A novel start-up strategy for mixotrophic denitrification biofilters by rhamnolipid and its performance on denitrification of low C/N wastewater.

A novel start-up strategy for sulfur-based mixotrophic denitrification biofilters (mDNBFs) by rhamnolipid was investigated for the first time. Rhamnolipid with gradient concentrations (0-120 mg/L) was added into five lab-scale mDNBFs. Results showed that rhamnolipid could promote biomass yield and nitrogen removal rate (NRR) by 71.7% and 68.7%, respectively, while its effect on EPS and adhesion force was concentration-dependent. The spatial distribution characteristics of microbial communities demonstrated the enrichment of main heterotrophic denitrifying bacteria outcompeted that of the autotrophs, with a more pronounced difference in high concentration rhamnolipid-treated mDNBFs. Furthermore, highest abundance of napA, narG, nirK and nosZ genes was observed in 80 mg/L rhamnolipid-treated mDNBF. Interfacial processes including solubilizing effect and hydration repulse and variations of organics were discussed to explicate the underlying mechanism. The study enlightened that an appropriate concentration (∼80 mg/L) of rhamnolipid may be a good solution for accelerating biofilm formation and enriching denitrifying bacteria to promote denitrification performance of mDNBFs treating low C/N wastewater.

Undesirable effects of exogenous N-acyl homoserine lactones on moving bed biofilm reactor treating medium-strength synthetic wastewater.

Exogenous AHLs are gradually reported to facilitate biofilm growth, however, whether they play a universal role in promoting biofilm formation and pollutants removal remains to be investigated. The pollutant removal, biofilm properties, microbial community and the distribution of AHLs were investigated in three lab-scale MBBRs by continuous dosing 100 nM N-Hexanoyl-L-homoserine lactone (C6-HSL) and N-Octanoyl-L-homoserine lactone (C8-HSL) in synthetic wastewater under normal nutrition (40 mg/L NH4+-N with C/N = 20). Results showed that adding AHLs didn't affect organics removal and exogenous C6-HSL even significantly suppressed NH4+-N removal by 0.44-20.29% after 16 days (p < 0.05). The introduction of AHLs both facilitated biofilm growth and extracellular polymeric substances secretion while suppressed ATP production especially during the stable operation period, with 48.96% by C6-HSL (p < 0.05) and 27.25% by C8-HSL, respectively. Exogenous AHLs inhibited the proliferation of Chryseobacterium, resulting in improvement in biofilm growth and it probably mediated ATP synthesis through regulating the release of 3OHC12-HSL in aqueous phase. Organics removal and biofilm growth were mainly attributed to the combined actions of multitudinous AHLs in biofilm phase rather than that in aqueous phase. The counterintuitive conclusions obtained in this study highlighted the importance of legitimately applying exogenous AHLs to accelerate biofilm formation and the start-up of MBBR in wastewater treatment.

Enhanced biofilm formation and denitrification in biofilters for advanced nitrogen removal by rhamnolipid addition.

Denitrification biofilters (DNBFs) are widely used in advanced nitrogen removal of wastewater with low C/N and effective biofilm formation is critical to their long-term operation. Hereby the influence of rhamnolipid addition in DNBFs was investigated for the first time. Gradient concentrations (0, 20, 40, 80, 120 mg/L) of rhamnolipid were applied to investigate nitrogen removal, biofilm properties and microbial community of lab-scale DNBFs. A significant increase of nitrogen removal was observed in rhamnolipid-treated DNBFs (p < 0.05). Total solid (TS), extracellular polymeric substances (EPS) and adhesion force of biofilms in DNBF with 120 mg/L rhamnolipid reached the maximum, which were 2.17, 2.15 and 3.36 times of those in the control, respectively. Moreover, rhamnolipid exhibited an improvement in abundance of Simplicispira and Gemmatimonas which were responsible for enhanced biofilm formation and denitrification. The results suggested that rhamnolipid addition can be a novel strategy to improve the start-up and denitrification performance of DNBFs.

Towards the biofilm characterization and regulation in biological wastewater treatment.

There is an increasing need for application of biofilm process in the upcycling of wastewater treatment plants all around the world in recent years, yet there are few literatures on summarizing wastewater biofilm during the life cycle. In particular, there is a vacancy on characterization at various stages of biofilm and its regulation. This review provided a whole look at biofilm formation and its development, accompanied by microbial physiology, ecology, and activity, where the initialization of biofilm formation and its characterization were stressed. The new progresses on biofilm physio-ecology analysis and methods on evaluating microbial activity were summarized, while it is worth mentioning that the concept of aging biofilm was also presented. Furthermore, regulations methods of biofilm were reviewed and future research trends on biofilm control were prospected, aiming at guiding biofilm control in biofilm-based wastewater treatment.

Exogenous N-acyl homoserine lactones facilitate microbial adhesion of high ammonia nitrogen wastewater on biocarrier surfaces.

Startup of biofilm process triggered by initial adhesion of bacteria is difficult in high ammonia nitrogen wastewater treatment. In this study, the influence of two commonly used N-acyl homoserine lactones (AHLs), N-Hexanoyl-l-homoserine lactone (C6-HSL) and N-Octanoyl-l-homoserine lactone (C8-HSL), on the adhesion of soluble macromolecules and bacteria in four types of high ammonia nitrogen wastewater to surfaces of model biocarriers (i.e. polystyrene, polyamide and polyethylene terephthalate) was investigated by using a quartz crystal microbalance with dissipation (QCM-D) monitoring technology. Results showed that the adhesion was enhanced by the addition of exogenous AHLs and there was more microbial retention attributed by C8-HSL. Greater deposition amount was generally found on PS and better enhanced performances of the adhesion were found on PA surface. Furthermore, viscoelastic film formed under synchronous high-low salinity and organic content and dominant bacteria of real wastewater determined the role of exogenous AHLs. The method of adding moderate amount of exogenous AHLs into bioreactors has important implications for accelerating the startup process treating high ammonia nitrogen wastewater by biofilm process.

Effect of adding low-concentration of rhamnolipid on reactor performances and microbial community evolution in MBBRs for low C/N ratio and antibiotic wastewater treatment.

This study aims to explore the potential of low-concentration of rhamnolipid in efficient treatment of wastewater with poor biodegradability. Six lab-scale moving bed biofilm reactors (MBBRs) were applied to investigate the effect of rhamnolipid concentration (0, 20, 50 mg/L) on pollutants removal, biomass accumulation, microbial morphology and community evolution in synthetic low C/N ratio (3:1) and antibiotic (50 µg/L tetracycline) wastewater. 20 mg/L rhamnolipid treated groups exhibited significant increase (p < 0.05) of chemical oxygen demand (COD) removal and volatile solid (VS) content in both synthetic wastewater. Hydrogenophaga and Aeromonas were dominant in all reactors in which Aeromonas was positively correlated with the removal of COD and ammonia nitrogen (NH4+-N). Besides, Methyloversatilis became dominant only in 20 mg/L rhamnolipid treated groups and was positively correlated with VS. This study provides a novel and feasible strategy for treating poorly biodegradable wastewater by biofilm process with moderate amount of rhamnolipid.

Calcium ion- and rhamnolipid-mediated deposition of soluble matters on biocarriers.

Start-up of biofilm process initiated by the deposition of soluble matters on biocarriers is a very important yet time-consuming procedure. However, rapid start-up methods especially in the enhancement of soluble matters deposition have been rarely addressed. In this study, a quartz crystal microbalance with dissipation monitoring (QCM-D) was applied to investigate the influences of calcium ion and rhamnolipid (RL) on the deposition of soluble matters from real and synthetic industrial wastewaters with different configurations of organics (bovine serum albumin and sodium alginate) and ionic strength on the model biocarriers polystyrene and polyamide. Results showed that deposition was effectively promoted by the addition of Ca2+ and along with the increase in Ca2+ content. However, RL enhanced the deposition effectively only in hyperhaline wastewater through breaking hydration repulsion and decreased the deposition in low-salinity wastewater, and its influence to the deposited layer property exhibited characteristics of negative feedback. The combined use of Ca2+ and RL had a better enhancement effect than that of separate use and the mechanism involved can not be soundly explained only by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The strategy of mediating the deposition of soluble matters on different biocarriers by adding Ca2+ and RL has important implications for regulating biofilm formation to accelerate the start-up process in attached-growth bioreactors.

Determination of thorium (IV) using isophthalaldehyde-tetrapyrrole as probe by resonance light scattering, second-order scattering and frequency-doubling scattering spectra.

The coordination reaction of thorium (IV) with a ditopic bidentate ligand to form supramolecular polymer was studied by resonance light scattering (RLS) spectra, second-order scattering (SOS) spectra and frequency-doubling scattering (FDS) spectra, respectively. The ditopic bidentate ligand is isophthalaldehyde-tetrapyrrole (IPTP). It was synthesized through a condensation reaction of isophthalaldehyde with pyrrole. The formation of supramolecular polymer results in remarkable intensity enhancements of the three light scattering signals. The maximum scattering wavelengths of RLS, FDS and SOS were 290, 568 and 340nm, respectively. The reaction was used to establish new light scattering methods for the determination of thorium (IV) by using IPTP as probe. Under optimum conditions, the intensity enhancements of RLS, SOS and FDS were directly proportional to the concentration of thorium (IV) in the ranges of 0.01 to 1.2µgmL-1, 0.05 to 1.2µgmL-1 and 0.05 to 1.2µgmL-1, respectively. The detection limits were 0.003µgmL-1, 0.012µgmL-1 and 0.021µgmL-1, respectively. The methods were suitable for analyzing thorium (IV) in actual samples. The results show acceptable recoveries and precision compared with a reference method.