Effect of operational strategies on activated sludge's acclimation to phenol, subsequent aerobic granulation, and accumulation of polyhydoxyalkanoates

The potential effects of N-Acyl homoserine lactones on aerobic sludge granulation during phenolic wastewater treatment

The formation of aerobic granular sludge (AGS) is relatively difficult during the treatment of refractory wastewater, which generally shows small granular sizes and poor stability. The formation of AGS is regulated by N-Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS). However, the potential role of AHLs in AGS formation under the toxic stress of refractory pollutants and the heterogeneity in the distribution and function of AHLs across different aggregates are not well understood. This study investigated the potential effects of AHLs on the formation of AGS during phenolic wastewater treatment. The distribution and succession of AHLs across varying granular sizes and development stages of AGS were investigated. Results showed that AGS was successfully formed in 13 days with an average granular size of 335 ± 39 μm and phenol removal efficiency of >99%. The levels of AHLs initially increased and then decreased. C4-HSL and 3-oxo-C10-HSL were enriched in large granules, suggesting they may play a pivotal role in regulating the concentration and composition of extracellular polymeric substances (EPS). The content of EPS constantly increased to 149.4 mg/gVSS, and protein (PN) was enriched in small and large granules. Luteococcus was the dominant genus constituting up to 62% after the granulation process, and exhibited a strong association with C4-HSL. AHLs might also regulate the bacterial community responsible for EPS production, and pollutant removal, and facilitate the proliferation of slow-growing microorganisms, thereby enhancing the formation of AGS. The synthesis and dynamics of AHLs were mainly governed by AHLs-producing bacterial strains of Rhodobacter and Pseudomonas, and AHLs-quenching strains of Flavobacterium and Comamonas. C4-HSL and 3-oxo-C10-HSL might be the major contributors to promoting sludge granulation under phenol stress and play critical roles in large granules. These findings enhance our understanding of the roles that AHLs play in sludge granulation under toxic conditions.

Recovery of polyhydroxyalkanoates (PHAs) polymers from a mixed microbial culture through combined ultrasonic disruption and alkaline digestion

PHAs are a form of cellular storage polymers with diverse structural and material properties, and their biodegradable and renewable nature makes them a potential green alternative to fossil fuel-based plastics. PHAs are obtained through extraction via various mechanical, physical and chemical processes after their intracellular synthesis. Most studies have until now focused on pure cultures, while information on mixed microbial cultures (MMC) remains limited. In this study, ultrasonic (US) disruption and alkaline digestion by NaOH were applied individually and in combination to obtain PHAs products from an acclimated MMC using phenol as the carbon source. Various parameters were tested, including ultrasonic sound energy density, NaOH concentration, treatment time and temperature, and biomass density. US alone caused limited cell lysis and resulted in high energy consumption and low efficiency. NaOH of 0.05-0.2 M was more efficient in cell disruption, but led to PHAs degradation under elevated temperature and prolonged treatment. Combining US and NaOH significantly improved the overall process efficiency, which could reduce energy consumption by 2/3rds with only minimal PHAs degradation. The most significant factor was identified to be NaOH dosage and treatment time, with US sound energy density playing a minor role. Under the semi-optimized condition (0.2 M NaOH, 1300 W L^-1, 10 min), over 70% recovery and 80% purity were achieved from a 3 g L^-1 MMC slurry of approximately 50% PHAs fraction. The material and thermal properties of the products were analyzed, and the polymers obtained from US + NaOH treatments showed comparable or higher molecular weight to previously reported results. The products also exhibited good thermal stability and rheological properties, compared to the commercial standard. In conclusion, the combined US and NaOH method has the potential in real application as an efficient process to obtain high quality PHAs from MMC, and cost-effectiveness can be further optimized.

Production and recovery of polyhydroxyalkanoates (PHA) from waste streams - A review

Polyhydroxyalkanoates (PHA) are the more attractive sustainable green plastic, and it has the potential to replace petroleum-based plastics (PBP) in the global market. Recently, most of the developed and developing countries have banned the use of traditional PBP. This increases the demand for green plastic production and positively impacts the global market. Producing green plastic from various waste streams such as whey, animal, and crude glycerol will be eco-friendly and cost-effective. However, the factors influencing the environmental sustainability of PHA production from different waste streams are still unclear. This review could be reinforced concrete to researchers to gather deep knowledge on techno-economic analysis, life-cycle assessment, environmental and ecological risks caused during PHA production from different waste streams.

Aerobic post-treatment of effluent from anaerobic reactors fed with residues from 1G and 2G sugarcane biorefineries

This study aimed to evaluate an activated sludge system as a post-treatment step of anaerobic effluents from the co-digestion of sugarcane vinasse and hemicelluloses hydrolysate. The system consisted, initially, of a two-stage anaerobic system followed by a continuously fed activated sludge, all in bench scale. After adaptation of aerobic microorganisms to effluent conditions, the anaerobic digestion was conducted in a single-stage anaerobic reactor, increasing the influent organic loading rate (OLR) of activated sludge from 0.73 to an average of 2.36 gCOD/L·day. Under optimal conditions (12-h hydraulic retention time [HRT]), a 62 ± 9% efficiency was observed on the aerobic post-treatment, resulting in effluent chemical oxygen demand (COD) of 414.3 ± 95 mg/L. Overall efficiency of the combined system (anaerobic + aerobic) averaged 88 ± 3%. Influent and effluent characteristics were then analyzed by Folin-Ciocalteau method, UV-Vis spectrophotometry, and gas chromatography-mass spectrometry (GC-MS) for identification of potentially toxic and recalcitrant compounds. Compounds that absorb light within the visible spectra were well removed by the combined treatment system. Most compounds identified by GC-MS in the influent were completely removed by aerobic microorganisms. Saturated fatty acids such as adipic acid, hexadecanoic acid, and octadecanoic acid were observed in the final effluent, as well as other potentially toxic compounds such as stigmasterol, di-isobutyl phthalate, and benzene. Activated sludge proved to be an efficient post-treatment for anaerobic co-digestion, able to cope with changes of anaerobic effluent quality and providing a final effluent of stable organic load. However, phenol removal was not efficient and further studies could be performed to optimize its degradation. PRACTITIONER POINTS: Conventional activated sludge with a 12-h HRT was capable of handling significant OLR variation, providing a final effluent with lower and stable COD concentration. Glucose addition for carbon supplementation was necessary during the start-up of activated sludge. Compounds that absorb light within the visible spectra were mostly removed by the combined (anaerobic-aerobic) treatment system. Most potentially toxic compounds were well removed in the post-treatment system. Saturated fatty acids, VFA, phenols, and low molecular weight aromatic compounds remained in the final effluent.

Shifts in structure and function of bacterial community in river and fish pond sediments after a phenol spill

Phenol is widely used in industrial processes and has microbial toxicity. However, the effects of a phenol spill on the microbial community are not clear. The present study explored the changes of bacterial communities in river and fish pond sediments after a phenol spill. The bacterial richness and diversity in river sediments were lower on day 30 (36 days after the spill) than on day 0, while they increased in fish pond sediments. The structures and functions of bacterial communities in both river and fish pond sediments were changed, and a more dramatical variation was detected in fish pond sediments. In river sediments, Proteobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Nitrospirae were the major bacterial phyla, and Chloroflexi was enriched. In fish pond sediments, genera Brevibacillus dominated bacterial communities initially, and bacterial composition showed a dramatic change on day 30. Most predicted metabolism functions, as well as genetic information processing functions of translation, replication, and repair, were enhanced in both river and fish pond sediments, while they showed an opposite change trend for xenobiotic degradation function. This work could strengthen our understanding of the effects of phenol spills on sediment bacterial communities in both lotic and lentic ecosystems.

The metabolic potential of plastics as biotechnological carbon sources - Review and targets for the future

The plastic crisis requires drastic measures, especially for the plastics' end-of-life. Mixed plastic fractions are currently difficult to recycle, but microbial metabolism might open new pathways. With new technologies for degradation of plastics to oligo- and monomers, these carbon sources can be used in biotechnology for the upcycling of plastic waste to valuable products, such as bioplastics and biosurfactants. We briefly summarize well-known monomer degradation pathways and computed their theoretical yields for industrially interesting products. With this information in hand, we calculated replacement scenarios of existing fossil-based synthesis routes for the same products. Thereby, we highlight fossil-based products for which plastic monomers might be attractive alternative carbon sources. Notably, not the highest yield of product on substrate of the biochemical route, but rather the (in-)efficiency of the petrochemical routes (i.e., carbon, energy use) determines the potential of biochemical plastic upcycling. Our results might serve as a guide for future metabolic engineering efforts towards a sustainable plastic economy.

Resource recovery in aerobic granular sludge systems: is it feasible or still a long way to go?

Lately, wastewater treatment plants are much often being designed as wastewater-resource factories inserted in circular cities. Among biological treatment technologies, aerobic granular sludge (AGS), considered an evolution of activated sludge (AS), has received great attention regarding its resource recovery potential. This review presents the state-of-the-art concerning the influence of operational parameters on the recovery of alginate-like exopolysaccharides (ALE), tryptophan, phosphorus, and polyhydroxyalkanoates (PHA) from AGS systems. The carbon to nitrogen ratio was identified as a parameter that plays an important role for the optimal production of ALE, tryptophan, and PHA. The sludge retention time effect is more pronounced for the production of ALE and tryptophan. Additionally, salinity levels in the bioreactors can potentially be manipulated to increase ALE and phosphorus yields simultaneously. Some existing knowledge gaps in the scientific literature concerning the recovery of these resources from AGS were also identified. Regarding industrial applications, tryptophan has the longest way to go. On the other hand, ALE production/recovery could be considered the most mature process if we take into account that existing alternatives for phosphorus and PHA production/recovery are optimized for activated sludge rather than granular sludge. Consequently, to maintain the same effectiveness, these processes likely could not be applied to AGS without undergoing some modification. Therefore, investigating to what extent these adaptations are necessary and designing alternatives is essential.

Rapid cultivation of the aerobic granules for simultaneous phenol degradation and ammonium oxidation in a sequencing batch reactor

The rapid cultivation strategy of aerobic granular sludge (AGS) for simultaneous phenol degradation and ammonium oxidation was studied in a sequence batch reactor (SBR). The short-term inhibitory kinetics of phenol was studied through batch experiments. For the sodium acetate fed AGS, the phenol inhibition constants (Ki) of specific oxygen utilization rate by heterotrophic bacteria (SOUR_h) was 508.6 mg/L. The Ki of specific ammonium utilization rate (SAUR) was 232.3 mg/L. After 28 days' acclimatization, the phenol and NH₄⁺-N removal rates of the SBR reached 94.0% and 96.4% when the influent phenol and NH₄⁺-N concentrations were 1000 and 33.5 mg/L, respectively. The phenol removal loading rate was 1.69 kg/(m³·d). For the mature phenol&ammonium degrading AGS, the polysaccharide (PS) and protein (PN) concentrations were 247.4 ± 10.3 and 68.6 ± 6.5 mg/g VSS, respectively. The functional groups analysis showed that the amount of OH, NH, CO and CC groups remained unchanged in the mature phenol&ammonium degrading AGS.

Aerobic degradation of 4-fluoroaniline and 2,4-difluoroaniline: performance and microbial community in response to the inocula

In this study, a distinct inoculum was investigated as an isolated variable within sequencing batch reactors via a comparison of the 4-fluoroaniline (4-FA) or 2,4-difluoroaniline (2,4-DFA) removal amounts. The inocula were derived from a treatment plant for treating pharmaceutical wastewater plus a small amount of municipal sewage (PMS), a treatment plant for treating fluoridated hydrocarbon wastewater (FHS), and a treatment plant for treating the comprehensive wastewater in an industrial park (CIS). There were slight differences among the degradation patterns of the 4-FA for the three inocula, whether during the enrichment period or the high concentration shock period. In contrast, it was observed that the degradation efficiency of 2,4-DFA initially varied with the inocula. The FHS-derived inoculum was determined to be optimal, exhibiting the earliest degradation reaction only after an acclimation of 7 days had the highest degradation rate constant of 0.519 h^-1, and had the fastest recovery time of three weeks after high concentration shock. Additionally, compared with the PMS-derived inoculum, the CIS-derived inoculum exhibited an earlier degradation reaction within three weeks, and a higher microbial diversity, but a lower shock resistance and degradation rate constant of 0.257 h^-1. High-throughput sequencing demonstrated that each final consortium was different in composition, and the microbial consortia developed well on the inoculum and substrate. In comparison of the similarity among the three 2,4-DFA enrichment cultures, the higher similarity (63.9-70.0%) among three final consortia enriching with 4-FA was observed. The results indicated that the inoculum played an important role in the degradation of FAs and the microbial bacterial communities of final consortia, and the effect extent might well depend on the fluorinated level of FAs.

Biodegradation performance and biofouling control of a halophilic biocarriers-MBR in saline pharmaceutical (ampicillin-containing) wastewater treatment

This work develops a halophilic biocarriers-MBR for saline pharmaceutical wastewater treatment. The system has effectively treated the ampicillin-containing saline wastewater for 32 days, when the ampicillin concentration is lower than 20 mg/L. The system can tolerate the saline organic wastewater with a reasonable biodegradability (removals of COD over 75%) when the ampicillin concentration is 50 mg/L. The system has a bad performance in biodegradation (COD removals around 60-70%) and fouled within 16 days at a high ampicillin concentration of 100 mg/L. At high transmembrane pressures over 30 KPa, some ampicillin molecules may permeate through the membrane causing decreases in the ampicillin removal. The concentrations of protein and carbohydrate in EPS and SMP have increased over time and with increasing the ampicillin concentration. The method of biofouling control in MBR for the ampicillin situations has been proposed based on monitoring the concentrations of EPS and SMP. The drying-assisted monitoring of membrane biofoulants has showed a better efficiency than the monitoring of transmembrane pressure for membrane anti-biofouling in the treatment of pharmaceutical saline wastewaters where a spectroscopic detection can be hardly applied. This work may benefit relative research works for the control of biodegradation performance and membrane biofouling to better treat saline pharmaceutical wastewaters.

Impact of high phenol loading on aerobic granules from two different kinds of industrial sludge along with thiocyanate and ammonium

Two sequencing batch reactors inoculated with two different kinds of industrial sludge; refinery sludge (R1) and brewery sludge (R2), were operated to observe the impact of high phenol loading (5.71 kg COD m^-3 day^-1) along with 100 mg L^-1 of ammonia-nitrogen and thiocyanate on the granular stability and performance. R2 granules were stable and degraded all the pollutants up to an organic loading of 5.71 kg COD m^-3 day^-1 with the large size and high extracellular polymeric substances of 2769.94 ± 62.26 µm and 114.83 ± 1.33 mg gVSS^-1, respectively, whereas R1 granules disintegrated at an organic loading of more than 3.32 kg COD m^-3 day^-1. At higher phenol loading, granular biomass activity was 3.43 and 16.35 mg COD removed mgVSS^-1 day^-1 in R1 and R2, respectively, from the initial sludge activities of 8.01 (refinery sludge) and 6.56 (brewery sludge) mg COD removed mgVSS^-1 day^-1.

Recent developments in Polyhydroxyalkanoates (PHAs) production - A review

Polyhydroxyalkanoates (PHAs) are inevitably a key biopolymer that has the potential to replace the conventional petrochemical based plastics that pose jeopardy to the environment globally. Even then the reach of PHA in the common market is so restricted. The economy of PHA is such that, even after several attempts the overall production cost seems to be high and this very factor surpasses PHAs usage when compared to the conventional polymers. The major focus of the review relies on the synthesis of PHA from Mixed Microbial Cultures (MMCs), through a 3-stage process most probably utilizing feedstocks from waste streams or models that mimic them. Emphasis was given to the works carried out in the past decade and their coherence with each and every individual criteria (Aeration, Substrate and bioprocess parameters) such that to understand their effect in enhancing the overall production of PHA.

Response and recovery of aerobic granular sludge to pH shock for simultaneous removal of aniline and nitrogen

Considering the pH fluctuation in industrial wastewater, the response and resilience to pH shock should be investigated during aerobic granular sludge (AGS) system operation. In this work, three AGS reactors, namely R1, R2, and R3 for simultaneous removal of aniline and nitrogen were exposed to neutral, acidic, and alkaline conditions, respectively. The removal efficiency of aniline and chemical oxygen demand with pH variation was over 99.9% and 91.0%, respectively after stable in the three reactors. The aniline removal rate modestly decreased in R2 and R3 after pH varied and denitrification was slightly improved in acidic environment with average removal efficiency of 61.2%. The mature AGS could maintain settleability in R1 and R2 with 30 min sludge volume index below 35 mL g^-1 but was unstable under alkaline condition. Correspondingly, the secretion of extracellular polymeric substances especially protein decreased notably in R3. The bacterial groups varied with pH shock, but some could recover after adjustment to original pH value. Proteobacteria was the predominant phylum in the three reactors and Bacteroidetes was enriched in alkaline conditions. In addition, the main functional genera such as Achromobacter, Defluviimonas, Enterobacter, Pseudomonas, and Pseudoxanthomonas, were detected in the system and were found to be responsible for reduction of aniline and nitrogen.

Investigation of rapid granulation in SBRs treating aniline-rich wastewater with different aniline loading rates

In this work, aerobic granules were cultivated in two reactors which were denoted as R_L and R_H under 0.6 and 1.8 kg m^-3 d^-1 of aniline loading rates, respectively. The aerobic granular sludge (AGS) in the two sequential batch reactors for treating aniline-rich wastewater was compared. The results showed that the AGS could be rapidly formed with sludge volume index below 30 mL g^-1. The AGS in R_L had more filamentous bacteria than that in R_H by microstructural observations while the secretion of protein in extracellular polymeric substances was improved in R_H and in turn increased relative hydrophobicity of AGS. Within 4-h cycle, the excellent removal of aniline and chemical oxygen demand (COD) were achieved in the two reactors. The removal efficiencies of aniline and COD were consistently over 99.7%, 89.6%, respectively in R_L and 98.6%, 86.6%, respectively in R_H. As for nitrogen removal, NH₄⁺-N released from aniline biodegradation could also be reduced efficiently via nitrification and no nitrite accumulation occurred in both the reactors. Total nitrogen removal performance in R_H was better, due to a more compact structure of AGS. The investigation of microbial community succession by pyrosequencing showed that the diversity of microorganisms decreased when AGS was developed. Proteobacteria especially Gammaproteobacteria significantly increased during aerobic granulation in both reactors. It was also found that the relative abundance of Actinobacteria was higher in R_H than that in R_L. Furthermore, the strains responsible for aniline biodegradation, nitrification, denitrification, and phosphorous accumulation were detected in the systems.

Polyhydroxyalkanoates (PHA) production from phenol in an acclimated consortium: Batch study and impacts of operational conditions

Microbial intracellular biopolymer PHA was synthesized from toxic pollutant phenol by an acclimated consortium. Various operational conditions were experimented for their effects on biomass growth and PHA accumulation. Carbon to nitrogen ratios from 5 to 40 (w/w) showed little impact, as did the levels of Fe, Ca and Mg in a short term. Acidic pH inhibited both growth and PHA synthesis, and an optimal dissolved oxygen level of 1-4 mg L^-1 was identified. Low temperature (7 °C) significantly slowed but did not totally repress microbial activities. A 2% NaCl shock retarded reactions and 4% NaCl caused irreversible damage. Various initial phenol (S0) and biomass concentrations (X0) were combined to study the effect of food to microbe (F/M) ratio. High S0 and F/M exerted toxicity, reducing reaction rates but generating higher ultimate PHA wt% in biomass. Increasing X0 alleviated phenol inhibition and improved productivity and carbon conversion from phenol. A pseudo-optimized F/M ratio of 0.2-0.4 and a maximum PHA% rate of 1.15% min^-1 were identified under medium S0/high X0. This study is the first to systematically investigate the feasibility of toxic industrial waste as the carbon source for PHA production, and likely the only one indicating potential for scaling-up and industrialization.

Aerobic granular sludge technology: Mechanisms of granulation and biotechnological applications

Aerobic granular sludge (AGS) is a novel microbial community which allows simultaneous removal of carbon, nitrogen, phosphorus and other pollutants in a single sludge system. AGS is distinct from activated sludge in physical, chemical and microbiological properties and offers compact and cost-effective treatment for removing oxidized and reduced contaminants from wastewater. AGS sequencing batch reactors have shown their utility in the treatment of abattoir, live-stock, rubber, landfill leachate, dairy, brewery, textile and other effluents. AGS is extensively researched for wide-spread implementation in sewage treatment plants. However, formation of AGS takes relatively much longer time while treating low-strength wastewaters like sewage. Strategies like increased volumetric flow by means of short cycles and mixing of sewage with industrial wastewaters can promote AGS formation while treating low-strength sewage. This article reviewed the state of research on AGS formation mechanisms, bioremediation capabilities and biotechnological applications of AGS technology in domestic and industrial wastewater treatment.

Enhancement of lipase activity for the oily wastewater treatment by an electrostimulation process

The efficacy of electrostimulation on bacterial lipase activity and COD removal was studied using a laboratory bioelectrochemical system.