4Center for Regional Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaragi 305-8506, Japan
5Department of Social and Environmental Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashihirosima, Hiroshima 739-8527, Japan
A newly developed natural rubber deproteinization process produces deproteinized natural rubber (DPNR) wastewater as an intermediate product containing a high concentration of sodium dodecyl sulfate (SDS) and rubber. In this study, a novel process to recover the residual rubber and energy as methane from DPNR wastewater was developed. As a pretreatment, SDS and residual rubber in DPNR wastewater were coagulated and recovered by addition of CaCl2 at Ca2+/SDS and Ca2+/rubber mass ratios of 0.070 and 0.055, respectively. The remaining organic matter in the pre-treated DPNR wastewater was converted to methane by using a mesophilic up-flow anaerobic sludge bed (UASB) reactor. The UASB reactor with the diluted pre-treated DPNR wastewater showed a total chemical oxygen demand (COD) removal efficiency of 92 ± 2% at a maximum loading rate of 6.8 ± 1.8 kgCOD·m-3·d-1 at a hydraulic retention time (HRT) of 12 h. Under the condition of effluent recirculation with raw pre-treated DPNR wastewater, the UASB reactor showed a total COD removal efficiency of 84 ± 8% at the maximum loading rate of 6.4 ± 1.7 kgCOD·m-3·d-1 at HRT of 39 h. The results suggest that the newly developed resource recovery process for DPNR wastewater could be a promising treatment system.