Removal and Survival of Fecal Indicators in a Constructed Wetland after UASB Pre-Treatment

Fabio Conti, Elena Cristina Rada, Paolo Viotti and Massimo Raboni
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Fabio Conti: Department of Theoretical and Applied Sciences, Insubria University, 21100 Varese, Italy
Elena Cristina Rada: Department of Theoretical and Applied Sciences, Insubria University, 21100 Varese, Italy
Paolo Viotti: Department of Civil and Environmental Engineering, Sapienza Università di Roma, 00184 Roma, Italy
Massimo Raboni: Department Hydraulics and Environmental Engineering, University of Pavia, 27100 Pavia, Italy

Sustainability, 2021, vol. 13, issue 16, 1-16

Abstract: The experimentation plant, based on a sub-surface horizontal flow phytodepuration (SSHFP) unit with a pre-treatment by an upflow anaerobic sludge blanket (UASB) reactor, proved valuable in treating the sewage of a small rural community located in north Brazil. During a six-month trial, the plant achieved an average removal efficiency of 98.2% (1.74 log removal) for fecal coliforms (FC) and 96.0% (1.40 log removal) for Enterococci (EN), as well as 95.6% for BOD 5 , 91.0% for COD,00 and 95.4% for suspended solids (SS). The contribution of the UASB reactor to this overall performance was very significant as, alone, it achieved a yield of 62.7% for FC and 60% for EN, in addition to 65.2% for BOD 5 and 65.0% for SS. EN was chosen, in addition to FC, because of its higher specificity and strong environmental persistence, leading to an increased risk to human health. In fact, the experimental results confirmed its lower removal efficiency compared to FC. The mechanical and biological mechanisms that led to such a removal efficiency of the two fecal indicators (FIs) are outlined in the article. The same mechanisms led to a good level of equivalence between the removal efficiency of the two FIs with the removal efficiency of SS and BOD 5 , for both the whole plant and the UASB reactor alone. The research demonstrated the close correlation between the concentrations of EN and FC for the plant effluent. This correlation can be explained by the following mathematical expression of the regression line Log EN = 0.2571 Log FC + 3.5301 , with a coefficient of determination R 2 = 0.912. This implies that the concentration of the more specific indicator EN could be calculated, with acceptable approximation, from the simple analysis of FC and vice versa. The experimental plant brought important health benefits to the local population. In particular, there were no significant odor emissions; moreover, the risk of fecal pathogenic diseases was drastically reduced; finally, there was no proliferation of insects and other disease vectors, due to the absence of stagnant or semi-stagnant water exposed to the atmosphere.

Keywords: constructed wetland; enterococci; fecal indicators; fecal coliforms; phytodepuration; sewage treatment; UASB (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2021
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