[show abstract][hide abstract] ABSTRACT: Limited filamentous bulking caused by low dissolved oxygen (DO) was proposed to establish a low energy consumption wastewater treatment system. This method for energy saving was derived from two full-scale field observations, which showed pollutants removal would be enhanced and energy consumption could be reduced by at least 10% using limited filamentous bulking. Furthermore, preliminary investigation including the abundance evaluation and the identification of filamentous bacteria demonstrated that the limited filamentous bulking could be repeated steadily in a lab-scale anoxic-oxic reactor fed with domestic wastewater. The sludge loss did not occur in the secondary clarifier, while COD and total nitrogen removal efficiencies were improved by controlling DO for optimal filamentous bacterial population. Suspended solids in effluent were negligible and turbidity was lower than 2 NTU, which were distinctly lower than those under no bulking. Theoretical and experimental results indicated the aeration consumption could be saved by the application of limited filamentous bulking.
[show abstract][hide abstract] ABSTRACT: With an increase in using seawater, saline sewage is necessarily disposed of to protect the ocean. The objective in this work is to evaluate the effect of influent salinity and inhibition time on short-cut nitrogen removal from real domestic saline sewage, and to detect the performance of nitrifiers in activated sludge in SBR. Microbial tests are used to establish the mechanism of salt inhibition. Dynamic response of salt is recorded during and after the salt inhibition stage. As microbial population tests support that NOB is strongly inhibited below 1% (w/v) salt content, three different salt levels (0.52%, 0.76% and 1.02%) are applied respectively in three parallel SBRs for 60 days. Results reveal that NARs all increase by 95% and keep steady after the 15th, 7th and 2nd day by adding salt. Ammonia is almost totally degraded at the steady state at salt levels below 0.75%; however, it degrades nearly half at 1.02%. After stopping salt addition, the ARE in a 1.02% system reaches 94.3% at the 18th cycle and the SAURs all apparently increase. The NAR in 0.52% and 0.76% systems decreases at the 9th and 20th cycle but still keeps above 95% in the 1.02% system. In order to gain steady shot-cut nitrification in a SBR, conditions of salinity greater than 0.76% and salt inhibition for more than 60 days are very competitive and favorable for application.