Removal of non-point pollutants from bridge runoff by a hydrocyclone using natural water head

A hydrocyclone using natural water head provided by bridge was operated for the treatment of stormwater runoff. The hydrocyclone was automatically controlled using electronic valve which is connected to a pressure meter. Normally the hydrocyclone was open during dry days, but it was closed after the capture of the first flush. The results indicated that the average pressure and the flow rate were directly affected by the rainfall intensity. The pressure head was more than 2 m when the rainfall intensity was above 5mm·h^-1. The percentage volume of underflow with high solids concentration decreased as the pressure and flow rate increased, but the percentage volume of overflow with almost no solids showed the opposite behavior. The total suspended solids （TSS） concentration ratio between the overflow and inflow （TSSover/TSSin） decreased as a function of the operational pressure, while the corresponding ratio of underflow to inflow （TSSunaer/TSSi,） increased. The TSS separation efficiency was evaluated based on a mass balance. It ranged from 25% to 99% with the pressure head ranging from 1.4 to 9.7 m, and it was proportional to pressure and flow rate. Normally, the efficiency was more than 50% when the pressure was higher than 2 m. The analysis of the water budget indicated that around 13% of the total runoff was captured by the hydrocyclone as a first flush, and this runoff was separated as underflow and overflow with the respective percentage volumes of 29% and 71%. The pollutants budget was also examined based on a mass balance. The results showed that the percentage of TSS, chemical oxygen demand （COD）, total nitrogen （TN）, and total phosphorus （TP） in underflow were 73%, 59%, 7.6%, and 49%, respectively. Thus, it can be concluded that the hydrocyclone worked well. It separated the first flush as solids-concentrated underflow and solids-absent overflow, and effectively reduced the runoff volume needing further treatment. Finally, four types of optional post treatment design are presented and compared.

Effects of Al^3+ on the microstructure and bioflocculation of anoxic sludge

The aluminum ions generated from mining aluminum,electrolytic aluminum and the industrial production of aluminum-based coagulants(such as AlCl3 and Al2(SO4)3)enter sewage treatment plants and interact with activated sludges.An anaerobic/anoxic/oxic(A2^O)process was used to reveal the effects of Al^3+on the pollutant removal efficiencies,bioflocculation and the micro structure of sludge.The results showed that a low concentration of Al^3+improved the pollutant removal efficiencies and increased the sludge particle size.However,a high concentration of Al^3+hindered microbial flocculation and reduced the pollutant removal efficiencies.With a 10 mg/L Al^3+addition,the chemical oxygen demand(COD),total nitrogen(TN)and NH4+-N increased by 3%,16%and 27%,and reached as high as 68%,60%and 87%,respectively.At the same time,the dehydrogenase activity,flocculation ability(FA)and contact angle of the sludge reached their maximum levels at 41.3 mg/L/hr,45%and 79.63°,respectively.The specific surface area of the sludge decreased to 7.084 m2/g and the sludge pore size distribution shifted to concentrate in the me soporous range.Most of Al^3+was adsorbed on the surface of sludge,changing the physicochemical properties and physical structure of the sludge.

NUMERICAL MODELING PURIFICATION PERFORMANCE OF POT TEST

A three-dimensional mathematical model was developed to simulate the pollutant removal efficiency of the soil and plants in the pot test. The advection, dispersion, diffusion, adsorption, biochemical reaction and plant uptake processes were taken into account in the model. The three-dimensional modified Richards equation was used in simulating flow field. The mass balance law was employed in deriving the equation for pollutant transport, where the diffusion and dispersion were described with the Fick-type law, the adsorption was macroscopically expressed as form isotherm, and the bio-chemical degradation process was assumed to follow the Monod kinetics. The mathematical model was descretized by the finite element numerical method. In the pot test, the hydraulic loading was assumed to have the intermittent pattern simulating the rainfall duration and the occurrence of frequency, and the concentrations of pollutants in the influent and effluent were measured. The computed overall removal rates for the CODCr and TN in four cases are in the range of 90.62% - 95.43% and 85.01% - 96.46%, respectively. The differences between the computed and tested overall removal rates for the CODCr and TN are smaller than 5%. The time-varying oscillation pattern of the concentrations of the CODCr and TN were rationally simulated, which showed that the model presented in this article could be used to assess the pollutant removal efficiency of the soil and plants in related cases.