A review of the fate of engineered nanomaterials in municipal solid waste streams.

Significant knowledge and data gaps associated with the fate of product-embedded engineered nanomaterials (ENMs) in waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies. This review paper was developed as part of the activities of the IWWG ENMs in Waste Task Group. The specific objectives of this review paper are to assess the current knowledge associated with the fate of ENMs in commonly used waste management processes, including key processes and mechanisms associated with ENM fate and transport in each waste management process, and to use that information to identify the data gaps and research needs in this area. Literature associated with the fate of ENMs in wastes was reviewed and summarized. Overall, results from this literature review indicate a need for continued research in this area. No work has been conducted to quantify ENMs present in discarded materials and an understanding of ENM release from consumer products under conditions representative of those found in relevant waste management process is needed. Results also indicate that significant knowledge gaps associated with ENM behaviour exist for each waste management process investigated. There is a need for additional research investigating the fate of different types of ENMs at larger concentration ranges with different surface chemistries. Understanding how changes in treatment process operation may influence ENM fate is also needed. A series of specific research questions associated with the fate of ENMs during the management of ENM-containing wastes have been identified and used to direct future research in this area.

Characterisation of the recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of waste.

This study investigates the use of UV absorption and fluorescence spectroscopy to assess the early development of recalcitrant organic compounds in leachates formed during the anaerobic biodegradation of municipal solid waste. Biochemical methane potential tests were carried out on fresh waste (FW) and composted waste (CW) over a period of 150 days and leachates produced from the degradation of two wastes were analysed for humic-like (H-L) and fulvic-like (F-L) structures by UV spectroscopy and fluorescence excitation-emission-matrix analyses. During anaerobic biodegradation, the synthesis and utilization of H-L and F-L structures in the leachates over time was indicative of the generation of the recalcitrant organic compounds. The results obtained from UV absorption and fluorescence spectroscopy suggested that CW leachates resulted in a higher concentration and more condensed form of recalcitrant H-L and F-L molecules than FW leachates. These findings demonstrate how fluorescence and UV absorption spectroscopy can be used as an indicator for monitoring the evolution of recalcitrant organic compounds (H-L and F-L substances) in leachates formed at different stages of waste biodegradation.

A pilot-scale comparison of mesophilic and thermophilic digestion of source segregated domestic food waste.

Source segregated food waste was collected from domestic properties and its composition determined together with the average weight produced per household, which was 2.91 kg per week. The waste was fed over a trial period lasting 58 weeks to an identical pair of 1.5 m(3) anaerobic digesters, one at a mesophilic (36.5 degrees C) and the other at a thermophilic temperature (56 degrees C). The digesters were monitored daily for gas production, solids destruction and regularly for digestate characteristics including alkalinity, pH, volatile fatty acid (VFA) and ammonia concentrations. Both digesters showed high VFA and ammonia concentrations but in the mesophilic digester the pH remained stable at around 7.4, buffered by a high alkalinity of 13,000 mg l(-1); whereas in the thermophilic digester VFA levels reached 45,000 mg l(-1) causing a drop in pH and digester instability. In the mesophilic digester volatile solids (VS) destruction and specific gas yield were favourable, with 67% of the organic solids being converted to biogas at a methane content of 58% giving a biogas yield of 0.63 m(3) kg(-1) VS(added). Digestion under thermophilic conditions showed potentially better VS destruction at 70% VS and a biogas yield of 0.67 m(3) kg(-1) VS(added), but the shifts in alkalinity and the high VFA concentrations required a reduced loading to be applied. The maximum beneficial loading that could be achieved in the mesophilic digester was 4.0 kg VS m(-3) d(-1).