Significance of dredging on sediment denitrification in Meiliang Bay,China:A year long simulation study

An experiment for studying the effects of sediment dredging on denitrification in sediments was carried out through a one-year incubation of undredged （control） and dredged cores in laboratory. Dredging the upper 30 cm of sediment can significantly affect physico-chemical characteristics of sediments. Less degradation of organic matter in the dredged sediments was found during the experiment. Denitrification rates in the sediments were estimated by the acetylene blockage technique, and ranged from 21.6 to 102.7 nmol N2/（g dry weight （dw）-hr） for the undredged sediment and from 6.9 to 26.9 nmol N2/（g dw-hr） for dredged sediments. The denitrification rates in the undredged sediments were markedly higher （p 〈 0.05） than those in the dredged sediments throughout the incubation, with the exception of February 2006. The importance of various environmental factors on denitrification was assessed, which indicated that denitrification was regulated by temperature. Nitrate was probably the key factor limiting denitrification in both undredged and dredged sediments. Organic carbon played some role in determining the denitrification rates in the dredged sediments, but not in the undredged sediments. Sediment dredging influenced the mineralization of organic matter and denitrification in the sediment; and therefore changed the pattern of inherent cycling of nitrogen.

Factors related to aggravated Cylindrospermopsis(cyanobacteria)bloom following sediment dredging in an eutrophic shallow lake

In recent years,Cylindrospermopsis raciborskii blooms have been widely found worldwide.Topics dealing with the mitigation of C.raciborskii bloom is of great importance for toxins produced could threaten public health.The paper first investigated C.raciborskii dynamics over three years following sediment dredging in a shallow eutrophic Lake Dongqian(China).Based on rpoC1 gene copies,C.raciborskii bloom formed with average density of 1.30×10^(6) cells/L on July 2009.One year later after sediment dredging,C.raciborskii cell density decreased below 1.17×10^(5) cells/L or under detected limits during summer days on 2010.While two years later,the C.raciborskii bloom period was returned with markedly increased cell density reaching up to 4.15×10^(7) cells/L on October 2011,and the maximum peak density was shown at 20.3C that was much lower than reported optimal growth temperature.Inferred from Spearman correlation analysis,linear regression showed C.raciborskii density was significant and positive with pH and SD,whereas they were significant and negative with TP and DO.Multiple regression analysis further demonstrated that TN,TP,SRP,pH and DO provided the best model and explained 53.1% of the variance in C.raciborskii dynamics.The approaches managing nutrients reduction might not control C.raciborskii bloom as extremely low TN(avg.0.18 mg/L)and TP concentrations(avg.0.05 mg/L)resulted in the highest C.raciborskii cell density after sediment dredging.

High-efficiency stabilization of dredged sediment using nano-modified and chemical-activated binary cement

High-efficiency disposal of dredged sediment(DS)has become an imperative geo-environmental engineering issue due to the limited landfilling space and severe environmental burdens.This study firstly developed a novel high-efficiency nano-modified and chemical-activated binary cement(NBC),which was composed of binary cement(BC)consisting ordinary Portland cement(OPC)and ground granulated blast-furnace slag(GGBS),chemical-activator and nano-modifier.The effects of chemical-activation and nano-modification on the strength development of BC-stabilized DS(BCDS),and the optimum mix of NBC were respectively achieved via a series of unconfined compressive strength and orthogonal tests.Then,the high-efficiency and economic applicability of NBC in DS stabilization were evaluated by comparing with OPC.Furthermore,the microstructure and mineral composition evolutions inside NBCstabilized DS(NDS)were explored by conducting X-ray diffraction(XRD)and scanning electron microscopy(SEM)tests.The results show that both chemical-activation and nano-modification could effectively improve the strength gain of BCDS,and compared with single chemical-activator and nanomodifier,the composite chemical-activators and nano-modifiers exhibited better performances.Based on BC with OPC/GGBS mass ratio of 1:1,both anhydrous sodium metasilicate/anhydrous sodium sulfate(SM/SS)and nano-SiO_(2)/nano-MgO(NS/NM)with mass ratio of 1:9 were respectively determined to be optimum chemical-activator and nano-modifier.The optimum mass ratio of BC,SM/SS and NS/NM was 20:2:1,i.e.the optimum mix of NBC.Compared with OPC,NBC exhibited higher stabilization efficiency and better economic applicability.The generation of calcium silicate hydrate(CSH),calcium aluminate hydrate(CAH)and ettringite contributed to the formation of dense cemented soil matrix inside NDS,and a conceptual micro-mechanism model characterizing the strength development under the coupling action of chemical-activation and nano-modification was proposed.

Utilization of Dredged River Sediment in Preparing Autoclaved Aerated Concrete Blocks

In this study,the dredged river sediment,soft texture and fine particles,is mixed with other materials and transformed into eco-friendly autoclaved aerated concrete(hereinafter referred to as AAC)blocks.The results indicated the bricks produced under the conditions of 30%–34%dredged river sediment,24%cement,10%quick lime,30%fly ash,2%gypsum and 0.09%aluminum powder with 0.5 water to material ratio,2.2 MPa autoclave pressure and 6 h autoclave time,the average compressive strength of 4.5 MPa and average dry density of 716.56 kg/m³were obtained,the two parameters(strength&density)both met the requirement of national industry standard.At the same time,the contents of dredged river sediment,cement,lime,fly ash,gypsum and aluminum powder were 15%,48%,20%,15%,2%and 0.09%,respectively,and the non-AAC block made of 0.5 water to material ratio,the average compressive strength of 3.1 MPa and average dry density of 924.19 kg/m³were obtained,the two parameters(strength&density)also met the requirement of national industry standard.In addition,the AAC block’s phase composition and morphology were micro-analyzed by SEM and XRD,the main substances in AAC block were found to be tobermorite and CSH,Among them,the chemical bond between Si-O-Si and Al-O-Al is broken,Al-O-Si is regenerated,Al substituted tobermorite with better strength is formed,and the compressive strength of AAC is further improved.

Tensile strength behavior of cement-stabilized dredged sediment reinforced by polypropylene fiber

This study evaluated the feasibility of using polypropylene fiber(PF)as reinforcement in improving tensile strength behavior of cement-stabilized dredged sediment(CDS).The effects of cement content,water content,PF content and length on the tensile strength and stress–strain behavioral evolutions were evaluated by conducting splitting tensile strength tests.Furthermore,the micro-mechanisms characterizing the tensile strength behavior inside PF-reinforced CDS(CPFDS)were clarified via analyzing macro failure and microstructure images.The results indicate that the highest tensile strengths of 7,28,60,and 90 d CPFDS were reached at PF contents of 0.6%,1.0%,1.0%,and 1.0%,exhibiting values 5.96%,65.16%,34.10%,and 35.83%higher than those of CDS,respectively.Short,3 mm,PF of showed the best reinforcement efficiency.The CPFDS exhibited obvious tensile strain-hardening characteristic,and also had better ductility than CDS.The mix factor(C_(C)^(a)/C_(w)^(b))and time parameter(q_(t0)(t))of CDS,and the reinforcement index(k_(t-PF))of CPFDS were used to establish the tensile strength prediction models of CDS and CPFDS,considering multiple factors.The PF“bridge effect”and associated cementation-reinforcement coupling actions inside CPFDS were mainly responsible for tensile strength behavior improvement.The key findings contribute to the use of CPFDS as recycled engineering soils.

滇池疏浚底泥脱水试验研究(英文)

[Objective] The technological parameter suitable for the dewatering of dredged sediment from Dianchi Lake was studied.[Method] By means of the treatment method of sewage sludge in sewage treatment plant,flocculants including FeCl3,Al2(SO4)3 and PAM were taken as dewatering agents which were added in dredged sediment.[Result] The results showed that Al2(SO4)3 had better dewatering effect than FeCl3 and PAM,and the optimum dosing quantity of Al2(SO4)3 in dredged sediment was 170 mg/L,in addition,the water quality of supernatant met the first class B standard of GB18918-2002 and could be directly discharged to nature water without pollution.[Conclusion] The study could provide a simple and feasible way for the rapid dewatering of dredged sediment from Dianchi Lake,which would be convenient for the disposal and resource utilization of dredged sediment.

Controlled sintering for cadmium stabilization by beneficially using the dredged river sediment

Cd-bearing solid wastes are considered to be a serious threat to the environment,and effective strategies for their treatment are urgently needed.Ceramic sintering has been considered as a promising method for efficiently incorporating heavy metal-containing solid wastes into various ceramic products.Mineral-rich dredged river sediment,especially Al and Si-containing oxides,can be treated as alternative ceramic precursors rather than being disposed of as solid wastes.To examine the feasibility of using waste sediment for Cd stabilization and the phase transition mechanisms,this study conducted a sintering scheme for the mixtures of CdO and dredged river sediment with different(Al+Si):Cd mole ratios.Detailed investigations have been performed on phases transformation,Cd incorporation mechanisms,elemental distribution,and leaching behaviors of the sintered products.Results showed that Cd incorporation and transformation in the sintered products were influenced by the mole ratio of(Al+Si):Cd.Among the high-Cd series((Al+Si):Cd=6:1),CdSiO_(3),Cd_(2)SiO_(4),CdAl_(2)(SiO_(4))_(2) and Cd_(2)Al_(2)Si_(2)O_(9) were predominant Cd-containing product phases,while Cd2Al2Si2O9 was replaced by CdAl_(4)O_(7) when the mole ratio of(Al+Si):Cd was 12:1(low-Cd series).Cd was efficiently stabilized in both reaction series after being sintered at≥900℃,with<5%leached ratio even after a prolonged leaching time,indicating excellent long-term Cd stabilization.This study demonstrated that both Cd-containing phases and the amorphous Al-/Si-containing matrices all played critical roles in Cd stabilization.A promising strategy can be proposed to simultaneously reuse the solid waste as ceramic precursors and stabilize heavy metals in the ceramic products.

Effects of sludge dredging on the prevention and control of algae-caused black bloom in Taihu Lake,China

Algae-caused black bloom （also known as black water agglomerate） has recently become a critical problem in some Chinese lakes.It has been suggested that the occurrence of algae-caused black bloom was caused by the cooperation of nutrient-rich sediment with dead algae,and sludge dredging was adopted to control black bloom in some lakes of China.In this article,based on the simulation of black bloom using a Y-shape apparatus for modeling natural conditions,both un-dredged and dredged sites in three areas of Taihu Lake,China were studied to estimate the effects of dredging on the prevention and control of black bloom.During the experiment,drained algae were added to all six sites as an additional organic load;subsequently,the dissolved oxygen decreased rapidly,dropping to 0 mg/L at the sediment-water interface.Black bloom did not occur in the dredged sites of Moon Bay and Nan Quan,whereas all three un-dredged sites at Fudu Port,Moon Bay and Nan Quan experienced black bloom.Black bloom also occurred at the dredged site of Fudu Port one day later than at the other sites,and the odor and color were lighter than at the other locations.The color and odor of the black water mainly result from the presence of sulfides such as metal sulfides and hydrogen sulfide,among other chemicals,under reductive conditions.The color and odor of the water,together with the high concentrations of nutrients,were mainly caused by the decomposition of the algae and the presence of nutrient-rich sediment.Overall,the removal of the nutrient-rich sediment by dredging can prevent the occurrence and control the degree of algae-caused black bloom in Taihu Lake.

An integrated method for the rapid dewatering and solidification/stabilization of dredged contaminated sediment with a high water content

To more efficiently treat the dredged contaminated sediment(DCS)with a high water content,this study proposes an integrated method(called PHDVPSS)that uses the solidifying/stabilizing(S/S)agents and prefabricated horizontal drain(PHD)assisted by vacuum pressure(VP).Using this method,dewatering and solidification/stabilization can be carried out simultaneously such that the treatment time can be significantly shortened and the treatment efficacy can be significantly improved.A series of model tests was conducted to investigate the effectiveness of the proposed method.Experimental results indicated that the proposed PHDVPSS method showed superior performance compared to the conventional S/S method that uses Portland cement(PC)directly without prior dewatering.The 56-day unconfined compressive strength of DCS treated by the proposed method with GGBS-MgO as the binder is 12–17 times higher than that by the conventional S/S method.DCS treated by the PHDVPSS method exhibited continuous decrease in leaching concentration of Zn with increasing curing age.The reduction of Zn leachability is more obvious when using GGBS-MgO as the binder than when using PC,because GGBS-MgO increased the residual fraction and decreased the acid soluble fraction of Zn.The microstructure analysis reveals the formation of hydrotalcite in GGBS-MgO binder,which resulted in higher mechanical strength and higher Zn stabilization efficiency.