen (N ) ultimately produced
3.7
membrane bioreactor
MBR
integrated wastewater treatment process combining a suspended growth biological treatment and a
membrane filtration system (UF/MF membrane) replacing conventional secondary clarifier
Note 1 to entry: The MF or UF membrane is submerged in the biological reactor (submerged MBR). Another
configuration has pressurized membrane modules externally coupled to the bioreactor, with the biomass
recirculated between the membrane modules and the bioreactor by pumping (side-stream MBR).
[SOURCE: ISO 20468-5:2021, 3.1.12]
3.8
filtrate
liquid by-product from a filter press or other sludge dewatering devices
4 Abbreviated terms
A/O anoxic or aerobic biological treatment
BOD five-day biochemical oxygen demand
CAPEX capital expenditure
COD chemical oxygen demand
Cr
DO dissolved oxygen
DTRO disc-tube reverse osmosis
HRT hydraulic retention time
IC internal circulation anaerobic reactor
MBR membrane bioreactor
MF microfiltration
MLSS mixed liquor suspended solids
MVR mechanical vapour recompression
NF nanofiltration
+
ammonium nitrogen as N
NH −N
OLR organic loading rate
OPEX operating expenditure
ORP oxidation-reduction potential
RO reverse osmosis
SBR sequencing batch reactor
SCE submerged combustion evaporation
SDI silt density index
SS suspended solids
STRO spiral-tube reverse osmosis
TDS total dissolved solids
TN total nitrogen
TP total phosphorus
UASB upflow anaerobic sludge blanket reactor
UBF upflow anaerobic sludge bed-filter reactor
UF ultrafiltration
VFA volatile fatty acids
5 General principles
5.1 General
The principles of safety, reliability, stability and economic viability and sustainability should be
incorporated in the design of the treatment and reuse system for the MSW leachate. The quality of
treated leachate should meet requirements for water reuse applications, be appropriate and safe for
end users and protect human health and the environment from the adverse impacts of pathogens, toxic
chemical contaminants and nutrients contained in the leachate.
5.2 Safety
The MSW leachate can contain highly concentrated salts, refractory organics, ammonium nitrogen,
pathogens and heavy metals, which can impact human health, the environment and equipment. For
example, highly concentrated salts can cause soil salinization, scaling and corrosion of equipment.
Organics and ammonium nitrogen can pollute water. Heavy metals and pathogens can impact human
health. It is important to take into consideration the quality of treated leachate in terms of physical,
chemical and microbiological indicators to ensure safe reuse.
Mature and reliable technologies should be applied to attaining required effluent and reuse quality, as
well as minimizing adverse environmental impacts. Validated and verified new technologies, processes,
materials and equipment can also be adopted to improve treatment efficiency and effectiveness,
optimize operation and management, save energy and reduce capital expenditure (CAPEX) and
operating expenditure (OPEX). In addition, the quantity and quality of the leachate, the objectives of
treatment, the intended purpose for water reuse, technological performance of the treatment facilities,
location of the treatment facilities and land availability should be considered in the selection of
technology and design of the process.
5.3 Reliability
The characteristics of the MSW leachate should be considered to ensure that the treatment and
reuse system can perform its prescribed function without failure and the effluent quality can meet
the demand of intended reuse purposes. The following aspects should be considered to ensure the
reliability of the treatment and reuse system:
a) the peak leachate quality and quantity;
b) the demand for water reuse applications;
c) redundancy of systems and/or equipment;
d) effectiveness and efficiency of treatment technologies and processes;
e) monitoring programme, including operational monitoring, water quality monitoring, alarm
systems and response plans for critical aspects to detect the performance of treatment processes
and effluent quality;
f) operations, control and proactive maintenance.
5.4 Stability
When designing the treatment system, the operational stability and effluent quality stability should
be assessed to ensure that the requirements of intended reuse applications are met. In view of the
complexities of the leachate quality, a combined process approach and online monitoring system should
be adopted to reduce the risks of effluent non-compliance. Redundant systems can also be considered,
which involves the addition of measures beyond the minimum needs to ensure performance targets are
consistently achieved.
The stability of treated leachate quality should also be considered by assessing parameters, such as pH,
alkalinity, temperature, hardness, anions such as sulfate and chloride and cations such as calcium and
magnesium.
5.5 Economic sustainability
Economic evaluations should consider both CAPEX and OPEX. CAPEX includes acquiring property,
plants, buildings, technology or equipment. OPEX includes operation, maintenance and repair. An
economic and technological comparison between different technologies should be conducted, taking
into account, for example, quality and quantity of the leachate, demand of water reuse applications and
energy cost, before designing a proper leachate treatment system.
5.6 Environment
The reuse of treated leachate should consider the environmental impacts of contaminants in leachate.
Water sampling should be at the main outlet of the reclaimed water system.
Preventive measures should be implemented to avoid adverse impacts caused by residual sludge, odour,
concentrate and noise generated during the operation of the leachate treatment and reuse system on
the ambient ecosystem (soil, air quality, noise levels and surface and groundwater).
6 Quantity and quality of the MSW leachate
6.1 Quantity
MSW leachate is generated principally by flushing the unloading platform and waste stacking and
fermenting, as shown in Figure 1. The determination of the quantity of leachate produced is of critical
concern for the design and operation of the treatment and reuse system. In general, the quantity of
the leachate generated from waste stacking and fermenting can be estimated based on the available
data from local MSW incineration plants or those in other similar regions. In the absence of reference
information, the quantity of the leachate can be estimated according to the MSW moisture content and
duration of waste stacking and fermenting. The quantity of flushing water can be estimated based on
the water consumption in a single flushing and the frequency of flushing. Cases of leachate quantity
data are given in Annex B.
Figure 1 — Flow chart of a typical MSW incineration plant
6.2 Quality
The MSW leachate varies in composition depending on the type of waste, and it can contain high
concentrations of organic matters, ammonium nitrogen and salts. Concentration of COD can reach
Cr
tens of thousands of milligrams per litre. Concentration of ammonium nitrogen and salts can also reach
several thousand milligrams per litre. The high concentrations of contaminants bring challenges to the
treatment process and if not treated properly can pose a potential risk to the environment. The quality
characteristics of the leachate affect the design and operation of the treatment process. The readily
biodegradable organic matter contained in MSW leachate makes biological processes practicable for
treatment. However, the high concentrations of ammonium nitrogen and high salinity in the MSW
leachate should be noted, as they can inhibit the microbial activity and thus affect the effectiveness and
efficiency of the biological treatment process or overwhelm the biological treatment.
The typical ranges of quality characteristics of the MSW leachate are given in Table 1. When data on
the leachate quality are unavailable, the value ranges given in Table 1 can serve as a reference for MSW
incineration power plants.
[9]–[17]
Table 1 — Characteristics of the leachate quality
Parameter Units Values
COD mg/l 20 000 to 75 000
Cr
BOD mg/l 10 000 to 50 000
+
mg/l 500 to 2 500
NH −N
TP mg/l 50 to 150
TN mg/l 1 500 to 3 000
SS mg/l 1 000 to 15 000
pH — 5 to 7
2−
mg/l 50 to 3 000
SO
2−
S mg/l 0 to 50
TDS mg/l 10 000 to 25 000
−
Cl mg/l 500 to 5 000
Na mg/l 1 000 to 4 000
Mg mg/l 300 to 1 500
Ca mg/l 500 to 6 000
Fe mg/l 0 to 1 000
Mn mg/l 0 to 50
Table 1 (continued)
Parameter Units Values
Zn mg/l 0 to 50
Pb mg/l 0 to 8
Ni mg/l 0,05 to 5
As μg/l 40 to 120
Pd mg/l 0,05 to 0,2
Cr mg/l 0,05 to 1,5
6.3 Influencing factors and considerations
The quantity and quality of the MSW leachate are affected by factors such as waste classification,
waste collection and transportation system, composition of domestic waste, separation of organics
and plastics, moisture content, duration of stacking and fermenting, seasonal changes, local climate
and residents’ living habits (Annex D). The varying waste classification systems from different areas
can change the composition and moisture content of MSW and can impact the quantity and quality
of leachate. In the rainy season or in rainy areas, the entry of rainwater during waste collection and
transportation can increase the quantity of leachate and at the same time lower the concentration of the
pollutants. Therefore, the factors mentioned should be fully considered when estimating the quantity
and quality of the leachate.
In determining the quantity and quality of leachate, data comparisons with local MSW incineration
plants and/or those in similar areas should also be considered in estimating ranges of the quality and
quantity of the MSW leachate. To ensure that the MSW leachate can be treated in a timely manner,
fluctuations of the quality and quantity of the leachate, and required operating time, should be
considered in determining the capacity of the treatment system.
7 Treatment system design for the MSW leachate
7.1 Treatment process
MSW leachate has a high concentration of pollutants with complex constituents. Treatment process
combinations with several different technologies are required to ensure the reliability and stability
of the treatment system. The leachate treatment system (Figure 2) normally comprises preliminary
treatment, biological treatment and advanced treatment. In some cases, the combined processes of
preliminary treatment + advanced treatment or biological treatment + advanced treatment can also be
adopted, depending on the quantity and quality of the leachate to be treated and the requirements for
reclaimed water quality and use.
Figure 2 — Process flow chart of the leachate treatment system
To increase safety and address reliability concerns, if temporary interruptions are not allowed
or alternative water resources are not available, equipment redundancy is required to ensure
performance targets are consistently achieved without interruption during maintenance and overhaul
of the treatment system. The treatment and reuse system should be designed in two or more trains so
that the total treatment capacity of all trains is sufficient for treating all MSW leachate. If the design
treatment capacity is relatively low, a single system design can also be considered.
The main objectives of preliminary treatment are to remove suspended solids (SS), gravel and other
solid granules from the leachate to reduce the risks of abrasion, blockage and damage to pipelines and
equipment. The technologies commonly used for the leachate preliminary treatment include screening,
regulating, filtering and sedimentation. Adjustment and control of leachate quantity and quality
entering the biological treatment process is required to ensure the stable performance of subsequent
treatment units.
Biological treatment is considered as a better alternative for the complex water quality of the leachate
due to its reliability, environmental friendliness and cost-effectiveness, and thus should be selected
as the main treatment process. Biological treatment can include an anaerobic process followed by an
aerobic process consisting of an anoxic unit and an aerobic unit. The anaerobic process is to remove
the majority of the organic contaminants from the leachate, produce biogas and convert the organic
nitrogen to ammonium nitrogen. The anoxic-aerobic units are used mainly to remove total nitrogen
(TN) from the anaerobic digestion process effluent via reactions of nitrification and denitrification
and further remove the remaining organics from the leachate. The resilience of biological treatment
systems should accommodate to the potential impact of variable contaminant loadings in order to
address the dramatic fluctuations in quality and quantity of leachate caused by seasonal variations and
climate change.
For reference, operational parameters for the biological treatment process are provided in Annex A.
Advanced treatment is adopted in reuse system to remove total dissolved solids (TDS) and/or trace
constituents (e.g. heavy metals), and especially salinity, from the effluent of the upstream unit, to
ensure water quality meets the requirements for reclaimed water. Membrane filtration processes,
including nanofiltration (NF) and reverse osmosis (RO), are generally used to remove TDS, salts and
heavy metals. For reference, operational parameters for NF and RO are provided in Annex A.
7.2 Treatment system
7.2.1 Preliminary treatment
7.2.1.1 Sedimentation tank
In the sedimentation tank, high concentrations of SS or solid granules can be settled from the leachate
through gravity to prevent deposition in the regulating pond. Based on the quantity of the leachate,
vertical flow sedimentation tanks are usually installed.
7.2.1.2 Regulating pond
The regulating pond is used to equalize both the quality and quantity of the leachate to minimize
variations to the subsequent biological treatment processes.
The regulating pond generally follows the sedimentation tank. A mixing device(s) should be included
in the regulating pond to avoid settling anaerobic conditions to ensure a homogenized leachate. As
leachate can generate unpleasant smells, odour-control measures should be taken in the regulating
pond. Dredging can be needed depending on leachate SS. The hydraulic retention time (HRT) of the
regulating pond should not be less than 7 days. Regulating ponds can also be used as emergency ponds.
7.2.1.3 Screen and filtering
Screen and filtering devices can be used to remove SS from the leachate before it flows into the
subsequent treatment system, to reduce the pollutant load and protect piping and equipment (e.g.
pumps) from being plugged or damaged.
7.2.2 Biological treatment
7.2.2.1 Anaerobic digestion system
Anaerobic digestion is mainly used to remove the organic pollutants in leachate. In general, the organics
removal rate for the anaerobic digestion process should be controlled in order to obtain the objectives
that the bulk of contaminants be biodegraded from the system effectively and efficiently and organics
remain for the subsequent biological process, especially for denitrification.
The anaerobic digestion system consists of an anaerobic digester, heating and insulation, biogas
collection and residual sludge disposal. Commonly used anaerobic digesters include upflow anaerobic
sludge blanket reactors (UASBs), upflow blanket filter reactors (UBFs) and internal circulation reactors
(ICs). Anaerobic digesters modified with the latest and validated technologies can also be considered.
The anaerobic digester can be constructed from reinforced concrete or steel. The inner wall of the
reinforced concrete structure requires anti-corrosion treatment and both the inner and outer walls
of the steel structure require anti-corrosion treatment. When the biogas produced by the anaerobic
process is burned with a flare, multiple protective measures, such as flame arresters and water seals,
should be included to prevent an explosion caused by flashback. The steel structure tanks should
be equipped with breather valves, explosion-proof membranes and positive or negative pressure
protection devices to maintain biogas pressure in the anaerobic digester within a normal range to
avoid pressure fluctuations under abnormal conditions and damage to the structure of the anaerobic
digester.
Explosion-proof equipment and other safety measures should be implemented to prevent explosions
and fires in areas where generation and accumulation of flammable or explosive gases can occur, such
as anaerobic digesters, regulating ponds and biogas collectors.
7.2.2.2 Anoxic or aerobic biological treatment process
The anoxic or aerobic biological treatment (A/O) process is mainly used to remove nitrogen and the
remaining organic matter from the anaerobic digestion process effluent. The aeration system for the
aerobic processes can use equipment such as jet aerators, aeration blowers and membrane aerators.
Commonly used aerobic processes include oxidation ditches, pure oxygen aeration reactors, membrane
bioreactors (MBRs), sequencing batch bioreactors (SBRs), biological aerated filters, contact oxidation
tanks and rotating biological disks. An MBR system is widely used to ensure the effluent quality meets
the requirements of influent quality to the subsequent advanced treatment systems (e.g. high-pressure
membrane filtration by NF or RO) or discharge requirements. An MBR system normally consists of
a bioreactor (aerobic unit) and UF/MF module in series. Membrane material with strong mechanical
properties is recommended to avoid membrane damage to prevent SS and other contaminants from
fouling the membrane. The types of MBR system generally include sidestream MBR (Figure 3) and
submerged MBR (Figure 4).
A typical A/O process for when sidestream MBR is adopted is given in Figure 3.
Figure 3 — Flow chart of a typical A/O process with sidestream MBR
A typical A/O process for when submerged MBR is adopted is given in Figure 4.
Figure 4 — Flow chart of a typical A/O process with submerged MBR
In some cases, the multiple-stage A/O process is selected to improve the effluent quality of the treatment
system; a typical process flow chart is shown in Figure 5. An additional carbon source will possibly be
required for the second stage A/O.
Figure 5 — Flow chart of a typical two-stage A/O process with sidestream MBR
Nitrate-rich mixed liquor from the aerobic MBR unit (Figures 3 and 4) is returned to the anoxic unit with
the purpose of nitrate reduction and sludge recirculation. As a result, TN is removed from the system
and the biomass concentration is able to be maintained at the desired level to ensure performance of
the biological units.
In the multiple-stage A/O process (Figure 5), nitrate-rich mixed liquor is internally recirculated in
the first-stage A/O process. As the SS concentration of mixed liquor recirculation is relatively low,
the separated sludge from the UF/MF module in the second stage A/O process is returned to the first
anoxic unit in order to avoid a decrease in biomass and ensure the performance of the multiple-stage
biological process.
Based on local economic and technical conditions, SBR or other approximate processes can also be
adopted to treat the effluent of anaerobic processes for nitrogen removal. In this case, a pilot study
should be carried out before process selection.
Due to the high organic contaminant concentrations of leachate, a higher biomass concentration and
longer HRT are required to ensure the performance of the A/O system. The biochemical reactions in the
aerobic unit can produce heat, thus a cooling system for the aerobic unit should be provided in summer
or in hot areas to prevent overheating in the unit. Bulking and foaming in activated sludge processes,
caused by poor sedimentation performance of activated sludge, should be carefully controlled by
adopting preventive and corrective measures (e.g. defoaming agents) in order to prevent the wash-out
of biomass.
7.2.3 Advanced treatment for reuse
The selection of advanced treatment processes should be dependent on the effluent quality from the
preceding biological treatment process(es), the requirements of the water reuse applications and the
economic viability of reclaimed water system(s) for the processes. High-pressure membrane filtration
systems, including nanofiltration (NF) and reverse osmosis (RO), are widely used as major components
for advanced treatment.
Usually, the effluent of biological treatment processes (e.g. MBR) can directly enter the high-pressure
membrane filtration system for advanced treatment. Effluent from non-MBR-type aerobic biological
treatment processes should undergo UF treatment before entering the advanced treatment system
(e.g. NF, RO). When the MBR process is implemented for the biological treatment process, the examples
of combined processes for advanced treatment given in Figure 6 can be considered after taking into
consideration the effluent quality of MBR and economics considerations.
a) Example I
b) Example II
Figure 6 — Typical examples of combined process for advanced treatment
DTRO and STRO can be considered in the reuse system.
To prevent or mitigate membrane fouling, substances (e.g. hardness, colloids, SiO ) that can cause
membrane fouling should be monitored and treated, if necessary, before feeding MBR effluent into the
advanced treatment system.
Some other processes and technologies of wastewater treatment (Annex C) can be potential options for
MSW leachate treatment.
7.3 Monitoring system
A sound monitoring programme, including operational monitoring and water-quality monitoring,
should be carried out in real time or on a regular basis in order to ensure that the performance of
treatment processes and effluent water quality are in compliance with target objectives and operation
failures can be detected and solved in a timely manner. Online monitoring facilities should be equipped
for providing monitoring data on system performance and water quality indicators. As part of the
online monitoring system, alarm measures should also be implemented to ensure the emergency
and performance deterioration can be identified in a timely manner. For parameters that cannot be
measured online, an offline monitoring scheme should be established.
The key performance indicators and operating parameters should be monitored to provide timely
information to indicate the potential operational non-compliance of the system. Special attention
should be paid to the quality of the influent and operating parameters that can affect microbial activity
and further affect the performance and stability of the leachate treatment system. The focus should be
on key performance indicators such as COD , BOD , ammonium nitrogen, TN and total phosphorus.
Cr 5
In addition, the monitoring of operating parameters for the anaerobic digestion process should
include temperature, pH, VFA, biogas flow rate and pressure, alkalinity and ORP. The monitoring of
operating parameters for anoxic units should include temperature, pH, ORP and MLSS. The monitoring
of operating parameters for aerobic units should include temperature, DO and MLSS. The monitoring
of operating parameters for NF and RO should include temperature, pH, pressure, COD , ammonium
Cr
nitrogen, ORP, SDI, membrane flux, flow rate, salinity of the influent, permeate and concentrate streams.
To ensure normal operation of each treatment process and unit, an inspection plan and preventive
maintenance measures should be developed to minimize the occurrence of system failures or
malfunctions (e.g. equipment, instruments, buildings and structures of the treatment and reuse system)
and improve process compliance of treatment and reuse systems.
7.4 Auxiliary treatment
7.4.1 General
The by-products, including excess sludge, concentrate, biogas, odour and noise created during the
processes of the treatment and reuse of the leachate, should be controlled by auxiliary treatment
systems in order to prevent adverse environmental impacts.
7.4.2 Sludge
The sludge is mainly generated in the processes of biological treatment and sedimentation. As the
amount of sludge is relatively low, it can be dewatered to improve its heat value and incinerated together
with MSW for power generation or be treated together with municipal sludge by a sustainable system.
The filtrate from sludge dewatering can be treated together with or separately from the leachate.
7.4.3 Concentrate
7.4.3.1 General
Concentrate is generated in the high-pressure membrane treatment process and contains refractory
organics, salinity and other contaminants. It is difficult to treat concentrate with a biological process.
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The concentrate can be treated by processes such as incineration, evaporation crystallization,
chemical oxidation or other capable processes. In some circumstances, the concentrate can also be
reused for slag cooling or lime slurry preparation, which can be used for the treatment of flue gas from
MSW incineration.
7.4.3.2 Incineration
Incineration is an economically efficient method that can be used to treat concentrate in MSW
incineration plants. The injection of concentrate into incinerators should have no negative impact on
MSW incineration.
Incineration of concentrate can lead to the accumulation of salinity in ash, and this issue should be
considered in the disposal of ash.
7.4.3.3 Evaporation crystallization
Evaporation crystallization processes, including MVR and SCE, can be used to reduce the volume of
concentrate.
In the MVR process, steam is compressed and then sent into an evaporator, where the heat is transferred
to concentrate and used to vaporize the concentrate. In the SCE process, biogas prod
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