Bioremediation of fishpond effluent and production of microalgae for an oyster farm in an innovative recirculating integrated multi-trophic aquaculture system

Abstract

Integrated multi-trophic aquaculture (IMTA) systems are a promising solution for sustainable aquaculture combining nutrient recycling with increased biomass production. An innovative land-based recirculating aquaculture system (RAS) was studied in France for a 60-day experiment. It combined a European sea bass (Dicentrarchus labrax) RAS with two other production systems: high rate algal ponds (HRAP) with natural marine polyspecific algal assemblages, and oysters in separate open tanks. The objective was the assessment of: 1) the efficiency and the stability of the microalgae bioremediation of the effluent from a fish RAS in spring and summer, 2) the abundance and the diversity patterns of the microalgae biomass for consumption in the oyster compartment of the IMTA. Silicate was added every week after the beginning of the experiment for maintaining a Si:N:P molar ratio of 10:5:1 in the HRAP to encourage the growth of diatoms. The HRAP have an overall removal efficiency of 98.6 ± 0.2% for NO3-N, 98.0 ± 0.4% for NO2-N, 97.3 ± 0.7% for NH4-N and 96.1 ± 0.6% for PO4-P, with removal rates of 335.8 ± 0.8, 23.6 ± 0.2, 30.9 ± 0.2, and 22.3 ± 0.2 mg m−2 d−1, respectively. The concentration of total suspended solid (TSS) and chlorophyll a (chl a) increased during the experiment and reached maximum values on day 46 (135.3 ± 34.7 mg TSS L−1 and 0.42 ± 0.03 mg chl a L−1) after which the microalgae collapsed due to a CO2 limitation (pH ca. 10). Sequencing analysis revealed that the microalgae community was dominated by Tetraselmis sp. from day 1 to day 16 (45.7% to 73.8% relative abundance). From day 30 to day 43 the culture was dominated by diatoms, Phaeodactylum sp. (83.4% to 98.1% relative abundance). Although the stable carbon isotope signatures confirmed that the microalgae were consumed, oysters' growth was limited in the RAS-IMTA, suggesting that oysters were under stress or not fed enough. Highlights ► Microalgae-based-IMTA has potential for N/P bioremediation. ► Adding silicate shifted algae to diatom of interest for oysters.

Integration of Algae to Improve Nitrogenous Waste Management in Recirculating Aquaculture Systems: A Review

“…Study 5b (Pagand et al, 2000) had a lower nitrogen removal rate than 5a because of the low light intensity during winter. For Studies 1 (Cahill et al, 2010) and 8 (Li et al, 2019), even though the nitrogen removal rate was 100%, which might indicate the efficiency of the algae, the nitrogen loading rates were low compared to other studies. For Studies 2 (Valeta and Verdegem, 2015) and 6 (Deviller et al, 2004), either light intensity or HRT was low, which caused the low nitrogen removal rate.…”

“…When a comparison is made between macroalgae and microalgae (Figure 2), the macroalgae biomass (g algae m −2 algae reactor) was higher than the microalgae/periphyton biomass. Except for Study 8 (Li et al, 2019), a relatively high microalgal biomass was observed. This could be due to the HRAP technique used in that study that enhanced the growth of microalgae (Brune et al, 2003).…”

“…The first method was reported in Study 1 (Cahill et al, 2010), Study 4 (SustainAqua, 2009), and Study 7 (Gál et al, 2003). The second method was reported in Studies 2 (Valeta and Verdegem, 2015), 5 (Pagand et al, 2000), and 8 (Li et al, 2019). The third method was reported in Studies 3 (Huang et al, 2013) and 6 (Deviller et al, 2004).…”

“…Studies 1 (Cahill et al, 2010), 2 (Valeta and Verdegem, 2015), and 4 (SustainAqua, 2009) reported the nitrogen loading rates measured in their studies. However, Studies 5 (Pagand et al, 2000), 6 (Deviller et al, 2004), 7 (Gál et al, 2003), and 8 (Li et al, 2019) did not report the nitrogen loading rate, and therefore, the nitrogen loading rate was estimated by the authors in this review using the nitrogen concentration and flow rate into the algal reactor or using the percentage of nitrogen removal rate in the studies. Similarly, Study 3 did not report nitrogen loading rates.…”

“…Study 5 (Pagand et al, 2000) and Study 6 (Deviller et al, 2004) used high-rate macroalgal based algal ponds (HRAP), and Study 7 (Gál et al, 2003) used an extensive fish pond (EFP). Study 8 (Li et al, 2019) used outdoor microalgal based raceway as methods to integrate algae in the RAS.…”