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Nitrous oxide, or N₂O, is a greenhouse gas that is largely considered to be the cause for depletion of the ozone layer. As nearly 70% of the global emissions seem to arise from bacterial and fungal denitrifications and nitrification processes in soils, there is a growing concern to identify mitigation techniques to improve the atmosphere in which we live. Fertilizers in agricultural soils are the primary source. This chapter will explain the causes of nitrous oxide emissions in the atmosphere as well as explore these mitigation methods that have been researched, tested and successfully implemented.

INDISIM-SOM models the dynamics and evolution of C and N related to organic matter in soils by using individual-based simulations. It is an Individual-based Model that controls a group of microbial cells at each time step, using a set of time-dependent variables for each microorganism. The space is divided into square cells. In each spatial cell, the amounts of different types of organic compounds are controlled. These are identified as polymerized organic C and N, labile organic C and N, and mineral compounds such us N_NH4, N_NO3, CO₂ and O₂. The model takes into account the activity of two types of microorganisms: decomposers (heterotrophic) and nitrifiers. Metabolic pathways and sources of C and N that they can use are identified. Some state variables and parameters related to soil organic matter and microbial activity are studied. This study presents a website at which the simulator INDISIM-SOM is accessible, and explains how to carry out some virtual experiments, in order to further advance the skills associated with this individual simulation model.

The development of new processes and technologies like aerobic granulation has increased the interest in recent years to cope with disadvantages observed in conventional activated sludge process for wastewater treatment. Due to the increased interest in this topic, the fundamentals and applications of aerobic granulation have been compiled. The main factors affecting granulation, the biological processes involved, and the application of aerobic granules for nutrient removal at laboratory and pilot scale were delineated.