UTILIZATION OF CEMENT KILN DUST FOR SEWAGE SLUDGE TREATMENT AND PRODUCTION OF BUILDING PRODUCTS

Abstract

This study aims to discuss the effect of adding cement kiln dust to sewage sludge for safe disposal and environmental protection also aims to study the production of blended cement using burnt sewage sludge. In part one; wastewater treatment plants are producing huge amounts of primary and secondary sewage sludge. On the other hand, large quantities of cement kiln dust (CKD) were produced from cement factories with negative impacts on the environment. CKD is a considerable by-product waste material of the industrial process. At the time being, remarkable advances have been achieved in the management and reuse of CKD. Due to its high alkalinity, huge amounts, negative impact and abundant source; it is considered as non-controlled source of pollution. The use of CKD for sewage sludge treatment has high potential as an additional low cost raw material, fertilizer, constructing material, adsorbent and improving sandy soil properties. In this study, CKD was used as chemical coagulant / flocculent sewage sludge and adsorbent for soluble pollutants and disinfectants as well. The optimum operating conditions were adjusted using Jar test experiment and tested sludge was analyzed. Results showed that on addition of8.0 g/l CKD to primary sludge and 7.0 g/l to return activated sludge (RAS), good efficiency was achieved for solids separation, BOD5, COD, (PO4)-3, and (NH4)+; respectively. Under the effect of high pH value, it was also beneficial in heavy metals immobilization and minimization of metal solubility in the treated sludge matrix. Consequently, metal ions were precipitated as hydroxides. Moreover, all pathogenic and viral species were destructed including total and fecal coliforms. In part two of this study; wet sewage sludge sample was collected then dried at 105°C then ignited at 800 °C for two hours also ordinary Portland cement (OPC) sample was collected for El-Sewedy cement factory. In this investigation, four OPC- Burnt sewage sludge (BSS) blends were prepared from the next OPC (Mix 0) and three OPC-BSS mixtures made by the partial substitution of OPC by 5, 10 and 15% of BSS by weight (Mixes M5, M10 and M15 respectively)and their water / cement ratios (W/C) of standard water of consistency were 29, 29.5, 30.5, 31% respectively. Physico-chemical characteristics for the four blends were studied in time interval 1, 3, 7, 28 days to evaluate the efficiency of BSS to be used in blended cement production. The results obtained show that the W/C ratio increase with the increase of BSS content in the pastes which indicates an increasing demand of water with increasing BSS content of initial porosity of the OPC-BSS blended cement pastes.The compressive strength increases with the increase of curing time for all the hardened neat OPC (mix 0) and OPC-BSS blended cement pastes (Mixes M5, M10 and M15). This is due to the formation of hydration products which act as binding centers between the remaining unhydrated parts of cement grains.The partial substitution of OPC by BSS resulted in a slight reduction in the chemically combined water content (Wn, %)values of OPC-BSS pastes at all hydration ages. This slight decrease in Wn-values increase with increasing substitution of OPC by BSS which indicate that BSS has a reasonable pozzolanic activity with an appreciable contribution in the Wn-values of hydration products as well as the development of compressive strength of the hardened OPC-BSS pastes at all hydration ages.