Preparation of Eco-environmental Protection Bricks from Lake Sludge

Eco-environmental protection hollow bricks manufactured from lake sludge collected from North Lake in Wuhan of China were investigated. At first, the recipes of round sam- pies（diameter in 5 cm and thickness in 1 cm） prepared by pressing molding under a pressure of 8 MPa and firing system were optimized, and properties such as bending strength, compressive strength, total shrinkage rate, water adsorption rate, apparent porosity and bulk density of the fired samples were tested. The experimental results showed that water adsorption rate and apparent porosity decreased, while bulk density increased with firing temperature increasing. Addition of additive can result in the improvement of strength of fired samples. At the same time, fly ash and additive may also broaden the firing temperature range and reduce firing temperature. Toxic characteristic leaching procedure （TLCP） tests of samples also show that the metal leaching level is low. The conditions for manufacturing good quality sample include 80% sludge with 10% additive and 10% flyash fired at 1000 ℃ for 60 min. Bending strength and compressive strength of samples prepared under the conditions are 24.64 MPa, 131.95 MPa, respectively,which are far beyond the requirements of clay solid bricks of CNS. Finally, according to the optimized recipe,the eco-environmental protection hollow bricks with the sizes of 40 mm × 38 mm ×25 mm were made and tested by extrusion molding. Compared with the Chinese National Standards （CNS： GB 13545-2003）, compressive strength, water adsorption and bulk denstiy of the hollow bricks are 11.55 MPa ,14.5% and 986 kg/m^3 when they were fired at 1040 ℃, which are far beyond the require of of CNS. Especially, its water adsorption arrives to standard of high-class products（16.0%） and compressive strength is above the hightest class（MU 10.0）.

Properties and Mechanism of CFBC Fly Ash-cement based Stabilizers for Lake Sludge

Circulating fluidized bed combustion（CFBC） fly ash was mixed with cement or lime at a different ratio as a stabilizer to stabilize lake sludge.In order to understand the influences of stabilizers on the lake sludge properties,tests unconfined compressive strength,water stability and SEM observation were performed.The experimental results show that with the increase of the curing time,the strength of all the stabilized specimens increase,especially the samples containing cement.The strength of the specimens is decreased with the increasing of the CFBC fly ash/cement ratio,the optimum ratio between CFBC fly ash and cement is 2：3.The water stability of CFBC fly ash-cement based stabilizers is higher than those of cement and lime.Moreover,the lake sludge stabilization mechanism of CFBC fly ash-cement based stabilizers includes gelation and filling of the hydration products,i e,C-S-H gel and the AFt crystal,which act as benders to solidify those particles together and fill in the packing void of the aggregates.

Porous Haydite Used as Waste Water Filter Medium for Lake Sludge

Porous haydite used as waste filter medium was prepared by dreging lake sludge to help solve the treatment problem of sludge and realize its reclamation. Several calcination regimes were considered and their effects on the pore structure and the properties such as the strength, the density, the filtering ability and the phosphate absorption ability of the haydite were investigated, For the mixture of 60% lake sludge and 40% fly ash in this experiment, the calcination regime with a pre-caleination period at about 600℃, a temperature keeping period at 1 200 ℃ and a moderate cooling rate are recommended to prepare haydite with reasonable pore structure and good performances for its usage as the waste water filter media.

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.