Partitioning of nutrients and micropollutants along the sludge treatment line: a case study
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A 2-year sampling campaign was conducted in three wastewater treatment plants of various sizes in the Rome area to assess the occurrence of nutrients and micropollutants among primary, secondary and digested sludge. The primary purpose was to evaluate the quality of different sludge types and their suitability for agricultural use. Primary sludge was consistently more polluted than secondary in terms of organic micropollutants, whereas heavy metals partitioned equally among the sludge types. In digested sludge, the heavy metal concentrations were always below limit values proposed for agricultural utilisation. In contrast, organic micropollutants concentrated during anaerobic digestion and affected the quality of the digested sludge. Secondary sludge resulted less polluted and richer in nitrogen and phosphorus (up to three times) than primary sludge and is hence more suitable for agricultural use. Separate processing of primary and secondary sludge might therefore be an innovative option for sludge management that could maximise the possibilities of agricultural use of secondary sludge and limit disposal problems only to primary sludge. In fact, primary sludge could be easily treated and disposed of by conventional processes including thickening, anaerobic digestion, centrifugation and incineration, whereas the difficult digestibility of secondary sludge could be improved by disintegration pre-treatment before stabilisation.
KeywordsSewage sludge Nutrients Agriculture Heavy metals Organic micropollutants Sludge separation
This research activity was funded by the European FP6 project Neptune (http://www.eu-neptune.org/index_EN) “New Sustainable Concepts and Processes for Optimisation and Upgrading Municipal Wastewater and Sludge Treatment.”
The monitoring campaign of the Italian WWTPs was conducted with the kind assistance and cooperation of ACEA s.p.a., the Municipal Agency for Electricity and the Environment.
The micropollutant analyses were performed in kind cooperation with Domenico Mastroianni, Giuseppe Bagnuolo and Ruggero Ciannarella at IRSA-CNR of Rome and Bari, respectively.
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