Technologies for Decentralized Wastewater Treatment

In our research on 'Technologies for Decentralized Wastewater Treatment', we investigate processes for decentralized wastewater treatment in urban and peri-urban areas. The new processes shall be used for on-site reactors, which will meet today's stringent effluent standards, but which will also be small, reliable and easy to control. The reactors could be used for setups of one to several hundred households.

Many of today's wastewater treatment processes do not meet these conditions. Some processes, such as enhanced nutrient removal with activated sludge, require sophisticated process control and continuous on-site monitoring. Others, such as septic tanks, can be used on-site, but the removal efficiency for nutrients, contaminants or pathogens is insufficient.

Research on 'Technologies for Decentralized Wastewater Treatment' is based on two concepts: 'source control' and 'waste design'. Wastewater from households can be separated into three waste streams: greywater, faeces and urine. Currently, we focus mainly − but not exclusively − on the treatment of urine, which is the most relevant contributor to the nutrient load in wastewater. Separate treatment of urine not only prevents environmental pollution, but it also allows for the reuse of nutrients in agriculture.

Recent research has shown that urine separation is a promising concept for wastewater management, especially for cities in emerging and developing countries. Industrially produced on-site reactors would be most suitable for the implementation of urine separation in cities. We investigate whether recently developed wastewater treatment processes would be feasible for small on-site reactors. Some examples of the processes we investigate are phosphorus recovery by struvite precipitation, nitrogen removal via partial nitritation / anammox, urine stabilization by nitrification and consecutive concentration of the nutrients by evaporation, electrochemical processes and bio-electrochemical processes.

Struvite recovery from urine in Nepal (STUN)

Nitrogen removal from urine with partial nitritation / anammox

Nitrogen stabilization in urine

Complete nutrient recovery

Electrochemical ammonia removal

Long-term observation of a urine collection system

Decentralized treatment and reuse of toilet wastewater in alpine areas

Single house wastewater treatment with water reuse

Greywater treatment in the living module SELF [pdf, 0.7 MB]

A vision for household technologies: nutrient recovery reactors will be so small that they can be integrated in the bathroom (pictures Kai Udert, Mariska Ronteltap)