Usage Of Coagulation With Ozonation For Treatment Of Model Wastewater Of Wood Processing With Aluminium Salts

摘要

One of the stages of raw material preparation for plywood producing is hydrothermal treatment of birch wood. Wastewater of hydrothermal basins are characterized by the high degree of contamination, because they contain hemicelluloses, lignin and woodextractive substances (HLES). The combination of physico-chemical methods, especially methods of coagulation and ozonation is an effective way to clean wastewater from HLES. To validate the viability decision of the application of coagulation and ozonation method was necessary to conduct comprehensive studies on the efficacy of HLES removal in the presence of aluminium salts and to determine effectiveness of ozonation stage.Based on the above the first objective of the present study was to investigate the coagulation efficiencies of polyaluminium chloride (PAC) in HLES removal from model wastewater of hydrothermal wood treatment and to compare with the degree of efficiency using aluminium sulfate and aluminum chloride at the same parameters of purification. It was established that the optimal PAC dosage is 100 mg L'1 and optimal pH is 6.0. It gives 80% reduction of HLES concentration, 54% of lignin removal, 43, 72 and 56% of COD, color and BOD5 removal, respectively. The residual aluminum concentration is 0.06 mg L'1. It is found that, using AI2(S04)3 with the dosage 100 mg L'1 at pH 6.0, the HLES removal amounts 75%, 41% of lignin removal, the decline of COD is 39% and the decrease of the solution BOD5 and color are 37% and 66%, respectively. The residual aluminum concentration is 0.38 mg L' Adding in the system AICI3 with a dosage 100 mg L'1 at pH 6.0, HLES removal is 90%, 52% of lignin removal, the decline of COD is to 43%, but the decreases of solution BOD5 and color are about 49 and 86%, respectively. The residual aluminum concentration is 0.13 mg L'1. The structural characteristics of coagulates were studied by FT-IR and 13C-NMR methods. It was identified that the coagulates isolated by coagulation from model solution mainly consisted of O-acetil-4-0-metil-D-glucuron-l3-D-xylan units and small amount of lignin residues. The second objective of the study was to determine the effects of ozone on HLES removal after coagulation.Ozonation of the pre-coagulated model wastewater demonstrated the beneficial effects on the removal of HLES. The results indicated that ozonation increased the removal of HLES on 98%, reduction of lignin concentration, color and BOD5 on 97, 94 and 92%, respectively. A combination of coagulation and ozonation stages can provide the norms of fault, and also possibilities to return purified wastewater in a main technological cycle.