SILVA, L. V. B. D.; http://lattes.cnpq.br/9189485400834209; SILVA, Leda Veronica Benevides Dantas.
Resumo:
The shortage of irrigation water is an obstacle to agricultural and social
development in arid and semiarid regions. Reuse of treated sewage water in agriculture is a
suitable alternative for such regions, since it not only increases water availability, but also
supplies organic matter and nutrients present in these effluents for plant nutrition. Despite the
potential benefits, reuse of domestic wastewater for agricultural purposes is not a risk free
practice, considering that the presence of salts, organic pollutants and pathogens could cause
damages to the environment, human health, soil, ground water and irrigated crops. For this
reason, it is important to study the efficiency of wastewater treatment methods in obtaining
effluents suitable for disposal on cultivated lands. Based on the above considerations, the
present research aimed to evaluate the potential of domestic sewage treated by anaerobic
processes and post treated in intermittent sand filters for cotton irrigation. The implications of
disposing of these effluents in terms of soil chemical properties were also investigated. For
this purpose, cotton plants were grown in pots containing haplustalfs soil submitted to the
treatments which resulted from the factorial combination between four sources of irrigation
water - (i) freshwater, (ii) effluent treated by an UASB reactor, (iii) effluent treated by an
UASB reactor and post treated by 2 intermittent sand filter in series, and (iv) effluent treated
by a septic tank and post treated in an intermittent sand filter - and five levels of nitrogen
fertilization - 0, 45, 90, 135 e 180 kg ha-1. Plants were irrigated for 123 days, and their growth
and leaf nitrogen accumulation were measured. At the end of the crop cycle, plant yield and
nutritional status were determined. The soil post cultivation was also evaluated to verify the
chemical changes caused by the cotton cultivation. According to the results, irrigation with
treated wastewater is beneficial for both cotton growth and nutrition, resulting in good crop
yields without affecting the quality of fiber. Treated wastewater is also suitable for replacing
the conventional nitrogen fertilization of cotton plants, which is reflected in greater financial
savings for the producers. Besides the fact of obtaining agronomic advantages, the use of
secondary effluents post treated by intermittent sand filters provides better health security,
since this treatment removes the helminth eggs which are an important cause of human
illness. However, it was found that irrigation with wastewater was not effective in restoring
nutrients exported by cotton crop and that it increased sodium levels in soil after cultivation.
Considering this, it is highly recommended to perform effective soil management of agricultural lands irrigated with treated wastewater in order to maintain soil fertility and to
prevent soil salinization and sodification.