## 3 Results and Discussion
### System Limitations and Future Improvements  
A system combining a vermifilter with a downstream hydroponic unit was used in this work for hog farm wastewater treatment. The use of hydroponic cultures in this study was tested for two main goals: removing eutrophicating contaminants from the vermifiltered wastewater and obtaining nutritious crops for human and/or animal consumption. A third goal was to save as much water as possible by reusing the final effluent for dilution. The obtained results suggest an interesting potential for both wastewater treatments and the production of marketable crops. The hydroponic plant cultures showed the capacity to remove inorganic phosphorus and nitrate from previously vermifiltered wastewater, provided that a good plant health and growth rate are ensured and contributing to the enhanced treatment of wastewater. To successfully attain both the wastewater treatment and crop production goals, the plants should be able to grow abundantly while consuming most of the nitrogen and phosphorus in the water. Not every crop is probably adequate for this function, and a comprehensive study must first address the crop selection problem. It is also critical to regularly control the nutrient composition of the vermifiltered water to be fed to the hydroponic cultures, since the swine wastewater will vary in composition, and so will the vermifilter effluents. The vermifilter effluent should be thoroughly analyzed for all the important nutrients, including the chemical forms of nitrogen, phosphorus, and sulphur, and other elements such as magnesium, potassium, calcium, manganese, iron, copper, zinc, and others. As was observed, vermifilter effluent pH can change over time  
Figure 3: Total coliforms in wastewater at different process stages. due to a complexity of factors, and EC tends to increase with increasing mineralization of recirculating wastewater. For each specific crop, the ideal medium composition, EC and pH should be known, and the feed corrected as necessary. Saving water through effluent recirculation should be feasible by introducing additional treatment modules for the removal of accumulated components. Temperature and moisture control in the facilities, as well as controlled light for photosynthesis, are other important requirements for optimized hydroponic crop production. Vermifiltered wastewater use as nutrient medium for hydroponic growth might be compromised by the proliferation of pathogens such as coliform bacteria and subsequent contamination of crops. Microorganisms, both those introduced with the wastewater and those growing within the system, should be characterized and controlled by periodic decontamination using ultraviolet light irradiation. The system might benefit greatly from the use of a community of plant species with different capacities and requirements. Once enough knowledge is available, it should be possible to develop the best hydroponic system configurations and plant species selection, combination and disposition within the hydroponic units. Possibly, non-nutritious plants must be used in a final treatment stage to remove most of the eutrophication-inducing pollutants remaining after feeding the commercial crops. Figure 4: Growth of hydroponically cultivated crops: (**a**) aerial parts length; (**b**) aerial parts spread; (**c**) stem height; (**d**) number of leaves. The implementation of similar systems on real scale will bring up further challenges. One potential setback could be the additional land use for hydroponic cultures; however, hydroponic cultivation can be designed to reduce land use by using vertical space, unlike traditional agriculture. Water treatment efficiency will depend on the liquid flow and the volume of each compartment. Slower flows and larger volumes will increase hydraulic residence times and conversion efficiency. On the other hand, slower flows will limit the throughput and could be useless in real hog farms.