Utilization of centrate for the outdoor production of marine microalgae at the pilot-scale in raceway photobioreactors

Abstract

In this study, the outdoor production of marine microalgae in raceway photobioreactors was investigated, modifying the centrate percentage in the culture medium (20, 30, 40 and 50%) and using two different dilution rates (0.2 day −1 and 0.3 day −1). The data obtained showed that microalgae are capable of producing biomass in addition to recovering the nutrients contained in the centrate. The best results for biomass productivity and light efficiency were obtained when the centrate was set at 20% with a dilution rate of 0.3 day −1. The biomass productivity was 32.42 g m −2 •day −1 while the photosynthetic efficiency was 0.74 g biomass •E −1 (3.66%). Regarding the nutrients, nitrogen (the majority being in the form of ammonium [NH 4 + ]) and phosphorus were only fixed into biomass when optimal conditions were set; if this was not the case, they were lost to stripping or precipitation. The maximal nutrient removal capacities under the optimal conditions were 28.72 mg N •l −1 •day −1 and 3.99 mg P •l −1 •day −1. Population changes were determined by the dilution rate set whilst the centrate percentage had little effect. Four strains were present in the culture, Nannochloropsis g. being the main one. Biochemical changes did not vary greatly between the conditions set for the culture, with a composition rich in proteins and carbohydrates being observed. One can conclude that to produce marine microalgal biomass for a range of potential commodities such as feed, biofertilizers and biofuels, it is possible to use centrate from anaerobic digestion as the sole nutrient source, as a way of reducing costs.

Integration of Microalgae Cultivation in a Biogas Production Process from Organic Municipal Solid Waste: From Laboratory to Pilot Scale

“…The stripping removal values found in our work are in accordance with others, with reported values between 21-73% [40,41]. The last nitrogen removal mechanism, i.e., biomass uptake, accounted for 11.8% of the inlet nitrogen, which is similar to the value of 14% found by Alcántara et al [20].…”

“…During manual feeding, just after the addition of fresh medium, the DO profile showed a biomass productivity obtained in our study with other pilot plants is difficult due to the different types of feed used for cultivation and geographical area. Other papers reported concentrations of 0.98 g TSS L −1 and productivities of 10-30 g TSS m −2 d −1 with other types of digestates [39][40][41], or 2.1-2.2 g TSS m −2 d −1 for indoor cultivation in high rate algal ponds (HRAP) [20,42]. Besides the value of productivity, it was here demonstrated that the cultivation in a real outdoor operating pilot plant fed with OFMSW digestate is feasible.…”

Outdoor microalgae‐based urban wastewater treatment: Recent advances, applications, and future perspectives

“…Microalgae reactors must be properly oriented to maximize microalgae performance. In raceway ponds, they have to be north–south oriented to minimize the shadow produced by the reactor's walls and baffles (Romero‐Villegas, Fiamengo, Acién‐Fernández, & Molina‐Grima, 2018).…”

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators

“…However, outdoor microalgae cultivation is still challenging due to the lower microalgae growth rates than other microorganisms such as heterotrophic bacteria. This means outdoor photobioreactors (PBRs) must be operated at long hydraulic retention times (HRTs) of around 3.5-10 d (Arbib et al, 2017;Romero-Villegas et al, 2018), which implies high cultivation area needs (Xu et al, 2019).…”