Research
Biofilms are known to make you sick!!! They are harmful and can form virtually in every imaginable environment on Earth. However, they have been promoting themselves to be beneficial too. The way they help us is the limit we set. So, I explore the latent potential of biofilms in granular forms (aerobic granules), mainly for N & P pathways involving granulation, and microbe- metal interactions having implications for freshwater and seawater-based wastewater treatment.
"I explore the potential of a fun-sized microbial world"
Part I: Latent potential of Aerobic Granular Sludge (AGS)
Microbial granules: yet to explore its full potential...
(I) Nitrogen and phosphorus
- Settleability of activated sludge (AS) was increased by activated carbon (AC) particles.
- Washout of AS inoculum was effectively minimized during start-up in granular SBRs.
- Nitrogen and phosphorus removals were in SBRs using acetate or acetate-propionate.
- AC particles decreased start-up periods for achieving efficient total nitrogen removal.
- P removal was 2-fold higher via EBPR pathway in SBRs augmented with AC particles.
- GAC addition promoted formation of biofilms and aerobic granular sludge (AGS).
- Segregation of PAOs in biofilms and AGS in GAC augmented SBR
- Higher abundance of PAOs in large (>0.5 mm) biomass size fraction
- Preferential enrichment of PAOs observed in biofilms than in the co-existing AGS.
- PAOs enrichment led to rapid establishment of EBPR in the presence of GAC particles.
- Removal of 4000 mg l−1 NH4+-N was achieved using AGS process.
- Functional and structural stability of AGS was maintained at low COD/N ratios.
- Bacterial diversity decreased at higher influent ammonium concentrations.
- Nitrite oxidizing bacteria washed out at higher NH4+-N and lower COD/N ratios.
- Nitritation-anammox was the major nitrogen removal pathway.
(II) Treatment of real wastewater
- GAC enhanced aerobic granulation in pilot-scale bioreactors treating real sewage.
- Efficient biological nitrogen and phosphorus removals in tropical climate (T ≈ 30 °C)
- Nitrogen removed via nitritation-denitritation due to nitrite oxidizing bacteria.
- GAC enriched polyphosphate accumulating organisms for enhanced bio-P removal.
- First report on pilot-scale granular SBR and GAC addition for sewage treatment
- De novo granulation of sewage-borne microorganisms for aerobic granular sludge (AGS) formation and nutrient removal.
- Novel activated sludge inoculum-independent method for AGS cultivation and sewage treatment.
- Granular activated carbon (GAC) enhanced de novo granulation of sewage-borne microbes.
- GAC addition biological nitrogen removal via nitritation-denitritation pathway.
- Higher enrichment of PAOs and EBPR in GAC-augmented AGS SBR.
The sludge was dominated by smaller granules at 15-20°C as compared to 30°C.
Granular stability was not impacted by short-term changes in temperature from 15 to 30°C.
N and P removals were impacted by sudden decrease in T from 30° to 15°C.
Effective N and P removals were maintained by decreasing T from 30° to 15°C in 5°C steps.
N and P were removed by partial nitrification and EBPR pathways at T ranging from 15 to 30℃.
- Sewage treatment by CAS, activated sludge SBR and aerobic granular sludge (AGS) SBR were compared.
- Biopolymer extraction reduced biosolids content of AGS by 54%
- Biopolymer of activated sludge from SBR formed hydrogel beads but not from CAS.
- Biopolymer of AGS was bestowed with superior gel-forming ability due to high GG blocks.
- Biopolymer extraction form AGS improves resource recovery and sustainability of WWTPs.
Aerobic granular sludge (AGS) was formed within 50 days during sewage treatment
AGS outperformed with 99% phosphorus removal as against 57% by activated sludge
High abundance of PAOs and enhanced bio-P removal in tropical climate (T=30°C)
AGS showed resilience to oxytetracyline (OTC) and maintained high nutrient removals
Nitrogen and phosphorus removals have dropped to 78% and 16%, respectively, with flocs
(III) Metal(loid) (Selenium/Tellurium) bioreduction, biomineralisation
- Simultaneous and efficient reduction of SeIV and SeVI by aerobic granular sludge.
- SeVI reduction rate was enhanced by pre-exposure of biomass to SeIV.
- Ammonium removal via nitriation-denitriation pathway at different Se-loadings.
- First report on sustained selenite reduction by aerobic granular sludge.
- Simultaneous COD, nitrogen and selenite removal by aerobic granular sludge.
- Efficient selenite bioreduction and better entrapment of Se (0) in AGS.
- Selenite reduction by AGS was associated with lower colloidal Se (0) in liquid.
- Ammonium was mainly removed through nitrogen removal via the nitrite pathway.
- Selenite reduction and Bio-Se0 retention were dependent on size of aerobic granules.
- Large sized aerobic granules showed efficient selenite reduction and Bio-Se0 entrapment.
- Microbacterium azadirachtae isolated from granules exhibited efficient selenite reduction.
- M. azadirachtae cells immobilized in alginate beads exhibited selenite reduction and Bio-Se0 entrapment.
- Ammonium was mainly removed through nitrogen removal via the nitrite pathway.
- Efficient bioreduction of SeIV and TeIV oxyanions by aerobic granular sludge (AGS).
- First report on bioreduction of tellurite using AGS sequencing batch reactor.
- Biogenic Se and Te were majorly associated with the AGS.
- Ammonium removal via nitritation-denitritation was not impacted by toxic metalloids.
- Bio-P removal was higher at 73% in the AGS bioreactor fed with SeIV and TeIV.
- Complete, sustained and lactate-dependent conversion of up to 175 mg/L TeIV to Te0
- Biogenic Te0 nanostructures were associated with aerobic granular sludge
- Partial inhibition of ammonium removal and lower abundance of AOB by TeIV
- Efficient nitrogen removal via nitritation-denitritation at different initial TeIV loadings
- Higher P-removal in TeIV-fed reactor due to hydroxyapatite precipitation
(IV) Recalcitrant compounds and their biomineralisation
- Aerobic granules had compact and stable microbial structure at low DO ≤ 2 mg L−1.
- Simultaneous removal of COD, ammonium and azo dye by aerobic granular sludge.
- Ammonium was removed mainly through ammonium removal via nitrite pathway.
- Azo dye biodecolourization by aerobic granules under microaerophilic conditions.
- Azo dye decolourizing and nitrifying (Nitrospirae) bacteria were detected.
- Aerobic granules cultivated by feeding acetate plus 2,4-dinitrotoluene for the first time.
- 2,4-dinitrotoluene was rapidly removed when fed along with acetate or lactate.
- 2-amino-4-nitrotoluene was formed in minor amounts during 2,4-DNT removal.
- Aerobic granules removed 2,4-DNT by both oxidative and reductive pathways.
- Nutrient removal by aerobic granules was not impacted by 10 mg L−1 2,4-DNT.
Aerobic granular sludge exhibited 35% higher oxytetracycline removal than activated sludge.
Oxytetracycline (OTC) removal was sustained by biotransformation and required carbon source.
AOB and PAOs abundance was decreased upon exposure to oxytetracycline
Nitrogen and phosphorus removals were >99% and 70%, respectively, in OTC fed SBR.
Micrococcus luteus grew as aggregates and exhibited OTC biotransformation potential.
Part II: Saline & Hypersaline waters: Strategy, performance, outlook
Biological treatment of saline wastewater is a herculean task. Be it salt inhibition, nutrients limitation/ overdose,.. Currently used activated sludge or AGS technology entails longer acclimation to develop halotolerant microbiome. However, several studies have reported severe loss of function or no function at all. Hence, a novel approach towards the issue is to use the halophilic microbiome instead of halotolerant microbiome. For this, we have used planktonic autochthonous (indigenous/native) community of seawater for developing halophilic aerobic granular sludge. And the results are super fascinating: rapid granulation engineering , effective biological nitrogen and phosphorus removal not just at saline (3.4% salt) but also at 12% salt conditions (that is 3.4 times saltier than seawater).
This demonstrates that, "we can engineer this system for an effective and sustainable saline and hypersaline wastewater treatment"
(I) Granulation of autochthonous seawater microbiome to halophilic aerobic granular sludge (hAGS)*
- Granulation of seawater microbes for saline wastewater treatment
- Development of granular sludge directly from microbes present in the seawater
- Simultaneous C, N & P removal under saline conditions
- Effective biological nitrogen and phosphorus removal by saline granular sludge
- Granules had lower species richness than seawater bacterial community
- hAGS was cultivated from autochthonous seawater-born microbes.
- Biological N and P removals were unaffected at 3.4 to 12% salt concentrations.
- Efficient NH4+-N removal via nitritation-denitritation pathway at 3.4 to 12% salt.
- Effective bio-P removal via EBPR pathway at 3.4 to 12% salt concentrations.
- Stappia was the dominant genus in halophilic aerobic granular sludge at 12% salt.
(II) halophilic micro-algae colonised AGS*
- First report of cultivation under saline conditions
- Use of autochthonous biofilm enabled rapid cultivation of halophilic AGS
- Effective total nitrogen and phosphorus removal by hAGS
- P was removed via enhanced biological phosphorus removal mechanism.
- Nutrient removal was rapidly established using autochthonous microbes.