Short Hydraulic Retention Time Research Articles

Sewage sludge as carbon source for polyhydroxyalkanoates: a holistic approach at pilot scale level

In the present study, polyhydroxyalkanoates (PHA) production by mixed microbial cultures (MMC) has been carried out using thermally pre-treated excess thickened waste activated sludge (WAS), applying the feast-famine approach at pilot scale. The preliminary results of WAS fermentation conducted both in mesophilic and thermophilic conditions, in combination with a thermal pre-treatment at 70 °C for 48 h, highlighted how the thermal hydrolysis has a crucial role for the solubilization of the chemical oxygen demand (COD), which allows a significant increase of the final volatile fatty acid (VFA) concentration (roughly 8.5 g CODVFA/L). Since thermophilic fermentation after thermal pre-treatment was the best performing condition, it has been applied at pilot scale in order to routinely produce VFA as precursors for the following PHA synthesis. The selection and enrichment of PHA-producing biomass was successfully established and maintained in a Sequencing Batch Reactor (SBR) during the whole experimentation period, under short hydraulic retention time (HRT; 2 days) and medium-low organic loading rate (OLR; 2.0–2.2 g COD/L d). At the end of the production process an average PHA content of 53 ± 3 %w/w was achieved. The polymer was finally extracted and recovered from the biomass using traditional chloroform and sodium hypochlorite extraction and then characterized for the quantification of thermal properties (Tm = 156.8–160.9 °C) and molecular weight (Mv = 396–405 kDa). A final overall mass balance, usually poorly reported in the literature, has been also assessed, resulting in an overall yield of 56 g PHA per kg of volatile solids (VS).

Integrated electrocatalytic packed-bed membrane reactor for nitrate removal

Nitrate pollution has become a widespread problem that poses a potential risk for public health. Although electrochemical reduction can be an effective and environmentally friendly strategy for nitrate removal, obtaining non-polluting products (nitrogen) in a short hydraulic retention time via this electrocatalytic process is still challenging. This work features an efficient reactor design that integrates an electrocatalytic packed-bed reactor with a membrane. Granular activated carbon (GAC) loaded with bimetal catalysts (Pd and Cu) was used as the bed packing material (Pd-Cu/GAC). The carbon membrane loaded Pd-Cu, served as cathode, filter, and current collector. The inner core packed with the Pd-Cu/GAC material functioned as an extended three-dimensional electrocatalytic cathode and catalyst. This carbon membrane system can remove 100% nitrate with the packed-bed catalyst in Na2SO4 electrolyte, but only 79.38% without the packed-bed catalyst. The packed-bed configuration can also enhance the nitrogen (N2) selectivity from 39.66 to 78.31%, increasing the NO3– removal rate from 1.72 × 10−4 to 3.62 × 10−4 mmol min−1 cm−2, respectively. Notably, when NaOH electrolyte was used, the single-pass nitrate removal can achieve 100% with a 94.25 % N2 selectivity. These excellent performances highlight the potential to apply the integrated electrocatalytic packed-bed membrane reactor system reported here for large-scale nitrate remediation.

Biohydrogen and biomethane production from food waste using a two-stage dynamic membrane bioreactor (DMBR) system

This study examined a two-stage dynamic membrane bioreactor (DMBR) system for biohydrogen and biomethane production from food waste (FW) in mesophilic condition. The two-stage DMBR system enabled high-rate H2 and CH4 production from particulate feedstock by enhanced microorganism retention. Chemical energy in FW was recovered up to 79% as renewable energy. The highest average hydrogen production rate of 7.09 ± 0.42 L/L-d was observed at a hydraulic retention time (HRT) of 8 h in the H2-DMBR, while the highest CH4 average production rate of 0.99 ± 0.02 L/L-d was observed at an HRT of 6 d in the CH4-DMBR. The high specific methanogenic activity of 71.7 mL CH4/g VSS-d was maintained at the short HRT, which also contributed to the high MPR. The genus Clostridium was dominant in the H2-DMBR, while bacterial and archaeal populations in the CH4-DMBR were dominated by the class Clostridia and genera Methanobacterium and Methanosaeta, respectively.

Machine learning-assisted identification of bioindicators predicts medium-chain carboxylate production performance of an anaerobic mixed culture

BackgroundThe ability to quantitatively predict ecophysiological functions of microbial communities provides an important step to engineer microbiota for desired functions related to specific biochemical conversions. Here, we present the quantitative prediction of medium-chain carboxylate production in two continuous anaerobic bioreactors from 16S rRNA gene dynamics in enriched communities.ResultsBy progressively shortening the hydraulic retention time (HRT) from 8 to 2 days with different temporal schemes in two bioreactors operated for 211 days, we achieved higher productivities and yields of the target products n-caproate and n-caprylate. The datasets generated from each bioreactor were applied independently for training and testing machine learning algorithms using 16S rRNA genes to predict n-caproate and n-caprylate productivities. Our dataset consisted of 14 and 40 samples from HRT of 8 and 2 days, respectively. Because of the size and balance of our dataset, we compared linear regression, support vector machine and random forest regression algorithms using the original and balanced datasets generated using synthetic minority oversampling. Further, we performed cross-validation to estimate model stability. The random forest regression was the best algorithm producing more consistent results with median of error rates below 8%. More than 90% accuracy in the prediction of n-caproate and n-caprylate productivities was achieved. Four inferred bioindicators belonging to the genera Olsenella, Lactobacillus, Syntrophococcus and Clostridium IV suggest their relevance to the higher carboxylate productivity at shorter HRT. The recovery of metagenome-assembled genomes of these bioindicators confirmed their genetic potential to perform key steps of medium-chain carboxylate production.ConclusionsShortening the hydraulic retention time of the continuous bioreactor systems allows to shape the communities with desired chain elongation functions. Using machine learning, we demonstrated that 16S rRNA amplicon sequencing data can be used to predict bioreactor process performance quantitatively and accurately. Characterizing and harnessing bioindicators holds promise to manage reactor microbiota towards selection of the target processes. Our mathematical framework is transferrable to other ecosystem processes and microbial systems where community dynamics is linked to key functions. The general methodology used here can be adapted to data types of other functional categories such as genes, transcripts, proteins or metabolites.EyqQhNrWeErXEyK2y7qF5JVideo

Identification of factors affecting removal of antibiotic resistance genes in full-scale anaerobic digesters treating organic solid wastes

Efficiencies of removing antibiotic resistance genes (ARGs) and intI1 were explored using eight full-scale anaerobic digesters. The digesters demonstrated different characteristics on the basis of substrate types (food waste, manure or sludge); configuration (single or two-stage); temperature (psychrophilic, mesophilic or thermophilic); hydraulic retention time (HRT) (9.7–44 days); and operation mode (continuous stirred tank reactor or plug flow reactor). Digesters’ configuration or operating parameters showed a greater effect on abundance of ARGs than the type of input substrate. Redundancy analysis (RDA) accounted for 85.2% of the total variances and digesters with the same configuration and operational conditions showed similar performance for removal of ARGs. The highest efficiencies of removing ARGs (99.99%) were observed in two-stage thermophilic digesters with relatively long HRTs (32 days). The lowest removal efficiency (97.93%) was observed in single-stage mesophilic with relatively short HRTs (9.7 days), likely due to vertical and horizontal gene transfer.

Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why?

BackgroundThis study examines the destiny of macromolecules in different full-scale biogas processes. From previous studies it is clear that the residual organic matter in outgoing digestates can have significant biogas potential, but the factors dictating the size and composition of this residual fraction and how they correlate with the residual methane potential (RMP) are not fully understood. The aim of this study was to generate additional knowledge of the composition of residual digestate fractions and to understand how they correlate with various operational and chemical parameters. The organic composition of both the substrates and digestates from nine biogas plants operating on food waste, sewage sludge, or agricultural waste was characterized and the residual organic fractions were linked to substrate type, trace metal content, ammonia concentration, operational parameters, RMP, and enzyme activity.ResultsCarbohydrates represented the largest fraction of the total VS (32–68%) in most substrates. However, in the digestates protein was instead the most abundant residual macromolecule in almost all plants (3–21 g/kg). The degradation efficiency of proteins generally lower (28–79%) compared to carbohydrates (67–94%) and fats (86–91%). High residual protein content was coupled to recalcitrant protein fractions and microbial biomass, either from the substrate or formed in the degradation process. Co-digesting sewage sludge with fat increased the protein degradation efficiency with 18%, possibly through a priming mechanism where addition of easily degradable substrates also triggers the degradation of more complex fractions. In this study, high residual methane production (> 140 L CH4/kg VS) was firstly coupled to operation at unstable process conditions caused mainly by ammonia inhibition (0.74 mg NH3-N/kg) and/or trace element deficiency and, secondly, to short hydraulic retention time (HRT) (55 days) relative to the slow digestion of agricultural waste and manure.ConclusionsOperation at unstable conditions was one reason for the high residual macromolecule content and high RMP. The outgoing protein content was relatively high in all digesters and improving the degradation of proteins represents one important way to increase the VS reduction and methane production in biogas plants. Post-treatment or post-digestion of digestates, targeting microbial biomass or recalcitrant protein fractions, is a potential way to achieve increased protein degradation.

Microbial fuel cell scale-up options: Performance evaluation of membrane (c-MFC) and membrane-less (s-MFC) systems under different feeding regimes.

In recent years, bioelectrochemical systems have advanced towards upscaling applications and tested during field trials, primarily for wastewater treatment. Amongst reported trials, two designs of urine-fed microbial fuel cells (MFCs) were tested successfully on a pilot scale as autonomous sanitation systems for decentralised area. These designs, known as ceramic MFCs (c-MFCs) and self-stratifying MFCs (s-MFC), have never been calibrated under similar conditions. Here, the most advanced versions of both designs were assembled and tested under similar feeding conditions. The performance and efficiency were evaluated under different hydraulic retention times (HRT), through chemical oxygen demand measures and polarisation experiments. Results show that c-MFCs displayed constant performance independently from the HRT (32.2 ± 3.9 W m−3) whilst displaying high energy conversion efficiency at longer HRT (NERCOD = 2.092 ± 0.119 KWh.KgCOD−1, at 24h HRT). The s-MFC showed a correlation between performance and HRT. The highest performance was reached under short HRT (69.7 ± 0.4 W m−3 at 3h HRT), but the energy conversion efficiency was constant independently from the HRT (0.338 ± 0.029 KWh.KgCOD−1). The c-MFCs and s-MFCs similarly showed the highest volumetric efficiency under long HRT (65h) with NERV of 0.747 ± 0.010 KWh.m−3 and 0.825 ± 0.086 KWh.m−3, respectively. Overall, c-MFCs seems more appropriate for longer HRT and s-MFCs for shorter HRT.

Full-scale application of a down-flow hanging sponge reactor combined with a primary sedimentation basin for domestic sewage treatment.

The down-flow hanging sponge (DHS) reactor is advantageous for sewage treatment since it produces an effluent quality that complies with the standards for reuse and there is little excess sludge. A full-scale DHS module was efficiently employed for the treatment of domestic sewage (200 m3day-1) flowing from a primary sedimentation basin (PSB), which was used to reduce the suspended solids loading rate and enhance the oxidation of organics by heterotrophs. The combined PSB-DHS was successfully operated at a total hydraulic retention time of 3.4h (2.4h for PSB and 1.0h for DHS) for the relatively long period of 600days at sewage temperatures of 10°C to 32°C. The PSB-DHS consistently produced an effluent quality with minimum values of chemical oxygen demand, biochemical oxygen demand, and suspended solids of 59 ± 15, 12 ± 3.0, and 15 ± 7mg L-1, respectively. The proposed system performed exceptionally well at removing organics and particulate matter over a short hydraulic retention time.

Pilot-scale continuous flow granular reactor for the treatment of extremely low-strength recirculating aquaculture system wastewater

To avoid toxic ammonium and nitrite concentrations in aquaculture systems is crucial to maintain the fish production. When recirculating aquaculture systems (RAS) operate in freshwater farms during the dry seasons, the concentrations of these pollutants increase. The objective of the present study is the evaluation of a Continuous Flow Granular Reactor (CFGR) for the treatment of freshwater RAS stream at pilot-scale during two consecutive dry seasons. The CFGR was fed with a extremely low-strength recirculation stream of a trout farm (0.12–1.84 mg NH4+-N/L and 2.2–8.14 mg C/L). Two different configurations were evaluated. The first configuration consisted on a CFGR fed from the bottom, being the up-flow velocity the only shear force to mix the biomass. The second configuration incorporated a mechanical stirrer and a sieve to improve the biomass mixing and retention. The CFGR was operated at short hydraulic retention times (HRT) which ranged from 11 to 68 min. The configuration with a mechanical stirrer and sieve was optimal in terms of biomass retention and nitrogen removal performance. Despite the low nitrogen and organic matter concentrations, granulation was achieved in 55 days, with an average granule diameter up to 0.47 mm. Ammonium and nitrite removal percentages up to 81% and 100% were achieved, respectively. The ammonium and nitrite production rate in the trout farm were lower than the removal achieved by the CFGR, which makes the implementation of this system appropriated to maintain the concentration of these compounds below toxic levels for rainbow trout.

Successful and stable operation of anaerobic thermophilic co-digestion of sun-dried sugar beet pulp and cow manure under short hydraulic retention time

This work consists of a long-term (621 days) experimental study about biogas production from sun dried sugar beet pulp and cow manure. Thermophilic (55 °C) anaerobic co-digestion was performed in semi-continuous reactors, testing ten hydraulic retention times (30-3 days) (HRTs) and organic loading rates (2–24 gVS/Lreactor∙d) (OLRs). Results showed that the best global system performance (regarding stability, biogas production, and organic matter removal) was achieved at an HRT as short as 5 days (OLR of 12.47 gVS/Lreactor∙d) with a biogas yield of 315 mL/gVSadded. The gradual OLR increase allowed system control and time-appropriate intervention, avoiding irreversible process disturbances and maintaining admissible acidity/alkalinity ratios (<0.8) for HRTs ranging from 30 to 4 days. The accumulation of acetic acid was the main cause of the process disturbance observed at short HRTs. It was deduced that for the HRT of 3 days, the methane productivity was mainly owing to the hydrogen-utilizing methanogens pathway. This research clearly shows how an adequate combination of agro-industrial wastes and livestock manure could be processed by anaerobic co-digestion in short HRTs with great efficiency and stability and deepens in the understanding of the start-up, stability and optimization of the co-digestion.

Impacts of hydraulic retention time and inflow water quality on algal growth in a shallow lake supplied with reclaimed water

Landscape lakes supplied with reclaimed water often face the threats of algal blooms. To guarantee the water quality in an artificial shallow lake (Lake M), algal growth and water quality changes were predicted by Delft3D. When the concentrations of influent total nitrogen (TN) and total phosphorous (TP) were fixed at 10 ​mg ​N/L and 0.2 ​mg ​P/L, respectively, increases in the hydraulic retention time (HRT) which was induced by water depth increased algal growth. The average algal density in Lake M was 6.42 ​× ​104 ​cells/mL when the HRT was 4 ​d, which increased to 2.14 ​× ​105 ​cells/mL when the HRT was 8 ​d. These results showed that the shallowness of the lake contributed positively to algae control. The shallower water depth came with the shorter HRT while nutrient load and light intensity were increased subsequently, which usually favor algal growth but not the dominant factors of algal density in Lake M. When the influent TN concentration was between 2 and 15 ​mg ​N/L of which nitrate changed, the HRT was fixed at 8 ​d, and the influent TP concentration was 0.2 ​mg/L, the algal density was approximately 2 ​× ​105 ​cells/mL. Algae were not sensitive to changes in the influent TN concentration, and TN should be considered as a secondary factor in algal growth. Increases in the TP concentration promoted algal growth because phosphorous is the dominant nutrient for algae to acquire from reclaimed water if there is sufficient nitrogen. When the HRT of the lake was 8 ​d and the influent TN concentration was 10 ​mg/L, the average algal density in the lake was on the order of 104 ​cells/mL as the TP concentration was 0.1 ​mg/L. Because the water depth determines the HRT, it should be carefully considered during design and construction of artificial lakes. Influent phosphorus should be monitored to control algal blooms during maintenance of artificial lakes.

Enhanced nutrient removal from stormwater runoff by a compact on-site treatment system

Efficient and space-saving technologies for on-site treatment of stormwater runoff are required to control water pollution in the urban surface. The intermittent nature of stormwater runoff and extremely limited land available greatly hindered the application of current wastewater treatment technologies, and thus synchronous removal of multiple contaminants (especially for nutrient) efficiently was failed by current processes. In this study, a new compact CFFA treatment system, consisting of coagulation, flocculation, filtration and ammonium ion exchange units, was constructed for on-site treatment of stormwater runoff based on batch test optimization and pilot-scale test verification. The coagulation process effectively aggregated particles and precipitated phosphorus by dosing Al2(SO4)3, while flocculation using anionic polyacrylamide further enlarged particle size for efficient micromesh filtration. The dynamic micromesh filtration obtained turbidity and phosphorus removal efficiencies comparable to 30 min gravity settling with greatly smaller footprint. Ion exchange by zeolite showed higher exchange capacity owing to lower initial ammonium nitrogen concentration in the stormwater runoff. The pilot-scale experiments with treatment capacity of 1 L/s showed that the CFFA treatment system achieved synchronous removal of particles (97.2%), nitrogen (79.7%), phosphorus (95.0%) and organic matters (83.3%) efficiently within short hydraulic retention time of 0.35 h, yielding effluent with chemical oxygen demand, suspended solids, total phosphorus and total nitrogen of 38.7, 7.80, 0.22 and 2.80 mg/L, respectively. The CFFA treatment system had the highest pollutant removal loads compared to reported runoff treatment processes in literatures, and was well suited to on-site treatment of stormwater runoff with high space utilization efficiency.

Realization of partial nitrification and in-situ anammox in continuous-flow anaerobic/aerobic/anoxic process with side-stream sludge fermentation for real sewage

A continuous-flow anaerobic/aerobic/anoxic reactor with complete suspended activated sludge using sludge alkaline fermentation products as carbon source was utilized to strengthen nitrogen removal performance for low C/N ratio (<4) wastewater. Long-time performance indicated that the nitrite accumulation rate reached 60.40%, which strengthened the contribution of anammox. The average total inorganic nitrogen removal efficiency improved 19.40%. The abundance of ammonia oxidizing bacteria has not changed, but the abundance of nitrite oxidizing bacteria reduced from 5.79% to 0.69%. Quantitative PCR results demonstrated that the abundance of anammox bacteria has raised by 80.5 times. These results indicated that side-stream sludge alkaline fermentation promoted the mainstream partial nitrification, consequently accelerating the in-situ enrichment of anammox bacteria. No external carbon source dosing and short oxic hydraulic retention time (5.3 h) save energy and reduce consumption significantly in this system.

Insights into the Anaerobic Hydrolysis Process for Extracting Embedded EPS and Metals from Activated Sludge.

The amount of sewage sludge generated from wastewater treatment plants globally is unavoidably increasing. In recent years, significant attention has been paid to the biorefinery concept based on the conversion of waste streams to high-value products, material, and energy by microorganisms. However, one of the most significant challenges in the field is the possibility of controlling the microorganisms’ pathways in the anaerobic environment. This study investigated two different anaerobic fermentation tests carried out with real waste activated sludge at high organic loading rate (10 g COD L−1d−1) and short hydraulic retention time (HRT) to comprehensively understand whether this configuration enhances extracellular polymeric substance (EPS) and metal solubilisation. The quantity of EPS recovered increased over time, while the chemical oxygen demand to EPS ratio remained in the range 1.31–1.45. Slightly acidic conditions and sludge floc disintegration promoted EPS matrix disruption and release, combined with the solubilisation of organically bound toxic metals, such as As, Be, Cu, Ni, V, and Zn, thereby increasing the overall metal removal efficiency due to the action of hydrolytic microorganisms. Bacteroidetes, Firmicutes, and Chloroflexi were the most abundant phyla observed, indicating that the short HRT imposed on the systems favoured the hydrolytic and acidogenic activity of these taxa.

Economic and environmental sustainability for anaerobic biological treatment of wastewater from paper and cardboard manufacturing industry

The sustainable application of an up-flow anaerobic baffled reactor (UABR) to treat real paper and cardboard industrial effluent (PCIE) containing bronopol (2-bromo-2-nitropropan-1, 3-diol) was investigated. At a hydraulic retention time (HRT) of 11.7 h and a bronopol concentration of 7.0 mg L−1, the removal efficiencies of total chemical oxygen demand (CODtotal), CODsoluble, CODparticulate, total suspended solids (TSS), volatile suspended solids (VSS), carbohydrates, and proteins were 55.3 ± 5.2%, 26.8 ± 2.3%, 94.4 ± 4.6%, 89.4 ± 2.6%, 84.5 ± 3.2%, 72.1 ± 1.8%, and 22.4 ± 1.8%, respectively. The conversion of complex organics (e.g., carbohydrates and proteins) into bio-methane (CH4) was assisted via enzyme activities of, in U (100 mL)−1, α-amylase (224–270), α-xylanase (171–188), carboxymethyl cellulase (CM-cellulase) (146–187), polygalacturonase (56–126), and protease (67,000–75300). The acidogenic condition was dominant at a short HRT of 2.9 h, where methane yield dropped by 32.5%. Under this condition, the growth of methanogenic bacteria could be inhibited by volatile fatty acids (VFA) accumulation. The analysis of Fourier-transform infrared (FTIR) spectra detected peaks relevant to methylene and nitro groups in the sludge samples, suggesting that entrapment/adsorption by the sludge bed could be a major mechanism for removing bronopol. The economic feasibility of UABR, as proposed to receive 100 m3 d−1 of PCIE, showed a payback period (profits from environmental benefits, biogas recovery, and carbon credit) of 7.6 yr. The study outcomes showed a high connection to the environmental-, economic-, and social-related sustainable development goals (SDGs).

Unraveling the role of ballast surface charge at floc growth behavior in ballasted flocculation

This study was emphasized on unraveling the concealed role of surface charge characteristics of employed ballasts at suspended solids interaction with employed ballasts during floc formation in ballasted flocculation (BF). The purpose was to investigate possibilities in surface charge modulation of employed ballasts leading to enhanced aggregation and ballast embedment during floc growth. The ballasts with varied surface charge (-37.8 mV to + 33.6 mV) and equivalent specific gravity (SG: 5.09) were employed in BF process in this study. This Ballasted flocculation study was conducted using a static mixer device in this study, and characteristics of ballasted flocs (size and settling velocity of aggregates) were analyzed by charge coupled device camera. These image analysis investigations revealed that ballast particles and suspended solids experience attractions and repulsions during aggregation subject to ballast surface charge. However, appropriate ballast selection (surface charge characteristics) corresponding to influent characteristics, and optimization of applied ballast concentration (2gL-1) corresponding to ballast surface charge characteristics (SC: +1.23) resulted in 99% clarification (1 NTU residual turbidity) accomplished in a quick settling interval (30 s) with efficient consumption of applied ballasts compared to previous studies. The real-time velocity observations (using CCD camera) also confirmed this rapid clarification exhibiting superficial sedimentation (102.4mh−1) of the aggregated flocs. Therefore, this study concluded that appropriate ballast selection and optimalization of applied ballast concentration corresponding to surface charge characteristics and influent properties can lead to rapid clarification of micropollutants, and instantaneous sedimentation with efficient ballast consumption. This can lead to efficient treatment facility design with shorter hydraulic retention time, compact space requirements, and capability to produce high quality effluent discharge from highly turbid influent.

Performance and enhancement mechanism of redox mediator for nitrate removal in immobilized bioreactor with preponderant microbes

The acceleration of nitrate removal in wastewater treatment by redox mediator (RM) is greatly weakened due to wash-out loss and mass transfer resistance (low hydrophilia) of RM during operation. In this study, an RM reactor with the fixed 1-Amino-4-hydroxyanthraquinone (AHAQ) and three core strains was established and achieved high nitrate removal efficiency (NRE) under low carbon to nitrogen ratio (C/N) and short hydraulic retention time (HRT) conditions, with the maximum efficiency of 99.41% (14.00 mg L−1 h−1) and average improvement by 11.97% (1.41 mg L−1 h−1). This acceleration led to more proportion of carbon consumption by denitrifying bacteria and improved their competitiveness against others in carbon deficiency, although resulting in nitrite accumulation (NIA) in lower C/N. The RM reactor induced the decorrelation tendencies between NRE and active extracellular organics and more sensitive denitrification toward C/N, which favored the stability of effluent organics and biological activities. The increase of oxidative phosphorylation and ubiquinone and other terpenoid-quinone biosynthesis pathway suggested electron transport activity was potentially enhanced by AHAQ. Although the lower C/N deteriorated the reactor NRE, the abundances of amino acids-, fatty acids- and carbohydrate-related metabolisms (45% of the total up-regulating pathways) were enhanced to utilize carbon source effectively. Meanwhile, the enhanced phosphotransferase system facilitated the balance between carbon and nitrogen metabolism. These indicated the changes in biological strategy to grow better and resist the adverse condition. This study highlighted the superior NRE by AHAQ in an immobilized reactor with core strains and more importantly, extended the RM application in wastewater treatment.

An approach of auxiliary carbohydrate source on stabilized biohythane production and energy recovery by two-stage anaerobic process from swine manure

In this study, a two-stage biohythane production system was used to treat swine manure to solve the high Chemical Oxygen Demand (COD) concentration and verify the total energy recovery between the two-stage and a traditional single-stage system. Experiments were carried out in single-stage methane production, two-stage biohythane production in long Hydraulic Retention Time (HRT), and short HRT. The COD removal efficiency and energy recovery were finally compared between single-stage (CH4 fermenter) and two-stage (H2+ CH4 fermenter) systems. The results showed that the methane production rate of 53.2 ± 2.7 mL/d.L, the COD removal efficiency of 29.6 ± 5.8%, and total energy recovery of 2.9 ± 0.1 kJ/L.d was obtained in the single-stage of methane production system with HRT 11.08 d, pH 7, and temperature 55 °C, respectively. In the two-stage of hydrogen and methane productions system, the hydrogen production rate of 1.8 ± 0.7 mL/d.L, the methane production rate of 65.7 ± 2.5 mL/d.L, the COD removal rate was 97.8 ± 1.7%, and the total energy recovery of 3.6 ± 0.1 kJ/L.d was obtained and stabilized when the sugary wastewater content gradually reduced to 0%. This study shows that the methane production rate increases 20%, COD removal efficiency increases to 97.8 ± 1.7%, and total energy recovery increases 30%. At the same time, the single-stage (CH4 fermenter) switched to a two-stage (H2+ CH4 fermenter) system. The two-stage anaerobic biohythane production system successfully treated the high organic swine manure and obtained a higher energy recovery against the traditional single-stage of the biomethane production system.

Effect of hydraulic selection pressure on the characteristics of partial nitritation/anammox granular sludge in a continuous-flow reactor

Strong hydraulic selection pressure is a control co-factor for maintaining the stability of granular sludge in a continuous-flow bioreactor. In this study, efficient nitrogen removal was achieved in a continuous partial nitritation/anammox (PN/A) granular reactor in a short hydraulic retention time (HRT), decreasing from 100 to 40 min, where more than 95% of ammonium and 80% of total inorganic nitrogen (TIN) were removed at a constant nitrogen loading rate of 2.0 kg (m 3 d) −1 . Results showed that the decreased HRT substantially influenced the observed biomass growth curve, with a trade-off between the growth and washout of microbial populations. Further, sludge characterization indicated that shorter HRT improved granular compactness with the accumulation of extracellular polymeric substances and increased the specific nitrogen removal rate, reaching q (TIN) = 39.9 mg N g −1 VSS ⋅ h −1 . These observations were consistent with shifts in the bacterial community structure of the PN/A sludge with different particle sizes. High-throughput pyrosequencing revealed that strong hydraulic selection pressure promoted the niche segregation of aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AnAOB) and washout of nitrite-oxidizing species in the granules. The effective retention of k -strategists AnAOB (dominated by genus Candidatus Kuenenia) occupying the interior layer of the granules exhibited a solid retention time (SRT) 10-fold longer than that of AOB (identified as Nitrosomonas ) enriched in the aerobic zone. A strategy involving HRT and SRT coordination in operation can enhance the efficiency and stability of PN/A systems, considering the potential development of small aggregates into mature granules. • Strong hydraulic selection pressure was applied in a CSTR with PN/A granules. • NH 4 + -N removal ≥ 95% and TIN removal ≥ 80% were achieved at an HRT of 40 min. • HRT influenced the observed biomass growth curve and granular functional activity. • Shorter HRT promoted niche segregation of AOB and AnAOB in PN/A sludge.

Dynamic changes in anaerobic digester metabolic pathways and microbial populations during acclimatisation to increasing ammonium concentrations

Transitions in microbial community structure in response to increasing ammonia concentrations were determined by monitoring mesophilic anaerobic digesters seeded with a predominantly acetoclastic methanogenic community from a sewage sludge digester. Ammonia concentration was raised by switching the feed to source segregated domestic food waste and applying two organic loading rates (OLR) and hydraulic retention times (HRT) in paired digesters. One of each pair was dosed with trace elements (TE) known to be essential to the transition, with the other unsupplemented digester acting as a control. Samples taken during the trial were used to determine the metabolic pathway to methanogenesis using 14C labelled acetate. Partitioning of 14C between the product gases was interpreted via an equation to indicate the proportion produced by acetoclastic and hydrogenotrophic routes. Archaeal and selected bacterial groups were identified by 16S rRNA sequencing, to determine relative abundance and diversity. Acclimatisation for digesters with TE was relatively smooth, but OLR and HRT influenced both metabolic route and community structure. The 14C ratio could be used quantitatively and, when interpreted alongside archaeal community structure, showed that at longer HRT and lower loading Methanobacteriaceae were dominant and hydrogenotrophic activity accounted for 77% of methane production. At the higher OLR and shorter HRT, Methanosarcinaceae were dominant with the 14C ratio indicating simultaneous production of methane by acetoclastic and hydrogenotrophic pathways: the first reported observation of this in digestion under mesophilic conditions. Digesters without TE supplementation showed similar initial changes but, as expected failed to complete the transition to stable operation.