Enhanced and Balanced Microalgal Wastewater Treatment (COD, N, and P) by Interval Inoculation of Activated Sludge

Abstract

Although chemical oxygen demand (COD) is an important issue for wastewater treatment, COD reduction with microalgae has been less studied compared to nitrogen or phosphorus removal. COD removal is not efficient in conventional wastewater treatment using microalgae, because the algae release organic compounds, thereby finally increasing the COD level. This study focused on enhancing COD removal and meeting the effluent standard for discharge by optimizing sludge inoculation timing, which was an important factor in forming a desirable algae/bacteria consortium for more efficient COD removal and higher biomass productivity. Activated sludge has been added to reduce COD in many studies, but its inoculation was done at the start of cultivation. However, when the sludge was added after 3 days of cultivation, at which point the COD concentration started to increase again, the algal growth and biomass productivity were higher than those of the initial sludge inoculation and control (without sludge). Algal and bacterial cell numbers measured by qPCR were also higher with sludge inoculation at 3 days later. In a semi-continuous cultivation system, a hydraulic retention time of 5 days with sludge inoculation resulted in the highest biomass productivity and N/P removal. This study achieved a further improved COD removal than the conventional microalgal wastewater treatment, by introducing bacteria in activated sludge at optimized timing.

Mixotrophic Cultivation of Microalgae Using Biogas as the Substrate

“…Increased organic matter in wastewater treatment using microalgae is a notorious issue. 44 The dissolved organic matter in Co-MM was significantly lower than in the single culture of microalgae (Figure 5b). The 3D-EEM shows that this is mainly due to the reduction of humic acid-like substances (Figure S7).…”

“…Increased organic matter in wastewater treatment using microalgae is a notorious issue . The dissolved organic matter in Co-MM was significantly lower than in the single culture of microalgae (Figure b).…”

Optimization of Cultivation Condition of Newly Isolated Strain Chlorella Sorokiniana pa.91 for CO2 Bio-Fixation and Nutrients Removal From Real Municipal Wastewater: Impact of Temperature and Light Intensity

“…It should be noted that the achieved final concentration of phosphate is below the acceptable level of the surface water quality standard (1 P-mgL -1 ). (China, 2002) Chemical oxygen demand (COD) has been reported as the most challenging problem in the treatment process due to its re-increasing in the wastewater (Lee et al, 2019). As illustrated in Fig 6d, the COD was eliminated gradually from 211 to 50.7 mgL -1 resulted in 76.3% removal rate of COD during 10 days cultivation of C. sorokiniana pa.91 in the photobioreactor.…”

Microalgae cultivation for the treatment of anaerobically digested municipal centrate (ADMC) and anaerobically digested abattoir effluent (ADAE)

“…wastewater treatment as it is an indicative measure of the organic load (strength of the effluent) in the wastewater and the amount of molecular oxygen that can be consumed for its oxidation (Lee et al, 2019;Otondo et al, 2018). Nonetheless, the fate of COD during microalgal based wastewater treatment procedures have not been well established when compared to other common nutrients such as nitrogen and phosphorus (Choi & Lee, 2012;Lee et al, 2019). In this study, the concentration of COD was found to decrease in both ADMC and ADAE from Day 0 to Day 7 (Table 3).…”