Improved biological phosphorus removal performance driven by the aerobic/extended-idle regime with propionate as the sole carbon source

Aerobic and anoxic utilization of organic matter for flexible nitrite supply in nutrient conversion pathways based on anaerobic ammonium oxidation: Microbial interactive mechanism

This study investigated nutrient conversion pathways and corresponding interactive mechanisms in a mainstream partial-nitritation (PN)/anaerobic ammonium oxidation (anammox)/partial-denitrification-(PD)-enhanced biological phosphorus-removal (EBPR) (PN/A/PD-EBPR) process. A laboratory-scale sequencing batch reactor was operated for 301 days under different operational strategies. Mainstream PN/A/PD-EBPR was successfully operated with aerobic and anoxic utilization of organic matter. Aerobic utilization of organic matter was an effective strategy for conversion to denitrifying polyphosphate-accumulating organism-based phosphorus removal, referring to a biological reaction that outperformed nitrite-oxidizing bacteria. Aerobically adsorbed organic matter could be used as a carbon source for PD, which further enhanced nitrogen removal by PN/A. Ultimately, the interaction between complex nutrient conversion pathways served to achieve stable performance. High-throughput sequencing results elucidated the core microbe functioning in the mainstream PN/A/PD-EBPR process with respect to various nutrients. The outcomes of this study will be beneficial to those attempting to implement mainstream PN/A/PD-EBPR.

The synergistic effect of chemical oxidation and microbial activity on improving volatile fatty acids (VFAs) production during the animal wastewater anaerobic digestion process treated with persulfate/biochar

Improving volatile fatty acid (VFA) production, rather than producing methane from the anaerobic digestion (AD) of waste, has become a new strategy of resource utilization. In regard to animal wastewater, the effectiveness of persulfate/biochar (potassium peroxodisulfate, PDS/BC) on the hydrolysis and acidogenesis stages and the reaction mechanisms are still unclear. In this study, the AD process on cow wastewater was controlled at the hydrolysis and acidification stages by setting the hydraulic retention time (HRT) at 25 days. The results showed that the contents of total solids (TS) and volatile solids (VS) were further reduced by PDS/BC treatment with 0.15 gPDS/gTS of PDS added. The VFAs production increased by 12.4 % from day 0 to 25 compared to the blank set. Based on our molecular analysis, the rate of increase for the dissolved organic matter with low molecular weight (0-10 kDa) was 699.5 mg/(L·d) in the first 10 days. The change rate increased nearly 2.1 times, leading to higher VFAs yield. Moreover, the activities of fermentative bacteria were enhanced and Anaerocella was determined to be the specific and critical genus. However, excessive PDS (0.3 gPDS/gTS) prolonged the acidification period and caused the inactivation of fermentative bacteria. Structural equation modeling demonstrated that PDS can directly affect VFAs yield and also had an indirect effect by influencing the decomposition of particulate matter and microbial activities. Therefore, the enhancement of VFAs production using the PDS/BC method could be due to synergistic chemical and microbial effects. Findings from this study can provide a practical strategy to enhance the VFAs production of AD technology for livestock wastewater and help reveal the reaction mechanism of PDS/BC treatment.

Exploring GHG emissions in the mainstream SCEPPHAR configuration during wastewater resource recovery

The wastewater sector paradigm is shifting from wastewater treatment to resource recovery. In addition, concerns regarding sustainability during the operation have increased. In this sense, many water utilities have become aware of the potential GHG emissions during the operation of wastewater treatment. This study assesses the nitrous oxide and methane emissions during the long-term operation of a novel wastewater resource recovery facility (WRRF) configuration: the mainstream SCEPPHAR. The long-term N₂O and CH₄ emission factors calculated were in the low range of the literature, 1 % and 0.1 %, respectively, even with high nitrite accumulation in the case of N₂O. The dynamics and possible sources of production of these emissions are discussed. Finally, different aeration strategies were implemented to study the impact on the N₂O emissions in the nitrifying reactor. Results showed that operating the pilot-plant under different dissolved oxygen concentrations (between 1 and 3 g O₂ m^-3) did not have an effect on the N₂O emission factor. Intermittent aeration was the aeration strategy that most mitigated the N₂O emissions in the nitrifying reactor, obtaining a reduction of 40 % compared to the normal operation of the pilot plant.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

The Feasibility of Maintaining Biological Phosphorus Removal in A-Stage via the Short Sludge Retention Time Approach: System Performance, Functional Genus Abundance, and Methanogenic Potential

The increasing concerns on resource and energy recovery call for the modification of the current wastewater treatment strategy. This study synthetically evaluates the feasibility of the short sludge retention time approach to improve the energy recovery potential, but keeping steady biological phosphorus removal and system stability simultaneously. SBRS-SRT and SBRcontrol that simulated the short sludge retention time and conventional biological phosphorus removal processes, respectively, were set up to treat real domestic sewage for 120 d. SBRS-SRT achieved an efficient COD (91.5 ± 3.5%), PO43−-P (95.4 ± 3.8%), and TP (93.5 ± 3.7%) removal and maintained the settling volume index around 50 mL/gSS when the sludge retention time was 3 d, indicating steady operational stability. The poor ammonia removal performance (15.7 ± 7.7%) and a few sequences detected in samples collected in SBRS-SRT indicated the washout of nitrifiers. The dominant phosphorus accumulating organisms Tetrasphaera and Hydrogenophaga, which were enriched with the shortened sludge retention time, was in line with the excellent phosphorus performance of SBRS-SRT. The calculated methanogenic efficiency of SBRS-SRT increased significantly, which was in line with the higher sludge yield. This study proved that the short sludge retention time is a promising and practical approach to integrate biological phosphorus removal in A-stage when re-engineering a biological nutrient removal process.

Evaluation of PAO adaptability to oxygen concentration change: Development of stable EBPR under stepwise low-aeration adaptation

Recent research has shown the adaptability of Biological Nutrient Removal (BNR) systems to very low level dissolved oxygen (DO) concentration, mainly focusing in the nitrification ability that maintains the nitrogen oxidation process even at very low DO levels. Although step-wise aeration decrease on Enhanced Biological Phosphorus Removal (EBPR) is not fully comprehended. This study investigated the effect of reaching micro-aeration with adaptation strategies on EBPR performance. A step-wise oxygen concentration decrease, arriving at an average aeration level of 0.4 mgO₂/L was evaluated, with an outcome of approximately 90 % phosphorus removal efficiency. Compared with different aeration modes, the highest phosphorus (P)-removal efficiency, P-release and lowest effluent phosphorus was achieved in gradual DO decrease strategy. On the other hand, an instant decrease in aeration from stable EBPR process from 2 mgO₂/L to 0.4 mgO₂/L adversely impacted P-removal by decreasing the efficiency to average 60 % and deteriorating the phosphorus removing microbial consortium. Comparison of results between instant and gradual DO-decrease, indicated the sensitivity of microorganisms to aeration. Microbial adaptation to decreased oxygen availability is crucial to reach high process performance. This study proposes, a potential aeration mode, which contributes in reduction of energy consumption in BNR systems through wastewater treatment.

Enhancement of simultaneous nitrogen and phosphorus removal using intermittent aeration mechanism

Biological nutrient removal grows into complicated scenario due to the microbial consortium shift and kinetic competition between phosphorus (P)-accumulating and nitrogen (N)-removing microorganisms. In this study, three sequential batch reactors with constant operational conditions except aeration patterns at 6 h cycle periods were tested. Intermittent aeration was applied to develop a robust nutrient removal system aimed to achieve high energy saving and removal efficiency. The results showed higher correspondence of P-uptake, polymeric substance synthesis and glycogen degradation in intermittent-aeration with longer interval periods compared to continuous-aeration. Increasing the intermittent-aeration duration from 25 to 50 min, resulted in higher process performance where the system exhibited approximately 30% higher nutrient removal. This study indicated that nutrient removal strongly depends on reaction phase configuration representing the importance of aeration pattern. The microbial community examined the variation in abundance of bacterial groups in suspended sludge, where the 50 min intermittent aeration, favored the growth of P-accumulating organisms and nitrogen removal microbial groups, indicating the complications related to nutrient removal systems. Successful intermittently aerated process with high capability of simple implementation to conventional systems by elemental retrofitting, is applicable for upgrading wastewater treatment plants. With aeration as a major operational cost, this process is a promising approach to potentially remove nutrients in high competence, in distinction to optimizing cost-efficacy of the system.

Organic carbon bioavailability: Is it a good driver to choose the best biological nitrogen removal process?

Organic carbon can affect the biological nitrogen removal process since the Anammox, heterotrophic and denitrifying bacteria have different affinities and feedback in relation to carbon/nitrogen ratio. Therefore, we reviewed the wastewater carbon concentration, its biodegradability and bioavailability to choose the appropriate nitrogen removal process between conventional (nitrification-denitrification) and Anammox-based process (i.e. integrated with the partial nitritation, nitritation, simultaneous partial nitrification and denitrification or partial-denitrification). This review will cover: (i) strategies to choose the best nitrogen removal route according to the wastewater characteristics in relation to the organic matter bioavailability and biodegradability; (ii) strategies to efficiently remove nitrogen and the remaining carbon from effluent in anammox-based process and its operating cost; (iii) an economic analysis to determine the operational costs of two-units Anammox-based process when compared with the commonly applied one-unit Anammox system (partial-nitritation-Anammox). On this review, a list of alternatives are summarized and explained for different nitrogen and biodegradable organic carbon concentrations, which are the main factors to determine the best treatment process, based on operational and economic terms. In summary, it depends on the wastewater carbon biodegradability, which implies in the wastewater treatment cost. Thus, to apply the conventional nitrification/denitrification process a COD_b/N ratio higher than 3.5 is required to achieve full nitrogen removal efficiency. For an economic point of view, according to the analysis the minimum COD_b/gN for successful nitrogen removal by nitrification/denitrification is 5.8 g. If ratios lower than 3.5 are applied, for successfully higher nitrogen removal rates and the economic feasibility of the treatment, Anammox-based routes can be applied to the wastewater treatment plant.

Adsorption of phosphate onto lanthanum-doped coal fly ash-Blast furnace cement composite

We develop a high-performance adsorbent for phosphate removal from water or wastewater by impregnating lanthanum (La) on a coal fly ash-blast furnace cement composite (La-FACC). The optimized impregnation percentage of La and calcination conditions of the La-FACC were 1% and 800 ℃ for 2 h, respectively. The adsorption kinetics of phosphate onto the La-FACC was well fit by the intra-particle diffusion model, indicating that film and intra-particle diffusion were the rate-controlling step in the adsorption process of phosphate onto the La-FACC. The pseudo second-order kinetic model could also describe the adsorption kinetics of phosphate. Hence, adsorption of phosphate onto the La-FACC occurred mainly via chemisorption. The Langmuir isotherm was appropriate for describing the phosphate adsorption behavior onto the La-FACC. The monolayer maximum adsorption capacity was 24.9 mg-P g^-1. The La-FACC showed high adsorption capacity and selectivity for phosphate with a wide range of pH, and with high concentrations of coexisting ions attributed to both formation of inner sphere complexes and electrostatic interaction. Magnesium ion slightly inhibited the adsorption of phosphate. Hence, the La-FACC developed in this study is a promising adsorbent for water treatment with a wide pH range and high ion strength.

Volatile fatty acids production from waste activated sludge during anaerobic fermentation: The effect of superfine sand

Superfine sand in waste activated sludge (WAS) increased the uncertainty of anaerobic fermentation. Experiments showed that VFAs production from WAS was positively affected by superfine sand, with an increase from 2513 mg COD/L in the control (without superfine sand) to 3002 mg COD/L with superfine sand. A mechanism study demonstrated that the main factor responsible for the improved VFAs accumulation in response to superfine sand was acetic acid, which increased by nearly 30%. Further investigation exhibited that the process of solubilization and acidification were facilitated by superfine sand and the abundance of anaerobic functional microorganisms was greatly increased. Moreover, the activities of acetate kinase (AK) as well as the quantity of AK encoding gene were greatly promoted by superfine sand. The heat release during WAS anaerobic fermentation with superfine sand was higher than that without superfine sand (25.8 × 10^-3 versus 24.7 × 10^-3 W·min at about 70 min).

Comparison of nitrite accumulation performance and microbial community structure in endogenous partial denitrification process with acetate and glucose served as carbon source

Although the combination of endogenous partial denitrification (EPD) and Anammox (EPD-AMX) were developed for deep-level nitrogen removal, the effects of different carbon source were not clear. In this study, the EPD performance was investigated comparatively with acetate (EPD_A) and glucose (EPD_G). Results revealed that through regulating chemical oxygen demand to phosphate ratio, Candidatus_Competibacter was highly enriched in EPD_A (54.2%) and EPD_G (51.3%), resulting high intracellular carbon storage efficiencies (90.2% and 85.3%, respectively). More stable nitrite accumulation was observed in EPD_G than EPD_A. But, higher specific nitrite generated rate (r_NO2, 8.25 > 7.04 mgN·gVSS^-1·h^-1) and nitrate-to-nitrite transformation rate (NTR, 87.9% > 85.2%) were achieved in EPD_A than those in EPD_G. The functional bacterium was also shifted to Defluviicoccus in both EPD_A (30.6%) and EPD_G (25.8%). Moreover, with whether acetate or glucose, the EPD-AMX processes could achieve the same level of total nitrogen removal efficiencies (88.7% and 91.3%, respectively) via anammox mainly (87.8% and 89.4%, respectively).

Phosphorus and ammonium removal characteristics from aqueous solutions by a newly isolated plant growth-promoting bacterium

An indigenous plant growth-promoting bacterium isolated from Peganum Harmala rhizosphere in the arid ecosystem was found to solubilize and accumulate phosphates. This isolate was identified as Pseudomonas sp. (PHR6) by partial 16S rRNA gene sequence analysis. Controlled batch experiments on nutrients removal by this isolate in mineral medium showed relatively high efficiencies after 24 h of aerobic incubation with average values of 117.59 and 335.38 mg gVSS^-1 for phosphorus (P-PO₄) and nitrogen (N-NH₄), respectively. Furthermore, the strain performed heterotrophic nitrification ranging from 48.81% to 84.24% of the total removed nitrogen. On the other hand, the experimental results showed that a short idle period (24 h) significantly enhanced P accumulation (up to 95%) and N assimilation (up to 50%) of the total removed amounts. However, long idle period (20 days) revealed firstly aerobic phosphorous release phase succeeded by another removal one within 24 h of incubation. Overall, the idle treatment enhances P removal efficiency from the mineral liquid medium without significant effects on N-NH₄ removal performance. The isolated strain showed also significant nutrient removal ability from synthetic wastewater providing an accumulated fraction of 98% from the total removed phosphorus amount. This study highlights the potential contribution of the selected rhizobacterium PHR6 to both environmental nutrient recycling and pollution control especially regarding phosphorus.

Norfloxacin-induced effect on enhanced biological phosphorus removal from wastewater after long-term exposure

In this study, long-term experiments were performed under synthetic wastewater conditions to evaluated the potential impacts of norfloxacin (NOR) (10, 100 and 500 μg/L) on enhanced biological phosphorus removal (EBPR). Experimental result showed that long-term exposure to 10 μg/L NOR induced negligible effects on phosphorus removal. The presence of 100 μg/L NOR slightly decreased phosphorus removal efficiency to 94.41 ± 1.59 %. However, when NOR level further increased to 500 μg/L, phosphorus removal efficiency was significantly decreased from 97.96 ± 0.8 5% (control) to 82.33 ± 3.07 %. The mechanism study revealed that the presence of 500 μg/L NOR inhibited anaerobic phosphorus release and acetate uptake as well as aerobic phosphorus uptake during long-term exposure. It was also found that 500 μg/L NOR exposure suppressed the activity of key enzymes related to phosphorus removal but promoted the transformations of intracellular polyhydroxyalkanoate and glycogen. Microbial analysis revealed that that the presence of 500 μg/L NOR reduced the abundances of polyphosphate accumulating organisms but increased glycogen accumulating organisms, as compared the control.

Free nitrous acid-based nitrifying sludge treatment in a two-sludge system obtains high polyhydroxyalkanoates accumulation and satisfied biological nutrients removal

A novel strategy to achieve substantial polyhydroxyalkanoates (PHA) accumulation in waste activated sludge (WAS) was developed, which was conducted in a two-sludge system consisted of an anaerobic/anoxic/oxic reactor (AAO-SBR) and a nitrifying reactor (N-SBR), where the nitrifying-sludge was treated by free nitrous acid (FNA). Initially, 0.98 ± 0.09 and 1.46 ± 0.10 mmol-c/g VSS of PHA were respectively determined in the control-SBR and AAO-SBR. When 1/16 of nitrifying sludge was daily treated with 1.49 mg N/L FNA for 24 h, ∼46.5% of nitrite was accumulated in the N-SBR, ∼2.43 ± 0.12 mmol-c/g VSS of PHA was accumulated in WAS in AAO-SBR without deteriorating nutrient removal. However, nutrient removal of control-SBR was completely collapsed after implementing the same FNA treatment. Further investigations revealed that the activity and abundance of nitrite oxidizing bacteria (NOB) was decreased significantly after FNA treatment. Finally, sludge with high PHA level to generate more methane was confirmed.

Enhanced short-chain fatty acids production from waste activated sludge by sophorolipid: Performance, mechanism, and implication

It was found in this study that the presence of sophorolipid (SL) enhanced the production of short-chain fatty acid (SCFA) from anaerobic fermentation of waste activated sludge (WAS). Experimental results showed that with an increase of SL addition from 0 to 0.1 g/g TSS, the maximal SCFA yield increased from 50.5 ± 4.9 to 246.2 ± 7.5 mg COD/g VSS. The presence of SL reduced the surface tension between hydrophobic organics and fermentation liquid, which thereby accelerated the disintegration of WAS and improved the biodegradability of the released organics. SL promoted the carbon/nitrogen ratio of the fermentation system, enhancing the conversion of proteins in WAS. Moreover, SL suppressed severely the activities of methanogens, probably due to the drop of pH caused by SL addition. Amplicon sequencing analyses revealed that SL increased the abundance of hydrolytic microbes such as Bacteroides sp. and Macellibacteroides sp., and SCFA producers (e.g., Acinetobacter sp.).

New framework for automated article selection applied to a literature review of Enhanced Biological Phosphorus Removal

AIMS

Enhanced Biological Phosphorus Removal (EBPR) is a technology widely used in wastewater treatment to remove phosphorus (P) and prevent eutrophication. Establishing its operating efficiency and stability is an active research field that has generated almost 3000 publications in the last 40 years. Due to its size, including over 119 review articles, it is an example of a field where it becomes increasingly difficult to manually recognize its key research contributions, especially for non-experts or newcomers. Therefore, this work included two distinct but complementary objectives. First, to assemble for the first time a collection of bibliometric techniques into a framework for automating the article selection process when preparing a literature review (section 2). Second, to demonstrate it by applying it to the field of EBPR, producing a bibliometric analysis and a review of the key findings of EBPR research over time (section 3).

FINDINGS

The joint analysis of citation networks, keywords, citation profiles, as well as of specific benchmarks for the identification of highly-cited publications revealed 12 research topics. Their content and evolution could be manually reviewed using a selection of articles consisting of approximately only 5% of the original set of publications. The largest topics addressed the identification of relevant microorganisms, the characterization of their metabolism, including denitrification and the competition between them (Clusters A-D). Emerging and influential topics, as determined by different citation indicators and temporal analysis, were related to volatile fatty acid production, P-recovery from waste activated sludge and aerobic granules for better process efficiency and stability (Clusters F-H).

CONCLUSIONS

The framework enabled key contributions in each of the constituent topics to be highlighted in a way that may have otherwise been biased by conventional citation-based ranking. Further, it reduced the need for manual input and a priori expertise compared to a traditional literature review. Hence, in an era of accelerated production of information and publications, this work contributed to the way that we are able to use computer-aided approaches to curate information and manage knowledge.

Population Structure and Morphotype Analysis of "Candidatus Accumulibacter" Using Fluorescence In Situ Hybridization-Staining-Flow Cytometry

"Candidatus Accumulibacter" is the dominant polyphosphate-accumulating organism (PAO) in denitrifying phosphorus removal (DPR) systems. In order to investigate the community structure and clade morphotypes of "Candidatus Accumulibacter" in DPR systems through flow cytometry (FCM), denitrifying phosphorus removal of almost 100% using nitrite and nitrate as the electron acceptor was achieved in sequencing batch reactors (SBRs). An optimal method of flow cytometry combined with fluorescence in situ hybridization and SYBR green I staining (FISH-staining-flow cytometry) was developed to quantify PAOs in DPR systems. By setting the width value of FCM, bacterial cells in a sludge sample were divided into three groups in different morphotypes, namely, coccus, coccobacillus, and bacillus. Average percentages that the three different PAO populations accounted for among total bacteria from SBR1 (SBR2) were 42% (45%), 14% (13%), and 4% (2%). FCM showed that the ratios of PAOs to total bacteria in the two reactors were 61% and 59%, and the quantitative PCR (qPCR) results indicated that IIC was the dominant "Candidatus Accumulibacter" clade in both denitrifying phosphorus removal systems, reaching 50% of the total "Candidatus Accumulibacter" bacteria. The subdominant clade in the reactor with nitrite as the electron acceptor was IID, accounting for 31% of the total "Candidatus Accumulibacter" bacteria. The FCM and qPCR results suggested that clades IIC and IID were both coccus, clade IIF was coccobacillus, and clade IA was bacillus. FISH analysis also indicated that PAOs were major cocci in the systems. An equivalence test of FCM-based quantification confirmed the accuracy of FISH-staining-flow cytometry, which can meet the quantitative requirements for PAOs in complex activated sludge samples.IMPORTANCE As one group of the most important functional phosphorus removal organisms, "Candidatus Accumulibacter," affiliated with the Rhodocyclus group of the Betaproteobacteria, is a widely recognized and studied PAO in the field of biological wastewater treatment. The morphotypes and population structure of clade-level "Candidatus Accumulibacter" were studied through novel FISH-staining-flow cytometry, which involved denitrifying phosphorus removal (DPR) achieving carbon and energy savings and simultaneous removal of N and P, thus inferring the different denitrifying phosphorus removal abilities of these clades. Additionally, based on this method, in situ quantification for specific polyphosphate-accumulating organisms (PAOs) enables a more efficient process and more accurate result. The establishment of FISH-staining-flow cytometry makes cell sorting of clade-level noncultivated organisms available.

Free ammonia-based pretreatment enhances phosphorus release and recovery from waste activated sludge

The recovery of phosphorus from waste activated sludge (WAS) was usually at low levels due to low phosphorus release. This study presents a novel, cost-effective and eco-friendly pretreatment method, e.g., using free ammonia (FA) to pretreat WAS, to enhance the phosphorus release from WAS. Experimental results showed that the phosphorus release from WAS was significantly increased after FA pretreatment at up to 189.4 mg NH₃-N L^-1 for 24 h, under which the released PO₄^3--P (i.e. 101.6 ± 6.7 mg L^-1) was higher than that pH 9 (i.e. 62.6 ± 4.54 mg L^-1) and control (without pH and FA pretreatment) (i.e. 15.1 ± 1.86 mg L^-1). More analysis revealed that the FA induced improvement in phosphorus release could be attributed to the disintegration of extracellular polymeric substances (EPS) and cell envelope of sludge cells. Moreover, the released phosphorus recovered as magnesium ammonium phosphate (MAP) was confirmed. The findings reported may guide engineers to develop an economic and practical strategy to enhance resources and energy recovery from WAS.

Free nitrous acid promotes hydrogen production from dark fermentation of waste activated sludge

Simultaneous sludge fermentation and nitrite removal is an effective approach to enhance nutrient removal from low carbon-wastewater. It was found in this work that the presence of nitrite largely promoted hydrogen production from acidic fermentation of waste activated sludge (WAS). The results showed that with an increase of nitrite from 0 to 250 mg/L, the maximal hydrogen yield increased from 8.5 to 15.0 mL/g VSS at pH 5.5 fermentation and 8.1-13.0 mL/g VSS at pH 6 fermentation. However, the maximal hydrogen yield from WAS fermentation at pH 8 remained almost constant (2.9-3.7 mL/g VSS) when nitrite was in the range of 0-250 mg/L. Further analyses revealed that free nitrous acid (FNA) rather than nitrite was the major contributor to the promotion of hydrogen yield. The mechanism investigations showed that FNA not only accelerated the disruption of sludge cells but also promoted the biodegradability of organics released, thereby provided more biodegradable substrates for subsequent hydrogen production. Although FNA inhibited activities of all microbes involved in the anaerobic fermentation, its inhibitions to hydrogen consumers were much severer than those to hydrolytic microorganisms and hydrogen producers. Further investigations with microbial community showed that FNA increased the abundances of hydrogen producers (e.g., Citrobacter sp.) and denitrifiers (e.g., Dechloromonas sp.), but reduced the abundances of hydrogen consumers (e.g., Clostridium_aceticum). This work demonstrated for the first time that FNA in WAS fermentation systems enhanced hydrogen production. The findings obtained expand the application field of FNA and may provide supports for sustainable operation of wastewater treatment plants.

Feasibility of enhancing short-chain fatty acids production from waste activated sludge after free ammonia pretreatment: Role and significance of rhamnolipid

This study reported a new, renewable and high-efficient strategy for anaerobic fermentation, i.e., using free ammonia (FA) to pretreat waste activated sludge (WAS) for 1 d and then combining with rhamnolipid (RL), by which the short-chain fatty acids (SCFA) production was remarkably improved. Experimental results showed the maximal SCFA production of 324.7 ± 13.9 mg COD/g VSS was achieved at 62.6 mg FA/L pretreatment combined with 0.04 g RL/g TSS, which was respectively 5.95-fold, 1.63-fold and 1.41-fold of that from control, FA pretreatment and RL pretreatment. Mechanism investigations revealed that FA + RL enhanced sludge solubilization and hydrolysis, providing more organics for subsequent SCFA production. It was also found that the combined method inhibited acidogenesis and methanogenesis, but the inhibition to methanogenesis was much severer than that to acidogenesis. Finally, the feasibility of NH₄⁺-N and PO^3-₄-P, released in fermentation liquor, being recovered as magnesium ammonium phosphate (MAP) was confirmed.

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.

Free ammonia-based sludge treatment reduces sludge production in the wastewater treatment process

Excessive sludge production is one of the major challenges for biological wastewater treatment plants. This paper reports a new strategy to enhance sludge reduction from the wastewater treatment process. In this strategy, 1/5 of the sludge is withdrawn from the mainstream reactor into a side-stream unit for sludge treatment with 16 mg/L free ammonia (FA) for 24-40 h. The FA-treated sludge mixture is then returned to the mainstream reactor. To demonstrate this concept, two reactors treating synthetic domestic wastewater were operated, with one serving as the experimental reactor and the other as the control. Experimental results showed that the experimental reactor exhibited 20% lower in sludge production than the control. FA treatment effectively disintegrated a portion of extracellular or intracellular substances of sludge cells in the FA treatment unit and lowered the observed sludge yields in the mainstream reactor, which were the main reasons for the sludge reduction. Although FA treatment decreased the activities of nitrifiers, denitrifiers, and polyphosphate accumulating organisms in the FA treatment unit, this strategy did not negatively affect the reactor performance and sludge properties of the experimental reactor such as sludge settleability, organic removal, nitrogen removal and phosphorus removal. Further investigation showed that the organics released from the FA treatment process could be used by PAOs and denitrifiers for carbon sources.

Effect of acetate to glycerol ratio on enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is a sustainable and promising technology for phosphorus removal from wastewater. The efficiency of this technology, however, is often discounted due to the insufficient carbon sources in influent. In this work, the effect of acetate to glycerol ratio on the EBPR performance was evaluated. The experimental results showed when the ratio of acetate to glycerol decreased from 100/0% to 50/50%, the EBPR efficiency increased from 90.2% to 96.2%. Further decrease of acetate to glycerol ratio to 0/100% decreased the efficiency of EBPR to 30.5%. Fluorescence in situ hybridization analysis demonstrated appropriate increase of glycerol benefited to increase the relative abundance of phosphate accumulating organisms. Further investigation revealed the proper addition of glycerol increased the amount of polyhydroxyalkanoates synthesis, and then produced sufficient energy for oxic luxury phosphorus in the subsequent oxic phase.

The acute effects of erythromycin and oxytetracycline on enhanced biological phosphorus removal system: shift in bacterial community structure

Since extensive application, an increasing amount of antibiotics has been released into wastewater treatment plants. In this study, the enhanced biological phosphorus removal (EBPR) system was fed with synthetic wastewater containing erythromycin (ERY) and oxytetracycline (OTC) for 7 days to evaluate the variations of solution ortho-P (SOP), volatile fatty acid (VFA), poly-bhydroxyalkanoates (PHAs), specific oxygen uptake rater (SOUR), and microbial community in the EBPR system. The obtained results showed that the P-removal efficiency decreased to 0.0%, and at the end of the experiment, only less than 20% of the VFA could be consumed. Besides, the variable processes of P and PHAs were destroyed. Moreover, to better grasp the inhibitory mechanism of antibiotics, microbial community compositions of activated sludge sampled in all reactors were investigated by high-throughput sequencing techniques. Results of comparative and evolutionary analysis revealed that high concentrations (5 and 10 mg/L) of ERY and OTC could seriously shift microbial communities, while combined antibiotics could induce more. Additionally, Accumulibacter and Competibacter were two primary microorganisms at the genus level in the EBPR system. Accumulibacter decreased seriously for exposure to antibiotics, while Competibacter increased in all experimental reactors especially in combined antibiotics reactor.

Understanding the impact of cationic polyacrylamide on anaerobic digestion of waste activated sludge

Previous investigations showed that cationic polyacrylamide (cPAM), a flocculant widely used in wastewater pretreatment and waste activated sludge dewatering, deteriorated methane production during anaerobic digestion of sludge. However, details of how cPAM affects methane production are poorly understood, hindering deep control of sludge anaerobic digestion systems. In this study, the mechanisms of cPAM affecting sludge anaerobic digestion were investigated in batch and long-term tests using either real sludge or synthetic wastewaters as the digestion substrates. Experimental results showed that the presence of cPAM not only slowed the process of anaerobic digestion but also decreased methane yield. The maximal methane yield decreased from 139.1 to 86.7 mL/g of volatile suspended solids (i.e., 1861.5 to 1187.0 mL/L) with the cPAM level increasing from 0 to 12 g/kg of total suspended solids (i.e., 0-236.7 mg/L), whereas the corresponding digestion time increased from 22 to 26 d. Mechanism explorations revealed that the addition of cPAM significantly restrained the sludge solubilization, hydrolysis, acidogenesis, and methanogenesis processes. It was found that ∼46% of cAPM was degraded in the anaerobic digestion, and the degradation products significantly affected methane production. Although the theoretically biochemical methane potential of cPAM is higher than that of protein and carbohydrate, only 6.7% of the degraded cPAM was transformed to the final product, methane. Acrylamide, acrylic acid, and polyacrylic acid were found to be the main degradation metabolites, and their amount accounted for ∼50% of the degraded cPAM. Further investigations showed that polyacrylic acid inhibited all the solubilization, hydrolysis, acidogenesis, and methanogenesis processes while acrylamide and acrylic acid inhibited the methanogenesis significantly.

The feasibility of enhanced biological phosphorus removal in the novel oxic/extended idle process using fermentation liquid from sludge fermentation

Carbon sources are essential for biological phosphorus removal (BPR); the carbon sources, however, are often inadequate in municipal wastewater treatment plants. This study demonstrated the feasibility of sludge fermentation liquid enhanced by biosurfactant alkylpolyglycosides (APG) as carbon sources to improve the performance of BPR in the novel oxic/extended idle (O/EI) reactor and the underlying mechanism was also investigated. The results showed that APG induced fermentation liquid could enhance the BPR performance in the O/EI reactor, and the BPR efficiency was 95.2%, which was significantly higher than that in the conventional anaerobic/oxic (A/O) reactor. Mechanism investigation showed that compared with the A/O reactor, the O/EI reactor enriched more polyphosphate accumulating organisms (PAOs) (38.2%), but less glycogen accumulating organisms (GAOs) when the APG-induced fermentation liquid was used as carbon source. The transformations of the polyhydroxyalkanoates (PHA) and glycogen in the O/EI reactor were lower than those in the A/O reactor. Further study found that the activities of polyphosphate kinase (PPK) and acetyl-CoA synthases (ACS) in the O/EI reactor were significantly higher than those of the A/O reactor, which was consistent with the higher BPR efficiency in the O/EI reactor.

Long-term effect of fermented liquid as carbon source on effluent COD and SOP in O/EI reactor.

Effect of ciprofloxacin on biological nitrogen and phosphorus removal from wastewater

In this work, both short-term and long-term experiments were therefore conducted to assess the effects of ciprofloxacin (0.2 and 2mg·L^-1) on wastewater nutrient removal. The results showed that both levels of ciprofloxacin had no acute and chronic adverse effects on the surface integrity and viability of activated sludge. Short-term exposure to all the ciprofloxacin levels induced negligible influences on wastewater nutrient removal. However, the prolonged exposure to ciprofloxacin decreased total phosphorus and nitrogen removal efficiencies from 96.8, 95.8% (control) to 91.7, 84.9% (0.2mg·L^-1) and 90.5%, 80.2% (2mg·L^-1), respectively. The mechanism study showed that ciprofloxacin exposure suppressed denitrification and phosphorus uptake processes. It was also found that ciprofloxacin affected the transformations of intracellular polyhydroxyalkanoates and glycogen in the oxic and anoxic stages. Moreover the activities of nitrite reductase and polyphosphate kinase were inhibited by the presence of ciprofloxacin. Further analysis with high-throughput sequencing revealed that compared with the control, the abundances of polyphosphate accumulating organisms, glycogen accumulating organisms and denitrifying bacteria in ciprofloxacin exposure reactors reduced, which were consistent with the decreased nutrient removal performance measured in these reactors.

The roles of loosely-bound and tightly-bound extracellular polymer substances in enhanced biological phosphorus removal

Extracellular polymeric substances (EPS) have be founded to participate in the process of enhanced biological phosphorus removal (EBPR), but the exact role of EPS in EBPR process is unclear. In this work, the roles of loosely-bound EPS (LB-EPS), tightly-bound EPS (TB-EPS) and microbial cell in EBPR were explored, taking the activated sludge from 4 lab-scale A/O-SBR reactors with different temperatures and organic substrates as objects. It was founded that the P of EBPR activated sludge was mainly stored in TB-EPS, but the P of non-EBPR activated sludge was primarily located in microbial cell. The P release and uptake of EBPR activated sludge was attributed to the combined action of TB-EPS and microbial cell. Furthermore, TB-EPS played an more important role than microbial cell in EBPR process. With the analysis of ³¹P NMR spectroscopy, both polyP and orthoP were the main phosphorus species of TB-EPS in EBPR sludge, but only orthoP was the main phosphorus species of LB-EPS and microbial cell. During the anaerobic-aerobic cycle, the roles of LB-EPS, TB-EPS and microbial cell in transfer and transformation of P in EBPR sludge were obviously different. LB-EPS transported and retained orthoP, and microbial cell directly anaerobically released or aerobically absorbed orthoP. Importantly, TB-EPS not only transported and retained orthoP, but also participated in biological phosphorus accumulation. The EBPR performance of sludge was closely related with the polyp in TB-EPS, which might be synthesized and decomposed by extracellular enzyme.

Free nitrous acid-based nitrifying sludge treatment in a two-sludge system enhances nutrient removal from low-carbon wastewater

A new method to enhance nutrient removal from low carbon-wastewater was developed. The method consists of a two-sludge system (i.e., an anaerobic-anoxic-oxic reactor coupled to a nitrifying reactor (N-SBR)) and a nitrifying-sludge treatment unit using free nitrous acid (FNA). Initially, 65.1±2.9% in total nitrogen removal and 69.6±3.4% in phosphate removal were obtained without nitrite accumulation. When 1/16 of the nitrifying sludge was daily treated with FNA at 1.1mgN/L for 24h, ∼28.5% of nitrite was accumulated in the N-SBR, and total nitrogen and phosphate removal increased to 72.4±3.2% and 76.7±2.9%, respectively. About 67.8% of nitrite was accumulated at 1.9mgN/L FNA, resulting in 82.9±3.8% in total nitrogen removal and 87.9±3.5% in phosphate removal. Fluorescence in-situ hybridization analysis showed that FNA treatment reduced the abundance of nitrite oxidizing bacteria (NOB), especially that of Nitrospira sp.

Aged refuse enhances anaerobic digestion of waste activated sludge

In this work, a low-cost alternative approach (i.e., adding aged refuse (AR) into waste activated sludge) to significantly enhance anaerobic digestion of sludge was reported. Experimental results showed that with the addition dosage of AR increasing from 0 to 400 mg/g dry sludge soluble chemical oxygen demand (COD) increased from 1150 to 5240 mg/L at the digestion time of 5 d, while the maximal production of volatile fatty acids (VFA) increased from 82.6 to 183.9 mg COD/g volatile suspended solids. Although further increase of AR addition decreased the concentrations of both soluble COD and VFA, their contents in these systems with AR addition at any concentration investigated were still higher than those in the blank, which resulted in higher methane yields in these systems. Mechanism studies revealed that pertinent addition of AR promoted solubilization, hydrolysis, and acidogenesis processes and did not affect methanogenesis significantly. It was found that varieties of enzymes and anaerobes in AR were primary reason for the enhancement of anaerobic digestion. Humic substances in AR benefited hydrolysis and acidogenesis but inhibited methanogenesis. The effect of heavy metals in AR on sludge anaerobic digestion was dosage dependent. Sludge anaerobic digestion was enhanced by appropriate amounts of heavy metals but inhibited by excessive amounts of heavy metals. The relative abundances of microorganisms responsible for sludge hydrolysis and acidogenesis were also observed to be improved in the system with AR addition, which was consistent with the performance of anaerobic digestion.

Approach of describing dynamic production of volatile fatty acids from sludge alkaline fermentation

In this work, a mathematical model was developed to describe the dynamics of fermentation products in sludge alkaline fermentation systems for the first time. In this model, the impacts of alkaline fermentation on sludge disintegration, hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes are specifically considered for describing the high-level formation of fermentation products. The model proposed successfully reproduced the experimental data obtained from five independent sludge alkaline fermentation studies. The modeling results showed that alkaline fermentation largely facilitated the disintegration, acidogenesis, and acetogenesis processes and severely inhibited methanogenesis process. With the pH increase from 7.0 to 10.0, the disintegration, acidogenesis, and acetogenesis processes respectively increased by 53%, 1030%, and 30% while methane production decreased by 3800%. However, no substantial effect on hydrolysis process was found. The model also indicated that the pathway of acetoclastic methanogenesis was more severely inhibited by alkaline condition than that of hydrogentrophic methanogenesis.

Effects of different ratios of glucose to acetate on phosphorus removal and microbial community of enhanced biological phosphorus removal (EBPR) system

In this study, the effects of different ratios of glucose to acetate on enhanced biological phosphorus removal (EBPR) were investigated with regard to the changes of intercellular polyhydroxyalkanoates (PHAs) and glycogen, as well as microbial community. The experiments were carried out in five sequencing batch reactors (SBRs) fed with glucose and/or acetate as carbon sources at the ratios of 0:100 %, 25:75 %, 50:50 %, 75:25 %, and 100:0 %. The experimental results showed that a highest phosphorus removal efficiency of 96.3 % was obtained with a mixture of glucose and acetate at the ratio of 50:50 %, which should be attributed to more glycogen and polyhydroxyvalerate (PHV) transformation in this reactor during the anaerobic condition. PCR-denaturing gradient gel electrophoresis (DGGE) analysis of sludge samples taken from different anaerobic/aerobic (A/O) SBRs revealed that microbial community structures were distinctively different with a low similarity between each other.

The behavior of melamine in biological wastewater treatment system

Melamine (MA) is a significant raw material for industry and home furnishing, and an intermediate for pharmacy. However it is also a hazardous material when being added to food as a protein substitute due to the high nitrogen content. In this study, the behavior of MA in activated sludge was investigated. Experiments showed that MA was removed during biological wastewater treatment process, and the removal was mainly achieved by activated sludge adsorption instead of biodegradation. Low levels of MA (0.001-0.10mg/L) in wastewater had negligible influence on the performance of activated sludge, but high levels of MA deteriorated biological nitrogen and phosphorus removal. The presence of MA (1.00 and 5.00mg/L) decreased total nitrogen removal efficiency from 94.15% to 79.47% and 68.04%, respectively. The corresponding concentration of effluent phosphorus increased from 0.11 to 1.45 and 2.06mg/L, respectively. It was also observed that MA inhibited the enzyme activities of nitrite oxidoreductase, nitrate reductase, nitrite reductase and exopolyphosphatase, which were closely relevant to nitrogen and phosphorus removal. Further investigation showed that the presence of high MA concentrations promoted the consumption and synthesis of glycogen, thereby providing the advantage for the growth of glycogen accumulating organisms.

Effect of nickel on the flocculability, settleability, and dewaterability of activated sludge

Short-term and long-term effects of nickel (Ni) (0.1-10mg/L) on the physicochemical properties of activated sludge, including the flocculability, settleability, and dewaterability, were investigated. It was found that these properties were unaffected after short-term exposure (1day) to Ni(II) even at the level of 10mg/L. After long-term exposure (60days) to 1 and 10mg/L of Ni(II), however, the sludge flocculability has seriously deteriorated, while the settleability, and dewaterability became gradually better than the control. The mechanism studies revealed that long-term exposure to Ni(II) resulted in the decrease of protein content in extracellular polymeric substances (EPS) and the damage to EPS structures. Although Ni(II) did not bring any adverse effect on the cell membrane, the relative hydrophobicity of activated sludge was significantly decreased. The negative effects on the flocculability and phosphorus removal performance of activated sludge could be completely eliminated by adding the chelator such as EDTA and citrate.

Influence of carbon sources on nutrient removal in A2/O-MBRs: Availability assessment of internal carbon source

Both internal carbon source and some external carbon sources were used to improve the nutrient removal in Anaerobic-Anoxic-Oxic-Membrane Bioreactor (A²/O-MBRs), and their technical and cost analysis was investigated. The experimental results showed that the nutrient removals were improved by all the carbon source additions. The total nitrogen and phosphorus removal efficiency were higher in the experiments with external carbon source additions than that with internal carbon source addition. It was found that pathways of nitrogen and phosphorus transform were different dependent on different carbon source additions by the mass balance analysis. With external carbon source addition, the simultaneous nitrification and denitrification occurred in aerobic zone, and the P-uptake in aerobic phase was evident. Therefore, with addition of C-MHP (internal carbon source produced from sludge pretreatment by microwave-H₂O₂ process), the denitrification and phosphorus-uptake in anoxic zone was notable. Cost analysis showed that the unit nitrogen removal costs were 57.13CNY/kg N of C-acetate addition and 54.48CNY/kgN of C-MHP addition, respectively. The results indicated that the C-MHP has a good technical and economic feasibility to substitute external carbon sources partially for nutrient removal.

Polyhydroxyalkanoates in waste activated sludge enhances anaerobic methane production through improving biochemical methane potential instead of hydrolysis rate

Anaerobic sludge digestion is the main technology for sludge reduction and stabilization prior to sludge disposal. Nevertheless, methane production from anaerobic digestion of waste activated sludge (WAS) is often restricted by the poor biochemical methane potential and slow hydrolysis rate of WAS. This work systematically investigated the effect of PHA levels of WAS on anaerobic methane production, using both experimental and mathematical modeling approaches. Biochemical methane potential tests showed that methane production increased with increased PHA levels in WAS. Model-based analysis suggested that the PHA-based method enhanced methane production by improving biochemical methane potential of WAS, with the highest enhancement being around 40% (from 192 to 274 L CH₄/kg VS added; VS: volatile solid) when the PHA levels increased from 21 to 143 mg/g VS. In contrast, the hydrolysis rate (approximately 0.10 d⁻¹) was not significantly affected by the PHA levels. Economic analysis suggested that the PHA-based method could save $1.2/PE/y (PE: population equivalent) in a typical wastewater treatment plant (WWTP). The PHA-based method can be easily integrated into the current WWTP to enhance methane production, thereby providing a strong support to the on-going paradigm shift in wastewater management from pollutant removal to resource recovery.

Simultaneous denitrification and denitrifying phosphorus removal in a full-scale anoxic-oxic process without internal recycle treating low strength wastewater

Performance of a full-scale anoxic-oxic activated sludge treatment plant (4.0×10(5) m(3)/day for the first-stage project) was followed during a year. The plant performed well for the removal of carbon, nitrogen and phosphorus in the process of treating domestic wastewater within a temperature range of 10.8°C to 30.5°C. Mass balance calculations indicated that COD utilization mainly occurred in the anoxic phase, accounting for 88.2% of total COD removal. Ammonia nitrogen removal occurred 13.71% in the anoxic zones and 78.77% in the aerobic zones. The contribution of anoxic zones to total nitrogen (TN) removal was 57.41%. Results indicated that nitrogen elimination in the oxic tanks was mainly contributed by simultaneous nitrification and denitrification (SND). The reduction of phosphorus mainly took place in the oxic zones, 61.46% of the total removal. Denitrifying phosphorus removal was achieved biologically by 11.29%. Practical experience proved that adaptability to gradually changing temperature of the microbial populations was important to maintain the plant overall stability. Sudden changes in temperature did not cause paralysis of the system just lower removal efficiency, which could be explained by functional redundancy of microorganisms that may compensate the adverse effects of temperature changes to a certain degree. Anoxic-oxic process without internal recycling has great potential to treat low strength wastewater (i.e., TN<35 mg/L) as well as reducing operation costs.

Improved biological phosphorus removal induced by an oxic/extended-idle process using glycerol and acetate at equal fractions

Variations of effluent SOP concentration and SOP removal efficiency in O/EI reactor during long-term operation.

Roles of extracellular polymeric substances in enhanced biological phosphorus removal process

Enhanced biological phosphorus removal (EBPR) process is known to mainly rely on the ability of phosphorus-accumulating organisms to take up, transform and store excess amount of phosphorus (P) inside the cells. However, recent studies have revealed considerable accumulation of P also in the extracellular polymeric substances (EPS) of sludge, implying a non-negligible role of EPS in P removal by EBPR sludge. However, the contribution of EPS to P uptake and the forms of accumulated extracellular P vary substantially in different studies, and the underlying mechanism of P transformation and transportation in EPS remains poorly understood. This review provides a new recognition into the P removal process in EBPR system by incorporating the role of EPS. It overviews on the characteristics of P accumulation in EPS, explores the mechanism of P transformation and transportation in EBPR sludge and EPS, summarizes the main influential factors for the P-accumulation properties of EPS, and discusses the remaining knowledge gaps and needed future efforts that may lead to better understanding and use of such an EPS role for maximizing P recovery from wastewater.

How Does Poly(hydroxyalkanoate) Affect Methane Production from the Anaerobic Digestion of Waste-Activated Sludge?

Recent studies demonstrate that, besides being used for production of biodegradable plastics, poly(hydroxyalkanoate) (PHA) that is accumulated in heterotrophic microorganisms during wastewater treatment has another novel application direction, i.e., being utilized for enhancing methane yield during the anaerobic digestion of waste-activated sludge (WAS). To date, however, the underlying mechanism of how PHA affects methane production remains largely unknown, and this limits optimization and application of the strategy. This study therefore aims to fill this knowledge gap. Experimental results showed that with the increase of sludge PHA levels from 21 to 184 mg/g of volatile suspended solids (VSS) the methane yield linearly increased from 168.0 to 246.1 mL/g of VSS (R(2) = 0.9834). Compared with protein and carbohydrate (the main components of a cell), PHA exhibited a higher biochemical methane potential on a unit VSS basis. It was also found that the increased PHA not only enhanced cell disruption of PHA cells but also benefited the soluble protein conversion of both PHA- and non-PHA cells. Moreover, the reactor fed with higher PHA sludge showed greater sludge hydrolysis and acidification than those fed with the lower PHA sludges. Further investigations using fluorescence in situ hybridization and enzyme analysis revealed that the increased PHA enhanced the abundance of methanogenic Archaea and increased the activities of protease, acetate kinase, and coenzyme F420, which were consistent with the observed methane yield. This work provides insights into PHA-involved WAS digestion systems and may have important implications for future operation of wastewater treatment plants.

Free nitrous acid serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge

Alkaline condition (especially pH 10) has been demonstrated to be a promising method for short-chain fatty acid (SCFA) production from waste activated sludge anaerobic fermentation, because it can effectively inhibit the activities of methanogens. However, due to the limit of sludge solubilization rate, long fermentation time is required but SCFA yield is still limited. This paper reports a new pretreatment method for alkaline fermentation, i.e., using free nitrous acid (FNA) to pretreat sludge for 2 d, by which the fermentation time is remarkably shortened and meanwhile the SCFA production is significantly enhanced. Experimental results showed the highest SCFA production of 370.1 mg COD/g VSS (volatile suspended solids) was achieved at 1.54 mg FNA/L pretreatment integration with 2 d of pH 10 fermentation, which was 4.7- and 1.5-fold of that in the blank (uncontrolled) and sole pH 10 systems, respectively. The total time of this integration system was only 4 d, whereas the corresponding time was 15 d in the blank and 8 d in the sole pH 10 systems. The mechanism study showed that compared with pH 10, FNA pretreatment accelerated disruption of both extracellular polymeric substances and cell envelope. After FNA pretreatment, pH 10 treatment (1 d) caused 38.0% higher substrate solubilization than the sole FNA, which indicated that FNA integration with pH 10 could cause positive synergy on sludge solubilization. It was also observed that this integration method benefited hydrolysis and acidification processes. Therefore, more SCFA was produced, but less fermentation time was required in the integrated system.

Interaction between phosphorus removal and hybrid granular sludge formation under low hydraulic selection pressure at alternating anaerobic/aerobic conditions

The hybrid granular sludge (HGS) formation and its performances on phosphorus removal were investigated in a sequencing batch airlift reactor. Under conditions of low superficial air velocity (SAV = 0.68 cm s(-1)) and relatively long settling time (15-30 min), aerobic granules appeared and coexisted with bio-flocs after 120 days operation. At the stable phase, 54% of total suspended solid (m/m) was granular sludge with the two typical sizes (D(mean) = 1.77 ± 0.33 and 0.89 ± 0.11 mm) in the reactor, where the settling velocity was 98.7 ± 12.4 and 37.8 ± 0.9 m h(-1) for the big and small granules. With progressive extension of anaerobic time from 15 to 60 min before aerobic condition per cycle during the whole experiment, the HGS system can be maintained at a high total phosphorus removal efficiency (ca. 99%) since Day-270. The phosphorus content (wt %) in biomass was respectively 9.54 ± 0.29, 7.60 ± 0.48 and 6.15 ± 0.59 for the big granules, small granules and flocs.

Enhancement of post-anoxic denitrification for biological nutrient removal: effect of different carbon sources

Previous research has demonstrated that post-anoxic denitrification and biological nutrient removal could be achieved in the oxic/anoxic/extended-idle wastewater treatment regime. This study further investigated the effect of different carbon sources on post-anoxic denitrification and biological nutrient removal. Acetate, propionate (volatile fatty acids (VFAs)), glucose (carbohydrate), methanol, and ethanol (alcohol) were used as the sole carbon source, respectively. The experimental results showed that VFA substrates led to an improvement in nitrogen and phosphorus removal. The total nitrogen and phosphorus removal efficiency values driven by acetate achieved 93 and 99%, respectively. In contrast, glucose present in mixed liquor deteriorated total nitrogen and phosphorus removal efficiency values to 72 and 54%. In the reactors cultured with methanol and ethanol, 66 and 63% of the total nitrogen were removed, and phosphorus removal efficiency values were 78 and 71%, respectively. The mechanism studies revealed that different carbon sources affected the transformations of intracellular polyhydroxyalkanoates (PHAs) and glycogen. PHAs are the dominant storages for microorganisms cultured with VFA substrates. Though glycogen is not the favorable energy and carbon source for polyphosphate-accumulating organisms, it can be consumed by microorganisms related to biological nitrogen removal and is able to serve as the electron donor for post-anoxic denitrification.

An efficient process for wastewater treatment to mitigate free nitrous acid generation and its inhibition on biological phosphorus removal

Free nitrous acid (FNA), which is the protonated form of nitrite and inevitably produced during biological nitrogen removal, has been demonstrated to strongly inhibit the activity of polyphosphate accumulating organisms (PAOs). Herein we reported an efficient process for wastewater treatment, i.e., the oxic/anoxic/oxic/extended-idle process to mitigate the generation of FNA and its inhibition on PAOs. The results showed that this new process enriched more PAOs which thereby achieved higher phosphorus removal efficiency than the conventional four-step (i.e., anaerobic/oxic/anoxic/oxic) biological nutrient removal process (41 ± 7% versus 30 ± 5% in abundance of PAOs and 97 ± 0.73% versus 82 ± 1.2% in efficiency of phosphorus removal). It was found that this new process increased pH value but decreased nitrite accumulation, resulting in the decreased FNA generation. Further experiments showed that the new process could alleviate the inhibition of FNA on the metabolisms of PAOs even under the same FNA concentration.

Performance of wastewater biological phosphorus removal under long-term exposure to CuNPs: adapting toxicity via microbial community structure adjustment

Copper nanoparticles (CuNPs) have been used in a wide range of applications, and the released CuNPs entering wastewater treatment plants (WWTP) might pose potential risks to the wastewater biological treatment process, such as phosphorus removal.