A laboratory bench-scale study was undertaken in order to investigate the anaerobic biological treatment of high-strength acidic organic wastewaters utilizing the Upflow Sludge Blanket (USB) treatment process. A synthetic wastewater was utilized having a pH of 4.2 and consisting primarily of acetic and propionic acids.
While operating at substrate loading rates of 1.1 and 2.4 kg COD/kg VSS/d (i.e., 10 and 30 kg COD/m3/d, respectively), the USB treatment process removed in excess of 90 per cent of the total COD present in the raw wastewater, for waste strengths of 2 to 32g COD/L and hydraulic retention times varying between 3.2 and 76.8 hours. The process demonstrated the ability to polish the effluent waste stream to effluent COD concentrations of less than 300 mg/L. The process was able to tolerate hydraulic and waste strength shockloads. No observable deterioration in pH or effluent quality was identified following sudden increases in wastewater concentration (e.g., 4 to 32g COD/L) or decreases in hydraulic retention time (e.g., 25.6 to 3.2 hours). The use of effluent recirculation did not influence treatment efficiency but was necessary in order to partially neutralize the influent low pH wastewater.
The results of this research also demonstrate the feasibility of utilizing the USB reactor as the methane forming reactor in a two-stage anaerobic wastewater treatment system. Recommendations are provided concerning the design of such a system.