Cement-bonded Boards From Wastewater Treatment Sludge of a Recycled Paper Mill

摘要

Paper mills in the Philippines generate large volumes of fibrous sludge each day and options for disposing of it are limited. The use of fibrous sludge as a reinforcement for cement-bonded fibreboard is one option that could help alleviate the paper industry's problems in disposing of the sludge, which is recovered after treatment of process water. Research was undertaken to determine the technical feasibility of using these waste fibres for the production of fibre-reinforced cement bonded boards. Cement and sludge were mixed in the ratios 60:40 and 50:50 and used to manufacture boards. Calcium chloride, sodium silicate and aluminium sulphate were added to accelerate curing and hardening of boards. Morphological characteristics of fibrous components of sludge such as fibre length, cell wall and cell lumen dimensions were determined. The percent thickness swelling and water absorption and mechanical properties of boards were measured. The average length of fibres in the sludge was 1.424 mm. The average dimensions of the cell wall and lumen were 0.006 mm and 0.0153 mm, respectively. The average densities of the boards were 1.232 g cm~(-3) for the 60:40 boards and 1.177 g cm~(-3) for the 50:50 boards. The 60:40 board containing aluminium sulphate exhibited the lowest thickness swelling while the 50:50 board with both sodium silicate and aluminium sulphate had the highest thickness swelling. In general, 60:40 boards absorbed less water than 50:50 boards. The 60:40 board with sodium silicate and aluminium sulphate had the highest modulus of rupture and modulus of elasticity, while the 50:50 board with sodium silicate had the lowest. The boards were also evaluated for their nail-head pull through strength. Results showed that the 60:40 board containing aluminium sulphate had the highest strength. Our findings suggest that cement boards manufactured with sludge as reinforcement have mechanical and physical properties comparable to those of other cement-bonded boards manufactured in the Philippines. The fibres bond well together and the sludge does not greatly inhibit the setting of cement. The results are sufficiently encouraging to suggest that the management of paper mills should consider using sludge for the production of cement-bonded boards.