Speciation, toxicity mechanism and remediation ways of heavy metals during composting: A novel theoretical microbial remediation method is proposed.

Heavy metals (HM) pollution is a major limitation to the application of composting products. Therefore, mitigating the toxicity of HM has attracted wide attention during composting. The toxicity of HM is mainly acted on microorganisms during composting, and the toxicity of different HM speciation is obviously various. There are many pathways to change the speciation to reduce the toxicity during composting. Therefore, in this review, the speciation distribution, toxicity mechanism and remediation ways of HM during composting were discussed in order to better solve HM pollution. The microbial remediation technology holds enormous potential to remediate for HM without damaging composting, however, it is hard to extract HM. The innovation of this review was to outline microbial remediation strategies for HM during composting based on two mechanisms of microbial remediation: extracellular adsorption and intracellular sequestration, to solve the problem how to extract microbial agents from the compost. Ultimately, a novel theoretical method of microbial remediation was proposed to remove HM from the compost.

Acinetobacter harbinensis sp. nov., isolated from river water.

A bacterial strain, HITLi 7T, with nitrifying ability was isolated from the surface water of the Songhua River in China. Cells were Gram-stain-negative, strictly aerobic, oxidase-negative, non-motile coccobacilli, capable of growth in mineral media with acetate as the sole carbon source and ammonia as the sole source of nitrogen. The cells did not grow at 37 °C, but did grow at 2 °C. The DNA G+C content was 45.5 mol%. Results of 16S rRNA gene sequence analysis indicated a close relationship between this isolate and Acinetobacter lwoffii (98.4% similarity for strain DSM 2403T). rpoB and gyrB gene sequences did not show significant similarity with those from other species of the genus Acinetobacter. Predominant cellular fatty acids were 9-octadecenoic acid (C18 : 1ω9c) and summed feature 4 (iso-C15:0 2-OH and/or C16:1ω7c). Acid was not produced from d-glucose, and gelatin was not hydrolysed by the isolate. Genotypic, phenotypic and chemotaxonomic data from this study indicate that the isolate should be classified as a representative of a novel species of the genus Acinetobacter. The name Acinetobacter harbinensis sp. nov. is proposed for the novel species, with HITLi 7T (=CGMCC 1.12528T=KCTC 32411T) as the type strain.

Positive effects of appropriate micro-aeration on landfill stabilization: Mitigating ammonia and VFAs accumulation.

The slow stabilization process of landfill had brought obstacles to urbanization. The paper investigated the efficacy and mechanism of micro-aeration intensity for landfill stabilization. The micro-aeration intensity of 0.05 L/(h·kg) resulted in a significant increase of volatile fatty acids (VFAs) in the hydrolysis stage, and the NH4+-N concentration was reduced by 22.1 %. At the end of landfill, VFAs were rapidly degraded and organic matter was reduced from 36 % to 16 %, which was 55.5 % more efficient than the control group. In addition, the community succession and structure of bacteria and archaea were analyzed. The micro-aeration intensity of 0.05 L/(h·kg) increased the abundance of hydrolyzing functional bacteria such as Pseudomonas and Bacillus, and allowed methanogenic bacteria such as Methanobacterium and Methanothrix to gradually establish oxygen tolerance in the microaerobic environment. The appropriate micro-aeration intensity can accelerate the stabilization process of landfill, which has environmental and economic benefits.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater.

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.

Synchronous reinforcement azo dyes decolorization and anaerobic granular sludge stability by Fe, N co-modified biochar: Enhancement based on extracellular electron transfer.

Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

Performance and mechanism of modified biological nutrient removal process in treating low carbon-to-nitrogen ratio wastewater.

For solving the challenge of difficult nutrient removal, high running cost and CO2 emission at low carbon-to-nitrogen (C:N) ratio, Bi-Bio-Selector for nitrogen and phosphorus removal (BBSNP) process was developed. Under parallel operation conditions, full-scale BBSNP was less influence by low C:N ratio (3.5-2) than Anaerobic-anoxic-aerobic (AAO) and achieved better nitrogen removal performance. The mechanism of performance advantage in BBSNP was analyzed by mass balance and high throughout sequencing. It demonstrated BBSNP developed unique microbial community at C:N ratio of 2. Higher abundance of Saccharibacteria, Ferruginibacter, Ottowia, Dokdonella, Candidatus_Nitrotoga and Nitrospira in BBSNP was responsible for better chemical oxygen demand (COD) utilization efficiency, denitrification, denitrifying phosphorus removal and nitrification. Meanwhile, under low C:N ratio, BBSNP could save 10% organic carbon and 15% oxygen requirement, reduce 53% running cost and 21% CO2 emission, which had practical value in relieving energy crisis and carbon emission of wastewater treatment plants (WWTPs).

Bacterial community and function of biological activated carbon filter in drinking water treatment.

OBJECTIVE: It aims to investigate the changes in composition and structure of bacterial communities developing on biological activated carbon (BAC) particles, and the bacterial functions. METHOD: A pilot plant had been in service for 180 days, aiming to develop bacterial communities on activated carbon naturally. After 180 days of operation, the bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) analyses of PCR-amplified 16S rRNA genes. The study on community composition and the phylogenetic relationships of the organisms was complemented by a sequence analysis of cloned PCR products from 16S rRNA genes. Gas chromatography-mass (GC-MS) measurement was used to determine organic chemical composition of inflow and outflow water on the 300th day. TOC and NH(4)(+)-N were also tested in this experiment. RESULTS: It showed that the stable bacterial structure did not develop on BAC particles until the 9th month during running time of the BAC filter. The communities were finally dominated by Pseudomonas sp., Ba-cillus sp., Nitrospira sp., and an uncultured bacterium. Stable bacterial communities played an important role in removal of NH(4)(+)-N and total organic carbon (TOC). Results from gas chromatography-mass (GC-MS) showed that 36 kinds of chemicals in feed water were eliminated, and concentrations of 5 kinds of chemicals decreased. These chemicals served as nutrients for the dominant bacteria. CONCLUSION: The findings from the study suggested that the stability of microbial structure was beneficial for improving NH(4)(+)-N and TOC removal efficiencies. The dominant bacteria had the advantage of biode-grading a wide range of organic chemicals and NH(4)(+)-N.

Application of glucose for improving NH4+-N removal in micro-polluted source water by immobilized heterotrophic nitrifiers at low temperature.

Bio-enhanced activated carbon (BEAC) filters have shown potential in source water purification. The key drawback of this system is the difficulty of the set-up at low temperature. Here, glucose was applied to help immobilize more functional heterotrophic nitrifiers and further improve NH4+-N removal by BEAC. Results showed that pre-loading glucose on granular activated carbon could achieve better immobilization efficiency with 5.12 × 108 CFU/g-DW C biomass and 3.77 mg TF/L/g-DW C dehydrogenase activity after artificial immobilization, which were separately 12.5 and 4.2 times of the control. 95-d running data at different conditions showed the superiority of both immobilization and NH4+-N removal could last and defend environment changes during relatively long period. Even at the end of operating, the abundance of targeting genus (Acinetobacter) still occupied 9.59% of microbial communities on BEAC, while this value was only 1.24% without pre-loading glucose. Biolog-ECO plate analysis found pre-loading glucose improved organic nitrogen metabolism effectively, along with carbohydrate, amino, alcohol, amine and carboxylic acid metabolism on BEAC.

Nitrate removal from low C/N wastewater at low temperature by immobilized Pseudomonas sp. Y39-6 with versatile nitrate metabolism pathways.

For solving the challenge in nitrate removal from low C/N wastewater at low temperature, Pseudomonas sp. Y39-6 was isolated and used in nitrate removal. It showed aerobic-heterotrophic denitrification with rate of 1.77 ± 0.31 mg/L·h and unusual aerobic-autotrophic nitrate removal (rate of 0.324 mg/L·h). The aerobic-autotrophic nitrate removal mechanisms were deep investigated by analyzing the nitrate removal process and genomic information. At aerobic-autotrophic condition, the strain Y39-6 could assimilate nitrate to amino acid (NO3- + PHA + CO2 â†’ C5H7O2N) with the carbon source from Polyhydroxyalkanoic acid (PHA) degradation and CO2 fixation. Flagella motivation, swarming activity and extracellular polymeric substances (EPS) production regulated Pseudomonas sp. Y39-6 forming biofilm. Carriers immobilized with Pseudomonas sp. Y39-6 were used in moving bed biofilm reactor (MBBR) and achieved 24.83% nitrate removal at C/N < 1 and 4 °C. Results of this study provided a practical way for nitrogen removal from low C/N wastewater in cold region.

Bio-enhanced activated carbon filter with immobilized microorganisms for removing organic pollutants in the Songhua River.

Five dominant microorganisms including four kinds of Pseudomonas and one kind of Bacillus were isolated from the Songhua River. The organic pollutants removal potential and community composition of these five dominant microorganisms immobilized on activated carbon filter, which is called the bio-enhanced activated carbon filter (BEAC), were investigated to compare with the naturally formed biological activated carbon (BAC) filter. Songhua River was used as the raw water. The pilot scale test results showed the biomass in the BEAC filter increased initially and then stabilized after 45 d of operation with an average value of 192 nmolPO(4)/g carbon. The corresponding biological activity reached 1,368 ng ATP/g carbon. The gas chromatography-mass spectrometry (GC-MS) results showed that the BEAC filter degraded the toxic organic substances more effectively than the BAC filter, especially for halogenated hydrocarbons and PAHs (polycyclic aromatic hydrocarbons). Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analysis revealed the eco-system of five dominant microorganisms did not change in the BEAC filter even on 180 d of operation. Two of the five dominant microorganisms, Bacillus subtilis and Pseudomonas balearica, had high biological activity and were more adaptable to the surface of the carbon media than the other three dominant microorganisms. The scanning electron microscope (SEM) photograph showed a large quantity of microorganisms developed on the BEAC filter. The toxicity test using Deltatox Bioassay Technology Analyzer indicated that the dominant microorganisms were safe to be applied in drinking water treatment process.

A study on the photocatalytic degradation performance of a [KNbO3]0.9-[BaNi0.5Nb0.5O3-δ ]0.1 perovskite.

In this study, [KNbO3]0.9-[BaNi0.5Nb0.5O3-δ ]0.1 (KBNNO) perovskite powder was synthesized via a conventional solid-phase reaction method. The crystal structure of the KBNNO powder was characterized on an X-ray diffractometer. The size and surface morphology of the particles were investigated via field emission electron scanning microscopy (FE-SEM). The KBNNO powder particles were stacked from a smooth flat layer. The photocatalytic activity of KBNNO was investigated using a methylene blue (MB) aqueous solution as a model organic substrate. The results showed that the KBNNO powder has excellent photocatalytic degradation performance. The effects of catalyst loading and the initial concentration of the MB solution on the photocatalytic activity were also investigated in this study. The experimental results proved that both catalyst loading and the initial dye concentration are important factors affecting photocatalytic degradation. As the catalyst loading increases, the photocatalytic activity increases. However, the growth rate of the degradation efficiency gradually decreases. Also, the degradation efficiency gradually decreased with the initial concentration of MB.

Effect of iron and manganese on ammonium removal from micro-polluted source water by immobilized HITLi7T at 2 °C.

In this study, trace metals (Fe & Mn) were applied to enhance NH4+-N removal in source water at 2 °C, and 22.7% of initial 2.20 mg/L NH4+-N was removed by pre-treating granular activated carbon (GAC) with Fe & Mn before immobilizing Acinetobacter harbinensis HITLi7T to form biological activated carbon (BAC). Biomass and dehydrogenase activity (DHA) on this modified BAC were 2.80 × 108 CFU/g-DW C and 0.50 mg/L/g-DW C, respectively, both the highest. Additionally, 4.76 times more biomass and 9.76 times higher DHA of HITLi7T were observed in the cultivation with Fe & Mn dosing. Extracellular polymeric substances (EPS) measurements found Fe & Mn dosing could increase total EPS amount (44.3% higher) and polysaccharide (PS) ratio (1.50% higher) secreted by HITLi7T. According to the results of 3D-excitation-emission matrix (3D-EEM) fluorescence spectra and infrared spectra (FTIR) analysis, Fe and Mn promoted the secretion of tryptophan-like substances and changed functional groups COH, COC, CO and COOH, which are associated with protein and PS.

Insight into transformation of dissolved organic matter in the Heilongjiang River.

Heilongjiang is a "browning" river that receives substantial terrestrial organic matter, where reactivity of dissolved organic matter (DOM) may have important effect on ecosystem function and carbon biogeochemical cycle. However, little is known about microbial transformations of different DOM components, which could provide valuable insight into biogeochemical reactivity of DOM. In this study, bioavailability experiments were conducted for 55 days to determine changes of different DOM components by microbial transformations. Labile matter (C1) was detected only in initial DOM, and tryptophan-like substances (C4) were observed from day 5 onwards. Thus, three individual components were identified at each sampling time of the bioavailability experiment. The increase of Fmax in DOM components revealed that microbial humic-like substances (C2), terrestrial humic-like substances (C3), and C4 were produced by microbial transformation, especially in the spring samples. Further, two-dimensional correlation spectroscopy (2D-COS) indicated that shorter wavelength tryptophan-like and microbial humic-like substances can be degraded by microbes or transformed into longer wavelength complex substances. Relatively simple microbial humic-like substances were preferentially produced compared to complex terrestrial humic-like substances. The results make sense to understand the biogeochemical cycling and environmental effects of DOM in the Heilongjiang River.

Substrates removal and growth kinetic characteristics of a heterotrophic nitrifying-aerobic denitrifying bacterium, Acinetobacter harbinensis HITLi7T at 2 °C.

In order to investigate the heterotrophic nitrification and aerobic denitrification ability of Acinetobacter harbinensis HITLi7T at 2 °C, both the growth parameters and substrates utilization characteristics were tested and appropriated kinetic models were obtained in this study. Under the initial concentration of 5 mg/L, the maximum NH4+-N and NO3--N degradation rates were 0.076 mg NH4+-N/L/h and 0.029 mg NO3--N/L/h, respectively. At the simultaneous presence of 2.5 mg/L NH4+-N and NO3--N, the maximum nitrate removal rate increased to 0.054 mg NO3--N/L/h (1.86 folds), while a slight decrease was observed in NH4+-N removal. Two double-substrate models, Contois-Contois (1) for NH4+-N and TOC, Monod-Contois (2) for NO3--N and TOC matched well with the experimental data. The kinetic parameters were determined as µmax1 = 0.095 h-1, BA1 = 0.012 mg/L, BT1 = 0.784 g TOC/g biomass (R12 = 0.9997), and µmax2 = 0.032 h-1, KN2 = 0.375 mg/L, BT2 = 1.108 g TOC/g biomass (R22 = 0.9731) by multiple regression equation.

Effect of the addition of exogenous precursors on humic substance formation during composting.

The aim of this work was to explore the effect of the addition of exogenous precursors on humic substance (HS) formation during composting. HS formation is a complex biochemical process that occurs during composting. In addition, HS precursors and bacterial communities were recognized as the key factors that affect HS formation. The addition of exogenous precursors can promote the humification process during composting, but few studies have explored the potential relationships between the proportion of additional exogenous precursors, the bacterial community and HS formation. Jointly adding benzoic acid (BA) and soybean residue after extracted oil (SR) treatment can promote HS formation, especially humic acid formation. In addition, the increase in the proportion of exogenous precursors added could strengthen the relationship among different precursors, thereby changing the bacterial community composition and further promoting the humification process during composting. In addition, a structural equation model (SEM) showed that precursors were the key factors to regulate HS formation and certain bacteria as the direct drivers to affect HS formation. This model provides more possibilities to regulate HS formation during composting and enhances its potential applicability under real conditions.

Response of humic acid formation to elevated nitrate during chicken manure composting.

Nitrate can stimulate microbes to degrade aromatic compounds, whereas humic acid (HA) as a high molecular weight aromatic compound, its formation may be affected by elevated nitrate during composting. Therefore, this study is conducted to determine the effect of elevated nitrate on HA formation. Five tests were executed by adding different nitrate concentrations to chicken manure composting. Results demonstrate that the concentration of HA in treatment group is significantly decreased compared with control group (p < 0.05), especially in the highest nitrate concentration group. RDA indicates that the microbes associated with HA and environmental parameters are influenced by elevated nitrate. Furthermore, structural equation model reveals that elevated nitrate reduces HA formation by mediating microbes directly, or by affecting ammonia and pH as the indirect drivers to regulate microbial community structure.

Effects of floodgates operation on nitrogen transformation in a lake based on structural equation modeling analysis.

Floodgates operation is one of the primary means of flood control in lake development. However, knowledge on the linkages between floodgates operation and nitrogen transformation during the flood season is limited. In this study, water samples from six sampling sites along Lake Xingkai watershed were collected before and after floodgates operation. The causal relationships between environmental factors, bacterioplankton community composition and nitrogen fractions were determined during flood season. We found that concentrations of nitrogen fractions decreased significantly when the floodgates were opened, while the concentrations of total nitrogen (TN) and NO3- increased when the floodgates had been shut for a period. Further, we proposed a possible mechanism that the influence of floodgates operation on nitrogen transformation was largely mediated through changes in dissolved organic matter, dissolved oxygen and bacterioplankton community composition as revealed by structural equation modeling (SEM). We conclude that floodgates operation has a high risk for future eutrophication of downstream watershed, although it can reduce nitrogen content temporarily. Therefore, the environmental impacts of floodgates operation should be carefully evaluated before the floodwaters were discharged into downstream watershed.

Seasonal-related effects on ammonium removal in activated carbon filter biologically enhanced by heterotrophic nitrifying bacteria for drinking water treatment.

To determine the potential effects of seasonal changes on water temperature and water quality upon removal of ammonium and organic carbon pollutants and to characterize the variations in microbial characteristics, a pilot-scale activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria was investigated for 528 days. The results show that 69.2 ± 28.6% of ammonium and 23.1 ± 11.6% of the dissolved organic carbon were removed by the biologically enhanced activated carbon (BEAC) reactor. It is shown that higher biodegradable dissolved organic carbon enhances ammonium removal, even at low temperatures. The C/N ratio consumed by the BEAC reactor reached a steady value (i.e., 3.3) after 2 months of operation. Despite seasonal fluctuations and competition of the indigenous community, the heterotrophic nitrifying bacteria (Acinetobacter sp. HRBLi 16 and Acinetobacter harbinensis strain HITLi 7) remained relatively stable. The amount of carbon source was the most significant environmental parameter and dramatically affected the microbial community compositions in the BEAC reactor. The present study provides new insights into the application of a BEAC reactor for ammonium removal from drinking water, resisting strong seasonal changes.

Ammonium removal of drinking water at low temperature by activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria.

We sought to confirm whether use of Acinetobacter strains Y7 and Y16, both strains of heterotrophic nitrifying bacteria, was practical for removing ammonium (NH4 (+)-N) from drinking water at low temperatures. To test this, ammonium-containing drinking water was treated with strains Y7 and Y16 at 8 and 2 °C. Continuous ammonium treatment was conducted in order to evaluate the performance of three biologically enhanced activated carbon (BEAC) filters in removing ammonium. The three BEAC filters were inoculated with strain Y7, strain Y16, and a mixture of strains Y7 and Y16, respectively. A granular activated carbon (GAC) filter, without inoculation by any strains, was tested in parallel with the BEAC filters as control. The results indicated that NH4 (+)-N removal was significant when a BEAC filter was inoculated with the mixture of strains Y7 and Y16 (BEAC-III filter). Amounts of 0.44 ± 0.05 and 0.25 ± 0.05 mg L(-1) NH4 (+)-N were removed using the BEAC-III filter at 8 and 2 °C, respectively. These values were 2.8-4.0-fold higher than the values of ammonium removal acquired using the GAC filter. The synergistic effect of using strains Y7 and Y16 in concert was the cause of the high-ammonium removal efficiency achieved by using the BEAC-III filter at low temperatures. In addition, a high C/N ratio may promote NH4 (+)-N removal efficiency by improving biomass and microbial activity. This study provides new insight into the use of biofilters to achieve biological removal of ammonium at low temperature.

Draft Genome Sequences of Acinetobacter harbinensis Strain HITLi 7T, Isolated from River Water.

Acinetobacter harbinensis HITLi strain 7(T), isolated from river water, has the ability to remove ammonium and organic chemicals at 2°C. The genome sequences might be useful for investigating the low-temperature adaptability and nitrogen or organic chemical metabolism.