Bacterial community and filamentous population of industrial wastewater treatment plants in Belgium.

The discharge of industrial water requires the removal of its pollutants, where biological wastewater treatment plants (WWTPs) are the most used systems. Biological WWTPs make use of activated sludge (AS), where bacteria are responsible for the removal of pollutants. However, our knowledge of the microbial communities of industrial plants is limited. Understanding the microbial population is essential to provide solutions to industrial problems such as bulking. The aim of this study was to identify at a high taxonomic resolution the bacterial population of 29 industrial WWTPs using 16S rRNA amplicon sequencing. Our results revealed that the main functional groups were dominated by Thauera and Zoogloea within denitrifiers, Dechloromonas in phosphate-accumulating organisms, and Defluviicoccus in glycogen-accumulating organisms. The activated sludge characterization indicated that 59% of the industrial plants suffered from bulking sludge, with DSVI values of up to 448 mL g-1. From the bulking cases, 72% corresponded to filamentous bulking with Thiothrix as the most abundant filament; meanwhile, the other 28% corresponded to viscous bulking sludge in which Zoogloea was the most abundant genus. Furthermore, the bacterial population did not share a core of taxa across all industrial plants. However, 20 genera were present in at least 50% of the plants comprising the general core, including Thauera, Ca. Competibacter, and several undescribed microorganisms. Moreover, statistical analysis revealed that wastewater salinity strongly affected the microbial richness of the industrial plants. The bacterial population across industrial plants differed considerably from each other, resulting in unique microbial communities that are attributed to the specificity of their wastewaters. KEY POINTS: • The general core taxa of industrial plants were mostly made up of undescribed bacterial genera. • Filamentous bacteria constituted on average 4.1% read abundance of the industrial WWTPs. • Viscous bulking remains a significant type of bulking within industrial WWTPs.

Is building up substrate during anaerobic feeding necessary for granulation?

For a successful granulation process in activated sludge systems, the stimulation of slow growing organisms such as glycogen accumulating microorganisms (GAOs) is a key factor. Here we show that the introduction of an anaerobic feast followed by an aerobic famine phase successfully transforms bulking sludge, caused by the abundance of genus Kouleothrix, to a hybrid floccular-granular sludge. Two sequencing batch reactors (SBRs) were operated for 228 days treating the same industrial wastewater derived from the cleaning of trucks transporting liquid food (the cargo consists of approximately 70% chocolate and 30% beer). By respectively applying a fast and slow feeding in two parallel SBRs, different degrees of substrate build-up were achieved in the two reactors during the feast phase. The F/M ratio over the feeding time was 1.41 ± 0.48 and 0.57 ± 0.16 kg COD·(kg VSS*d)-1 for the fast-fed and the slow-fed SBR respectively. Our results demonstrate that substrate build-up during the anaerobic selection step is not necessary to obtain well-settling granular-like sludge.

Nitrous oxide formation during simultaneous phosphorus and nitrogen removal in aerobic granular sludge treating different carbon substrates.

The impact of different substrates on N2O dynamics and gene expression of marker enzymes (nirS, nirK and nosZ) involved in denitrifying enhanced biological phosphorus removal (d-EBPR) was investigated. Aerobic granular sludge fed with VFAs led to an anoxic P-uptake (27.7 ± 1.2 mg PO43--P.gVSS-1) and N2O emissions up to 80.7 ± 3.4% N2O-N. A decisive role of Accumulibacter in N2O formation was observed. Dosage of amino acids (12.0 ± 1.2 mg PO43--P.gVSS-1) and glucose (1.5 ± 0.9 mg PO43--P.gVSS-1) as sole substrate did not support d-EBPR activity. Presence of NO2- resulted in higher N2O formation in comparison to nitrate and a nosZ/(nirS + nirK) ratio lower than 0.3. A linear correlation (R2 > 0.95) between the nosZ/(nirS + nirK) ratio and the N2O reductase rate was found only when dosing the same type of substrate. This suggests an interplay between the microbial community composition and different polyhydroxyalkanoates derivatives, when dosing different substrates.

A dynamically controlled anaerobic/aerobic granular sludge reactor efficiently treats brewery/bottling wastewater.

This study investigated the application of a dynamic control strategy in an aerobic granular sludge (AGS) reactor treating real variable brewery/bottling wastewater. For 482 days, the anaerobic and aerobic reaction steps in a lab-scale AGS system were controlled dynamically. A pH-based control was used for the anaerobic step, and an oxygen uptake rate (OUR) based control for the aerobic step. Additionally, the effect of an elongated aerobic step, and the effect of the removal of the suspended solids from the influent, on AGS formation were also investigated. In comparison to a static operation, the dynamic operation resulted in similar reactor performance, related to effluent quality and the anaerobic dissolved organic carbon (DOC) uptake efficiency, while the organic loading rate was significantly higher. The removal of suspended solids from the influent by chemical coagulation with FeCl3 turned hybrid floccular-granular sludge into fully granular sludge. The granulation coincided with a significant increase in the abundance of the glycogen-accumulating Candidatus Competibacter and an increase in the content of gel-forming EPS to respectively around 14% and 30%. In conclusion, this study showed the successful application of a dynamic control strategy based on common and low-cost sensors for AGS treatment of industrial wastewater.

Impact of the substrate composition on enhanced biological phosphorus removal during formation of aerobic granular sludge.

Performance of enhanced biological phosphorus removal (EBPR) is often investigated with simple synthetic wastewater containing volatile fatty acids (VFAs). In this study, various (fermentable) substrates, individually and in mixtures, were examined during the application of a granulation strategy. In addition, the microbial community and N2O formation were monitored. Sludge densification was observed in all systems. Stable EBPR, associated with the presence of Accumulibacter and an anaerobic P-release up to 21.9 mgPO43--P.gVSS-1, was only obtained when VFAs were present as sole substrate or in mixture. Systems fed with VFAs were strongly related to the formation of N2O (maximum of 6.25% relative to the total available nitrogen). A moderate anaerobic dissolved organic carbon (DOC) uptake was observed when amino acids (64.27 ± 3.08%) and glucose (75.39 ± 5.79%) as sole carbon source were applied. The substrate/species-specific enrichment of Burkholderiaceae and Saccharimonadaceae respectively, resulted in unstable EBPR in those systems.

Influence of mixed feeding rate in a conventional SBR on biological P-removal and granule stability while treating different industrial effluents.

In this study, the influence of the anaerobic mixed feeding rate on granule stability and reactor performance in a conventional sequencing batch reactor (C-SBR) was investigated while treating various industrial wastewaters. A laboratory-scale SBR fed with malting wastewater rich in phosphorus was operated for approximately 250 days, which was divided into two periods: (I) mixed pulse feed and (II) prolonged mixed feed. Initially, no bio-P activity was observed. However, by lowering the feeding rate biological P-removal was rapidly established and no effect on the aerobic granular sludge (AGS) characteristics was observed. Additionally, to investigate the effect of the mixed feeding rate when treating an industrial effluent with low phosphorus content, i.e. brewery wastewater, a laboratory-scale reactor was operated for approximately 400 days applying different mixed feeding rates. Morphological and molecular analysis indicated that a low substrate concentration promoted the enrichment of anaerobic carbon storing filaments when fed with brewery wastewater. Findings suggest that a prolonged mixed feeding regime can be used as a tool to easily establish bio-P removal in a C-SBR system for the treatment of phosphorus-rich wastewaters. It should however be considered that under P-limiting conditions, enrichment of poly-P storing filaments may occur, possibly due to their higher substrate affinity under anaerobic conditions.

Performance and stability of a dynamically controlled EBPR anaerobic/aerobic granular sludge reactor.

Treatment of rapidly varying wastewaters in anaerobic/aerobic aerobic granular sludge (AGS) systems remains problematic. This study investigated AGS formation and the impact of varying COD and phosphorus concentrations on an enhanced biological phosphorus removal (EBPR) AGS SBR with a conductivity based anaerobic and OUR based aerobic dynamically controlled step. Phase 1 investigated the development of AGS. Phase 2 examined the flexibility of the dynamic control strategy and AGS efficiency while rapidly altering the influent composition. AGS was formed successfully in phase 1: the DV50 increased to 285 µm, and the SVI5 and SVI30 decreased to 51 and 40 ml/g respectively. In phase 2 the effluent COD and PO4-P concentration remained low at respectively 58 ±â€¯27 mg/L and 0.53 ±â€¯0.77 mg/L. With an anaerobic DOC uptake efficiency of 98.4 ±â€¯0.9%.

Formation of aerobic granular sludge and the influence of the pH on sludge characteristics in a SBR fed with brewery/bottling plant wastewater.

A laboratory-scale sequencing batch reactor (SBR) was operated for 450 days to assess aerobic granule formation when treating brewery/bottling plant wastewater by consistent application of a feast/famine regime. The experiment was divided into three major periods according to the different operational conditions: (I) no pH control and strong fluctuations in organic loading rate (OLR) (1.18 ± 0.25 kgCOD·(m3·day)-1), (II) pH control and aeration control strategy to reduce OLR fluctuations (1.45 ± 0.65 kgCOD·(m3·day)-1) and (III) no pH control and stable OLR (1.42 ± 0.18 kgCOD·(m3·day)-1). Aerobic granule formation was successful after 80 days and maintained during the subsequent 380 days. The aerobic granular sludge was characterized by SVI5 and SVI30 values below 60 mL.g-1 and dominated by granular, dense structures. An oxygen uptake rate based aeration control strategy insured endogenous respiration at the end of the aerobic phase, resulting in stable SBR operation when the influent composition fluctuated. The quantitative polymerase chain reaction results show no significant enrichment of Accumulibacter or Competibacter during the granulation process. The 16S rRNA sequencing results indicate enrichment of other, possibly important species during aerobic granule formation while treating brewery wastewaters.

SBR treatment of tank truck cleaning wastewater: sludge characteristics, chemical and ecotoxicological effluent quality.

A lab-scale activated sludge sequencing batch reactor (SBR) was used to treat tank truck cleaning (TTC) wastewater with different operational strategies (identified as different stages). The first stage was an adaptation period for the seed sludge that originated from a continuous fed industrial plant treating TTC wastewater. The first stage was followed by a dynamic reactor operation based on the oxygen uptake rate (OUR). Thirdly, dynamic SBR control based on OUR treated a daily changing influent. Lastly, the reactor was operated with a gradually shortened fixed cycle. During operation, sludge settling evolved from nearly no settling to good settling sludge in 16 days. The sludge volume index improved from 200 to 70 mL gMLSS-1 in 16 days and remained stable during the whole reactor operation. The average soluble chemical oxygen demand (sCOD) removal varied from 87.0% to 91.3% in the different stages while significant differences in the food to mass ratio were observed, varying from 0.11 (stage I) to 0.37 kgCOD.(kgMLVSS day)-1 (stage III). Effluent toxicity measurements were performed with Aliivibrio fischeri, Daphnia magna and Pseudokirchneriella subcapitata. Low sensitivity of Aliivibrio was observed. A few samples were acutely toxic for Daphnia; 50% of the tested effluent samples showed an inhibition of 100% for Pseudokirchneriella.

Aeration control strategies to stimulate simultaneous nitrification-denitrification via nitrite during the formation of aerobic granular sludge.

In this study, a sequencing batch reactor (SBR), treating synthetic wastewater (COD/N = 5), was operated in two stages. During stage I, an aeration control strategy based on oxygen uptake rate (OUR) was applied, to accomplish nitrogen removal via nitrite >80%. In stage II, the development of aerobic granular sludge (AGS) was examined while two aeration control strategies (OUR and pH slope) maintained the nitrite pathway and optimized the simultaneous nitrification-denitrification (SND) performance. Stimulation of slow-growing organisms, (denitrifying) polyphosphate-accumulating organisms (D)PAO and (denitrifying) glycogen-accumulating organisms (D)GAO leads to full granulation (at day 200, SVI10 = 47.0 mL/g and SVI30 = 43.1 mL/g). The average biological nutrient removal efficiencies, for nitrogen and phosphorus, were 94.6 and 83.7%, respectively. Furthermore, the benefits of an increased dissolved oxygen concentration (1.0-2.0 mg O2/L) were shown as biomass concentrations increased with approximately 2 g/L, and specific ammonium removal rate and phosphorus uptake rate increased with 33 and 44%, respectively. It was shown that the combination of both aeration phase-length control strategies provided an innovative method to achieve SND via nitrite in AGS.

Formation of aerobic granular sludge during the treatment of petrochemical wastewater.

In this study, petrochemical wastewater from the port of Antwerp was used for the development of aerobic granular sludge. Two different reactor setups were used, (1) a completely aerated sequencing batch reactor (SBRae) with a feast/famine regime and (2) a sequencing batch reactor operated with an anaerobic feast/aerobic famine strategy (SBRan). The seed sludge showed poor settling characteristics with a sludge volume index (SVI) of 285mL.gMLSS-1 and a median particle size by volume of 86.0µm±1.9µm. In both reactors, granulation was reached after 30days with a SVI of 71mL.gMLSS-1 and median granule size of 264.7µm in SBRan and a SVI of 56mL.gMLSS-1 and median granule size of 307.4µm in SBRae. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal was similar in both reactors and above 95%. The anaerobic DOC uptake increased from 0.13% to 43.2% in 60days in SBRan.

The effect of the feeding pattern of complex industrial wastewater on activated sludge characteristics and the chemical and ecotoxicological effluent quality.

Research has demonstrated that the feeding pattern of synthetic wastewater plays an important role in sludge characteristics during biological wastewater treatment. Although considerable research has been devoted to synthetic wastewater, less attention has been paid to industrial wastewater. In this research, three different feeding strategies were applied during the treatment of tank truck cleaning (TTC) water. This industry produces highly variable wastewaters that are often loaded with hazardous chemicals, which makes them challenging to treat with activated sludge (AS). In this study, it is shown that the feeding pattern has a significant influence on the settling characteristics. Pulse feeding resulted in AS with a sludge volume index (SVI) of 68 ± 15 mL gMLSS-1. Slowly and continuously fed AS had to contend with unstable SVI values that fluctuated between 100 and 600 mL gMLSS-1. These fluctuations were clearly caused by the feeding solution. The obtained settling characteristics are being supported by the microscopic analysis, which revealed a clear floc structure for the pulse fed AS. Ecotoxicological effluent assessment with bacteria, Crustacea and algae identified algae as the most sensitive organism for all effluents from all different reactors. Variable algae growth inhibitions were measured between the different reactors. The chemical and ecotoxicological effluent quality was comparable between the reactors.

Performance of aerobic nitrite granules treating an anaerobic pre-treated wastewater originating from the potato industry.

In this study nitrogen removal via nitrite >80% was achieved after approximately 80days in a sequencing batch reactor (SBR) treating pre-treated industrial wastewater originating from the potato industry. Thereafter, SBR performance was investigated during the formation of aerobic nitrite granules (ANG). The first granules appeared after 26days leading to full granulation after 64days. ANG showed excellent settling properties, as the Sludge Volume Index (SVI) went down to 16mL/g and a SVI10/SVI30=1 was obtained. qPCR analysis showed that slow growing organisms, especially polyphosphate accumulating organisms (PAO) were stimulated by an anaerobic feeding strategy. The average nitrogen removal was 95.3% over the entire operational period, and it mainly followed the "nitrite-route". Moreover, with ANG also phosphorus removal efficiencies up to 65.7% could be achieved. However, it has to be mentioned that nitrous oxide was an important denitrification product, which implies some environmental concerns.