Microalgae–bacteria systems are used for the treatment of effluents, using a technology that has stood out with excellent results, as reported in the literature. However, investigating these systems in more depth can improve our understanding of the removal mechanisms for a wide range of existing and emerging pollutants and help improve the guidelines for design and operation, in order to improve the treatment efficiency as well as biomass productivity. This work studied the impact of the feeding regime on the removal of metals and pathogens from primary domestic wastewater in high rate algal ponds (HRAPs). For this, one reactor was fed continuously (HRAP1) while two reactors were fed in semi-continuous mode, during 12 h day−1 (HRAP2) and 0.1 h day−1 (HRAP3). Although removal efficiencies of 82 ± 5% for Mn and 90% for E. coli were reached in the semi-continuously fed reactors, there was no significant difference between the conditions studied. On the other hand, for biomass productivity, the semi-continuous feeding regime was more advantageous with a growth of ≈ 22 mg L−1 day−1.

The influence of CO₂ addition and feeding regime (continuous versus semicontinuous) on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus, Enterococcus faecalis, and Escherichia coli (E. coli) from three shaded high-rate algal ponds (HRAPs) treating raw sewage (RS) was studied. The three HRAPs were operated at an analogous hydraulic retention time (HRT) for 5 days and with shading of 50%. The CO₂ addition and feeding regime had no statistically significant influence on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus sp., and Enterococcus faecalis, with 2.39–3.01, 2.07–2.31, 3.02–3.38, and 3.14–3.45 log units, respectively. However, the removal of E. coli decreased significantly with the feeding regime of 0.1 h d⁻¹ and 2.23–3.29 log units. The productivity and the total suspended solids (TSS) removal efficiency were significantly improved with the semicontinuous feeding regime and CO₂ addition. The highest productivity was obtained in the semicontinuous feeding regime, 5.93 g m² d⁻¹, while the TSS removal efficiency was similar between the semicontinuous feeding regime and CO₂ addition (31–36%). The control of light intensity led to greater variability in the algal community, and was present in the three reactors, in different proportions, in the form of the microalgae Scenedesmus acutus, Scenedesmus obliquus, and Chlorella sp.

Conventional biological wastewater treatment systems have a low pathogen removal capacity. Microalgae-based systems are sustainable and low-cost alternatives for wastewater treatment and are capable of removing pathogens from domestic effluents. Other microorganisms have been identified as alternative indicators of disinfection since they have greater resistance than Escherichia coli, either because of the formation of spores or because of other mechanisms of protection, and because they spread in wastewater treatment plants; the most important are Clostridium perfringens and Staphylococcus spp. This study assessed the influence of microalgal strains (e.g., Chlorella vulgaris and Scenedesmus acutus Meyen) and the addition of CO₂ and O₂ on the removal of C. perfringens and Staphylococcus spp. from domestic wastewater in microalgal–bacterial systems. The removal of C. perfringens (2.5 to 3.2 log units) and Staphylococcus sp. (1.8 to 2.0 log units) was higher when using Chlorella sp. inoculum. The addition of CO₂ and O₂ did not have a significant effect on the removal of pathogenic bacteria. The main mechanism of C. perfringens removal was by means of toxins and bactericidal substances produced by the microalgae, while Staphylococcus spp. removal also occurred through photooxidative processes.

O trabalho teve a finalidade de avaliar quais tipos de cultivo e condições operacionais são mais eficientes na remoção de nutrientes do esgoto doméstico primário em sistemas de microalgas-bactérias. Para isso, diferentes condições experimentais foram estudadas utilizando como inóculo microalgas e/ou bactérias bem como o efeito da luz e a adição de gases (gás carbônico e ar atmosférico). As remoções foram mais expressivas nos fotobiorreatores inoculados com microalgas (com predominância de Chlorella vulgaris) e bactérias, em presença de luz. Além disso, as condições que receberam suplementação de gás (MB+CO2 e MB+O2) obtiveram remoções superiores às demais condições, em relação ao nitrogênio total (93 ± 0,2% e 95 ± 1,8%, respectivamente), carbono orgânico total (84 ± 0,2 e 86 ± 0,1%) e carbono inorgânico (95 ± 0,7 e 95 ± 0,3%). Por fim, foram também nestas condições que se obtiveram os melhores resultados de crescimento da biomassa, com produtividade máxima de 179 e 267 mgSST L-1 d-1. Palavras-chave: Carbono. Chlorella vulgaris.Fósforo. Nitrogênio. Tratamento de efluentes.