A predictive model for N2O production in anammox-granular sludge reactors: Combined effects of nitrite/ammonium ratio and organic matter concentration.

Once the use of anammox reactors has been increasing on a global scale, it is important to understand the mechanisms of N2O emissions and how to minimise the emissions by optimising the operating conditions. In this study, the influence of chemical oxygen demand (COD) (from 0 mgO2 L-1 to 100 mgO2 L-1) and nitrite/ammonium ratio from 0.79 to 2.21 (maintaining ammonium at 100 mgN L-1 and varying nitrite from 79 mgN L-1 to 221 mgN L-1) in the N2O emissions from anammox-granular sludge reactor was investigated in two steps. Step 1 consisted of batch tests, using central composite design, and Step 2, long-term operation of a 6.5 L continuous up-flow reactor. The results showed that the N2O emissions were minimized by controlling, in the influent, the NO2--N/NH4+-N ratio from 1.1 to 1.3 and maintaining the COD concentration below 100 mgO2 L-1. TN removal efficiencies were higher than 70% in all conditions tested".

Biochemical characterization and anaerobic degradability of flower wastes: Preliminary assessment and statistical interpretation towards energy recovery.

The use of ornamental flowers and plants is widespread in several regions of the world, but the management of flower (or floral) waste (FW), classified as herbaceous biomasses, is scarcely addressed in the literature. However, climate change, population growth and the depletion of resources are expected to push towards the development of FW management strategies, according to principles of flexibility and integration of technologies. This study focuses on the characterization of ten different varieties of flowering plants, of which the wastes are of concern in the Pistoia Province (Italy). The possibility of recovering energy by means of anaerobic digestion is also preliminarily investigated. The interpretation of data through Principal Component Analyses proved to be effective to orientate the selection of technological solutions. The three main parts of each plant variety were analysed separately, showing that the biochemical composition of stems is statistically different from that of leaves and flowers, thus suggesting the viability of adopting different strategies to optimize material (value-added products) recovery from FW. Conversely, regarding biogas generation and energy recovery, the methane yield (in the range 82-330 NmLCH4.gVS-1) is not significantly affected by the type of FW part, nor by the variety of flowering plant or by the use of pesticides during cultivation, whereas lower kinetics were observed for stems compared to leaves and flowers. In view of full-scale application, and depending on FW amounts locally produced, a careful evaluation is required, encompassing aspects of technical feasibility and economic expenses associated with FW parts separation.