Difference of high-salinity-induced inhibition of ammonia-oxidising bacteria and nitrite-oxidising bacteria and its applications

Membrane-enhanced methanogenesis efficiency and biomass retention in EGSB-AnMBR for food waste press filtrate treatment

In this study, an anaerobic membrane bioreactor (AnMBR) system was integrated with the expanded granular sludge bed (EGSB) to enhance the treatment performance and stability of food waste press filtrate (FWPF) digestion. A long-term continuous experiment was conducted at organic loading rates (OLRs) of 6.7, 13.4 and 20.1 g-COD/L/d. The optimal OLR was determined to be 13.4 g-COD/L/d, achieving a methane yield of 0.25 L-CH4/g-COD. At the OLR of 6.7 g-COD/L/d, both the EGSB and EGSB-AnMBR exhibited excellent COD removal efficiencies of 95.1% and 98.4%, respectively, with the membrane contributing only a marginal 3.0% improvement in the methanogenic performance of EGSB. However, at an increased OLR of 13.4 g-COD/L/d, the COD removal efficiency of the EGSB dropped to 77.3% due to granular sludge disintegration. In contrast, biomass retention by the membrane enabled the EGSB-AnMBR to maintain a significantly higher COD removal efficiency of 97.0%. The membrane enhanced the methanogenic performance of the EGSB by 34.5%, primarily by retaining all biodegradable COD. Of this enhancement, 3.6% was specifically attributed to membrane-rejected SCOD. Membrane fouling analysis revealed that cake layer formation was the dominant fouling mechanism under low-flux operation. Dissolved organic matter characterization provided further insights into fouling dynamics. These findings highlight the potential of the EGSB-AnMBR system as a robust and efficient solution for FWPF treatment, particularly in overcoming the limitations of conventional EGSB reactors.

Intelligent FA/FNA alternating strategy for nitrite-oxidizing bacteria inhibition: Data-driven prediction and process control

Alternating treatment with free ammonia (FA) and free nitrous acid (FNA) is an effective strategy to inhibit nitrite-oxidizing bacteria (NOB) in partial nitrification (PN) process. However, the current alternating treatment relies on manual assessment of nitrite accumulation rate (NAR), which poses challenges for automation. This study proposed an intelligent control system for automatic real-time switching between FA/FNA inhibition strategy and real-time control of inhibition concentration to realize stable NOB inhibition. By comparing the prediction performance of three models with different complexities for both classification and regression methods, support vector machine (SVM) was used to determine whether to alternate the strategies based on whether NAR was below 96 % and multilayer perceptron (MLP) was used for real-time control of FNA concentration by predicting the nitrite concentration. The high prediction accuracy of these two sub-models provides a solid foundation for the automatic control model of FA/FNA. Both models were trained and tested using an experimental dataset with manual alternating FA/FNA strategy over 180 days of a continuous flow PN reactor. After optimizing algorithms, the SVM had a 91.67 % classification accuracy, while the MLP showed an R2 of 0.96 and an RMSE of 53.16. During the real-time control of the intelligent control system, the SVM showed a classification accuracy of 97.5 % compared to actual measurements, and the R2 between the controlled FNA and the actual FNA is 0.83, with an RMSE of 0.04. The real-time operation demonstrates that the intelligent control system can promptly realize FA/FNA alternating and accurately control FNA concentration, maintaining NAR above 95.55 % while ammonium removal efficiency above 52.99 %. Compared to the current alternating treatment, the intelligent control strategy simplifies the manual operations and enables the automation of the FA/FNA alternating inhibition strategy, contributing to the stable and efficient operation of the PN process and promoting the application of PN/A process.

Robust aeration coefficient control based on pH feedback towards stable NO2--N/NH4+-N ratio in large pilot-scale partial nitritation reactor treating food waste digestate

Two-stage partial nitritation/anammox (PNA) system is a promising technology for treating food waste digestate (FWD). Maintaining a stable NO2--N/NH4+-N ratio in partial nitritation (PN) is essential for the successful implementation of two-stage PNA. Although the aeration coefficient (AC) is a key regulatory parameter, its stability is challenged by fluctuations in chemical oxygen demand (COD). In this study, a robust AC control strategy based on pH feedback was developed to achieve precise PN ratio. The pH was negatively correlated with the ratio, with the optimal value achieved at pH 7.91. This strategy effectively mitigated the impact of COD variations, maintaining a stable NO2--N/NH4+-N of 1.27 ± 0.10. Furthermore, the relative abundance of Nitrosomonas increased from 1.0 % to 24.2 %, ensuring stable PN performance. These findings highlight that integrating AC control with pH feedback is an effective approach to maintaining the NO2--N/NH4+-N ratio, facilitating the engineering-scale application of two-stage PNA for FWD treatment.

Ammonia-oxidizing activity and microbial structure of ammonia-oxidizing bacteria, ammonia-oxidizing archaea and complete ammonia oxidizers in biofilm systems with different salinities

Ammonia-oxidizing activity of different ammonia-oxidizing microorganisms (AOMs), such as ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and complete ammonia oxidizers (comammoxs), were investigated by adding the inhibitors such as 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, octyne, and KCLO3 in biofilm systems with different salinities. It was found that the ammonia-oxidizing activity of all AOMs gradually decreased with increasing salinity. The ammonia-oxidizing activity of AOB was consistently higher than those of AOA and comammox at different salinities. Moreover, nitrite-oxidizing bacteria (NOB) were more sensitive to changes in salinity than AOMs. Metagenomic analysis revealed that nitrifiers were detected at high level, with the AOB Nitrosomonas sp. comprising 24.9 % and the NOB Nitrospira sp. comprising 47.2 % of all nitrifiers. The main functional genes involved in the nitrification reaction were amoABC, hao, and nxrAB. This study demonstrates that higher abundance of functional microorganisms and genes is related to the ammonia-oxidizing activity and ammonia removal contribution rate.

Unraveling microbial community ecology and its effects on function and structure of halophilic aerobic granular sludge under varying salinities

Halophilic aerobic granular sludge (HAGS) can effectively treat saline wastewater characterized as high salinity and change of salinity, which was discharged from various industries. The stable microbial community ecology is the key to successful operation of HAGS, while its change and outcome under varying salinities is unexplored. In this study, HAGS systems under different salinities were studied to elucidate microbial community ecology process and its effects on HAGS. The study found that the salinity variation intensified competition interaction of bacteria and fungi due to the niche overlap. The decreased salinity from 40 to 0 g/L resulted in functional bacteria loss and fungal population increase by 94.46 %. The HAGS disintegration was caused by insufficient extracellular polymeric substances, which were secreted by bacteria and fed by fungi. This study is the first to reveal role of microbial community ecology on stability and function of HAGS in response to salinity variation.

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

Comparison of nitrification performance in SBR and SBBR with response to NaCl salinity shock: Microbial structure and functional genes

Ammonia removal by nitrifiers at the extremely high salinity poses a great challenge for saline wastewater treatment. Sequencing batch reactor (SBR) was conducted with a stepwise increase of salinity from 10 to 40 g-NaCl·L-1, while sequencing batch biofilm reactor (SBBR) with one-step salinity enhancement, their nitrification performance, microbial structure and interaction were evaluated. Both SBR and SBBR can achieve high-efficiency nitrification (98% ammonia removal) at 40 g-NaCl·L-1. However, SBBR showed more stable nitrification performance than SBR at 40 g-NaCl·L-1 after a shorter adaptation period of 4-15 d compared to previous studies. High-throughput sequencing and metagenomic analysis demonstrated that the abundance and capability of conventional ammonia-oxidizing bacteria (Nitrosomonas) were suppressed in SBBR relative to SBR. Gelidibacter, Anaerolineales were the predominant genus in SBBR, which were not found in SBR. NorB and nosZ responsible for reducing NO to N2O and reducing N2O to N2 respectively had s strong synergistic effect in SBBR. This study will provide a valuable reference for the startup of nitrification process within a short period of time under the extremely high NaCl salinity.

Microbial community analysis of membrane bioreactor incorporated with biofilm carriers and activated carbon for nitrification of urine

The integration of powdered activated carbon and biofilm carriers in a membrane bioreactor (MBR) presents a promising approach to address the challenge of long hydraulic retention time (HRT) for nitrification of hydrolysed urine. This study investigated the effect of the incorporation in the MBR on microbial dynamics, focusing on dominant nitrifying bacteria. The results showed that significant shifts in microbial compositions were observed with the feed transition to full-strength urine and across different sludge growth forms. Remarkably, the nitrite-oxidizing bacteria Nitrospira were highly enriched in the suspended sludge. Simultaneously, ammonia-oxidizing bacteria, Nitrosococcaceae thrived in the attached biomass, showing a significant seven-fold increase in relative abundance compared to its suspended counterpart. Consequently, the incorporated MBR displayed 36% higher nitrification rate and 40% HRT reduction compared to the conventional MBR. This study provides valuable insights on the potential development of household or building scale on-site nutrient recovery from urine to fertiliser.