Spatio-temporal variation of septage characteristics of a semi-arid metropolitan city in a developing country

Abstract

Septage is the solid sludge that accumulates in septic tanks over a period of time. Many of the developing countries in the world face the challenging task of septage management. Due to the high variability in the nature of septage, there is a need to study its physical and chemical characteristics in order to suggest a sustainable treatment methodology. The present study deals with the characterization of septage collected from different locations of Chennai city in India, in two different seasons (summer and winter). The characterization includes parameters such as solids, organics, inorganics, nutrients and heavy metals. Septage showed significant difference in concentrations of pollutants from one season to the other (p > 0.05). The average total solids concentration is found to be 1.6 times higher during winter season than compared to summer season. Average concentrations of solids were 2185 ± 1070 and 3555 ± 2935 mg/L during summer and winter, respectively. Liquid characterization of septage showed total chemical oxygen demands (COD) of 905 ± 603 mg/L (summer) and 1460 ± 1295 mg/L (winter). Similarly, average soluble biochemical oxygen demand (sBOD) was found to be 117 ± 54 mg/L during summer and 211 ± 220 mg/L during winter season. Studies also showed that septage was rich in nutrients such as total nitrogen (4-500 mg/L), ammoniacal nitrogen (2-129 mg/L), total phosphate (5-236 mg/L) and heavy metals such as copper, zinc, lead and manganese. Overall characterization indicates that the collected septage samples are highly variable in nature with respect to sources, season and locations of collection. As the septage is rich in organic matter and nutrients, it can be used as a resource like soil conditioner or as a substitute for chemical fertilizer in agriculture, after proper treatment, leading to a new evolution in sanitation.

Dewatering and Treatment of Septage Using Vertical Flow Constructed Wetlands

“…The solids and organic content of septage could be 10-100 times higher than municipal wastewater; hence, it has to be treated properly to reduce its contribution to environmental degradation [1]. Septage management is still a challenge in developing countries [2]. In Sarawak, a state of Malaysia, there are more than 370,000 individual septic tanks in operation, which serve approximately 1.9 million people in the entire state [3].…”

Characterization of fecal sludge as biomass feedstock in the southern Indian state of Tamil Nadu

“…The average TS in Tiruppur (3.3%) is higher than in Coimbatore (2%), and also higher than the 1-2% reported in the literature for septic tanks in Africa (Fanyin-Martin et al, 2017;Muspratt et al, 2014). The TS values measured in Coimbatore and Tiruppur are an order of magnitude higher than the 0.2-0.3% reported for the metropolitan area of Chennai, which is also located in the state of Tamil Nadu (Krithika et al, 2017). However, based on the driver survey results, only 36% of the sources in Coimbatore and 11% of the sources in Tiruppur received graywater in addition to blackwater.…”

“…The average TS is skewed high due to a few samples with a very high TS concentration (larger than 5%), so the median value is a better estimate of the FS volume available as biomass feedstock in these cities. This study did not examine the effect of different seasons on the TS content, which has been reported to decrease during the rainy seasons (Krithika et al, 2017). For the city of Tiruppur, sampling was carried out during both seasons, but no significant difference was found.…”

“…While the percentage of sources including graywater relies on self-reported data, this data aligns well with the higher values of TS measured in settings with low percentage of graywater inclusion, and is comparable to septage in African cities (Fanyin-Martin et al, 2017;Muspratt et al, 2014). The study by Krithika and colleagues that took place in a geographically similar region did not track graywater inclusion, but did report a very high emptying frequency (from days to one month), which suggests the likelihood of graywater being included (Krithika et al, 2017).…”

“…Septage properties are expected to be system-and locationdependent due to different structural and environmental conditions and personal hygiene habits, particularly whether toilet paper is used or, as in India, water is used for cleansing. Recently, a survey of the septage composition in the metropolitan area of Chennai, India reported very low solids content (0.2-0.35%) (Krithika et al, 2017).…”