Design of the water loop in the little stone stable

Within the Hydrousa Project ELT has transformed an old stone stable into a new lodge which can host two to a maximum of three customers. This leads to an additional overall water demand. The Waterloop 1 focuses on two aspects around the new lodge:

  1. avoidance: maximal reduction of water consumption through NBS (Natural Based Solutions)
  2. reuse: reclaiming the unavoidably consumed water through NBS (Natural Based Solutions)

On the avoidance side ELT singled out the biggest water consumer within the touristic facility which is the water flushing toilet. The ELT team focused on a design that renders the use of a water driven sanitation system unnecessary while maintaining customer satisfaction. With the scope of achieving an immediate water utilization reduction of around 25%.

The unavoidable water consumption is treated with a NBS Constructed Wetland, reclaimed and disinfected for unrestricted irrigation. The NBS for reclaiming water through the sewage treatment process, play a key role in providing nutrient rich utility water, during the dry summer period.

Within the Project the agricultural activities of ELT are upscaled in cultivated area size, diversity and intensity contributing to the hyper local food production within the facility and the local market.

These small buildings that can be found all over the island dating back to the 19th century, were the farmers shelter, where they kept their animals, their crops and one room usually for them to sleep in. The fields being far away from the villages, people had to walk for hours to reach them, so at the time of harvest they stayed on their fields, for the whole period. Their architecture is unique, built totally out of stone and earth, with huge stones placed on the roof and an oval structural shape inside. These buildings are a cultural and historical heritage of the island.

In respect to the beauty of the cultural anthropogenic landscape the design approach was to integrate the sewage treatment and collection system into the terraced landscape as it would be part of it. This is way the perimeter walls are created out of stone work so the structure can blend into the surrounding stone walls (see figure 1.10).

The design is guided by the underlying concept of stacking functions which means that a targeted intervention like a sewage treatment facility can simultaneously create many other beneficial side effects which interact with the broader overall design of ELT as an off grid agro-eco-seminar facility.

As already mentioned above for ELT it was important to design not only a technical NBS sewage treatment unit but also to create an attractive water feature that combines a place of interest for relaxation and observation with the benefits of a reed biotope for the local wildlife. The holistic approach of the Hydrousa project makes it vital to consider also broader aspects to every intervention. In the dry summer months, typical to the Cycladic islands wetland habitats become scarce but essential for Bees, Dragonflies, Birds, Frogs etc. On the other hand these animals are essential to an agricultural site due to their ecosystem services like pollination, pest predation and an overall intact habitat with its complex interdependencies. Also the close proximity to the lodge created the need for an attractive integrative design which people can actually use and are drawn to due to its natural beauty.

The second consideration arose from the decision of creating a separate new treatment system that should be as small as possible in order to save space and keep the costs as low as possible. The NBS for sewage treatment need a certain surface area according to the BOD and COD load contained in the waste water stream. In order to minimize the surface area the load has to be minimized accordingly. This lead to the biggest single alteration in the design approach of the new system: the separation-dry-composting sanitation system of the new lodge. ELT had considered this sanitation concept at the initial design of Ecolodge Tinos but depraved it due to concerns of the social acceptance on the client’s side. At a later stage ELT designed and built two composting toilets for the seminar participants staying in tents. This four year experience with the dry sanitation approach and a lot of positive feedback from the users, lead to a reconsideration of this facility. Besides the social aspect, this low tech solution is overall superior to all other solutions known to us.

The separation-dry-composting sanitation system designed for the new lodge is a very low tech NBS. The key benefit concerning the waste water treatment is the complete separation of feces and urine from the wastewater stream, leaving only dark gray water for processing. This lead to a space and material reduction of around 50% concerning the CW-vf. Also it reduces the total water demand by 20-30% due to the fact that the demand created by the toilet flush system becomes obsolete. Considering the nutrient loop with in the holistic approach of the Hydrousa project the separation-compost toilet keeps the urine stream pure for easier further processing into fertilizer and the dry feces stream can be composted directly in changeable barrels.


In order to reach the required sanitation level of the effluent, a UV-disinfection unit purifies the water at the point of demand, which is the irrigation of the herb plantation.

From the treated water tank, the water is pumped by a pressure switch-controlled pump through the UV-unit and injected into the according irrigation zones.

The UV disinfection technology is the most suitable for the ELT case due to its simplicity. The issue arising within the off-grid situation is the electricity demand created by the unit. The commonly used low pressure mercury vapor lamp (HPLC) emitting the UV radiation has the disadvantage inherit to the lamp characteristics that it degrades by switching it on and off. So, the commercial units operate in a normally on configuration. The lamp power needed to effectively treat the effluent in this case is around 17W. This would generate a daily power consumption of 0.408 kWh and would mean a 10th of the total power consumption of the existing ELT unit. Covering this kind of power consumption day and night by an off-grid photo-voltaic system becomes disproportional costly. This led to the investigation of alternatives solutions.

Fairly new on the market are UV-C light emitting diodes (LED) that have reached a development point where the first market available units are deployed for small scale application. The biggest benefit of this unit in this context is the possibility of cycling the operational state (on/off) without effecting the lifespan. This leads to an enormous reduction of electric power consumption, if configured in an on-demand setup. In this way the unit can be triggered by the pressure switch controlling the pump and the UV-unit when water is demanded.

Returning to the HPLC technology it was necessary to reduce electricity demand. After intensive discussions with the manufacturer the possibility of actually switching the lamps was reconsidered. According to the information provided, the lamps degrade per switching cycle one hour of their expected lifespan. Also, the lamp needs a certain time to reach the full emitting spectrum and dosage depending on the lamp manufacturer.

This new possibility lead to a circuit setup where the lamp is triggered, and the pump is switched by a delay timer according to the startup time of the lamp in a time shift mode. In this way the units work in demand mode and the degradation of the lamp is reasonable. HPLC lamps have a life expectancy of around 10,000h or 13.9 months with a daily switching cycle the lifespan will be reduced by 15 days. This extra degradation is proportionally to the reduced power consumption neglectable.

In order to irrigate the herbs from the effluent tank, around 650 L within one hour are needed, so the unit closest to this value was selected, with a capacity of 1m3/h. The pump was configured according to the flow rate of around 650 L/h with a minimum hydraulic head due to the down slope irrigation setup.

According to the projected reclaimed water production of 0.6m3 a week the UV-unit will run one hour per week. In this configuration the electric power consumption is reduced from the initial 0.408 kWh hence 2.8 kWh per week, to around 0.017kWh per week.


Throughout the years ELT has acquired intensive customer feedback on the different water management practices involved. This experience has shown that the average customer has limited knowledge about his water consumption and the quantities needed in order to run basic sanitation systems or agricultural production. When showing the different systems at the welcome tour a common reaction to the water cistern of 100m3 is that it is huge. When explaining further how little water it is compared to his own needs and how it is distributed according to the consumption, most people become skeptical. Down the line it is noticed that most customers are much more flexible and open to new approaches than normally assumed. These discussions throughout the years encouraged the design of Waterloop1.

In the experience of ELT, this contributes greatly to the Metabolic rift between the user and his natural environment. This is addressed more thoroughly within Waterloop1 where the user is taken out of his habitual comfort zone and is actively engaged in a new way of dealing with his excrement’s and the involved material flows.

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