Nitrogen Isotope Fractionation during Composting of Sewage and Agri-Food Sludge with Pruning Waste

Abstract

This work studies the changes in δ15N signature during the composting of sewage sludge (MS) and agri-food sludge (AS) with different bulking agents and the potential relationships between the changes in this parameter with both the source of the organic matter used as a raw material and the stability of the end-materials obtained. For this, eleven mixtures were prepared in commercial composting conditions using sewage sludge from municipal wastewater in a range of 60–85% (on a fresh weight basis) or agri-food sludge in a range of 65–75%, mixed with seven different pruning wastes as bulking agents. The thermal profile was monitored throughout the composting processes, and the main physico-chemical and chemical parameters were determined. The results obtained confirmed a correct development of the composting processes, observing slight differences in process evolution depending on the type of sludge used. The composts obtained showed adequate contents of nitrogen, phosphorus and potassium (NPK) and reached a good degree of maturity. Significant differences in the specific nitrogen isotopic composition were found in the initial materials. Moreover, the results suggest that the type of sludge had a main contribution in the δ15N value of the initial composting mixtures. The use of δ15N is recommended as an indicator of the composting process, especially to evaluate N dynamics, and the quality of the resultant compost.

Management of Green Waste Streams from Different Origins: Assessment of Different Composting Scenarios

“…The pruning wastes also showed similar physicochemical properties to sea plant wastes, but the contents of organic matter were higher in these wastes, also having greater concentrations of the main macronutrients (NPK). On the other hand, sewage sludge showed an acidic pH, lower salinity than most green wastes considered, and the highest concentrations of N and P, with values within the usual ranges for sewage sludge samples, as reported by Sáez et al [12]. A total of five composting heaps (Table 2) were developed at the composting pilot plant (CompoLab) of the EPSO campus of the Miguel Hernández University, located in Orihuela (Alicante, Spain).…”

Evolution of Composting Process in Maize Biomass Revealed by Analytical Pyrolysis (Py-GC/MS) and Pyrolysis Compound Specific Isotope Analysis (Py-CSIA)

“…It is known that, after fixation by primary producers, the stable isotope composition of light major elements C and N in organic matter varies with decay or decomposition, and this feature can be used to study biomass evolution during composting [24,25]. Normally, N is progressively enriched in the heavy isotope, and δ 15 N values increase with the composting process [26], whereas a δ 13 C depletion has been usually observed during composting [14].…”