applied sciences  
A Combined Vermifiltration-Hydroonic System for Swine Wastewater Treatment  
[PERSON],*, [PERSON], [PERSON] and [PERSON]  
Laboratory of Separation and Reaction Engineering-Laboratory of Catalysis and Materials (LSRE-LCM), School of Technology and Management (ESTG), Polytechnic Institute of Leiria, 2411-901 Leiria, Portugal; [EMAIL_ADDRESS] (L.M.I.A. ); [EMAIL_ADDRESS] (J.S.V. )Applied Molecular Biosciences Unit (UCIBIO)-REQUIMITE, Department of Chemistry, NOVA School of Science and Technology (FCT), NOVA University of Lisbon, 2829-516 Caparica, Portugal; [PERSON]@fct.unl.ptCorrespondence: [EMAIL_ADDRESS]  
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pollution [4] and to carry large amounts of coliform bacteria [6]. If left untreated, swine manure will contaminate surface waters, soils, and groundwaters, posing threats to public health and to the environment by causing ecotoxicity and water eutrophication. The simplest way to treat swine manures and wastewaters is to use them directly as soil fertilizer. However, this is not the best option, as the bioavailability of nutrients in manures to agricultural crops was found to be limited (only 20% of N, 40% of P2O5 and 29% of K2O available) [7]. Agricultural reuse of untreated wastewaters can alter soil pH, increase organic compounds, salinity, nitrogen, metals and emerging contaminants, and change microbial community structure and activities [8]. Most commonly, swine manures are treated in loco by temporary deposition in non-aerated lagoons for decomposition of organic matter, with or without previous removal of solids. The low cost of this treatment technique [9] makes it attractive and widely used. Lagoon treatment is, however, ineffective, as it fails to remove and rather increases inorganic nitrogen and phosphorus contaminants [10]. Furthermore, lagoons have a limited holding capacity; if uncovered, they are prone to overflowing under heavy precipitation. Aerated lagoons are more efficient as they promote nitrification, eliminate toxic substances and foul odours, but aeration makes them much more expensive [9; 10]. Additional treatments have been studied, including composite of solids [9], overload flow through artificial isolated plots of soil with vegetation [10], constructed wetlands [11], controlled digester tanks [9], trickling filters [10], and immobilized nitriifying bacteria culture reactors [10]. Overland flows and constructed wetlands have proven to be naturally limited [10; 11], while more technological treatments are more expensive [9; 10]. Vermicomposting of manures [12] and vermifiltration of swine wastewaters [13] are examples of cheap nature-based treatments for hog farm wastes. Earthworm activity is complex and involves a multitude of processes: (1) mechanical mixing, aeration, and reduction of particles to smaller size through burrowing and grinding, with the advantages of increased surface area, improved filtration efficiency, and sorption; (2) chemical and biochemical effects of digestion and biologically active substances excreted with the vermicast; (3) inoculation of the substrate with earthworm gut bacteria [14; 15].