Gilbert Y.S. Chan

Characteristics of bioaerosol profile in office buildings in Hong Kong

Abstract A series of bioaerosol measurements have been conducted at two typical offices in Hong Kong for both a 4-day and a weekly period. Both the investigated offices were installed with heating ventilation and air-conditioning (HVAC) systems coupling with air handling units and fan coil units. Measurements were performed starting from early morning by the Anderson N6 impactor. The primary objectives of these measurements were to determine the temporal concentration profile of bioaerosol inside office environments during office hours, and to determine the effects of air change rate on the concentration profile. The highest bacteria concentrations were recorded to be 2912 CFU/m3 at the early morning hours during the starting-up period of HVAC systems. The highest fungi concentrations were recorded to be 3852 CFU/m3 during the weekend mornings. The results of studies also revealed that the air change rate inside the office environment had less significant effects than filtration on airborne bioaerosols. The background fungi concentration was found to have strong correlation with the indoor relative humidity level provided that the relative humidity level could be maintained for a certain period of time. Of the sampled bacteria 80% were found to be gram positive, while the dominating genera of fungi was found to be Cladosporium and Penicillium.

Biological processes for treatment of landfill leachate

This review presents an overview with critical analysis of the technical applicability of biological treatments for landfill leachate. A particular focus is given to activated sludge (AS), sequencing batch reactors (SBR), aerated lagoons (AL), and upflow anaerobic sludge blankets (UASB). Their advantages and limitations in application are evaluated. Selected information is presented such as pH, hydraulic retention time (HRT), organic loading rate (OLR), characteristics of leachate and treatment performance. It is evident from the literature survey of 188 papers (1976-2010) that none of the individual biological treatments presented is universally applicable for removing recalcitrant contaminants from leachate. Among the biological treatments reviewed, AS, SBR and UASB are the most frequently applied. These treatments are effective not only to remove over 90% of COD with a concentration ranging from 3500-26 000 mg L(-1), but also to achieve 80% of NH(3)-N removal with a concentration ranging from 100-1000 mg L(-1). A combination of physico-chemical and biological treatment into an integrated process is effective for leachate treatment. Almost complete removal of COD and NH(3)-N was reported for combined reverse osmosis (RO) and UASB with an initial COD concentration of 35 000 mg L(-1) and NH(3)-N concentration of 1600 mg L(-1). Integrated Fentons oxidation and AS could achieve about 98% and 99% of COD and NH(3)-N removal, respectively, with initial COD and NH(3)-N concentrations of 7000 mg L(-1) and 1800 mg L(-1). Overall, the selection of the most suitable treatment for leachate depends on its characteristics, technical applicability and potential constraints, effluent limit required, cost-effectiveness, regulatory requirements and long-term environmental impacts.

Organophosphorus pesticide ozonation and formation of oxon intermediates

In the present study, organophosphorus pesticides (OPs) (diazinon, methyl parathion, and parathion) were oxidized by bubbling ozone into a glass reactor. OP residues were detected using HPLC and ozonation intermediates were identified using GC-MS. The degradation of OPs followed pseudo-first-order kinetics through direct ozone oxidation and indirect hydroxyl radical oxidation. Diazinon, based on its relatively higher degradation constant, was easily degraded by ozonation. Increasing the pH of the solution accelerated diazinon degradation, but little effect was observed for methyl parathion or parathion. Diazoxon, methyl paraoxon and paraoxon were identified as ozonation intermediates of diazinon, methyl parathion and parathion, respectively. The ozonation of the PS group results in the formation of oxon intermediates, which suggests that OPs with this group would be degraded in a similar manner to that seen for the OPs tested in this study. Diazoxon was completely decomposed by ozonation in 30min, while trace methyl paraoxon and paraoxon accumulated to different amounts when the solution pH was varied. The presence of oxon intermediates should be noted in OP removal by ozonation.

Growth response of Sesbania rostrata and S. cannabina to sludge-amended lead/zinc mine tailings. A greenhouse study.

Legumes are ideal for revegetation of metal-mined wastelands which lack nitrogen (N). A greenhouse study was conducted to investigate the feasibility of using Sesbania rostrata and S. cannabina for the reclamation of lead/zinc (Pb/Zn) mine tailings and to evaluate the effects of organic amendment using sewage sludge (0%, 25%, 50%, and 75%, v/v). The results showed that both species could continue to grow on the highly toxic tailings substrata for at least 80 days, although their growth suffered from adverse effects. That S. rostrata with stem and root nodules had better growth (biomass, growth rates, and biomass of nodules) than S. cannabina suggested that S. rostrata is a better choice as a pioneer species for revegetation of the mine tailings. Stem nodules had less obvious adverse effects imposed by tailings than root nodules. Application of sewage sludge increased contents of total carbon (C), N, phosphorus (P), and potassium (K), and reduced total Zn, Pb, Cd, and DTPA-extractable Pb and Cd in tailings substrata. These, in turn, reduced metal (Zn, Pb, and Cd) uptake and accumulation in plant tissues, and improved plant growth performance, including biomass, growth rates, stem nodulation. Fifty percent (v/v) of sludge application rate was the best loading rate for plant growth.

Nitrous oxide flux from landfill leachate-sawdust nitrogenous compost

Composted nitrogenous waste has the potential to produce excessive amounts of nitrous oxide (N2O), a potent greenhouse gas that also contributes to stratospheric ozone depletion. In this laboratory study, sawdust was irrigated with varying amounts of landfill leachate with high NH4+-N content (3950 mg l(-1)). Physicochemical properties, including the amount of N2O produced, were monitored during the composting process over 28 days. A rapid decline in NH4+-N in the first 4 days and increasing NO3--N for 11 days was followed by lower but stabilized levels of available-N, even with repeated leachate irrigation. Less than 0.03% of the leachate-applied N was lost as N2O. Higher leachate applications as much as tripled N2O production, but this represented a lesser proportion overall of the total nitrogen. Addition of glucose to the composting process had no significant effect on N2O production. The derived sawdust-leachate compost supported healthy growth of Sesbania rostrata. It is concluded that compost can be produced from sawdust irrigated with landfill leachate without substantial emission of N2O, although excessive flux of N2O remains about high application rates over longer time periods.