Improvement and monitoring of a wastewater treatment unit and agricultural application of gray water in the Brazilian semiarid region

Abstract

Water scarcity associated with environmental problems is a factor for encouraging the development of technologies that enable the sustainable reuse of water for agricultural and forestry purposes. In this context, this research is aimed to improve and follow up on the performance of a wastewater treatment unit installed at the Universidade Federal Rural do Semi-Árido in Mossoró/RN and to evaluate the agricultural application of gray water. The wastewater treatment unit is comprised of an equalization tank, septic tank, anaerobic filter, artificial ultraviolet reactor, and infiltration ditch. The experiment was set up in a completely randomized design with four replications, the samples consisted of gray water from the equalization tank (raw sample) and gray water from the artificial ultraviolet reactor (treated sample). The gray water sampling was carried out approximately every 32 days, over a period of four months. The samples were assessed to determine pH, temperature, electrical conductivity, turbidity, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5.20), total suspended solids, total solids, total coliforms and E. coli. The data was submitted to a descriptive statistical analysis to obtain the mean and standard deviation values. It was observed that the increase in the number of lamps from two to four lamps in the artificial ultraviolet reactor had meaningful influence on the decay of the E. coli population. This feature allowed the treated water to be within the standards of the COEMA Resolution n° 02/2017 for agricultural reuse. The studied treatment system showed removals above 95% of the turbidity, total suspended solids, COD, BOD and removal of 2.86 and 4.09 in logarithmic units in relation to population numbers of total coliforms and E. coli, respectively.