Technology Study On Making Sidewalk Brick Using City Sewage Sludge

The construction of the urban sewage treatment plants has a positive effect on water pollution control, but how to solve the problem of the treatment and disposal of a large number of sewage sludge followed. Previously due to the impact of technology, capital and other factors, our country for a long time only attaches great importance to the sewage treatment, and neglected the sludge disposal. Today, the state increased investment for sludge disposal, provided the policy support and financial support for us to research new methods of sludge utilization.The use of building materials especially the sludge brick is the focus of the research and application of sludge resources for a long time. But in general, many research use the dry sludge and sludge incineration asht to make brick, and sludge drying and incineration requires a lot of energy.In this study, the characteristics of wet sludge with high water content is used, the wet sludge was directly mixed with materials such as clay for aging, make mixture reaches a certain humidity,and does not need to add extra water or only few when molding, curing heavy metals, eliminating pathogenic microorganisms,reducing energy consumption, saving water resources.We found that by detecting the physical and chemical properties of the four Xi’an municipal sewage treatment plant sludge, the content of Cd、Zn in some sludge is higher than the agricultural standard,and we can make the garden fertilizer and brick to disposal it.We take the clay and wet sludge as main material, combined with the test results, select the engineering sand and coal powder as auxiliary admixtures, the rates were 8% and 3%.After determining the auxiliary admixture proportion, we select sludge content, firing temperature, holding time, and molding pressure as the main factors, three levels of each factor to do the orthogonal test. The results of orthogonal test showed that the sludge content is far greater than the other three factors that affect the brick compressive strength, water absorption rate, holding time had the weakest effect. When the sludge content is 20%, the brick can keep a certain compressive strength and water absorption.,can be use as sidewalk brick.The results of the single factor analysis showed that in the same experimental conditions, with the increase of sludge content, the compressive strength of the brick body reduced, the firing density decreased, water absorption rate increased. To improve the molding pressure and firing temperature have improved the performance of compressive strength.The results show that there is no pan cream on the surface of the sludge fired brick in the wet environment. The results of freezing thawing tests show that when the sludge content is less than 24%, the sludge firred brick had certain frost resistance and the loss rate of freezing thawing quality can be controlled within 2%.The concentration of as Pb、Cd、Cr 6 kinds of heavy metals in sludge clay fired brick leaching were detected before and after firing. Results show that the fired brick has obvious effect on curing heavy metal.So,using it as sidewalk brick will be feasible.Finally determined, when the wet sludge content is less than 24%, the firing temperature is controlled at about 1050℃, molding pressure 20 MPa, the strength of sludge fired brick reached 10-20 MPa, meet the national standard 《bricks》(GB5101- 2003) MU10 strength requirements.Making fired brick using wet sludge, can disposal sludge, reach energy conservation and environmental protection, conservation of water resources and land resources, has good economic and social benefits. Sludge disposal need diversified recycling use.