[Characteristics and contribution of the strengthening units of composite constructed wetland for treating urban sewage].

There are some defects in constructed wetland, including the uneven distribution of flow, easily blocked, lack of oxygen supply systems and the unsatisfactory phosphorus adsorption capacity of the substrates, etc. The research mainly studied the function and contribution of the pool of hydrolysis acidification, the natural reoxygenation/sinking device and strengthen slot for reducing nitrogen and phosphorus. The results showed the removal efficiency of COD and SS in hydrolysis-acidification pool accounted for 38.05% and 34.82% of the total removal efficiency of system. The SS removal efficiency of the natural reoxygenation/sinking device accounted for 22.01% of the total removal efficiency of system, and the concentration of DO kept above 2.5 mg.L-1. The two strengthen slots can ensure the TP, TN, COD up to the standard of the level 1 of GB 18918-2002.

Vitellogenin induction by a mixture of steroidal estrogens in freshwater fishes and relevant risk assessment.

The study method on combined effects of environmental contaminant mixture and ecological risk assessment was discussed. Batch tests were conducted to assess the in vivo potency of binary mixtures of estrogens using plasma vitellogenin concentrations in male crucian carp as the endpoint. The estrogenic potencies of 17beta-estradiol (E(2)) and 17alpha-ethynylestradiol (EE(2)) were determined following 14 day exposure to the individual chemicals and equipotent binary mixtures. A Nonlinear regression was obtained and 95% confidence limits of effect concentration were achieved using the bootstrap method. Concentration-response curve for fixed ratio binary mixtures of E(2) and EE(2) was compared with those for individual chemicals, using the biomathematical models of concentration addition (CA) and independent action (IA). A complete overlap was found for the CA predictions with the 95% confidence interval of the best-fit regression line of the observed responses, and the IA predictions was shown lower than the observations. The observed mixture effects were considerably higher than those of the hormone alone and far exceeded the 95% confidence interval of the estrogen regression lines. The predicted effects of binary mixtures at different mixture ratios indicated that the potential impact of components on mixture would depend predominantly on its concentration, the mixture ratio and its relative potency. Results suggested that E(2) and EE(2) acted together in an additive manner and the combined effects can be accurately predicted in whole range of exposure concentration by the models of CA and IA, the model of CA might be realistic, but more useful for ecological risk assessment.

[Mixture effects to vitellogenin induction by four environmental estrogens in freshwater fish].

Combined effects of estrogenic compounds to high risk life-form were demonstrated, and the study method on combined effects of environmental contaminant mixture and environmental risk assessment were also discussed. A nonlinear aggression was determined on the changes of plasma vitellogenin concentration in crucian carp via the environmental pollutant exposure concentration, and the concentration-response relationship was determined for the single chemical of estradiol, ethynylestradiol, bisphenol A, and octylphenol, and that of the mixed compounds at equipotent concentrations. The combined effects of the four xenoestrogens were tested using indices of mixture toxicity and the biomathematical models of concentration addition or independent action. Weibull function was indicated as the best-fit function (R2 > or = 0.92) with curve estimation, the 95% confidence limits of effect concentration was achieved using the bootstrap method, the media effective concentration (EC50) with 95% confidence interval was 0.007 9 (0.006 8-0.010 0), 0.098 7 (0.090 0-0.111 0), 63.50 (56.58-70.62) and 250.59 (228.46-271.99) Mg x L(-1) respectively. Results suggested that estrogenic chemicals acted together in an additive manner and the combined effects can be accurately predicted in whole range of exposure concentration by the concept of similar joint action or concentration addition.It is proved as a scientific and feasible method to apply the model of joint action whereas the outcome of indices with a great deal of indetermination.

[Clogging characteristics of the subsurface flow wetland].

In order to resolve clogging problem of constructed wetlands caused by improper design or imperfect management and reveal the clogging mechanism, clogging characteristics of the horizontal flow reed wetland and vertical flow reed wetland were studied. Operation stabilities of two types of wetlands were compared. It shows that organic matter accumulates in medium and the concentration is 1.5% - 5%. It mostly occurs in the fore section of top layer in wetland and the concentration is 4% - 5%. The negative correlation between the organic matter content and the subsurface depth was demonstrated. The clogging mechanisms in the horizontal flow wetland and the vertical flow wetland are different. The hydraulic retention time of the horizontal flow wetland is 3.5154 d which is shortened by 21.88%. While the hydraulic retention time of the vertical flow wetland is 5.4648 d and extended by 21.44%. The results indicate that clogging decreases the treatment capacity and running stability conspicuously. The clogging phenomenon of the vertical flow wetland is worse comparatively.

[Intensity of nitrification and denitrification in subsurface-flow constructed wetlands].

To reveal the nitrogen purification mechanism in subsurface-flow constructed wetlands, nitrification and denitrification intensities were studied in reed, canna and unplanted wetlands respectively. The results show that nitrification intensity in subsurface-flow wetlands is remarkably influenced by temperature and closely correlative with total and ammonia nitrogen removal efficiency. It appears in upright direction that nitrification and denitrification intensities in upper layer are higher than that in the lower. For the reed wetland, nitrification intensity is low in both ends but high in the middle of upper layer, while it decreases gradually along distance in lower layer. The change of denitrification intensity along distance is not obvious. Average nitrification intensity is higher in vertical-flow wetland than that in horizontal-flow wetlands, higher in planted wetlands than that in unplanted wetland and higher in reed wetland than that in canna wetland. The secretion from plant roots directly results in the gradual decrease of nitrification intensity in plant rhizosphere. Results also show that intensity of denitrification is obviously higher than that of nitrification. Thereby, subsurface-flow wetland has strong denitrification potential.

[Study on running characteristics of aerating subsurface flow wetlands].

Aim at the low dissolved oxygen concentration and nitrogen removing efficiency in constructed wetlands, the running parameters of aeration measure, influence on plants and bacteria, the dissolved oxygen concentration and purifying efficiency after aeration were studied. The results show that aeration should be run in the forepart of wetland. The best gas-flow ratio is 6. Continuous aeration is adopted. The influence of aeration on plants in wetlands is inconspicuous. The quantity of nitrifying bacteria and denitrifying bacteria are increased. Aeration improves the oxygen condition, which is under 0.6 mg/L before aeration but over 1 mg/L after aeration. The purifying efficiency of wetlands is improved, removing efficiency of organic matter increases 10%, and removing efficiency of total nitrogen is higher than 60%. So aeration has the value of research and application.

[Environmental behavior in wetland soil of organic chlorine from pulp bleaching wastewater].

The adsorption equilibrium and leaching characteristics of organic chlorine on soils were studied by mean of soil column method using bleaching water in laboratory condition. Soil samples were also collected from the wetland that irrigated with pulp wastewater from one to three years, and analyzed for the distributing characteristics of organic chlorine in soils. The results showed that measured equilibrium isotherms for absorbable organic chlorine (AOCl) in the soils were of Freundlich type with the adsorption constant 7.3410 in the soils without irrigated and 4.9501 irrigated for 2 years. The nonlinear constants were 0.5024 and 0.6108, respectively. The AOCl was detected in the leachate, it was found that most of the AOCl was adsorbed by the soils, especially topsoil. The average contents of extractable organic chlorine (EOCl) were 4.48 microg/g, 10.35 microg/g and 10.07 microg/g in the topsoil irrigated for la, 2a and 3a respectively, which had increased distinctly compared with the background value.

[Study on the oxygen condition in subsurface flow wetlands in operation].

Horizontal flow wetlands with various kinds of plants grown were studied on their operation characteristics and oxygen condition in treating the sewage out from the primary sedimentary basin. The rules of oxygen condition changed with space and time were studied. Researches showed the oxygen concentration was low in wetlands, and it appeared as a rule that low in both ends, but high in middle of beds. It descended in upright direction. The oxygen concentration changed with seasons as summer > spring > autumn > winter. In one day, the highest oxygen concentration appeared on 14:00, and the concentration was higher in forenoon than afternoon. Reed > canna > camellia > dracaena sanderiana > ipomoea aquatica forsk by comparison of ability of oxygen supply. Experiments demonstrate that the study of oxygen condition in constructed wetlands is propitious to reveal the purifying mechanism of wetlands and improve the purifying efficiency.