Abstract
Hydroponic farms produce wastewater that need to be treated before being released into the environment. A three-step screening process (microplate, batch, and semi-continuous flasks experiments) initially designed to select an efficient microalgae strain allowed the isolation of a consortium that naturally developed in the hydroponic farm wastewater. During the non-optimized semi-continuous experiments, the best performing microalgae strain, Scenedesmus obliquus UTEX393 and the wastewater-born consortium cultures achieved good average linear growth rate (0.186 and 0.198/d, respectively) and high average nitrogen removal rates (23.5 mgN/L/d and 21.9 mgN/L/d, respectively). Phosphorus removal was very high probably due to precipitation. An integrated process was designed to treat the hydroponic farm wastewater using the wastewater-born consortium. Despite relatively low coagulation efficiencies in the preliminary tests, when integrated in a continuous process, chitosan was efficient to harvest the naturally wastewater-born consortium. The process was also efficient for removing nitrate and phosphate in less than seven days (average removal of 98.2 and 87.1% for nitrate and phosphate, respectively). These very promising results will help to define a pre-industrial pilot process.
Highlights
Agriculture is producing large amount of wastewaters that contains high levels of pollutants such as nitrogen, phosphorus, and organic matter [1,2].Hydroponic or soilless culture is a method where the plants are grown without soil under a greenhouse
We have investigated the potential of microalgae to treat hydroponic farm wastewaters (HFWW) while producing a valuable biomass
Four microalgae strains (Chlorella vulgaris NIES227, Parachlorella kessleri NIES2152, Scenedesmus obliquus UTEX393, Scenedesmus quadricauda UTEXB614), and one consortia isolated from ponds that are depolluting phytosanitary effluents (the Phytobarre system from the ADEQUABIO company (Pertuis, France), https://www.adequabio.fr/) named consortium B1 were selected for this study for their fast-growing potential and their ability to assimilate mineral nutrients
Summary
Hydroponic or soilless culture is a method where the plants are grown without soil under a greenhouse These systems are effective in removing the problem of soilborne pathogens, increasing the crop yield and the quality of the product, and improving the nutrient and water usage, especially in closed system where the nutrition water is recycled [3]. In these systems, some of the recycled water need to be discharged due to the increase in salinity and to the remaining ions that are not assimilated by plants [4] These hydroponic farm wastewaters (HFWW) are rich in mineral pollutants (nitrate, phosphate, and sulfate) and poor in organic matter [5]
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