Effect of sludge retention time on continuous-flow system with enhanced biological phosphorus removal granules at different COD loading

Evaluation of the potential toxicity of effluents from the jeans manufacturing industry before and after treatment

Wastewater from the textile industry is an emerging contaminant and is toxic to aquatic organisms. The objective of this study was to evaluate the Lethal Concentration (LC50)1 of raw textile effluent (RTE)2 on Artemia salina and Rhamdia quelen fish (larvae and juveniles), as well as treated textile effluent (TTE)³ on A. salina, and its effects on R. quelen and Allium cepa roots. The textile effluent was collected from the jeans manufacturing industry and tested on A. salina for 48 h and on R. quelen for 96 h. Juveniles of R. quelen were exposed to RTE and TTE for seven days, and in A. cepa for 72 h for biomarker analysis. Genetic damage tests, histological tests and micronucleus tests were carried out. RTE was toxic to the test organisms, resulting in a CL50-48 h of 6.06% for A. salina, CL50-96 h of 3.40% (v/v) for larvae and 13.42% (v/v) for juveniles of R. quelen. The CL50-48 h for A. salina exposed to TTE after a pause in effluent treatment was 21.38% and continuous circulation was 44.65%, reducing the toxicity of the waste. The effluents did not alter the mitotic index and nuclear changes in onion roots. For R. quelen, there was histological and genetic damage, but there was no significant difference. The raw textile effluent caused more effects than the treated one for all the data analyzed, demonstrating the importance of efficient treatments to promote sustainability.

Response of anammox to organics with different degradation characteristics and exposure time: Performance, sludge characteristics and bacterial community

The effects of typical organic compounds including easily degradable organic matters sodium acetate, yeast and methanol, and refractory organic matter (ROM) humic acid on anaerobic ammonium oxidation (anammox) systems in short-term and medium-term exposure time were studied. During short-term experiments, nitrogen removal activity (NRA) was inhibited at sodium acetate level of 150 mg L-1 total organic carbon (TOC) and methanol level of 30-150 mg L-1 TOC, but humic acid and yeast (≤150 mg L-1 TOC) enhanced nitrogen removal in anammox systems. The greatest NRA of 30.10 mg TN g-1 VSS h-1 was recorded at yeast level of 90 mg L-1 TOC. In medium-term experiments, organics significantly inhibited the nitrogen removal ability. As a ROM, humic acid enhanced sludge aggregation and biological diversity, but decreased the bioactivity and extracellular polymeric substances levels. Due to the endogenous denitrification, the relative abundance of anammox bacteria (AnAOB) was decreased. Candidatus Kuenenia is still dominant in sludge with methanol and humid acid, but AnAOB are not dominant due to the addition of sodium acetate and yeast. This research would be beneficial for the full-scale application of the anammox process in treating real wastewater with organics and ammonia.

Enhanced granulation of activated sludge in an airlift reactor for organic carbon removal and ammonia retention from industrial fermentation wastewater: A comparative study

Ammonia retention and recovery from high-nitrogenous wastewater are new concepts being used for nitrogen management. A microaerophilic activated sludge system was developed to convert organic nitrogen into ammonia and retain it for its recovery; however, the settleability of activated sludge remains a challenge. Therefore, this study proposed an aerobic granular sludge system as a potential solution. Two types of sequencing batch reactors-airlift and upflow reactors-were operated to investigate the feasibility of fast granule formation, the performance of organic carbon removal and ammonia retention, and the dynamics of microbial community composition. The operation fed with industrial fermentation wastewater demonstrated that the airlift reactor ensured a more rapid granule formation than the upflow reactor because of the high shear force, and it maintained a superior ammonia retention stability of approximately 85 %. Throughout the operational period, changes in hydraulic retention time (HRT), settling time, and exchange ratio altered the granular particle sizes and microbial community compositions. Rhodocyclaceae were replaced with Comamonadaceae, Methylophilaceae, Xanthomonadaceae, and Chitinophagaceae as core taxa instrumental in granulation, likely because of their extracellular polymeric substance secretion. As the granulation process progressed, a significant decrease in the relative abundances of nitrifying bacteria-Nitrospiraceae and Nitrosomonadaceae-was observed. The reduction of settling time and HRT enhanced granulation and inhibited the activity of nitrifying bacteria. The success in granulation for ammonia conversion and retention in this study accelerates the paradigm shift from ammonia removal to ammonia recovery from industrial fermentation wastewater.

Microbial Ecology of Granular Biofilm Technologies for Wastewater Treatment: A Review

Nowadays, the discharge of wastewater is a global concern due to the damage caused to human and environmental health. Wastewater treatment has progressed to provide environmentally and economically sustainable technologies. The biological treatment of wastewater is one of the fundamental bases of this field, and the employment of new technologies based on granular biofilm systems is demonstrating success in tackling the environmental issues derived from the discharge of wastewater. The granular-conforming microorganisms must be evaluated as functional entities because their activities and functions for removing pollutants are interconnected with the surrounding microbiota. The deep knowledge of microbial communities allows for the improvement in system operation, as the proliferation of microorganisms in charge of metabolic roles could be modified by adjustments to operational conditions. This is why engineering must consider the intrinsic microbiological aspects of biological wastewater treatment systems to obtain the most effective performance. This review provides an extensive view of the microbial ecology of biological wastewater treatment technologies based on granular biofilms for mitigating water pollution.

Full-scale application and performance of a new multi-self-reflow decentralized Wastewater treatment device: Impact of hydraulic and pollutant loads

Decentralized treatment of wastewater in rural areas usually has several challenges, which include large fluctuations in pollutant concentration and water quantity, complicated operation and maintenance of conventional biochemical treatment equipment, resulting in poor stability and a low compliance rate of the wastewater treatment process. In order to solve the above problems, a new integration reactor is designed, which uses gravity and aeration tail gas self-reflux technology to realize the reflux of sludge and the nitrification liquid, respectively. The feasibility and operation characteristics of its application for decentralized wastewater treatment in rural areas are explored. The results demonstrated that, under constant influent, the device showed strong tolerance to the shock of pollutant load. The chemical oxygen demand, NH₄⁺-N, total nitrogen and total phosphorus fluctuated in the ranges of 95-715 mg/L, 7.6-38.5 mg/L, 9.32-40.3 mg/L and 0.84-4.9 mg/L, respectively. The corresponding effluent compliance rates were 82.1%, 92.8%, 96.4% and 96.3%, respectively. When the wastewater discharge was non-constant and the maximum single-day Q_max/Q_min reached 5, all indicators of the effluent met the relevant discharge standard. The integrated device also demonstrated high phosphorus enrichment levels in its anaerobic zone; the concentration of phosphorus reached a maximum of 26.9 mg/L, which created a good environment for phosphorus removal. The microbial community analysis showed that sludge digestion, denitrification, and phosphorus-accumulating bacteria all played an important role in pollutant treatment.

Current progress of continuous-flow aerobic granular sludge: A critical review

Aerobic granular sludge (AGS) is promising for water resource recovery. Despite the mature granulation strategies in sequencing batch reactor (SBR), the application of AGS-SBR in wastewater treatment is usually costly as it requires extensive infrastructure conversion (e.g., from continuous-flow reactor to SBR). In contrast, continuous-flow AGS (CAGS) that does not require such infrastructure conversion is a more cost-effective strategy to retrofit existing wastewater treatment plants (WWTPs). Formation of aerobic granules in both batch and continuous-flow mode depends on many factors, including selection pressure, feast/famine conditions, extracellular polymeric substances (EPS), and environmental conditions. Compared with AGS in SBR, creating proper conditions to facilitate granulation in continuous-flow mode is challenging. Researchers have been seeking to tackle this bottleneck by studying the impacts of selection pressure, feast/famine conditions, and operating parameters on granulation and granule stability in CAGS. This review paper summarizes the state-of-the-art knowledge regarding CAGS for wastewater treatment. Firstly, we discuss the CAGS granulation process and effective parameters (i.e., selection pressure, feast/famine conditions, hydrodynamic shear force, reactor configuration, the role of EPS, and other operating factors). Then, we evaluate CAGS performance in removing COD, nitrogen, phosphorus, emerging pollutants, and heavy metals from wastewater. Finally, the applicability of the hybrid CAGS systems is presented. At last, we suggest that integrating CAGS with other treatment methods such as membrane bioreactor (MBR) or advanced oxidation processes (AOP) can benefit the performance and stability of granules. However, future research should address unknowns including the relationship between feast/famine ratio and stability of the granules, the effectiveness of applying particle size-based selection pressure, and the CAGS performance at low temperatures.

Resolution of conflict of reduced sludge production with EBPR by coupling OSA to A2/O process in a pilot scale SBR

The pinnacle of all the efforts of nutrient removal is practically put-down the moment biological cells are lysed, hydrolyzed or digested causing subsequent reappearance of assimilated nitrogen and phosphorus in any biological process. While sludge reduction requires high SRT, the enhanced phosphorus assimilative uptake demands low SRT. A novel reactor configuration for enhanced sludge and phosphorus removal was put to test by incorporating a side stream anaerobic reactor to an Anaerobic-Anoxic-Aerobic (A²O) SBR with a pre-anoxic chamber and an influent receiving inlet anaerobic reactor. The reactor was operated at the average and lowest range of prevailing carbon/phosphorus (C/P) ratio of 50 and 15 in the sewage. The phosphorus enrichment was 0.0469-0.135 mgTP/mgVSS resulting in 1.76-5.05-fold increase from cellular content by virtue of maintaining sludge recycle from SBR aeration tank to side stream anaerobic reactor from 3.78 to 9.78 (average 4.4-8.2) gVSS/gVSS present in the reactor. However, the sludge was also reduced from 3% to 51% on an average basis during the same recirculation regime. This novel configuration consists of an inlet anaerobic reactor, one pre-anoxic chamber and one intermittent oxic anoxic reaction SBR and a side stream anaerobic reactor. The first anaerobic reactor at inlet followed by pre-anoxic chamber was provided for increased ortho-p released and nitrification respectively and a side stream anaerobic reactor for sludge reduction through sludge fasting mechanism. The EBPR and lesser sludge growth were two conflicting parameters reconciled to the extent that if sludge recycled up to 6.41 gVSS/gVSS the sludge growth would be reduced by 25% and phosphorus enrichment could be attained up to 3.46 times the stoichiometric value. Any further recirculation would reduce the sludge further but at the expense of enhanced phosphorus uptake as released phosphorus from side stream anaerobic reactor also recycled back to main SBR causing looping and at more than 6.41gVSSrecycled/gVSS it nullified the enhanced effect.

Start-up of an aerobic granular sludge system from stored granules: Evaluating the impact of storage period on biomass activity and stability and the effect of temperature on nitrification and phosphorus removal rates

Aerobic granular sludge (AGS) has been considered a breakthrough within the wastewater treatment sector. However, the long reactor start-up for the formation of granules is challenging and may hinder the spread of this technology. To circumvent this obstacle, inoculation of the reactors with pre-formed granules from existing plants is an interesting approach. In this context, issues related to biomass storage becomes very relevant. In this study, reactivation of aerobic granular biomass after storage was evaluated in a sequencing batch reactor (SBR) designed for achieving simultaneous organic matter, nitrogen and phosphorus removal. Two different scenarios, short (40 days) and long (180 days) storage periods, were assessed, and their influence on the granules physical properties and bioactivity was addressed. The results revealed that the granules stored for a shorter period showed higher resistance to breakage and underwent smooth color changes. On the other hand, the biomass stored for a longer period acquired a dark color and was more susceptible to disruption during reactivation. The granules stored for 6 months become swollen and exhibited an irregular morphology and fluffy structure within the first days of reactivation. Consequently, their settling properties were adversely affected, and some parameters such as the food-to-microorganism ratio had to be adjusted to prevent granules disintegration. Regarding the bioactivity of important microbial functional groups, COD removal was rapidly restored within a few days of SBR operation with the biomass stored for a shorter period. However, it took longer for the biomass stored for 180 days to reach the same performance observed for the granules stored for 40 days. A similar trend is valid for nitrification. In the experiments with sludge stored for a longer time, it took almost twice as long to reach effluent ammonium concentrations lower than 1 mg NH₄⁺-N L^-1 compared to the test using biomass stored for 40 days. Phosphate removal was strongly affected by biomass storage, especially after 180 days of inactivity, a condition found to be detrimental for polyphosphate-accumulating organisms. Finally, cycle tests were also conducted to assess substrate conversion rates for comparison between different trials and evaluate the influence of temperature (10-35 °C) on nitrification and phosphate removal rates.

Enhancing stability of aerobic granules by microbial selection pressure using height-adjustable influent strategy

Optimizing granules size distribution is critical for both reactor performance and stability. In this research, an optimal size range of 1800 to 3000 μm was proposed regarding mass transfer and granules stability based on granules developed at DO around 8.0 mg L^-1 with the feed COD:N:P at 100:5:1. A height-adjustable influent strategy was applied to facilitate the nutrient storage of granules at optimum size range via microbial selective pressure. Results suggested insufficient hydraulic shear stress led to overgrowth of granules size. High abundance of filamentous bacteria (Thiothrix sp.) was observed in oversized granules, which detached and affected the remaining granules, resulting in severe sludge bulking. Strong hydraulic shear stress suppressed uncontrolled growth of granules. However, fewer abundance of simultaneous nitrification and denitrification (SND) bacterium was acquired, which led to unfavored SND effect and total nitrogen (TN) removal efficiency. The height-adjustable influent strategy facilitated the poly-β-hydroxybutyrate (PHB) storage of granules at optimum size range, while limiting the overgrowth of granules size. Additionally, more than 87.51% of total granules situated in optimal sizes range, which led to higher abundance of SND bacterium and higher TN removal efficiency.

Performance and operational strategy of simultaneous nitrification, denitrification, and phosphorus removal system under the condition of low organic loading rate in wet weather

A pilot-scale aerobic granular sequencing batch reactor (SBR) with domestic wastewater was operated to evaluate the effects of the low organic loading rate (OLR) due to wet weather flow conditions on simultaneous nitrification, denitrification, and phosphorus removal (SNDPR). As the OLR decreased from 0.85 to 0.43 kg COD m^-3 d^-1, the total nitrogen (TN) and total phosphorus (TP) removal efficiencies decreased from 84.0% and 94.1% to 51.3% and 73.8%, respectively, the sludge volume index (SVI) increased from 42.3 to 85.5 mL g^-1, and the average granular size decreased from 1022 to 742 μm; however, no sludge disintegration and biomass loss were observed. The poor nutrient removal efficiencies and settling ability were due to the shrinking anoxic zone and substrate scarcity inside the granules, wherein the activity decay of ammonia-oxidizing bacteria and overgrowth of filamentous bacteria played an important role. Alternating the aeration intensity was effective in enhancing nitrogen removal and sludge settling by improving the anoxic activity in granules and inhibiting the proliferation of filamentous bacteria. Returning 20% of sludge from the end of one anaerobic stage to the beginning of the next anaerobic stage (midway sludge return) was beneficial for phosphorus removal as it improved phosphorus storage by phosphorus-accumulating bacteria. A smaller granular size with stronger stability and better nutrient removal performance was the new steady state of the SNDPR system under wet-weather flow conditions.

Effect of different operational modes on the performance of granular sludge in continuous-flow systems and the successions of microbial communities

Continuous flow reactors with time intermittent operational (TIO) mode and spatial intermittent operational (SIO) mode were operated to evaluate the effects of operational modes on the removal performances, the characteristics of granules and the dynamics of microbial communities in simultaneous nitrification, denitrification and phosphorus removal (SNDPR) granular system. The results showed that the removal efficiency of TP, TN were 81.3%, 86.7% under TIO mode, and 70.6%, 77.4% under SIO mode, respectively. Meanwhile, the PN and value of PN/PS in SIO were higher than those in TIO. Besides, results of high-throughput pyrosequencing illustrated that the combination of filamentous archaea (Methanothrix) and filamentous bacteria (Thiothrix) had resulted in the increase of EPS and SVI under SIO mode. Finally, functional bacterial and archaeal species, involving HMA, AMA, AOA, DPAOs etc., were identified to reveal the effects of operational modes on the mechanism of nutrients removal in granular SNDPR continuous-flow system.

Effect of aeration modes on simultaneous nitrogen and phosphorus removal and microbial community in a continuous flow reactor with granules

In this study, a continuous flow reactor with simultaneous nitrification, denitrification and phosphorus removal (SNDPR) granular sludge was operated in the continuous aeration (CA) and intermittent aeration (IA) modes to examine the effect of aeration on the performance of continuous-flow system. Then the experimental results showed that the IA₁ mode (4 h aeration and 1 h non-aeration) could improve the simultaneous nitrogen and phosphorus removal and the settleability of granules in continuous flow system. Results of high-throughput pyrosequencing illustrated that the methanogens, AOA, ANAMMOX, DNB, denitrifying polyphosphate-accumulating organisms (DPAOs) were the important participant of simultaneous biological nutrients removal (SBNR), meanwhile, the IA₁ mode could effectively inhibit the growth of filamentous microorganisms (Thiothrix and Acinetobacter). Finally, a conceptual model of the SNDPR granular microbial ecosystem under IA₁ mode was proposed as a base for analyzing the mechanism of simultaneous nutrient removal in continuous flow system.

Aerobic granular sludge operation and nutrients removal mechanism in a novel configuration reactor combined sequencing batch reactor and continuous-flow reactor

A novel aerobic granular sludge (AGS) system called SBR (sequencing batch reactor)-CF (continuous-flow) system merging the advantages of sequencing batch reactors (SBRs) and continuous flow (CF) reactors was developed. The AGS was successfully operated in the SBR-CF system which consisted of four same SBRs (each served as settling tank/anaerobic feeding tank/aerobic reacting tank in turn). The effects of aeration intensity and hydraulic retention time (HRT) on the SBR-CF system were studied. The results showed strong aeration intensity (9.74 h^-1 in this study) and appropriate HRT (9 h in this study) were more favorable to the nutrients removal. The EEM-PARAFAC analysis was applied to characterize the LB-EPS, TB-EPS and domestic wastewater, as results TB-EPS was found play an important role in the biosorption in COD removal of the SBR-CF system. In addition, a preliminary conceptual reaction process model in the SBR-CF system was built using high-throughput pyrosequencing and phylogenetic assignment.

Factors affecting SVI in small scale WWTPs

This paper analyses factors associated with bulking in 195 small scale wastewater treatment plants (WWTPs) in Estonia. Operational data from each plant were collected and analysed statistically. The key factors associated with bulking were infiltration into sewage pipes, the type and purpose of process reactor, operational practices and influent characteristics. Both anaerobic fraction and volumetric fraction of the anaerobic reactor compared to the aerobic reactor resulted in a positive correlation with sludge volume index (SVI) <150 ml/g values. Good operation and maintenance practice as well as an operator's competence play a crucial role in bulking prevention. Using the 30 minute settling test (V₃₀) as the single process control parameter can mislead an operator's judgement in process control strategies and cause effluent violations. Misjudgements in process control decisions can lead to unwanted conditions in small WWTPs (e.g. excessive chemical addition favoured bulking). Use of instrumentation, control and automation helped to keep the process conditions more stable and reduce the probability of bulking. Analyses of variance showed that the factors associated with Microthrix parvicella growth were long solids retention time (SRT), low food-to-microorganism ratio (F/M) and lack of carbon content compared against nitrogen and phosphorus contents.

State of the art of aerobic granulation in continuous flow bioreactors

In the wake of the success of aerobic granulation in sequential batch reactors (SBRs) for treating wastewater, attention is beginning to turn to continuous flow applications. This is a necessary step given the advantages of continuous flow treatment processes and the fact that the majority of full-scale wastewater treatment plants across the world are operated with aeration tanks and clarifiers in a continuous flow mode. As in SBRs, applying a selection pressure, based on differences in either settling velocity or the size of the biomass, is essential for successful granulation in continuous flow reactors (CFRs). CFRs employed for aerobic granulation come in multiple configurations, each with their own means of achieving such a selection pressure. Other factors, such as bioaugmentation and hydraulic shear force, also contribute to aerobic granulation to some extent. Besides the formation of aerobic granules, long-term stability of aerobic granules is also a critical issue to be addressed. Inorganic precipitation, special inocula, and various operational optimization strategies have been used to improve granule long-term structural integrity. Accumulated studies reviewed in this work demonstrate that aerobic granulation in CFRs is capable of removing a wide spectrum of contaminants and achieving properties generally comparable to those in SBRs. Despite the notable research progress made toward successful aerobic granulation in lab-scale CFRs, to the best of our knowledge, there are only three full-scale tests of the technique, two being seeded with anammox-supported aerobic granules and the other with conventional aerobic granules; two other process alternatives are currently in development. Application of settling- or size-based selection pressures and feast/famine conditions are especially difficult to implement to these and similar mainstream systems. Future research efforts needs to be focused on the optimization of the granule-to-floc ratio, enhancement of granule activity, improvement of long-term granule stability, and a better understanding of aerobic granulation mechanisms in CFRs, especially in full-scale applications.

Stability of algal-bacterial granules in continuous-flow reactors to treat varying strength domestic wastewater

Stability of algal-bacterial granules was investigated in two continuous-flow systems to treat synthetic domestic wastewater using single (R₁) and series (R₂=R_2-1+R_2-2 with automatically internal recirculation) reactors by seeding 50% (w/w) algal-bacterial granules. Almost similar organics and phosphorus removal efficiencies were obtained from the two systems, with no significant difference found for each between the designed two operation stages. However, R₂ exhibited superior performance on total nitrogen (TN) removal (76%). When double increased strength influent fed to R₁, R₁ achieved better denitrification with TN removal increased from 29% to 80%, possibly due to the increased influent organics concentration favored the denitrification process. Most importantly, the two systems well maintained their granular stability, and all granules became algal-bacterial ones with very little change detected in algae content in granules after 120days' operation. At last, the mechanisms were proposed regarding the formation and enhanced stability of new algal-bacterial granules in continuous-flow reactors.

Effects of calcium on the performance, bacterial population and microbial metabolism of a denitrifying phosphorus removal system

A sequencing batch reactor was operated to study the effects of influent Ca²⁺ on the efficiency, bacterial population, and microbial metabolism of denitrifying phosphorus removal system. Results showed that high Ca²⁺ loading (≥80mg/L) significantly inhibited the performance of simultaneous nitrogen and phosphorus removal. The abundance of phosphorus removal-related organisms (Dechloromonas and Candidatus Accumulibacter) decreased with increasing Ca²⁺ concentration from 20 to 140mg/L, while the abundance of glycogen-accumulating organisms and other bacteria increased. Metabolomic analyses revealed that the metabolic profiles of microbial community were also affected by high influent Ca²⁺ concentrations. 3-Hydroxybutyrate, acetate, alanine, and glutamate were the main differentiated metabolites in the system. An accumulation of amino acids and a reduction of nucleotides and amines were important response to high Ca²⁺ loading. Long-term Ca²⁺ loading had a reversible effect on the denitrifying phosphorus removal system as it could revive after a 50-day recovery process.