Systems alternative for treating wastewater for irrigation in a vertical production system

The growing need to increase productivity in smaller areas guides agricultural research to develop and improve technologies that seek to meet this demand. The possibility of producing vegetables in areas where land is a limiting factor is something that draws attention, especially for family farmers and residents of urban areas who wish to produce their food. The vertical cultivation system is a technique developed focusing on the production of medicinal, horticultural, and ornamental crops, mainly in places without the ideal space for conventional production, and widely used for those that seek sustainable and organic production. The vertical system build with 200 liters drums allows the farmer to produce 52 plants in about 1 m², and all the researches carried out with these systems shows high productivity and a water use efficiency superior to conventional production systems. The use of wastewater allows the irrigator to produce in places where clean water is scarce, in addition to taking advantage of the nutritional content present in it, thus reducing fertilizer costs. For this, it is necessary to ensure that the effluent undergoes treatments to avoid possible contamination. As treatment options tested that provide safe agricultural reuse of wastewater, we present three solutions: a low-cost and nature-based treatment system compound by the combination of a biological filter bed (BFB) and a solar disinfection (SODIS) reactor, a low-cost anaerobic filter, and the SODIS reactor + H₂O₂. The BFB consists of four equals rectangular fiberglass water tanks presenting the following dimensions: 100 x 35x 31 cm. The water tanks were connected in series by a PVC pipe of 50 mm. Gravel with size ranging from 4.8 to 9.5 mm were used as biofilter media. The wastewater filtered by the BFB was directed to the SODIS reactor. The SODIS reactor was made of concrete and shaped in the form of an inverted truncated cone with the following dimensions: 1.0 m of larger radius, 0.25 m of smaller radius and 0.30 m of height. The anaerobic filter consists of six identical plastic 200 liters drums connected in series through a PVC pipe of 32 mm, filled with gravel that presented an average diameter of 14 mm. In order to speed up the SODIS process in the reactor, in a wastewater depth of 0.10 m, it was added 125 mg L^-1 of H₂O_2. Wastewater treatment can provide wastewater with concentrations of fecal coliform ≤ 1000 MPN 100 mL^-1. The wastewater treated by the treatment options described here can be safely reused to irrigate crops cultivated in vertical systems. Several studies have been showing that in crops irrigated with wastewater, crop yield can be higher than those irrigated with tap water. It is evident the need to combine treatment strategies to better take advantage of the benefits provided by the reuse of wastewater in irrigated agriculture, while using alternative ways of producing food, thus the producer can grow his food even with little available space, and avoids circulation in public places to purchase their food.