Utilization of sludge as brick materials

https://doi.org/10.1016/S1093-0191(02)00037-0Get rights and content

Abstract

Bricks manufactured from dried sludge collected from an industrial wastewater treatment plant were investigated. Results of tests indicated that the sludge proportion and the firing temperature were the two key factors determining the brick quality. Increasing the sludge content results in a decrease of brick shrinkage, water absorption, and compressive strength. Results also showed that the brick weight loss on ignition was mainly attributed to the organic matter content in the sludge being burnt off during the firing process. With up to 20% sludge added to the bricks, the strength measured at temperatures 960 and 1000 °C met the requirements of the Chinese National Standards. Toxic characteristic leaching procedure (TCLP) tests of brick also showed that the metal leaching level is low. The conditions for manufacturing good quality bricks is 10% sludge with 24% of moisture content prepared in the molded mixtures and fired at 880–960 °C.

Introduction

In Taiwan, the annual sludge (dewatered) production from 34 industrial wastewater treatment plants is approximately 0.67 million tons. While sanitary landfills are commonly used for disposal of sludge in Taiwan, rapid urbanization has made it increasingly difficult to find suitable landfill sites (Lin and Weng, 2001). Utilization of sludge as an addition to construction and building material including building bricks, lightweight artificial aggregates, and cement-like materials is a win–win strategy because it not only converts the wastes into useful materials but it also alleviates the disposal problems. The prospective benefits of using sludge or sludge ash as the brick or tile additive include immobilizing heavy metals in the fired matrix, oxidizing organic matter and destroying any pathogens during the firing process, and reducing the frost damage based on the results of several full or bench scale studies (Alleman and Berman, 1984, Tay, 1987, Trauner, 1991, Alleman et al., 1990, Okuno and Takahashi, 1997, Wiebusch and Seyfried, 1997, Tay and Show, 1999, Weng and Lin, 2000, Lin and Weng, 2001). Nevertheless, utilization of sludge as a building material in Taiwan has not yet been a productive reality because the legal approval and public acceptance in this regard are not yet overcome.

In this study, the suitable conditions of using dried sludge in manufacturing of bricks under the criteria of Chinese National Standards (CNS) were investigated. The influence of sludge proportion in the raw materials, the temperature in relating to the brick qualities, and metal leach ability were examined.

Section snippets

Material and methods

The filter press dewatered and oven-dried sludge samples were obtained from a local industrial wastewater treatment plant. The dried sludge samples were taken from the outlet of a dryer which burnt 1 ton of dewatered sludge at 250 °C for 2 h. A clay sample of normal bricks was obtained from a local brick manufacturing plant. Table 1 shows the sludge and clay characteristics and their metal content. In general, the dried sludge has a higher heavy metal content than that of the dewatered sludge

Specific surface area of clay-sludge mixtures

The results of specific surface area obtained for the mixtures are shown in Table 3. The specific surface area of sludge is almost the same order of magnitude as for clay, 0.51 and 0.564 m2/g, respectively. As the amount of sludge increases, the specific surface area of the mixture increases proportionally. The higher specific surface area of the mixture indicates the need for more water being used in the brick molding processes. Thus, when a rather high amount of sludge is applied in replacing

Conclusions

This work has demonstrated the suitable conditions for using dried sludge as a clay substitute to produce an engineering quality of brick. The proportion of sludge in the mixture and the firing temperature are the two key factors affecting the quality of brick. In all, the recommended proportion of sludge in brick is 10%, with a 24% optimum moisture content, prepared in the molded mixtures and fired between 880 °C and 960 °C to produce a good quality brick.

Acknowledgments

This study was partly supported by the Industrial Development Bureau, Ministry of Economic Affairs of Republic of China. The findings do not necessarily represent the endorsement of this agency.

Chih-Huang is an Associate Professor in the Department of Civil Engineering at the I-Shou University, Taiwan. His research interests are in the areas of environmental engineering.

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Chih-Huang is an Associate Professor in the Department of Civil Engineering at the I-Shou University, Taiwan. His research interests are in the areas of environmental engineering.

Deng-Fong is an Associate Professor in the Department of Civil Engineering at the I-Shou University, Taiwan. His research interests are in the areas of pavement engineering.

Pen-Chi is a Professor in the Graduate Institute of Environmental Engineering at the National Taiwan University, Taiwan. His research interests are in the areas of environmental engineering.

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