Dear Colleagues,

Biological wastewater treatment is an essential process in the purification and recycling of water resources that is aimed at removing various contaminants from wastewater using natural biological mechanisms. Wastewater possesses an abundant amount of nutrients that may lead to significant eutrophication if discharged into water bodies without any treatment. In the past, wastewater has been considered a significant concern for both the environment and public health. However, with the development of sustainable technologies, it is now recognized as a valuable resource. Energy is required for effective biological treatment processes, and incomplete nitrification/denitrification processes can release greenhouse gases such as nitrous oxide, which is more potent than CO₂. Wastewater treatment plants can treat wastewater by removing nitrogen (N), phosphorus (P), and organic pollutants. However, it is crucial to extract nutrients and valorize the wastewater, which may be possible by combining its treatment with resource recovery.

The effectiveness of biological wastewater treatment relies on the principles of biodegradation and microbial metabolism. Through a series of well-designed processes, organic matter, nutrients, pathogens, and toxic substances present in wastewater can be efficiently degraded and removed. Oxygen availability, temperature, pH levels, retention time, and the availability of specific microorganisms are key factors that influence the performance and efficiency of biological treatment systems. The focus of the research in this area has been on learning about new communities of microorganisms; trying out new methods like biofilm reactors, activated sludge systems, and constructed wetlands; and looking into how advanced technologies like genetic engineering and nanotechnology can be used in the treatment process. There are many methods for the valorization of wastewater, such as anaerobic digestion (AD) and bioelectrogenesis. These processes harness the power of microorganisms, such as bacteria, fungi, and algae, to break down organic and inorganic pollutants and enable the extraction of bioenergy in the form of biogas (specifically biomethane, biohydrogen, and bioelectricity), which leads to the production of biobased products such as platform chemicals, volatile fatty acids, and bioammonium.

This Special Issue aims to address the advancements, challenges, and opportunities in the field of biological wastewater treatment. It welcomes interdisciplinary studies encompassing microbiology, engineering, chemistry, biotechnology, and environmental sciences. Additionally, topics such as (i) biotechnological methods to extract resources from wastewater and turn them into value-added products, (ii) the integration of processes for bioenergy and biochemical production, and (iii) nutrient recovery for the circular economy and environmental management will be considered in this SI. The goal is to contribute to the development of sustainable wastewater treatment technologies that minimize environmental impact and maximize resource recovery. By disseminating cutting-edge research, this Special Issue aims to foster collaboration and encourage the adoption of novel approaches in the field of biological wastewater treatment.

Dr. Omprakash Sarkar
Dr. J. Shanthi Sravan
Guest Editors

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• wastewater treatment
• nutrient recovery
• bioenergy generation
• biobased products
• anaerobic digestion
• volatile fatty acids
• bioammonium
• bioelectricity