Response of rotating biological contactor started up by heterotrophic nitrification-aerobic denitrification bacteria to various C/N ratios

Comparison of moving bed biofilm reactor and bio-contact oxidation reactor start-up with heterotrophic nitrification-aerobic denitrification bacteria and activated sludge inoculation under high ammonia nitrogen conditions

To overcome poor ammonia tolerance and removal performance of bio-contact oxidation (BCO) reactor inoculated with activated sludge for high-ammonia nitrogen (NH4+-N) chemical wastewater treatment, this study compared inoculating heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in moving bed biofilm reactor (MBBR) with activated sludge inoculation in BCO reactor under simulated high NH4+-N conditions. Results revealed that MBBR achieved faster biofilm formation (20 days vs. 100 days for BCO) with notable advantages: 27.6 % higher total nitrogen (TN) and 29.9 % higher NH4+-N removal efficiency than BCO. Microbial analysis indicated optimal enrichment of the key nitrogen removal (NR) bacterium Alcaligenes, leading to increased expression of NR enzymes hydroxylamine reductase, ensuring the superior NR efficiency of the MBBR. Additionally, functional enzymes and genes analysis speculated that the NR pathway in MBBR was: NH4+-N → NH2OH → NO3--N → NO2--N → NO → N2O → N2. This research offers a practical and theoretical foundation for extending HN-AD bacteria-inoculated MBBR processes.

Enhanced denitrification of biodegradable polymers using Bacillus pumilus in aerobic denitrification bioreactors: Performance and mechanism

Nitrate accumulation is an important issue that affects animal health and causes eutrophication. This study combined biodegradable polymers with degrading bacteria to lead to high denitrification efficiency. The results showed polycaprolactone had the highest degradation and carbon release rate (0.214 mg/g∙d) and nitrogen removal was greatest when the Bacillus pumilus and Halomonas venusta ratio was 1:2. When the hydraulic retention time was extended to 12 h, the nitrate removal rate for H. venusta with B. pumilus and polycaprolactone increased by 48 %. Furthermore, the group with B. pumilus contained more Proteobacteria (77.34 %) and denitrifying functional enzymes than the group without B. pumilus. These findings indicated B.pumilus can enhance the degradation of biodegradable polymers especially polycaprolactone to improve the denitrification of the aerobic denitrification bacteria H.venusta when treating maricultural wastewater.

Optimization of operational parameters using RSM, ANN, and SVM in membrane integrated with rotating biological contactor

Membrane fouling is a critical bottleneck to the widespread adoption of membrane separation processes. It diminishes the membrane permeability and results in high operational energy costs. The current study presents optimizing the operating parameters of a novel rotating biological contactor (RBC) integrated with an external membrane (RBC + ME) that combines membrane technology with an RBC. In the RBC + ME, the membrane panel is placed external to the bioreactor. Response surface methodology (RSM) is applied to optimize the membrane permeability through three operating parameters (hydraulic retention time (HRT), rotational disk speed, and sludge retention time (SRT)). The artificial neural networks (ANN) and support vector machine (SVM) are implemented to depict the statistical modelling approach using experimental data sets. The results showed that all three operating parameters contribute significantly to the performance of the bioreactor. RSM revealed an optimum value of 40.7 rpm disk rotational speed, 18 h HRT and 12.4 d SRT, respectively. An ANN model with ten hidden layers provides the highest R2 value, while the SVM model with the Bayesian optimizer provides the highest R2. RSM, ANN, and SVM models reveal the highest R-square values of 0.97, 0.99, and 0.99, respectively. Machine learning techniques help predict the model based on the experimental results and training data sets.

Insight into biofilm formation of wastewater treatment processes: Nitrogen removal performance and biological mechanisms

Biofilm formation affects biological nitrogen (N) removal, and a sequencing batch biofilm reactor (SBBR) was set up to evaluate the changes in N removal and microbial characteristics during biofilm formation. The results indicated that the average effluent concentration of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total nitrogen (TN) in the SBBR were 27.48, 1.41, and 13.52 mg L-1, respectively after biofilm formation. Furthermore, this process increased microbial richness, but reduced microbial diversity. Patescibacteria, Proteobacteria, and Bacteroides were the dominant phyla that did not change after biofilm formation. After biofilm formation, Firmicutes was eliminated while Spirochaetes involved in the interspecies relationship. Biofilm increased the nitrification and denitrification relating coding genes abundance (hao, narG, narZ, nxrA, narH, narY, nxrB, napA, napB, norB, norC and nosZ), and enhanced the processes of N respiration and denitrification, carbohydrate metabolism, amino acid metabolism and membrane transport. Meanwhile, correlation analysis between genera and transcriptome reflected that Zooglea, Micropruina, Aeromonas and Tessaracoccus played essential roles in biofilm formation and N removal. The key enzyme abundance of EC:1.7.99.1, EC:1.7.2.4, and EC:1.1.1.42 of N and tricarboxylic acid (TCA) cycle increased after biofilm formation. This study can reveal the effect of biofilm formation on biological N removal and provide a theoretical foundation for the application of biofilm process.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

Treatment of Landfill Leachate Reverse Osmosis Concentrates by Advanced Oxidation-Heterotrophic Nitrification-Aerobic Denitrification Combination process

This study aimed to develop a multistage treatment system for highly toxic wastewater named reverse osmosis concentrates of landfill leachate. Therefore, a combination of the ammonia stripping process (ASP), catalytic ozone oxidation process (COP), and heterotrophic nitrification-aerobic denitrification process (HNADP) was proposed and the quality of effluent was evaluated for the concentration of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total nitrogen (TN). ASP had moderate removal efficiency of NH4+-N, and TN in the effluent. COP was catalyzed by cerium-supported-activated carbon achieved good performance in disposal of COD. The effluent of HNADP had the most significant removal efficiency of COD, NH4+-N, and TN. As a result, the effluent of combined process successfully met the discharge standards for NH4+-N and TN according to Table 1 of GB 16889-2008 in China. To investigate the microbial mechanism of pollutant removal in HNADP, 16S rRNA high-throughput sequencing was performed and the results suggested that the relative abundance and diversity of microorganisms fluctuated with the changes of COD/TN ratio in HNADP. Truepera and Halomonas were identified as the key genera involved in the simultaneous degradation of COD and nitrogen-containing pollutants, the functional genes (hao, amoA, nirS, and nirK) were predicted in nitrification and denitrification process. Overall, this study demonstrates a feasible multistage system for treatment of concentrates and propose that further explorations of combined techniques may lead to even more satisfactory removal efficiencies.

Enhanced nitrogen removal in immersed rotating self-aerated biofilm reactor: nitrogen removal pathway and microbial mechanism

To achieve energy-efficient treatment of the rural wastewater with satisfying performance, a novel immersed rotating self-aerated biofilm reactor (iRSABR) was proposed in this study. The iRSABR system showed better biofilm renewal performance and higher microbial activity. The effect of different regulation strategies on the iRSABR system was investigated in this study. The 70% immersion ratio and 4 r/min rotation speed (stage III) exhibited the best performance, with a total nitrogen removal efficiency of 86% and a simultaneous nitrification-denitrification (SND) rate of 76%, along with the highest electron transport system activity. The nitrogen removal pathway revealed that the SND was achieved through autotrophic/heterotrophic nitrification and aerobic/anoxic denitrification. The regulation strategy in the iRSABR system established a synergistic microbial community with main functional bacteria of nitrification (Nitrosomonas), anoxic denitrification (Flavobacterium, Pseudoxanthomonas), and aerobic denitrification (Thauera). This study highlighted the feasibility and adaptability of the iRSABR system toward energy-efficient rural wastewater treatment.

The potential and sustainable strategy for swine wastewater treatment: Resource recovery

Swine wastewater is highly polluted with complex and harmful substances that require effective treatment to minimize environmental damage. There are three commonly used biological technologies for treating swine wastewater: conventional biological technology (CBT), microbial electrochemical technology (MET), and microalgae technology (MT). However, there is a lack of comparison among these technologies and a lack of understanding of their unique advantages and efficient operation strategies. This review aims to compare and contrast the characteristics, influencing factors, improvement methods, and microbial mechanisms of each technology. CBT is cost-effective but has low resource recovery efficiency, while MET and MT have the highest potential for resource recovery. However, all three technologies are affected by various factors and toxic substances such as heavy metals and antibiotics. Improved methods include exogenous/endogenous enhancement, series reactor operation, algal-bacterial symbiosis system construction, etc. Though MET is limited by construction costs, CBT and MT have practical applications. While swine wastewater treatment processes have developed automatic control systems, the application need further promotion. Furthermore, key functional microorganisms involved in CBT's pollutant removal or transformation have been detected, as have related genes. The unique electroactive microbial cooperation mode and symbiotic mode of MET and MT were also revealed, respectively. Importantly, the future research should focus on broadening the scope and scale of engineering applications, preventing and controlling emerging pollutants, improving automated management level, focusing on microbial synergistic metabolism, enhancing resource recovery performance, and building a circular economy based on low-cost and resource utilization.

Enhanced in-situ sludge reduction of the side-stream process via employing micro-aerobic approach in both mainstream and side-stream

Side-stream reactor (SSR), as an in-situ sludge reduction process with high sludge reduction efficiency (SRE) and less negative impact on effluent, has been widely researched. In order to reduce cost and promote large-scale application, the anaerobic/anoxic/micro-aerobic/oxic bioreactor coupled with micro-aerobic SSR (AAMOM) was used to investigate nutrient removal and SRE under short hydraulic retention time (HRT) of SSR. When HRT of SSR was 4 h, AAMOM system achieved 30.41% SRE, while maintaining carbon and nitrogen removal efficiency. Micro-aerobic in mainstream accelerated the hydrolysis of particulate organic matter (POM) and promoted denitrification. Micro-aerobic in side-stream increased cell lysis and ATP dissipation, thus increasing SRE. Microbial community structure indicated that the cooperative interactions among hydrolytic, slow growing, predatory and fermentation bacteria played key roles in improving SRE. This study confirmed that SSR coupled micro-aerobic was a promising and practical process, which could benefit nitrogen removal and sludge reduction in municipal wastewater treatment plants.

Heterotrophic nitrification-aerobic denitrification performance of a novel strain, Pseudomonas sp. B-1, isolated from membrane aerated biofilm reactor

A heterotrophic nitrification-aerobic denitrification (HN-AD) strain isolated from membrane aerated biofilm reactor (MABR) was identified as Pseudomonas sp. B-1, which could effectively utilize multiple nitrogen sources and preferentially consume NH₄-N. The maximum degradation efficiencies of NO₃-N, NO₂-N and NH₄-N were 98.04%, 94.84% and 95.74%, respectively. The optimal incubation time, shaking speed, carbon source, pH, temperature and C/N ratio were 60 h, 180 rpm, sodium succinate, 8, 30 °C and 25, respectively. The strain preferred salinity of 1.5% and resisted heavy metals in the order of Mn²⁺ > Co²⁺ > Zn²⁺ > Cu²⁺. It can be preliminarily speculated from the results of enzyme assay that the strain removed nitrogen via full nitrification-denitrification pathway. The addition of strain into the conventional MABR significantly intensified the HN-AD performance of the reactor. The relative abundance of the functional bacteria including Flavobacterium, Pseudomonas, Paracoccus, Azoarcus and Thauera was obviously increased after the bioaugmentation. Besides, the expression of the HN-AD related genes in the biofilm was also strengthened. Thus, strain B-1 had great application potential in nitrogen removal process.

Bioelectrochemical systems for enhanced nitrogen removal with minimal greenhouse gas emission from carbon-deficient wastewater: A review

Nitrogen pollution and the rising amount of wastewater generation are calling for advanced wastewater treatments, which is particularly necessary for carbon-deficient wastewater that contains multi-species inorganic nitrogen, since conventional heterotrophic denitrification processes cannot remove nitrogen completely when carbon sources are insufficient. For that, bioelectrochemical systems (BES) have been recently developed because they can simultaneously produce electricity and remove resistant nitrogen from the carbon-deficient wastewater. However, the simultaneous removal of multi-species inorganic nitrogen cannot be achieved by electroautotrophic denitrification using BES alone. Moreover, the efficiency of nitrogen removal and power generation has been thwarted by the low energy output, high internal resistance of the device, and electron competition in non-denitrification pathways. This review article discusses the latest developments for nitrogen removal through BES-enhanced denitrification and elucidates multiple coupled BES-based denitrification pathways to remove multi-species inorganic nitrogen simultaneously. Focus points of the research area include coupling BES technologies with emerged methods, electron transfer enhancement, and avoiding electron competition that improves performance with less cost. The prospect of reducing emissions of greenhouse gases is also critically reviewed, in the hope of reducing potential intermediate products of denitrification, such as nitrous oxide (a potent greenhouse gas), through multi-factor regulation. We imply that BES is a good choice for future scale-up applications of MFC coupled with MEC to treat carbon-deficient wastewater. Overall, this review will provide useful information for the development of advanced technologies to treat carbon-deficient wastewater with less emission of greenhouse gases.

Aerobic denitrifying using actinobacterial consortium: Novel denitrifying microbe and its application

The aerobic denitrifying capacity of actinomycete strain has been investigated recently, while little is known about nitrogen and carbon substrate removal by mix-cultured aerobic denitrifying actinobacteria (Mix-CADA) community. Hence, three Mix-CADA consortiums, named Y23, X21, and Y27, were isolated from urban lakes to investigate their aerobic denitrification capacity, and their removal efficiency for nitrate and dissolved organic carbon were >97 % and 90 %, respectively. Illumina Miseq sequencing revealed that Streptomyces was the most dominant genus in the Mix-CADA consortium. Network analysis indicated that Streptomyces exfoliates, as the core species in the Mix-CADA consortium, majorly contributed to dissolved organic carbon and total nitrogen reduction. Moreover, the three Mix-CADA consortiums could remove 78 % of the total nitrogen and 61 % of the permanganate index from the micro-polluted l water. Meanwhile, humic-like was significantly utilized by three Mix-CADA consortiums, whereas Mix-CADA Y27 could also utilize aromatic protein and soluble microbial by-product-like in the micro-polluted raw water purification. In summary, this study will offer a novel perspective for the purification of micro-polluted raw water using the Mix-CADA consortium.

Simultaneous nitrification and denitrification in a novel rotating self-aerated biofilm reactor for decentralized wastewater treatment

Decentralized wastewater pollution in rural areas has become a serious problem for the rural environment. In this study, a novel rotating self-aerated biofilm reactor was developed for decentralized wastewater treatment without any aeration equipment. After the long-term operation of 110 days, the removal efficiency reached to 96.06 % (COD), 98.06 % (NH₄⁺-N), and 62.58 % (TN) in the last phase. Under high dissolved oxygen level, the simultaneous nitrification-denitrification (SND) maintained at a stable ratio of 62.53 % and the denitrification rates reached over 28.37 mg/L/h. With the organic loading rate increased, key nitrogen functional bacterial communities such as anoxic denitrifiers (Thiothrix, Flavobacterium, Pseudoxanthomonas, Aquimonas and Azoarcus) and aerobic denitrifiers (Hydrogenophaga, Zoogloea and Terrimonas) increased obviously. Overall, microbial analysis and nitrogen metabolism pathway indicated that an integration of SND process was achieved in this single reactor by the combined action of nitrification, denitrification and comammox without any aeration equipment.

In-situ enrichment and application of heterotrophic nitrification-aerobic denitrification bacteria in membrane aerated biofilm reactor

In order to reduce the resource and energy consumption of traditional biological nitrogen removal (BNR) process, heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was in situ enriched in membrane aerated biofilm reactor (MABR) by inoculating conventional activated sludge. Contaminants removal performance, EPS composition and microbial community were explored. The results indicated that the average removal efficiency of COD and TN under optimal condition reached 84.13% and 91.54%, respectively, which demonstrated that the reactor possessed excellent contaminants removal capacity. EPS analysis suggested that abundant protein especially tryptophan protein-like substance played a vital role in maintaining the microbial stability of biofilms. Multiple HN-AD genera, mainly Paracoccus, were detected with the highest relative abundance of 54.70%, which confirmed the successful enrichment of the HN-AD bacteria. Conventional nitrifiers and denitrifiers also thrived in biofilm, which demonstrated the synergistic nitrogen removal of multiple microorganisms. This study provided important insights into application of HN-AD bacteria and synergistic nitrogen removal in BNR system.

Effects mechanism of bio-carrier filling rate on rotating biofilms and the reactor performance optimization method

Benefited from the massive filling bio-carriers, the packed cage rotating biological contactors (RBCs) have better performance and application potentiality in wastewater treatment. Investigating the effects mechanism of bio-carrier filling rate is crucial for such reactors management. In this study, the pollutants removal performance, biofilms physical characteristics, and microbial communities of the biofilms under a series of bio-carrier filling rates were analyzed. The results shown, the pollutant removal rate and amount were quite different under different filling rates, and biofilms structure and microbial composition were the main factors affecting the pollutants removal performance. With the increasing filling rates, the biofilms were more mass increased (dry weight from 0.066 to 0.148 g/per carrier), thicker (from 340.30 to 850.84 μm) and lower dense (from 0.068 to 0.060 g/cm³). The microbial community composition of those biofilms was also quite different at the genus level. The effects mechanism of bio-carrier filling rate can be summarized: the filling rates affect the physical and biological characteristics of biofilms, which will further affect the microenvironment and microbial distribution in biofilms, and then determines the pollutant metabolic rate and metabolic pathway. This study will contribute to design better bio-carrier filling rate according to different wastewater treatment scenario, and promote the performance optimization of packed cage RBCs.

Mature landfill leachate treatment using granular sludge-based reactor (GSR) via nitritation/denitritation: Process startup and optimization

Mature landfill leachate wastewater (LLW) was characterized by high ammonia, refractory chemical oxygen demand (COD) and heavy metal contents, which limits the nitrogen removal in conventional activated sludge systems. Granular sludge is known to be more resistant to toxic compounds because of its dense structure and diverse microbial community. Here, granular sludge-based reactor (GSR) was applied with nitritation/denitritation (Nit/DNit) process for effective ammonia-rich mature LLW treatment at 20 °C. After a short startup period, the efficiencies of ammonia removal and total inorganic nitrogen removal stabilized at 99 % and 93 %, respectively, under a hydraulic retention time (HRT) of 6 h. High ammonia oxidation rate (~ 0.64 g N/g VSS/d) was achieved, with ~93 % ammonia conversing to nitrite before being reduced to nitrogen gas. Microbial analysis results revealed that Nitrosomonas (ammonia oxidizing bacteria) and Thauera (denitrifiers) were the dominant bacteria with key functional genes involved in the Nit/DNit. With an increase in the LLW loading, increased ammonia oxidation rates and biomass retention were also observed. This study demonstrated that granular sludge-based technology is feasible for mature LLW treatment.

Acceleration of start-up of moving bed biofilm reactor at low temperature by adding specialized quorum sensing bacteria

This study aims to accelerate biofilm formation and operational performance of moving bed biofilm reactor (MBBR) at 5 ℃ by adding specialized Quorum Sensing bacteria (sphingomonas rubra BH3^T). Results showed that bio augmented MBBR (R_S) achieved a higher chemical oxygen demand and NH₄⁺-N removal rate (93% and 75%), which in accordance with its increased biofilm thickness, higher biofilm activity, and nitrifying bacteria abundance (Nitrospira). The increased biofilm thickness (60.23 %) during the whole operating time, accompanied by more potent adhesion force (61.59 %), was related to increased polysaccharides and proteins in the biofilm. Pyrosequencing analysis indicated that BH3^T contributed to higher species richness and triggered the rapid growth of precursor microorganisms (Nakamurella, Micropruina, and Zoogloea) and the enrichment of multifunctional microorganisms (Pseudomonas, Aeromonas, Arcobacter, Dechloromonas, and Flavobacterium) at low temperatures. This study provides an economical and practical new insight into accelerating start-up of MBBR system at low temperature.