Role of Microalgae in the Recovery of Nutrients from Pig Manure

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.

Optimisation of Scenedesmus almeriensis production using pig slurry as the sole nutrient source

“…The concentration at the outlets ranged from 26.5 to 39.9 mg•L -1 , demonstrating that the cultures were not phosphorus-limited. The removal rates varied from 1.9 mg•L -1 •day -1 in S-PS5% to 2.4 mg•L -1 •day -1 in S-PS1%, which is comparable to results reported in previous research [36]. The lower P-PO4 3removal rate in S-PS5% was caused by this cultures' low biomass productivity.…”

“…almeriensis, with maximum P-PO4 3removal rates of 1.9 mg•L -1 •day -1 [36]. The results were also similar to those obtained when processing undiluted pig slurry using Chlorella vulgaris, with the total nitrogen and phosphorus contents dropping from 362.5 and 18.3 mg•L -1 to 155.9 and 10.2 mg•L -1 , respectively [47].…”

Annual production of microalgae in wastewater using pilot-scale thin-layer cascade photobioreactors

“…The exploitation of photosynthesis to process wastewater is particularly interesting: microalgae use sunlight (an inexhaustive source of energy) and carbon dioxide (a chemical compound we want to get rid of) to transform inorganic nutrients (such as ammonia, nitrates, and phosphates) into oxygen and valuable biomass (Lafarga, 2020). The oxygen produced by microalgae is used by heterotrophic bacteria, present in wastewater, to oxidise organic matter into inorganic nutrients and produce carbon dioxide, both needed for microalgal growth (Sánchez-Zurano et al, 2021). One of the main advantages of this strategy is that the biomass produced during wastewater treatment could be further used to formulate products for agriculture, such as biofertilisers or biostimulants, or animal feeds and other high-value applications.…”

Potential of the cyanobacteria Anabaena sp. and Dolichospermum sp. for being produced using wastewater or pig slurry: Validation using pilot-scale raceway reactors

“…However, no differences were observed when the strains were produced using pig slurry as the nutrient source. Several reports highlighted the potential of microalgae and cyanobacteria for being produced using pig slurry as the main nutrient source [17][18][19][20].…”