Abstract
Animal production inevitably causes the emission of greenhouse gases and the generation of large amounts of slurry, both representing a serious environmental problem. Photosynthetic microorganisms such as microalgae and cyanobacteria have been proposed as alternative strategies to bioremediate agricultural waste while consuming carbon dioxide and producing valuable biomass. The current study assessed the potential of the microalga Scenedesmus sp. to remove nutrients from piggery wastewater (PWW) and the influence of the microalga on the microbial consortia. Maximum N-NH4+ consumption was 55.3 ± 3.7 mg·L−1·day−1 while P-PO43− removal rates were in the range 0.1–1.9 mg·L−1·day−1. N-NH4+ removal was partially caused by the action of nitrifying bacteria, which led to the production of N-NO3−. N-NO3− production values where lower when microalgae were more active. This work demonstrated that the photosynthetic activity of microalgae allows us to increase nutrient removal rates from PWW and to reduce the coliform bacterial load of the effluent, minimising both their environmental impact and health risks. Microalgae assimilated part of the N-NH4+ present in the media to produce biomass and did not to convert it into N-NO3− as in traditional processes.
Highlights
Animal production will increase because of an increasing population, expected to reach 9–10 billion people by 2050 [1]
Investigations on microalgae-based bioremediation led to thethat understanding that nutrivestigations on microalgae-based bioremediation led to the understanding nutrient ent removal is causedanaerobic by assimilation, anaerobic ammonia oxidation, nitrification, and removal is caused by assimilation, ammonia oxidation, nitrification, and denidenitrification, amongHowever, other processes
This work demonstrated that the photosynthetic activity of microalgae allows us to improve the nutrient removal rates in piggery wastewater (PWW) and to reduce the coliform bacterial load of the effluents
Summary
Animal production will increase because of an increasing population, expected to reach 9–10 billion people by 2050 [1]. Meat production is one of the main causes of greenhouse gas emissions [2] and inevitably causes large amounts of slurry, which is a serious environmental concern [3]. Pig manure has been traditionally used as a fertiliser in rural areas. Spanish regulations limit the utilisation of pig manure as an organic fertilizer to up to 170 kgN·ha−1 ·year−1 (Directive 91/676/CEE) and this causes waste management problems in regions where agricultural lands are scarce and high amounts of manure are produced. Microalgae-bacteria consortia have been proposed as a strategy to process wastewater and pig manure because of their ability to recycle organic matter and nutrients [4]. An added advantage of microalgae is that they fix atmospheric carbon dioxide, one of the main problems associated with agriculture and food production. Two important issues must be considered when microalgae are used for piggery wastewater (PWW) treatment: (i) high ammonium concentrations, such as those present in PWW, can lead to ammonia toxicity [6], and (ii) microalgae can affect the microbial community structure that appears naturally in PWW [7]
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