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In late 2009, Gurney Environmental Ltd. completed the installation of an internationally tendered, World Bank funded project to address wastewater processing issues in the city of Santa Cruz de la Sierra, Bolivia. The 2.5 million population city’s infrastructure is under stress due to significant population growth. The wastewater treatment plant (wwtp) had been in an overloaded condition resulting in low rates of processing, sludge accumulation and odour issues. The operations company, SAGUAPAC, owns and operates the wwtp, which is located in a northern suburb of the city.

The North wwtp utilises facultative lagoons of about 50 hectares and in 2009 received a flow of 34,000 m3/day and a BOD load of 3,400 kg/day. The aerial loading on the two primary facultative lagoons averaged 249 kg BOD/hectare/day. With a complete lack of dissolved oxygen (DO) in the water column, the wwtp was suffering from odour and processing problems.

Normally SAGUAPAC would have constructed more lagoons to increase treatment capacity but as no land was available at this wwtp (being hemmed in on all sides by the city’s encroachment) another option was needed. In similar situations in other parts of the world, a more mechanised method of wastewater treatment, such as activated sludge for instance, might have been chosen, but this was not deemed cost effective or sustainable.

Instead, a Gurney Environmental Accel-o-Fac® design and equipment upgrade was installed as shown on the General Arrangement drawing. Within 6 weeks of commissioning, the lagoons established a positive DO content – the first time this had happened. The odour had dissipated and the processing rates and treatment performance increased significantly. The lagoons continued to operate at pre installation flows and loadings and maintained a good DO level throughout with a healthy green colour as would be expected.

In order to be able to keep up with the increasing wastewater flows, during 2010 SAGUAPAC gradually increased the wastewater loading on the primary lagoons up to about 1.7 times pre installation levels, at which point the lagoons started to lose their colour and the DO levels dropped off, albeit no odour resulted. SAGUAPAC has since reduced the loading to about 1.5 times pre installation levels and has elected to operate the lagoons under these conditions ever since.

The Accel-o-Fac® system has provided an overall improvement in lagoon treatment capacity enabling a 50% increase in flow throughput with only a modest expense in equipment and a negligible increase in operating costs. Compared with alternatives, Accel-o-Fac® offered best value for money and through the use of the abundant winds, the most sustainable upgrade option.