[Study on the effect of total phosphor removing by constructed submerged hydrophyte bed for urban landscape river].

A kind of modularized and air adjustable constructed submerged plant bed (CSPB) was used to restore the eutrophic water. This CSPB helps hydrophytes to grow up under poor conditions, like frequently changed water depth, blurred water transparency, algae bloom and duckweed rampant in summer, which are not suitable for growing water plants naturally. The experiments in Waihuan River of Tianjin show that total phosphor (TP) reduces 30%-40% in growing season and 7%-20% in winter when the detention time is 5.48 days. The variation between the concentration of TP and the detention time follows the first-order kinetic equation, the correlation coefficients (R2) is above 0.9. The attenuation coefficients k of the kinetic equation changes with the water temperature. When the water temperature is quite low or quite high, the value of k is not significantly changed with the temperature of water. While when the temperature is in a moderate range, an increase of water temperature leads to a rapid increase of k value.

[Effect of intermittent artificial aeration on nitrogen and phosphorus removal in subsurface vertical-flow constructed wetlands].

Shale and T. latifolia were used as subsurface vertical-flow constructed wetland substrate and vegetation for eutrophic Jin River water treatment, and investigate the effect of intermittent aeration on nitrogen and phosphorus removal. In this study, hydraulic loading rate was equal to 800 mm/d, and ratio of air and water was 5:1. During the entire running period, maximal monthly mean ammonia-nitrogen (NH4+ -N), total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) removal rates were observed in August 2006. In contrast to the non-aerated wetland, aeration enhanced ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus removal: 10.1%, 4.7%, 10.2% and 8.8% for aeration in the middle, and 25.1%, 10.0%, 7.7% and 7.4% for aeration at the bottom of the substrate, respectively. However, aeration failed to improve the nitrate-nitrogen removal. During the whole experimental period, monthly mean NO3(-) -N removal rates were much lower for aerated constructed wetlands (regarding aeration in the middle and at the bottom) than those for non-aerated system. After finishing the experiment, aboveground plant biomass (stems and leaves) of T. latifolia was harvested, and its weight and nutrient content (total nitrogen and total phosphorus) were measured. Analysis of aboveground plant biomass indicated that intermittent aeration restrained the increase in biomass but stimulated assimilation of nitrogen and phosphorus into stems and leaves. Additional total nitrogen removal of 11.6 g x m(-2) and 12.6 g x m(-2) by aboveground T. latifolia biomass for intermittent artificial aeration in the middle and at the bottom of the wetland substrate, respectively, was observed.

[Optimization of nitrogen and phosphorus removal in vertical subsurface flow constructed wetlands by using polypropylene pellet as part of substrate].

Constructed wetlands experiments were conducted by using shale and Typha latifolia L. as vertical subsurface flow constructed wetland substrate and plant for eutrophic Jin River water treatment, and part of shale with polypropylene pellet was replaced to investigate its effect on nitrogen and phosphorus removal. In this study, hydraulic loading rate was equal to 800 mm/d, theoretic residence time was equal to 12 h. During the entire running period, maximal monthly mean ammonia-nitrogen (NH(4+) -N), total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) removal rates were observed in August 2006. In contrast to the full shale used wetland, polypropylene pellet enhanced ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus removal by 13.38%, 8.9%, 9.29% and 8.25% respectively. After finishing the experiment, aboveground plant biomass (stems and leaves) of Typha latifolia L. was harvested, and its weight and nutrient content (total nitrogen and total phosphorus) were measured. Analysis of aboveground plant biomass indicated that polypropylene pellet restrained the increase in biomass but stimulated assimilation of nitrogen and phosphorus into stems and leaves. The subsequent harvesting of the plants resulted in the additional removal of total nitrogen and phosphorus of about 29.382 g x m(-2) and 13.469 g x m(-2), respectively.

Experimental investigation of the effect of flow turbulence and sediment transport patterns on the adsorption of cadmium ions onto sediment particles.

The mechanism of flow turbulence, sediment supply conditions, and sediment transport patterns that affect the adsorption of cadmium ions onto sediment particles in natural waters are experimentally simulated and studied both in batch reactors and in a turbulence simulation tank. By changing the agitation conditions, the sediment transport in batch reactors can be categorized into bottom sediment-dominated sediment and suspended sediment-dominated sediment. It is found that the adsorption rate of bottom sediment is much less than that of suspended sediment, but the sediment transport pattern does not affect the final (equilibrium) concentration of dissolved cadmium. This result indicates that the parameters of an adsorption isotherm are the same regardless of the sediment transport pattern. In the turbulence simulation tank, the turbulence is generated by harmonic grid-stirred motions, and the turbulence intensity is quantified in terms of eddy diffusivity, which is equal to 9.84F (F is the harmonic vibration frequency) and is comparable to natural surface water conditions. When the turbulence intensity of flow is low and sediment particles stay as bottom sediment, the adsorption rate is significantly low, and the adsorption quantity compared with that of suspended sediment is negligible in the 6 h duration of the experiment. This result greatly favors the simplification of the numerical modeling of heavy metal pollutant transformation in natural rivers. When the turbulence intensity is high but bottom sediment persists, the rate and extent of descent of the dissolved cadmium concentration in the tank noticeably increase, and the time that is required to reach adsorption equilibrium also increases considerably due to the continuous exchange that occurs between the suspended sediment and the bottom sediment. A comparison of the results of the experiments in the batch reactor and those in the turbulence simulation tank reveals that the adsorption ability of the sediment, and in particular the adsorption rate, is greatly over-estimated in the batch reactor.