Avaliação da eficiência de wetland construído de fluxo vertical para o tratamento de águas residuais domésticas em Moçambique

Abstract

Mozambique is a developing country that presents treatment technologies of wastewater, mostly decentralized characterized by septic tanks, latrines improved facilities and dry latrines. Only a part of the population in urban areas accesses sewage system, which means that the basic sanitation service of the environment does not cover the majority of the Mozambican population, making it exposed to disease. Therefore, the The present work had as main objective to evaluate the efficiency of a wetland built vertical flow for domestic wastewater treatment. This is a low system cost of operation and maintenance, operational simplicity, with high robustness and suitable to different realities of tropical regions. A vertical wetland type Wastewater Treatment System was built for the treatment of domestic wastewater from septic tanks at the Infulene Wastewater Treatment. This system had a maximum capacity of 13 m 3 (an area of ​​29.1 m two and 0.7 m deep), and three layers arranged from bottom to top (layer 1: 0.15 m with 19-50 mm stones; layer 2: 0.15 m with 4.8-25 mm stones; layer 3: 0.4 m with 2.4-12.5 mm stones; and a freeboard of 0.3 m). two types of tests were carried out (1) to determine the optimum wetland discharge time and (2) to determine the efficiency of removal of organic matter, suspended solids and nutrients. From the test to determine the optimal time to discharge the waste water, it was observed that up to the sixth day, BOD5, COD and TSS removal rates were 79%, 79% and 98%, respectively, and nutrient loads also recorded significant removal rates of 94%, 85% and 65% for N-NH4 + , N-NO3 - and PT, respectively. In the tests carried out for determination of pollutant removal efficiency, it was observed that the wetland presents high efficiency in reducing BOD5 when the load of MO in the influent is low and the efficiency of TSS removal is independent of the load of suspended solids in the influent. The rates of average removals recorded, for a six-day retention time of BOD5, COD and SST were 75%, 60% and 94%, respectively. It was found that the COD and TSS concentrations of the effluent treated in the first phase of the project did not meet domestic effluent emission standards set by the legislation which implies that the effluent could not be disposed of in a receiving environment but and can be used to irrigate crop fields and plantations. Therefore, the The present work suggests that future scientific investigations on the subject address the possibility of series association of another WCFV system to reach the emission standards required by law and the possibility of using treated effluent for irrigation of crop fields and plantations in rural areas.