Nutrient recovery in wastewater treatment plants: comparative assessment of different technological options for the metropolitan region of Buenos Aires.

Abstract

In the metropolitan region of Buenos Aires, the load of nutrients discharged to urban rivers and shores is producing a severe eutrophication problem in the estuary of La Plata River. That problem could be alleviated by recovering nitrogen (N) and phosphorus (P) through the production of fertilizer products in the existing activated sludge treatment plants. Four nutrient recovery options were considered: struvite precipitation in the centrate line; acidic leaching of the sludge followed by struvite precipitation of the centrate; Ion Exchange in the centrate line; and a combination of struvite precipitation in the centrate line plus an Ion Exchange unit to further polish the secondary effluent. Those options were compared with basis on their economic sustainability and their capacity to reduce the load of N and P discharged to the coastal waters and rivers. The economic assessment indicated that producing fertilizer products in the existing facilities, using the four considered options, would be unprofitable. In the best case, which is struvite precipitation in the centrate line, the potential revenues would only cover 38.5 % of the operational expenses. Environmental benefits could justify that cost, as in some urban rivers the load of P could be reduced by 42.5 % by struvite precipitation. Regarding the load of nutrients that is discharged to the estuary, the impact of the considered nutrient recovery options ranges from a decrease in 0.5 % N and 3.7 % P (struvite precipitation) to a decrease in 8.2 % N and 4.4 % P (combination of struvite precipitation + Ion Exchange).