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There are other ways to manage our sewage safely and with much less infrastructure. Keeping the sewage from toilets separate from other contaminated “grey” water, such as that from washing, allows alternative, water-less treatment to kill pathogens and recover the nutrients and or energy (Zeeman and Kujawa-Roeleveld, 2011). Meanwhile, less intensive treatment, or no treatment, allows the grey water to be reused where quality demands are lower, e.g. in parks and gardens. Such decentralised schemes can operate at a very local scale, e.g. buildings and streets.

Clearly, such approaches are niche in the near term. Conventional safe treatment and management of human waste mostly relies on expert engineers and water managers, and the infrastructure in homes, schools and workplaces mostly relies on connection to waste water treatment plants. Experiments with building-focused sewage treatment and water reuse have already shown the problems associated with construction mistakes, where effluents from other non-drinking water systems in buildings have been introduced into the drinking water distribution system, compromising human health (EC, 2021). Less immediate, environmental harm may be caused if the waste from ourselves and our houses continues to be contaminated with micropollutants (Zintz et al, 2021; Comber et al, 2014). However, households with individual treatment systems such as septic tanks tend to be careful not to poison those systems (Mulder, 2019). Realising the ambitions of the Chemicals Sustainability Strategy over the longer term is key to reduce harmful micropollutants at source. “Hybrid grey and green” water infrastructure combines centralised and decentralised water treatment, leading to reduced water loss, increased water reuse, optimising the exploitation of alternative water sources in a circular economy, and strengthening resilience against climate change events (WE, 2020).

One of the features of such a local approach is that it already provides the opportunity for small, remote or under-served communities to tackle sewage treatment in areas where that is still lacking, and to develop skills and capabilities in “new” technologies (or rather, re-learning traditional recycling). New developments in urban areas, such as the brownfield site at Buiksloterham (see text box), can provide opportunities in purpose-built, decentralised treatment approaches.

Text box: Case study – Collaboration, city level - Amsterdam, the Netherlands.

In Buiksloterham, a collaboration between the water board, municipality and housing corporation is piloting a study on separation of waste water at source, to test the sustainability of decentralized sewage treatment. An innovative vacuum sewer and floating treatment plant has been built with a capacity of 1550 p.e., with vacuum toilets installed in 47 floating homes.

The  traditional waste water sewer system is replaced by a multiple sewer system, which consists of  a vacuum pipe with a small diameter for  the concentrated collection of sewage and a free-fall pipeline for grey water. This collection method enables efficient local water treatment and raw materials (phosphate), heat and energy (biogas) can be recovered and reused locally. This primarily provides raw materials and energy, but also saves energy through avoidance of pumping waste water over long distances.

Amsterdam plans to learn from Buiksloterham in its development of Strandeiland, a new island in IJburg where approximately 8,000 homes will be built. The water board and the municipality want to apply New Sanitation there, as well as using thermal energy from waste water and surface water to make Strandeiland energy neutral.