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
The influence of pH (7, 8 and 9) and CO2 source (pure CO2 or CO2 from flue gas) on both the performance of secondary domestic wastewater treatment and biomass productivity and composition in three outdoors pilot raceways was evaluated for 6 months. Average COD, TN, TP and E. coli removal efficiencies of 84±7%, 79±14%, 57±12% and 93±7%, respectively, were recorded. The influence of pH on wastewater treatment was negligible, while the supply of CO2 from flue gas supported higher COD, TOC and TP removals. Biomass productivities ranged from 4±0 g m-2 d-1 in December to 17±1 g m-2 d-1 in July. The highest C, N and P biomass contents (64.8%, 12.6 % and 2.4 %, respectively) were recorded when flue gas was supplied. Finally, while the protein content in the biomass remained constant (38.2±3.3%), the lipid and carbohydrate contents ranged from 5.8% to 23.0% and from 38.0% to 61.2%, respectively.
In horticultural practice, accelerated plant development, and particularly earlier flowering, has been reported with microalgae applications. Therefore, the objective of this work was to study the effects of foliar spraying with Scenedesmus sp. and Arthrospira platensis hydrolysates on Petunia x hybrida plant development and leaf nutrient status. Three treatments were tested: T1 (foliar application with water, the control), T2 (foliar application with Arthrospira) and T3 (foliar application with Scenedesmus). Foliar spraying was applied 5 times (0, 14, 28, 35 and 42 days after transplanting). The concentration of both microalgae was 10 g L-1. At the end of the trial, biometric parameters and nutrient concentration in photosynthetic organs (the leaves) were measured. The results of this assay show that foliar application of Scenedesmus accelerated plant development in terms of higher rates of root growth, leaf and shoot development and earliness of flowering. Arthrospira enhanced the root dry matter, the number of flowers per plant and the water content. Nevertheless, a reduction was found in the conductive tissue (stem+petiole) dry weight with Arthrospira compared with Scenedesmus and the control. The results also show that microalgae hydrolysate supply can improve the plant nutrient status. Based on these results, it is advisable to use Scenedesmus hydrolysates in foliar applications to increase the blooming of Petunia x hybrida. 1.Introduction There is a growing need to develop environmentally friendly strategies for sustainable culturing of horticultural crops with high yields involving less environmental damage (Alves-Dias et al., 2016). This consists of reducing or substituting the use of chemical inputs, especially fertilizers and pesticides, with natural or
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