Lessons in keeping a low wastewater profile
Générale des Eaux must have wondered whether its efforts to construct a WwTP that would comply fully with the EU Urban Wastewater Treatment Directive (UWWTD) and satisfy the demands of residents of the wealthy resort town would ever bear fruit. Nine years after its completion, Antibes STP remains one of Générale des Eaux's greatest French success stories.
In fact, the entire 2.5ha site is subject to a long-term landscaping programme that, crucially, involves regular inspections. Although the site is not easily visible from the beach (which holds an EU Blue Flag certification for water quality), it is overlooked by several large homes. The landscaping programme is in place largely to satisfy the demands of these neighbours. More than 100 native species have been planted; misleading people into choosing the site for their picnic lunches.
The station also fully complies with the UWWTD. Treating 9Mm3 of water per year, the WwTP has a 1.6km outfall pipe and employs both secondary and tertiary - that is, biological - treatments.
In winter, the amount of wastewater treated averages at 30,000m3/day, and in summer it rises to 35-40,000m3/day. An average of 90% of COD is eliminated during the summer and more than 90% of suspended solids. In winter, treatment standards require an average of 70% elimination of COD, and more than 70% elimination of suspended solids.
Despite meeting EU standards, Jay and her staff are not resting on their laurels. Most recently, they've responded to a request from Antibes to improve treatment further. From this winter, wastewater will be treated to the summer standard all year around.
With EU compliance part of the plant's initial design, the next stage in environmental improvement involved preparing for and receiving ISO 14001 certification. With an environmental management system (EMS) as ISO 14001's main feature, a decision was taken to pass up ISO 9000 certification in lieu of ISO 14001. In September 1996, after a year of compiling documentation, the Antibes STP became the first public water works to be awarded ISO 14001 certification anywhere in the world, and staff have succeeded in renewing the certificate. "Initially, it was expensive," admits Jay, referring to the year's preparation. But, according to Jay, it was worth it. "This is one of the most efficient plants in the region and since the ISO procedures have been in place operational costs have reduced."
Options for sludge disposal
With a tailor-made EMS in place, environmental targets and procedures were laid out. Five priorities were identified. They were:
- Constant wastewater treatment performances despite increase in users and decrease in non conformities
- Decrease in the number of odour incidents and decrease in H2S discharge
- Reduction by 3 decibels of noise recorded and decrease in the number of noise claims
- At least 25%, aiming for 29%, siccity level for sludge quality
- Maintenance of grounds inspected by an expert
- Constant maintenance of the building and impact assessment for every modification
What to do with sludge is an issue that will only become more pressing in future. With residents fighting plans for a new landfill site and construction of an incinerator still four to five years away, it isn't the ISO environmental target alone that has led Jay to investigate sludge recycling. In addition to recycling and incineration possibilities, giving sludge away to farmers is also on trial. Since 1998, 2000 of the 9000t of sludge produced annually has been transported 150km - having undergone 20% dehydration - by lorry to Rhöne valley farmers. But farmers are increasingly concerned that sludge may be seen to pose a health risk, and Jay knows that sludge disposal - already one third of the plant's operating budget - is an issue that won't solve itself.
With space constraints and odour control as priorities, the Antibes plant makes use of two OTV innovations. Sedimentation tanks are inclined and ridged to achieve a surface area seven times greater than a classic tank.
More importantly, from the neighbours' point of view, is the deodorization system. All new urban STPs served by Générale des Eaux incorporate air treatment, but Antibes was the first to employ it. Air leaving the plant through one of two towers filled with rings. The rings increase the surface area to 500m2 per tower, allowing a capacity of 50,000m2 per hour. Air is treated in three hours and involves:
- Sulphuric acid to treat ammonia odour
- Chlorine to treat sulphur odour
- Removal of odours created during treatment
- Release of air through silencers