Advanced nitrogen removal from mature landfill leachate based on novel step-draining partial nitrification-denitrification and Anammox process: Significance of low volume exchange ratio.

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

An Innovative Process for Mature Landfill Leachate and Waste Activated Sludge Simultaneous Treatment Based on Partial Nitrification, In Situ Fermentation, and Anammox (PNFA).

An innovative partial nitrification, in situ fermentation, and Anammox (PNFA) system was developed to achieve mature landfill leachate and waste activated sludge simultaneous treatment. Three separate sequencing batch reactors (SBRs) were used for partial nitrification (PN-SBR), integrated fermentation-denitrification (IFD-SBR), and partial nitrification-Anammox (PNA-SBR). After 200 days of continuous operation, a satisfactory nitrogen removal efficiency (NRE) of 99.2 ± 0.1% was obtained, with an effluent total nitrogen (TN) of 15.2 ± 3.2 mg/L. In IFD-SBR, the volatile fatty acids generated from fermentation drove efficient denitrification, obtaining sludge and nitrogen reduction rates of 4.2 ± 0.7 and 0.61 ± 0.04 kg/m3·day, respectively. Furthermore, unwanted fermentation metabolites (134.1 mg/L NH4+-N) were further treated by PNA-SBR using a combination of step-feed and intermittent aeration strategies. In PNA-SBR, Anammox significantly contributed to 82.1% nitrogen removal, and Anammox bacteria (Candidatus Brocadia, 2.3%) mutually benefited with partially denitrifying microorganisms (Thauera, 4.2%), with 66.3% of generated nitrate reduced to nitrite and then reutilized in situ by Anammox. Compared with the conventional nitrification-denitrification process, PNFA reduced oxygen energy consumption, external carbon source dosage, and CO2 emission by 21.3, 100, and 38.9%, respectively, and obtained 50.1% external WAS reduction efficiency.

Advanced nitrogen removal from landfill leachate via a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA).

In this study, a two-stage combined process of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) was established achieving advanced nitrogen removal from landfill leachate. The PNA sludge used to treat reject water adapted to the leachate in 37 days, resulting in fast start-up of the PNA process with a nitrogen removal rate (NRR) of 0.22 kgN/(m3·d). Partial denitrification (PD) was induced using sodium acetate and proceeded in a stepwise manner using sludge fermentation liquid (SFL), achieving a NO3--N to NO2--N transformation ratio (NTR) of 52.1 ± 1.1% within 16 days. PDA was established via the addition of mature Anammox biofilms. The nitrogen removal efficiency (NRE) of this system was 97.6 ± 1.5%, of which PNA and PDA contributed 74.8 ± 4.0% and 18.7 ± 4.1%, respectively. Nitrosomonas (2.6% in PNA), Thauera (16.0% in PDA) and Candidatus Brocadia (23.0% in PNA, 1.4% in PDA) were dominant in the two-stage system. This study provides valuable and novel insights, supporting the practical application of PNA-PDA processes in landfill sites.

Stable nitritation of mature landfill leachate via in-situ selective inhibition by free nitrous acid.

In-situ free nitrous acid (FNA) and free ammonia (FA) treatments are more feasible than side-stream methods to achieve nitritation. To assess the optimum conditions and long-term performance of in-situ inhibition by FNA, batch tests and a sequencing batch reactor (SBR) treating mature landfill leachate were conducted and established. As a result, the selective inhibition characteristic by FNA was more conspicuous than FA, and FNA (0.175 mg N/L, 6 h) treatment are more biocidal to nitrite oxidizing bacteria (NOB). Moreover, ammonia oxidizing bacteria (AOB) were more sensitive to the FA environment but its activity recovered preferentially compared to NOB. The SBR achieved a sustained nitrite accumulation rate above 90% for 200 days, with a significant decrease of NOB activity and microbial abundance according to qPCR and 16S rRNA gene sequencing results. In-situ selective inhibition by FNA (0.175 mg N/L, 6 h) has been proved to be effective to maintain stable nitritation.

Achieving synergetic treatment of sludge supernatant, waste activated sludge and secondary effluent for wastewater treatment plants (WWTPs) sustainable development.

A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH4+-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO3--N = 58.6 mg/L). Three separated reactors were used for partial nitrification (PN-SBR), integrated fermentation and denitrification (IFD-SBR) and combined Anammox-partial denitrification (AD-UASB), respectively. The process resulted in excellent nitrogen removal efficiency (NRE) of 98.7%, external sludge reduction efficiency (SRE) of 44.6% and external sludge reduction rate of 4.1 kg/m3 after 200 days of continuous operation. IFD-SBR and AD-UASB contributed towards 89.4% and 9.2% nitrogen removal, respectively. In AD-UASB, cooperation between Anammox bacteria (4.1% Candidatus Brocadia) and partial denitrifying bacteria (3.2% Thauera) resulted in significant stability of Anammox pathway, which contributed up to 84.1% nitrogen removal in the combined Anammox-partial denitrification process. NFAD saved up to 100% organic resource demand and 25% of aeration consumption compared with the traditional nitrification-denitrification process.

Novel insights into overcoming nitrite oxidation bacteria acclimatization problem in treatment of high-ammonia wastewater through partial nitrification.

A partial nitrification sequencing batch reactor was operated to reveal mechanisms behind nitrite oxidation bacteria (NOB) acclimatization in high-ammonia wastewater treatment. The influent NH4+-N increased stepwise from 499.7 ± 4.2 mg/L to 6994.5 ± 7.5 mg/L with initial free ammonia (FA) concentration rising from 37.9 ± 3.2 mg NH3-N/L to 715.3 ± 47.3 mg NH3-N/L, respectively. NOB acclimatized this FA range with NO3--N production increasing from 29.2 ± 2.6 mg/L to 144.1 ± 31.0 mg/L in a cycle, which was caused by the shift of dominant NOB genus from Nitrospira to Nitrolencea. Nitrosomonas as ammonia oxidation bacteria, could sustain its activity of 62.1 ± 0.1 mg NH4+-N/(gVSS∙L∙h) under the same condition. Hydroxylamine addition could be implemented as an emergency measure to alleviate NOB acclimatization in short-term operation. The findings expanded knowledge about NOB acclimatization types and provided novel insights for addressing this problem in a targeted way.

Efficient and advanced nitrogen removal from mature landfill leachate via combining nitritation and denitritation with Anammox in a single sequencing batch biofilm reactor.

A novel combined partial nitrification-Anammox and partial denitrification-Anammox (PnA/PdA) single sequencing batch biofilm reactor (SBBR) was established to realize efficient and advanced nitrogen removal from mature landfill leachate with low biodegradability. Nitrogen removal rate and nitrogen removal efficiency were increased to 2.83 ± 0.06 kgN/(m3∙d) and 98.6 ± 0.2% by stepwise increase of dissolved oxygen (DO, from 0.5 to 3.5 mg/L) and continuous carbon source feeding. Comparable activities of ammonia oxidation bacteria and Anammox bacteria were realized during aerobic period. More organic carbon was redirected from complete denitrification to partial denitrification during anoxic period. The main pathway PnA jointly synergized with PdA, which contributed to 76.04% and 19.44% nitrogen removal, respectively. Nitrosomonas, Thauera, and Kuenenia dominated in floc sludge (0.78%, 5.38%, and 1.14%, respectively) and biofilm (0.34%, 5.18%, and 0.98%, respectively). Overall, this study provides new insight into the high-efficiency treatment of landfill leachate at full-scale landfill sites.

New insights into co-treatment of mature landfill leachate with municipal sewage via integrated partial nitrification, Anammox and denitratation.

As a low consumption and high efficiency process, Partial Nitrification-Anammox/denitratation (PNAD) was applied to co-treat mature landfill leachate with municipal sewage for 300 days. Specifically, ammonia (670.2 ± 63.7 mg N/L) contained in mature landfill leachate was firstly oxidized to nitrite (611.5 ± 28.1 mg N/L) in sequence batch reactor (SBRPN); meanwhile, organic matter in municipal sewage was partially removed in another reactor (SBROMR); finally, nitrite produced (611.5 ± 28.1 mg N/L) in SBRPN and ammonia (53.1 ± 6.4 mg N/L) residing in pretreated municipal sewage were simultaneously degraded through combined Anammox-denitratation process in an up-flow anaerobic sludge bed (UASBAD). A satisfactory effluent quality of 10.3 mg/L TN was obtained after long-term operation, with Anammox and denitrification contributing to 86.2% and 5.8% nitrogen removal efficiency, respectively. Mass balance confirmed 67.2% nitrate generated from Anammox could be reduced to nitrite and in-situ reused. Anammox bacteria genes and nitrate reductase/nitrite reductase ratio were highly detected, accelerating combined Anammox-denitratation. Further, Ca. Brocadia triumph among various Anammox bacteria groups, increasing from 1.2% (day 120) to 3.6% (day 280).

Culturing sludge fermentation liquid-driven partial denitrification in two-stage Anammox process to realize advanced nitrogen removal from mature landfill leachate.

The two-stage partial nitrification (PN)-Anammox process, during long term treatment of high-ammonia nitrogen leachate, faces challenges such as the adaptation of nitrite oxidation bacteria (NOB) and failure of real-time control of pH. Resultant instabilities including NH4+-N and NO3--N accumulation were overcome by culturing sludge fermentation liquid (SFL)-driven partial denitrification (PD) in situ in the Anammox process. Biodegradation of slowly biodegradable organics (SBO) in SFL created organics restriction condition, which limited the activity of denitrification bacteria and achieved its balance with Anammox bacteria. Produced NO3--N is reduced to NO2--N through PD, which further improved the removal of NH4+-N through Anammox. NO2--N was utilized timely by Anammox bacteria, which avoid further reduction of NO2--N to N2, and result in a high nitrate to nitrite transformation ratio (NTR) of 93.3%. Satisfactory nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 99.6% and 822.0 ± 9.0 g N/(m3∙d) were obtained, respectively. Key genera related to degradation of SBO, PD and Anammox were enriched. The value of narG/(nirK+nirS) increased from 0.05 on day 1-0.15 on day 250. Combining SFL-driven PD with two-stage Anammox process provided a novel insight for applying this process to realize advanced nitrogen removal in practical engineering.

Enrichment and retention of key functional bacteria of partial denitrification-Anammox (PD/A) process via cell immobilization: A novel strategy for fast PD/A application.

Cell immobilization was used to enrich and retain functional bacteria within partial denitrification-Anammox (PD/A) process to achieve its fast start-up for the first time. To do so, residue sludge and Anammox sludge were immobilized in poly (vinyl alcohol)/sodium alginate (PVA/SA) gel for PD cultivation and Anammox bacteria inoculation, respectively. Stable PD with NO3--N to NO2--N transformation ratio (NTR) of 72.0% was achieved within 13 days at 25 °C and successfully combined with Anammox on 14th day. The hydrous porous PVA/SA gel matrix played the role of extracellular polymeric substance (EPS) and thus protected the microbes against low temperature. Satisfactory nitrogen removal rate (NRR) (301.6 ± 6.1 g N/(m3·d)) was achieved even when temperature decreased to 13 °C. The contribution of nitrogen removal via Anammox was as high as 77.10%. Abundance of Thauera and Candidatus Kuenenia increased from 0.9% and 1.1% to 30.6% and 2.1%, respectively.