Sustainable sewage sludge management based on separate processing of primary and secondary sludge
Mininni, G., Braguglia, C.M., Mascolo, G. and Gianico, A., CNR – Istituto di Ricerca Sulle Acque, Italy
(free)
The objective of this work is to demonstrate that a more sustainable management of sewage sludge can be attained through a separation of primary and secondary sludge treatment. In fact secondary sludge, normally poorer in pollutants than primary sludge, should be segregated and treated separately from primary sludge to increase chances of secondary sludge utilisation in agriculture. Most organic micropollutant load of sewage may be associated with suspended solids and therefore are mainly removed in primary sludge. If such a primary sludge is blended with secondary one it may render the mixed sludge no longer acceptable for agricultural use.
Moreover, secondary sludge may be richer in nitrogen and phosphorus with consequent better profit for crops which need less amount of sludge for balancing nutrients requirement.
It would thus be possible to maintain agricultural utilisation for the biological sludge (secondary) and to dispose only the primary sludge. The advantages of this innovative sludge management system are therefore specifically linked to sludge final outlets, with consequent considerable cost reduction.
Primary and secondary sludge were sampled from two urban WWTPs in the Lazio region. Results showed that secondary sludge was always richer in nitrogen and phosphorus. Organic micropollutants (anionic surfactants, extractable organic halogens (EOX) and total hydrocarbons C10-C40) were mostly adsorbed on primary sludge for both the WWTPs, supporting the hypothesis of a “cleaner” secondary sludge suitable for reuse.
No significant differences in heavy metals content were instead monitored between primary and secondary sludge in the two WWTPs, being the concentrations significantly lower with respect to the limit values suggested by EU for agricultural use.
