Modeling nitrogen removal performance based on novel microbial activity indicators in WWTP by machine learning and biological interpretation.

Modeling the pollutant removal performance of wastewater treatment plants (WWTPs) plays a crucial role in regulating their operation, mitigating effluent anomalies and reducing operating costs. Pollutants removal in WWTPs is closely related to microbial activity. However, there is extremely limited knowledge on the models accurately characterizing pollutants removal performance by microbial activity indicators. This study proposed a novel specific oxygen uptake rate (SOURATP) with adenosine triphosphate (ATP) as biomass. Firstly, it was found that SOURATP and total nitrogen (TN) removal rate showed similar fluctuated trends, and their correlation was stronger than that of TN removal rate and common SOURMLSS with mixed liquor suspended solids (MLSS) as biomass. Then, support vector regressor (SVR), K-nearest neighbor regressor (KNR), linear regressor (LR), and random forest (RF) models were developed to predict TN removal rate only with microbial activity as features. Models utilizing the novel SOURATP resulted in better performance than those based on SOURMLSS. A model fusion (MF) algorithm based on the above four models was proposed to enhance the accuracy with lower root mean square error (RMSE) of 2.25 mg/L/h and explained 75% of the variation in the test data with SOURATP as features as opposed to other base learners. Furthermore, the interpretation of predictive results was explored through microbial community structure and metabolic pathway. Strong correlations were found between SOURATP and the proportion of nitrifiers in aerobic pool, as well as between heterotrophic bacteria respiratory activity (SOURATP_HB) and the proportion of denitrifies in anoxic pool. SOURATP also displayed consistent positive responses with most key enzymes in Embden-Meyerhof-Parnas pathway (EMP), tricarboxylic acid cycle (TCA) and oxidative phosphorylation cycle. In this study, SOURATP provides a reliable indication of the composition and metabolic activity of nitrogen removal bacteria, revealing the potential reasons underlying the accurate predictive result of nitrogen removal rates based on novel microbial activity indicators. This study offers new insights for the prediction and further optimization operation of WWTPs from the perspective of microbial activity regulation.

Insights of microalgal municipal wastewater treatment at low temperatures: Performance, microbiota patterns, and cold-adaptation of tubular and aeration column photobioreactors.

In order to refine the treatment of microalgae consortium (MC) for municipal wastewater (MWW) during the winter, this study investigated the effectiveness of tubular and aeration column photobioreactors (TPBR and APBR) in wastewater treatment plant (WWTP) during winter by two start-up modes: microalgae/microalgae-activated sludge (AS). The operation results showed that under 5.7-13.1 °C, TPBR enhanced the assimilation of N and P pollutant by microalgal accumulation, meeting the Chinese discharge standard within 24 h (NH4+-N, TP, and COD ≤8.0, 0.5, and 50 mg·L-1). The microbial community profiles were identified and showed that inoculating AS under low-temperature still promoted bacterial interspecific association, but influenced by the inhibition of microbial diversity by the homogeneous circulation of TPBR, the nitrogen transfer function of MC was lower than that of APBR at low temperatures, except nitrogen fixation (K02588), nitrosification (K10944, K10945, and K10946), assimilatory nitrate reduction (K00366), and ammonification (K01915 and K05601). And the intermittent aeration in the APBR was still beneficial in increasing microbial diversity, which was more beneficial for reducing COD through microbial collaboration. In the treatment, the cryotolerant MGPM were Delftia, Romboutsia, Rhizobiales, and Bacillus, and the cold stress-related genes that were highly up-regulated were defense signaling molecules (K03671 and K00384), cold shock protein gene (K03704), and cellular protector (K01784) were present in both PBRs. This study provided a reference for the feasibility of the low temperature treatment of MC with the different types of PBR, which improved the application of wastewater treatment in more climatic environments.

Lighting the way to sustainable development: Physiological response and light control strategy in microalgae-based wastewater treatment under illumination.

The Sustainable Development Goals link pollutant control with carbon dioxide reduction. Toward the goal of pollutant and carbon reduction, microalgae-based wastewater treatment (MBWT), which can simultaneously remove pollutants and convert carbon dioxide into biomass with value-added metabolites, has attracted considerable attention. The photosynthetic organism microalgae and the photobioreactor are the functional body and the operational carrier of the MBWT system, respectively; thus, light conditions profoundly influence its performance. Therefore, this review takes the general rules of how light influences the performance of MBWT systems as a starting point to elaborate the light-influenced mechanisms in microalgae and the light control strategies for photobioreactors from the inside out. Wavelength, light intensity and photoperiod solely or interactively affect biomass accumulation, pollutant removal, and value-added metabolite production in MBWT. Physiological processes, including photosynthesis, photooxidative damage, light-regulated gene expression, and nutrient uptake, essentially explain the performance influence of MBWT and are instructive for specific microalgal strain improvement strategies. In addition, light causes unique reactions in MBWT systems as it interacts with components such as photooxidative damage enhancers present in types of wastewater. In order to provide guidance for photobioreactor design and light control in a large-scale MBWT system, wavelength transformation, light transmission, light source distribution, and light-dark cycle should be considered in addition to adjusting the light source characteristics. Finally, based on current research vacancies and challenges, future research orientation should focus on the improvement of microalgae and photobioreactor, as well as the integration of both.

Findings on agricultural cleaner production in the three Gorges Reservoir Area.

The 'rural revitalization strategy' is important to achieve sustainable development in the Three Gorges Reservoir Area (TGRA), the largest reservoir in China, located in the poverty alleviation region of the Qinling-Daba mountains, and characterized as mountainous and hilly dominated by backwards resettlements. Pig farming around the reservoir area is a key industry, accounting for 0.90% of the arable land area in the country, while the annual pig market represents a 1.37% share of the national figure. Here, 12 study sites were investigated on-site for understanding agricultural green development in the TGRA. We found two main prevailing models: one of ecological circulation (EC), based on animal husbandry and recycling. Of the 12 site, six cases of the ecological circulation model relied on pig husbandry, combined with cropping (grains/fruits/vegetables) by eco-industrial chains, such as pig-biogas-fruit (grain/vegetables), to prevent environmental pollution, while promoting agricultural economic growth by recycling fecal residues and wastewater (FSW) from pig-husbandry facilities to the fields. Our analysis predicted that a farm holding 10,000 pigs may save inorganic nitrogen and phosphorus fertilizers by as much as 74.36 and 11.15 ton·a-1, respectively. On the other hand, five cases of ecological models oriented towards agritourism provided tourists with high-quality ecological products while coordinating environment protection with economic development. In addition, 11 research points applied water and fertilizer integration system for the purpose of saving water. However, lack of sufficient supporting arable land made intensive pig farming a risk of ecological degradation. Green control technologies are rarely used leading to an increase in the type and amount of pesticides. Our study has theoretical and practical significance for decision-makers to promote agricultural cleaner production (ACP).

Co-cultivation of microalgae-activated sludge for municipal wastewater treatment: Exploring the performance, microbial co-occurrence patterns, microbiota dynamics and function during the startup stage.

Microalgae consortium is a promising technology for achieving low-carbon and resource utilization goals in municipal wastewater treatment. However, little is known about how the consortium affects the treatment performance in the startup stage of co-cultivation. Herein, photobioreactors were constructed with different contents of microalgae and activated sludge (AS) (wt.microalgae: wt.AS ≥ 50 %). The results showed that the concentration of microalgae increased by more than 20 % with AS, and the effluents were close or lower than Chinese discharge standards within HRT 24 h (NH4+-N, TP, and COD ≤ 5.0, 0.5, and 50 mg L-1). Furthermore, the co-occurrence pattern of microbial populations experienced inhibition-reconstruction and reconstruction-inhibition processes, respectively, and the inter-species relationship was directly related to the effluent quality. Microalgal concentration and temperature were the key factors to the microbial community profiling. The potential microorganisms in AS could promote the growth of microalgae, and the bacteria and fungi formed co-metabolism through functional complementation.

COD/TN ratios shift the microbial community assembly of a pilot-scale shortcut nitrification-denitrification process for biogas slurry treatment.

In this study, effects of carbon to nitrogen (COD/TN) ratios of biogas slurry on shortcut nitrification-denitrification in a pilot-scale integrated fixed film activated sludge (IFAS) system were investigated. Lowering the COD/TN ratio from 11.7 to 6.2 exerted a negative impact on shortcut nitrification-denitrification performance. Accordingly, the NH3-N and TN removal rates decreased from 94.4 to 91.2% and 92.3 to 85.9%, respectively. The dynamics of microbial assembly was analyzed by MiSeq sequencing, and the denitrifying functional genes were quantified by qPCR. The results showed that ammonia oxidizing bacteria and amoA gene were more abundant on the biofilm of oxic tank, indicating they play a key role in NH3-N removal. Autotrophic, endogenous, and fast heterotrophic kinetics denitrifiers were coexisted and enriched in the IFAS system with a decreasing of COD/TN ratio. TN removal was mainly affected by denitrifiers (including Arenimonas, Acidovorax, and Thaurea) harboring narG and nirS genes. Canonical correspondence analysis proved that COD/TN ratio was the most critical factor driving the succession of microbial community. Dissolved oxygen (DO) and pH were found positively correlated with denitrifiers at low COD/TN ratio conditions. As a result, NH3-N and TN removal were effectively enhanced when the DO level in the oxic tank of IFAS system was increased to 1.0-3.0 mg/L.

Dynamics of antibiotic resistance genes and microbial community in shortcut nitrification-denitrification process under antibiotic stresses.

In this study, the performance of shortcut nitrification-denitrification (SCND) at different TC and SD stress conditions (0 µg/L, 1-97 days; 100 µg/L, 98-138 days; 500 µg/L, 139-175 days) was investigated. Higher level antibiotic stress (500 µg/L) led to the serious deterioration of nitrogen removal, and denitrification was more sensitive to antibiotic stress than nitrification. The dynamics of antibiotic resistance genes (ARGs) and microbial community were revealed by quantitative real-time PCR and 16S rDNA high-throughput sequencing, respectively. Tet-genes (tetA, tetQ, tetW), sul-genes (sulI, sulII), and mobile genetic element (intI1) in activated sludge increased by 1.2 ~ 2.5 logs with long-term exposure of antibiotic stress, and sulI, tetA, tetQ, and tetW were significantly positively correlated with intI1. Long-term antibiotics stress caused the decrease of most denitrifiers, and five genera were identified as the potential host of ARGs. The key impact factors of SCND drove the dynamics of ARGs and microbial community. Except for sulII gene, DO and FA were significantly positively correlated with ARGs, while FNA, NAR, and NO2--N showed opposite effects to ARGs. Overall, maintaining relative lower DO, higher FNA, NAR, and NO2--N conditions are not only benefit to the stable operation of SCND, but may also conducive to the control of ARG dissemination. This study provides theoretical basis on the control of ARGs in the SCND process.

Adaptation mechanisms of Rhodococcus sp. CNS16 under different temperature gradients: Physiological and transcriptome.

Rhodococcus exhibits strong adaptability to environmental stressors and plays a crucial role in environmental bioremediation. However, seasonal changes in ambient temperature, especially rapid temperature drops exert an adverse effect on in situ bioremediation. In this paper, we studied the cell morphology and fatty acid composition of an aniline-degrading strain Rhodococcus sp. CNS16 at temperatures of 30 °C, 20 °C, and 10 °C. At suboptimal temperatures, cell morphology of CNS16 changed from short rod-shaped to long rod or irregular shaped, and the proportion of unsaturated fatty acids was upregulated. Transcriptomic technologies were then utilized to gain detailed insights into the adaptive mechanisms of CNS16 subjected to suboptimal temperatures. The results showed that the number of gene responses was significantly higher at 10 °C than that at 20 °C. The inhibition of peptidoglycan synthase expression and up-regulation of Filamentous Temperature Sensitive as well as unsaturated fatty acid synthesis genes at suboptimal temperatures might be closely related to corresponding changes in cell morphology and fatty acids composition. Strain CNS16 showed loss of catalase and superoxide dismutase activity, and utilized thioredoxin-dependent thiol peroxidase to resist oxidative stress. The up-regulation of carotenoid and Vitamin B2 synthesis at 10 °C might also be involved in the resistance to oxidative stress. Amino acid metabolism, coenzyme and vitamin metabolism, ABC transport, and energy metabolism are essential for peptidoglycan synthesis and regulation of cellular metabolism; therefore, synergistically resisting environmental stress. This study provides a mechanistic basis for the regulation of aniline degradation in Rhodococcus sp. CNS16 at low temperatures.

Mixed nitrifying bacteria culture under different temperature dropping strategies: Nitrification performance, activity, and community.

In this study, the nitrification performance, metabolic activity, antioxidant enzyme activity as well as bacterial community of mixed nitrifying bacteria culture under different temperature dropping strategies [(#1) growth temperature kept at 20 °C; (#2) sharp1 decreased from 20 °C to 10 °C; (#3) growth at 20 °C for 6 days followed by sharp decrease to 10 °C; and (#4) gradual decreased from 20 °C to 10 °C] were evaluated. It was shown that acclimation at 20 °C for 6 days allowed to maintain better nitrification activity at 10 °C. The nitrite oxidation capacity of nitrifiers was significantly correlated with the relative light unit (RLU) (p < .05) and the fluctuation of superoxide dismutase (SOD) enzyme activity (p < .01). With serial #3 showed the highest RLU levels and the least SOD enzyme fluctuation as compared to serials #2 and #4. Throughout the experimental period, Nitrosospira and Nitrosomonas as well as Nitrospira were identified as the predominant ammonia-oxidizing bacteria (AOB) and nitrate-oxidizing bacteria (NOB). The dynamic change of AOB/NOB ratios and nitrification activity in serials #2-#4 demonstrated that AOB recovered better than NOB with long-term 10 °C exposure, and the nitrification performance was mainly limited by the nitrite oxidation capacity of NOB. Applying 6 days acclimation at 20 °C was beneficial for the mixed nitrifying bacteria culture to cope with low temperature (10 °C) stress, possibly due to the maintenance of metabolic activity, antioxidant enzyme activity stability as well as appropriate AOB/NOB ratio.

A review: Driving factors and regulation strategies of microbial community structure and dynamics in wastewater treatment systems.

The performance and stabilization of biological wastewater treatment systems 1are closely related to the microbial community structure and dynamics. In this paper, the effects and mechanisms of influent composition, process configuration, operating parameters (dissolved oxygen [DO], pH, hydraulic retention time [HRT] and sludge retention time [SRT]) and environmental condition (temperature) to the change of microbial community structure and process performance (nitrification, denitrification, biological phosphorus removal, organics mineralization and utilization, etc.) are critically reviewed. Furthermore, some strategies for microbial community structure regulation, mainly bioaugmentation, process adjustment and operating parameters optimization, applied in the current wastewater treatment systems are also discussed. Although the recent studies have strengthened our understanding on the relationship between microbial community structure and wastewater treatment process performance, how to fully tap the microbial information, optimize the microbial community structure and maintain the process performance in wastewater treatment systems are still full of challenges.

Bioaugmentation for treatment of full-scale diethylene glycol monobutyl ether (DGBE) wastewater by Serratia sp. BDG-2.

A novel bacterial strain BDG-2 was isolated and used to augment the treatment of silicon plate manufacturing wastewater that primarily contains diethylene glycol monobutyl ether (DGBE). BDG-2 was identified as a Serratia sp. Under the optimal conditions of 30 °C, pH 9 and DGBE concentration of 2000 mg L(-1), the bioaugmented system achieved 96.92% COD removal after 39.9h. Laboratory-scale technological matching results indicated that, in a biofilm process with the addition of 100 mg L(-1) ammonia and 5 mg L(-1) total phosphorus (TP), 70.61% COD removal efficiency could be obtained in 46 h. Addition of polyaluminium chloride (PAC) to the reactors during the suspension process enhanced the settleability of the BDG-2 culture. Subsequently, successful start-up and stable operation of a full-scale bioaugmented treatment facilities were accomplished, and the volumetric organic load in the plug-flow aeration tank was 2.17 ± 0.81 kg m(-3) d(-1). The effluent COD of the facilities was stable and always below 100 mg L(-1).

Bioaugmentation treatment of PV wafer manufacturing wastewater by microbial culture.

The wastewater of silicon photovoltaic (PV) battery manufacturing contained polyethylene glycol (PEG) and detergents, which possessed the characteristics of high content of organics and low bioavailability, and then resulted in high treatment costs. To address the difficulties of existing treatment facilities in stably meeting discharge standards, eight tons of microbial culture (consisting of Bacillus sp. and Rhodococcus sp.) were added into the aerobic treatment unit. Subsequently, the effectiveness of the microbial culture in small-scale biological wastewater treatment was evaluated, and the operating conditions for engineering applications were optimized. The application study showed that the average chemical oxygen demand (COD) removal efficiency reached 95.0% when the pH value was 7, the gas-water ratio was 28:1, the reflux ratio was 50%, which indicated an increase of 51.2% contrasting with the situation without bioaugmentation. The volume load of the treatment facilities after augmentation increased by 127.9% and could tolerate the COD shock load reached 2,340 mg·L(-1). At last, the effluence met the class I standard of the Integrated Wastewater Discharge Standard (GB8978-1996).

Impact resistance of different factors on ammonia removal by heterotrophic nitrification-aerobic denitrification bacterium Aeromonas sp. HN-02.

To give reference for the application of heterotrophic nitrification-aerobic denitrification bacteria in actual wastewater treatment, the impact resistance of extreme pH, low temperature, heavy metals and high salinity on ammonia removal by a typical heterotrophic nitrifying-aerobic denitrifying bacterium Aeromonas sp. HN-02 was investigated. The results showed that HN-02 demonstrated strong acid- and alkali-resistance. In addition, it remained active at 5°C, and the removal rates of ammonia and COD were 0.90 mg L(-1)h(-1) and 22.34 mg L(-1)h(-1), respectively. Under the same extent of immediate temperature drop, the temperature correction coefficients of ammonia, COD removal rates and cell growth rate were close. Moreover, HN-02 could survive in the solution containing 0.5 mg L(-1) Cu(2+) or 8 mg L(-1) Zn(2+), or 0.5 mg L(-1) of equivalent Cu(2+)-Zn(2+). Furthermore, efficient ammonia removal was retained at salinity below 20 g L(-1), thus it could be identified as a halotolerant bacterium. At last, stronger stress resulted in higher ΔCOD/ΔTN ratio.