Evaluation of a treatment system for domestic wastewater reuse

In Mexico there are rural and urban marginal zones without sewage and the wastewater is directly discharged in the soil, revains and water courses, which generates health and pollution issues. The objective of this work was to evaluate a system of easy and economical operation and maintenance that could treat the wastewater from one house. This wastewater treatment system (WTS) combines the operation in series of a septic tank (ST) a biofilter (BF) and a constructed wetland (CW). The BF uses wood chips as filtration media (FM). The CW works with a horizontal sub-superficial flow, and was packed with gravel and seeded with papyrus and other ornamental plants. The WTS was full scale and has a capacity for 2-4 people in regions with a low access and low per capita dotation of water (130 L/d). The WTS was operated for 220 days to evaluate the effect of applying two different flows (Q): 0.2 m3/d and 0.4 m3/d, affecting the hydraulic retention time (HRT) of the ST (5.5 d and 2.75 d), the filtration velocity (FV) into the BF (1.26 m/d and 2.52 m/d) and the FV into the CW (0.05 m/d and 0.1 m/d). The combined WTS presented an excellent performance, and when the slowest flow was applied, the effluent quality obtained was good enough to be directly reused in yards, washing activities, irrigation of green areas and toilet use, considering the analyzed parameters (biochemical oxygen demand, fecal coliforms, helmint eggs, oil and greases), and according to the Mexican norm NOM-003-ECOL-1997 and the American (USEPA 2004) regulations. If the second flow (0.4 m3/d) wants to be applied, an additional disinfection is necessary.