For many centuries, society has been plagued by various diseases which, in some cases, have claimed millions of lives. Fortunately, with the progress of science and the increased knowledge about the importance of health care, basic sanitation has become accessible to a large part of the world’s population.

Although to this day many people have no access to this benefit, it is undeniable that this was a great achievement, responsible for saving billions of lives. Nevertheless, the work continues and it is essential for us to be knowledgeable at all times about new techniques and strategies for water treatment.

With this in mind, we prepared a special article on sludge treatment in basic sanitation. Please go on reading and ask your key questions about one of the most important processes for ensuring water quality!

What is sludge?

First of all, let’s recap or learn the definition of sludge. This is the kickoff so that we can move forward in our studies on the treatment of these compounds in water. Let’s go!

Sludge is the name given to a type of waste derived from industrial processes, from processes that take place at water treatment stations and wastewater treatment stations. It arises from the process that causes compounds to decant and accumulate in this structure.

Therefore, sludge is a mixture of compounds. Some of the items in sludge composition are sand, clay, colloids and decomposer microorganisms, which makes wastewater treatment critical for the quality of the effluent treatment.

The next point of attention is the differentiation between the concepts of sludge, mud and sediments. Mud is the name given to effluent composed of clay, earth and water. Sediment, in turn, corresponds to solid particles that precipitate or float in liquids, thus impacting water visibility and depth.

Now, it’s time to learn a little more about sludge, which can be rated in different ways. Let’s check out the main types below!

Primary sludge

Primary sludge is also called raw sludge. It is composed mainly of organic solid sediments. It is the sludge obtained from the processing in the primary decanter in the process of treatment of this material.

Secondary sludge

This type of sludge is obtained from the processing in reactors and can be classified between digested and septic sludge.

Biological sludge

Biological sludge is composed mainly of organic matter. It is widely used from positive disposal. It is forwarded for biological uses such as use in fertilizers and others.

Physical/chemical sludge

Physical/chemical sludge comes from water physical or chemical treatment, such as the use of coagulants to aggregate the solids and leave only the component of the sludge free to be removed. Aluminum is good example of a compound that can be used in this process.

Organic sludge

Organic sludge carries more organic substances in its composition, such as agents from the decomposition of other living beings.

Inorganic sludge

Inorganic sludge, in turn, has a predominance of inorganic substances in its composition. Some examples are nitrogen, magnesium, phosphorus and calcium.

There are also other classifications, such as thickening, stabilization, dewatering and urban or industrial origin. This characterization involves a series of technological processes, such as chromatography and bacteriological analysis of the compounds involved, and is essential for the personnel responsible to know how to continue the treatment.

What are the risks of the presence of sludge in water?

After learning what sludge is, it’s time to check out some of the biological risks of excess of this compound in effluents. Learn more below!

Aggregation of pollutants into the compound

Sludge is a major bioaccumulator, i.e., its presence causes potentially harmful compounds to accumulate on its surface. Good examples are heavy metals, which end up being a strong presence in most samples of sludge collected at treatment stations.

Development of infectious / contagious diseases

Water contaminated with sludge is a great danger for human and animal life. After all, sludge is also a powerful accumulator of microorganisms that often cause diseases (pathogens). Some diseases generated by untreated water are cholera, hepatitis A and giardiasis, among many others.

Development of several health problems

Whether by the diseases mentioned above (such as hepatitis) or for other reasons (such as accumulation of heavy metals), it is important to note that untreated water can also cause systemic damage or problems to specific organs of the body. Commonly affected regions are the intestines, kidneys and liver.

What are the challenges of the sludge treatment process in sanitation?

It is obvious that sludge treatment is indispensable in basic sanitation, right? However, there are some challenges involved in this process. That’s what we’re going to talk about now!

Elimination of disease-causing agents

As discussed earlier, one of the major problems of sludge is its capacity for bioaccumulation. Eliminating these potentially toxic compounds is also a major challenge that requires careful treatment and the use of various recycling strategies, as we will see later.

Search for ways to reuse sludge without harming the environment

Finally, an existing challenge is the search for appropriate ways to dispose or reuse this material. Fortunately, there are increasingly more options, but even so, many of them require a lot of work for sludge biostabilization, releasing it for safe use with no ham for the environment.

What are the processes involved in the sludge treatment?

The time has come to find out what processes are involved in sludge treatment in sanitation. To know what these processes are, just go on reading!

Anaerobic digestion

Anaerobic digestion takes place via decomposition of organic compounds potentially harmful to humans. One of the major benefits of this strategy is generation of biogas, which can be used to produce sustainable energy.

In addition to biogas, the product of this reaction is the solid waste material, which, in turn, can also be reused in composting processes.

Aerobic digestion

In this type of treatment, aerobic microorganisms are used to perform digestion. Therefore, no biogas is generated, as seen in the example above.

However, this technique has other advantages, such as reducing polluting agents, reducing the volume and mass of processed sludge, reducing unpleasant odors and attenuating the bioaccumulation potential of this product, making it more stable and safer for use.


Same as aerobic digestion, densification also has the characteristic if reducing the volume of the treated sludge. As its name says, the density of the material increases.

The process is carried out by a machine known as densifier. It removes water through a rotating screen, leaving it denser and ready to follow to other steps.


Sludge is a material composed of large amounts of water. This can impair its mobility, make it more unstable and contribute to the proliferation of even more microorganisms in its composition.

For this reason, dewatering is carried out, which consists of physically removing water. It is a process made by centrifuges. The centrifugal decanter is used to separate the solid from the liquid phase, dewatering the solid and clarifying the liquid. The liquid to be clarified enters the machine through a horizontal tube coaxial to its main axis, and is thrown to the peripheral surface of the drum by centrifugal force. The two outlets of the separated phases, cake and clarified liquid, are at the opposite ends of the drum; the solids leave the trunk/conical end and the clarified liquid leaves at the cylindrical end. The clarified liquid leaves the drum through circular holes in a specially shaped ring. The level of the spillway is determined by an adjusting ring placed at the desired diameter, so as to determine the level of the liquid inside the drum. The choice of the setting ring diameter, and consequently the level of the liquid ring, depends on the type of product to be treated and the results to be achieved. The solid product leaves the drum through radial holes in its trunk/conical end and is thrown, by centrifugal force, into a collection chamber and directed to the solids discharge hopper, feeding the screw that takes the solid phase out of the machine or falling into a bucket in a lower level.


Finally, we have drying, a process that also focuses on reducing the water content in the material, but in a more “natural” way.

In this type of treatment, the focus is on waiting for drainage and evaporation of liquids, either with the disposal of the material in an oven or in the so-called “drying beds”. There is also heat drying, which uses large sources of heat to catalyze the process.

What is the destination of the sludge removed in the basic sanitation process?

At another point in our conversation, we stated that one of the challenges involved in the treatment of sludge in basic sanitation is precisely the difficulty to discard it in the possible way.

This is mainly due to disposal in landfills, which ends up harming the environment because of the absorption of chemical compounds by the soil. Contamination of groundwater is also caused by this type of system.

However, there are some possibilities of destination for this waste, most of which are extremely advantageous for the environment and even for society, with the promotion of new job openings and much more. Let’s check that!

Water treatment

Despite being a product of water treatment, treated sludge can return to this process and help stabilize many issues involving the quality of water resources.

Some examples are production of greater sedimentability in slightly turbid water, causing sediments to settle more quickly, and controlling hydrogen sulfide in water, a compound that is highly harmful to humans and animals..


Next, we have composting, an essential strategy to optimize the results obtained in planting eating vegetables for the population. The goal here is to use the microorganisms present in the sludge to catalyze soil optimizing reactions.

Some types of sludge need to undergo biostabilization before being released for use in composting. Others, such as solid sludge, are used directly without requiring any extra treatment.

Cement manufacturing

This is a more recent technique, not widely used in Brazil. The process consists of reusing sludge to manufacture the concrete used, for example, in the restructuring of broken sidewalks for access to the sewage network from which they are removed.

The use of sludge for this type of product does not harm its functionality; it is a sustainable and safe alternative. However, it is necessary to study what the purpose of the material used will be, since the studies are conducted only for structures that get little external pressure.

Commercial grass cultivation

Sludge from treatment stations can also be used for the composition of commercial grass, which can later be used in the making of “emerald” type grass carpets.

The positive side is that the levels of heavy metals in the samples of these grass carpets were within the safety established by the responsible agencies, i.e., this is a viable option for the use of this type of material.

Manufacture of other products

Moreover, the sludge from treatment stations can be directed to the manufacture of bricks and ceramics, an interesting strategy to boost economy and generate jobs.

In this case, the sludge is used after undergoing dewatering. The products made are extremely safe and can be used without posing any kind of risk to the structures built with them.

Use in agriculture

Finally, we have the use of sludge in agriculture as fertilizers. This is one of the most important uses of this material when it comes to sustainable development and environmental protection.

As they are rich in compounds such as nitrogen, phosphorus, zinc and others, it is possible to use sludge as a substrate for plant growth. Sludge is very commonly used to plant citrus fruit, which require a large contribution of the nutrients mentioned above.

As we can see, sludge treatment in basic sanitation is a very extensive process full of details. All this work is critical for the well-being of the population and, of course, for economic development of cities. For this reason, we must always be aware of the news of the sector.