Xu Zuxin

Study on improved BP artificial neural networks in eutrophication assessment of China eastern lakes

Abstract An improved back propagation artificial neural network model for eutrophication evaluation of China eastern was constructed, and a new approach producing training set data, testing set data and critical values set data distributed a normal distribution between the critical values was established. The model was applied to 4 eastern lakes and the results shows that the method is suitable for eutrophication assessment of lakes.

Numerical Modeling of Wastewater Transport and Degradation in Soil Aquifer

Modeling of wastewater transport and degradation in soil aquifer is a problem of concern with regard to the optimization of design and operation of the wastewater soil treatment system. To solve this problem, three-dimensional groundwater flow and wastewater transport and degradation model was developed using MODFLOW and MT3DMS modeling. The developed model was calibrated using the Soil Infiltration Treatment System (SITS) in the Chongming island of China after considering the river—groundwater interaction and the regional geological and hydrological conditions. Using the calibrated model, the following problems with regard to the design and operation of SITS were discussed: (1) Allowable hydraulic load. The hydraulic load increases with the drop in the water level of the adjoining river, the increase in the actual soil area under operation, and the increase in the distance among the individual operation units of SITS. (2) Optimized layout of the groundwater monitoring wells. The concentration contour of the simulated contaminants is very useful to depict the typical areas that are most severely polluted and very sensitive to the peripheral environment,, thus lesser number of monitoring wells can be set up based on the model, and the goal of the accurate assessment of the influence of soil-infiltrated wastewater on groundwater can be achieved.

OPTIMIZED DESIGN OF NATURAL ECOLOGICAL WASTEWATER TREATMENT SYSTEM BASED ON WATER ENVIRONMENT MODEL OF DYNAMIC MESH TECHNIQUE

A Natural Ecological Wastewater Treatment System (NEWTS) is usually built on natural terrain with necessary topography modification to improve water flowing route and pattern, and then the topography modified NEWTS should also have a reasonable water storage volume and hydraulic retention time so as to achieve the anticipated water purification effect. In this study, the dynamic mesh technique based on the finite element method and element storativity coefficients was presented to develop a two-dimensional hydrodynamic and water quality model, which was used to optimize the design of NEWTS under the dynamic land-water boundary due to various water storage volume. The models were employed in the optimized design of NEWTS from a large abandoned coal mine, which purifies the polluted water flowing into a large water storage lake, as part of the East Route South-to-North Water Transfer Project in China. Specifically, the natural topography modification scheme was presented, and further, a reasonable water storage volume and hydraulic residence time was obtained, based on the reasonable estimation of roughness coefficient and pollutant removal rate of the NEWTS with phragmites communis.

Influencing Factors Investigation of On-Site Rural Domestic Wastewater Treatment with Water Hyacinth in Shanghai

Using water hyacinth to treat the domestic wastewater, on-site, from dispersed farmhouses in Shanghai rural area, the relevant influencing factors that are temperature, hydraulic retention time (HRT), water depth (h) and water hyacinth density (WHD), were investigated. The influence of temperature was that water hyacinth had different growth rate in different seasons, which lead to varied pollution abatement ratio in this method. The results showed, when HRT was 60d, the removal efficiency of COD, TN, NH4 +-N and TP was 81.3%, 96.9%, 98.7% and 97.5% respectively; when HRT was adjusted to 30 d, the removal efficiency of those indexes had a decrease of 8.3,13.1, 16.0, and 1.5; the decrease became 0, 13.8, 9.7 and 11.4 when HRT was reduced from 30 d to 20 d. Three h, 0.4 m, 0.8 m and 1.2 m, were studied, and the results showed that the removal efficiency of COD and TP decreased first then increased, with the rise of h, but the removal efficiency of TN and NH4 +-N always decreased. As TN and NH4 +-N were concerned, when HRT was 30 d or 20 d, the change of WHD did not have much influence on them; but the removal efficiency was increased with the increase of WHD when HRT was 15 d. It was also concluded that among HRT and WHD, performance of this method showed higher sensitivity to HRT.

Eco-Hydraulics Techniques for Controlling Eutrophication of Small Scenery Lakes—A Case Study of Ludao Lake in Shanghai*

The Ludao Lake with an area of 0.86 km2 and 50% water surface ratio, was taken as an example to study the eco-hydraulics techniques for preventing lake eutrophication. Besides external water inflow and outflow, the term related to internal local flow circulation was added in the continuity equation of two-dimensional horizontal hydrodynamic model, and further the hydrodynamic model was calibrated by the scenario of no water exchange. The velocity of 0.2 m/s was suggested to be the critical velocity of controlling algal bloom. To achieve the critical velocity in the whole lake, three factors were analyzed, which are wind, artificial external inflow augmentation and internal local flow disturbance by pump circulation. It is found that the role of wind can be disregarded. For the eco-hydraulics technique of external lake water inflow augmentation, the water flowing route should be firstly optimized, further, the lake inflow has a critical value under specified water level due to the narrow inlets, so the whole lake is difficult to reach the critical velocity to prevent algal bloom, and a combination of external inflow augmentation and internal local flowing disturbance should be considered. Simulation results show that the combination of external water inflow augmentation and internal local flow disturbance requires less eco-flow to achieve the global critical velocity than the sole internal local flow disturbance, for the Ludao Lake, the former requires total eco-flow of 25 m3/s, which reduces by 50% than the latter requiring total eco-flow of 52 m3/s.

Wireless Real-time Observation System for Water Level of Urban Drainage

Real-time water level observation in urban drainage is essential o control rainwater or sewage storage so as to reduce overflow pollution. To achieve real-time data accessing, wireless communication and ultrasonic water level gauge are integrated to design the observation system. A developed wireless real-time observation system for Caohejing drainage system in Shanghai, with the area of 3.74 km2, is presened to show how to control storm drainage so as to reduce dry-weather pump discharging, which also displays reliability of the system.

Study on transport of powdered activated carbon using a rotating circular flume

This study employed a rotating flume to examine the Powdered Activated Carbon (PAC) transport with water flow. The initial PAC concentration was 10 mg/L-30 mg/L, and PAC concentration versus time under a specified cross-sectional averaging fluid shear was observed. Results show that compared with PAC deposition in still water, PAC is depleted to zero faster under a fluid shear of 0.02 Pa, due to PAC agglomeration with the fluid shear. However, since PAC floc size only ranges from a single particle (2 μm) to approximate 6 μm, an increasing of instantaneous turbulent fluctuations could counteract the force of PAC floc settling downward, and as a result the steady PAC concentration increases with the increase of shear stress. It is found that the critical shear stress for PAC deposition is about 0.60 Pa, and further the PAC deposition probability is presented according to the experimental scenarios between 0.02 Pa and 0.60 Pa. Combining the PAC transport and deposition formula with PAC-pollutant removal model provides an insight into PAC deployment in raw water aqueduct for sudden open water source pollution.

Study on the Erosion Rate of Powdered Activated Carbon in Raw Water Aqueduct

Growing interest in using Powdered Activated Carbon (PAC) in raw water aqueduct, as a method of polluted surface water treatment, raises the question of transport of PAC in the aqueduct, which is related to the potential PAC erosion along the aqueduct. By means of a recently developed re-circulating flume, erosion rates of PAC with the grain size of 230 meshes (less than 62 μm) depending on shear stress and bulk density were the discussed with real-time measurement of suspended PAC concentration. Lateral cross sectional averaging shear stress was decided by the actual value in the raw water conveying aqueduct of upstream Huangpu River, Shanghai, China, smaller than 1.8 N·m−2. As for the bulk density, it was measured with compacting times varying from 1 d to 15 d, equivalent to 1 550 kg/m3–1 800 kg/m3. Experiments were conducted for the shear stress and bulk density separately, so as to isolate and quantify the effects of one of the parameters. The results demonstrate that, for a particular PAC particle, the erosion rate increases with shear stress and decreases with bulk density as a function of power form. A product of powers of the lateral cross sectional averaging shear stress and bulk density to estimate PAC erosion rate is presented by approximating experimental data sets.

Wireless Real-Time System for Monitoring the Storage of Urban Storm Drainage: A Case Study of Caohejing Drainage System, Shanghai

For the purpose of abating overflow pollution from storm pumping discharge, a real-time monitoring system for storm drainage storage was developed, based on pipe storage model, ultrasonic sensors, wireless communication and web-based geographic information system. The monitoring system has been applied into Caohejing drainage system, Shanghai, a separate drainage system with dry-weather pollution entry into storm pipes. It demonstrates added storm drainage on the basis of terminal drainage water elevation of 2.6m, the current critical condition to operate storm pumps. The real-time monitoring system lays foundation for development of real-time control system of the study area.