The City of Ayacucho is located in the south-central Andean region, about 600 km south-west of the capital Lima, and is the capital of the province of the same name. Its altitude is 2,760 m above the sea.
The existing wastewater treatment plant was started up in 1974 and provided with a manually raked bar screen, a grit trap, two Imhoff tanks and a pair of non-aerated lagoons. During 1999 the author, working for Consulting Engineers Salzgitter GmbH (CES), designed new trickling filters and maturation ponds. He also designed upgrading of the mechanical pre-treatment with automatically raked screens and new grit chambers. He specified three step screens with 6 mm spacing.
The responsible officer of the regulatory authority in Lima did not approve the design specifications of the step screen. He was convinced it would not work and argued that there was not a single self-cleaning screen in Peru. A step screen would not be able to automatically remove 2 m³/d screenings and the personnel would not be able to operate and maintain such screens properly. After long negotiations, finally two step screens and a screw conveyor as well as their installation and operator training were specified in the tender documents.
HUBER supplied, installed and started up two Step Screen®s SSF 4000 and a screw conveyor Ro 8t together with the control panel in February 2004 and trained the operators for 10 days. The system was officially commissioned in May 2004. In June HUBER replaced a defective PLC in the control panel as part of their warranty. Since our Step Screen®s have been operating for over 16,000 hours and remove an average of 3 m³/d of screenings.
After two and a half years the operators are very happy with our equipment and particularly our technical support. After this long and good operator experience with our first reference system in this country, the regulating officers in Lima are now even recommending step screens for mechanical pre-treatment. It took a long time to take this hurdle.
by Luis Guijarro, Consulting Engineer of CES