Abstract
This study determined how the activity and number of nitrogen-converting microorganisms varied with changes in hydraulic retention time (HRT) and the operating regime of aerobic granular sequencing batch reactors (GSBRs) treating high-nitrogen wastewater. Continuously aerated (O-mode) GSBRs were operated at HRTs of 10-, 13- and 19-h. Then the same reactors were operated at identical HRTs but the cycles started with an anoxic phase (A/O mode). To investigate the microbial communities, DNA- and RNA-based relative real-time PCR was used. In all experimental reactors ammonium was fully removed with a removal rate up to 75 mg N–NH4 +/(L·h), and nitrification efficiency was above 90 %. The efficiency of the removal of oxidized nitrogen forms decreased with the lengthening of HRT. The study found that variable oxic conditions (A/O mode) in the GSBR cycle stimulated the simultaneous activity of ammonium oxidizing bacteria (AOB), N2O-reducers, and Anammox bacteria in aerobic granules. With both modes, the activity of nitrogen-converting bacteria was highest with a 13-h HRT. Shortening HRT, resulted in higher chemical oxygen demand and nitrogen loadings, which favored the growth of Anammox microorganisms in granules and caused a decrease in the number of AOB. With all HRTs, the number of Anammox microorganisms was about 1.5-times higher in A/O mode than in O mode.Electronic supplementary materialThe online version of this article (doi:10.1007/s11274-014-1766-1) contains supplementary material, which is available to authorized users.
Highlights
In recent years, there has been intensive development of wastewater treatment based on aerobic granular sludge cultivated in sequencing batch reactors (GSBRs)
The study found that variable oxic conditions (A/O mode) in the granular sequencing batch reactors (GSBRs) cycle stimulated the simultaneous activity of ammonium oxidizing bacteria (AOB), N2O-reducers, and Anammox bacteria in aerobic granules
Ammonium was fully removed by the granules within the first 5 or 4 h of the cycle in O or A/O mode, respectively, which corresponded to average ammonium removal rates of 65 and 75 mg N–NH4?/(LÁh)
Summary
There has been intensive development of wastewater treatment based on aerobic granular sludge cultivated in sequencing batch reactors (GSBRs). This is because aerobic granules offer several advantages when compared to activated sludge: they have greater size, more compact structure and higher resistance to organic load and toxic substances. If HRT is too long, energy consumption for aeration is high and the starvation phase in the GSBR cycle is long. Too short an HRT increases the risk of inefficient pollutant removal and produces a large excess of biomass as a result of a high pollutant loading
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