A comparison of CSTR and SBR bioslurry reactor performance

A continuous-flow stirred tank reactor (CSTR) and a soil slurry-sequencing batch reactor (SS-SBR) were maintained in 81 vessels for 180 days to treat a diesel fuel-contaminated soil. The SS-SBR provided markedly enhanced cont aminant degradation relative to the CSTR. Diesel fuel removal efticiency wa s 96% in the SS-SBR, compared with 75% in the CSTR. Microbial growth was ap proximately 25% greater in the SS-SBR than the CSTR. However, significant b iosurfactant production and foaming occurred in the SS-SBR, whereas none wa s observed in the CSTR. Surfactants were produced in the SS-SBR at concentr ations up to 70 times the critical micelle concentration (CMC), but were bi odegraded by the end of the cycle. Reactor operation was reversed after 80 days. The reactor converted from an SS-SBR to a CSTR lost surfactant produc tion and showed reduced diesel fuel degradation. Converting the CSTR to an SS-SBR resulted in surfactant production and enhanced diesel fuel degradati on. These results indicate that fill-and-draw operation selected for microb es with a greater ability to produce surfactants and degrade diesel fuel th an the CSTR operation. Decreasing the diesel fuel addition rate in the SS-S BR by four times on day 160 reduced the maximum surfactant concentration an d foam thickness by more than three times without affecting diesel fuel rem oval. (C) 2000 Elsevier Science Ltd. All rights reserved.