Contents lists available at ScienceDirect Aquacultural Engineering journal homepage: www.elsevier.com/locate/aque Application of nitrification and denitrification processes in a direct water reuse system for pacific white shrimp farmed in biofloc system Marcos Estevão Santiago de Melo Filho a , Marco Shizuo Owatari b, *, José Luiz Pedreira Mouriño b , Katt Regina Lapa b , Hugo Moreira Soares a a Federal University of Santa Catarina, Chemical and Food Engineering Department, Florianopolis, SC, Brazil b Federal University of Santa Catarina, Aquaculture Department, Florianopolis, SC, Brazil ARTICLE INFO Keywords: Nitrification Denitrification Superintensive system Shrimp Biofloc Aquaculture ABSTRACT The aim of the present study was to propose a low-cost nitrogen removal system through the nitrification / denitrification process in order to maintain the water quality required for the Pacific white shrimp super- intensive cultivation in closed systems without water renewal. The increase in productivity consequently causes the accumulation of organic matter and nitrogenous compounds, especially ammonia nitrogen and nitrite, which in high concentrations can be lethal to aquatic organisms. In addition, the accumulation of solids in the system provides conditions for the emergence of opportunistic pathogens, microalgae booms, and increases the pro- ducer's cost of inputs to maintain the equilibrium physicochemical relationships required for shrimp farming. The experimental productive cycle lasted 36 days using Litopenaeus vannamei shrimps with 7.1 g ± 0.56 g and density of 350 shrimps m - ³. The nitrogen removal efficiency observed during the study period was 71.3 ± 5.3 %, and the shrimp had a survival of 92.9 % and a final weight of 13.1 ± 1.4 g. Thus, we established a system (ammonia and nitrite), capable of managing solids without interaction with the sea, ensuring high biosecurity against exogenous diseases in marine shrimps farms. 1. Introduction Water resources are of vital importance for the development of any economic activity in the world. However, aquaculture is one of the activities that most needs large volumes of water, inevitably. The need to produce larger quantities of food due to population growth has contributed to the growth of the sector, which currently moves around US $ 243 billion (FAO, 2018). In this sense, one of the biggest chal- lenges of aquaculture concerns the rational use of water resources. Marine shrimp are a commodity, and as such, highly traded. Mon- etarily, its represents the second largest group of exported aquaculture species. Typically, farms are present in coastal aquaculture and are an important economic source for many developing countries in Asia and Latin America, moving around $ 1.51 billion / year, mostly consumed by developed countries markets. (FAO, 2015, 2018). In traditional farms (6–20 shrimps m -3 ) nurseries of up to 10 ha can exceed productivity of 10 ton / ha / year. In this case, the water from the ponds is renewed daily at a rate of between 5 and 20 % of the total volume, thus ensuring adequate water quality conditions for the ani- mals' development (Barbieri Júnior and Ostrensky Neto, 2002; Lightner, 2005). It is estimated that producing 1 kg of shrimp in these systems requires 50 m 3 of water, most of which is discharged into ad- jacent water bodies without any treatment (Krummenauer et al., 2014; Timmons and Ebeling, 2007), increasing the risks of spreading patho- gens in the environment. In recent years the shrimp farming industry has been systematically affected by the occurrence of diseases, particularly viral diseases, which have caused great losses in the most diverse producing regions of the world. In addition, poor weather conditions have been a constant challenge for some major Asian producers, particularly Thailand and China, causing large economic losses for activity (Lightner, 2005; Subasinghe, 2017; FAO, 2018). Therefore, several models aiming at greater biosecurity and super- intensive production have been proposed. In some cases productivity may be increased by more than 800 % and the amount of water used reduced to less than 100 L kg shrimp -1 (Boyd and Clay, 2002; Burford et al., 2003; Krummenauer et al., 2014). Among these models, note- worthy is the Bioflocs system (BFT), developed in the early 1990s at the Waddel Mariculture Center, South Carolina, United States, modified and adapted a few years later for commercial productions in Belize https://doi.org/10.1016/j.aquaeng.2020.102043 Received 16 August 2019; Received in revised form 9 January 2020; Accepted 9 January 2020 ⁎ Corresponding author. E-mail address: owatarimarco@hotmail.com (M.S. Owatari). Aquacultural Engineering 88 (2020) 102043 Available online 10 January 2020 0144-8609/ © 2020 Elsevier B.V. All rights reserved. T