Doctoral dissertation
Ramita Khanongnuch

Dissertation: Biological removal of hydrogen sulfide from biogas using nitrate-containing wastewaters for sustainable biogas cleanup

The simultaneous treatment of hydrogen sulfide-contaminated biogas and nitrate-containing wastewater is a future potential for sustainable waste management. In her doctoral dissertation, Ramita Khanongnuch developed and optimized biological systems to enhance process efficiency.

Biogas is a renewable energy source generated from the anaerobic digestion of organic waste and high-strength wastewaters. Biogas consists mainly of methane and carbon dioxide, along with various contaminants such as hydrogen sulfide.

In her doctoral dissertation, Ramita Khanongnuch studied different bioreactor configurations for the simultaneous treatment of hydrogen sulfide-contaminated waste streams and nitrate-containing wastewaters.

“Hydrogen sulfide is highly toxic, odorous and corrosive to gas distribution systems and other equipment. It also limits the application of biogas for heat and power generation. Therefore, it needs to be removed from biogas before its application,” Khanongnuch notes.

The removal of hydrogen sulfide from biogas can be accomplished using various physical and chemical methods, including scrubbing, adsorption, absorption and chemical precipitation. These technologies have high operating costs and negative environmental impacts, however, due to the generation of chemical wastes.

“The biological processes for hydrogen sulfide removal from biogas show great promise in offering a cleaner and less expensive alternative. The biological processes rely on the activity of microorganisms, so we need to understand the conditions in which the microorganisms remain active and how fast they can recover from process disturbances. In order to degrade hydrogen sulfide efficiently, we must also develop functional and resilient bioprocess configurations,” Khanongnuch says.

Khanongnuch demonstrated that the influent nitrate and nitrogen-to-sulfur ratio in the system were the key operational parameters to enable efficient hydrogen sulfide removal. She demonstrated the possibility of simultaneously removing three compound pollutants, hydrogen sulfide, nitrate and organic carbon, from contaminated waste streams.

In Khanongnuch’s findings, the biological systems were resilient to fluctuations in the influent composition, which is important for practical applications. She also applied the artificial neural network model to optimize the operational conditions and predict bioreactor performance during transient-state conditions.

The doctoral dissertation of MSc (Tech) Ramita Khanongnuch in the field of environmental technology titled Hydrogen Sulfide Removal from Synthetic Biogas using Anoxic Biofilm Reactors will be publicly examined in the Faculty of Engineering and Natural Science at Tampere University at 9:15 am on Tuesday, 21 May 2019 in the room FA032 (Pieni sali 1) of the Festia building (address: Korkeakoulunkatu 8, Tampere, Finland). The Opponents will be Professor Pavel Jeníček (University of Chemistry and Technology, Czech Republic), Professor David Gabriel (Universitat Autònoma de Barcelona, Spain) and Associate Professor Marta Izquierdo Sanchis (University of Valencia, Spain). The Custos will be Professor David Gabriel from Universitat Autonoma de Barcelona (Spain).

Ramita Khanongnuch comes from Thailand and her doctoral research has been conducted in the framework of the Advanced Biological Waste to Energy Technologies (ABWET) Innovative Training Network (ITN) European Joint Degree Programme. ABWET has four partner organizations: University of Cassino and Southern Lazio (Italy, coordinator), Université Paris-Est (France), IHE Delft (the Netherlands) and Tampere University (Finland). The Examination Committee of Ramita Khanongnuch's doctoral dissertation includes one representative from each partner organization.

The dissertation is available in the faculty of Engineering and Natural Sciences (Konetalo building K2222A) at Tampere University and by request from

Watch the defence online here.