Effects of Recirculating Aquaculture System Wastewater on Anammox Performance and Community Structure

Abstract

Recirculating aquaculture systems (RAS) are good candidates for the sustainable development of the aquaculture sector. A current limitation of RAS is the production and accumulation of nitrogenous waste, which could affect fish health. We investigated the potential of the anaerobic ammonia oxidation (anammox) process to treat marine wastewater from a cold-water RAS. We show that the marine anammox bacteria Candidatus Scalindua is a promising candidate. However, its activity was affected by unknown compounds in the RAS wastewater and/or the sub-optimum of essential trace elements (TEs). Anammox activity dropped to 2% and 13% in NH4+ and NO2- removal, respectively, when nitrate-rich RAS wastewater was used as a medium in the absence of TE supplementation. A TE supplementation was added to the RAS wastewater in a subsequent phase, and a recovery in anammox activity was shown (25% and 24% in NH4+ and NO2- removal, respectively). Future studies need to identify the unknown factor and determine the specific needs regarding TE for optimal RAS wastewater treatment by Candidatus Scalindua.

Candidatus Scalindua, a Biological Solution to Treat Saline Recirculating Aquaculture System Wastewater

“…In our previous study, we have demonstrated that Ca. Scalindua remained the dominant species found in the granules of our anaerobic anammox rector throughout the different experimental phases, including after exposure to RAS WW [33]. In this experiment, the anammox was either fed a standard synthetic anammox feed enriched with NH 4 + and NO 2 − and supplemented with a mix of trace elements (TE) or they were abruptly exposed to 100% RAS WW enriched with NH 4 + and NO 2 − for short periods, in the absence or presence of TE.…”

“…5 g wet weight) was brought to the University in Gothenburg in August 2019 and was used as inoculum into a glass column reactor (Ø 50 mm; volume, 325 cm 3 , KF-50, AS ONE, Tokyo, Japan, Figure 2) with a nonwoven fabric sheet (Japan Vilene, Tokyo, Japan) as biofilm carrier material. The reactor was fed with synthetic marine WW (Aquaforest, Brzesko, Poland) supplemented with nitrogen (NH 4 + and NO 2 − ) and TE, as described earlier [33,34] (Table 1). The reactor temperature was maintained at 28 • C throughout the experimental period, and the initial hydraulic retention time (HRT) was 4.6 h (Table 3).…”

“…The reactor used in this study was operated for 280 days in 3 experimental phases. During Phase 1 (days 0-83), the reactor was fed with the same synthetic marine WW supplemented with nitrogen (NH4 + and NO2 -) and TE as was arranged earlier [33,34]. During Phase 2 (days 84-200), the reactor was exposed to gradually increasing concentrations of RAS WW.…”

“…This TE mix, composed of 9 TE (Table 1)) was developed when the first freshwater anammox species was isolated and is currently used as a standard in anammox cultures worldwide [34]. The nitrogen removal capacity of the anammox was negatively affected by the abrupt changes to 100% RAS WW without TE, while a subsequent addition of TE led to a slight recovery [33]. We concluded that the reduction in activity could be caused by the abrupt change of medium (from synthetic feed to RAS WW), either because of high levels of unknown compounds (i.e., NO 3 − ) present in the RAS WW, and/or the lack/or inappropriate concentration of certain key TE in this new medium.…”

“…Scalindua, and (2) if the TE supplementation is necessary for the normal functioning of this marine strain of anammox bacteria. As all the 9 TE elements used in the standard feed [34] are already present in seawater [33], there might not be a need for a supplementation.…”