Wastewater treatment by alkali bacteria and dynamics of microbial communities in two bioreactors

Preparation of blast furnace dust particle electrodes and their application in synergistic electrochemical degradation of saline polyvinyl alcohol wastewater

Polyvinyl alcohol (PVA) has been widely used as a water-soluble plastic in laundry and dish detergent pods, yet wastewater contaminated with PVA is too difficult to be treated due to its high salinity and foaming. Here, we fabricated blast furnace dust (BFD) particle electrodes, and developed a three-dimensional electrocatalytic system (3DEC) to treat saline PVA wastewater. The optimum preparation condition for BFD particle electrode was iron carbon ratio of 2:1 doping with TiO2. The optimal parameters of 3DECs for PVA wastewater degradation were thoroughly investigated, with current density of 30 mA/cm2, electrode distance of 30 mm, pH value of 7.0, and particle electrode filling rate of 50%. PVA wastewater degradation rate could reach 89.33% within 120 min. The underlying mechanism of iron-carbon micro electrolysis and electrocatalytic system was further studied. PVA wastewater was degraded by direct catalytic oxidation from electrodes. A scavenger experiment showed that free radicals consisting of •OH and HClO mainly contributed to the PVA wastewater degradation. HClO was generated by Cl- at the electrocatalysis and micro electrolysis of particles. In addition, the lifetime of the prepared BFD particle electrode was 120 h, which exhibited electrochemical stability. These findings highlight that the 3DECs coupled with BFD particle electrode is a promising electrocatalysis process for the removal of PVA wastewater.

Towards passive bioremediation of dye-bearing effluents using hydrous ferric oxide wastes: Mechanisms, products and microbiology

A novel, circular economy-inspired approach for the "passive" (non-powered and reagent-free) treatment of dye-bearing effluent is presented. The treatment utilises the biogeochemical interaction of dye-bearing wastewater with hydrous ferric oxide (HFO) bearing sludges. The work presented demonstrates for the first time the reuse of HFO-rich waste sludges from potable water and mine water treatment. The waste was used directly without modification or reagent addition, as media/substrate in simple flow-through reactors for the decolourisation and biodegradation of methyl orange (MO) and mixed dyes textile effluent. Three phases of exploratory proof of concept work were undertaken. Columns containing HFO sludges were challenged with solution of MO, and MO amended with glycerol (Phase I), MO in a synthetic textile effluent recipe (Phase II), and real mixed textile effluent containing a mixture of dyes (Phase III). After an initial lag period extensive decolourisation of dye was observed in all cases at rates comparable with pure strains and engineered bioreactor processes, with evidence of biodegradation beyond simple cleavage of the mono azo chromophore and mineralisation. The microbiology of the initial sludge samples in both cases exhibited a diverse range of iron oxidising and reducing bacteria. However, post experiment the microbiology of sludge evolved from being dominated by Proteobacteria to being dominated by Firmicutes. Distinct changes in the microbial community structure were observed in post-treatment MWTS and WTWS where genera capable of iron and sulphate reduction and/or aromatic amine degradation were identified. Average nitrogen removal rates for the columns ranged from 27.8 to 194 g/m³/day which is higher than engineered sequential anaerobic-aerobic bioreactor. Postulated mechanisms for the fast anaerobic decolourisation, biodegradation, and mineralisation of the dyes (as well nitrogen transformations) include various direct and indirect enzymatic and metabolic reactions, as well as reductive attack by continuously regenerated reductants such as Fe(II), HFO bound Fe(II), FeS, and HS^-. The ability of iron reducers to degrade aromatic rings is also considered important in the further biodegradation and complete mineralisation of organic carbon. The study reveals that abundant and ubiquitous HFO-rich waste sludges, can be used without amendment, as a substrate in simple flow-through bioremediation system for the decolourisation and partial biodegradation of dyes in textile effluent.

Study on treatment of acid red G with bio-carbon compound immobilized white rot fungi

Corn straw biochar was used as a carrier to immobilize white rot fungi and the removal performance of immobilized pellets for acid red G (ARG) dye was studied. The results showed that the removal rate of ARG could reach 96.17% under the best preparation conditions of immobilized pellets (3% sodium alginate concentration, 0.7% corn straw biochar, 5% white rot fungus mycelium suspension, 4% CaCl₂, and 36 h immobilization time). The orthogonal test results showed that the best combination was the immobilized pellets dosage of 200/100 mL, pH of 4.5, rotation speed of 150 r/min, and initial concentration of 20 mg/L dye at 30 °C. The degradation pathway of ARG by immobilized microspheres was studied by ultraviolet-visible spectrometer, Fourier transform infrared spectroscopy, and liquid chromatography-mass spectrometry. The results showed that ARG was degraded into aniline and 5-(acetamino)-4-hydroxy-3-amino-2,7-naphthalene disulfonic acid. Aniline was further deaminated to form benzene, and benzene was ring opened to form other organic compounds; 5-(acetylamino)-4-hydroxy-3-amino-2,7-naphthalene disulfonic acid was dehydroxylated to form 5-(acetylamino)-3-amino-2,7-naphthalene disulfonic acid. This study shows that the prepared biochar immobilized pellets can be used as an efficient water treatment material to remove ARG dye from wastewater.

Treatment of polyvinyl alcohol containing wastewater in two stage spiral symmetrical stream anaerobic bioreactors coupled a sequencing batch reactor

This work aimed to study the treatment of polyvinyl alcohol containing wastewater (PVA-containing wastewater) discharged from textile industry. The batch experiment verified the feasibility of anaerobic treatment and determined that the optimal substrate COD was around 3000 mg/L. The single spiral symmetrical stream anaerobic bioreactor (SSSAB) was used for treating PVA-containing wastewater, which shows the stability of SSSAB and the improvement of biodegradability of wastewater. Finally, two stage SSSABs coupled SBR was proposed. By this scheme, under the influent COD of 3014 mg/L and PVA of 413 mg/L, the COD and PVA removal reached 89.4% and 90.7%, respectively, which were higher than the values obtained by other schemes. Contribution rates of reactors show that each reactor plays an essential role, and SEM images show the unique of microbial flora in each SSSAB. The SSSAB-SSSAB-SBR process can provide an alternative to the chemical methods for treating PVA-containing wastewater.

Responses of bacterial and bacteriophage communities to long-term exposure to antimicrobial agents in wastewater treatment systems

The occurrence of antibacterial agents has received increasing concern due to their possible threats to human health. However, the effects of antibacterial residues on the evolution and dynamics between bacteria and bacteriophages in wastewater treatment systems have seldom been researched. Especially for phages, little is known about their response to antimicrobial exposure. In this study, two identical anoxic-aerobic wastewater treatment systems were established to evaluate the responses of bacterial and phage communities to long-term exposure to antimicrobial agents. The results indicated simultaneous exposure to combined antimicrobials significantly inhibited (p < 0.05) the abundance of phages and bacteria. Metagenomic sequencing analysis indicated the community of bacteria and phages changed greatly at the genus level due to combined antibacterial exposure. Additionally, long-term exposure to antimicrobial agents promoted the attachment of receptor-binding protein genes to Klebsiella, Escherichia and Salmonella (which were all members of Enterobacteriaceae). Compared to that in the control system, the numbers of receptor-binding protein genes on their possible phages (such as Lambdalikevirus and P2likevirus) were also obviously higher when the microorganisms were exposed to antimicrobials. The results are helpful to understanding the microbial communities and tracking the relationship of phage-bacterial host systems, especially under the pressure of antimicrobial exposure.

Characterization of tetracycline resistant bacterial community in saline activated sludge using batch stress incubation with high-throughput sequencing analysis

An innovative and cost-effective method, i.e., batch stress incubation with tetracycline in combination with Cloning-Sanger sequencing and Illumina high-throughput sequencing was developed to identify tetracycline resistant bacteria (TRB) in activated sludge (AS) treating saline sewage. This method overcomes the drawbacks of culture-based approach (unrepresentative and biased results) and utilizes both the advantages of Cloning-Sanger sequencing and Illumina high-throughput sequencing, that is, long length read for correct taxonomic assignment at lower ranks and enough sequencing depth for accurate quantification of TRB communities with medium to low abundances, respectively. High precision (relative deviation ≤ 16.1%) was obtained for all taxon ranks with relative abundances over 0.01%. In the AS sample, TRB consisted of 13 genera with Haliea, Microbacterium and Paracoccus as dominate genera and 6 new TRB genera, i.e., Haliea, Rheinheimera, Alishewanella, Idiomarina, Pseudorhodobacter and Algoriphagus. The increase of tetG and tetA abundance might be associated with the significant increase of Pseudomonas (tetG and tetA host) in the AS after tetracycline stress incubation. tetS abundance also showed an obvious increase after 20 mg/L tetracycline treatment. This method provided a new tool to screen other antibiotic resistant bacteria, bacteria resistant to heavy metals or disinfectants in AS samples.

Evolution of the microbial community in a full-scale printing and dyeing wastewater treatment system

In this study, the dynamics of bacterial, fungal and archaeal populations in two-stage biological processes of a full-scale printing and dyeing wastewater treatment system were traced using cultivation and molecular biological techniques. The enumeration results indicated that bacteria were the dominant population in the system, in which the ratio of fungi to bacteria decreased in all the treatment units, while the ratio of archaea to bacteria increased significantly, especially in samples from the second-stage biological treatment process. PCR-denaturing gradient gel electrophoresis (DGGE) analysis showed that the microbial diversity increased with system running and 64.6% of bacterial, 57.6% of fungal and 38.2% of archaeal populations remained in the system from the seed sludge during system start-up. In spite of variation in the microbial community and composition of the influents, some bacterial species such as Thauera sp. and Xanthomonadaceae were present simultaneously in all the collected samples.

Fast and highly efficient removal of dyes under alkaline conditions using magnetic chitosan-Fe(III) hydrogel

The dyeing effluent of high alkalinity, which could not be treated efficiently by traditional wastewater technologies, highlighted the need to explore a technically feasible, highly efficient and cost effective method. Thus, a fast and highly efficient method for the removal of dyes under alkaline conditions using magnetic chitosan-Fe(III) hydrogel was proposed. Firstly, chitosan-Fe(III) hydrogel was prepared by a chelation procedure with cheap and environmentally friendly chitosan and iron salts. We characterized the sorption and desorption of C. I. Acid Red 73, a common type of anionic dye, on magnetic chitosan-Fe(III) hydrogel, to understand its availability for alkaline dyeing wastewater. Sorption of dye to chitosan-Fe(III) hydrogel was fast (adsorption could reach equilibrium in less than 10 min) in a wide pH range, and agreed well to the Langmuir-Freundlich adsorption model with a high maximum adsorption capacity of 294.5 mg/g under pH = 12. Meanwhile, 1 mol/L NaOH was used to desorb the dye efficiently (desorption efficiency 94.4%) and 0.1 mol/L HCl was applied to regenerate the chitosan-Fe(III) hydrogel. The results showed that the chitosan-Fe(III) hydrogel could retain its high efficiency after the desorption and regeneration. The common coexisting ions almost had no negative effect on the dye adsorption of chitosan-Fe(III) and the removals of a variety of anionic dyes suggest that the magnetic chitosan-Fe(III) hydrogel could efficiently adsorb both the acid and reactive dyes under alkaline condition. Overall, the results reported herein indicated that magnetic chtisoan-Fe(III) with high adsorption efficiency and strong magnetic property is very attractive and implies a potential of practical application for alkaline dyeing effluent treatment.

Purification of waste gas containing high concentration trimethylamine in biotrickling filter inoculated with B350 mixed microorganisms

A biotrickling filter packed with ceramic particles and seeded with B350 microorganisms was applied to remove trimethylamine (TMA) from gaseous waste. A 100% removal efficiency (RE) was obtained when the empty bed residence time (EBRT) was larger than 110 s at an inlet concentration of 0.30 m g/L. Maximum elimination capacity (EC) was 13.13 g m(-3)h(-1) (RE=64.7%) at 55 s of EBRT. TMA concentrations <0.20mg/L at 83 s of EBRT did not affect the REs (100%). Maximum EC was 13.95 g m(-3)h(-1) (RE=78.1%) at a TMA concentration of 0.42 mg/L. Approximately 53.1% of the carbon in TMA was completely mineralized. Bacterial community analysis in the bioreactor revealed more than 21 species in a stable state. Based on all these results, biotrickling filter inoculated with B350 microorganisms is deemed highly capable of ridding waste gas of TMA.