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- From piggery wastewater to wheat using microalgae towards zero wastePublication . Ferreira, Alice; Figueiredo, Daniel; Ferreira, Francisca; Marujo, Ana; Bastos, Carolina; Martin-Atanes, Guillermo; Ribeiro, Belina; Štěrbová, Karolína; Marques-dos-Santos, Cláudia; Acién, F. Gabriel; Gouveia, LuisaMicroalgae production is still expensive, driving the need to lower costs while strengthening the industry's environmental sustainability. Microalgae are recognized tools for efficient wastewater treatment, offering the recycling of nutrients and water for agriculture, and producing biomass rich in growth-promoting compounds to improve plant productivity and resistance to adverse conditions. The use of wastewater can reduce cultivation costs as it is a source of nutrients and water. Alternative low-cost methods can significantly decrease harvesting costs, which represents one of the most expensive steps of the whole process.The goal of this work was to evaluate the potential of wastewater-grown microalga biomass for agriculture purposes. To reduce production costs, the microalga Tetradesmus obliquus was produced in pre-treated photo-Fenton (PF) piggery wastewater in combination with the use of different harvesting techniques - electro-coagulation, flocculation, and centrifugation, and different combinations. From the wastewater treatment pro-cess, two fractions (biomass and supernatant) were evaluated for germination and growth of wheat (Triticum aestivum L.) plants and compared to non-harvested microalga culture (MC), distilled water, and Hoagland (synthetic) solution. The concentrated resulting from PF was also tested as a biofertilizer.The results confirm that both biomass and supernatants are useful for agricultural applications. The obtained biomass elicited a 20-105 % increase in germination index compared to the control, while supernatants were inhibiting. The opposite trend was observed at later stages of wheat growth, where the nutrient-enriched su-pernatants and the PF concentrate (PF-CC) increased the number of tillers (3-5) and leaves (30-42) after 83 days. Wheat plants treated with MC and PF-CC produced similar number of ears (3.4 & PLUSMN; 0.5 and 6.0 & PLUSMN; 4.1 ears per plant, respectively) than the synthetic control (5.7 & PLUSMN; 1.4) after 182 days. All fractions obtained from the process can be used in a zero-waste process.
- Impact of high-pressure homogenization on the cell integrity of tetradesmus obliquus and seed germinationPublication . Ferreira, Alice; Figueiredo, Daniel; Ferreira, Francisca; Ribeiro, Belina; Reis, Alberto; da Silva, Teresa Lopes; Gouveia, LuisaMicroalgae have almost unlimited applications due to their versatility and robustness to grow in different environmental conditions, their biodiversity and variety of valuable bioactive compounds. Wastewater can be used as a low-cost and readily available medium for microalgae, while the latter removes the pollutants to produce clean water. Nevertheless, since the most valuable metabolites are mainly located inside the microalga cell, their release implies rupturing the cell wall. In this study, Tetradesmus obliquus grown in 5% piggery effluent was disrupted using high-pressure homogenization (HPH). Effects of HPH pressure (100, 300, and 600 bar) and cycles (1, 2 and 3) were tested on the membrane integrity and evaluated using flow cytometry and microscopy. In addition, wheat seed germination trials were carried out using the biomass at different conditions. Increased HPH pressure or number of cycles led to more cell disruption (75% at 600 bar and 3 cycles). However, the highest increase in wheat germination and growth (40-45%) was observed at the lowest pressure (100 bar), where only 46% of the microalga cells were permeabilised, but not disrupted. Non-treated T. obliquus cultures also revealed an enhancing effect on root and shoot length (up to 40%). The filtrate of the initial culture also promoted shoot development compared to water (21%), reinforcing the full use of all the process fractions. Thus, piggery wastewater can be used to produce microalgae biomass, and mild HPH conditions can promote cell permeabilization to release sufficient amounts of bioactive compounds with the ability to enhance plant germination and growth, converting an economic and environmental concern into environmentally sustainable applications.
- Aquaculture wastewater treatment through microalgal. Biomass potential applications on animal feed, agriculture, and energyPublication . Viegas, Catarina; Gouveia, Luisa; Goncalves, MargaridaThe use of microalgae to remediate raw effluent from brown crab aquaculture was evaluated by performing batch mode growth tests using separately the microalgae Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc), Isochrysis galbana (Ig), Nannocloropsis salina (Ns), and Spirulina major (Sp). Removal efficiencies in batch growth were 100% for total nitrogen and total phosphorus for all microalgae. Chemical oxygen demand (COD) remediations were all above 72%. Biomass productivity varied from 20.9 mg L-1 day- 1 (N. salina) to 146.4 mg L-1 day- 1 (C. vulgaris). The two best performing algae were C. vulgaris and S. obliquus and they were tested in semicontinuous growth, reaching productivities of 879.8 mg L-1 day- 1 and 811.7 mg L-1 day- 1, respectively. The bioremediation of the effluent was tested with a transfer system consisting of three independent containers and compared with the use of a single container. The single container had the same capacity and received weekly the same volume of effluent as the three containers together. The remediation capacity of the 3 containers was much higher than the single one. The supplementation with NaNO3 was tested to improve the nutrient removal microalgae? capacity, with positive results. The removal efficiencies were 100% for total nitrogen and total phosphorus and higher than 96% for COD. The obtained C. vulgaris and S. obliquus biomass were composed of 31 and 35% proteins, 6 and 8% lipids, 39 and 30% carbohydrates, respectively. The composition of these biomass suggest that it can be used as novel and sustainable ingredients in aquaculture feeds. The algal biomass of Cv and Sc were used as biostimulants in the germination of wheat and watercress, and very promising results were attained, with increases in the germination index for Cv and Sc of 175% and 48% in watercress and 84% and 98% in wheat, respectively. The biomasses of Cv and Sc were also subjected to a torrefaction process with 72.5 ? 1.7% char yields. The obtained biochars were tested as biostimulants for germination seeds (wheat and watercress) and as bio-adsorbent of dye solutions.