Can a moving bed bioreactor reduce toxicity of complex industrial wastewater?
MeadWestvaco Corporation in DeRidder, Louisiana refines crude tall oil (a byproduct of black liquor) to produce a variety of specialty chemicals products. The facility generates approximately 0.46 million gallons per day (mgd) of wastewater that require treatment for total recoverable phenols (TRP), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and whole effluent toxicity (WET). Potential plant expansions and modifications may require improvement and/or expansion of the wastewater treatment process, and moving bed bioreactor (MBBR) technology was proposed as part of this expansion. Pilot-scale testing of media from AnoxKaldnes and Hydroxyl Systems was conducted to evaluate the MBBR technology. This study demonstrated that MBBR technology, in spite of its known benefits, is not necessarily a silver bullet for treatment of complex industrial wastewater streams such as this tall oil refinery effluent. The MBBR systems were efficient with respect to removal of easily biodegradable organics (i.e., BOD) and significant fractions of COD and TRP. The removals were insufficient for meeting permit limits of COD, and TRP, and WET. No significant differences were observed between the media provided by the vendors. The reason for the inability of the MBBRs to meet the discharge limit was primarily a function of the composition and concentration of the wastewater rather than an inherent flaw in the MBBR technology. When considering MBBR technology or any other biological treatment technology during a planned plant expansion or process change, it is important to consider the composition and concentration of the wastewater and how that composition will affect the wastewater treatment process. Thus use of MBBR technology is not the appropriate solution to the planned plant expansion. Rather, there is need to use alternative treatment processes in place of the MBBR and/or use MBBR plus additional pre- or post treatment of the wastewater. Such alternatives are being considered at the plant.