Water chemistry influences on long-term dissolution kinetics of CdSe/ZnS quantum dots.

Widespread usage of engineered metallic quantum dots (QDs) within consumer products has evoked a need to assess their fate within environmental systems. QDs are mixed-metal nanocrystals that often include Cd2+ which poses a health risk as a nanocrystal or when leached into water. The goal of this work is to study the long-term metal cation leaching behavior and the factors affecting the dissolution processes of mercaptopropionic acid (MPA) capped CdSe/ZnS QDs in aphotic conditions. QD suspensions were prepared in different water conditions, and release of Zn2+ and Cd2+ cations were monitored over time by size exclusion chromatography-inductively coupled plasma-mass spectrometry. In most conditions with dissolved O2 present, the ZnS shell degraded fairly rapidly over ~1 week, while some of the CdSe core remained up to 80 days. Additional MPA, Zn2+, and Cd2+ temporarily delayed dissolution, indicating a moderate role for capping agent detachment and mineral solubility. The presence of H2O2 and the ligand ethylenediaminetetraacetate accelerated dissolution, while NOM had no kinetic effect. No dissolution of CdSe core was observed when O2 was absent or when QDs formed aggregates at higher concentrations with O2 present. The shrinking particle model with product layer diffusion control best describes Zn2+ and Cd2+ dissolution kinetics. The longevity of QDs in their nanocrystal form appears to be partly controlled by environmental conditions, with anoxic, aphotic environments preserving the core mineral phase, and oxidants or complexing ligands promoting shell and core mineral dissolution.

Co-composting of oil-based drilling cuttings by bagasse.

The feasibility of using a locally abundant bulking material (sugarcane bagasse) in Khuzestan province, Iran, to remove petroleum hydrocarbons from oil-based drill cuttings (OBDCs), using composting process, was investigated. OBDCs were collected from the discharge point of a drilling rig and bagasse was collected from a sugarcane agro-industry near Ahwaz. Experiments were performed in the dark and at room temperature, using different bagasse to OBDCs ratios. Degradation extent and kinetics of total petroleum hydrocarbons (TPHs) and poly aromatic hydrocarbons (PAHs), as well as dehydrogenase and urease enzymes activities and number of heterotroph bacteria during the co-composting of OBDCs and bagasse were studied and measured. Highest PAHs and TPH removals were observed when OBDCs were composted with 15% bagasse. After 70 days of incubation, PAHs and TPH were removed up to 24.8% and 67.5%, respectively. Studying the enzymes activities and number of heterotrophs with TPH and PAHs concentrations over time suggests that biodegradation is the main mechanism in the degradation process. The first-order kinetic model was fitted to the TPH and PAHs degradation data and contaminants half-lives were estimated to be in the range of 40-80 and 170-240 days respectively. DT90 values for TPH and PAHs were in the range of 120-260 and 560-1260 days, depending on the bagasse content.

Attenuation of tetracyclines during chicken manure and bagasse co-composting: Degradation, kinetics, and artificial neural network modeling.

The main objective of this study was to investigate the feasibility of using a locally abundant bulking material (bagasse) in the composting process to remove tetracycline from chicken manure in Khuzestan Province, Iran. Degradation extent and kinetic of three types of tetracycline (tetracycline hydrochloride (TCH), chlortetracycline (CTC), and oxytetracycline (OTC)) during co-composting of chicken manure and bagasse were investigated. After 56 days of incubation in the dark and room temperature, TCH, CTC, and OTC were removed up to 99.0%, 99.3%, and 99.5%, respectively. Highest Tetracyclines (TCs) removals were observed when chicken manure was composted with 14% bagasse. Both simple and availability-adjusted first-order kinetic models fitted TCH, CTC, and OTC degradation data. Half-lives estimated by both models were close together. TCH, CTC and OTC half-lives were estimated to be 8, 5, and 4 days, respectively. An artificial neural network model was developed to model TCs degradation. Artificial neural network analysis showed the relative importance of time, antibiotic type, bagasse percentage, and initial antibiotics concentration, in TCs degradation to be 80.43%, 7.95%, 6.43%, and 5.17%, respectively.

Composting plant leachate treatment by a pilot-scale, three-stage, horizontal flow constructed wetland in central Iran.

Handling and treatment of composting leachate is difficult and poses major burdens on composting facilities. The main goal of this study was to evaluate usage of a three-stage, constructed wetland to treat leachate produced in Isfahan composting facility. A pilot-scale, three-stage, subsurface, horizontal flow constructed wetland, planted with vetiver with a flow rate of 24 L/day and a 15-day hydraulic retention time, was used. Removal of organic matter, ammonia, nitrate, total nitrogen, suspended solids, and several heavy metals from Isfahan composting facility leachate was monitored over a 3-month period. Constructed wetland system was capable of efficiently removing BOD5 (87.3%), COD (74.5%), ammonia (91.5%), nitrate (87.9%), total nitrogen (87.8%), total suspended solids (85.5%), and heavy metals (ranging from 70 to 90%) from the composting leachate. High contaminant removal efficiencies were achieved, but effluent still failed to meet Iranian standards for treated wastewater. This study shows that although a three-stage horizontal flow constructed wetland planted with vetiver cannot be used alone to treat Isfahan composting facility leachate, but it has the potential to be used as a leachate pre-treatment step, along with another complementary method.