Comparative performance of RBC operated under pressure and open to the atmosphere at high loading conditions

The aim of this research was to investigate the effects of pressure on aerobic biological wastewater treatment processes. For the purpose of the investigation two specially designed, identical, laboratory-scale rotating biological contactor (RBC) units were constructed. One of these was held in a steel pressure vessel while the other, as reference unit, was operated open to the atmosphere. The treatment capabilities of the pressurized unit, compared to those of the reference unit, were determined for a variety of organic loading rates at a 5-bar pressure. The unit under pressure was able to produce a much better effluent, in comparison with the reference unit when operating at higher loading conditions. The filtered BOD5 in the effluent from the unit under pressure was always less than 10 mgL(-1), whereas the sludge yield coefficient was as low as 0.21 kg dry solids/kg BOD5 removed, even with the unit loaded even at an organic loading rate of 27.0 g BOD5/m(2) (.) day. However, the development of the nitrification decreased sharply as the organic loading increased. The indication is that the unit under pressure is able to operate over a wide range of loading with a small variation in the effluent quality. The principal benefits of increasing pressure were recorded to be significantly improved nitrification and a decrease in the sludge yield coefficient.