Cultivation of the Acidophilic Microalgae Galdieria phlegrea with Wastewater: Process Yields

Abstract

Algal based wastewater treatment offers the opportunity to recover, in the form of biomass, the nutrients and internal chemical energy of wastewater. Recently, there has been a growing interest in the use of extremophilic microalgae, as they can easily adapt to difficult and often pollutant-rich environments. The thermo-acidophilic microalga Galdieria phlegrea is a species of recent discovery and great metabolic versatility, but it has still been poorly studied. Here, G. phlegrea was cultivated using raw municipal wastewater in 1 L Erlenmeyer flasks with 700 mL working volume at 37 °C for up to nine days. During the cultivation phase, biomass growth, phycocyanin content, ammonium and phosphate removal from the wastewater, lipid fraction, total carbon and nitrogen in the biomass, and variation in δ13C and δ15N isotopic ratios (a novel analytical contribution in these experiments) were monitored. Results indicated that G. phlegrea was able to grow in raw effluent, where it removed more than 50% ammonium and 20% phosphate in 24 h; total lipid content was in the range of 11–22%, while average C-N content was of 45% and 6%, respectively; isotopic analyses proved to be a useful support in identifying C and N metabolic pathways from effluent to biomass. Overall, G. phlegrea showed consistent performance with similar Cyanidiophyceae and is a potentially viable candidate for municipal wastewater valorization from a circular economy perspective.

A Review on the Reliability and the Readiness Level of Microalgae-Based Nutrient Recovery Technologies for Secondary Treated Effluent in Municipal Wastewater Treatment Plants

“…The temperature range for freshwater algal growth, regardless of the strain, is typically between 15 and 30 • C (optimal of 20-25 • C). Some thermophilic strains can withstand higher temperatures of up to 56 • C and some psychrophilic strains can live in environments with temperatures of 17 • C [8,25,76,79,99,100]. Generally, the algal activity significantly drops (in some cases with more than 90%) with temperatures under 15 • C, leading to decreased nutrient removal efficiency and removal rate retardation [8,25,76,79].…”

Real-Time Monitoring and Static Data Analysis to Assess Energetic and Environmental Performances in the Wastewater Sector: A Case Study

“…In the specific case study of the Agropoli WWTP, as can be seen from the data shown in Table 3, the urban wastewater is characterized by an average temperature of about 22 • C and an average sub-acid pH (5,7). A wastewater with these values, used in an enclosed environment (e.g., greenhouse) and with a further non-invasive acidification (up to pH 4) could potentially be suitable for the use with extremophilic thermoacidophilic microalgae, which are currently among those of greatest interest on the market for their great adaptive capacity, tolerance to heavy metals and toxic substances in the environment, high productivity of bio-compounds with high market value (phycobiliproteins, pigments, glycogen and other reserve carbohydrates, secondary metabolites with antioxidant and antibacterial activity) [14,[36][37][38].…”

“…The use of these practices, however, is still at a testing stage in most of the realities that have chosen to adopt these solutions for the increase of their performance indices [13]. Therefore, since it is not always possible to adopt this type of sustainable solutions, in order to improve the energy-environmental performance of these systems, it is still essential to optimize the use of energy within the facilities, through system auditing and the accurate monitoring of process variables [14]. The first tool is the one that allows to gather all the qualitative and quantitative information on the observed system in order to firstly frame its operating conditions and overall performance, based on data collected offline (static data) [15].…”

Cyanidiophyceae (Rhodophyta) Tolerance to Precious Metals: Metabolic Response to Palladium and Gold

“…Recently, biological methods have been developed to ensure the recovery of small quantities of these metals from wastewater systems [5], using mainly bacteria [9][10][11][12] or plants known for their ability to immobilize heavy metals in the cell wall and to compartmentalize them in vacuoles [13]. Interestingly, polyextremophilic algae have intrinsic properties that make them capable of selective removal and concentration of metals, thanks to their adaptation to live in geothermal and volcanic sites [14][15][16][17]. Geothermal fluids leach out of hot volcanic rocks and are enriched by enormous amounts of minerals and metals, including lithium, sulphur, boric acid, and precious metals such as gold, platinum, palladium, and silver [18].…”

“…The Cyanidioschyzon and Cyanidium species are obligatory autotrophs, while the Galdieria species can grow auto-, mixo-, and heterotrophically and tolerate high concentrations of salts [21]. This makes Galdieria particularly suitable for biotechnological applications [14]. The ability of Galdieria sulphuraria to recover REEs has already been assessed [5,22] and confirmed by an approved patent [23].…”