Green pit technology as a rural sanitation component for the semiarid region of Brazil

ABSTRACT The green pit module corresponds to an alternative model to treat domestic sewage in rural areas, which considers water reuse in productive yards, contributing to rural sanitation. The present investigation has assessed the green pit module performance based on 70 modules installed in the semiarid region of Brazil and includes sanitary quality test of cultivated vegetables, sizing proposal, rate of accumulation of the sludge produced and evaluation of the maintenance period of the green pit module. A design method was presented, which is based on water consumption, and has been assessed on site for two kinds of homes: those with (R1) and without (R2) tap water supply. In addition, we measured the sewage contribution and return coefficient for each case. The analyzed samples of tomato (Solanum esculentum), pepper (Capsicum chinense), banana (Musa sp.) and “malvarisco” leaves (Plectranthus amboinicus L.) presented low levels of coliform (below ten colony-forming units per gram) and absence of Salmonella sp., which complies with the Brazilian sanitation legislation. The water consumption for R1 and R2 were 50 and 34 L.resident-1.day-1, whereas sewage per capita production totaled 13.1 and 1.2 L.resident-1.day-1 for R1 and R2, respectively. This indicates return coefficients of 26 and 3% for R1 and R2, respectively, which differs significantly from the usually recommended value (80%). The system presents low maintenance demand: the sludge should be removed every 5.3 years, on average.