The Cerro Gordo mill water treatment plant (WTP) has significantly improved its performance and treated water quality in 2011.
Since its start-up in 1994, the WTP attained good treatment levels to comply with federal regulations. However, the plant experienced periodic instabilities due to filamentous bacteria and recurring attacks of Nocardia, a very aggressive organism, which caused high levels of total suspended solids and forced complete evacuation of the microbiological sludge.
Initially, a programme using nutrients and enzymes was implemented to mitigate the instabilities. Then, the causes of the predominance of filamentous bacteria were identified. These causes were addressed through modifications of the primary treatment, adjustment of operational parameters and a new nutrient for better metabolism. Since January 2011, the nutrient is used on a regular basis. It rapidly promoted the growth of higher-order micro-organisms and increased treatment efficiency. COD reduction efficiency increased to 90% and the annual cost of nutrients has been reduced by 69% since 2008.