Features of aerobic granular sludge formation treating fluctuating industrial saline wastewater at pilot scale

Monitoring the stability of aerobic granular sludge under increasing fractions of slowly biodegradable substrate using quantitative image analysis

This work investigates the effects of increasing fraction of slowly biodegradable chemical oxygen demand (sbCOD) on the morphology, stability, and performance of aerobic granular sludge (AGS) used for wastewater treatment. A sequencing batch reactor (SBR) was supplied with synthetic wastewater containing acetate as readily biodegradable COD (rbCOD) and increasing concentrations of oleate as slowly biodegradable carbon source. The sbCOD fraction was gradually increased, reaching up to 50% of the total influent biodegradable COD (bCOD). Quantitative image analysis (QIA) revealed a significant shift in granule morphology and size distribution due to increasing sbCOD fractions. Larger granules (Deq >1.0 mm) become predominant due to the washout of smaller granules (Deq <1.0 mm), which evidenced deterioration in several structural parameters. In contrary, larger granules maintained stable compactness, robustness, and extent. These morphological and size distribution changes were concomitant with variations in reactor performance: total inorganic nitrogen (TIN) removal efficiency improved up to 94%, due to enhanced denitrification capacity, supported by the predominance of larger granules and increase in granules size at higher sbCOD fractions. In contrast, P-PO43- removal efficiency declined, associated with the leakage of rbCOD to the aerobic phase, filamentous growth, and deteriorated sludge settling properties. These findings highlight the complex interactions between oleate characteristics, AGS morphology, and reactor performance, emphasizing the need for optimized strategies to mitigate process instability in AGS systems treating lipid-rich wastewater, ensuring sustainable and efficient wastewater treatment in real-world applications.

Effect of in situ ultrasonic wave and influent ammonia nitrogen fluctuation on stability of aerobic granular sludge

This study elucidates the impact of fluctuating influent conditions and in situ ultrasonic wave exposure on the stability of aerobic granular sludge (AGS) in the treatment of simulated wastewater emanating from rare earth mining operations. During a stable influent period spanning from Day 1 to Day 95, the seed granules underwent an initial disintegration followed by a re-granulation phase. The secondary granulation was achieved on Day 80 and Day 40 for the ultrasonic reactor (R1) and the control reactor (R2), respectively. Notably, granules formed in R1 exhibited a more porous structure compared to those generated in R2. Subsequently, when the ammonia nitrogen in the influent oscillated between 100 and 500 mg/L during Days 96-140, both reactors yielded compact and densely structured granules. Nitrogen removal profiles were comparable between the two reactors: the removal efficiencies for ammonia nitrogen and total inorganic nitrogen escalated from 95% and 80%, respectively, during Days 1-95, to 95% and 90%, respectively, post-Day 140. A suite of performance metrics indicated that steady-state granules from R1 outperformed those from R2 across several parameters. Specifically, the nitrification/denitrification rates, and relative abundance of denitrifying bacteria were all higher in granules from R1. Conversely, the relative abundance of nitrifying bacteria was comparable between granules from both reactors. However, R1 granules demonstrated lower sludge concentration and smaller average particle size than their R2 counterparts. In conclusion, the AGS system demonstrated robust resilience to fluctuating ammonia nitrogen, and the application of ultrasonic waves significantly enhanced granular activity while achieving in situ sludge reduction.

Impact of salinity and organic matter on the ammonia-oxidizing archaea and bacteria in treating hypersaline industrial wastewater: amoA gene abundance and ammonia removal contributions

Studies published recently proposed that ammonia-oxidizing archaea (AOA) may be beneficial for hypersaline (salinity > 50 g NaCl L-1) industrial wastewater treatment. However, knowledge of AOA activity in hypersaline bioreactors is limited. This study investigated the effects of salinity, organic matter, and practical pickled mustard tuber wastewater (PMTW) on AOA and ammonia-oxidizing bacteria (AOB) in two sequencing batch biofilm reactors (SBBRs). Results showed that despite observed salinity inhibition (p < 0.05), both AOA and AOB contributed to high ammonia removal efficiency at a salinity of 70 g NaCl L-1 in the two SBBRs. The ammonia removal efficiency of SBBR2 did not significantly differ from that of SBBR1 in the absence of organic matter (p > 0.05). Batch tests and quantitative real-time PCR (qPCR) reveal that salinity and organic matter inhibition resulted in a sharp decline in specific ammonia oxidation rates and amoA gene copy numbers of AOA and AOB (p < 0.05). AOA demonstrated higher abundance and more active ammonia oxidation activity in hypersaline and high organic matter environments. Salinity was positively correlated with the potential ammonia oxidation contribution of AOA (p < 0.05), resulting in a potential transition from AOB dominance to AOA dominance in SBBR1 as salinity levels rose. Moreover, autochthonous AOA in PMTW promoted the abundance and ammonia oxidation activities of AOA in SBBR2, further elevating the nitrification removal efficiency after feeding the practical PMTW. AOA demonstrates greater tolerance to the challenging hypersaline environment, making it a valuable candidate for the treatment of practical industrial wastewater with high salinity and organic content.

Insights into nitrogen removal and microbial response of marine anammox bacteria-based consortia treating saline wastewater: From high to moderate and low salinities

Marine anammox bacteria (MAB) have promising nitrogen removal performance in high saline wastewater treatment. Nevertheless, the impact resulting from moderate and low salinities on MAB is still unclear. Herein, MAB were applied to treat saline wastewater from high to moderate and low salinities for the first time. Independent of salinities (35-3.5 g/L), MAB consistently exhibited good nitrogen removal performance, and maximum total nitrogen removal rate (0.97 kg/(m³·d)) occurred at 10.5 g/L salts. More extracellular polymeric substances (EPSs) were secreted by MAB-based consortia to resist hypotonic surroundings. However, a sharp EPS decrease was accompanied by the collapse of MAB-driven anammox process, and MAB granules disintegrated due to long-term exposure to salt-free environment. The relative abundance of MAB varied from 10.7% to 15.9% and 3.8% as salinity decreased from 35 to 10.5 and 0 g/L salts. These findings will provide practical implementation of MAB-driven anammox process treating wastewater with different salinities.

Technological, Ecological, and Energy-Economic Aspects of Using Solidified Carbon Dioxide for Aerobic Granular Sludge Pre-Treatment Prior to Anaerobic Digestion

The technology of aerobic granular sludge (AGS) seems prospective in wastewater bio-treatment. The characteristics as well as compactness and structure of AGS have been proved to significantly affect the effectiveness of thus far deployed methods for sewage sludge processing, including anaerobic digestion (AD). Therefore, it is deemed necessary to extend knowledge on the possibilities of efficient AGS management and to seek viable technological solutions for methane fermentation of sludge of this type, including by means of using the pre-treatment step. Little is known about the pre-treatment method with solidified carbon dioxide (SCO₂), which can be recovered in processes of biogas upgrading and enrichment, leading to biomethane production. This study aimed to determine the impact of AGS pre-treatment with SCO₂ on the efficiency of its AD. An energy balance and a simplified economic analysis of the process were also carried out. It was found that an increasing dose of SCO₂ applied in the pre-treatment increased the concentrations of COD, N-NH₄⁺, and P-PO₄^3- in the supernatant in the range of the SCO₂/AGS volume ratios from 0.0 to 0.3. No statistically significant differences were noted above the latter value. The highest unit yields of biogas and methane production, reaching 476 ± 20 cm³/gVS and 341 ± 13 cm³/gVS, respectively, were obtained in the variant with the SCO₂/AGS ratio of 0.3. This experimental variant also produced the highest positive net energy gain, reaching 1047.85 ± 20 kWh/ton total solids (TS). The use of the higher than 0.3 SCO₂ doses was proved to significantly reduce the pH of AGS (below 6.5), thereby directly diminishing the percentage of methanogenic bacteria in the anaerobic bacterial community, which in turn contributed to a reduced CH₄ fraction in the biogas.

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%.

Novel Polymeric Membranes Preparation and Membrane Process

Polymer-based membranes have advanced or novel functions in the various membrane separation processes for liquid and gaseous mixtures, such as gas separation, pervaporation (PV), reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), and in other critical applications of membranes such as water purification, solvent concentration, and recovery [...]

Enhancing the Stability of Aerobic Granular Sludge Process Treating Municipal Wastewater by Adjusting Organic Loading Rate and Dissolved Oxygen Concentration

Aerobic granular sludge (AGS) application in treating municipal wastewater has been greatly restricted due to its low stability. It has been found that operation parameters have a great impact on stability. The organic loading rate (OLR) and dissolved oxygen (DO) concentration are two very important parameters that impact stability. In this study, the organic loading rate (OLR) and aeration rate were studied to verify their influence on AGS system stability, which is indicated by determining pollutant removal performance, including chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen (TN). The physical and chemical property changes of AGS and the effects of pollutant removal during the formation of AGS were systematically investigated. The AGS was formed after about 25 days and remained stable for about 45–50 days. The AGS was light-yellow globular sludge with an average particle size of 1.25 mm and a sludge volume index (SVI) of 33.9 mL/g. The optimal condition was obtained at an OLR of 4.2 kg COD/m3·d, aeration rate of 4 L/min, and a hydraulic retention time (HRT) of 4 h. The corresponding removal efficiencies of COD, ammonia nitrogen, and TN were 94.1%, 98.4% and 74.1%, respectively. The study shows that the AGS system has great potential for pollutant removal from wastewater.

Rapid start-up of photo-granule process in a photo-sequencing batch reactor under low aeration conditions: Effect of inoculum AGS size

The photo-granule process is an effective and economically feasible alternative for wastewater treatment, but little information is available regarding how to speed up the photo-granulation process. In this study, the effect of inoculum aerobic granular sludge (AGS) size on the start-up of the photo-granule process was investigated under low aeration conditions (superficial gas velocity of 0.5 cm/s). For this purpose, the inoculum AGS was sorted into various size-categories (0.4-0.8 mm, 0.8-1.4 mm, 1.4-2.2 mm, and > 2.2 mm) to serve as individual inoculum sludge. The excellent settling properties (SVI₅ of 39.3 mL/g), strong mechanical strength, efficient nutrient removal (COD: 94.2-97.1%; TN: 80.1-84.8%; TP: 60.4-91.5%), and high biodiesel yields (12.11 mg/g MLSS) were rapidly achieved in the system inoculated with 0.8-1.4 mm AGS. The granulation process was facilitated by filamentous algae as the nucleus, extracellular polymeric substances as the backbone, and the enrichment of functional bacteria (such as Thauera and Sphingorhabdus). Furthermore, the inherent influencing mechanisms of inoculum AGS size on the photo-granulation were revealed from cellular hydrophobicity, surface thermodynamics, and sludge aggregation behavior. This study provides a novel start-up approach of the photo-granule process by inoculating with the optimal AGS size, which is convenient, practically feasible and significantly reduced the aeration consumption.

A Pilot-Scale Treatment of Steel Plant Wastewater by PVDF Hollow Fiber Ultrafiltration Membrane with Low Packing Density

The treatment of wastewater from the iron and steel industry is difficult due to its complex and changeable characteristics. This paper introduces the application of polyvinylidene fluoride (PVDF)-pressurized ultrafiltration membrane with low packing density that produced via thermally induced phase separation (TIPS) in wastewater of iron and steel industry, to study the effects of packing density of ultrafiltration membrane modules as well as the membrane performance under different operation conditions, in order to provide guidance for the subsequent development of other ultrafiltration applications in wastewater of iron and steel. The results show a significant positive effect of smaller packing density on the transmembrane pressure difference (TMP) reducing and higher permeability. Under 30 min filtration cycle and 65 L m−2 h−1 (LMH) operation flux, the permeability can be stabilized to 200 L/(m2·h)/0.1 MPa, which is two times higher than that of the membrane module with 0.3 m2/m3 higher packing density under the same condition. It is obvious that compared with enhanced flux maintenance (EFM), chemically enhanced backwash (CEB) is a more effective cleaning method for iron and steel wastewater, which maintains TMP (30 kPa) without any significant increase under the premise of ensuring the high-flux (65 LMH) operation. The results also suggest reasonable parameters based on the test water quality, which include the filtration cycle and operation flux. The scanning electron microscopy (SEM) analysis and the turbidity of the permeate show that the ultrafiltration membrane has good intercept ability and high anti-pollution performance.