**2.2 Critical absence of secondary treatment of effluent and poor primary treatment to begin with**

Many factors influence the performance of a septic tank as a primary treatment unit, and none of them preclude the necessity of a secondary component for the management of the effluent that a septic tank releases. The septic tank does not act on pathogens and stabilises the settled solids, or sludge, to an extent (a reduction of 30–50% in the Biochemical Oxygen Demand (BOD) and up to 50% in that of Total Suspended Solids (TSS) can be expected). Tweaking the design of the basic septic tank – whether big or small, with or without partitions, with wide or narrow channels, shallow or deep, can increase or decrease the primary treatment efficiency, i.e. the ability to separate liquids and solids and effect partial digestion of stored solids over time. But, no matter how perfect the primary treatment, the effluent from a septic tank needs further treatment due to the significant remnant pollution load (**Table 1**).

The Indian Code of Practice recognises the distinction between a 'septic tank' and a 'septic tank system' too and declares that 'under no circumstances should effluent from a septic tank be allowed into an open channel drain or body of water without adequate treatment'. The survey data shows that 72% of septic tanks discharge the tank effluent into drains designed for stormwater management. In 60% of the cases, the drains are uncovered and exposed to the environment, while in 12%, the drains have a covering. Related research investigating

**Figure 2.**

*Type of on-site system based on financing of toilet construction.*

*Managing Non-Sewered Sanitation for Achieving Sustainable Development Goal 6 in India DOI: http://dx.doi.org/10.5772/intechopen.98597*


#### **Table 1.**

*Characteristics of septic tank effluent and standards for wastewater treatment.*

the epidemiological impact of this phenomenon in peri-urban areas of Bolivia has related it to an increased incidence of diarrhoea in children under age five. It cautions against the poor quality and mismanagement of tank effluent attenuating the gains from increased access to toilets and improved on-site sanitation systems [11].

Just as significantly, greywater, or wastewater from activities such as washing, bathing, and other non-toilet related purposes, produced by the households too ends up in these drains, with 92% of all on-site systems being receiving only blackwater as input. Only 8% of the households reported treating the greywater in the same on-site system as the one for their blackwater or a separate one. Although greywater is minimally pathogenic compared to blackwater, it still contains pollutants and microcontaminants from residual pharmaceuticals, personal care products, aerosols, pigments, and other such products. Due to a lack of interception of the drains and treatment of waste flows, the disposal of tank effluent and greywater into drains holds the potential to not only cause adverse outcomes in health at source but also serve as a diffuse source of water pollution.

### **2.3 Household preference for septic tanks that are an order of magnitude larger than the recommended size**

The issuing of the National Policy on Faecal Sludge and Septage Management, 2017, unlocked investments for the creation of city-level FSM infrastructure and

assets. The Policy arrived two years into the Atal Mission for Rejuvenation and Urban Transformation (AMRUT), a massive urban infrastructure development programme with a total outlay of INR 77,640 crores (USD ~10.41 billion) covering 500 of the country's largest cities. The programme allocated 95% of its outlay towards water supply, wastewater management, and drainage. However, at its inception, AMRUT did not feature FSM as a component of wastewater management. Due to the National Policy and continuing advocacy on the importance of FSM to achieve citywide sanitation, AMRUT recognised and incorporated FSM as an investment area in its purview. Now, in 2021, the Covid-19 pandemic has emerged as the new foreground for reinvigorated investments in water supply and wastewater management. In India, MoHUA announced the second phase of SBM (2021–2026), which promotes FSM as a wastewater management solution for all cities with a population of less than 1,00,000.

The increased influx of national investments would bolster the smooth scaling up of FSM already underway in the country – going from standalone pilots 2015 onward to scale-up of FSM in AMRUT cities and further across all cities and towns in states like Maharashtra and Odisha that have been early champions of FSM. These investments usually mean setting up FSTPs in the city and acquiring vacuum trucks to desludge the on-site systems and convey faecal sludge to the FSTP(s). Though the capacity of local governments – big and small - to provide mechanised desludging services is on the rise, the engagement of informal and small-scale service providers, including manual labour, for desludging continues to be a reality of the non-networked sanitation ecosystem in India.

Owing to the pernicious entrenchment of sanitation-work within castebased social hierarchies in India, the national government had notified 'The Prohibition of Employment as Manual Scavengers and their Rehabilitation Act' in 2013. The Act does not disallow per se the engagement of manual labour for desludging provided they adopt the prescribed safety equipment and protocols. However, largely, the engagement of manual labour takes the form of 'hazardous cleaning' or the manual cleaning of a septic tank without the prescribed protective gear, cleaning equipment, and safety precautions, which the Act deems a criminal offence [12]. More generally, the traditional norms of purity and pollution too have shaped the sanitation practices in India, with a significant body of research finding that these notions impact whether or not a household chooses to own and use a toilet facility [13, 14].

Within this context, the authors' survey finds that both households and masons consider an on-site system that does not require frequent maintenance, and thus engagement with the system, the gold standard in design. One of the masons interviewed as part of the primary data collection reported with confidence that the last septic tank he constructed would not require emptying for the next 40–50 years. Another mason acknowledged that with the large sizes of the tanks and a small number of users, the tanks would take 25–30 years to fill up. Overall, in the perception of both the households and the masons, on-site systems appear to be largely divorced from their role as a treatment system and are instead viewed as a mere containment structure that should be able to store faecal waste for as long as possible. Accordingly, while the Indian Code of Practice recommends a septic tank size of ~1,100 litres for five users, the average size of the septic tank for the same number of users is ~11,000 litres, as reported on the ground. The size shows a clear relationship with the economic status of the household, but not the size of the household as theory and the technical standard would dictate (**Figure 3**).

Along with the household's economic status, the lot size of the dwelling presents a physical constraint to the size of the septic tank and is positively associated with it. The third factor which strongly associates with the septic tank size, albeit

*Managing Non-Sewered Sanitation for Achieving Sustainable Development Goal 6 in India DOI: http://dx.doi.org/10.5772/intechopen.98597*

**Figure 3.**

negatively, is whether the household constructed the toilet on their own or with support from the government programme. In the case of the latter, the average reported size of the septic tank dropped down by 50% to ~5,620 litres. Winneberger remarked, "Modern septic tank design has evolved mostly as a function of construction convenience, low cost, and repetitive practice" about the evolution of septic tank design in 1984 [15]. As it holds, his remark bears insight into the deviations constituting contemporary construction practices and the phenomenon of the household's preference for large septic tank sizes too.

#### **2.4 Desludging frequencies running into decades due to large sizes**

Like any wastewater management system, on-site systems require periodic maintenance too. Leaching pits are simple in their operation and perform the function of dispersing the incoming wastewater into the surrounding subsurface. Over time, the remnant solids occupy the full volume of the pit requiring its desludging. On the other hand, the accumulation of solids in the septic tank begins to constrain its settling performance long before they fully fill it up to the point of non-usability. As the volume of sludge builds up in the tank, the hydraulic retention time of the incoming wastewater reduces, in turn reducing the BOD removal rate and, resultingly, the quality of the exiting tank effluent. The Indian Code of Practice recommends desludging the tank when the scum layer at the top of the septic tank and the sludge layer together exceed half of the effective septic tank depth. Guidance on appropriate desludging rates from other countries like Australia and Ireland use the same yardstick, with limiting values for the volume of sludge ranging from 30% to 50% of the total working volume of the system.

Applying the principle to calculate the desludging rate for the average urban Indian septic tank with five users leads to a safe frequency of 8–10 years (**Table 2**). This means, that in theory, a septic tank under these conditions would continue to impart the acceptable level of performance until 8–10 years of operation. Nonetheless, in the absence of sludge level sensors, subsoil dispersion systems that begin to clog as septic tank performance deteriorates, and a periodic inspection programme for septic tanks, households cannot be expected to know when the sludge has crossed the halfway mark. Accordingly, as per the survey, 65% of the households reported issues like the clogging of their toilet and backflow from the tank to the toilet as the triggers for seeking desludging services. This means that households tend to desludge the tank when the sludge has accumulated as high as the water line, way beyond the recommended


**Table 2.**

*Estimated desludging frequencies (in years) for different sizes of septic tank and number of users.*

level. Then it is not a surprise that with their large sizes, the septic tanks that have been desludged have been in operation for 21 years on average. Overall, only 13% of all tanks had been emptied even once in their lifetime (13 years on average).
