We also took the opportunity to talk to Living Water, the system’s developers, to find out what makes ETS unique. Below is a summary of these conversations.

ETS are ecological alternatives to conventional wastewater treatment systems. Conventional wastewater treatment systems typically rely on a combination of mechanical action and/or bacterial processes to breakdown and reduce wastewater contamination. Ecological systems on the other hand, create habitats that support complex food webs between a wide range of fauna (bacteria, microorganisms, invertebrates and fungi) and flora (plants) to clean wastewater.

Simon Howie Foods were attracted to the ETS following a period of fast growth that put their original turn-key waste treatment system under pressure to meet SEPA discharge consents. Having taken into consideration other solutions, Simon Howie Foods chose an ETS due to it’s:

• low capital and operational costs,
• attractive payback period (which for an ETS can typically be less than two years),
• ability to complement the existing treatment system, and
• flexibility to cope with planned expansion and effluent peaks.

In ETS, carefully selected plants (and their root systems) provide a home for a range of organisms and remove specific wastes and pollutants, whilst micro-organisms consume other wastes and pollutants in the wastewater.  In an ETS attention is also paid to the substrate, where three sizes of washed, graded aggregate are placed over a liner. Graded aggregate are used to manage water flow and help recreate the conditions required by the different micro-organisms and plant roots.

ETS’ biological diversity makes them extremely resilient to fluctuating wastewater volumes and pollution levels, which is attractive in circumstances where operations experience peak periods a few times a year.

Another advantage of ETS is that they require virtually no maintenance (occasional pruning and weeding).

Whilst ETS are bespoke solutions designed to address specific requirements in particular sites, the one at Simon Howie Foods is a good example. The illustration above and photographs below will help understand the concept.

To accomodate planned, phased expansion, the ETS at Simon Howie Foods is made up of a parallel series of three wetland cells (approx. 5m wide, 10m long and 0.5m deep) planted with a succession of species, a coppiced willow cell and a wetland scrape. The first series of wetland cells were commissioned in 2007, whilst the second was planted (commissioned) during the summer of 2011. In total, there are over 13,000 plants, with 32 species of which 18 are willows.

As the effluent flows through the three wetland cells, it becomes progressively cleaner and over time, the vegetation and micro-organisms on each cell adapt to the characteristics of the incoming effluent. A willow cell removes nutrients not absorbed by the wetland cells and reduces the volume of water through evaporation and evapotranspiration. Any water not absorbed or evaporated in the Willow cell flows into a wetland scrape, the final cell in the system, where the more open environment and vegetation further maximise opportunities for evaporation and evaportranspiration.

Ecological Treatment System at Simon Howie's factory in Dunning. The established wetland cells are in the background (in front of the factory building & connifer cluster), whilst the recently planted first wetland cell in the second series is prominent in the foreground. Copyright Sustainable Food & Drink.

Ecological Treatment System  - vegetation detail (not at Simon Howie). Copyright Living Water.

Ecological Treatment System  - detail of vegetation on the second (established) wetland cell at Simon Howie.Copyright Sustainable Food & Drink.