Microalgal biomass production and nutrients removal from domestic sewage in a hybrid high-rate pond with biofilm reactor

Abstract

a b s t r a c tIn this study, biomass production and domestic sewage treatment in hybrid systems under bacterialmicroalga consortia were assessed. Biomass was grown suspended in the growth media of high-rate ponds (HRPs) and attached in biofilm reactors (BRs). These hybrid systems were operated with and without the addition of CO 2 (HS2 and HS1, respectively) in the HRP growth media. The performances of these systems were compared with that of a conventional HRP with CO 2 supplementation. Regarding sewage treatment with microalgae and bacteria consortia, the three systems showed no significant differences in the removal of organisms associated with faecal contamination, organic matter and most nutrients. However, nitrate levels were increased in the hybrid systems due to the presence of BRs. There were no differences in algal biomass production among the three systems, which remained in the 0.6-0.7 g m −2 range. HS1 showed the highest total biomass production of 101.31 g m −2 at a production rate of 6.79 g m −2 day −1 . The BR of HS1 was able to supply the necessary CO 2 and therefore no additional gas supplementation was required. This result indicates that a conventional HRP with CO 2 supplementation can be replaced by a hybrid system with biofilm reactor, with additional advantages of resources saving, operational simplicity and easier harvesting.

Application of microalgae cultivated on pine bark for the treatment of municipal wastewater in cylindrical photobioreactors

“…According to Babu (2011), providing the possibility of attachment of nitrifying and denitrifying bacteria to the substrate is crucial for the effectiveness of nitrogen removal from sewage. These bacteria prefer growth on a solid substrate (Babu, 2011;de Assis et al, 2017), which in the case of this study was pine bark, as well as the layer of microalgae (mainly filamentous green algae). The structure of biofilm is beneficial for nitrifiers as well as denitrifiers because it has an aerobic zone (outer layers) and an anaerobic zone (inner layers) (Babu, 2011).…”

“…Wastewater treatment systems based on microalgae cultivation (phycoremediation) allow not only to obtain an adequate reduction of pollutants in sewage, but also valuable biomass which can be used as a material for the production of biofertilizers, biofuels of the third generation and biogas (Rawat et al, 2011;Abdel-Raouf et al, 2012;Boelee et al, 2012;Su et al, 2016;de Assis et al, 2017). Studies show that microalgae can grow in domestic, municipal, industrial, livestock and agriculture sewage (Abdel-Raouf et al, 2012;Choi and Lee, 2012;Prajapati et al, 2013; Application of microalgae cultivated on pine bark for the treatment of municipal wastewater in cylindrical photobioreactors…”

“…The microalgal biofilm system is characterized by a high nutrients removal ratio and also reduces the costs of biomass harvesting compared to microalgae grown in the suspended systems (Boelee et al ., 2011; Su et al ., 2016; Ting et al ., 2017). In addition, the biofilm increases the biomass concentration, the tolerance of microalgae to the change in local environmental conditions and to the effect of toxic substances (microorganisms in the biofilm can be 600‐fold more resistant to heavy metals than free‐swimming cells (Kloc and González, 2012)) and reduces energy consumption due to the lack of mixing biomass with sewage (Tam et al ., 1998; Boelee et al ., 2011; de Assis et al ., 2017). Wastewater treatment by biofilm can be conducted in PBRs and due to the immobilisation of biomass, the time of contact of algae with wastewater increases, which enhances the treatment process (Abdel‐Raouf et al ., 2012).…”

“…Wastewater treatment by biofilm can be conducted in PBRs and due to the immobilisation of biomass, the time of contact of algae with wastewater increases, which enhances the treatment process (Abdel‐Raouf et al ., 2012). During the growth of algae, the biofilm entraps consortia of autotrophic and heterotrophic microorganisms in the exopolymeric matrix (Boelee et al ., 2012; Sukačová et al ., 2015; de Assis et al ., 2017). Due to such symbiosis, it is possible for the system to operate without an external source of CO 2 (Boelee et al ., 2012; Choi and Lee, 2012; Ting et al ., 2017).…”

“…Due to such symbiosis, it is possible for the system to operate without an external source of CO 2 (Boelee et al ., 2012; Choi and Lee, 2012; Ting et al ., 2017). Research (de Assis et al ., 2017) showed that using biofilm in hybrid PBRs it is possible to replace conventional HRP (High‐Rate Pond) systems fed with CO 2 . During photosynthesis, microalgae secrete O 2 used during the aerobic oxidation of organic compounds.…”