Untapped: How Sri Lanka’s septic tanks could become a sustainable support for farming

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Farmers in Sri Lanka are positioned to benefit from a new policy that recognizes waste from septic tanks as an untapped resource. 

The new sanitation policy, supported by research carried out in close partnership by the International Water Management Institute (IWMI) and the Sri Lankan government since 2013, recognizes septic waste as a resource, with potential benefits for income generation and sustainable organic waste management.

In a country where septic tanks are more commonly used than sewers, the new policy takes the problem of what to do with the resulting waste, and turns it into an opportunity. 

Through the use of circular economy technology, as tested over two decades by IWMI in Africa and Asia, waste from septic tanks can be safely treated and reused to fertilize and irrigate crops, creating a sustainable nutrient cycle. 

Taking advantage of this technology in Sri Lanka would not only save water and nutrients from going down the drain, but also present solutions for human and environmental health, as well as opportunities for jobs and growth. 

A hidden resource

Septic tanks, latrines and other onsite systems are the main method of human waste disposal in Sri Lanka, used by 96% of households – as little as 4% of the population is connected to formal sewerage systems.

“While some might consider this [low percentage] a disadvantage,” says Pay Drechsel, a principal researcher at IWMI and flagship leader of the CGIAR Research Program on Water, Land and Ecosystems (WLE), “more sewer systems would multiply household water needs for toilet flushing and not support the safe recovery of nutrients as non-sewered systems do.”

Septic tanks are an effective solution for handling household waste and keeping it free of the chemicals common in sewers – which carry all types of domestic and industrial wastewater, making it far costlier to separate nutrients, for example, from heavy metals.

The sludge from septic tanks contains nutrients like phosphorous and nitrogen, as well as organic matter that is in short supply in tropical soils.

But at present, less than 10 percent of septic waste in Sri Lanka is treated. The rest ends up polluting water in rivers, wetlands or the sea, or contaminating land after it is buried or dumped untreated in landfill.

By recognizing septic waste as a potential resource, Sri Lanka’s new sanitation policy turns the problem of waste management on its head. Viewed this way, the work of desludging septic tanks, transporting and treating the waste matter, and finding ways to reuse it present untapped business opportunities in support of crop or green energy production.

“There are many options for public-private partnerships to turn harmful waste and an otherwise lost resource into an income stream for the benefit of waste management and agriculture,” says Drechsel.

Tried and tested

IWMI researchers have already found a way to recover organic matter and nutrients from septic waste. The sludge can be dried, co-composted and turned into safe fertilizer pellets to meet local farmers’ needs, or pressed into fuel briquettes that can be burned for energy.

The work in Sri Lanka builds on ten years of experience in Ghana, where fertilizer made using this technology is already on the market.

Extensive field trials in Ghana over the past decade have supported the launch of a commercial product branded as Fortifier, made from treated septic waste combined with organic municipal waste. 

Before the introduction of Fortifier, farmers in Ghana were already appreciating the fertilizer value of septic waste, but had no alternative to using untreated sludge, which posed a potential health hazard. The IWMI method of co-composting fecal waste with other organic matter provides a cheap, healthy alternative that meets local and international safety standards.

The fertilizer is being produced at a plant founded under a public-private partnership between a local city government and a waste management company, with additional investment from the national government. 

A second facility is now under construction. The first plant has the capacity to treat 12,500 cubic meters of septic waste – the amount generated by 100,000 people over the course of a year – and 700 tons of food waste to produce 500 tons of the organic fertilizer pellets. 

The pellets have been demonstrated to improve the yields of staples like maize and rice, as well as commonly grown vegetables like okra, tomatoes, pepper and cabbage. Compost created in the process can also be used for tree plantations or landscaping.

Putting it into practice

Farmers in Sri Lanka are receptive to, or even enthusiastic about reusing septic waste as fertilizer, considering it as another type of manure, according to first market assessment studies. 

“Sri Lanka has fantastic infrastructure to make this circular concept work,” says Josiane Nikiema, who leads IWMI’s Resource Recovery and Reuse group. “The country has already invested in more than 100 compost plants, which could be upgraded to accept fecal sludge from septic tanks, which adds value and nutrients to the municipal compost.”

The Sri Lankan government hopes that its new sanitation policy will help the country meet Sustainable Development Goal 6 on clean water and sanitation. Dialogue is ongoing with key players in ministries, municipalities and local authorities to put the policy into action, and IWMI has been invited by the national government to support the process. 

For this, IWMI’s research is going beyond advice on low-cost technologies and looking into institutional and business models for the management of waste from septic tanks, as well as municipal solid waste and wastewater, with an eye to creating a sustainable cycle between waste management and agricultural production. 

This research was conducted for the CGIAR Research Program on Water, Land and Ecosystems (WLE) with support from contributors to the CGIAR Trust Fund, the Bill & Melinda Gates Foundation, the Swiss Agency for Development and Cooperation, the International Fund for Agricultural Development, and Germany’s Federal Ministry of Economic Cooperation and Development.

Photo: Sri Lanka could benefit from innovative technologies tested in Ghana and elsewhere to recycle human waste captured in household septic tanks into safe fertilizer for crops. Photo by N. Palmer/IWMI 

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