Do you want learn how to apply concepts of sustainable faecal sludge management (FSM) on a city-wide scale? This course starts with an overview of what faecal sludge is and an introduces you to the engineering fundamentals and required information for the design and selection of technologies. Sanitation solutions are prone to failure if an integrated planning approach that includes stakeholder involvement and the development of appropriate institutional, management and financial arrangements is not implemented. The course therefore dedicates a complete week to presenting the full picture, in addition to technology, that needs to be considered for sustainable solutions. It concludes with a focus on current research and innovations in technologies, to provide an understanding of the most up-to-date options. This course is one of four in the series “Sanitation, Water and Solid Waste for Development".
5.7 Innovations in ammonia and lime treatment
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来自 École Polytechnique Fédérale de Lausanne 的课程
Introduction to Faecal Sludge Management
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从本节课中
Innovations in faecal sludge management
Faecal sludge management is a relatively new and rapidly growing field. As a result, many solutions are not yet fully developed, which has to be carefully considered in technology implementation. Week 5 will focus on current research and innovations in technologies, to provide an understanding of the most up-to-date options, and what needs to be considered for further development and implementation.
与讲师见面
Dr. Linda StrandeGroup leader
Management of Excreta, Wastewater and Sludge (MEWS), Eawag-Sandec
The number one treatment objective in faecal sludge management
is always protection of public health.
Through protecting people from pathogens that make them sick.
In this module we'll introduce you to two treatment technologies
that can achieve high levels of pathogen inactivation:
Ammonia and lime treatment.
Following this module
you will be able to explain how pathogen inactivation
occurs in ammonia and lime treatment.
Discuss operational maintenance requirements of these technologies.
And considerations for their implementation.
Ammonia treatment
for pathogen inactivation faecal sludge
is currently in the research and development phase.
Ammonia treatment relies on the toxicity of ammonia
to pathogens.
Ammonia can be added to the faeces in the form of urea.
But this treatment technology is really interesting
because ammonia can also be provided through urea
that is included in urine.
Nitrogen urine is in the form of urea,
but which is converted to ammonia by the urea's enzyme,
that is available throughout the environment.
Ammonium nitrogen and ammonia nitrogen
are in equilibrium with each other.
This graph shows the fraction of nitrogen
that is available as ammonia as a function of pH and temperature.
As shown in this graph,
by increasing the pH
for example by the addition of lime or ash,
the ammonia nitrogen concentration can be increased.
At a pH below 8.5
a mixture of urine and faeces
will still have a lower ammonia concentration
for pathogen inactivation.
At this pH,
most of the nitrogen is in the form of ammonia
that is not harmful for pathogens.
An increase in temperature also increase ammonia concentrations.
Next to the toxicity of ammonia
the high pH is also additional mechanism
for pathogen inactivation in an ammonia treatment.
Faecal sludge collected from septic tanks and pit latrines
is mostly water,
which dilutes the ammonia and results in low concentrations
to be available for pathogen inactivation.
Even at an elevated pH.
Loss of ammonia and ammonium
that are volatile to open manholes and septic tanks,
or drop holes and pit latrines,
also reduce the concentration
of ammonia available for pathogen inactivation.
In contrast to this type of sludge,
high levels of pathogen inactivation
could be feasible with faeces and urine
when we lower the amount of flushing water
and we are in sealed tanks.
In laboratory experiments in Sweden
at 20° C and a pH of 9,
ammonia treatment could inactivate 99% of Ascaris eggs,
which is the common Helminths egg in only 24 days.
A decrease in a temperature and an increase in flush water,
increase desaturation
for the same level of pathogen inactivation
from several weeks
to several months.
So moving from the laboratory,
how could these results be used in practice?
One attempt at the safe sludge project
that is based on the collection of faeces and urine
without any flush water.
In the first step,
faeces and urine are mixed together with the contact time of 4 hours,
to convert urea
with the enzyme urease into ammonium.
Following, a material increasing the pH,
which is lime and ash, is added
which converts ammonium into ammonia.
Then this is kept for hours or days for inactivation of pathogens.
It is important to convert urea into ammonium
before increasing the pH;
as an increase in pH inhibits the enzyme urease.
In the laboratory experiments in the United States,
99% of ascaris eggs were inactivated through this process.
Such a treatment and process
could be implemented for pathogen inactivation
in innovative on-site sanitation technologies
after treatment following separate collection of faeces and urine,
As shown here with these jericans for urine collection,
and a tank for storage, in Bolivia.
Lime treatment, which is also called alkaline treatment,
is a common treatment technology for waste water sludge.
But also has been implemented full-scale for faecal sludge
for example for the treatment of septic tank sludge
in the United States or in the Philippines.
Lime is a fine white powder.
Based on available litterature on waste water sludge,
the most common form of lime that is used in lime treatment
is hydrated lime, or calcium hydroxide.
In lime treatment,
sufficient amount of lime are added
to the faecal sludge to increase the pH to 12
for several hours to a month.
Such a high pH slows down or stops biological processes
that are responsive for odors and it inactivate pathogens.
As discussed before for ammonia treatment,
the increase in pH
also results in the increase of ammonia concentrations
that can contribute to further pathogen inactivation.
Lime can be addible to liquid,
sludge, and also sludge following the watering.
Addition of lime to more liquid faecal sludge
has the added benefit
it could improve solid-liquid separation processes.
During laboratory research that we conducted
together with our research partners in Dakar,
lime improved dewatering by 90-95%
compared to an untreated control without lime.
This can reduce the time and space required for dewatering,
for example on unplanted drying beds.
The dosage of lime to adequately raise the pH
is an important design and operational parameter
for lime treatment.
The average dosage of several lime treatment applications
in the United States with septic tank sludge,
and also application in Philippines
was 20% lime per dry mass of sludge.
In one study in Blantyre, Malawi,
addition to 20-35% lime per dry mass of sludge
was successful in increasing the pH to 12.
As lime is dosed as a function of total solids
and they can be variable
and also the chemical characteristics of sludge
can be variable that influence lime treatment
it is always important to determine
the required dosage based on a local sludge characteristic.
This can be done by a simple bench and pilot scale experiment
where different amounts of lime are added to faecal sludge
as shown here in the Philippines.
Following mixing of the lime and the faecal sludge,
the pH can be monitored over time with a handheld pH meter.
This picture shows an example of lime treatment
of a septic tank faecal sludge in the Philippines.
The workers are adding lime in a mixing tank
The workers are adding lime
in a mixing tank
to the faecal sludge in powder form,
or a slurry prepared with water.
Lime is highly corrosive for infrastructure and equipment
and personal protective equipment such as safety goggles, boots,
long-sleeve clothes and face masks should always be worn.
This is because the same process
that increase the pH in faecal sludge,
also increase the pH most surface in humans,
such as the skin, eyes and lungs.
Following addition of lime,
thorough mixing is required
to ensure contact of faecal sludge with lime.
As shown in this picture,
this can be done manually,
but mechanical mixing can be more effective
and has the potential to produce higher pH values
at the same lime dosage.
So how effective is lime treatment in the inactivation of pathogens?
In one study in Blantyre,
and in another study in Phnom Penh, Cambodia,
additional lime reduced E. coli concentrations
below the limits recommended by the World Health Organization
for use in agriculture.
However, knowledge from lime treatment of waste water sludge
suggests that because Helminth eggs are more persistent bacteria,
treatment may require longer storage durations at a high pH.
Also the effectiveness of a pathogen inactivation
will depend on the type of the pathogen
and the initial concentration of pathogens in a local context.
It is always important to assess the inactivation of pathogens
as a function of pH and time for the local context.
Wrong assumptions can have a severe public health impact.
Lime treatment has the benefit that is relatively quick, robust
and effective for pathogen inactivation.
It also has a small treatment footprint.
All of these characteristics also make it suitable
for emergency situations.
However it is important to consider these benefits
and balance them with the operating cost,
which are mainly purchase of the lime.
Price for lime can vary considerably between countries.
For example, in the Philippines of price 150-100 dollars per tonne,
in Senegal of 250 dollars per tonne,
and in Malawi of 800 US dollars per tonne has been reported
in the literature.
Lime treatment inhibits biological process
is harmful for the pathogens by increasing the pH.
It is important to consider that this process can only be temporary
and pathogen regrowth might occur if the pH drop below 11.
For example during storage,
transport, or use of the treatment product.
Pathogen in incubation only remain safe at a pH of 12.
Another important consideration,
is that lime treatment does not reduce the sludge volume,
as for example anaerobic digestion.
In contrast,
the addition of lime increase the mass of sludge
that needs to be managed and disposed.
It is also important to consider the characteristics of the sludge
following lime treatment
as it can influence subsequent treatment steps
and resource recovery.
Co-composting, for example,
is based on microorganisms that inhibited the lime treatment
and the high pH following lime treatment
may not be beneficial for all soils.
Lime is also inorganic
and therefore doesn't contribute to the fuel value,
which means that lime treatment uses the energy value
for energy recover of solid fuels.
In this module,
we introduced lime and ammonia treatment,
that are two technologies for pathogen inactivation.
In both treatment technologies,
the toxicity of ammonia nitrogen and a high pH
are the main mechanisms for pathogen inactivation.
The effect of these technologies for pathogen inactivation
will depend on the type of concentration of pathogens
the dosage of lime and ammonia required to produce environments
that are toxic to pathogens, and the contact time.
For long-term operations of these treatments
it is important to consider that both technologies
rely on reliable supply of ammonia
in the form of urine urea and lime.
