What is anaerobic treatment of industrial wastewater and when to apply it

Industries that generate wastewater with a high organic load are increasingly seeking solutions that allow them to comply with discharge limits, reduce operating costs, and take advantage of the resources present in these streams.

In this scenario, anaerobic wastewater treatment has become established as a technology capable of purifying industrial effluents while generating biogas that can be used as an energy source.

At SITRA we design, build and operate biogas plants adapted to your industry → Learn about our biogas production service.

Compared to other biological processes, it offers particularly interesting advantages when the characteristics of the wastewater make the energy recovery of organic matter viable.

However, not all industries or all effluents require an anaerobic system. The choice depends on factors such as the pollutant load, flow rate, water composition, or the plant's objectives.

In this article we explain how the process works , in what cases it is recommended and what aspects should be analyzed before implementing this technology.

What is anaerobic wastewater treatment?

Anaerobic wastewater treatment is a biological process in which different communities of microorganisms degrade organic matter in the absence of oxygen.

Unlike conventional treatments that require a continuous supply of air to keep the biomass active, here anaerobic bacteria are responsible for transforming organic compounds into a mixture of gases composed mainly of methane and carbon dioxide, known as biogas.

How does the anaerobic process work in industrial water?

The anaerobic process of industrial wastewater occurs in several consecutive biological stages . Each group of microorganisms participates in the transformation of organic matter until stable end products are obtained.

In simplified terms, the process follows this sequence:

• Hydrolysis: Complex organic matter (proteins, fats, and carbohydrates) is broken down into simpler compounds.
• Acidogenesis: These compounds are transformed into volatile fatty acids, alcohols, hydrogen, and CO₂.
• Acetogenesis: The above products are mainly converted into acetate, hydrogen, and carbon dioxide.
• Methanogenesis: Methanogenic archaea produce methane from acetate or hydrogen and CO₂.

All of this takes place inside reactors specially designed to maintain a high concentration of biomass and maximize system performance.

To learn more about these technologies, you can consult our article on → What is an anaerobic reactor and when is it used.

What role does industrial anaerobic digestion play?

Industrial anaerobic digestion is the core of the purification process when the objective is to harness the energy potential of waste.

In addition to significantly reducing Chemical Oxygen Demand (COD) , this technology allows obtaining biogas that can later be used to produce electricity, heat or feed cogeneration processes within the industrial facility itself.

In other words, some of the pollution present in wastewater ceases to be waste and becomes an energy resource.

When is it appropriate to apply an anaerobic treatment?

Although anaerobic technology in water has been implemented in different industrial sectors for decades, its application is especially efficient when certain conditions are met.

Before selecting a technological solution, it is advisable to analyze the characteristics of the effluent and the operational needs of the plant.

Waters with a high organic load

Anaerobic treatment offers its best results when the waters have high concentrations of biodegradable organic matter, usually expressed by high COD values.

Under these circumstances, the amount of available material allows for a stable production of biogas and an interesting energy yield.

Large industrial flows

Industries that generate large volumes of wastewater often find this technology a very competitive alternative, especially when the goal is to reduce energy consumption associated with purification.

Industries where it is most used

Industrial anaerobic digestion is widely implemented in sectors such as:

• Food industry.
• Drinks and breweries.
• Dairy industry.
• Sugar mills.
• Paper and paperboard.
• Chemical industry.
• Biofuels.
• Agroindustry.

All of them generate currents with a high concentration of organic matter that can be transformed into biogas.

When there is interest in valorizing biogas

One of the great attractions of anaerobic water technology is that the process does not end with purification.

The biogas produced can be used to cover part of the factory's own energy demand, reducing the consumption of conventional fuels and improving the overall energy balance of the facility.

Precisely for this reason, many plants integrate anaerobic reactors with energy recovery systems, a solution that SITRA is developing within its bioenergy projects.

Anaerobic vs aerobic treatment: what are the differences?

Choosing between an anaerobic or aerobic process is not about deciding which is better in general, but which one best suits the characteristics of the wastewater and the objectives of the facility.

In many industrial projects, in fact, both systems are combined to achieve more efficient treatment.

While anaerobic treatment is aimed at reducing large loads of organic matter with very low energy consumption, aerobic processes are usually used to complete the purification and achieve the required discharge parameters.

We recommend you consult this article → Anaerobic vs aerobic technology: A technical and economic comparison for your industry.

Main differences between both processes

This comparison between anaerobic vs aerobic treatment shows that both technologies are not mutually exclusive.

It is common for an anaerobic reactor to remove most of the organic load and for an aerobic treatment to subsequently act as a refining stage to meet the requirements for disposal or reuse.

Which technology is best suited to each case?

The decision depends on several factors:

• Concentration of organic matter (COD and BOD).
• Flow generated by industry.
• Effluent variability.
• Available space.
• Energy operating costs.
• Possibility of utilizing the generated biogas.
• Reuse or disposal objectives.

You might be interested in → Royal Decree 1085/2024: how SITRA helps you with the Water Reuse Regulation.

When wastewater has a high organic load and there is interest in recovering energy, anaerobic wastewater treatment usually offers better economic and environmental results.

On the other hand, if the effluent has a low load or the objective is to obtain a very demanding final quality without an additional stage, an aerobic system may be more suitable.

Advantages of anaerobic wastewater treatment

The implementation of anaerobic water treatment technology offers benefits that extend beyond wastewater purification. For this reason, more and more industries are incorporating it into their energy efficiency and circular economy strategies.

• Reduce energy consumption: Since it does not require aeration systems to supply oxygen to the microorganisms, electricity consumption is considerably lower than that of an aerobic treatment.

• Generates usable biogas: One of the main added values ​​of industrial anaerobic digestion is the production of biogas, which can be used for:

• Heat production.
• Electrical cogeneration.
• Boiler feed.
• Other industrial processes that require thermal energy.

Extensive information about our → biogas production service

• It produces less sludge.This implies a reduction in the costs associated with management and transport of these wastes, one of the main operating expenses in many industrial wastewater treatment plants.
• It promotes the circular economy: The anaerobic process of industrial water transforms waste into an energy resource, favoring a more efficient production model.

Aspects to consider before implementing an anaerobic system

Although it offers numerous advantages, anaerobic treatment is not a universal solution. Its performance depends on proper design and a prior analysis of the effluent's characteristics.

Before selecting this technology, it is advisable to study different variables.

Wastewater characterization

The first step is to know in detail the composition of the water (COD, suspended solids, fats, nutrients, temperature, pH, etc…)

This information allows us to determine if the effluent is suitable for an anaerobic process and to select the most efficient configuration.

Learn more here → pH control in industrial water: why it is critical and how to manage it.

Process stability

Anaerobic biomass needs relatively stable conditions to maintain its activity.

Sudden changes in water composition, significant temperature variations, or the presence of toxic substances can affect reactor performance.

Selecting the appropriate reactor

The choice depends on the flow rate, the organic load, the presence of solids, and the objectives of the installation.

• UASB reactors, widely implemented in waters with a high organic load.
• EGSB Reactorswhich allow working at higher upward speeds and improve contact between biomass and wastewater.
• IC Reactors (Internal Circulation)designed for very high loads and large processing capacities.

Learn more about → UASB reactors: The anaerobic technology that transforms waste into energy

At SITRA, the design of each solution always starts from the specific analysis of the industrial process, selecting the configuration that best suits the characteristics of the effluent and the operating needs of the plant.

Designing the right solution is just as important as choosing the technology.

Each project requires a preliminary analysis that takes into account the effluent characteristics, production needs, discharge requirements, and energy recovery possibilities . Only from this study is it possible to define the most suitable combination of processes, whether through exclusively anaerobic treatment or by integrating it with other wastewater treatment technologies.

At SITRA we develop anaerobic treatment solutions for industrial wastewater tailored to each facility, from engineering and process design to commissioning, optimization and plant operation.

If you want to know which technology best suits your industrial process, our team can help you evaluate the different alternatives and design the most suitable solution for your facility.