Natural Pigments and Biogas Recovery from Microalgae Grown in Wastewater

Abstract

This study assessed the recovery of natural pigments (phycobiliproteins) and bioenergy (biogas) from microalgae grown in wastewater. A consortium of microalgae, mainly composed by Nostoc , Phormidium , and Geitlerinema , known to have high phycobiliproteins content, was grown in photobioreactors. The growth medium was composed by secondary effluent from a high rate algal pond (HRAP) along with the anaerobic digestion centrate, which aimed to enhance the N/P ratio, given the lack of nutrients in the secondary effluent. Additionally, the centrate is still a challenging anaerobic digestion residue since the high nitrogen concentrations have to be removed before disposal. Removal efficiencies up to 52% of COD, 86% of NH 4 + -N, and 100% of phosphorus were observed. The biomass composition was monitored over the experimental period in order to ensure stable cyanobacterial dominance in the mixed culture. Phycocyanin and phycoerythrin were extracted from harvested biomass, achieving maximum concentrations of 20.1 and 8.1 mg/g dry weight, respectively. The residual biomass from phycobiliproteins extraction was then used to produce biogas, with final methane yields ranging from 159 to 199 mL CH 4 /g VS. According to the results, by combining the extraction of pigments and the production of biogas from residual biomass, we would not only obtain high-value compounds, but also more energy (around 5–10% higher), as compared to the single recovery of biogas. The proposed process poses an example of resource recovery from biomass grown in wastewater, moving toward a circular bioeconomy.

Behavior of UV Filters, UV Blockers and Pharmaceuticals in High Rate Algal Ponds Treating Urban Wastewater

“…Oxygen is generated through photosynthesis and used by heterotrophic aerobic bacteria to degrade the organic matter present in the water. This way, these systems have the capacity of treating wastewater efficiently whereas producing microalgae biomass which, after an appropriate harvesting/separation technique from the aqueous phase, can be further profited to produce bioenergy (biogas) or other added-value bioproducts such as pigments, biofertilizers or bioplastics [5][6][7][8][9]. In consequence, if this biomass is managed properly, the waste generated during microalgae treatment (biomass) is considerably reduced, as well as the operation and maintenance costs when compared to conventional WWTPs.…”

Biogas Production from Microalgal Biomass Produced in the Tertiary Treatment of Urban Wastewater: Assessment of Seasonal Variations

“…This is expected because the GreenDune biomass samples grow under suboptimal conditions subjected to competition from different microalgal species but also to grazing due to the presence of predatory or parasitic (micro)organisms. These effects leave a lower proportion of biodegradable organic matter on the volatile solids of the biomass which, after predation or parasitism, consists of material richer in recalcitrant organics, with a lower availability of biodegradable organic matter for anaerobic digestion [32].…”

Circular Bio-economy—Paradigm for the Future: Systematic Review of Scientific Journal Publications from 2015 to 2021

“…Longhurst et al (2019) [131] have done exactly that in a UK case study and have concluded that these bio-fertilisers pose negligible risks to human, animal, environmental and crop receptors, when the appropriate stipulated risk management controls are adhered to. Ferreira et al (2018 [37,38] experimented with the algal-bacterial treatment of different types of wastewater streams-swine, cattle, poultry, dairy, brewery and urban-to grow microalgae which was subsequently dark-fermented to yield bioproducts, while Wicker et al (2020) [39] treated nutrient-rich liquid digestate with a microalgal-bacterial consortia to accomplish the triple objectives of wastewater treatment, nutrient recovery for reuse in agriculture and cultivation of biomass to be put to multiple uses [40]. Waste streams with higher nutrient concentrations resulted in a marked improvement in the microalgal productivity [37,38,41].…”