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.

The organics-mediated microbial dynamics and mixotrophic metabolisms in anammox consortia under micro-aerobic conditions

The engineering applications of mainstream anaerobic ammonium oxidation (anammox) have raised increasing attention due to its energy-efficient, however, the organics-mediated microbial dynamics and mixotrophic metabolisms in anammox consortia under micro-aerobic conditions are still elusive. Here, the response of the anammox process to sodium acetate and glucose at a C/N ratio ranging from 0 to 0.5 was investigated under micro-aerobic conditions, respectively. Results showed that the additional glucose could promote the nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of anammox processes at a low C/N ratio (0.3), representing 84.00% and 0.53 N kg·m^-3·d^-1. The introduced organics could regulate the diversity of the microbial community and simplify the microbial relationship in anammox consortia. Anammox could not benefit from the introduced sodium acetate, while glucose could effectively enhance the anammox activity and microbial interactions in anammox consortia. Glucose might also stimulate the mixotrophic mechanism of Ca. Kuenenia, further promotes the proliferation of anammox sludge under micro-aerobic conditions. This study reveals that glucose could positively mediate microbial interactions and mixotrophic metabolism in anammox consortia under micro-aerobic conditions, which raises a new horizon for the proliferation of anammox sludge for mainstream engineering applications.

Bioaugmentation with methanogens cultured in a micro-aerobic microbial community for overloaded anaerobic digestion recovery

Anaerobic digestion (AD) is widely used for conversion of waste materials into biogas, but inhibition of methane production caused by overloading can be a major problem. The micro-aerobic microbial community MC1 was used to successfully culture methanogens, Methanosarcina acetivorans C2A and Methanosaeta thermophila NBRC 101360. The maximum 16S rRNA gene concentrations of Methanosarcina acetivorans C2A and Methanosaeta thermophila NBRC101360 were 1.06 × 10⁶ and 1.35 × 10³ copies/mL, respectively. The five key bacteria in MC1 were quantified to assess the effect of inoculation on the abundances of the bacteria in the mixed culture. The original MC1 total 16S rRNA gene concentration was 1.93 × 10⁸ copies/mL, and the total 16S rRNA gene concentration had increased to 4.79 × 10⁹ copies/mL on day 9 (p < 0.05). The proportions of the key strains in MC1+MST had changed by day 9. Cells were harvested and used to bioaugment and increase the pH values of the high- and medium-temperature anaerobic systems. After bioaugmentation, thermophilic AD recovered well. The cumulative amounts of gas produced were 44.78% and 28.28% higher in the MC1+MST and MC1 groups, respectively, than the sterilized control. The MC1+MST group gave better results than the chemical addition control group (CaCO₃). There was no clear effect of bioaugmentation in mesophilic AD. When compared with traditional pure culture of methanogens as inoculants, methanogen cultivation in MC1 was simple and there was no need to separate and purify the target strains. This simplified methanogenic bioaugmentation agent was useful to study the mechanism of bioaugmentation for the recovery from low pH inhibition, showing the potential for practical application.

The influence of combined low-strength ultrasonics and micro-aerobic pretreatment process on methane generation and sludge digestion: Lipase enzyme, microbial activation, and energy yield

Low-frequency ultrasonics is a potential technology to reduce the hydrolysis phase period in anaerobic digestion process. In this study, theinfluence of combined low frequency ultrasonics and micro-aerobic (MA) pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion were assessed. Initially, the effect of ultrasonic density (0.012, 0.014, 0.016, 0.018, 0.1, 0.12 and 0.14 W/mL) and irradiation time (1, 3, 5, 8, 9, 10 and 12 min) of 20 kHz frequency waves were investigated. Accordingly, the effect of micro-aerobic pretreatment (Air flow rate (AFR) = 0.1, 0.2, 0.3 and 0.5 VVM) within 20, 30, 40.48 and 60 h were examined. In addition, the effect of combined pretreatment on COD solubilization, lipase enzyme activation, ATP, percentage of live bacteria and methane gas production during the anaerobic process were examined. The results showed that the highest lipase activity (14.9 Umol/mL) was obtained under the effect of ultrasonic density of 0.1 W/ml within 9 min. The highest solubilization (65%) was observed under optimal micro-aerobic conditions: AFR = 0.2 (VVM) and micro-aerobic time: 40 h. Combined ultrasonic and micro-aerobic (US + MA) pretreatment increases the solubilization (70%), microbial activity (2080%) and lipase enzymatic activity (129%) compared to individual pretreatment. The Biogas production during anaerobic digestion pretreated with combined methods increased by 193% compared to the control, while the elevated values of biogas production in reactors pretreated by ultrasonic and micro-aerobic pretreatment alone were observed to be 101% and 165%, respectively. The net energy in reactor with the combined pre-treatment methods was calculated to be 1.26 kWh, while this value for control, pretreated ultrasonic and micro-aerobic reactors were obtained to be 0.56, 0.67 and 1.2 kWh, respectively.

Sulfate reduction at micro-aerobic solid-liquid interface in landfill

H₂S can be produced under aerobic conditions, which goes against the traditional view of an obligatory anaerobic metabolism process. In this research, the sulfate-reduction behavior at the micro-aerobic solid-liquid interface in a landfill was investigated. H₂S emission from mineralized waste from the landfill material could be enhanced when exposed to O₂. The highest H₂S concentration of 56.54 mg·m^-3, observed at an O₂ concentration of 2%, was 4.5 times higher than the highest concentration of H₂S recorded under anaerobic conditions. The presence of leachate influenced protection of the anaerobic sulfate-reducing bacteria against O₂, allowing the bacteria to survive and even undergo significant sulfate reduction under micro-aerobic conditions. The sulfate concentration could be maintained at a high level because of possible oxidation-reduction cycling under micro-aerobic conditions and the risk of H₂S emission was always high. This research provides a theoretical basis for controlling the release of H₂S within landfills.

Impacts of ammonia nitrogen on autothermal thermophilic micro-aerobic digestion for sewage sludge treatment

The concentration of ammonia nitrogen is relatively high during autothermal thermophilic micro-aerobic digestion (ATMAD), which could significantly affect the sludge stabilization. This paper aims to investigate the impacts of ammonia nitrogen on ATMAD process, batch experiments were carried out with dosage of certain amount of NH₄HCO₃ into digestion system. The total ammonia nitrogen (TAN) was considered as a suitable indicator to characterize the ammonia inhibition. As the TAN reached to approximately 1000 mg L^-1, the sludge digester presented a relatively low removal of volatile solids, due to adverse effects of ammonia nitrogen on sludge digestion. Three pathways that closely related to ammonia inhibition were investigated in this research. Digestion system could be inhibited by high TAN due to K⁺ deficiency of the cells and the decline of Mg²⁺ in the cytoplasm, and the accumulations of reactive oxygen species lead to oxidative stress for the microbes. Ammonia inhibition can be mitigated by the increase of oxidative enzyme.

Response of the reactor performance and microbial community to a shift of ISDD process from micro-aerobic to anoxic condition

Micro-aerobic condition has proven to be effective in enhancing sulfide oxidation to elemental sulfur (S⁰) during integrated simultaneous desulfurization and denitrification process (ISDD). In this study we investigated and compared the performance and microbial community of ISDD process operating under initially anoxic, then micro-aerobic and finally switch back to anoxic condition. For all the three tested scenarios, comparable bioreactor performance in terms of sulfate (95.0 ± 4.4%, 90.6 ± 3.8%, 89.8 ± 3.5%) and nitrate (∼100%) removal was achieved. However, a shift of ISDD bioreactor from micro-aerobic to anoxic environment clearly increased the S⁰ production (30.6%), relative to that at initial anoxic condition (14.2%). Further anoxic bioreactor operation with different influent nitrate concentrations also obtained satisfactory performance particularly in terms of S⁰ production. Microbial community analysis results showed that functional microorganisms selectively enriched at micro-aerobic condition, particularly sulfide-oxidizing bacteria (SOB), could also function well and enhance S⁰ production when bioreactor switching from micro-aerobic to anoxic environment. We proposed that micro-aerobic strategy could function as a bio-selector and provide a new idea in functional microorganisms selectively enrichment for wastewater treatment.

Sludge reduction and microbial structures of aerobic, micro-aerobic and anaerobic side-stream reactor coupled membrane bioreactors

An anoxic/oxic membrane bioreactor (MBR) and three side-stream reactor (SSR) coupled membrane bioreactors were operated in parallel to investigate effects of dissolved oxygen (DO) level in SSR on sludge reduction and microbial community structure of SSR-MBRs. The four MBRs were equally efficient in COD and ammonium nitrogen removal. The anaerobic and micro-aerobic SSR favored nitrogen removal through denitrification, simultaneous nitrification and denitrification and autochthonous substrate release as carbon source. The micro-aerobic SSR achieved greatly higher sludge reduction efficiency (61.1%) than anaerobic (37.3%) and aerobic SSR (7.9%). Micro-aerobic SSR obtained the highest endogenous decay constant (0.035 d^-1) compared to anaerobic (0.023 d^-1) and aerobic SSR (0.015 d^-1). High-throughput sequencing results revealed that anaerobic SSR enriched hydrolytic and fermentative bacteria, aerobic environment favored the growth of slow-growing bacteria, and micro-aerobic SSR stimulated biological activities of both anaerobic and aerobic bacteria.

Sludge reduction by a micro-aerobic hydrolysis process: A full-scale application and sludge reduction mechanisms

The process performance of a full-scale sludge process reduction activated sludge (SPRAS) system in long-term operation were investigated by inserting a micro-aerobic tank and a clarifier before conventional activated sludge process. The full-scale SPRAS for industrial park wastewater treatment achieved efficient pollutants removal and a low observed sludge yield of 0.074 g SS/g COD. Batch tests showed that influent feeding into the micro-aerobic tank favored sludge reduction, and obtained a sludge decay constant of 0.168 d^-1. The SPRAS enriched slow growers and hydrolytic bacteria for sludge reduction, showed high simultaneous nitrification and denitrification efficiency in the micro-aerobic tank with abundant denitrifying bacteria, and improved sludge settleability by enriching floc-forming bacteria. Process configuration of the SPRAS was beneficial to enhance maintenance metabolism, cyclic micro-aerobic and anaerobic uncoupling, and lysis-cryptic growth for sludge reduction. Techno-economic analysis showed that the SPRAS greatly reduced sludge production with small footprint and low cost.

Metabolomics analysis of Pseudomonas chlororaphis JK12 algicidal activity under aerobic and micro-aerobic culture condition

Utilization of algicidal bacteria as a biological agent have been receiving significant interest for controlling harmful algal blooms. While various algicidal bacterial strains have been identified, limited studies have explored the influence of bacterial culture conditions on its algicidal activity. Here, the effect of oxygen on the algicidal activity of a novel bacterium JK12, against a model diatom, Phaeodactylum tricornutum (P. tricornutum) was studied. Strain JK12 showed high algicidal activity against P. tricornutum and was identified as Pseudomonas chlororaphis (P. chlororaphis) by 16S ribosomal RNA gene analysis. JK12 culture supernatant exhibited strong algicidal activity while washed JK12 cells showed no obvious activity, indicating that JK12 indirectly attacks algae by secreting extracellular algicidal metabolites. Micro-aerobic culture condition dramatically enhanced the algicidal activity of JK12 by 50%, compared to that cultured under aerobic condition in 24 h. Extracellular metabolomic profiling of JK12 using gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry analysis revealed significantly higher amounts of allantoic acid, urocanic acid, cytidine 2′,3′-cyclic phosphate, uridine 2′,3′-cyclic phosphate, and chlorinated tryptophan in the micro-aerobic culture. This is the first report to demonstrate the important role of oxygen on the algicidal activity of a non-pathogenic strain P. chlororaphis. In addition, the metabolomics analysis provided insights into the algicidal mechanism of P. chlororaphis.

Correlation of microbial community structure with pollutants removal, sludge reduction and sludge characteristics in micro-aerobic side-stream reactor coupled membrane bioreactors under different hydraulic retention times

A micro-aerobic side-stream reactor (MSSR) was inserted in returned sludge line of a membrane bioreactor (MBR) for sludge reduction. Three MSSR coupled MBRs (M-MBRs) and an anoxic/oxic MBR (AO-MBR) were operated in parallel to investigate effects of micro-aerobic condition and hydraulic retention time (HRT) of MSSR (HRT_M) on process performance. M-MBRs and AO-MBR were equally effective in COD and NH₄-N removal. Rising HRT_M from 3.3 to 6.7 h increased sludge reduction from 10.8% to 47.5%, and promoted dissolved organic matters release and utilization by enriching hydrolytic, fermentative and predatory bacteria. M-MBR at HRT_M of 3.3 h obtained the highest nitrogen removal, and enriched denitrifiers (Thauera and Hyphomicrobium) in the MSSR. The highest relative abundance of polyphosphate-accumulating organisms was observed in M-MBR at HRT_M of 5.0 h, which achieved the highest phosphorus removal. Prolonging HRT_M to 6.7 h improved sludge dewaterability by enriching floc-formation bacteria (Nannocystis) and inhibiting filamentous bacteria (Candidatus_Alysiosphaera).

Effect of different transport conditions and media on Helicobacter pylori isolation

AIM: To optimize transport conditions and medium for Helicobacter pylori (H. pylori) isolation and culture.

METHODS: Live H. pylori bacteria were added into Broth medium with sucrose (1 g/mL) and 50% (mL/mL) calf serum and skim milk quantitatively. The bacteria in transport media were placed at different temperatures in different atmospheres for 6 hours, and then inoculated onto Columbia agar medium supplemented with 10% defibrinated sheep blood and cultured at 37 ℃ micro-aerobically for 5 d. H. pylori colonies were counted and compared. Twenty gastric mucosa specimens from patients diagnosed with gastritis or gastric ulcer were inoculated into Columbia agar and hydrolyzed casein agar supplemented with 10% defibrinated sheep blood and selective antibiotics, then incubated for 5 d at 37 ℃ micro-aerobically. Growth of H. pylori was observed and compared.

RESULTS: The number of live bacteria in calf serum medium was higher than that in skim milk. The number of live bacteria in micro-aerobic and candle jar was higher than that in air and transporting media covered with paraffin oil. The number of bacteria in calf serum media placed micro-aerobically at 37 ℃ (or 26 ℃) was higher than that at 6 ℃ (P < 0.05). There was no significant difference in the number of live bacteria when placed micro-aerobically or in candle jar (P > 0.05). The positive rate (75%) of 20 samples isolated with hydrolyzed casein blood agar was higher than that isolated with Columbia blood agar (45%) (χ² = 4.401, P < 0.05).

CONCLUSION: H. pylori clinical samples can be placed in calf serum medium in micro-aerobic conditions and transported to the laboratory for isolation. Hydrolyzed casein agar supplemented with 10% defibrinated sheep blood is better than Columbia agar medium supplemented with 10% defibrinated sheep blood for H. pylori isolation.