Enhanced removal of refractory humic- and fulvic-like organics from biotreated landfill leachate by ozonation in packed bubble columns.

Biotreated landfill leachate contains much refractory organics such as humic and fulvic acids, which can be degraded by O3. However, the low O3 mass transfer and high energy cost limit its wide application in landfill leachate treatment. Previous studies proved that packed bubble columns could enhance the O3 mass transfer and increase the synthetic humic acids wastewater degradation, but the performance of packed bubble columns in real wastewater treatment has not been investigated. Therefore, this study aims to evaluate the feasibility of application of packed bubble column in the real biotreated landfill leachates treatment and provide insights into the transformation of organic matters in leachates during ozonation. Packed bubble columns with lava rocks or metal pall rings (LBC or MBC) were applied and compared with a non-packed bubble column (BC). At an applied O3 dose of 8.35 mg/(Lwater sample min), the initial COD (400 mg/L) was only removed for 26% in BC and 32% in MBC while this was 46% in LBC, indicating LBC has the best performance. GC-MS analysis shows that raw biotreated leachate contains potential endocrine disruptors such as di(2-ethylhexyl) phthalate (DEHP). 61% of DEHP was removed in LBC and the least intermediate oxidation products from humic- and fulvic-like organics was detected in LBC. The highest O3 utilization efficiency (89%) and hydroxyl radical (OH) exposure rate (3.0 × 10-10 M s) were observed in LBC with lowest energy consumption (EEO) for COD removal of 18 kWh/m3. The enhanced ozonation efficiency in LBC and MBC was attributed to the improved O3 mass transfer. Besides, LBC had additional adsorptive and catalytic activity that promoted the decomposition of O3 to generate OH. This study demonstrates that a packed bubble column increases removal and decreases energy use when treating landfill leachate, thus promoting the application of ozonation.

Roof runoff contamination: Establishing material-pollutant relationships and material benchmarking based on laboratory leaching tests.

Because roofs represent a major part of the urban impervious surface, it is hypothesized that roof runoff is an important source of urban stormwater contamination. However, the contribution of different roofing materials to this contamination has only been examined to a limited extent. In this study, a resource and time efficient methodology, which uses some of the principles of a standardized leaching test (CEN/TS16637-2), was developed to identify material-pollutant relationships for sixteen commonly used roofing materials (EPDM, PVC, TPO, EVA, PU and bitumen membranes). Metals were detected in concentrations ranging from several µg/L in the leachate of synthetic materials up to 2.5 mg/L for Zn in the leachate of EPDM materials. Cd and Cr were not detected in any of the leachates. Furthermore, polycyclic aromatic hydrocarbons were detected in most leachates, with phenanthrene and naphthalene being most frequently detected in concentrations up to 4.5 µg/L for naphthalene. Further insights on organic pollutants' leaching from the tested materials were obtained by a non-target GC-MS screening of the leachates. Several commonly used additives such as flame retardants and light stabilizers were detected. Although no information on long-term leaching and material behavior under outdoor conditions could be obtained by the developed methodology, the laboratory test results could be used to benchmark the materials for their potential impact on roof runoff quality by the calculation of material indexes (which summarize the material-pollutant relationships). EPDM and PU roofing materials were identified as the materials having the highest potential to affect roof runoff quality.