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April 2022

No solution without decentralized treatment

In the series “The Problem with Wastewater”, we have previously written about the ways in which our handling of wastewater damages our health, the economy, and the ecosystems we live in. Effective wastewater handling requires a multi-layered approach which ensures treatment accessibility and coverage regardless of location and economic horsepower – a feat that can be achieved with the introduction of a new generation of decentralized wastewater treatment systems.

Why decentralized wastewater systems?

Until recently, centralized, large-scale, and costly treatment facilities have represented the only viable options to treat our wastewater. However, full scale wastewater treatment facilities are costly and generally require multi-million-dollar investments – making them unattainable for large parts of the developing world. Even with such large investments, these facilities do not always satisfy regulatory requirements. Moreover, large-scale facilities are simply not viable for villages or businesses with insufficient wastewater volumes.


As roughly 45% of the global population still lives in rural areas, succeeding with wastewater treatment on a small, decentralized basis is imperative to solving the problem with wastewater. Beyond being the only viable option in remote areas, there are other potential advantages of decentralized treatment; for one, it reduces the need for costly infrastructure connecting the source of generation to the treatment center. It also opens pathways for reuse of the water and sludge in the communities where it is generated – which has become increasingly important as approximately 1.1 billion people in the world lack access to fresh water.

What exactly is decentralized wastewater treatment?

Decentralized wastewater treatment systems are often small, individual systems that treat wastewater near the source of generation – typically from individual homes or small communities, but also farms and businesses without access to wastewater infrastructure. Some common systems in use globally are septic tanks, soil infiltration systems, constructed wetlands, sand filters, and prefabricated treatment plants.


While these systems vary in complexity, they all have a common goal of reducing pollution (pathogens, nitrogen, and phosphorus) in wastewater to tolerable levels and to ultimately discharge clean water to natural waterbodies and groundwater.  


So what’s the problem?

In the EU, regulations require removal of 70-90% BOD, 75% COD, and 80% nitrogen and phosphorus from wastewater. In developing countries, the requirements are generally lower. However, most systems are unable to meet regulatory removal requirements for biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen and phosphorus for wastewater discharge – not to mention the inherent requirements of the local ecosystems in which they exist.


Technological limitations due to the small scale of the systems – in addition to maintenance requirements not being met – typically lead to unsatisfactory treatment outcomes. As a result, there have been limitations to the widespread application of decentralized wastewater treatment systems despite the recognition of its benefits for water reuse. According to Christopher Gasson, the publisher of Global Water Intelligence:

“On the wastewater side, the obstacle to growth is not really

lowering the cost of the process. […] It is about technologies that help

change the paradigm. Specifically, we need decentralized

systems that reduce the need for investment in collection networks,

real-time water quality monitoring systems which give the public

confidence in direct potable reuse […]”

Harmonically discharging our wastewater to nature requires removing the lion’s share of BOD and total solids, including phosphorus and nitrogen –which is hard to achieve with today’s available technology. For example, septic tanks which are the most common on-site treatment technology remove only 30-50% BOD, 50% COD, and 20% nitrogen and phosphorus.


What Scandi offers

Scandi Energy is now working with players in aquaculture, municipal wastewater, and biogas in Norway to introduce its “next generation” system of efficient decentralized wastewater treatment.


As previously reported, the Dwater Unit technology has proven immensely efficient at a smolt aquaculture farm and municipal wastewater treatment plant in removing nitrogen, phosphorous, total solids, and BOD while simultaneously sanitizing the sludge and wastewater. Overall, the goal is to treat wastewater on site and therefore pave the way for more decentralized treatment options for businesses and communities alike.


A test program with strategic partners in the aforementioned fields is already planned for 2022, the year when the technology enters the market. As the results become public, policy-makers and users alike will be presented to the opportunities arising from the next generation of decentralized wastewater treatment.


April, 2022


External resources:

  1. Current Treatment Performance and Rehabilitation of the Decentralized Wastewater Treatment Systems in Frøya

  2. The World Bank – Rural Population (“% of total population) , 2020

  3. What is decentralized treatment?

  4. World Wildlife Fund – Threats | Water Scarcity

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