COMPARISON OF PERFORMANCE AMONG 4 DIFFERENT PROCESSES FOR THE ANAEROBIC TREATMENT OF WASTE-WATER WITH A LOW CONCENTRATION OF ORGANIC-MATTER

As anaerobic treatment of wastewater with a low concentration of organic matter (low-strength wastewater), an improved conventional process with recycling of sludge (hereafter called sludge-recycling process) and some novel processes were tested using synthetic wastewater (TOC, 100 to 2000 mg l-1) at a volumetric loading rate of TOC of 0.8 g l-1 d-1 and performance of each process was evaluated. The sludge-recycling process was unsuitable for the treatment of the synthetic wastewater of 2000 mg TOC l-1, and an ORP (oxidation-reduction potential)-control system was even worse. By contrast, the novel processes involving an anaerobic fluidized-bed reactor (AFBR) an upflow anaerobic sludge blanket (UASB) and an upflow anaerobic filter process (UAFP), which can hold a high concentration of sludge, each process treated low-strength wastewater efficiently. In particular, AFBR and UASB reached a removal efficiency of TOC of 80% for the lowest-strength wastewater (TOC of 100 mg l-1, which corresponded to a B0D of 250 mg l-1). Under appropriate conditions (volumetric loading rate, 0.8 g TOC l-1d-1; concentration of TOC in influent, 100 mg/l) AFBR also maintained a removal efficiency of TOC of 80%, even when the temperature of treatment was lowered to 15-degrees-C. Under these conditions, it was found that the treatment by AFBR could be performed with a very short hydraulic retention time (HRT) of three hours, even if the volume of the support medium in the reactor was neglected in the calculation.