H2S AND ODOR REMOVAL AT BIOGAS PLANTS
 
IT'S TIME TO REPLACE TRADITION WITH INNOVATION

 
BIOGAS

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

 
 

 
An overview of possible ozone applications in the biogas production process.
 
 

 
APPLICATION
PURPOSE
RESULT
Substrate pre-treatment to enhance biogas yield Breaking down large polymers into monomers Up to 100 % higher substrate conversion to biogas
H2S reduction for methane upgrading Enable biofuel methane purity through H2S removal Up to 30% more methane produced
Odor control Removal of odorous and corrosive contaminants Minimized odor and H2S
 
 

Did you know...
 
 

One single ozone system can be used to treat both air and water simultaneously. This will remove odor and H2S, while increasing the biogas yield.

 
 
 
SULFUR IS THE ISSUE

In each stage of the biogas production process, sulfur compounds and ions are commonly present. These compounds are often responsible for a variety of issues affecting the overall performance. For instance, high amounts of sulfur ions in the feedstock enhance the activity of sulfur reducing

bacteria (SRB) in the digester, inhibiting the activity of methane-producing microorganisms such as archaea. As a result, the yield of methane production is reduced while the production of reduced-sulfur compounds, such as H2S, is favored. When high concentrations of H2S are released from the digester,

the process may cause odor and corrosion problems. In particular, odor problems are common in biogas plants, since H2S has one of the lowest odor threshold known, making the human nose very sensitive even to trace concentrations.

 
FEEDSTOCK PRETREATMENT

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.

 
PHYSICAL PRETREATMENTS
Mechanical Milling to reduce particle size, increasing the biomass availability.
Leads to increased complexity increasing process sensitivity and cost.
Thermal Heating (200oC), disrupting hydrogen bonds (chemical macro-structures), increasing the biomass availability.
Leads to a high energy demand.
CHEMICAL PRETREATMENTS
Alkali Alkali treatment over several weeks, easing the degradation of ligno-cellulosic compounds.
Requires large amounts of chemicals, chemical handling and leads to a slow process.
Ozone treatment Inline ozonation, significantly increasing the biodegradability of stable organic matter,
potentially tripling biogas production.
BIOLOGICAL PRETREATMENTS
Microbiological Compostation, an aerobic pretreatment step forming hydrolytic enzymes,
facilitating the first step of the anaerobic digestion.
Fungal Pure cultures of an aerobic fungi during a 4 day incubation time can result in up to 40% more biogas produced,
and an increase in the grade.

Common pre-treatments for the feedstock prior to anaerobic digestion.

 


BENEFITS OF FEEDSTOCK OZONE TREATMENT

Ozone is known for its highly oxidative properties, and has been shown to be able to degrade parts of the complex organic matter used as feedstock for an anaerobic digester. For example, when applying ozone to a feedstock of waste activated sludge, the effects are multiple. When ozone is properly dosed, the substrate conversion to biogas can be greatly increased, as shown by the figure to the right.
In many cases, such as biogas production from waste activated sludge, the results show a strong positive impact of the ozone treatment. This result is due to the high content of aerobic bacteria and non-degraded organic matter in this type of feedstock. Under these conditions,

ozone quickly oxidizes any unsaturated bond, forming radicals, which continue to oxidize other organic matter. This reaction mechanism leads to a higher biodegradability of the feedstock, which is translated to a higher biogas production. The increase of biogas production is proportional to the ozone injection in the system. The more ozone is used, the higher the biodegradability and the methane yield. As shown in the study to the right by Bougrier et. al. at “Laboratoire de Biogechnologie de l’Environnement”, the ozone pretreatment improves the biogas production, with an optimum around 0.15 g O3 per g total solids, resulting in an increase of approx.150% in the biogas production, compared to the untreated feedstock.

The effect of ozone treatment on substrate biodegradability for waste activated sludge. TS=Total solids.
 
 

Did you know...
 
 

The operational costs of ozone treatment are normally less than half compared to competing technologies.

 
 
ANAEROBIC DIGESTION

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 a two-stage process only the reaction steps until the acetogenesis are carried out in the first digester.

STEP
DESCRIPTION
Hydrolysis Breaking down of large substrate, such as cellulose
and proteins to glucose and amino acids
Fermentation Formation of volatile organic acids and alcohols
Acetogenesis Formation of acetate, carbon dioxide, and hydrogen
Methanogenesis Formation of methane and carbon dioxide
The steps of anaerobic digestion stage.

The following methane production is performed in a second stage, called methane upgrading stage. By splitting the process in two stages, it is possible to increase the methane concentration

in the biogas up to 70%. Therefore, the system becomes more efficient and the costs for the following biogas purification are reduced.



BENEFITS OF H2S REDUCTION BY OZONE TREATMENT IN THE DIGESTER

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.
 
 
BIOGAS AFTER TREATMENT

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.

 

 
BENEFITS OF ODOR CONTROL WITH OZONE-BASED SOLUTIONS

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).


The operating cost for a traditional solution (left) is four times higher than any of the three possible Ozonetech solutions. Our solution will be 1) RENA Pro ozone treatment, or 2) Nodora air filter or 3) RENA Pro and Nodora. The total cost increases with the ozone concentration produced by RENA Pro - with the lowest total cost obtained at an optimal combination of ozone and Nodora.

READ MORE
 
REUSE OF LIQUID EFFLUENT

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, thus 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.



GREEN BUSINESSES SHOULD USE GREEN TECHNOLOGIES

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.
 
 
OUR ODOR TREATMENT SOLUTIONS AT BIOGAS PLANTS

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.


The existing ventilation is the treatment chamber
 

We recommend
Odor Control

Digester Ozonation

Nodora Odor Control

 


NO RECONSTRUCTION NEEDED. MINIMAL OPERATING COST.

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
 

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