The use of reclaimed wastewater for irrigation purposes: influence on soil capacity for natural attenuation of emerging organic contaminants

Reclaimed wastewater for agricultural fields and public green spaces irrigation is gaining increasing importance. The discussion around this subject is linked with the fact that actions like these may help save large volumes of potable water which, due to climate change aspects, is becoming scarce. However, the use of reclaimed wastewater leads to questions regarding the presence of pharmaceuticals and personal care products (PPCPs) on the effluents, as these products are not completely eliminated during conventional wastewater treatment stages. By irrigating agricultural fields with reclaimed wastewater, we might be enabling a large micro contaminants input on soil and, consequently, these contaminants might be absorbed through plants´ radicular system. Given the importance of this subject it is necessary to know whether a soil is able to naturally attenuate PPCPs present on the reclaimed wastewater. Another issue raised is how a systematic irrigation with effluent alters the capacity of the soil to respond to the presence of these organic contaminants. With this in mind, the main purpose of this dissertation was to evaluate de degradation capacity of three types of soil: one systematically irrigated with effluent (SE), a second soil irrigated with effluent and fertilized with biosolids (SL) and, a third soil irrigated with surface water and used to grow biologic tomatoes (ST). In all cases, these soils were irrigated in the laboratory with deionized water or tertiary effluent spiked with a mixture of 10 PPCPs: Caffeine (CAF); sulfamethoxazole (SMX), carbamazepine (CBZ), diclofenac (DCF), oxibenzone (OXY), triclosan (TCS), bisphenol A (BPA), 17β-estradiol (E2), 17α-ethynylestradiol (EE2) and ibuprofen (IBU)]. A control was also performed in which irrigation was performed with non-spiked samples. The experiments lasted for 14 days, being monitored on the 0, 3rd, and 7th day. An additional condition has been studied in which the soil was preserved at 4 ºC for 14 days. The results showed that soils SE and ST presented a higher capacity for decreasing contaminants levels (degradation). With the SE soil, the best degradation rates were obtained for the samples watered with spiked deionized water, whereas ST soil responded better when the irrigation was performed with spiked tertiary effluent. Regarding the contaminants the decreasing degradation order was IBU ≈ E2 > BPA ≈ DCF ≈ SMX ≥ EE2 > OXY ≥ TCS > CBZ. IBU and E2 achieved 100% degradations and CBZ did not degraded (on the worst case) or has been poorly degraded, < 35%. Caffeine was excluded from the quantitative analysis, but it was still detected in the soil samples after 14 days, indicating that it is not completely removed. The preliminary evaluation on the formation of possible degradation products showed that mineralization was not complete, and this deserves a deeper analysis