Startup strategy for nitrogen removal via nitrite in a BAF system.

A biological aerated filter (BAF) pilot plant consisting of two reactors (aerobic and anoxic one) was used to determine a strategy to remove nitrogen via nitrite. RNA/DNA analysis was performed to assess microbial activity and support chemical results. In less than 13 days the pilot plant was able to remove COD and suspended solids. Nitrogen removal via nitrite pathway could not be observed until day 130 when the empty bed contact time (EBCT) was set at 0.71 h. Nitrite was detected in the aerated BAF effluent but never nitrate. qPCR of amoA gene from RNA and DNA extracts of the aerobic biofilm confirmed that ammonia oxidizing bacteria (AOB) were present from the beginning of the operation but not active. AOB activity increased with time, reaching stability from operational day 124. The combination of both, low EBCT together with high OLR, has been demonstrated to be a feasible strategy to startup a BAF to achieve nitrogen removal via nitrite.

Characterization and mitigation of nitrous oxide (N2 O) emissions from partial and full-nitrification BNR processes based on post-anoxic aeration control.

It has been reported that a directional change from anoxic to aerobic conditions is a common trigger for nitrous oxide (N2 O) production by ammonia oxidizing bacteria (AOB). By extension, during anoxic-aerobic cycling, post-anoxic dissolved oxygen (DO) concentrations might likely play a role in the magnitude of N2 O emissions observed. The overall goal of this study was to determine the impact of three select post-anoxic DO concentrations (0.8, 2.0, and 3.0 mg O2 /L) on N2 O emissions from partial-nitrification (PN) and full-nitrification (FN) reactors subjected to anoxic-aerobic cycling and, ultimately, to explore the development of strategies to minimize N2 O emissions from PN and FN based biological nitrogen removal (BNR) processes. Statistically similar N2 O emissions were observed during anoxia for both PN (0.62 ± 0.21% N load) and FN (0.61 ± 0.070% N load) processes. In contrast, N2 O emissions were statistically lower for PN (0.86 ± 0.25% N load) than for FN (4.6 ± 2.8% N load), during the post-anoxic aerobic phase, when compared together for all three post-anoxic DO concentrations. Further, for PN, the highest N2 O emissions were observed at the highest post-anoxic DO concentration of 3.0 mg O2 /L (1.2% N load), likely due to the highest corresponding AOB specific growth rate. In contrast, for FN, the highest N2 O emissions were at the lowest post-anoxic DO concentration of 0.8 mg O2 /L (8.5% N load). The higher emissions from FN process at low DO concentrations were associated with a lag in nitrite oxidizing bacteria activity upon recovery to aerobic conditions. This lag phase contributed to transient nitrite accumulation, and in turn correlated positively to the observed N2 O emissions. Based on our findings, a gradual ramp up in post-anoxic DO concentrations can minimize N2 O emissions during PN-based BNR, whereas a completely different strategy, entailing a rapid increase in post-anoxic DO concentrations can minimize emissions during FN-based BNR operations.

Landfill Leachate Treatment by Using Second-Hand Reverse Osmosis Membranes: Long-Term Case Study in a Full-Scale Operating Facility.

Landfill leachate (LFL) has a complex inorganic, organic and microbiological composition. Although pressure-driven membrane technology contributes to reaching the discharge limits, the need for frequent membrane replacement (typically every 1-3 years) is an economical and environmental limitation. The goal of this work is to evaluate the feasibility of using second-hand reverse osmosis (RO) membranes to treat LFL in an industrially relevant environment. End-of-life RO membranes discarded from a seawater desalination plant were first tested with brackish water and directly reused or regenerated to fit with requirements for LFL treatment. A laboratory scale test of second-hand membrane reuse was carried out using ultrafiltered LFL. Then, a long-term test in an LFL full-scale facility was performed, where half of the membranes of the facility were replaced. The industrial plant was operated for 27 months with second-hand membranes. The permeate water quality fit the required standards and the process showed a trend of lower energy requirement (up to 12 bar lower transmembrane pressure and up to 9% higher recovery than the average of the previous 4 years). Direct reuse and membrane regeneration were successfully proven to be an alternative management to landfill disposal, boosting membranes towards the circular economy.

Long-term operation of a partial nitritation pilot plant treating leachate with extremely high ammonium concentration prior to an anammox process.

The goal of this work was to demonstrate the feasibility of treating leachate with high ammonium concentrations using the SBR technology, as a preparative step for the treatment in an anammox reactor. The cycle was based on a step-feed strategy, alternating anoxic and aerobic conditions. Results of the study verified the viability of this process, treating an influent with concentration up to 5000 mg N-NH(4)(+) L(-1). An effluent with about 1500-2000 mg N-NH(4)(+) L(-1) and 2000-3000 mg N-NO(2)(-) L(-1) was achieved, presenting a nitrite to ammonium molar ratio close to the 1.32 required by the anammox. Furthermore, taking advantage of the biodegradable organic matter, the operational strategy allowed denitrifying about 200 mg N-NO(2)(-) L(-1). The extreme operational conditions during the long-term resulted on the selection of a sole AOB phylotype, identified by molecular techniques as Nitrosomonas sp. IWT514.