Optimization of Hydraulic Retention Time and Biomass Concentration in Microalgae Biomass Production from Treated Sewage with a Membrane Photobioreactor

Abstract

Treated sewage is a promising source of nitrogen and phosphorus in microalgae biomass production for carbon-neutral biofuel and chemical products. In this study, Chlorella vulgaris was continuously cultivated in membrane photobioreactors (MPBRs) under short hydraulic retention times (HRTs) and with different numbers of submerged membrane modules to investigate potential microalgae productivity when treated sewage was used as a nutrient source. Microalgae biomass concentrations were independent of HRT in MPBRs with one membrane module owing to microalgae biomass deposition on the membrane. Installation of an additional submerged membrane module effectively reduced deposition on the submerged membrane, resulting in increased microalgae biomass concentration and volumetric productivity. Growth kinetics suggested that HRT is the essential parameter influencing the volumetric productivity of microalgae under nutrient-limited conditions, and that optimization of the biomass concentration, which depends on the surface/volume ratio of the photobioreactor and initial light intensity, is critical to maximization of the volumetric productivity under light-limited conditions.

Utilization of Anaerobic Digestion Supernatant as a Nutrient Source in Microalgal Biomass Production with a Membrane Photobioreactor

“…Light restriction is one of the possible reasons which could inhibit the microalgal growth. However, it was negligible in this case since the SS concentrations in this research were lower than other reports using various types of photobioreactors [6,12,13]. Another factor could be carbon dioxide concentration in the aeration.…”

“…Another factor could be carbon dioxide concentration in the aeration. In the research by Honda et al [6], they used the same light source but higher CO 2 concentration (1%) since their target was aeration tank in sewage treatment process. Although the N and P concentrations were higher in diluted SADS than general municipal wastewater, some nutrients not measured might be at insufficient level for microalgal growth.…”

“…The introduction of the membrane enables the replacement of cultivating media without washing out the microalgae, obtaining large microalgal retention time. It has been shown that the application of MPBR for growing green microalgae with urban-treated sewage was effective [5,6], although the growth efficiency still did not reach a practical level. Besides, anaerobic digestion supernatant or anaerobic digestion effluent is a by-product which can be obtained from activated sludge in the wastewater treatment process.…”

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

“…5). Short HRT and higher biomass were achieved by the two-module membrane photobioreactor for sewage treatment [35], but this membrane photobioreactor was difficult to adopt to a scaled-up wastewater process, because it costs much more than simple photobioreactors. In addition, mixed microalgae/ sludge was used to treat pre-treated swine manure at HRT of 10 days [36].…”

Growth performance and nutrient removal of a Chlorella vulgaris-Rhizobium sp. co-culture during mixotrophic feed-batch cultivation in synthetic wastewater

“…Enhanced nutrient consumption and high microalgae biomass productivity caused by lower HRTs was also observed during continuous cultivation of C. vulgaris in treated sewage in membrane photobioreactors [39,40]. Thus, as no washout effect was observed at HRT 3, this short residence time seems to be suitable to maintain a long-term cultivation and achieve an efficient removal of pollutants, even at large scale outdoors, although the risk of contamination by detrimental microorganisms might increase [41].…”