SWITCH: Managing Water for the City of the Future

Managing Water for the City of the Future

Recycling wastewater and nutrients

Lima, Peru

Due to scarcity of rain and the pressure on the water supply, green spaces and productive activities around Lima use piped water, raw wastewater, treated wastewater or river water for irrigation. Agriculture in urban areas has increased in the last decade as a strategy to increase access to food (vegetables) and to generate income and improve the environment. The potential of using treated wastewater for these productive uses has generated interest as national and municipal authorities respond to the need to reduce demand for piped water for uses other than consumption, and to monitor and increase the quality of water used for irrigation of crops in peri-urban areas and green spaces in urban areas.

The demonstration project was designed and implemented in the district of Villa el Salvador, Lima. The Eco-Productive Park, named OGAPU (in Spanish: Optimising Water Management to Combat Urban Poverty), was designed in a participative way through a series of workshops with the community and community based organisations, architects, and authorities. It has four components: recreation (games for children, chess table); sports (a grass football field, cycle path); production (growing ornamental bushes that are sold to city parks); and a tertiary treatment pond for wastewater. OGAPU aimed to show how this decentralised (re)use of treated wastewater could green a 2Ha area of what was a fairly typical desert like area. The project looked into the possibility of using the water for food production, but it appeared not possible because legislation did not permit using wastewater for this purpose.

The reuse guidelines were reviewed and finalised with members of the National Learning Alliance in October 2008 and presented in December 2008 at a special session of the National Conference on Water and Sanitation (PERUSAN). The Peruvian Government formally approved them in November 2010. The Policy Guidelines will act as a strategic agenda for the institutions involved. IPES and the Ministry have developed a training package for capacity building of these institutions.

The demo has shown overall improvement in the area: social (community building, recreation, social inclusion, etc.), an economic (income), and environmental (green space, improvement of air, reuse of waste, etc.).

Accra, Ghana

Irrigated urban vegetable production in Accra provides up to 90 per cent of the city's need for the most perishable vegetables, especially lettuce, which benefits around 250,000 people daily. Production yields an average monthly net income of US$ 40-57 per farm. Nevertheless, it is associated with health and environmental risks from the use of polluted water and attendant contamination of vegetables with pathogens. Local and international initiatives have responded to some of these constraints. Notably are research projects on safer vegetable production as supported by IWMI, WHO, IDRC, FAO, and RUAF.

SWITCH built upon these experiences by developing technological and institutional innovations designed to minimise risks associated with urban wastewater reuse for agriculture. The action research and demonstration at plot level took place with farmers at the Dzorwulu-Roman Ridge site, within the Accra Metropolitan Area – the Odaw-Korle catchment.

A first demo and related action research focused on improvement of farmer innovations, using dugout ponds. Based on the principle of sedimentation and the use of multiple ponds and macrophytes, improvement in treatment was developed in a farmer field school setting.

In a second demo, part of the farmer groups were involved in linking production with sustainable sanitation. It involved the collection, treatment and use of urine for farming at the demo site. Urine is a readily available resource for use in urban agriculture, but the cost of transportation is usually too high, hence farmers were encouraged to store urine on farm site in mini disposal units. In addition agronomic field trials, economic feasibility and perception studies were undertaken, while farmers and extension staff were trained.

Tel Aviv, Israel

The conventional long-term Soil Aquifer Treatment (SAT) is one of the oldest, largest and efficient natural tertiary treatment system in Israel and the world. Although a proven technology a solution was needed to address the lack of land for construction of new fields, gradual decrease of the infiltration velocity and manganese precipitation causing clogging of the irrigation systems.

In the EU Reclaim Project-018309.a UF-short SAT (30-35 days retention in the aquifer compared to 6-12 months in the current full-scale system) solution was investigated The technique produced good chemical and microbiological quality water but did not remove all measured micro-pollutants effectively due to the short retention time in the aquifer before the water is pumped out.

In SWITCH demo secondary effluents were treated by a short SAT-NF process for indirect potable reuse. The efficiency of short SAT as pretreatment on the performance of nano-filtration membranes (DOW NF 270 and NF 90) was investigated. This technique efficiently reduced micropollutants including hardly biodegradable antibiotics and organic iodine. It showed that short SAT as pretreatment prior to NF can be an effective technology for unrestricted water reuse and indirect potable reuse while also reducing GHG emissions (smaller carbon footprint) as compared to the more conventional UF-RO systems.

Chengdu, China

Approximately 300 decentralised wastewater reclamation systems (DWRSs) are in operation in China, producing 50,000 – 60,000m3 / day of second quality water that is used for toilet flushing, landscape irrigation, street cleaning and car washing. The Ministry of Construction aims to upscale this approach across China within a current program on sustainable building.

This SWITCH demonstration, at the Chengdu CMC New Campus, aimed to assess the potential benefits of decentralised urban wastewater systems with use of treated grey water for landscaping.

Unfortunately, due to construction delays, all monitoring results could not be finished by the end of SWITCH, However, a design report of the system and the monitoring plan are available.

It is expected that the demonstration will have a China wide exposure because it is part of a wider sustainable building program of the Chinese Ministry of Construction. As such it may contribute to alleviating water scarcity in over 450 cities in China.

Łódż, Poland

The Łódż Waste Water Treatment Plan produces 70,000 ton of sewage sludge per year (200 tons/day). The sewage sludge can be used for non-food agriculture provided that the heavy metals content is kept within the limits laid down in the Polish legislation.

A solution was sought that would harmonize traditional treatment technologies with ecological methods of sewage sludge use, heavy metals removal and bioenergy production. To meet these aims a SWITCH demonstration on short rotation forestry (experimental willow plantation) within the protective zone of the treatment plant was developed.

The demonstration activities included:

  1. Establishing and exploitation of the willow plantation for sewage sludge utilization, biomass production and heavy metals removal;
  2. Regular monitoring and research of the above processes for their optimization and adaptive assessment management;
  3. Assessment of sewage sludge toxicity and elaboration of methods for minimizing toxicity of the sewage sludge substratum to willows; and
  4. Development of the Decision Support System (mathematical model) for management of willow plantations for sewage sludge utilization, based on the literature review and the obtained results.

To date some benefits from the willow plantation include:

Key documents:

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