GOT International

The Big Clean-up
A sewage treatment plant isn’t exactly a venue for bird watching. But that was where a small band of GOT birders gathered one freezing Sunday morning in November. Not to spot birds, but to find out more about how our rivers and streams – critical habitat for hundreds of bird species -- are being fouled up, and the unceasing battle to save them.

At the forefront of this battle is the Consortium for the Defence of the Besos River Basin, an organisation which operates wastewater treatment plants on behalf of some 50 Catalan municipalities which lie within the watershed of the Besos and its five major tributaries, the Mogent, Congost, Tenes, Riera de Caldes, and Ripoll rivers.

The Besos at Santa Coloma  -- a truly spectacular transformation in one generation 

The Consortium was created in 1988, when it became evident that the management of the watershed, a vast area of 1038 sq km covering a 530km waterway network, had to be a collective, unified effort. That decision has paid off spectacularly: during the 1970s and 80s the Besos held the dubious honour of being the most contaminated river in Europe. Less than a generation later it has been transformed into one of the cleanest and best managed in the country.

The proper treatment of household sewage and wastewater from baths, showers, kitchens and sinks has played a principal role in this transformation, especially during the population boom and rapid urbanization of recent decades. Together with industrial and agricultural effluence, sewage pumped into the rivers became the scourge of river ecosystems and waterways. Within the Mediterranean region, it is one of the most critical environmental problems of the 21st century.

GOT members had a detailed insight into the situation during the tour of the Consortium’s wastewater treatment plant in Granollers, capital of the Valles Oriental County. The plants are called EDAR’s, acronym for Estacions Depuradores d’Aigües Residuals. Catalonia, with a population of over 7,000,000 has 387 wastewater treatment plants, 16 of which, serving some 360,000 inhabitants, are operated by the Consortium.

 At EDAR Granollers: Manel Isnard (4th from right) explaining how it all works

Our guide was Mr. Manel Isnard i Blanchar, the Consortium’s head of Fluvial Environment, who gave us some surprising statistics

·         EDAR Granollers caters for 94,200 people living in three municipalities: Les Franqueses, Canovelles and Granollers.

·         Construction of the plant, established in 1992,  cost €20.1 million, and it has a current annual operating expenditure of €1.1 million.

·         The plant also handles wastewater from 1,052 business establishments and factories.

·         There are 22,175 metres of sewers draining into the treatment plant.

·         EDAR Granollers has been producing an astonishing 8 million cubic metres of fully treated non-potable water annually in recent years. That represents an average of 21,917 cu. metres of ‘cleaned’ water each day, or 254 litres a second – and a large part of this water is released into the rivers to replenish the waterways and revitalise the ecosystem. Treated water has today become the lifeblood of the rivers.

·         Apart from treated water, EDAR Granollers annually produces about 6,399,000 kg of solid waste or sludge, which may be reused as fertilizer, and some 472,000 kg of oils, greases, gravel and sand, much of which end up in landfills.

How does the dirty water you flush down your toilet get cleaned before it’s pumped back into the rivers?

Manel Isnard explained that wastewater treatment is a relatively straightforward process designed to remove physical, biological and chemical contaminants present in raw sewage and effluent, a term which includes liquid waste from homes, industry and commercial activity. The objective: to produce environmentally-safe but non-potable water, and sludge which can be easily disposed of or reused.

What goes in: untreated waste water... 

Wastewater carried by sewers first enters the plant through steel-bar screens which trap and remove large objects like rags, wood, branches,  plastic and all the big stuff that get into the wastewater stream.

It then hits the grit chambers which allow smaller solids such as sand, grit and gravel to drop to the bottom. This is the preliminary treatment stage.

The filtered water is next channelled into huge circular sedimentation or settling tanks where it gets its primary treatment.  These tanks hold the water for several hours allowing solids that are suspended in the water to settle to the bottom. At the same time, surface skimmers remove lighter stuff like oils and grease which rise to the surface.

After this, secondary treatment begins. This involves a bit of biology – and a bunch of very tiny but very hungry creatures called microorganisms which love dining on dissolved solids.

As these microscopic megamunchers -- bacteria, fungi, algae, or protozoa -- eat away all day, everyday, ceaselessly, they bring about what is called biological conversion: transforming the dissolved solids into suspended solids, which can then be removed.

Some of the organisms are carnivorous, i.e. meat eaters; others are herbivores i.e. they’re strict vegans, while the in-betweens – the omnivores – go for either. They’re very small but very smart, and they know what they want, declared Manel Isnard with a grin.

A further step in secondary treatment involves adding oxygen into the wastewater and microorganism combination, which makes the microorganisms multiply and the process accelerated. The mixture then goes to a secondary sedimentation tank where the microorganisms and the now suspended solids are allowed to settle to the bottom before being removed.

...and what comes out: ‘cleaned’ water 

Chlorine is added at this stage to disinfect the water by killing off dangerous microorganisms. Finally, because chlorine is toxic to aquatic life,  the water is dechlorinated, and we obtain treated effluent which is pumped back into the environment.

What happens to the solids that have been removed?

The sludge or ‘biosolids’ at the very end of
the process. It is used either as fertilizer
or ends up in a landfill

Well, the trash and the  sand, grit and gravel collected at the initial stages are  sent to a landfill. The sludge or “biosolids” that settles to the bottom during the primary and secondary treatments undergoes various processes to squeeze out every drop of water it may contain. The final, dry product is either turned into fertilizer or sent to a landfill.

Manel Isnard assured us that every stage of the process called for careful monitoring, testing and control to make sure that what goes in comes out in a form that doesn’t upset the environmental balance.

End of story for EDAR Granollers? Not quite. One of the Consortium’s jobs is to educate both industry and the public on the dire consequences of river pollution, whether unconscious or intentional. It sponsors educational programmes at schools, sports and recreational clubs, civic centres and commercial and industrial institutions through talks, seminars, visits like the one made by GOT members, and technical workshops for universities and colleges.

Just as vital is its role as defender of the fluvial environment, drawing up plans and launching projects to improve the environment and protect the freshwater ecosystem.

One of its most ambitious projects is its collaboration in the restoration of the Can Cabanyes fluvial ecosystem. Can Cabanyes is an 80,000sq metre nature reserve through which the Congost River runs. EDAR Granollers lies just adjacent the nature reserve, on the east bank of the river.

The Can Cabanyes park seen  from the operations room of EDAR Granollers. In the background, surrounded a a thick row of trees,  are the upper stands of the Formula One  Circuit of  Catalunya.

For sometime now, the treatment plant has been diverting some of  its treated water from the river to previously polluted lakes and wetlands in Can Cabanyes, and studying how much the biological impact  of natural plant microorganisms in the wetlands would enhance the quality of the water and promote the growth of freshwater biodiversity.  The results have been encouraging, paving the way for similar projects elsewhere.

Manel Isnard made a clear distinction between the non-potable water which treatment plants produce, and potable water obtained from ‘purifying’ water from reservoirs.

At the moment we have two extremes, he noted: ‘pure’ water for drinking, and high quality treated water to be pumped back into the natural environment. In the future, he said, wastewater treatment may have to conform to a set of criteria different from what has been imposed upon treatment plants today.  This would allow for the production of multiple-level quality non-potable water to cater for the different needs of the community, industry and agriculture.

In a world where the threat of water shortages looms large, it doesn’t seem to make sense, he added, that we’re still using the purest water i.e. drinking water to flush our toilets.
Words & Pictures: Abul Fazil