Septic Tanks 101: Everything you ever wanted or didn’t want to know

What does a septic tank do?

A septic tank is an underground, water-tight chamber usually made of concrete, fibreglass, or polyethylene attached to individual homes, residential complexes or commercial establishments. Its function is to store and process wastewater generated in the establishment for a period of time. While the solids settle down forming sludge, oil and grease float to the top. The remaining liquid either flows out to a larger wastewater treatment plant in urban areas for further processing or is released into the environment after the appropriate onsite breakdown of waste. Septic tank systems typically depend on anaerobic microbes and other naturally-occurring bacteria to do the work of preliminary decomposition of the waste.

47% of urban Indian households are connected to septic tanks. When we talk about septic tanks, it is common to hear about safe and efficient decomposition at the hands of these naturally occurring microbes. A properly functioning septic tank should ideally ensure that pathogens  (disease-causing by-products of waste) are trapped within, not allowing them to be leached out. But there many factors and influences that can put the natural balance of these bacteria out of whack, which may compromise the way in which the tank manages decomposition. This can then lead to an unhealthy discharge of untreated, undecomposed wastewater in the area around the tank – posing a health hazard to life around and a real risk of groundwater contamination, setting off a cycle of perpetual pollution.

How does it work?

A septic tank works to break down organic matter, separating it from scum like solid and semi-solid substances such as oils and grease and solid waste from sewage. There are different kinds of septic tank systems. Soil-based systems are designed to release the separated and treated liquid via a network of pipes buried in what is called a ‘leach field’ which gradually releases these effluents into the soil. Other systems employ pumps and/or gravity to direct the effluents through surrounding soil and wetlands. The ‘good’ bacteria present within the tank are responsible for the process of neutralising pathogens such as nitrogen, phosphorus, and other contaminants before what is known as ‘greywater’ is discharged back into the soil or a nearby waterway through which it makes its way to the sea.

What is greywater? And why does it matter?

Greywater is the wastewater produced domestically, minus sewage. Sewage, which contains solid waste from toilets and bathrooms is also called blackwater and is characterised by a much higher composition of ‘organic loading’. Greywater is made up of the water that runs out from kitchens, bathrooms, gardens and is commonly called ‘wastewater’. In recent times, with the growing awareness around groundwater leaching, people are waking up to the alternative uses for greywater and developing means to re-generate, upcycle and reuse it within the establishment, for a range of purposes excluding human consumption, after a basic process of filtration and cleaning.

Greywater in septic tanks is bifurcated in to 3 categories:

1.      Thick, bottom scum

2.     Floating solids in the upper layer

3.     Clarified layer of  fluids between these two

Healthy, well-functioning septic tanks will have a relatively clean separation of these, while poorly maintained tanks tend to get clogged and cause emission of foul odour and backflows. However, routine household activities and the presence of antimicrobial compounds in chemical cleaners can upset the microbial balance that handles the healthy and efficient breakdown of organic matter, ushering in a slow failure of the septic tank to manage the waste efficiently. The nature and composition of greywater then becomes an accurate indication of how well the septic tank is functioning.

Septic tanks and sanitation

Since septic tanks are the starting point of the efficient and effective cycle to treat wastewater, they form a fundamental component of the sanitation system. However, a proliferation of hazardous chemicals present in household cleaning products, irresponsible flushing away of harmful liquids down drains as well as mismanaged, and faulty septic tanks have caused a significant imbalance in the presence of the microbial composition that shoulders the bulk of the decomposition work.

Most septic systems are not designed to help keep groundwater safe from chemicals found in household products, and they can pose a high risk to human health and the environment when not used or degraded properly. When these chemicals enter a septic tank in overly large doses or concentrations, they impact toxicity levels and trigger a cycle of pollutants being released back into the ecosystem. Hazardous chemical components that remain unprocessed and flow back into the ecosystem unchecked are responsible for polluting waterways, the sea, groundwater, soil and the ecological balance.

This is why, at a policy level, for a developing nation that is looking to end open-defecation, it is not enough to merely stop at providing toilets for the underserved but also to look at how the waste from these is being managed.

Maintaining a septic tank

How often do we thoughtlessly drain liquid waste down the sink or tub in our homes? It is the quickest go-to when disposing of liquids. So often these include leftover oil, chemical-laden cleaners, paints, etc. Out-of-sight-out-of-mind at work, we assume that once it is down the drain, these liquids will be treated just as other waste is. But the truth is, several chemicals and ingredients in these products, especially household cleaning products can cause irreparable harm to the health of your septic tank. Chemicals such as ammonia, bleach and nonylphenol ethoxylate surfactants and phosphates can severely harm the microbial balance required for the septic tank to breakdown pathogens.

Most septic systems are not built to guard against chemicals found in household products. So, when these chemicals find their way into the septic tank, they harm the beneficial bacteria that break down the contents. In the long run, this can destroy septic tanks and worse, the larger ecosystem.

Since the health of a septic tank depends on the balance of naturally occurring bacteria and microbes, it’s crucial to ensure that everything that is flushed down the drain is safe and non-hazardous. Once the septic tanks capacity to contain pathogens is compromised, it can lead to clogging, overflow, back-flow and the release of harmful effluents into the environment.

To know more, read about where sewage waste goes once it leaves you home, how septic tanks play a role in impacting sanitation and health and how chemical cleaners are posing significant risks to human health and the environment.

Post by Khushboo Shroff

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