Search Results (3)

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 BOD₅, 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 BOD₅ 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 BOD₅, 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 R² = 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. Full article

The wastewater generated by isolated houses without access to public sewers can cause environmental problems, like the contamination of aquifers with nitrates and phosphates, as occurs in southeastern Spain. The effectiveness of a previously built horizontal subsurface flow constructed wetland (HF-CW) was studied over two years as a possible solution. This HF-CW measured 27 m2; it was planted with Phragmites australis(Cav.) Trin. Ex Steuds sp. Altissima and the parameters studied were those required by European Union (EU) legislation and adopted by Spain. Average abatement efficiency rates, for the first and the second year of study, were: biochemical oxygen demand over five days (BOD5) (96.4%, 92.0%), chemical oxygen demand (COD) (84.6%, 77.7%), total suspended solids(TSS) (94.8%,89.9%),total nitrogen(TN)(79.5%,66.0%),ammonium nitrogen(NH4+-N)(98.8%, 86.6%) and total phosphorous (TP) (83.7%, 82.8%). Average abatement efficiency for nitrate nitrogen (NO3−-N) (−1280.5%, −961.1%) and nitrite nitrogen (NO2−-N) (−5.8%, −40.0%) were negative because its content in influent wastewater was very low and they appear mainly from influent NH4+-N, as a result of purification processes carried out in the HF-CW bed. The abatement rates make the system suitable to produce discharges into the environment in accordance with Spanish law. It is noteworthy that the HF-CW patch suffered an episode of bed drying during the summer of 2013, whereby the causes were related to system oversizing and high evapotranspiration in the area. As a consequence, the decrease in the abatement of water pollutants during the second year can be attributed to the creation of preferential water flow paths and short circuits through the constructed wetland (CW) bed. As a result of the oversizing of the CW, a theoretical resizing based on BOD5, TSS, TN or TP is proposed. The calculated values for the redesign were: 5.22 m2 considering DBO5, 0.18 m2 considering TSS, 10.14 m2 considering TN and 23.83 m2 considering TP. Considering the area where the HF-CW was located and in accordance with Spanish law for non-sensitive areas (no TN or TP requirements for wastewater discharge), BOD5 is the most appropriate parameter for design; it is 5.2 times lower than the HF-CW initially built and without risk of bed drying. Full article

The paper presents the results of an experimental process designed for the treatment of the sewage generated by a rural community located in the north-east of Brazil. The process consists of a preliminary mechanical treatment adopting coarse screens and grit traps, followed by a biological treatment in a UASB reactor and a sub-surface horizontal flow phytodepuration step. The use of a UASB reactor equipped with a top cover, as well as of the phytodepuration process employing a porous medium, showed to present important health advantages. In particular, there were no significant odor emissions and there was no evidence of the proliferation of insects and other disease vectors. The plant achieved the following mean abatement efficiencies: 92.9% for BOD₅, 79.2% for COD and 94% for Suspended Solids. With regard to fecal indicators average efficiencies of 98.8% for fecal coliforms and 97.9% for fecal enterococci were achieved. The UASB reactor showed an important role in achieving this result. The research was also aimed at evaluating the optimal operating conditions for the UASB reactor in terms of hydraulic load and organic volumetric loading. The achieved results hence indicated that the process may be highly effective for small rural communities in tropical and sub-tropical areas. Full article