350 पटक हेरिएको 
Kathmandu: Most of us consider household septic tanks merely a matter of sanitation and environmental health. However, the collective impact of these small septic tanks contributes to climate change by emitting greenhouse gases, particularly methane.
In countries like Nepal, where traditional on-site sanitation systems (septic tanks and pits) are widely used, the rate of greenhouse gas emissions is even higher. Therefore, overlooking this issue is equally risky.
Septic tanks are not the main drivers of climate change. Yet, the human excreta collected in these tanks, even in small amounts but across large numbers, makes a significant contribution to greenhouse gas emissions.
Key Points
√ Methane (CH₄) Production: In anaerobic (oxygen-deprived) conditions inside septic tanks, human waste and organic matter decompose and produce methane. Methane is about 25 times more potent as a greenhouse gas than carbon dioxide.
√ Nitrous Oxide (N₂O): In some cases, incomplete decomposition of nitrogen releases nitrous oxide, which is nearly 300 times more powerful than carbon dioxide.
√ Carbon Dioxide (CO₂): During long-term degradation of organic material, small amounts of carbon dioxide are also released.
Why Do Septic Tanks Emit Gases?
Septic tanks are mostly anaerobic. When organic materials in human waste and wastewater decompose under such conditions, microorganisms produce methane.
Studies have shown that methane has a very high long-term impact on climate change. Even small emissions can cause a large effect. If septic tanks are poorly designed, leaking, or not properly maintained, emissions can be much higher.
Context in Nepal
A large portion of Nepalese households rely on on-site sanitation systems. According to the Department of Water Supply and Sewerage Management, about 89 percent of Nepal’s population uses on-site sanitation facilities.
There are variations in toilet types, septic tank designs, emptying practices, and maintenance across urban, peri-urban, and rural areas. These factors directly influence greenhouse gas emissions. Regularly emptied and well-designed tanks tend to emit less methane, whereas sealed, stone-covered, long-neglected, or overflowing tanks are likely to emit more.
The Way Forward
• Enhancing Local Research and Monitoring: Field-based monitoring should be conducted to determine emission factors specific to Nepal’s context. This would make national emission inventories more reliable.
• Improved Design and Maintenance: Proper septic tank design, regular emptying, and timely maintenance reduce unnecessary emissions. Coordination and collaboration between local governments and communities are essential.
• Biogas Production: In some parts of Nepal, toilets are connected to biogas systems, and the gas produced is used for cooking. With support from the Asian Development Bank and the Alternative Energy Promotion Center, local entrepreneurs have also started commercial biogas production in certain areas.If biogas units are integrated with on-site sanitation systems to capture methane for use as energy, methane emissions can be reduced, thereby lowering contributions to climate change.
• Policy Development and Implementation: Municipalities should establish new septic tank construction standards, particularly for new housing. Local governments also need to introduce monitoring systems and provide incentives or subsidies.
• Awareness and Training: Households should be made aware of proper septic tank construction and use. Simple education such as what not to dispose of in tanks and when to empty them can bring long-term improvements.
Therefore, septic tanks should not be viewed merely as small-scale human waste management systems. They require inclusive and policy-level attention in the climate discourse. In a country like Nepal, where on-site sanitation systems are widespread, even small shifts in priority can make a significant difference in national emissions.
With science- and evidence-based local data, Nepal can develop national strategies that jointly advance public health, environmental protection, and climate goals.
