Alex T. Chow

Production of dissolved organic carbon (DOC) and trihalomethane (THM) precursor from peat soils.

Water passing through the Sacramento-San Joaquin Delta contains elevated concentrations of dissolved organic carbon (DOC) and trihalomethane (THM) precursor relative to upstream waters from the Sacramento River and the San Joaquin River. Drainage from agricultural peat soils has been identified as one of the major sources of DOC and THM precursor. A series of controlled laboratory experiments were conducted to evaluate abiotic and biotic effects on the quantity and the nature of DOC and THM precursors produced from oxidized surface and reduced subsurface soils in the Delta. For abiotic effects, DOC was extracted from both soils with synthetic solutions containing a range of salinity (0-4 dS/m) and sodicity (0 to infinity ). The results showed that an increase in salinity significantly decreased the concentration of DOC in the soil-water from both soils but increased its aromaticity, as indicated by specific ultraviolet absorbance at 254 nm (SUVA). For biotic effects, peat soils were incubated over a range of temperatures (10 degrees C, 20 degrees C and 30 degrees C) and soil moisture contents (0.3-10 g water/g soil). After 8 weeks of incubation, only extracted DOC from flooded conditions and flooded and non-flooded cycles showed an increase in DOC. These findings indicate that neither salinity nor sodicity is the major factor for DOC production, but both can affect the solubility and mobility of DOC in the Delta soils. We believe wetting processes in oxidized peat soils produce significant amounts of DOC found in agricultural drainage discharged into the Delta waters.

Photocatalytic oxidation of polycyclic aromatic hydrocarbons: intermediates identification and toxicity testing.

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic pollutants and their low water solubility limits their degradation in aqueous solution. The presence of water-miscible solvent such as acetone can increase the water solubility of PAHs, however acetone will also affect the degradation of PAH. In this study the effects of acetone on the photocatalytic degradation efficiency and pathways of 5 selected PAHs, namely naphthalene (2 rings), acenaphthylene (3 rings), phenanthrene (3 rings), anthracene (3 rings) and benzo[a]anthracene (4 rings) were investigated. The Microtox toxicity test was used to determine whether the PCO system can completely detoxify the parental PAHs and its intermediates. The addition of 16% acetone can greatly alter the degradation pathway of naphthalene and anthracene. Based on intermediates identified from degradation of the 5 PAHs, the location of parental PAHs attacked by reactive free radicals can be correlated with the localization energies of different positions of the compound. For toxicity analysis, irradiation by UV light was found to induce acute toxicity by generating intermediates/degradation products from PAHs and possibly acetone. Lastly, all PAHs (10 mg l(-1)) can be completely detoxified by titanium dioxide (100 mg l(-1)) within 24h under UVA irradiation (3.9 mW cm(-2)).

Characterizing redox status of paddy soils with incorporated rice straw

Redox status is one of the more difficult soil quality criteria to characterize especially in paddy soils. The soil system chosen in this study was an ongoing paddy field trial on alternative practices of incorporating rice straw instead of traditional burning of straw. Upon flooding, rapid changes in redox potential (Eh) occur in paddy soil due to the decomposition of soil organic matter (SOM), including rice straw. This investigation evaluated three methods of characterizing redox status: (i) Eh, a conventional method using Pt black electrode; (ii) terminal electron-accepting processes (TEAPs), a method of diagnosing microbially mediated electron acceptor (oxidized species) consumption, intermediate product concentration of H2 and accumulation of final products (reduced species); and (iii) oxidative capacity (OXC), a comprehensive analysis of the algebraic sum of oxidized and reduced species into a single descriptive parameter. There was a need to develop a sampling technique for anaerobic soil pore water in rice paddy (without exposure to the atmosphere) to measure all the redox parameters required by these methods. The setup comprised of a capped piezometer (sampling well) back-filled with sand and sealed with bentonite, and vacuum extraction of pore water containing dissolved constituents. The pore water containing dissolved gases was collected into previously evacuated 400-ml two-port PVC bags from which gaseous phase sub-samples were withdrawn with a syringe into 10-ml vacutainers previously flushed with N2 gas for H2 and CH4 determinations in the laboratory. Unstable water quality parameters such as DO, Eh, pH and S2− were measured on site using fresh samples, while other parameters such as NO3−, SO42−, EC, Fe(II) and Fe(III), and Mn(II) were analyzed in the laboratory. The above three methods of evaluating redox status were applied to monitoring the paddy pore water over 3 years of field observations (1997–1999). Eh is a simple measure, but it gives at best only qualitative assessment of redox status because this electrode may not respond to many of the important redox couples. The adaptation of TEAPs to assess non-equilibrium redox conditions in flow pathways in large-scale ground water systems to small-scale rice rootzone was not entirely successful because of differences in the two systems and the significant overlapping among electron acceptors in paddy soils. OXC, a non-equilibrium capacity-type redox parameter, clearly identified geochemical redox classes of oxic, post-oxic, sulfidic and methanic conditions in the paddy pore waters during the course of the rice-growing season. Based on data observed for 3 years, it is concluded that straw incorporation does enhance more reducing conditions development compared to that without straw incorporation. We conclude that OXC provides a better characterization of redox status in paddy soils.

Improved fluorescence excitation-emission matrix regional integration to quantify spectra for fluorescent dissolved organic matter.

The purpose of this short communication is to demonstrate the importance of numerical analysis and wavelength increment selection when characterizing fluorescent dissolved organic matter (FDOM) using fluorescence excitation-emission matrix (EEM) regional integration. A variety of water samples, representing a landscape gradient and different types of FDOM, were analyzed for their percentage distribution of five operationally defined FDOM fractions (aromatic protein I, aromatic protein II, fulvic acid-like, soluble microbial byproduct-like, and humic acid-like) using three numerical methods in integrating volume under the surface of the fluorescence EEMs: Riemann summation, composite trapezoidal rule, and composite Simpsons rule. The influence of wavelength increment was also examined for the precision of the percentage distribution of each fraction. Our results show that the FDOM fraction estimated by Riemann summation with a 10- or 5-nm excitation wavelength can cause >40% or >5% errors, respectively, when compared with the best estimated values obtained by averaging results from composite trapezoidal rule and composite Simpsons rule with 1-nm excitation wavelength at the same emission increment. Also, our experiments show that fluorescence matrix regional integration could underestimate the two aromatic protein fractions but could overestimate the soluble microbial byproduct-like and humic acid-like fractions if improper increment and integral methods are used. The error can be reduced if a smaller wavelength increment is used. The smallest increment in a spectrofluorometer and composite Simpsons rule should be used for scanning fluorescence EEMs and calculating the percentage distribution of each FDOM fraction. Alternatively, 5-nm wavelength increments with composite Simpsons rule could be cost effective, and the error of each FDOM fraction commonly falls within 5% compared with those estimated by 1-nm increments.

The chelonian trade in the largest pet market in China: scale, scope and impact on turtle conservation

China is the largest consumer of turtles in the world and international trade has been cited as the greatest threat to Asian turtles. Two main types of trade in live turtles occur in China: for food and traditional Chinese medicine, and for pets, including those for release by Buddhists. The food trade involves the largest quantities of turtles. In recent years, however, the international pet turtle trade has increased dramatically. Yuehe Pet Market in Guangzhou is the largest pet market in China. selling live chelonians and other animals. To understand the potential impacts of the pet trade on chelonians we conducted seven surveys in Yuehe Pet Market from August 2006 to March 2008. Over 39,000 individual chelonians of 61 species were recorded (19.1% of the global total of 319 species). Fifteen (24.6%) of these species are native to China and 46 (75.4%) are native to other countries. Two are designated as grade II key state-protected species in China. Thirty-eight (62.3%) are CITES listed species (four in CITES Appendix I, 26 in CITES II and eight in CITES III). Four are categorized on the IUCN Red List as Critically Endangered, 16 as Endangered and 19 as Vulnerable. Our surveys indicate that increasing demand and the illegal international pet trade could be having a severe impact on chelonian conservation, and we make recommendations for law enforcement and conservation.

Nitric oxide removal from flue gas with a biotrickling filter using Pseudomonas putida

The development of an effective biotrickling filter (BF) system to inoculate a newly isolated strain of Pseudomonas putida SB1 for the effective treatment of nitric oxide (NO) is described. The experiments were carried out in a bench-scale BF under high concentrations of O(2) and NO in simulated flue gas. A method including alternating aeration in screening and rescreening based on the pH changes for cultivating natural aerobic denitrifying bacteria was employed. The SB1 showed a denitrifying capability of 95% nitrate removal rate over a 24h period in an aerobic environment, with no nitrite accumulation. The BF system was able to consistently remove 82.9-94.2% NO when the inlet NO was 400ppm in an enriched oxygen stream of 2-20%. The oxygen had no negative effect on the aerobic denitrifier SB1, but rather enhanced the total efficiency in part by chemical oxidation and in part by the strain activities. A kinetic relation between the oxygen concentration and biological NO removal was developed to confirm that the microbial metabolism played the main role. 79.3% of the total NO removal can be attributed to bio-denitrifying at 20% oxygen, and most chemical oxidation occurred concurrently. Overall, the study demonstrates that NO removal by the aerobic denitrifying process in BF is feasible in flue gas.

Disinfection byproduct formation from chlorination of pure bacterial cells and pipeline biofilms

Disinfection byproduct (DBP) formation is commonly attributed to the reaction between natural organic matters and disinfectants, yet few have considered the contribution from disinfecting bacterial materials - the essential process of water disinfection. Here, we explored the DBP formation from chlorination and chloramination of Escherichia coli and found that most selected DBPs were detectable, including trihalomethanes, haloacetonitriles, chloral hydrate, chloropicrin, and 1,1,1-trichloro-2-propanone. A positive correlation (P = 0.08-0.09) between DBP formation and the log reduction of E. coli implied that breaking down of bacterial cells released precursors for DBP formation. As Pseudomonas aeruginosa is a dominant bacterial species in pipeline biofilms, the DBP formation potentials (DBPFPs) from its planktonic cells and biofilms were characterized. Planktonic cells formed 7-11 times greater trihalomethanes per carbon of those from biofilms but significantly lower (P < 0.05) chloral hydrate, highlighting the bacterial phenotypes impact on the bacteria-derived DBPFP. Pipe material appeared to affect the DBPFP of bacteria, with 4-28% lower bromine incorporation factor for biofilms on polyvinyl chloride compared to that on galvanized zinc. This study revealed both the in situ disinfection of bacterial planktonic cells in source water and ex situ reaction between biofilms and residual chlorine in pipeline networks as hitherto unknown DBP sources in drinking water.

Litter contributions to dissolved organic matter and disinfection byproduct precursors in California oak woodland watersheds.

Export of dissolved organic matter (DOM) from California oak woodland ecosystems is of a great concern because DOM is a precursor for carcinogenic disinfection byproducts (DBPs) formed during drinking water treatment. Fresh litter and decomposed duff materials for the four dominant vegetation components of California oak woodlands: blue oak (Quercus douglassi H. & A.), live oak (Quercus wislizenii A. DC.), foothill pine (Pinus sabiniana Dougl.), and annual grasses, were exposed in natural condition for an entire rainy season (December to May) to evaluate their contributions of particulate (POC) and dissolved (DOC) organic carbon, particulate (PON) and dissolved (DON) organic nitrogen, inorganic nitrogen (NH4+ and NO3-), and trihalomethane (THM) and haloacetonitrile (HAN) formation potentials, to surface waters. Litter and duff materials can be significant sources of DOC (litter=29-126 mg DOC g(-1) C; duff=6.5-37 mg DOC g(-1) C) and THMs and HANs (up to 4600 mg-THMs g-C(-1) and 137 microg-HANs g-C(-1)). Blue oak litter had the highest yield of DOC, THM, and HAN precursors. When scaled to the entire watershed, leachate production yielded 445 kg-DOC ha(-1), as compared to DOC export via streams of 5.25 kg-DOC ha(-1). DOC transport to surface waters is facilitated by subsurface lateral flow through A horizons during storm events. The majority of DOM and DBP precursors was leached from plant materials in the initial rainfall events and thus may explain the seasonal stream pattern of a DOC pulse early in the rainy season.

Simultaneous chromate reduction and azo dye decolourization by Brevibacterium casei: Azo dye as electron donor for chromate reduction

Chromate [Cr(VI)] and azo dyes are common pollutants which may co-exist in some industrial effluents. Hence studies of biological treatment of industrial wastewater should include investigation of the co-removal of these two pollutants. Brevibacterium casei, which can reduce Cr(VI) in the presence of the azo dye Acid Orange 7 (AO7) under nutrient-limiting condition, was isolated from a sewage sludge sample of a dyeing factory. Response surface methodology, which is commonly used to optimize growth conditions for food microorganisms to maximize product(s) yield, was used to determine the optimal conditions for chromate reduction and dye decolourization by B. casei. The optimal conditions were 0.24 g/L glucose, 3.0 g/L (NH(4))(2)SO(4) and 0.2 g/L peptone at pH 7 and 35 degrees C. The predicted maximum chromate reduction efficiencies and dye decolourization were 83.4+/-0.6 and 40.7+/-1.7%, respectively. A new mechanism was proposed for chromate reduction coupling with AO7 decolourization by B. casei. Under nutrient-limiting condition, AO7 was used as an e(-) donor by the reduction enzyme(s) of B. casei for the reduction of Cr(VI). The resulted Cr(III) then complexed with the oxidized AO7 to form a purple coloured intermediate.

Effect of constructed wetlands receiving agricultural return flows on disinfection byproduct precursors

The effects of wetland treatment on disinfection byproduct precursors were evaluated for six constructed wetlands receiving agricultural return flows in the Central Valley of California. Wetlands varied in size, age, vegetation, hydrologic residence time (0.9-20 days) and water management (continuous flow vs. flood pulse). The effects of wetland treatment were determined by analyzing input and outflow waters for dissolved organic carbon concentration and quality, bromide concentration, and formation potentials for nine disinfection byproduct species, including trihalomethanes, haloacetronitriles, chloral hydrate, and haloketones. We hypothesized that hydraulic residence time was a key factor governing differences in disinfection byproduct precursors. Small wetlands (<3 ha) with short hydraulic residence times (<2 days) did not produce significant changes in disinfection byproduct precursor concentrations with respect to the agricultural return flows input to the wetlands. In these wetlands hydraulic residence times were not long enough to promote processes that adversely affect dissolved organic carbon and bromide quantity, such as evapoconcentration and leaching from vegetation. Thus, less negative effects were associated with disinfection byproduct formation. In contrast, larger wetlands (>100 ha) with long hydraulic residence times (>10 days) resulted in higher dissolved organic carbon and bromide levels, increasing disinfection byproduct formation by factors ranging between 1.7 and 10.2 compared to agricultural return flows. Results from this study provide important information for optimizing the design and management of constructed wetlands to effectively combine control of disinfection byproduct precursors with other water quality parameters.