Integrating vertical flow constructed wetlands to improve septic tank and stabilization ponds effluent quality for recycling water and nutrients at cherry tomato production

The low rate of domestic sewage registered in cities in Latin America, the Caribbean, Asia, and Africa is the result of a centralized view, which does not allow access for all (decentralized), and which only uses conventional Sewage Treatment Plants to treat sewage without evaluating the potential for reuse and use of the by-products generated (sludge and gasses), adding value to them. Therefore, the objective of this study was to evaluate the efficiency of vertical flow constructed wetlands (VF-CW), as post-treatment of sewage (stabilization ponds and septic tanks) and to integrate it with the production of cherry tomatoes (Solanum lycopersicum var. Cerasiforme), by reusing the treated effluent. The purpose is to evaluate the processes and to allow a new business model. To study the cherry tomato production, VF-CW with coarse sand and part of the filtering medium composed of soil were evaluated, for a comparative agronomic study (plant adaptation), with 20 cm of soil and 40 cm of coarse sand. The effluents used were post septic tank (VF-CW-ST), and post stabilization pond (VF-CW-SP). The VF-CW received a hydraulic application rate of 170 mm.day-1 and organic application ranging from 10-75 gCOD.m-2.d-1 and 10-60 gBOD.m-2.d-1. It was possible to verify that the VF-CW-ST and the VF-CW-SP with soil plus sand as a filtering medium, presented a worse performance in the removal of pollutants, although the plants reached the highest heights (75 cm). The VF-CW-ST with sand presented a better performance in the removal of pollutants, mainly to promote nitrification. Removal of: 89% of total nitrogen (TN) and 98% of ammoniacal nitrogen (NH4-N), post septic tank and 86% of TN and 93% of NH4-N, after maturation pond; 70% and 44% of BOD, post septic tank and maturation pond, respectively; 77% and 67% of phosphorus, post septic tank, and maturation pond, respectively; and 91% Turbidity for post septic tank and maturation pond. The load of pollutants, post septic tank, allows a greater supply of nutrients and organic matter that significantly influence the growth of plants. Tomatoes irrigated with water reached an average height of 40 cm, while those irrigated with effluent after maturation pond, 50 cm and with effluent post septic tank, 63 cm at the end of 75 days. Therefore, this is a viable option to avoid the use of mineral fertilizer and contribute to the fixation of carbon and nutrients in the soil and the production of biomass and food. The use of post septic tank VF-CW in (multi) single-family housing shows great potential for urban agriculture in a circular economy concept.