This post was originally published on sei.org.

As part of a collaboration developed over the past three years between sWASH&grow and the Agency for the Environment in Cuba, the SEI-led team hosted a Cuban delegation in Sweden in August 2022. They visited Swedish sites that mix climate change adaptation with a focus on circular value chains for water and the bioeconomy.

sWASH&grow’s work in Cuba explores the opportunities for testing and deploying gridless solutions in water, sanitation and energy in Cuba by:

• assessing technology needs and matching them with existing solutions; 
• exploring potential management and business models to finance, implement and scale gridless solutions; and 
• making an inventory of required and existing capacities for implementation and maintenance.

Recent field visits to locations in Sweden by the Cuban delegation over the first week of August showed these principles in practice.

The director of the Cuban Environmental Agency and experts from other institutes visited the Stockholm Royal Seaport and Trosa’s human-made wetland, two examples of how ecosystem services can be integrated in landscape planning to assist with water management. These sites show how nature-based solutions help city planners manage water flows while promoting wellbeing in urban areas.

While designing the conversion of Stockholm Royal Seaport (Norra Djurgården) from an industrial area into a residential neighbourhood, city planners kept climate change adaptation in mind from the very start. Among the innovative solutions visitors observed during the guided tour were low-lying green areas that catch surface water run-off and stormwater, replacing ditches and pavement to sewers; green spaces for recreation; and “green corridors” that link grass patches and gardens among apartment buildings to help insects to thrive.

Similarly, Trosa, a small coastal town located in the south of the Stockholm region, uses a double treatment system for wastewater: a treatment plant and a human-made wetland. The wetland provides time for sedimentation of small particles and for bacteria to decompose the compounds wastewater contains, thus improving water quality in the river and bay. In addition, the wetland is also used as a recreational area, where town residents can enjoy green spaces close by.

Urban planners can also integrate their cities into the surrounding green spaces and agricultural lands in Sweden by taking into consideration what has been called “brown gold”. Sewage from household toilets contains nitrogen and phosphorous in high amounts, which, when treated and returned to the soil, can help grow agricultural crops.

Wastewater treatment and recycling solutions

Karl-Axel Reimer, the head of unit ecology and water protection for Södertalje municipality, presented Hölö farm to the InnovaCuba visitors. A patented treatment technique allows the farmer to make use of sewage collected from public vacuum toilets in the surrounding areas as a fertilizer.

Sewage from vacuum toilets contains less water than from normal toilets, reducing transport costs. The toilet’s vacuum could be powered by the sun, using solar cells, which was of particular interest in the context of Cuba, where electricity shortages are common. After treatment, the resulting sludge is free from pathogens and can be used on agricultural land safely.

At a smaller scale, Kiholm community in Södertäjle use so-called dry toilets in every bathroom in the allotment association (koloniförening). The toilets separate urine from faeces, which are collected in septic tanks for treatment offsite. A pipe connects the toilet’s urine collector to a container outside. Neighbours can use a water pump that mixes urine from the outside container with water, in a 4:1 ratio, to water their gardens.

Both solutions described above facilitate the upcycling of nutrients back into the soil while providing a wastewater treatment solution for areas disconnected from a centralized wastewater management system. A common challenge is that the transport of sewage water can be inefficient because of its high weight, compared to the low concentration of nutrients per volume.

At the Swedish University of Agricultural Sciences, Professor Björn Vinnerås explained his vision on water sanitation and introduced an innovative solution that tries to address the inefficiency linked to transporting treated sewage to recycle its nutrients back into the soil. After using a urine-diverting toilet with an “urine trap”, urine is then processed through an alkaline treatment and dehydrated to a powder containing high concentrations of nitrogen and phosphorous per volume.

The powder can be used as a long-lasting, dry and easy way to transport fertilizer. In addition to having the potential to reintroduce compounds back into the agricultural system, it could also reduce the costs and dependency on artificial fertilizers in agriculture.

Fly larvae solutions 

Another project InnovaCuba visited at the Swedish University of Agricultural Sciences (SLU) showcased larvae of the black soldier fly (Hermetia illucens). The larvae rapidly increase in mass over three weeks. High in proteins and fat content, they make good food for hens and fish – and they eat organic waste.

Although the expertise required for breeding the larvae is high, this solution could both provide income from selling larvae to feed livestock and assist in returning nutrients into the agricultural system. The waste that makes the black soldier fly larvae fat could be organic waste or food that would otherwise go uneaten.

Closing the loops with nature-based solutions – whether with human-made infrastructure or animals as intermediaries – could make good sense for treating water and strengthening the bioeconomy in Cuba, as well as in Sweden. The projects visited still need to be expanded to larger scales to make a difference in climate resilience and more. After exploring how nature-based and off-grid solutions can work in practice, the InnovaCuba project could assist in untapping the potential for the future of bioeconomy in Cuba – and perhaps eventually in Sweden as well.

Written by: Karina Barquet & Anna Calvo, SEI.