Optimizing external carbon source addition in domestics wastewater treatment based on online sensoring data and a numerical model

First application of the novel anaerobic/aerobic/anoxic (AOA) process for advanced nutrient removal in a wastewater treatment plant

The stringent effluent quality standards in wastewater treatment plants (WWTPs) can effectively mitigate environmental issues such as eutrophication by reducing the discharge of nutrients into water environments. However, the current wastewater treatment process often struggles to achieve advanced nutrient removal while also saving energy and reducing carbon consumption. The first full-scale anaerobic/aerobic/anoxic (AOA) system was established with a wastewater treatment scale of 40,000 m3/d. Over one year of operation, the average TN and TP concentration in the effluent of 7.53 ± 0.81 and 0.37 ± 0.05 mg/L was achieved in low TN/COD (C/N) ratio (average 5) wastewater treatment. The post-anoxic zones fully utilized the internal carbon source stored in pre-anaerobic zones, removing 41.29 % of TN and 36.25 % of TP. Intracellular glycogen (Gly) and proteins in extracellular polymeric substances (EPS) served as potential drivers for post-anoxic denitrification and phosphorus uptake. The sludge fermentation process was enhanced by the long anoxic hydraulic retention time (HRT) of the AOA system. The relative abundance of fermentative bacteria was 31.66 - 55.83 %, and their fermentation metabolites can provide additional substrates and energy for nutrient removal. The development and utilization of internal carbon sources in the AOA system benefited from reducing excess sludge production, energy conservation, and advanced nutrient removal under carbon-limited. The successful full-scale validation of the AOA process provided a potentially transformative technology with wide applicability to WWTPs.

Insights into greenhouse gas emissions from a wastewater treatment plant in vulnerable water areas of China

Wastewater treatment plants (WWTPs) are a significant anthropogenic source of greenhouse gas (GHG), but the quantitative assessment of GHG emissions from WWTPs in vulnerable water areas under stricter discharge limits remains unclear. Herein, depending on a case WWTP in southern China, we investigated the impacts of discharge standard improvement and key drivers of GHG emissions using daily operating data. We demonstrated that the stricter discharge limits increased the total GHG emission intensity by 18.2 %, with direct emissions increasing more than indirect GHG emissions. The GHG emissions were negatively correlated with water quantity, showing the scale effect, which became more pronounced after the discharge standard improvement. Increasing influent chemical oxygen demand and total nitrogen concentrations significantly drove the variations in GHG emissions, which were accelerated under stricter discharge limits. This study provides insights into the evaluation of GHG emission from WWTPs in vulnerable water areas and carbon-neutral wastewater management policies.

Performance of anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal system overwhelmingly dominated by Candidatus_Competibacter: Effect of aeration time

The anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal process (AOA-SNDPR) is a promising technology for enhanced biological wastewater treatment and in situ sludge reduction. Herein, the effects of aeration time (90, 75, 60, 45, and 30 min, respectively) on AOA-SNDPR were evaluated including simultaneous nutrients removal, sludge characteristics, and microbial community evolution, where the role of a denitrifying glycogen accumulating organisms, Candidatus_Competibacter, was re-explored given its overwhelming dominance. Results revealed that nitrogen removal was more vulnerable, and a moderate aeration period of 45-60 min mostly favored nutrients removal. Low observed sludge yields (Y_obs) were obtained with decreased aeration (as low as 0.02 g MLSS/g COD), while MLVSS/MLSS got increased. The dominance of Candidatus_Competibacter was proven to be the key to endogenous denitrifying and in situ sludge reduction. This study would aid the more carbon- and energy-efficient aeration strategy for AOA-SNDPR systems treating low-strength municipal wastewater.

Balance nitrogen and phosphorus efficient removal under carbon limitation in pilot-scale demonstration of a novel anaerobic/aerobic/anoxic process

Nutrient removal in carbon limited wastewater with high efficiency and energy saving remains a bottleneck for wastewater treatment plants (WWTPs). This study established a pilot-scale anaerobic/aerobic/anoxic (AOA) system with processing capacity of 100 m³/d for the first time. During almost 300 days of stable operation, enhanced nitrogen and phosphorus removal at a C/N of 5 was achieved, and the concentrations of total nitrogen (TN) and total phosphorus (TP) in effluent were 3.60 ± 1.55 and 0.24 ± 0.13 mg/L. Tetrasphaera and Candidatus Competibacter were the dominant phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) in the AOA system. Moreover, the low phosphorus release ensured sufficient intracellular carbon storage by endogenous denitrification, which was the critical factor for nitrogen and phosphorus removal in carbon limited wastewater. The denitrification phosphorus removal (DPR) ability further removed phosphorus and prevented secondary phosphorus release to maintain a low phosphorus concentration in effluent. Finally, rapid start-up, high nutrient removal efficiency and low energy consumption make the proposed AOA process suitable for application in newly constructed and renovated WWTPs.

Intensified nitrogen removal by endogenous denitrification in a full-scale municipal wastewater treatment plant

In this study, for the first time, endogenous denitrification (ED) was enhanced in a practical anaerobic-anoxic-oxic-[post-anoxic]-[post-oxic] (AAO-AO) process, contributing to a remarkable increase in the nitrogen removal efficiency (NRE). The long-term operation (203 days) result showed that the NRE was improved by 7% compared to the theoretical maximum NRE (68-70%) of AAO processes, with the effluent total nitrogen (TN) decreasing from 13.7 (1 d) to 6.1 mg/L (203 d). Approximately 99.4% of the influent COD was transformed to poly-β-hydroxyalkanoates (PHAs) in the anaerobic zone. The synthesized PHAs were consumed in the following zones and the secondary sedimentation tank accompanied by over 32.5% N-loss, indicating that the ED process could be responsible for the enhanced NRE. 16S rRNA amplicon sequencing results further confirmed that denitrifying glycogen-accumulating organisms, which are capable of ED, were enriched with the relative abundance of 2.10%. Our findings provide a novel cost- and energy-efficient strategy to improve nitrogen removal without external carbon additions but by enhancing ED performance.

Microbial explanation to performance stratification along up-flow solid-phase denitrification column packed with polycaprolactone

In this study, the fluctuating profiles of physicochemical and microbial characterizations along different filling heights of continuously up-flow solid-phase denitrification (SPD) columns packed with polycaprolactone (PCL) were investigated. It was found both the PCL filling area and non-filling area made significant contributions to treatment performance and denitrification mainly occurred near the bottom of the filling column. Nitrate displayed a high proportional removal (≥98.7%) among all the cases except the one with the lowest filling ratio (FR30) and highest NLR (3.99 ± 0.12 gN/(L·d)), while nitrite and ammonium displayed a weak accumulation in final effluents (nitrite ≤ 0.40 mg/L; ammonium ≤ 0.98 mg/L). The intensity of PCL hydrolysis in the top substrate was stronger than those in the middle or bottom. Both dissimilatory nitrate reduction to ammonium (DNRA) and microbial lysis contributed to ammonium accumulation, and nitrate was mainly removed via traditional denitrification and DNRA. JGI_0000069-P22_unclassified and Gracilibacteria_unclassified might contribute to denitrification.

Denitrification Process Enhancement and Diversity of the Denitrifying Community in the Full Scale Activated Sludge System after Adaptation to Fusel Oil

Implementation of anaerobic digestion of primary sludge in modern wastewater treatment plants (WWTPs) limits the availability of organic carbon for denitrification in conventional nitrification-denitrification (N/DN) systems. In order to ensure efficient denitrification, dosage of the external carbon source is commonly undertaken. However, application of commercial products, such us ethanol or acetate, greatly increases operational costs. As such, inexpensive and efficient alternative carbon sources are strongly desirable. In this study, the use of the fusel oil, a by-product from the distillery industry, was validated in terms of the denitrification process enhancement and impact on the activated sludge bacterial community structure. The experiment was conducted at a full scale biological nutrient removal facility (210,000 PE), in the set of the two technological lines: the experimental line (where fusel oil was introduced at 45 cm3/m3 dose) and the reference line (without an external carbon source addition). During the experimental period of 98 days, conventional nitrate utilization rate (NUR) measurements were carried out on a regular basis in order to assess the biomass adaptation to the fusel oil addition and denitrification process enhancement. While the NURs remained at a stable level in the reference line (1.4 ± 0.1 mg NO3-N/g VSS·h) throughout the entire duration of the experiment, the addition of fusel oil gradually enhanced the denitrification process rate up to 2.7 mg NO3-N/g VSS·h. Moreover, fusel oil contributed to the mitigation of the variability of NO3-N concentrations in the effluent from the anoxic zone. The bacterial community structure, characterized by 16S rRNA PCR—DGGE and the clone libraries of the genes involved in the denitrification process (nirS and nirK), was comparable between the reference and the experimental line during the entire experimental period. In both analyzed lines, the most frequent occurrence of denitrifiers belonging to the genera Acidovorax, Alcaligenes, Azoarcus, Paracoccus and Thauera was noticed. Our results proved that fusel oil would a valuable substrate for denitrification. The addition of fusel oil enhances the process rate and does not reflect a severe selection pressure on the bacterial community at applicable doses. Practical application of fusel oil generates opportunities for the WWTPs to meet effluent standards and reduce operational costs, as well as optimizing waste management for the distillery industry.

Short-chain fatty acids resource recovery potential from algal sludge via anaerobic fermentation under various pH values

The harvesting of algal sludge from eutrophic lakes, including the large quantity of organic matters, has the potential to be used as valuable products through the process of resource recovery. This study investigates the fatty acid production potential from algal sludge via anaerobic fermentation under different pH values. The results indicated that the recovery of short-chain fatty acids (SCFAs) was the highest (3269.25 ± 32.89 mg·COD/L) at pH 11 after 7 days of fermentation. The SCFAs concentration at pH value 11 was 6.24, 1.27, 4.90, and 0.53 times higher compared with that at pH value 3, 5, 7, and 9, respectively. The SCFAs production was continually increased from day 1 to day 7 at pH value 7, 9, and 11. Much fewer middle- and long-chain fatty acids were produced compared with SCFAs. Gross. fatty acid production was the highest at pH 11. The concentrations of soluble protein and polysaccharide were the highest at pH 11, implying that the disruption of algal cells could have a high value at pH 11. The polysaccharide concentration was the lowest at pH 7. The fluorescence excitation-emission matrix profile implied that the disruption of algal cells was the greatest at pH 11. Methane production was greatest at pH 7 and 9. Overall, the results of this study revealed that a pH of 11 was optimal for the recovery of SCFAs from algal sludge due to the higher cell disruption, suitable ORP condition for SCFAs production and inhibition of methanogens.

Dairy wastewater processing and automatic control for waste recovery at the municipal wastewater treatment plant based on modelling investigations

Based on the calibrated model for an Anaerobic-Anoxic-Oxic (A²O) municipal wastewater treatment plant (WWTP), this research investigated and proposed feasible solutions, control system configurations and optimal operating conditions for the dairy wastewater processing. The steady state study on adding different daily amounts of dairy wastewater in the WWTP water line revealed the most efficient amount to be treated by finding a minimum of the total nitrogen concentration in the water effluent. The dynamic investigations on adding different daily amounts of diary wastewater demonstrated the incentives of the proposed cascade control system configurations, based on the ammonia or nitrates concentration control in the aerated reactors, associated to nitrates and nitrites concentration control in the anoxic reactor. The best periods of time and duration for scheduling the dairy wastewater processing were searched and found. Preliminary results showed the incentives of the additional dairy wastewater distribution during 2 h, at the highest influent concentration moments. Further investigations, relying on the genetic algorithm optimization method revealed that better daily scheduling of the dairy wastewater addition may be obtained. Compared to normal operation, the optimal scheduling program of the dairy wastewater treatment showed an overall performance index improvement of 13.36%, when the daily 1:52 p.m. moment of time and the duration of about 1 h program, found by optimization, were applied. Results demonstrate the dual incentives of the carbon and nutrients recovery, associated to the energy and effluent quality benefits on WWTP operation.

Innovative technology of municipal wastewater treatment for rapid sludge sedimentation and enhancing pollutants removal with nano-material

This study aims to develop a novel technology for actual municipal wastewater treatment to achieve rapid sludge sedimentation and high pollutants removal efficiency. The SBRs were modified and operated with periodic addition of 20 μL·L^-1 nanofloc®. Results revealed that NH₄⁺-N and chemical oxygen demand (COD) was efficiently removed in both laboratory- and pilot-scale SBRs, and the average removal efficiency of total nitrogen (TN) and total phosphorus (TP) was as high as 72.43 ± 2.66% and 98.63 ± 0.74%, respectively, with hydraulic retention time (HRT) of 8 h. Besides, the sludge volume index at 30 min (SVI₃₀) was only 40.06 ± 1.99 mL·g^-1, comparable with aerobic granular sludge (AGS). This novel technology could be proposed as a competitive method to upgrade, reconstruct and delay the expansion of municipal wastewater treatment plants (WWTPs) due to its rapid sludge sedimentation and efficient pollutants removal with low HRT.

Effects of Temperature on the Characteristics of Nitrogen Removal and Microbial Community in Post Solid-Phase Denitrification Biofilter Process

In order to solve the problems of high energy consumption, complex process and low nitrogen removal efficiency in the currently available low carbon source wastewater treatment processes, a novel coagulation sedimentation/post-solid-phase denitrification biofilter process (CS-BAF-SPDB) was proposed. The effect of temperature on the nitrogen removal performance of BAF-SPDB was intensively studied, and the mechanism of the effect of temperature on nitrogen removal performance was analyzed from the perspective of microbial community structure by using the polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that, to realize favorable nitrifying and denitrifying performance simultaneously in the BAF-SPDB unit, the operation temperature should be set above 18 °C. In addition, the influence of the macro operation parameters on the performance of the BAF and SPDB has a direct relationship with the dynamic changes of the micro microbial community. The influence of temperature on nitrification performance in BAF was mainly embodied in the change of composition, amount and activity of ammonia oxidizing bacteria Candidatus Nitrospira defluvii and nitrite oxidizing bacteria Nitrosomonas sp. Nm47, while that on denitrification performance in SPDB is mainly embodied in the change of composition and amount of solid carbon substrate degrading denitrifying bacteria Pseudomonas sp., Myxobacterium AT3-03 and heterotrophic denitrifying bacteria Dechloromonas agitate, Thauera aminoaromatica, Comamonas granuli and Rubrivivax gelatinosus.

Aerobic granular sludge and naphthenic acids treatment by varying initial concentrations and supplemental carbon concentrations

Aerobic granular sludge (AGS) has previously been utilized in the treatment of toxic compounds due to its diverse and dense microbial structure. The present study subjected mature AGS to model naphthenic acids (NAs) representative of the Canadian oil sands. To this effect, three NA concentrations (10, 50 and 100 mg/L) and three supplemental carbon source concentrations (600, 1200 and 2500 mg/L) were studied in batch reactors for 5 days. The responding variables were chemical oxygen demand (COD), NA concentrations and nutrients. Cyclohexane carboxylic acid (CHCA), cyclohexane acetic acid (CHAA) and 1-adamantane carboxylic acid (ACA) were chosen to study structure-based degradation kinetics. The optimal COD according to the runs was 1200 mg/L. CHCA was removed completely with biodegradation rate constants increasing with lower NA concentrations and lower COD concentrations. CHAA was also removed completely, however, an optimal rate constant of 1.9 d^-1 was achieved at NA and COD concentrations of 50 mg/L and 1200 mg/L, respectively. ACA removal trends did not follow statistically significant regressions; however, degradation and sorption helped remove ACA up to 19.9%. Pseudomonas, Acinetobacter, Hyphomonas and Brevundimonas spp. increased over time, indicating increased AGS adaptability to NAs.

Aerobic granules cultivated with simultaneous feeding/draw mode and low-strength wastewater: Performance and bacterial community analysis

Sequence batch reactors (SBR) with simultaneous feeding/draw mode and low-strength wastewater were used for the cultivation of aerobic granules, and analysis of bacterial community diversity were conducted. Results revealed that the ratio of chemical oxygen demand/total nitrogen removal amount for R1 with real wastewater and R2 with synthetic wastewater decreased from 9.9 to 8.7 and, 29.9 to 21.1, respectively, when volumetric exchange ratio (VER) decreased from 90% (stage I) to 50% (stage II), indicating that organic matter in real and low-strength wastewater was fully utilized with lower VER by denitrifying bacteria. Relative abundances of the genus Dechloromonas, Pseudomonas, Bacillus in R1, which are responsible for denitrifying phosphorus removal, were much higher than that in R2, accounting for the high efficiency of nitrogen and phosphorus removal from real wastewater with low influent C/N ratio of 3.6 on average. These results provide useful information for improving wastewater treatment efficiency in the future.