Effects of reductive inorganics and NOM on the formation of chlorite in the chlorine dioxide disinfection of drinking water

Chlorine dioxide(ClO_(2))disinfection usually does not produce halogenated disinfection byproducts,but the formation of the inorganic by-product chlorite(ClO^(–)_(2))is a serious consideration.In this study,the ClO^(–)_(2)formation rule in the ClO_(2)disinfection of drinking water was investigated in the presence of three representative reductive inorganics and four natural organic matters(NOMs),respectively.Fe^(2+)and S^(2–)mainly reduced ClO_(2)to ClO^(–)_(2)at low concentrations.When ClO_(2)was consumed,the ClO^(–)_(2)would be further reduced by Fe^(2+)and S^(2–),leading to the decrease of ClO^(–)_(2).The reaction efficiency of Mn^(2+)with ClO_(2)was lower than that of Fe^(2+)and S^(2–).It might be the case that Mn O 2 generated by the reaction between Mn^(2+)and ClO_(2)had adsorption and catalytic oxidation on Mn^(2+).However,Mn^(2+)would not reduce ClO^(–)_(2).Among the four NOMs,humic acid and fulvic acid reacted with ClO_(2)actively,followed by bovine serum albumin,while sodium alginate had almost no reaction with ClO_(2).The maximum ClO^(–)_(2)yields of reductive inorganics(70%)was higher than that of NOM(around 60%).The lower the concentration of reductive substances,the more ClO^(–)_(2)could be produced by per unit concentration of reductive substances.The results of the actual water samples showed that both reductive inorganics and NOM played an important role in the formation of ClO^(–)_(2)in disinfection.

How do inundation provoke the release of phosphorus in soil-originated sediment due to nitrogen reduction after reclaiming lake from polder

Different N and P fractions inmicrocosm incubation experiment was measured using highresolution in-situ Peeper and DGT techniques combining with sequential extraction procedure.The results showed the synchronous desorption and release of PO_(4)^(3-),S^(2-)and Fe^(2+)from the solid soil-originated sediment.This trend indicated that the significant reduction of Fe-P and SO_(4)^(2-) occurred in the pore water during the inundation.The concentrations of PO_(4)^(3-) in the overlying water and pore water increased to more than 0.1 and 0.2 mg/L at the beginning of the incubation experiment.Decreased NO_(3)^(-) concentrations from more than 1.5 mg/L to less than 0.5 mg/L combining with increasing NH^(4+) concentrations from less than 1mg/L tomore than 5 mg/L suggested the remarkable NO_(3)-reduction via dissimilatory nitrate reduction to ammonia(DNRA)pathway over time.High NH^(4+) concentrations in the pore water aggravated the release of Fe^(2+) through reduction of Fe(Ⅲ)-P as electric acceptors under anaerobic conditions.This process further stimulated the remarkable releasing of labile PO_(4)^(3-) from the solid phase to the solution and potential diffusion into overlying water.Additionally,high S^(2-) concentration at deeper layer indicated the reduction and releasing of S^(2-)from oxidation states,which can stimulated the NO_(3)^(-)reduction and the accumulation of NH^(4+)in the pore water.This process can also provoke the reduction of Fe-P as electric acceptors following the release of labile PO_(4)^(3-)into pore water.Generally,inundation potentially facilitate the desorption of labile P and attention should be paid during the reclaiming lake from polder.

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.

Characteristics of pollutants behavior in a stormwater constructed wetland during dry days

A stormwater wetland treating non-point source pollution （NPS） from a 64 ha agricultural watershed was monitored over a period of five months. The results indicated that pH and dissolved oxygen （DO） were increased in the wetland due highest total suspended solids to the algal growth. The （TSS） concentration was observed in the aeration pond due to the resuspension of solids, decreased in the wetland. The respective decreases in total nitrogen （TN） and total kjeldahl nitrogen （TKN） were 15.9% and 28.7% on passing through the wetland. The nitrate and ammonia were increased by 45.4% and decreased by 79.9%, respectively. These variations provided strong evidence for the existence of nitrification. The total phosphorus （TP） and phosphate had respective reductions of 52.3% and 58.2% over the wetland. The total chemical oxygen demand （TCOD） and soluble chemical oxygen demand （SCOD） were also decreased. Generally, the TN, TP and phosphate removal etticiencies were positive. These positive removal efficiencies were mainly due to microbial activities, uptake by plants, and chemical precipitation at high pH. Negative removal efficiencies can be caused by continuous rainfall activities, with short antecedent dry days （ADDs） and unstable hydraulic conditions, some other biogeochemical transformations and algal growth also being important parameters.