PRIMARY FERMENTATION OF SOLUBLE AND PARTICULATE ORGANIC-MATTER FOR WASTE-WATER TREATMENT

A new reactor based on upflow sludge blanket technology (USB) for ferm entation of both the particulate and soluble fractions of domestic was tewater is presented. The process is fed with the total wastewater flo w, and carries out suspended solids (SS) retention, fermentation and c larification of the fermented effluent in a single reactor. The study was carried out using pilot scale reactors, under six different operat ing conditions with regards to hydraulic load (hydraulic retention tim e, HRT, varying between 1.1 and 4.3 hours) and at a constant temperatu re (20 +/- 1 degrees C). With regards to primary treatment, the proces s has been shown to ensure low SS residuals in the fermented effluent under all operating conditions tested. Very low residuals, with an ave rage below 50 mg SS/I, were obtained with an upflow velocity of betwee n 0.75 and 0.9 m/h. These trials have also highlighted the important r ole played by the adsorption of particulate organic matter on the biol ogical flocs of the sludge blanket in the elimination of SS. Fermentat ion efficiencies are superior to those of existing fermenters, the res ults clearly proving that a majority of the volatile fatty acids produ ced originate from the soluble fraction of the wastewater. Under the o ptimum conditions tested, with an HRT = 2.8 hours, 0.17 mg HAc/mg tota l COD are produced, over 60% of which is generated by the fermentation of the influent soluble organic matter. Under these operating conditi ons, maximum solubilisation of the particulate fraction has been estim ated at 0.13 mg of filtered COD/mg particulate COD (total COD-filtered COD).