Effect of heterotrophic growth on autotrophic nitrogen removal in a granular sludge reactor

Abstract

This study deals with the influence of heterotrophic growth on autotrophic nitrogen removal from wastewater in a granular sludge reactor. A mathematical model was set-up including autotrophic and heterotrophic growth and decay in the granules from a partial nitritation-anammox process. A distinction between heterotrophic bacteria was made based on the electron acceptor (dissolved oxygen, nitrite or nitrate) on which they grow, while the nitrogen gas produced was 'labelled' to retrieve its origin, from anammox or heterotrophic bacteria. Taking into account heterotrophic growth resulted in a lower initial nitrogen removal, but in a higher steady state nitrogen removal compared with a model in which heterotrophic growth was neglected. The anammox activity is related with the fact that heterotrophs initially use nitrite as electron acceptor, but when they switch to nitrate the produced nitrite can be used by anammox bacteria. Increased anammox activity in the presence of heterotrophs, therefore, resulted in a marginally increased N2 production at steady state. Heterotrophic denitrification of nitrate to nitrite also explains why small amounts of organic substrate present in the influent positively affect the maximum nitrogen removal capacity. However, the process efficiency deteriorates once the amount of organic substrate in the influent exceeds a certain threshold. The bulk oxygen concentration and the granule size have a dual effect on the autotrophic nitrogen removal efficiency. Besides, the maximum nitrogen removal efficiency decreases and the corresponding optimal bulk oxygen concentration increases with increasing granule size.

Microbial community analysis of a full-scale DEMON bioreactor

“…Studies conducted before over the bacterial community structure of DEMON bioreactors have focused over the diversity of AOB and anammox bacteria [5,19] and have disregarded other bacteria that might be important for the performance of the system, as has been reported before [12,13]. However, this pyrosequencing analysis was able to capture a richer diversity of microorganisms, which leads to a better understanding of the functioning of the system.…”

“…In this way, phylotypes not related to these bacterial groups have never been investigated in these systems. Moreover, studies conducted over autotrophic nitrogen removal bioreactors have aimed that the presence of bacterial communities not related to AOB or anammox bacteria might have an effect over the performance of these systems [13,14]. In this way, an accurate analysis of all bacterial communities thriving in the DEMON bioreactor and the identification of their ecological roles is needed for a deeper understanding of the performance of the system.…”

Analysing the effects of the aeration pattern and residual ammonium concentration in a partial nitritation-anammox process

“…Previous studies have examined the effect of granule size and heterotrophic growth on autotrophic nitrogen removal systems. [2,13] The sensitivity and the effect of temperature on a completely autotrophic ammonium removal over nitrite system have also been studied. [14,15] The influence of mass transfer and microbial kinetics was investigated in a sensitivity analysis study of an autotrophic N removal granular bioreactor.…”

“…Therefore, the nitrification of nitrite to nitrate has to be repressed by outcompeting the nitrite-oxidizing bacteria (NOB). [2] The application of anammox bacteria in the sidestream of wastewater treatment plants has several advantages compared to the N/DN technology. The aeration requirements decrease by 60%, sludge production decreases by approximately 90% and there is no need for organic carbon.…”

“…[21] Since there is no real distinction between these heterotrophic groups, the corresponding reaction rates were expressed in terms of the total amount of heterotrophic bacteria (X HET = X O2,HET + X NO2,HET + X NO3,HET ). The production of organic materials from biomass decay was taken into account using the death-regeneration approach, [2] where living cells are turned partly into biodegradable substrate and partly into inert material. [22] In this model, the direct formation of soluble organic substrate (S S ) rather than particulate organic substrate, assumes that decay and not hydrolysis is the rate limiting step of soluble substrate formation from decay.…”