Assessment of pathogen removal efficiency of vertical flow constructed wetland treating septage

Abstract

Septage refers to the semi-liquid waste material that accumulates in septic tanks and other onsite sanitation systems. It is composed of a complex mixture of human excreta, wastewater, and various solid particles. Septage is a potential source of water pollution owing to presence of high organic content, significant pathogen concentrations, and a range of nutrients like nitrogen and phosphorus. The harmful impacts of septage pollution poses significant risks to public health through the contamination of drinking water sources, eutrophication of water bodies and spread of water borne diseases. Conventional septage treatment technologies often face limitations such as high operational costs, energy requirements, and the need for extensive infrastructure. Therefore, with an aim to treat septage through an alternative cost effective and energy-efficient technology, a laboratory-scale constructed wetland (CW) system (0.99 m2) consisting of a sludge drying bed and a vertical flow wetland bed was utilized for the treatment of septage. The sludge drying bed and vertical flow beds were connected in series and filled with a combination of gravel with varying sizes (ranging from 5 to 40 mm) and washed sand. Canna indica plants were cultivated on both beds to facilitate phytoremediation process. The system was operated with intermittent dosing of 30 Ltrs of septage every day for 2 months. The HRT of the system was fixed at 48 h. The average inlet loads of Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), and Total Suspended Solids (TSS) were measured as 150 ± 65.7 g m−2 day−1, 713 ± 443.9 g m−2 day−1, and 309 ± 66.3 g m−2 day−1, respectively. After treatment, the final effluent had an average load of 6 g m−2 day−1 for BOD5, 15 g m−2 day−1 for COD, and 51 g m−2 day−1 for TSS, indicating that the CW system achieved an average removal efficiency of 88% for BOD, 87% for COD, and 65% for TSS. The average load of total coliforms and helminthes eggs in the influent was recorded as 4 × 108 Colony-Forming Units (CFU) m−2 day−1 and 3 × 107 eggs m−2 day−1, respectively. However, the CW system demonstrated significant effectiveness in reducing microbial contamination, with an average removal efficiency of 99% for both total coliforms and helminthes eggs. The vertical flow constructed wetland system, equipped with pretreatment by sludge drying bed, has proven to be efficient in treatment of septage.

Tratamiento de aguas residuales domésticas en humedal del Barrio Santiaguito, Texcoco de Mora, México

“…In this work, the EC value did not exceed 3.5 mS•cm -1 , so total coliforms (TC) and fecal coliforms (FC) were analyzed as indicators of fecal enterococci. With statistically significant differences, both parameters are reduced as they flow from (Singh et al, 2023). It is worth mentioning that the treatment in the Santiaguito wetland, Texcoco, generates an effluent that complies with the permissible limits established by NOM-003- SEMARNAT-1997(DOF 1998: 1 000 MPN•100 mL -1 for agricultural use, and 240 NMP•100 mL -1 for public service with direct and indirect contact.…”

“…To calculate the removal efficiency as a percentage of each of the parameters evaluated, Equation (1) was used, where A is the value of the parameter in the influent and B is the value in the effluent (Singh et al, 2023): Source: Self-made based on a visit to the wetland to the results obtained from the samples collected at the different wastewater processing stages to measure spatial variation, using InfoStat 2020e software (Di Rienzo et al, 2008).…”

“…Considering the parameters analyzed, the quality of the wastewater treated by the Santiaguito neighborhood wetland only has limitations in terms of TSS and BOD 5 . The low pollutant removal efficiency can be attributed to the clogging of pipes due to the growth of the root system of the installed macrophytes (Masharqa et al, 2023), as well as other species transported by wind and torrential rain, in addition to saturation of the filter material over time (Tatoulis et al, 2017) and poor sedimentation pretreatment (Pérez-Molina et al, 2021;Singh et al, 2023).…”