Post-treatment of high-rate activated sludge effluent via zeolite adsorption and recovery of ammonium-nitrogen as alternative fertilising products.

This study investigates the potential to connect nutrient flows between wastewater treatment and agriculture through a two-stage nitrogen (N) recovery system composed of high-rate activated sludge treatment in contact stabilisation mode (HRAS/CS) and column adsorption with zeolite. The HRAS/CS process removes organic matter and suspended solids in wastewater, leaving N behind in the effluent. The N was successfully recovered with the zeolite column under different scenarios, generating N and K-rich by-products. The regeneration effluent from the zeolite column with KCl contained 60-845 mg NH4+-N/L and 1.6-14.3 g K/L, having potential for use as fertigation water. The N-saturated zeolite contained 1.5-8.4 mg N/g and 14.3-19.3 mg K/g of the product fresh weight and low contaminant content, making it potentially eligible as various fertilising products. Adsorption can thus concentrate N from HRAS/CS effluent and produce by-products with potential agricultural value while meeting chemical oxygen demand and total nitrogen discharge standards.

Implementation of an anaerobic selector step for the densification of activated sludge treating high-salinity petrochemical wastewater.

Sludge bulking is a common challenge in industrial biological wastewater treatment. Leading to difficulties such as bad sludge settling and washout, which is a problem also encountered in the petrochemical industry. Anaerobic feeding strategies can be used to induce the growth of storage-capable organisms, such as glycogen-accumulating organisms (GAO), leading to denser sludge flocs and better settling. In this study, the implementation of an anaerobic feeding strategy was investigated for high-salinity petrochemical wastewater (±35 g salts·L-1), using a sequencing batch reactor. Influent, effluent and sludge characteristics were analyzed throughout the operational period, which can be divided into three stages: I (normal operation), II (increased influent volume) and III (longer anaerobic mixing). Good effluent quality was observed during all stages with effluent chemical oxygen demand (COD) < 100 mgO2·L-1 and removal efficiencies of 95%. After 140 days, the sludge volume index decreased below 100 mL·g-1 reaching the threshold of good settling sludge. Sludge morphology clearly improved, with dense sludge flocs and less filaments being present. A maximum anaerobic dissolved oxygen carbon (DOC) uptake was achieved on day 80 with 74% during stage III. 16S rRNA amplicon sequencing showed the presence of GAOs, with increasing relative read abundance over time from 1 to 3.5%.

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.

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%.