Partitioning of nutrients and micropollutants along the sludge treatment line: a case study

Abstract

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.

Behavior of PBTC, HEDP, and Aminophosphonates in the Process of Wastewater Treatment

“…Primary sludge is known to contain metals in precipitated, insoluble form: Calcium with >20,000 mg/kg is the most abundant metal in primary sludge [22]. Aluminum and iron follow with contents generally at 4500 mg/kg-14,000 mg/kg [23], followed by Zn, Mn, Cu, Pb, and Cr between 10 mg/kg and 1000 mg/kg each [24]. Phosphonates adsorb preferably on mineral surfaces such as calcite [25], aluminum oxide [26], iron oxide [10], zinc oxide [27], and hydroxyapatite [28].…”

Land Application of Biosolids in Europe: Possibilities, Con-Straints and Future Perspectives

“…The average content of total N, total P and total K in digested sludge is reported to be around 4.7% dw, 2.3% dw and 0.3% dw, respectively [2]. The agricultural benefit and environmental acceptability of sludge utilization in agriculture is well documented [2][3][4]. Therefore, sewage sludge could represent a renewable source of phosphorus, since white phosphorus (P 4 ) and phosphate rock are included among the 20 critical raw materials (CRM) for the EU, as reported in the "Report on critical raw materials for the EU" released by the European Commission in 2017 [5].…”

Enhanced Versus Conventional Sludge Anaerobic Processes: Performances and Techno‐Economic Assessment

“…A sustainable sewage sludge management system for largesize water resource recovery facilities (WRRFs), might be attained through a separation of primary and secondary sludge before their treatment and disposal. It would thus be possible to maintain agricultural utilization for waste activated sludge (WAS) and to convert to inert material by thermal treatments only primary, more polluted, sludge (Gianico et al, 2013a;Mininni et al, 2004;Winter and Pearce, 2010). Sludge originating from WRRFs could contain pathogens and represents a health hazard to the general public (Sidhu and Toze, 2009).…”