The process of biogas production is a series of complex stages aimed at producing methane from waste. Traditional biogas plants can use different types of waste as feedstock, including, for instance, biomass. Since the feedstock is renewable, biogas plants produce green energy, contributing to a circular economy. According to the World Bioenergy Association, the sector of biogas production is one of the fastest growing

among all biofuel sectors. The average growth of biogas production was 11.2% in 2014, reaching an overall production of 58.7 billion Nm³. Almost half of this amount was produced in Europe where approximately 17 000 biogas plants are in operation. Germany is the leading country in terms of number of biogas plants, with a total of 11 000 installation, followed by Italy with 1 600 and France with 800.

Ozone can be useful in several parts of the biogas production process. Among other possibilities, we identified three main applications for ozone treatment in biogas plants:

• Substrate pre-treatment to enhance biogas yield
• H₂S reduction for methane upgrading
• Odor control

Prior to the anaerobic digestion stage, a pretreatment step is often implemented. The purpose of this step is to reduce the workload of the hydrolytic fermentative bacteria by

making the substrate more easily biodegradable. This includes properties such as increasing the surface area, dissolving complex matter, reducing crystallinity in

polymers such as cellulose etc. The most common types of pretreatment applied today are summarized in the tables below.

After the pretreatment stage, the feedstock enters the digester for the biochemical conversion. In this unit, several types of microorganisms react with the feedstock in different stages. All stages are anaerobic i.e. in absence of oxygen. These are summarized in the table to the right.

The methane production through anaerobic digestion may be performed with a single-stage or two-stage process. In the first case, all the reactions steps above are carried out in the same reactor. The substrate is converted into methane with a concentration of 50-55% in the biogas, depending on the type of substrate. In twostage process only the reaction steps until the acetogenesis are carried out in the first

When the biogas is produced in a two-stage process, it is possible to reduce the H₂S concentration before the methane upgrading by injecting ozone in the digester. In this way, the H₂S is reduced even before the methane production, resulting in a more efficient system

and lower costs for the final biogas cleaning. Since the digestion process is anaerobic, the ozone injection needs to be carefully controlled for not compromising the process conditions. Normally, the ozone is injected in the air pocket above the bio-bed in the digester unit.

Alternatively, it can be injected in an intermediate tank between the digester and the methane upgrading unit.

Read more on H₂S reduction for methane upgrading.

In the biogas after the methane upgrading, high concentrations of hydrogen sulfide are often present, creating issues for the following process steps. Corrosion is one of the issues to be considered, since very high H₂S levels may corrode pipes and process instrumentation, resulting in costs up to several thousand euros

per year. Odor is also one of the major problems related to the methane upgrading off-gas. This is due to the high sensitivity of the human nose to hydrogen sulfide, since the odor receptors are triggered for concentrations in the part-per-billion (ppb) range.

Therefore, even a small leak in the process lines or an opening in a process step, may create an odor issue for a large area, since the emitted gas needs to be diluted up to 200 000 times before the odor is masked.

Starting from traditional solutions, Ozonetech developed innovative ozone-based solutions for odor emissions, greatly improving the costeffectivity of the process and keeping high standards in terms of removal grade. A summary of the operational costs of a traditional solution, compared to our ozone-based solutions, is presented in the figure to the right.
From the figure to the right, it can be seen that the operating costs of an Ozonetech’s solution are more than four times lower than the ones of a traditional solution, even for sub-optimal configurations. The lower operational costs result in great economic savings every year, for a value up to 100 000 euros per year. The figure also highlights the flexibility of our solution. Since each biogas process is different and has different requirements, it is important to adjust our system to the needs of the customers. Therefore, every

solution is carefully designed and tailor-made for maximizing the benefits for the customer, as the operating costs in the presented case. Besides the great costs savings, the Ozonetech solution ensures a high-efficiency and robust performance throughout its lifetime, resulting in an effective odor removal for a very long time.

A common Ozonetech’s solution for odor control is composed by several stages, including the RENA Pro ozone units and the Nodora Odor control Solution.

Read more on Odor Control, RENA Pro and Nodora Odor control Solution (brochure).

After the production of biogas, the liquid effluent still has a high content of nitrogenous compounds which constitute an important resource. These can be reused in agriculture as crops fertilizer, hus providing important economic savings. However, a further treatment is needed, prior an effective reuse, for removing emitted odors and unpleasant colors.

Ozone can be used for solving both problems at once. By injecting in the effluent, the benefits starts at the source, minimizing odors even before the emission. In addition, the COD content is greatly reduced, resulting in a color change which enables these effluents to be reused as fertilizers.

Read more about Odor Control and the RENA Pro Ozone Solution, for treating odors.

Read more about COD Treatment and the RENA Vivo Ozone Solution, for reducing COD.

One of the challenges of biogas plants is the strict requirement of H₂S removal after the anaerobic digestion stage, before upgrading.

Another constant source of concern is the odors emitted from the biogas plant. Today, both can be solved effectively, and green.

We have developed a catalyst specifically for H₂S removal: the RubicatTM. Even without oxygen, H₂S is removed, leaving no traces before the upgrading

stage. As the working mechanism is catalytic, the Rubicat has a much longer lifespan compared to traditional technologies, such as activated carbons. The Nodora CAT can yield a 40-95% reduction in operating costs.

In addition, one can handle the odor problems inside the plant by producing ozone very costeffectively on-site. The ozone is lead into the existing ventilation to reduce odorants to then pass through a Nodora ADS as final polishing

stage, before discharge.

Ambitious biogas producers have an additional option: to treat the biomass with ozone, which in some applications can double the amount of biogas yield.

Regardless of application, the treatment will be efficient, green and easy to manage.

H₂S REMOVAL BEFORE UPGRADING

With our solution you don’t need several technologies to handle the H₂S. No activated carbon, no ozone or other treatment methods. Our in-house developed Nodora CAT equipped with the Rubicat is sufficient. The Nodora system is designed to constantly make use of all active material, highly increasing H₂S removal efficiency and the filter material lifetime.

INHOUSE ODOR REMOVAL

The odors from inhouse sources are removed through the ventilation and the collected odors can then be treated using RENA Pro and Nodora ADS before the air is discharged into the environment.

Our most important advice is to carefully analyze the air. The analyses and pilot tests we perform at our facilities focus on flows and concentrations, preparing the design of the optimal treating method.

Nodora is installed in industries with strong regulatory requirements for odor reduction. All Nodora systems are tailored to the current load to achieve maximum possible H₂S and odor reduction. One of many benefits when combining

ozone treatment and Nodora is that the active material is active at least five times longer than a solution without prior ozone treatment.

A standard solution using activated carbon treatment is both costly and ineffective compared to our Nodora CAT. The high performance of Nodora CAT is due to the the advanced active material used, the material mix and the overall design making use of all filter material equally. The experiments were conducted in Stockholm, with the collaboration of KTH Royal Institute of Technology. Real biogas conditions were tested with a H₂S concentration of 1000 ppm.

Using Nodora CAT will cut costs in half compared to traditional activated carbon. When replacing a traditional activated carbon system, the return of investment will be less than two years.

RENA PRO OZONE SYSTEM
Treatment method: ozonation
Odor reduction: up to 98%
Removal ability: hydrogen sulfide, mercaptans and volatile organic compounds
Operating cost: minimal: inexpensive consumables and electricity consumption of the ozone system
Handling: minimal, on/off or automatic
Monitoring: remote 24/7 with service agreement RENA premium
Raw material: ambient air to produce oxygen
Ozone distribution: 8 mm tubes
Footprint: 80x60 cm

NODORA CAT
Treatment method: catalysis
H₂S reduction: up to 100%
Removal ability: hydrogen sulfide
Operating cost: minimal compared to activated carbons due to much longer lifetime
Handling: none, no electricity or heat required
Monitoring: N/A
Active material: Rubicat
Footprint: 1160x760 mm

NODORA ADS
Treatment method: selective adsorption
Odor reduction: up to 100%
Removal ability: mercaptans, volatile organic compounds and amines
Operating cost: minimal compared to activated carbons due to much longer lifetime
Handling: none, no electricity or heat required
Monitoring: N/A
Active material: tailored for each application
Footprint: 1160x760 mm

ADDITIONAL SERVICES
Service agreement: adapted to the customer’s need and requirements and can include full annual maintenance service
Air analysis: performed at Ozonetech premises
Tailored process design: performed at Ozonetech premises
Manufacturing: at our facilities in Sweden