Comparison of nutrients degradation in small scale membrane bioreactors fed with synthetic/domestic wastewater.

Two membrane bioreactors were operated with biological phosphorus removal, carbon degradation and denitrification to check how comparable and representative they were compared to full-scale plants. One was fed with synthetic municipal wastewater and was switched from pre- to post-denitrification without carbon dosing. The influent of the second plant was drawn from a separate sewer. This plant worked the whole time with post-denitrification without carbon dosing. The synthetic wastewater was designed to achieve a realistic COD:TN:TP ratio and tested for long time biodegradability. The eliminations were >94% (COD) and >97% (TP) for both plants. This was within the range of commercial plants, as well as the TN elimination for the pre-denitrification of plant I (>75%). The eliminations of TN for post-denitrification were above 80% for both plants despite the high influent concentrations and the missing carbon source for post-DN. A calculation of the nitrification rates gave values similar to those found in literature (1-6 mgN/(gMLVSSh)). A comparison of the denitrification showed expected rates for pre-denitrification (7.5 mgN/(gMLVSSh)) for plant I. The values (on average 1.8 mgN/(gMLVSSh)) for post-denitrification in plant II were higher than endogenous denitrification rates which are commonly reported as 0.2-0.8 mgN/(gMLVSSh). The rates for post-denitrification in plant I were only slightly higher than endogenous ones (0.9 mgN/(gMLVSSh)).