Evaluation of key factors for residual rubber coagulation in natural rubber processing wastewater

Key factors for residual rubber coagulation in natural rubber (NR) processing wastewater were evaluated via a laboratory-scale system comprising an anaerobic baffled reactor (ABR) and a downflow hanging sponge (DHS) reactor (ABR-DHS system). Hydraulic retention time (HRT), seeding of the core rubber, and existence of air are selected as key factors for rubber coagulation. In the ABR, longer HRT and seeding of the core rubber was not affected for rubber coagulation. Only biodegradable substances were consumed in the ABR. On the other hand, the DHS reactor achieved high removal efficiency of residual rubber by both coagulation and biological degradation. In addition, seeding of the core rubber to the DHS reactor enhanced rubber coagulation. The genera Gordonia, known as a rubber-degrading bacteria, were detected from the retained sludge in the DHS reactor. Therefore, the wastewater-air and wastewater-core rubber contacts are considered as key factors for residual rubber coagulation in the NR wastewater treatment. Furthermore, biodegraded residual rubber was considered as carbon source for denitrification in the DHS reactor.