Characterization and treatment of tunneling wastewater using natural and chemical coagulants

In this research, characterization of the wastewaters before and after treatment was carried out by chemical analysis and by various techniques for particle characterization. Based on the characterization, laboratory work was conducted to evaluate the effectiveness of sedimentation and the use of coagulants to remove particles and particle-associated contaminants. Both natural (i.e., chitosan) and chemical coagulants, including ferric chloride sulfates and polyaluminium chloride solution, were applied in a conventional jar-test system. The results indicated that short-time sedimentation alone substantially reduced the particle content and particle-associated pollutants, including metal(loid)s, while subsequent chemical coagulation was required to comply with discharge limits. The optimum dosages of chitosan, PIX, and PAX for water 1 after pretreatment (15 min sedimentation) were 1 mg/L, 3 mg Fe/L, and 3 mg Al/L, respectively, while a dosage of 2 mg Al/L gave the best results in water 3. Furthermore, chemical coagulation significantly decreased the volume density of particles in the diameter range of 1-100 mu m, showing that coagulants are efficient for the removal of smaller particles not removed by conventional sedimentation.