Alice Chiapetti Bolsan

The recovery of resources from agri-food residues is an exciting alternative to contribute to a sustainable economy, conservation of ecosystems, and reducing the dependence on finite natural resources. In this sense, the biorefinery concept has been proposed to increase the profitability of the agro-industrial sector and, at the same time, guarantee environmental sustainability. The biorefinery approach integrates waste and biomass conversion processes to produce fuels, energy, and valuable chemicals using micro-organisms. This chapter is dedicated to discussing obtaining compounds with an added value more significant than their base substrates using the anaerobic digestion of agro-industrial residues. This concept can also recover essential nutrients, such as part of the nitrogen present in the residues, biofuels, amino acids, proteins, and volatile fatty acids.

The anaerobic ammonium oxidation (anammox) process has attracted significant attention as an economic, robustness, and sustainable method for the treatment of nitrogen (N)‐rich wastewater. Anammox bacteria (AnAOB) coexist with other microorganisms, and particularly with ammonia‐oxidizing bacteria (AOB) and/or heterotrophic bacteria (HB), in symbiosis in favor of the substrate requirement (ammonium and nitrite) of the AnAOB being supplied by these other organisms. The dynamics of these microbial communities have a significant effect on the N‐removal performance, but the corresponding metabolic pathways are still not fully understood. These processes involve many common metabolites that may act as key factors to control the symbiotic interactions between these organisms, to maximize N‐removal efficiency from wastewater. Therefore, this work overviews the current state of knowledge about the metabolism of these microorganisms including key enzymes and intermediate metabolites and summarizes already reported experiences based on the employment of certain metabolites for the improvement of N‐removal using anammox‐based processes.Practitioner Points: Approaches knowledge about the biochemistry and metabolic pathways involved in anammox‐based processes. Some molecular tools can be used to determine enzymatic activity, serving as an optimization in nitrogen removal processes. Enzymatic evaluation allied to the physical–chemical and biomolecular analysis of the nitrogen removal processes expands the application in different effluents.

In this paper, we explore the applications of bacteriophages and the advantages of using these viruses to elucidate the possibility of applying them to control substrate competition organisms in anammox-based processes. The partial nitrification/anammox offers economic and structural advantages compared to conventional nitrogen removal processes. However, the appearance of substrate competing bacteria is typical, as is the case of nitrite-oxidizing bacteria (NOB), which tend to grow unrestrainedly in the system, converting all ammonia to nitrate, globally impacting the system once substrate availability is compromised. Thus, control measures to prevent this substrate competition are vital for process efficiency. We used a literature review depicting the main applications of bacteriophages in wastewater treatment plants. Initial studies demonstrated bacteriophages have great potential to be applied in anammox-based processes, such as partial nitrification/anammox (PN/A) acting to combat NOB, a valuable economic and environmental tool to improve the efficiency of nitrogen removal processes. Although these viruses have already been studied in various applications to optimize treatment plant processes, technology transfer remains a challenge due to the limitations of the technique and the complexity of biological systems. The research development focused on application strategies in conjunction with molecular biology techniques can expand this study area, enabling the discovery of bacteria and bacteriophages.

Phosphorus (P) is essential for life and has a fundamental role in industry and the world food production system. The present work describes different technologies adopted for what is called the second-generation P recovery framework, that encompass the P obtained from residues and wastes. The second-generation P has a high potential to substitute the first-generation P comprising that originally mined from rock phosphates for agricultural production. Several physical, chemical, and biological processes are available for use in second-generation P recovery. They include both concentrating and recovery technologies: (1) chemical extraction using magnesium and calcium precipitating compounds yielding struvite, newberyite and calcium phosphates; (2) thermal treatments like combustion, hydrothermal carbonization, and pyrolysis; (3) nanofiltration and ion exchange methods; (4) electrochemical processes; and (5) biological processes such as composting, algae uptake, and phosphate accumulating microorganisms (PAOs). However, the best technology to use depends on the characteristic of the waste, the purpose of the process, the cost, and the availability of land. The exhaustion of deposits (economic problem) and the accumulation of P (environmental problem) are the main drivers to incentivize the P’s recovery from various wastes. Besides promoting the resource’s safety, the recovery of P introduces the residues as raw materials, closing the productive systems loop and reducing their environmental damage.