Wastewater treatment using microalgae: how realistic a contribution might it be to significant urban wastewater treatment?

Abstract

Microalgae have been proposed as an option for wastewater treatment since the 1960's but still this technology has not been expanded to an industrial scale. In this paper, the major factors limiting the performance of these systems are analysed. The composition of the wastewater is highly relevant, and especially the presence of pollutants such as heavy metals and emerging compounds. Biological and engineering aspects are also critical and have to be improved to at least approximate the performance of conventional systems, not just in terms of capacity and efficiency but also in terms of robustness. Finally, the harvesting of the biomass and its processing into valuable products poses a challenge; yet at the same time, an opportunity exists to increase economic profitability. Land requirement is a major bottleneck that can be ameliorated by improving the system's photosynthetic efficiency. Land requirement has a significant impact on the economic balance but the profits from the biomass produced can enhance these systems' reliability, especially in small cities.3

Optimising an outdoor membrane photobioreactor for tertiary sewage treatment

“…The filtration of microalgae also allows operating at shorter hydraulic retention times (HRTs) and longer biomass retention times (BRTs), enabling to recover large quantities of nutrients without washing out the microalgae culture (Gao et al, 2019). This can improve the microalgae performance while increasing the nutrient load to the system which would reduce the large areas of land that are needed for microalgae cultivation (Acién et al, 2016). By way of example, Bilad et al (2014) reported in lab conditions 9fold higher microalgae biomass productivity than a PBR system when HRT and BRT were decoupled by membrane filtration.…”

“…BRT: biomass retention time; PS: pumping system; NPV: non-photic volume; HRT: hydraulic retention time; a: HRT = 2-4 days; b: HRT = 4.5 days; group of numbers (1,2,3,4,5,6): non statistically significant differences.…”

Using an Algal Photo-Bioreactor as a Polishing Step for Secondary Treated Wastewater

“…[10] in an SBR photo-bioreactor operated at SRT of 15 days and MLSS concentrations up to 2.41 g/L. MLSS concentrations in the range of 0.5 to 2.0 g/L are expected and depend on the photo-bioreactor type and the culture conditions [6]. Fig.…”

“…Moreover, new concepts are emerging for other algal biomass uses such as animal feed or chemicals, bioplastics, and biofuels [6].…”

“…Therefore, research on algae-based wastewater treatment has recently focus on algal photobioreactors, which are effective, require a small footprint, have high algal biomass production, and can be controlled efficiently [9][10][11]. The coexistence of bacteria and microalgae in algal-bacterial systems improves organic matter and nutrient removal where microalgae deliver the oxygen required for heterotrophic and autotrophic bacteria while consuming the CO 2 released by the bacteria [6,12]. It was previously reported that nitrifying organisms is a main contributor in ammonia removal by nitrification in a lab-scale photobioreactor [10].…”