The growth of the world's population increases the demand for fresh water, food, energy, and technology, which in turn leads to increasing amount of wastewater, produced both by domestic and industrial sources. These different wastewaters contain a wide variety of organic and inorganic compounds which can cause tremendous environmental problems if released untreated. Traditional treatment systems are usually expensive, energy demanding and are often still incapable of solving all challenges presented by the produced wastewaters. Microalgae are promising candidates for wastewater reclamation as they are capable of reducing the amount of nitrogen and phosphate as well as other toxic compounds including heavy metals or pharmaceuticals. Compared to the traditional systems, photosynthetic microalgae require less energy input since they use sunlight as their energy source, and at the same time lower the carbon footprint of the overall reclamation process. This mini-review focuses on recent advances in wastewater reclamation using microalgae. The most common microalgal strains used for this purpose are described as well as the challenges of using wastewater from different origins.We also describe the impact of climate with a particular focus on a Nordic climate. | INTRODUCTIONSince the industrial revolution, water pollution has increasingly become a concern to the public and societal authorities. With the development of the industrial world and a growing population, the demands for freshwater are drastically increasing. The global water demand for agriculture, industry, and municipalities is expected to rise by 20-30% by 2050 (Boretti & Rosa, 2019). One of the consequences of this increase is the generation of larger quantities and varieties of wastewaters, contaminated with a wide range and concentrations of chemicals. Besides utilizing several tons of pesticides per year, the agricultural sector also produces considerable amounts of organic waste (Bockstaller et al., 2009), and is one of the most significant sources of water contamination.These pollutants can have dire consequences for the environment and for ecosystems into which they are discharged. Some pollutants, mainly those of organic nature, are generally degradable (either naturally or with the help of microorganisms) and therefore do not cause major problems for the environment. However, some persistent organic pollutants (POPs), typically present in trace amounts, are known to bioaccumulate and exert toxic chronic health effects on animals (Schwarzenbach et al., 2010). Chemical Martin Plöhn and Olivia Spain contributed equally to this study.

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This paper presents the results from the stability experiments carried out on a selected set of chemical compounds. These experiments represent one of the steps for their qualification as oil/water partitioning tracers for measurement of residual oil saturation in the inter-well region. Single-well chemical tracer tests (SWCTT) are a proven tool, frequent in the industry, to measure residual oil saturation (SO) in the near well region. SWCTT are "push-and-pull" tests where an oil/water partitioning ester will partially hydrolyze, generating a passive water tracer, often an alcohol. Oil saturation is then determined from the lag in back production experienced by the ester in relation to the passive water tracer produced during the test. Partitioning inter-well tracer tests (PITT) explore the same delay experienced by the partitioning tracer to determine SO in the swept volume between an injector and one or more producers in an oilfield. Unlike SWCTT, PITT are not frequently used in the industry, and a small number of compounds is qualified as tracer in this application. The development of new PITT tracers will help to widen the use of this technology, which has the potential to significantly contribute to enhance efficiency in oil production. To be used as oil reservoir PITT tracers, the candidate compounds must perform as required by the application under static stability and dynamic experiments. In this work, fifteen PITT tracer candidates from four families of chemicals were tested for thermal, chemical and biological stability in reservoir temperature conditions, ranging from 25 °C to 150 °C. Their interaction with three types of rock materials (sandstone, limestone and kaolinite) was also investigated in the same range of temperatures. Results suggest that six of the investigated compounds possess suitable characteristics for use as PITT tracers, while another five compounds may be used to retrieve other information from the reservoir, such as temperature or geochemical data.

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