Research Of Sewage Sludge Pretreatment And Its Application In Silicate Building Products

Disposal of sewage sludge is having been a serious problem all over the country, as sewage sludge containing a variety of harmful components and having caused serious damage to ecosystem. At the same time, Development of new kinds of wall materials has become the industry trend with a ban on the use of clay solid brick which has caused damage to the arable land ordered by China. In the view of its components, sewage sludge has the potential to make building materials. At present, relevant researches are mostly focused on the sintering products, rarely on steamcured or autoclaved products. From the perspective of using sewage sludge as building materials, research of its application in silicate building products was carried out in this paper, to provide support for achieving combination of sewage sludge disposal and development of new kinds of building materials.In this paper, based on the results of its TG-DTA analysis, drying sewage sludge was firstly carried out by direct heating and then its physical and chemical propertie s were studied by various analytical methods. What’s more, the proper amount of sludge and the suitable curing conditions were determined by the variation of mechanical properties and hydration products of silicate building products mixed with dry sludge, lime, fly ash and sand. Different types of properties of the silicate building products were studied, i.e. physical property, durability and environmental safety.Results showed that: the dry sludge, with large specific surface area and irregular particle morphology, was mainly composed of Si O2, Fe2O3 and Al2O3, also containing P2O5, SO3, heavy metals, other harmful substances and a small amount of organic matter. Sludge was feasible to be applied in silicate building products, when directly heated at 300℃ and then mixed with lime, with carbohydrate, protein, other organic matter and amide decomposed. The main hydration products of the sludge-fly ash silicate building products, including tobemorite, C-S-H(I) gel, katoite and ettringite, were demonstrated in the morphologies of samples. Mix proportion and curing conditions would significantly affect the performance of sludge-fly ash silicate building products. With the increase of the dosage of sludge, the crystallinity and porosity of the product were markedly increased, while more internal defects were observed, which lead to low compressive strength, flexural strength, high bibulous rate and poor durability. Under suitable curing conditions, the maximum ratio of sludge in the products was 20%, with which the mechanical performance and the toxicity characteristic leaching procedure could still meet the standard. However, due to its poor durability, sludge should control in within 20% in practical applications.