## 4 Conclusions  
A working pilot-scale system was built, combining vermifiltration with hydroponic crop cultivation for hog farm wastewater treatment and reusing part of the treated effluent as feed dilution water. Vermifiltration treatment was able to efficiently remove ammonia, nitrite, and BOD\({}_{5}\) from the wastewater, and nitrate accumulation was observed. Coliform bacteria were reduced by 54% by vermifiltration. Hydroponic treatment of vermifiltered wastewater was able to remove phosphorus and, modestly, nitrate under the studied conditions. A further decrease in BOD\({}_{5}\) was observed due to the hydroponic treatment. Nitrite and nitrate tended to stabilize at certain levels over time due to final effluent reuse for feed dilution. Coliforms were able to recover in the hydroponic unit, suggesting the need to control their population. Pointed cabbage (_Brassica oleracea L._, var. _capitata_) was able to grow on vermifiltered swine wastewater, diluted 10-fold with reused final effluent, as long as its nutritional requirements were met.  
The proposed system aimed to treat piggery wastewater, while producing commercial crops. Efficient water treatment implies the removal of most pollutants, while good crop productivity needs excess nutrients to be present in the hydroponic medium. To ensure both, a very good knowledge of the crops' needs and control of medium composition are necessary. Continuous systems with effluent recirculation and long hydraulic residence times create additional complications for efficient nitrogen removal and microbiological safety. However, the present study shed light on several important aspects that can be henceforth addressed through batch optimization of biological components and physicochemical conditions, followed by implementation and control in continuous systems.  
Scale-up for implementation at real hog farms will require careful sizing to optimize both the throughput and treatment efficiency, and investment in equipment, electrical power, and workforce will be required. Overall, the tested system showed positive perspectives of the use of vermifilters coupled with downstream hydroponic cultivation units as biological solutions for the treatment of animal farming effluents and other heavily contaminated wastewaters.  
Figure 5: Evidence of nutrient deficiency observed on cabbage leaves: (**a**) leaf yellowing in-between veins; (**b**) leaf blade wrinkling; (**c,d**) blade tip necrosis.  
**Author Contributions:** Conceptualization, K.I. and L.M.I.A.; methodology, K.I. and L.M.I.A.; validation, K.I., L.M.I.A., N.D.L., and J.S.V.; formal analysis, K.I.; investigation, K.I. and L.M.I.A.; resources, K.I., L.M.I.A., and J.S.V.; writing--original draft preparation, K.I.; writing--review and editing, K.I., L.M.I.A., N.D.L., and J.S.V.; visualization, K.I.; supervision, L.M.I.A. and N.D.L.; project administration, J.S.V.; funding acquisition, J.S.V. and N.D.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by Base Funding--UIDB/50020/2020 of the Associate Laboratory LSRE-LCM, funded by national funds through FCT/MCTES (PIDDAC), and by the Applied Molecular Biosciences Unit--UCIBIO, which is financed by national funds from FCT (UIDP/04378/2020 and UIDB/04378/2020).  
Not applicable.  
The authors declare no conflict of interest.