greenWATERrecycling – utilization of greywater for energy recovery and for providing greywater-filtrate for watering green walls

Motivation and research question

In the field of thermal insulation of buildings, the recovery of ventilation heat losses and the energy efficiency of electrical applications, constant technological progress is taking place due to numerous research efforts. In contemporary building standards, the proportion of hot water provision has thus developed being the largest energy consumption component of the building. Here again, the lack of use of waste heat from hot water preparation stands out clearly. Current legislative developments, which will mandate new efficiency standards soon as well as the sustainable use of resources, underpin the urgency for comprehensive solutions for the building sector. The greenWATERrecycling project is investigating the extent to which heat energy can be recovered from greywater and at the same time greywater can be made recyclable as service water.

Initial situation/status quo

The products from wastewater heat recovery are currently used for freshwater preheating or the central heating system. Advantages of decentralised use lie in the short transport distances of the water and the resulting low distribution losses. The wastewater inevitably leads to fouling (e.g. biofilm formation) of the heat exchange system, so that its temperature transfer efficiency decreases over time. Some systems with storage principle have automatic cleaning systems but subsequently require high maintenance costs to maintain the effect of heat recovery. Continuous flow systems avoid direct contact of dirt with the heat exchangers and clean themselves through turbulent filter flows. However, experience has shown that they are fundamentally less efficient as a result.

Project contents and objectives

The aim of this project is to design a technically mature system solution ("STREBEL greywater recycling plant") for the material and thermal recycling of greywater to be able to use the treated greywater for irrigation purposes and to recover the waste heat, which has hardly been used so far, in a highly efficient way. In this way, drinking water shortages that are to be expected in dry summer months due to climate change can be alleviated and an irrigation of urgently needed green infra structures to reduce urban heat islands can be achieved at the same time. The approach of such an efficient utilisation of grey water, namely in terms of both material and thermal aspects, is unique and new.

The greenWATERrecycling project results in four visionary cornerstones that go beyond the state of the art and can contribute to the energy- and water-efficient operation of a building:

• High degree of heat recovery due to low distribution losses due to decentralized use in conjunction with cleaning of the wastewater before it is fed to the heat exchanger.
• Use of STREBEL treated greywater as a heat source for a heat pump, especially for water heating.
• Exploring the possibilities of using the cooling potential of STREBEL treated greywater (after heat extraction) to contribute to the cooling of buildings.
• Greywater recycling: The possible use of STREBEL-treated greywater for irrigation of green infrastructures or domestic water use is possible.

Methodical procedure

A technical system was compiled for a residential building with 200 residents. For this purpose, the greywater quantities produced, and the utilisation potential of the recovered energy were analysed. The accumulating amount of STREBEL treated greywater was analysed for its physical potential (e.g. regarding suspended matter) for the irrigation of different greening systems. In an experimental garden, selected plants were specifically irrigated with the STREBEL treated greywater and compared with a control group. Over two vegetation periods, the effects on growth and relative photosynthesis as well as the developmental ability of the plants were investigated. The technical system design of all project components was based on the knowledge gained in the project.
Furthermore, the technical, legal and hygienic framework conditions for the material use of greywater for the irrigation of green spaces, building and façade greening were analysed. A simulation and evaluation of the climate-improving effects of additional greening (on the façade itself as well as on the forecourt), which can be irrigated with greywater, was carried out on an actual building that serves as a reference building for the project.

Results and conclusions

The grey water analyses showed that the STREBEL treated grey water complies with the limit values specified in ÖNORM EN 16941-2 & 1. AEVkA and meets the quality requirements. With regard to the chemical-physical and microbiological parameters, the STREBEL treated greywater is suitable for use in toilet flushing, garden irrigation (except springle application) and cleaning (dishwasher and washing machine). From a plant physiological point of view, STREBEL treated greywater is suitable for the irrigation of green infrastructures. Due to possible residues in the STREBEL treated grey water (e.g. medicines), however, appropriate handling must be ensured so that no contact with herbs, fruit or other plants and trees with edible fruit is possible.

Outlook

Based on the project results, an initial test plant was developed and prepared for implementation as part of a research project from the Climate and Energy Fund's "Smart Cities Demo - Living Urban Innovation 2019" programme. This plant will be used for the first time to gather experience and measurement data on the subject of thermal and material recycling of warm greywater under real conditions in a residential building. Through the project, the actual implementation on the scale of a real laboratory could be successfully prepared to optimally utilise the project results.

Research can help to understand people's perceptions, attitudes and acceptance of greywater and to develop appropriate communication and education strategies to achieve broad acceptance.

Project management

Schöberl & Pöll GmbH (consortium leader)

Project or cooperation partners

• GEBE-STREBEL GmbH (applicant)
• OeAD-Wohraumverwaltungs GmbH
• Institute of Building Research & Innovation ZT GmbH
• Universität für Bodenkultur Wien – Institut für Ingenieurbiologie und Landschaftsbau (IBLB)

DI Klemens Schlögl
Schöberl & Pöll GmbH
Lassallestraße 2/6-8
A-1020 Wien
Tel.: +43 (1) 726 45 66/14
Fax: +43 (1) 726 45 66/18
E-mail: klemens.schloegl@schoeberlpoell.at
Web: www.schoeberlpoell.at