Effect of operational factors on bioregeneration of binary phenol and 4-chlorophenol-loaded granular activated carbon using PVA-immobilized biomass cryogels

The effects of dry biomass density in cryogel beads, shaking speed and initial concentration ratio of phenol to 4-chlorophenol (4-CP) on the bioregeneration efficiencies of binary phenol and 4-CP-loaded granular activated carbon (GAC) for phenol and 4-CP, respectively, were investigated under the simultaneous adsorption and biodegradation approach. The results revealed higher bioregeneration efficiencies of binary-loaded GAC for phenol and 4-CP at higher dry biomass density but moderate shaking speed. The optimum dry biomass density in cryogel beads and shaking speed for use in bioregeneration were found to be 0.01 g/mL and 250 rpm, respectively. With respect to the initial phenol to 4-CP concentration ratio, the bioregeneration efficiencies were lower under increasing phenol and 4-CP initial concentrations, respectively, with the effect being more conspicuous under increasing 4-CP concentration. Higher bioregeneration efficiencies were achieved with the use of immobilized rather than suspended biomasses.     

Effect of water content on transient nonequilibrium NAPL-gas mass transfer during soil vapor extraction

The effect of water content on the volatilization of nonaqueous phase liquid (NAPL) in unsaturated soils was characterized by one-dimensional venting experiments conducted to evaluate the lumped mass transfer coefficient. An empirical correlation based upon the modified Sherwood number, Peclet number, and normalized mean grain size was used to estimate initial lumped mass transfer coefficients over a range of water content. The effects of water content on the soil vapor extraction SVE process have been investigated through experimentation and mathematical modeling. The experimental results indicated that a rate-limited NAPL-gas mass transfer occurred in water-wet soils. A severe mass transfer limitation was observed at 61.0% water saturation where the normalized effluent gas concentrations fell below 1.0 almost immediately, declined exponentially from the initiation of venting, and showed long tailing. This result was attributed to the reduction of interfacial area between the NAPL and mobile gas phases due to the increased water content. A transient mathematical model describing the change of the lumped mass transfer coefficient was used. Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization. The nonequilibrium mass transfer limitations were controlled by the soil mean grain size and pore gas velocity, were well described by beta values below 1.0 at low water saturation, and were well predicted with beta values greater than 1.0 at high water saturation.     

Impact of ozone assisted ultrasonication pre-treatment on anaerobic digestibility of sewage sludge

Impact of ultrasonication(ULS) and ultrasonication–ozonation(ULS-Ozone) pre-treatment on the anaerobic digestibility of sewage sludge was investigated with semi-continuous anaerobic reactors at solid retention time(SRT) of 10 and 20 days. The control, ULS and ULS-Ozone reactors produced 256, 309 and 348 m L biogas/g CODfedand the volatile solid(VS) removals were 35.6%, 38.3% and 42.1%, respectively at SRT of 10 days. At SRT of20 days, the biogas yields reached 313, 337 and 393 m L biogas/g CODfedand the VS removal rates were 37.3%, 40.9% and 45.3% in the control, ULS and ULS-Ozone reactors, respectively.ULS-Ozone pre-treatment increased the residual organic amount in the digested sludge.These soluble residual organics were found to contain macromolecules with molecular weights(MW) larger than 500 k Da and smaller polymeric products with MW around 19.4and 7.7 k Da. These compounds were further characterized to be humic acid-like substances with fluorescent spectroscopy analysis.     

Nitrous oxide emission by denitrifying phosphorus removal culture using polyhydroxyalkanoates as carbon source

Nitrous oxide (N₂O) emission has been reported to be enhanced during denitrification when internally-stored compounds are used as carbon sources. However, negligible N₂O emissions have been detected in the few studies where polyhydroxyalkanoates (PHA) were specifically used. This study investigated and compared the potential enhancement of N₂O production, based on utilization of an internally-stored polymer and external carbon (acetate) by a denitrifying phosphorus removal culture. Results indicated that at relatively low chemical oxygen demand-to-nitrogen (COD/N) ratios, more nitrite was reduced to N₂O in the presence of an external carbon source as compared to an internal carbon source (PHA). At relatively higher COD/N ratios, similar N₂O reduction rates were obtained in all cases regardless of the type of carbon source available. N₂O reduction rates were, however, generally higher in the presence of an internal carbon source. Results from the study imply that when the presence of an external carbon source is not sufficient to support denitrification, it is likely competitively utilized by different metabolic pathways of denitrifying polyphosphate accumulating organisms (DPAOs) and other ordinary denitrifiers. This study also reveals that the consumption of PHA is potentially the rate-limiting step for N₂O reduction during denitrification.     

Fetal methylmercury exposure as measured by cord blood mercury concentrations in a mother-infant cohort in Hong Kong

This study was designed to examine newborn infants in Hong Kong prenatally exposed to levels of methylmercury considered to increase risk of neurotoxic effects and to examine subject characteristics that modify the degree of prenatal mercury exposure. Mercury concentrations in 1057 sets of maternal and cord blood samples and 96 randomly selected maternal hair samples were measured. Subject characteristics were measured or collected by questionnaire. Of the 1057 cord blood samples collected only 21.6% had mercury concentrations less than 29 nmol/L (5.8 micro g/L). Median maternal hair mercury concentration was 1.7 ppm. The geometric mean cord to maternal blood mercury ratio was 1.79 to 1. Increasing maternal fish consumption and maternal age were found to be associated with increased cord blood mercury concentrations. Marine fish consumption increased cord blood mercury concentrations more than freshwater fish (5.09%/kg vs 2.86%/kg). Female babies, maternal alcohol consumption and increasing maternal height were associated with decreased cord blood mercury concentrations. Pregnant women in Hong Kong consume large amounts of fish and as a result, most of their offspring have been prenatally exposed to moderately high levels of mercury. In this population, pregnant women should choose freshwater over marine fish and limit fish consumption.     

Determination of effects of turbulence flow in a cathode environment on electricity generation using a tidal mud-based cylindrical-type sediment microbial fuel cell

We examined the possibility of harvesting electricity from the surface of a tidal mud flat using a cylindrical-type sediment microbial fuel cell (SMFC), a marine mud battery (MMB), which can be applied in a sea environment where the ebb and flow occur due to tidal difference. In addition, we indirectly investigated the influence of ebb and flow in a lab, using aeration, argon gassing, and by agitating the cathodic solution. The MMBs consisted of cylindrical acrylic compartments containing a nylon membrane, an anode, and a cathode in a single body. The MMBs were stuck vertically into an artificial tidal mud flat such that the anode electrode was in direct contact with the tidal mud surface. As a result, the maximum current and power density generated were 35 mA/m² and 9 mW/m², respectively, thus verifying that it is possible to harvest electricity from the surface of a tidal mud flat using an MMB without burying the anode electrode in the tidal mud. Furthermore, the results of tests using an artificial turbulence flow showed the flow induced by the tidal ebb and flow could allow the performance of MMBs to be enhanced.     

Fines migration from soil daily covers in Hong Kong landfills

Laboratory tests using 240 mm diameter columns were conducted to study fines migration in conditions that simulate daily soil covers in Hong Kong municipal solid waste landfills. Five factors suspected to affect fines migration were examined: moisture content at soil compaction, overburden pressure, pumping rate, cover thickness, and soil-waste interface condition. The results show that moisture content at compaction, cover thickness, and soil-waste interface are the most influential parameters on fines migration in completely decomposed granite daily covers. The measured equivalent sizes of migratory fines from the soil covers were in the range of 4–140 μm. The majority of migratory fines migrated during first permeations, representing 64–86% of the total by mass. Larger particles tended to migrate from the soil mass during the saturation process. In a typical run, about 0.0018% of the total cover soil (by dry weight) was washed out during a typical 1 h rainfall event. The results of the laboratory studies point to important engineering implications on the operation of local MSW landfills regarding the use of sandy daily covers.     

Respiratory Suspended Particulate (RSP) Concentration and its Implications to Roadside Workers: A Case Study of Hong Kong

The adsorption behaviour of Diphenylamine (DPAM), napthylamine ( NAM), napthylamine ( NAM)and aniline on pyrolusite and activated carbon has been studied.Pyrolusite shows remarkable sorption capacity for DPAM and NAM as compared to aniline; (the adsorption followed theorder:Activated Carbon: DPAM = NAM > AnilinePyrolusite: DPAM: NAM > NAM> Aniline)The maximum adsorption of NAM occurred in theconcentration range 4–20 g mL^-1 on pyrolusite (95%)and 4–50 g mL^-1 on activated carbon (100%). Theeffect of various doses of activated carbon on the adsorption of NAM confirm Langmuir and Freundlich isotherms where asFreundlich isotherm is obeyed by pyrolusite. The adsorption of NAM on both the absorbents is not affected in presence ofDPAM over a wide range of their initial concentrations (20–60g mL^-1). The desorption studies of NAM onpyrolusite was carried out by batch as well as column processes.Excellent results were obtained when a mixture of n-hexane andisopropanol (91:1) was used as eluent.     

Environmental Quality Of Urban Parks And Open Spaces In Hong Kong

It is widely purported that urban parks and open spaces can improve the urban environment by cleansing the air and reducing the noise. However, such environmental functions can be constrained by the size and the location of urban parks in very dense cities. This study examines the air and acoustic environment and heavy metal contamination in Hong Kong urban parks and open spaces. Using a hybrid field measurement and computer simulation approach, the study has found that while the air quality in urban parks is better than that of the roadside, it is not significantly different from that of the ambient conditions. Noise levels in the urban parks are not significantly lower than those at the typical home environment in Hong Kong. Heavy metals in urban park dust are slightly lower than that found at the roadside and are broadly comparable to those found at typical homes and nursery schools. These findings lend support to the postulation that the capability of urban parks and open spaces in dense cities to improve the urban environment is rather limited and call for a re-examination of the role of urban parks in enhancing urban livability. The findings also have implications on how urban parks in dense cities should be designed and managed.