The effect of propionic to acetic acid ratio on anaerobic-aerobic (low dissolved oxygen) biological phosphorus and nitrogen removal

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq- > •OH > 1O2 > •O2- > ONOO-, while the contribution order to microcystin-LR degradation was eaq- > •OH > •O2- > 1O2 > ONOO-. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

The modified properties of sludge-based biochar with ferric sulfate and its effectiveness in promoting carbon release from particulate organic matter in rural household wastewater

The scarcity of carbon sources presents a significant challenge for the bio-treatment of rural domestic wastewater (RDW). This paper presented an innovative approach to address this issue by investigating the supplementary carbon source through in-situ degradation of particulate organic matter (POM) facilitated by ferric sulfate modified sludge-based biochar (SBC). To prepare SBC, five different contents of ferric sulfate (0%, 10%, 20%, 25%, and 33.3%) were added to sewage sludge. The results revealed that the pore and surface of SBC were enhanced, providing active sites and functional groups to accelerate the biodegradation of protein and polysaccharide. During the 8-day hydrolysis period, the concentration of soluble chemical oxidation demand (SCOD) increased and peaked (1087-1156 mg L^-1) on the fourth day. The C/N ratio increased from 3.50 (control) to 5.39 (25% ferric sulfate). POM was degraded the five dominant phyla, which were Actinobacteriota, Firmicutes, Synergistota, Proteobacteria, and Bacteroidetes. Although the relative abundance of dominant phyla changed, the metabolic pathway remained unchanged. The leachate of SBC (<20% ferric sulfate) was beneficial for microbes, but an excessive amount of ferric sulfate (33.3% ferric sulfate) could have inhibition effects on bacteria. In conclusion, ferric sulfate modified SBC holds the potential for the carbon degradation of POM in RDW, and further improvements should be made in future studies.

Mechanism of dielectric barrier plasma technology to improve the quantity and quality of short chain fatty acids in anaerobic fermentation of cyanobacteria

The recycling of high value carbon resources from cyanobacteria has become a research hotspot. This work investigated the possibility of dielectric barrier discharge (DBD) plasma pretreatment to improve the anaerobic fermentation performance of cyanobacteria. The maximum accumulations of short-chain fatty acids (SCFAs) and acetic acid in DBD group were 3.30 and 1.49 times of that in control group. The physical effects of DBD plasma and the oxidative stress response of cyanobacteria cells could improve the solubilization of cyanobacteria polymer. The destruction of humus by DBD plasma can reduce the negative impact of humus on the early stage of anaerobic fermentation, thus facilitating the rapid start of anaerobic fermentation. The contents of Bacteroidetes, Firmicutes and Chloroflexi in DBD group were higher than those in control group, while the content of Proteobacteria was on the contrary, which was conducive to the hydrolysis and acidification process. The decrease of Methanosaeta sp. and Methanosarcina sp. abundance in DBD group might be another reason for the increase of acetic acid ratio. Under the joint action of plasma chemical oxidation and microbial degradation, the degradation effect of microcystin-LR in the anaerobic fermentation supernatant of DBD group was better than that of the control group, which was conducive to the recycling of cyanobacteria anaerobic fermentation supernatant. Therefore, DBD pretreatment was conductive to recycling valuable carbon source from cyanobacteria and can be further developed as a potential new pretreatment technology.

Mechanism of dielectric barrier discharge plasma technology to improve the quantity of short-chain fatty acids in anaerobic fermentation of waste active sludge

The mechanism of improving the anaerobic fermentation performance of waste active sludge by using dielectric barrier discharge (DBD) plasma pretreatment technology was investigated. The maximum accumulation of short-chain fatty acids (SCFAs) was observed on the 7th day of anaerobic fermentation when the DBD power was 76.50 W, which was 1726.70 mg COD/L, 1.50 times of the control group. The ratio of acetic acid in DBD group was 9.30% higher than that in the control. Further mechanism research indicated that DBD pretreatment can destroy the structure of extracellular polymer substances and release organic substances such as protein and polysaccharide. The dissolved organic matter analysis indicated that the DBD technique could increase the release of biodegradable organics (eg., tyrosine proteins, soluble microbial by-products), thus accelerate the biotransformation of organic substance. Bacterial community structure analysis showed that the increase in the abundance of Firmicutes and Bacteroidetes and the decrease in the abundance of Proteobacteria in DBD group were beneficial to the accumulation of SCFAs. Besides, further archaeal analysis indicated that the decrease of Methanosaeta sp. and Methanosarcina sp. abundance in the DBD group facilitate acetic acid accumulation. This study demonstrated that the DBD technique can be used as an effective and potential pretreatment method to improve sludge anaerobic fermentation performance.

Vacuum-enhanced anaerobic fermentation: Achieving process intensification, thickening and improved hydrolysis and VFA yields in a single treatment step

This study assessed the feasibility of a novel vacuum-enhanced anaerobic digestion technology, referred to as IntensiCarb^TM (IC), under mild vacuum pressure (110 mbar), compared to a control (conventional fermenter), and evaluated the impact of the vacuum on the activities of various microbial groups. Both fermenters (test and control) were operated with mixed (50% v/v) municipal sludge at solids concentrations of 2-2.5%, pH of 7.8-8.1, 40-45 °C, a theoretical solids retention time (SRT) of 3 days with different hydraulic retention times (HRT). The intensification factor (IF) of the IC, defined as SRT/HRT, was controlled at 1.3 and 2.0. Simultaneous thickening and fermentation intensification were achieved. Compared with the control, the IC, despite the shorter HRTs, achieved 29.5 to 90.2% increase in the VFA yield (79 to 116 mg ΔVFA/ g VSS vs 61 mg ΔVFA/ g VSS), and 16.2% to 56.4% increase (280 to 377 mg ΔsCOD/ g VSS vs 241 mg ΔsCOD/ g VSS), in the hydrolysis yield. Fermentate from the IC exhibited comparable specific denitrification rates to acetate. Further, the solids-free condensate contained low nutrient concentrations, and thus was far superior to a typical centrates from dewatering as a carbon source. No adverse effects of vacuum on the activity of fermentative bacteria and methanogens were observed. This study demonstrated that the IC can be deployed as an intensification technology for both fermentation and anaerobic digestion of biosolids with the additional significant advantage, i.e. elimination of sidestream ammonia treatment requirements.

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.

Valorization of methane from environmental engineering applications: A critical review

Wastewater and waste management sectors alone account for 18% of the anthropogenic methane (CH₄) emissions. This study presents a critical overview of methanotrophs ("methane oxidizing microorganisms") for valorizing typically discarded CH₄ from environmental engineering applications, focusing on wastewater treatment plants. Methanotrophs can convert CH₄ into valuable bioproducts including chemicals, biodiesel, DC electricity, polymers, and S-layers, all under ambient conditions. As discarded CH₄ and its oxidation products can also be used as a carbon source in nitrification and annamox processes. Here we discuss modes of CH₄ assimilation by methanotrophs in both natural and engineered systems. We also highlight the technical challenges and technological breakthroughs needed to enable targeted CH₄ oxidation in wastewater treatment plants.

Nitrite-shunt and biological phosphorus removal at low dissolved oxygen in a full-scale high-rate system at warm temperatures

This study presents results from the City of St. Petersburg's (Florida) Southwest Water Reclamation Facility. This high-rate BNR plant (SRT ~ 5 days; HRT < 8 hr) achieves combined bioP and shortcut simultaneous nitrification and denitrification (SND) via nitrite in a simple BNR configuration-an anaerobic-aerobic (A/O) process without mixed liquor recycle and a 25% unaerated fraction. N removal to low effluent and nitrate and nitrite ( NO 3 -  +  NO 2 - ) concentrations occurs mainly via SND by operating the aerated zone at low DO, but still achieving near-complete ammonium ( NH 4 + ) removal. Despite the low DO operation, very good bioP performance is achieved. Full-scale performance data and detailed bench-scale testing were conducted to assess the nitrogen and phosphorus removal at low DO conditions. Full-scale results showed that the plant achieves effluent total inorganic nitrogen (TIN) and total phosphorus (TP) concentrations of approximately 2.0 mgN/L and 0.5 mgP/L, respectively, at an average influent C:N ratio of 7:1 mgCOD:mgN. PRACTITIONER POINTS: Simple anaerobic-aerobic (A/O) process demonstrated combined N and P removal Ammonia oxidation was not hampered by low DO (<0.5 mg/L) operation Low DO (<0.5 mg/L) operation sustained SND via nitrite pathway in a high-rate process (HRT < 6 hr) P uptake was demonstrated at low DO which counters to the widely held understanding that high DO (>1.5 mg/L) is necessary Heterotrophic consumption of nitrite at low DO was the key to the out-selection of nitrite-oxidizing bacteria.

Simultaneous nitrification, denitrification and phosphorus recovery (SNDPr) - An opportunity to facilitate full-scale recovery of phosphorus from municipal wastewater

Sewage treatment plants are a potential point source for recycling of phosphorus (P). Several technologies have been proposed to biologically recover P from wastewater. The majority of these technologies are side-stream processes and rely on an external source of soluble organic carbon to facilitate P recovery. To date, no studies have demonstrated the potential to facilitate main-stream recovery of P, using carbon that is naturally present in wastewater. Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) is an elegant process that can uptake influent carbon and effectively remove both nitrogen (N) and P from wastewater. SNDPR studies to date, however, have failed to facilitate an end-of-anaerobic-phase P rich liquor, that enables economies of scale to recover influent P. Therefore, this study examined the feasibility of achieving a P rich liquor (e.g. > 70 mg-P/L) in a granular SNDPR process. A synthetic influent that replicated the nutrient and carbon concentrations of municipal wastewater was used to investigate whether carbon in the influent wastewater could enable both nutrient removal and P recovery from wastewater. Our granular SNDPR process was able to facilitate an end-of-anaerobic-phase liquor with P enriched to approximately 100 mg-P/L. A dissolved oxygen (DO) concentration of 0.5 mg/L in a sequencing batch reactor (SBR) was found to be essential to achieve complete nutrient removal and a high P concentration at the end of the anaerobic phase. At this steady state of reactor operation, the abundance of polyphosphate accumulating organisms (PAOs) was 2.6 times the abundance of glycogen accumulating organisms (GAOs). The study also demonstrated the importance of denitrifying polyphosphate accumulating organisms (DPAOs) and glycogen accumulating organisms (DGAOs) to achieve complete removal of N from the effluent. Compared to nitrifying bacteria, the polyphosphate accumulating organisms (PAOs) had a higher affinity towards DO. This study, for the first time, showed that the mainstream recovery of P is feasible using a SNDPR process.

Municipal wastewater biological nutrient removal driven by the fermentation liquid of dairy wastewater

Carbon substrate is required by biological nutrient removal (BNR) microorganism, but it is usually insufficient in the influent of many municipal wastewater treatment plants. In this study the use of ethanol-enriched fermentation liquid, which was derived from dairy wastewater, as the preferred carbon substrate of BNR was reported. First, the application of dairy wastewater and food processing wastewater and their fermentation liquid as the carbon substrate of BNR was compared in the short-term tests. The fermented wastewater showed higher BNR performance than the unfermented one, and the fermentation liquid of dairy wastewater (FL-DW), which was obtained under pH 8 and fermentation time of 6 day, exhibited the highest phosphorus (95.5%) and total nitrogen (97.6%) removal efficiencies due to its high ethanol content (57.9%). Then, the long-term performance of FL-DW acting as the carbon substrate of BNR was compared with that of acetate and ethanol, and the FL-DW showed the greatest phosphorus and total nitrogen removal. Further investigation showed that the use of FL-DW caused the highest polyhydroxyalkanoates (PHAs) synthesis in BNR microbial cells, and more PHAs were used for phosphorus uptake and denitrification rather than glycogen synthesis and microbial growth. The FL-DW can be used as a preferred carbon substrate for BNR microbes.

ABBREVIATIONS

AB: aerobic end sludge active biomass; BNR: biological nutrient removal; DW: dairy wastewater; FL-DW: fermentation liquid of dairy wastewater; FPW: food processing wastewater; FL-FPW: fermentation liquid of food processing wastewater; PHAs: polyhydroxyalkanoates; PHB: poly-3-hydroxybutyrate; PHV: poly-3-hydroxyvalerate; PH2MV: poly-3-hydroxy-2- methylvalerate; PAOs: phosphorus accumulating organisms; SBR: sequencing batch reactor; SOP: soluble ortho-phosphorus; TN: total nitrogen; TSS: total suspended solids; VSS: volatile suspended solids; VFAs: volatile fatty acids; WWTPs: wastewater treatment plants.

Pilot plant demonstration of stable and efficient high rate biological nutrient removal with low dissolved oxygen conditions

Aeration in biological nutrient removal (BNR) processes accounts for nearly half of the total electricity costs at many wastewater treatment plants. Even though conventional BNR processes are usually operated to have aerated zones with high dissolved oxygen (DO) concentrations, recent research has shown that nitrification can be maintained using very low-DO concentrations (e.g., below 0.2 mg O₂/L), and therefore, it may be possible to reduce energy use and costs in BNR facilities by decreasing aeration. However, the effect of reduced aeration on enhanced biological phosphorus removal (EBPR) is not understood. In this study, we investigated, at the pilot-scale level, the effect of using minimal aeration on the performance of an EBPR process. Over a 16-month operational period, we performed stepwise decreases in aeration, reaching an average DO concentration of 0.33 mg O₂/L with stable operation and nearly 90% phosphorus removal. Under these low-DO conditions, nitrification efficiency was maintained, and nearly 70% of the nitrogen was denitrified, without the need for internal recycling of high nitrate aeration basin effluent to the anoxic zone. At the lowest DO conditions used, we estimate a 25% reduction in energy use for aeration compared to conventional BNR operation. Our improved understanding of the efficiency of low-DO BNR contributes to the global goal of reducing energy consumption during wastewater treatment operations.

Is denitrifying anaerobic methane oxidation-centered technologies a solution for the sustainable operation of wastewater treatment Plants?

With the world's increasing energy crisis, society is growingly considered that the operation of wastewater treatment plants (WWTPs) should be shifted in sustainable paradigms with low energy input, or energy-neutral, or even energy output. There is a lack of critical thinking on whether and how new paradigms can be implemented in WWTPs based on the conventional process. The denitrifying anaerobic methane oxidation (DAMO) process, which uses methane and nitrate (or nitrite) as electron donor and acceptor, respectively, has recently been discovered. Based on critical analyses of this process, DAMO-centered technologies can be considered as a solution for sustainable operation of WWTPs. In this review, a possible strategy with DAMO-centered technologies was outlined and illustrated how this applies for the existing WWTPs energy-saving and newly designed WWTPs energy-neutral (or even energy-producing) towards sustainable operations.

Community Assembly and Ecology of Activated Sludge under Photosynthetic Feast-Famine Conditions

Here, we demonstrate that photosynthetic oxygen production under light-dark and feast-famine cycles with no mechanical aeration and negligible oxygen diffusion is able to maintain phosphorus cycling activity associated with the enrichment of polyphosphate accumulating organisms (PAOs). We investigate the ecology of this novel system by conducting a time series analysis of prokaryotic and eukaryotic biodiversity using the V3-V4 and V4 regions of the 16S and 18S rRNA gene sequences, respectively. In the Eukaryotic community, the initial dominant alga observed was Desmodesmus. During operation, the algal community became a more diverse consortium of Desmodesmus, Parachlorella, Characiopodium, and Bacillariophytina. In the Prokaryotic community, there was an initial enrichment of the PAO Candidatus Accumulibacter phosphatis (Accumulibacter) Acc-SG2, and the dominant ammonia-oxidizing organism was Nitrosomonas oligotropha; however, these populations decreased in relative abundance, becoming dominated by Accumulibacter Acc-SG3 and Nitrosomonas ureae. Furthermore, functional guilds that were not abundant initially became enriched including the putative Cyanobacterial PAOs Obscuribacterales and Leptolyngbya and the H₂-oxidizing denitrifying autotroph Sulfuritalea. After a month of operation, the most-abundant prokaryote belonged to an uncharacterized clade of Chlorobi classified as Chlorobiales;SJA-28 Clade III, the first reported enrichment of this lineage. This experiment represents the first investigation into the ecological interactions and community assembly during photosynthetic feast-famine conditions. Our findings suggest that photosynthesis may provide sufficient oxygen to drive polyphosphate cycling.

Denitrification of nitrate and nitrite by 'Candidatus Accumulibacter phosphatis' clade IC

Phosphate accumulating organisms (PAO) are assumed to use nitrate as external electron acceptor, allowing an efficient integration of simultaneous nitrogen and phosphate removal with minimal organic carbon (COD) requirements. However, contradicting findings appear in literature regarding the denitrification capacities of PAO due to the lack of clade specific highly enriched PAO cultures. Whereas some studies suggest that only PAO clade I may be capable of using nitrate as external electron acceptor for anoxic P-uptake, other studies indicate that PAO clade II may be responsible for anoxic P-removal. In the present study, a highly enriched PAO clade IC culture (>99% according to FISH) was cultivated in an SBR operated under Anaerobic/Oxic conditions and subsequently exposed to Anaerobic/Anoxic/Oxic conditions using nitrate as electron acceptor. Before and after acclimatization to the presence of nitrate, the aerobic and anoxic (nitrate and nitrite) activities of the PAO I culture were assessed through the execution of batch tests using either acetate or propionate as electron donor. In the presence of nitrate, significant P-uptake by PAO I was not observed before or after acclimatization. Using nitrite as electron acceptor, limited nitrite removal rates were observed before acclimatization with lower rates in the acetate fed reactor without P-uptake and slightly higher in the propionate fed reactor with a marginal anoxic P-uptake. Only after acclimatization to nitrate, simultaneous P and nitrite removal was observed. This study suggests that PAO clade IC is not capable of using nitrate as external electron acceptor for anoxic P-removal. The elucidation of the metabolic capacities for individual PAO clades helps in better understanding and optimization of the relation between microbial ecology and process performance in enhanced biological phosphate removal processes.

Enhanced excess sludge hydrolysis and acidification in an activated sludge side-stream reactor process with single-stage sludge alkaline treatment: a pilot scale study

A pilot-scale side-stream reactor process with single-stage sludge alkaline treatment was employed to systematically investigate characteristics of excess sludge hydrolysis and acidification with alkaline treatment and evaluate feasibility of recovering a carbon source (C-source) from excess sludge to enhance nutrient removal at ambient temperature. The resulting C-source and volatile fatty acid specific yields reached 349.19 mg chemical oxygen demand (COD)/g volatile suspended solids (VSS) d^-1 and 121.3 mg COD/g VSS d^-1, respectively, the process had excellent C-source recovery potential. The propionic-to-acetic acid ratio of the recovered C-source was 3.0 times that in the influent, which beneficially enhanced biological phosphorus removal. Large populations and varieties of hydrolytic acid producing bacteria cooperated with alkaline treatment to accelerate sludge hydrolysis and acidification. Physicochemical characteristics indicated that recovered C-source was derived primarily from extracellular polymeric substances hydrolysis rather than from cells disruption during alkaline treatment. This study showed that excess sludge as carbon source was successfully recycled by alkaline treatment in the process.

A new activated primary tank developed for recovering carbon source and its application

A novel activated primary tank process (APT) was developed for recovering carbon source by fermentation and elutriation of primary sludge. The effects of solids retention time (SRT), elutriation intensity (G) and return sludge ratio (RSR) on this recovery were evaluated in a pilot scale reactor. Results indicated that SRT significantly influenced carbon source recovery, and mechanical elutriation could promote soluble COD (SCOD) and VFA yields. The optimal conditions of APT were SRT=5d, G=152s(-1) and RSR=10%, SCOD and VFA production were 57.0mg/L and 21.7mg/L. Particulate organic matter in sludge was converted into SCOD and VFAs as fermentative bacteria were significantly enriched in APT. Moreover, the APT process was applied in a wastewater treatment plant to solve the problem of insufficient carbon source. The outcomes demonstrated that influent SCOD of biological tank increased by 31.1%, which improved the efficiency of removing nitrogen and phosphorus.

Enhancing the quantity and quality of short-chain fatty acids production from waste activated sludge using CaO2 as an additive

The effect of calcium peroxide (CaO2) addition on anaerobic fermentation of waste activated sludge (WAS) was investigated. The lab-scale experiments were conducted at 35 °C with CaO2 doses ranging from 0.05 to 0.3 g/g VSS. The performances of hydrolysis and acidification of WAS were significantly enhanced by CaO2 addition, whereas the production of methane was inhibited. Maximum total short-chain fatty acids (TSCFA) production (284 mg COD/g VSS) occurred at a CaO2 dose of 0.2 g/g VSS and fermentation time of 7 d, which was 3.9 times higher than the control tests. Further, CaO2 addition led to the conversion of other SCFAs to acetic acid. Acetic acid comprised 60.2% of TSCFA with the addition of 0.2 g CaO2/g VSS compared with 45.1% in the control tests. The mechanism of improved SCFAs generation was analyzed from the view of both chemical and biological effects. Chemical effect facilitated the disintegration of WAS, and improved the activities of both hydrolytic enzymes and acid-forming enzymes. Illumina MiSeq sequencing analysis revealed that bacteria within phylum Firmicutes increased significantly due to CaO2 addition, which played an important role in the hydrolysis and acidification of WAS. In addition, CaO2 oxidized most refractory organic contaminants, which were difficult to biodegrade under the ordinary anaerobic condition. Hydroxyl radicals were the most abundant reactive oxygen species released by CaO2, which played a key role in the removal of refractory organic compounds. We developed a promising technology to produce a valuable carbon source from WAS.

Cassava stillage and its anaerobic fermentation liquid as external carbon sources in biological nutrient removal

The aim of this study was to investigate the effects of one kind of food industry effluent, cassava stillage and its anaerobic fermentation liquid, on biological nutrient removal (BNR) from municipal wastewater in anaerobic-anoxic-aerobic sequencing batch reactors (SBRs). Experiments were carried out with cassava stillage supernatant and its anaerobic fermentation liquid, and one pure compound (sodium acetate) served as an external carbon source. Cyclic studies indicated that the cassava by-products not only affected the transformation of nitrogen, phosphorus, poly-β-hydroxyalkanoates (PHAs), and glycogen in the BNR process, but also resulted in higher removal efficiencies for phosphorus and nitrogen compared with sodium acetate. Furthermore, assays for phosphorus accumulating organisms (PAOs) and denitrifying phosphorus accumulating organisms (DPAOs) demonstrated that the proportion of DPAOs to PAOs reached 62.6% (Day 86) and 61.8% (Day 65) when using cassava stillage and its anaerobic fermentation liquid, respectively, as the external carbon source. In addition, the nitrate utilization rates (NURs) of the cassava by-products were in the range of 5.49-5.99 g N/(kg MLVSS⋅h) (MLVSS is mixed liquor volatile suspended solids) and 6.63-6.81 g N/(kg MLVSS⋅h), respectively. The improvement in BNR performance and the reduction in the amount of cassava stillage to be treated in-situ make cassava stillage and its anaerobic fermentation liquid attractive alternatives to sodium acetate as external carbon sources for BNR processes.

The impact of aeration on the competition between polyphosphate accumulating organisms and glycogen accumulating organisms

In wastewater treatment plants (WWTPs), aeration is the major energetic cost, thus its minimisation will improve the cost-effectiveness of the process. This study shows that both the dissolved oxygen (DO) concentration and aerobic hydraulic retention time (HRT) affect the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). At low DO levels, Accumulibacter PAOs were shown to have an advantage over Competibacter GAOs, as PAOs had a higher oxygen affinity and thus largely maintained their aerobic activity at low DO levels, while GAO activity decreased. Bioreactor operation at low DO levels was found to increase the PAO fraction of the sludge. Furthermore, an increase in aerobic HRT (at a DO level of 2 mg O2/L), promoted the proliferation of GAOs over PAOs, decreasing the EBPR efficiency. Overall, this study shows that low aeration can be beneficial for EBPR performance through selecting for PAOs over GAOs, which should be incorporated into WWTP models in order to minimise energetic costs and improve WWTP sustainability.

Impact of butyrate on microbial selection in enhanced biological phosphorus removal systems

Microbial selection in an enhanced biological phosphorus removal system was investigated in a laboratory-scale sequencing batch reactor fed exclusively with butyrate as a carbon source. As reported in the few previous studies, butyrate uptake was slow and phosphorus (P) release occurred during the entire anaerobic period. Polyphosphate-accumulating organism (PAO), i.e. Candidatus Accumulibacter phosphatis (named as Accumulibacter), glycogen-accumulating organisms (GAOs), i.e. Candidatus Competibacter phosphatis (named as Competibacter) and Defluviicoccus-related, tetrad-forming alphaproteobacteria (named as Defluviicoccus) were identified using fluorescence in situ hybridization analysis. The results show that Accumulibacter and Defluviicoccus were selected in the butyrate-fed reactor, whereas Competibacter was not selected. P removal was efficient at the beginning of the experiment with an increasing percentage relative abundance (% RA) of PAOs. The % RA of Accumulibacter and Defluviicoccus increased from 13% to 50% and 8% to 16%, respectively, and the % RA of Competibacter decreased from 8% to 2% during the experiment. After 6 weeks, P removal deteriorated with the poor correlation between the percentage of P removal and % RA of GAOs.

Enhancement of propionic acid fraction in volatile fatty acids produced from sludge fermentation by the use of food waste and Propionibacterium acidipropionici

Volatile fatty acids (VFA) can be used as the additional carbon source of biological nutrient removal (BNR), and the increase of propionic acid percentage in VFA has been reported to facilitate the performance of BNR. In this study a new method for significantly improving the propionic acid fraction in VFA derived from waste activated sludge was reported, which included (1) mixing food waste with sludge and pre-fermenting the mixture (first stage), and (2) separating the mixture, sterilizing the pre-fermentation liquid and fermenting it after inoculating Propionibacterium acidipropionici (second stage). By optimizing the first stage with response surface methodology, a propionic acid content of 68.4% with propionic acid concentration of 7.13 g COD/L could be reached in the second stage, which was much higher than that reported previously. Lactic acid was found to be the most abundant product of the first stage and it served as the substrate for propionic acid production in the second stage. Further investigation showed that during the first stage the addition of food waste to the pre-fermentation system of sludge significantly increased the generation of lactic acid due to the synergistic effect, which resulted in the improvement of propionic acid production in the second stage. Finally, the use of propionic acid-enriched VFA as a superior carbon source of BNR was tested, and its performance was observed to be much better than using acetic acid-enriched VFA derived from sludge by the previously documented method.

Effect of fermented wastewaters from butter production on phosphates removal in a sequencing batch reactor

This study determined the potential for fermented wastewaters from butter production plant to act as a carbon source to facilitate phosphates removal. Synthetic dairy wastewaters were treated using SBR, with doses of fermented wastewaters. An increase in the fermented wastewater doses were found to improve the effluent quality in respect of phosphates and nitrates. The lowest concentrations of phosphate and nitrates, respectively 0.10 ± 0.04 mg PO(4)-PL(-1) and 1.03 ± 0.22 mg NO(3)-NL(-1), were noted in the effluent from the reactor fed with fermented wastewaters in a dose of 0.25 L d(-1) per 0.45 L d(-1) of wastewaters fed to the reactor. In the case of the two highest doses, an increase in effluent COD was stated. The higher effectiveness resulted from the fact that the introduction of fermented wastewaters caused an increase in the easily-available carbon compounds content and the predominance of acetic acid amongst VFAs available to dephosphatating and denitrifying bacteria.

Bi-stage control of dissolved oxygen to enhance cyclic adenosine monophosphate production by Arthrobacter A302

Experiments confirmed dissolved oxygen (DO) definitely affects cyclic adenosine monophosphate (cAMP) production by Arthrobacter A302. Production of cAMP by batch fermentation was investigated under various DO conditions. A two-stage DO control strategy was proposed to achieve optimal production of cAMP based on the kinetic analysis: the DO level was controlled at 40% during the first 18 h and then switched to 30%. Relatively high cAMP production (9.9 g L(-1)) was achieved by applying this strategy. The cAMP productivity (0.14 g L(-1) h(-1)) was also successfully improved by 85.1, 59.3, 15.1 and 28.0%, compared to cases in which DO was uncontrolled or DO levels were held at 20, 30 and 40%, respectively. This is the first report of the use of a two-stage DO control strategy in cAMP production, and it was verified to be an effective method for enhancing the cAMP yield via this strain.

Biological phosphorus removal performance and relevant microorganism characteristics of activated sludge in municipal wastewater treatment plants, China

Municipal wastewater discharge is threatening the ecological security of the local water environment. This study investigated the field process performance and microorganism characteristics of enhanced biological phosphorus removal (EBPR) in municipal wastewater treatment plants (WWTPs) in China. The results showed that three WWTPs met the required criteria of phosphorus for discharge (< or = 1 mg/L), but with a low level of Accumulibacter (6.4 to 3.8%, on average) and a relatively high level of Competibacter (3.2 to 9.1%) in sludge. The phosphorus release and uptake rates were varied from 0.224 to 7.770 mg/gVSS x h and 0.386 to 7.901 mg/gVSSh, respectively. Denitrifying polyphosphate-accumulating organisms were estimated to be 28.2% of the polyphosphate-accumulating organisms. Sludge characteristics (phosphorus release and uptake rates) were positively correlated with the abundance of Accumulibacter and negatively correlated with the proportion of Competibacter. Moreover, the lower the ratio of anaerobic phosphorus/acetate (e.g., 0.496) is, the more abundant the Competibacter would be. Further discussion on an improvement strategy for these WWTPs for EBPR should be comprehensively based on the data of periodic investigations on field operation, sludge activities, and microbial populations.

Effects of ZnO nanoparticles on wastewater biological nitrogen and phosphorus removal

With the increasing utilization of nanomaterials, zinc oxide nanoparticles (ZnO NPs) have been reported to induce adverse effects on human health and aquatic organisms. However, the potential impacts of ZnO NPs on wastewater nitrogen and phosphorus removal with an activated sludge process are unknown. In this paper, short-term exposure experiments were conducted to determine whether ZnO NPs caused adverse impacts on biological nitrogen and phosphorus removal in the unacclimated anaerobic-low dissolved oxygen sequencing batch reactor. Compared with the absence of ZnO NPs, the presence of 10 and 50 mg/L of ZnO NPs decreased total nitrogen removal efficiencies from 81.5% to 75.6% and 70.8%, respectively. The corresponding effluent phosphorus concentrations increased from nondetectable to 10.3 and 16.5 mg/L, respectively, which were higher than the influent phosphorus (9.8 mg/L), suggesting that higher concentration of ZnO NPs induced the loss of normal phosphorus removal. It was found that the inhibition of nitrogen and phosphorus removal induced by higher concentrations of ZnO NPs was due to the release of zinc ions from ZnO NPs dissolution and increase of reactive oxygen species (ROS) production, which caused inhibitory effect on polyphosphate-accumulating organisms and decreased nitrate reductase, exopolyphosphatase, and polyphosphate kinase activities.

Laboratory scale examination of the effects of overloading on the anaerobic digestion by glycerol

The anaerobic digestion of pure glycerol, which produces a baseline acetic acid to propionic acid ratio of 0.2, was studied in laboratory scale reactors (3 l working volume) at mesophilic temperature (37 °C) with 3000 mg chemical oxygen demand (COD)l(-1) d(-1). During the experiment tVFA and C2-C6 VFA analysis and daily biogas yield measurement were carried out. Following 10 days of a 15% d(-1) increase in the organic loading rate (OLR) of 3.0-10.5 g COD l(-1) d(-1), the concentration of propionic acid increased to 6200-8000 mg l(-1). Then the inoculum was divided into three parts feeding with 100% glycerol, 50% glycerol + 50% acetic acid, and 50% glycerol + 50% thick stillage, (presented in % of 2.60 g COD l(-1) d(-1) OLR), respectively. The application of co-substrates reduced the recovery period by 5 days compared to feeding with pure glycerol. When the reactors were loaded with glycerol again (10% OLR raise per day) the previously applied co-substrates had a positive effect on the VFA composition and the biogas yield as well.

Study on the inhibition of methane production from anaerobic digestion of biodegradable solid waste

The inhibition effects and mechanisms of chlorinated methane, anthraquinone and acetylene on methanogenesis in the anaerobic digestion process of biodegradable solid wastes were investigated. It was found that both chloroform and acetylene could effectively inhibit methanogens. Acetylene inhibited the activity of methanogens, while chloroform inhibited metabolic process of methanogenesis. A central composite design (CCD) and response surface regression analysis (RSREG) were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of methane and hydrogen production. Acetylene promoted the inhibition efficiency (F = 31.14; P < 0.01) more effectively than chloroform (F = 2.46; P > 0.05). In addition, a maximum hydrogen production of 1.6 ml was estimated under the optimum conditions of chloroform concentration of 6.69 mg kg(-1) and acetylene concentration of 3.08 x 10(-3) (v/v). Chloroform had a significant effect on enhancing the production of propionic acid and a minimum molar ratio of acetic acid to propionic acid of 0.707 was reached with the chloroform concentration of 9.24 mg kg(-1) and acetylene concentration of 4.0 x 10(-3) (v/v). Hence, methanogens can be inhibited while the stabilization process of solid wastes can still work well. Moreover, co-inhibition technology practice at landfills was feasible and the environmental damage was negligible, according to the analysis and experimental results.

Long-term effect of dissolved oxygen on partial nitrification performance and microbial community structure

In this study, the performance of partial nitrification via nitrite and microbial community structure were investigated and compared in two sequencing batch reactors (SBR) with different dissolved oxygen (DO) levels. Both reactors achieved stable partial nitrification with nitrite accumulation ratio of above 95% by using real-time aeration duration control. Compared with high DO (above 3 mg/l on average) SBR, simultaneous nitrification and denitrification (SND) via nitrite was carried out in low DO (0.4-0.8 mg/l) SBR. The average efficiencies of SND in high DO and low DO reactor were 7.7% and 44.9%, and the specific SND rates were 0.20 and 0.83 mg N/(mg MLSS h), respectively. Low DO did not produce sludge with poorer settling properties but attained lower turbidities of the effluent than high DO. Fluorescence in situ hybridization (FISH) analysis in both the reactors showed that ammonia-oxidizing bacteria (AOB) were the dominant nitrifying bacteria and nitrite-oxidizing bacteria (NOB) did not be recovered in spite of exposing nitrifying sludge to high DO. The morphology of the sludge from both two reactors according to scanning electron microscope indicated that small rod-shaped and spherical clusters were dominant, although filamentous bacteria and few long rod-shaped coexisted in the low DO reactor. By selecting properly DO level and adopting process control method is not only of benefit to the achievement of novel biological nitrogen removal technology, but also favorable to sludge population optimization.

The investigation of effect of organic carbon sources addition in anaerobic-aerobic (low dissolved oxygen) sequencing batch reactor for nutrients removal from wastewaters

The effect of addition of organic carbon sources (acetic acid and waste activated sludge alkaline fermentation liquid) on anaerobic-aerobic (low dissolved oxygen, 0.15-0.45 mg/L) biological municipal wastewater treatment was investigated. The results showed that carbon source addition affected not only the transformations of polyhydroxyalkanoates (PHA), glycogen, nitrogen and phosphorus, but the net removal of nitrogen and phosphorus. The removal efficiencies of TN and TP were, respectively, 61% and 61% without organic carbon source addition, 81% and 95% with acetic acid addition, and 83% and 97% with waste activated sludge alkaline fermentation liquid addition. It seems that the alkaline fermentation liquid of waste biosolids generated in biological wastewater treatment plant can be used to replace acetic acid as an additional carbon source to improve the anaerobic-aerobic (low dissolved oxygen) municipal wastewater nutrients removal although its use was observed to cause a slight increase of effluent BOD and COD concentrations.

Co-inhibition of methanogens for methane mitigation in biodegradable wastes

The inhibition effects and mechanisms of chlorinated methane and acetylene on methanogenesis in the anaerobic digestion process of the biodegradable wastes were investigated. It was found that both chloroform and acetylene could effectively inhibit methanogens while the biodegradability of the wastes was not affected. Acetylene inhibited the activity of methanogens, while chloroform inhibited metabolic process of methanogenesis. A central composite design (CCD) and response surface regression analysis (RSREG) were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of inhibition efficiency, production of volatile fatty acids (VAF) and molar ratio of propionic acid to acetic acid. Chloroform had significant effect on enhancing the production of VFA (F = 121.3; p < 0.01), and acetylene promoted the inhibition efficiency (F = 99.15; p < 0.05) more effectively than chloroform (F = 9.72; p > 0.05). In addition, a maximum molar ratio of propionic acid to acetic acid of 1.208 was estimated under the optimum conditions of chloroform concentration of 9.05 mg/kg and acetylene concentration of 3.6x10(-3) (V/V). Hence, methanogens in the wastes can be inhibited while the stabilization process of the biodegradable wastes can still work well, as propionic acid generated during the inhibition process could hardly be utilized by methanogens.

Biological phosphorus removal in sequencing batch reactor with single-stage oxic process

The performance of biological phosphorus removal (BPR) in a sequencing batch reactor (SBR) with single-stage oxic process was investigated using simulated municipal wastewater. The experimental results showed that BPR could be achieved in a SBR without anaerobic phase, which was conventionally considered as a key phase for BPR. Phosphorus (P) concentration 0.22-1.79 mg L(-1) in effluent can be obtained after 4h aeration when P concentration in influent was about 15-20 mg L(-1), the dissolved oxygen (DO) was controlled at 3+/-0.2 mg L(-1) during aerobic phase and pH was maintained 7+/-0.1, which indicated the efficiencies of P removal were achieved 90% above. Experimental results also showed that P was mainly stored in the form of intracellular storage of polyphosphate (poly-P), and about 207.235 mg phosphates have been removed by the discharge of rich-phosphorus sludge for each SBR cycle. However, the energy storage poly-beta-hydroxyalkanoates (PHA) was almost kept constant at a low level (5-6 mg L(-1)) during the process. Those results showed that phosphate could be transformed to poly-P with single-stage oxic process without PHA accumulation, and BPR could be realized in net phosphate removal.