Pilot-scale ELAN ® process applied to treat primary settled urban wastewater at low temperature via partial nitritation-anammox processes

Abstract

A single stage partial nitritation and anammox granular pilot scale reactor (600 L) was operated to treat primary settled sewage in an urban wastewater treatment plant. The fed wastewater contained low total nitrogen concentrations of 6-25 mg TN/L and the system operated without temperature control ranging from 18 to 12 ºC. A control strategy, based on the pH value, was applied to stop the aeration supply. The pH setpoint was fixed at 6.0 and allowed obtaining a total nitrogen removal efficiency approximately of 50% treating a load of 67 mg TN/(L•d) without the addition of any chemicals. Although nitrite oxidizing bacteria were present in the inoculated sludge, when the pH-based control was implemented (day 30) the ammonium oxidation was favored compared to the nitrite oxidation activity. Then, the system operated stable the rest of the operational period (days 30-94) despite the presence of organic matter in the wastewater and the high variability of nitrogen load and temperature during the

Performance of partial nitritation-anammox processes at mainstream conditions in an IFAS system

“…The low effluent quality was already pointed out as one of the drawbacks of the continuously fed PN/AMX systems by Hoekstra et al (2018) who operated a 4-m 3 complete mixed reactor where NRR as high as 97 g N/(m 3 •d) at 13.4 ± 1.1 °C were reached. In this sense, the plug flow reactors (Lotti et al, 2015;Yang et al, 2017) or SBRs (Laureni et al, 2016;Pedrouso et al, 2018) are presumably more suitable for effluent quality optimization than the continuous complete mixed ones. Actually, it was demonstrated that using a residual ammonium concentration (2 -5 mg N/L) as set point either to terminate the reaction (Laureni et al, 2016) or to adjust the airflow rate (Yang et al, 2017) or the HRT (Malovanyy et al, 2015), higher NRE are achieved.…”

Partial denitrification coupled with immobilization of anammox in a continuous upflow reactor

“…[1][2][3] However, its independent use is limited since it requires nitrite nitrogen as an electron acceptor. At present, partial nitrication is the main route to obtain NO 2 À -N; however, it has high control requirements, is easily destroyed, 4,5 and is difficult to recover once destroyed. Therefore, new approaches are urgently required.…”

Possible mechanism of efficient mainstream partial nitritation/anammox (PN/A) in hybrid bioreactors (IFAS)

“…Those reactors type must have allowed keeping higher N-NH 4 bulk concentrations over the substantial period of time (after starting aeration cycle in SBR). As explained above, the positive effect of such conditions on nitrogen removal rate by AOB was possibly reinforced by high residual N-NH 4 [17,18,25,28,30,34,39]. There are proofs that biomass growing in the PN/A systems can be enriched with AOB by the application of high nitrogen loading rate [25].…”

“…Although the studies of Regmi et al [6,7] and Al-Omari et al [8] explained the logic of application of an aeration strategy with a relatively high dissolved oxygen concentration (above 1 mgO 2 /l) and intermittent aeration, in the available literature there is no explicit proof that a specific range of dissolved oxygen concentration (DO) and intermittent aeration leads to efficient mainstream PN/A process (Figure 1(B) 'MBBR') [4,5,31,[38][39][40]. That strategy had a desired effect only when AOB bacteria were kept in the system, in the form of activated sludge, by recirculating a detached biofilm from the secondary clarifier to bioreactor or inoculation of the MBBR bioreactor with the activated sludge originated from a conventional SBR for municipal wastewater treatment (transition of the bioreactor operation from MBBR to IFAS mode) [4,5].…”