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| Author(s): |
Alexandra Vieira Suhogusoff
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Geociências (IG/BT) |
| Defense date: | 2010-06-24 |
| Examining board members: |
Ricardo Cesar Aoki Hirata;
Reginaldo Antonio Bertolo;
Didier Gastmans;
Ivanildo Hespanhol;
Ari Roisenberg
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| Advisor: | Ricardo Cesar Aoki Hirata |
| Abstract | |
The main purpose of this project was to create a set of integrated actions that could minimize impacts of septic systems on groundwater resources. Since the septic tanks, even the well-constructed ones, are not effective on areas where the population density is high, an alternative latrine improved with reactive barriers was developed and applied in Jardim Santo Antônio settlement (Parelheiros, São Paulo, SP). In order to degrade the microorganisms, the reactive material was BOF (Basic Oxygen Furnace) slag from steel producer facilities, and in order to enhance the denitrification, the material of the reactive barrier was sawdust. The sawdust barrier was the main issue in this project. A risk assessment questionnaire was developed and it was applied to an area where 178 residences were evaluated, totalizing 218 water wells and 182 latrines. A Cluster Analysis was used to select the questions that would be related to the risk of contamination by bacteria or nitrate. It was observed that the inapropriated construction and operation of the wells are poorly related to the level of nitrate contamination, what suggests that the nitrate contamination is a more regional problem. On the other hand, it was found a good relationship between the level of bacteria contaminations and the characteristics of construction and operation of the wells, what suggests that this contamination has a local factor. Before the installation of the enhanced septic tank, soil columns breakthrough experiments were conducted in laboratory to test the efficiency of sawdust in nitrate removal. Three soil columns were set up: one filled only with sediments of Jardim Santo Antonio settlement, and another two with the same kind of sediments and sawdust layers introduced with 10cm and 20cm thickness. The results showed an efficiency of sawdust to denitrification of 96,5% and 99,7%, respectively. Two septic tanks were installed in the study area: the alternative latrine enhanced with reactive barriers (AL), and the control latrine (CL), equivalent to the usual tanks founded on the area. In AL, structured with reactive barriers containing BOF (1m below the wastewater tank) and sawdust (under the BOF layer, but first separate from it by 1m of sand package), it\'s possible to discern few parameter behaviors. BOF, which is rich in calcium oxides and iron oxides, incrises the electrical conductivity and the pH of the effluent (~12). The sawdust barrier, in its turn, was characterized by low concentration of dissolved oxygen and by the presence of dissolved organic carbon, essential conditions denitrification ocurrence. The denitrification efficiency of the sawdust barrier was affected by the high pH observed in the effluent that crossed the BOF barrier, which perturbed the denitrifying bacteria performance. In CL, the vertical distribution of the ions was more regular. The samples from this system presented high levels of ammonium and DOC and low values for dissolved oxygen. For this case, the nitrification must happen in the unsaturated zone bellow the tank, so the nitrate formed can reach the groundwater. (AU) | |