Veolia Water Technologies South Africa recently refurbished the upflow anaerobic sludge blanket (UASB) effluent treatment plant that processes effluent generated by Ceres’ Fruit Processors and Fruit Juices facilities in the Western Cape.
Having been in operation for more than 18 years, the plant was due for substantial preventative maintenance, beginning to show signs of overloading, acidification and biomass build-up. It required an overhaul of certain systems to ensure the plant could achieve its effluent discharge standard with maximum efficiency.
The UASB plant’s original design basis was to treat 3 574 m3/day of effluent with COD of 4 900mg/l for a 17.5 tonnes COD load/day together with a more than 80 per cent COD removal efficiency.
Having designed, supplied and commissioned the original plant, Veolia (then known as Envig (Pty) Ltd), has conducted regular scheduled maintenance and testing since the installation assumed operation in 1997.To ensure the effluent was still being treated efficiently according to the required standard, Ceres commissioned Veolia to conduct a full audit into the plant’s operation and performance in September 2014.
The results of this audit recommended overhauling the two digester compartments; refurbishment of the pre-treatment, hot water, gas recovery and chemical dosing systems; and replacing the parabolic screen to ensure biomass does not accumulate in the dams.
The most complex aspect of the refurbishment was the overhaul of the digester compartments, as an external inspection provided no meaningful information on its internal condition. The refurbishment of the digester compartments included seal systems, separation systems and gas offtake systems together with complex rigging, cranage and scaffolding inside the compartments.
These maintenance interventions have ensured that Ceres can continue to effectively treat a COD load which is 45 per cent higher than the original design (25.5 tonnes/day on average, peaking at 40 tonnes/day), together with exceptional COD removal efficiencies of 94 per cent.
The maintenance work was not allowed to disrupt any fruit processing at the factory and only two six-hour periods of zero flow to the effluent plant were allowed. Furthermore, only one UASB compartment was refurbished at a time.
The refurbishment was carried out by Veolia’s Engineered Systems division from the company’s recently-relocated Paarl office.