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Aerobic bioconversion of aquaculture solid waste into liquid fertilizer: Effects of bioprocess parameters on kinetics of nitrogen mineralization

Khiari, Zied, Kaluthota, Soba, Savidov, Nick
Aquaculture 2019 v.500 pp. 492-499
ammonification, ammonium, aquaculture farms, aquaponics, bioprocessing, bioreactors, biotransformation, fish, liquid fertilizers, livestock, mineralization, nitrates, nitrification, nitrifying bacteria, nitrogen, nutrients, operating costs, oxidation, pH, seafoods, solid wastes, temperature
Aquaculture has experienced a burgeoning growth worldwide in the last decade resulting in nearly 50% of seafood originating from aquaculture farms. However, there are less studies on the utilization of the manure produced by aquatic organisms in comparison to warm-blooded livestock. Aquaponics offers more efficient utilization of nutrients and can reduce the operational costs in aquaculture. This paper presents the results of a study to identify the optimal settings to digest fish manure through a microbial-assisted aerobic bioprocess, using endogenous heterotrophic and nitrifying bacteria. The effects of pH (5.5, 6.0 and 6.5), temperature (30, 35 and 40 °C) and duration (1–30 days) on kinetics of nitrogen mineralization were investigated and compared to a control bioreactor (carried out without pH adjustment). The mineralization dynamics for all pH-controlled bioreactors revealed that only ammonification occurred. No nitrification was observed for all three-temperature conditions and throughout the entire bioprocessing period. The mineralization process in the control bioreactor, on the other hand, followed the typical non-inhibited nitrogen mineralization (i.e., release of ammonium followed by oxidation into nitrate). However, nitrate was only observed at temperatures <40 °C indicating a complete suppression of nitrification at higher temperatures. Analytical data and modeled parameters indicated that the bioprocessing of aquaculture solid waste for 15 days at 35 °C using either pH 6.0 or 6.5 maximized nitrogen bioconversion in the form of ammonium ions (NH4+). This study indicates the importance of temperature and pH optimization for more efficient processing of aquaculture solid waste such as fish manure.