Thermophilic biological nitrogen removal in industrial wastewater treatment

Nitrification is an integral part of biological nitrogen removal processes and usually the limiting step in wastewater treatment systems. Since nitrification is often considered not feasible at temperatures higher than 40 °C, warm industrial effluents (with operating temperatures higher than 40 °C) need to be cooled down prior to biological treatment, which increases the energy and operating costs of the plants for cooling purposes. This study describes the occurrence of thermophilic biological nitrogen removal activity (nitritation, nitratation, and denitrification) at a temperature as high as 50 °C in an activated sludge wastewater treatment plant treating wastewater from an oil refinery. Using a modified two-step nitrification–two-step denitrification mathematical model extended with the incorporation of double Arrhenius equations, the nitrification (nitrititation and nitratation) and denitrification activities were described including the cease in biomass activity at 55 °C. Fluorescence in situ hybridization (FISH) analyses revealed that Nitrosomonas halotolerant and obligatehalophilic and Nitrosomonas oligotropha (known ammonia-oxidizing organisms) and Nitrospira sublineage II (nitrite-oxidizing organism (NOB)) were observed using the FISH probes applied in this study. In particular, this is the first time that Nitrospira sublineage II, a moderatedly thermophilic NOB, is observed in an engineered full-scale (industrial) wastewater treatment system at temperatures as high as 50 °C. These observations suggest that thermophilic biological nitrogen removal can be attained in wastewater treatment systems, which may further contribute to the optimization of the biological nitrogen removal processes in wastewater treatment systems that treat warm wastewater streams.     

Partial nitrification in a sequencing batch reactor treating acrylic fiber wastewater

A sequencing batch reactor was employed to treat the acrylic fiber wastewater. The dissolved oxygen and mixed liquor suspended solids were 2–3 and 3,500–4,000 mg/L, respectively. The results showed ammonium oxidizing bacteria (AOB) had superior growth rate at high temperature than nitrite oxidizing bacteria (NOB). Partial nitrification could be obtained with the temperature of 28 °C. When the pH value was 8.5, the nitrite-N accumulation efficiency was 82 %. The combined inhibitions of high pH and free ammonium to NOB devoted to the nitrite-N buildup. Hydraulic retention time (HRT) was a key factor in partial nitrification control, and the optimal HRT was 20 h for nitrite-N buildup in acrylic fiber wastewater treatment. The ammonium oxidation was almost complete and the transformation from nitrite to nitrate could be avoided. AOB and NOB accounted for 2.9 and 4.7 %, respectively, corresponding to the pH of 7.0. When the pH was 8.5, they were 6.7 and 0.9 %, respectively. AOB dominated nitrifying bacteria, and NOB was actually washed out from the system.     

Activated sludge under free ammonia treatment using gel immobilization technology for long-term partial nitrification with different initial biomass

To achieve stable partial nitrification, activated sludge from a wastewater treatment plant using free ammonia (FA) inhibition was immobilized in a polyvinyl alcohol carrier. After FA treatment at 16.44 mg L⁻¹ for 1 day, due to the increased growth rate gap between ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), AOB enrichment and NOB inhibition were achieved within 12 days, with AOB and NOB accounting for 65.61 and 0.05%, respectively. Subsequently, with dissolved oxygen concentrations of 4−5 mg L⁻¹, pH of 7.6–7.8 and temperature of 25 ± 1 °C, the immobilized carrier made of activated sludge achieved more than 90% and more than 86% of nitrite accumulation rate at the influent ammonia concentration of 90−110 mg L⁻¹ and 35−50 mg L⁻¹, respectively. After 50 days operation, the NOB content was 0.10%, indicating the immobilized carrier provided favorable conditions for maintaining the low NOB content. Furthermore, due to the low NOB content in the inoculum and the oxygen-limited environment formed by the increase in the AOB numbers in the carrier, immobilized carrier with different initial biomass (1, 2.5 and 5%) can achieve stable partial nitrification.     

Mesophilic and thermophilic aerobic digestion of municipal sludge in an airlift U-shape bioreactor

Aerobic digestion of primary and secondary sludges was studied in airlift bioreactors at mesophilic and thermophilic temperatures. The experimental studies were conducted with a laboratory U-shape airlift reactor (operating volume 23 liters) and in a pilot U-shape airlift reactor of 1150 liters operating volume. In the laboratory reactor, with cold (6°C) and concentrated (3–4% solids) feed of primary and secondary municipal sludge, a 30% volatile suspended solids (VSS) reduction was achieved with a hydraulic retention time (HRT) of 2·5 days. A VSS loading rate of 8·2 kg VSS/m³/day was achieved. This loading is comparable to that obtained in a pure-oxygen sparged, mixed reactor.In the pilot-plant reactor at mesophilic temperature (31–33°C), a VSS loading rate of 7·9 kg VSS/m³/day and a VSS reduction of 40% were achieved with a HRT of 4 days.     

Reactivation of aerobic and anaerobic ammonium oxidizers in OLAND biomass after long-term storage

The biomass of an oxygen-limited autotrophic nitrification/denitrification (OLAND) biofilm reactor was preserved in various ways to find a storage method for both aerobic and anaerobic ammonium-oxidizing bacteria (AerAOB and AnAOB). Storage occurred at −20°C with and without glycerol as cryoprotectant and at 4 and 20°C with and without nitrate as redox buffer. After 2 and 5 months, reactivation of AerAOB and AnAOB was achieved with the biomass stored at 4°C with and without nitrate and at 20°C with nitrate. Moreover, the presence of the AerAOB and AnAOB was confirmed with fluorescent in situ hybridization (FISH). Preservation in a nitrate environment resulted in a lag phase for the AnAOB reactivation. The supplied nitrate was denitrified during storage, and a real-time polymerase chain reaction with nitrifying and denitrifying genes allowed to estimate that at least 1.0 to 6.0% of the OLAND biofilm consisted of denitrifiers. It was concluded that reactivation after long-term storage is possible and that preservation at 4°C without nitrate addition is the recommended storage technique. The possibility to store OLAND biomass will facilitate research on AnAOB and can overcome larger-scale start-up and inhibition problems of novel nitrogen processes involving AnAOB.     

Effective anaerobic treatment of fresh leachate from MSW incineration plant and dynamic characteristics of microbial community in granular sludge

We investigated the treatment of fresh leachate from municipal solid waste incineration plants with high-strength organics using a lab-scale expanded granular sludge bed (EGSB) reactor. The reactor was operated at a mesophilic temperature (33 °C) for 118 days. The influent chemical oxygen demand (COD) of the leachate gradually increased to over 70,000 mg/L, and the organic loading rate increased to 18 kg COD/(m³?day). An average COD removal efficiency of 86.7 % was achieved when the reactor was fed with raw leachate, which suggests the feasibility of the EGSB process for leachate treatment. The microbial communities in the sludge from the reactor during the trial operation were constructed by denaturing gradient gel electrophoresis, clone libraries, and real-time quantitative polymerase chain reaction. The dominant group for archaea was Methanosaeta, with 68.4 % proportion at the start of the operation, and then changed to Methanosarcina, with a proportion of 62.3 %, after 118 days of operation. The dominant group of eubacteria was confirmed to be Firmicutes throughout the operation process, with the proportion increasing from >50 to 81.2 %. Almost all the operational taxonomic units of Firmicutes belonged to the order Clostridiales, with characteristic spore formation. The microbial diversity of the population was low under raw leachate as feed in the reactor. The dynamics of the microbial community in the anaerobic granular sludge was discussed relating with the operating status of the EGSB reactor.     

Analysis of the characteristics of short-cut nitrifying granular sludge and pollutant removal processes in a sequencing batch reactor

Aerobic granular sludge is a new type of microbe auto-immobilization technology; in this paper, short-cut nitrification and denitrification were effectively combined with the granular sludge technology. Simultaneous nitrification and denitrification granules were developed in a sequencing batch reactor (SBR) using synthetic wastewater with a high concentration of ammonia nitrogen at 25 °C with a dissolved oxygen concentration above 2.0 mg/L and a 15 days sludge retention time. The characteristics of the sludge and the removal efficiency were studied, and the removal mechanisms of the pollutants and the process of short-cut nitrification were analyzed. The average granule diameter of the granular sludge was 704.0 μm. The removal rates of pollutants and the accumulation rate of nitrite in the SBR were studied. During treatment of wastewater with a high concentration of ammonia nitrogen, simultaneous nitrification, and denitrification and the stripping process could contribute to the removal of total nitrogen. The high pH value, the high concentration of free ammonia, and the delamination of granular sludge were the main factors contributing to the short-cut nitrification property of granular sludge in the reaction process.     

Nitrogen removal performance and operation strategy of anammox process under temperature shock

Sequencing batch reactors were used to study anaerobic ammonium oxidation (anammox) process under temperature shock. Both long-term (15–35 °C) and short-term (10–50 °C) temperature effects on nitrogen removal performance were performed. In reactor operation test, the results indicated that ammonium removal rate decreased from 0.35 kg/(m³ day) gradually to 0.059 kg/(m³ day) when temperature dropped from 35 to 15 °C. Although bacteria morphology was not modified, sludge settling velocity decreased with decreasing temperature. In batch test, apparent activation energy (E_a) increased with decreasing temperature, which suggested the activity decrease of anaerobic ammonium oxidizing bacteria (AAOB). Low temperature inhibited AAOB and weakened nitrogen removal performance. The cardinal temperature model with inflection was first used to describe temperature effect on anammox process. Simulated results revealed that anammox reaction could occur at 10.52–50.15 °C with maximum specific anammox activity of 0.50 kg/(kg day) at 36.72 °C. The cold acclimatization of AAOB could be achieved and glycine betaine could slightly improve nitrogen removal performance at low temperature.     

The effect of sub-optimal temperature on specific sulfidogenic activity of mesophilic SRB in an H2-fed membrane bioreactor

The sulfidogenic activity of two mesophilic sulfate reducing enrichment cultures was studied in H₂-fed membrane bioreactors. The two enrichment cultures had different origins; one of them was a mesophilic and the other a psychrotolerant mesophilic culture. The operational temperatures of the reactors were gradually changed: for one the temperature was increased from 9 to 30 °C and for the other it was decreased from 35 to 9 °C. The specific sulfidogenic activities were 21–31, 52–53 and 57–92 mmol SO₄²⁻ g VSS⁻¹ d⁻¹ at 9, 15 and 30–35 °C, respectively. The sulfate reduction rate of the SRB stabilized to a lower level after the temperature was decreased. The percent electron flow to sulfate reduction was on average 24–32, 50 and 47–69% at 9, 15 and 30–35 °C, respectively. The capability of mesophilic SRB to oxidize electron donor decreased as the temperature was decreased. The results indicate that starting of the reactor operation at 9 °C resulted in higher sulfidogenic activity at sub-optimal temperatures and selective enrichment of the psychrotolerant species improved. The start-up of the reactor at 35 °C resulted in decreased sulfidogenic activity as the temperature was decreased. This indicates that the operational temperature of bioreactors with mesophilic SRB can be decreased to 15–20 °C and the sulfidogenic activity will decrease by 10–40%. Moreover, an operational temperature of 9 °C seems to be close to the lower limit of active sulfate reduction for the mesophilic enrichment cultures used in this study.     

Trichloroethylene removal and bacterial variations in the up-flow anaerobic sludge blanket reactor in response to temperature shifts

Trichloroethylene (TCE) degradation and the variations of bacteria composition and structure in the up-flow anaerobic sludge blanket (UASB) reactor were investigated by increasing the operating temperature from 20 to 40 °C. The influent was supplemented with 36.5 mg/L of TCE. There was a rise in the chemical oxygen demand (COD) removal efficiency from 20 to 35 °C and a decline when temperature enhanced to 40 °C. It reached maximum at 35 °C. In addition, TCE removal efficiency increased with temperature varying from 20 to 35 °C, and it dropped dramatically to 78.38 % at 40 °C, which presumably because the genus of Dehalobacter, a kind of bacteria with the ability to dechlorinate TCE to the corresponding chlorinated products, was not detected at 40 °C according to sequencing results. The Illumina MiSeq platform was adopted to explore the bacteria composition and structure in response to temperature shifts. The results indicated that temperature impacted greatly on the dominance and presence of specific populations at different taxonomic levels. Importantly, the class Dehalococcoidia was detected from 25 to 40 °C, in which there were many well-known Dehalococcoides sp. strains that were capable of complete dechlorination of TCE to ethene. It also suggested the potential function of the dominant genera (non-dechlorinating bacteria and dechlorinating bacteria) in the reactor.     

From mesophilic to thermophilic conditions: one-step temperature increase improves the methane production of a granular sludge treating agroindustrial effluents

Objectives

To assess the effect of one-step temperature increase, from 35 to 55 °C, on the methane production of a mesophilic granular sludge (MGS) treating wine vinasses and the effluent of a hydrogenogenic upflow anaerobic sludge blanket (UASB) reactor.

Results

One-step temperature increase from mesophilic to thermophilic conditions improved methane production regardless of the substrate tested. The biomethane potentials obtained under thermophilic conditions were 1.8–2.9 times higher than those obtained under mesophilic conditions. The MGS also performed better than an acclimated thermophilic digestate, producing 2.2–2.5 times more methane than the digestate under thermophilic conditions. Increasing the temperature from 35 to 55 °C also improved the methane production rate of the MGS (up to 9.4 times faster) and reduced the lag time (up to 1.9 times). Although the temperature increase mediated a decrease in the size of the sludge granules, no negative effects on the performance of the MGS was observed under thermophilic conditions.

Conclusions

More methane is obtained from real agroindustrial effluents at thermophilic conditions than under mesophilic conditions. One-step temperature increase (instead of progressive sequential increases) can be used to implement the thermophilic anaerobic digestion processes with MGS.

     

Microbial activity of suspended biomass from a nitritation–anammox SBR in dependence of operational condition and size fraction

Single-stage nitritation–anammox combines the growth of aerobic ammonium-oxidizing bacteria (AOB) and anaerobic ammonium oxidizing bacteria (AnAOB) in one reactor. The necessary compromise of their milieu conditions often leads to the growth of nitrite-oxidizing bacteria (NOB). For this study, a sequencing batch reactor (SBR) for nitritation–anammox was operated for 180 days with sewage sludge reject water (removal capacity, 0.4 kg?N?m^?3?day^?1). The growth of NOB was favored by enhanced oxygen supply rather than extended aerobic phases. Suspended-type biomass from this SBR was taken regularly and sieved into three size fractions (all of them <1,000 μm). Batch experiments as well as fluorescence in situ hybridization were performed to study the distribution and activity of AnAOB, AOB, and NOB within those size fractions. Both the measured conversion rates and detected abundances decreased with increasing size fraction. The highest anammox conversion rates (15 g NH₄ ⁺–N per kilogram VSS per hour) and the highest abundances of Brocadia fulgida were found in the medium size fraction (100–315 μm). The batch experiments proved to be accurate tools for the monitoring of multiple processes in the reactor. The results were representative for reactor performance during the 6 months of reactor operation.     

Influence of the thermochemical sludge pretreatment on the nitrification of A/O reactor with the removal of phosphorus by simultaneous precipitation

In the present study, a laboratory scale anoxic/oxic (A/O) reactor is used for the removal of nutrient and sludge reduction. Phosphorus removal was achieved through simultaneous precipitation, and sludge production was reduced through thermochemical pretreatment. The main objective of the study was to investigate the influence of sludge pretreatment on the nitrification rate. Total phosphorus in the effluent was maintained around 0.5 ～ 1.0 mg/L by simultaneous precipitation, using coagulant alum at 2.2 mole ratio. Before simultaneous precipitation, the nitrification rate of the A/O reactor was found to be 0.050 g N-NH₄ ⁺/g MLVSS.d. The thermochemical sludge pretreatment began on the 120^th day at pH 11 and 80°C. The initiation of sludge pretreatment brought about a significant reduction of the A/O reactor nitrification rate, which fell to 0.038 g N-NH₄ ⁺/g MLVSS/day. The effect of sludge pretreatment was reflected in the reduction of the nitrogen removal efficiency from 85 to 74%. Recycling of the thermochemically pretreated sludge accounted for 57% sludge reduction, which had an adverse influence on the nitrification rate of the system.     

Effects of dual stress (high salt and high temperature) on the photochemical efficiency of wheat leaves (Triticum aestivum)

In this study, we have focused on those components of Photosystem (PS) II which are significantly affected by dual stress (high salt and temperature) on wheat as measured by Plant Efficiency Analyser (PEA). It was observed that some of the chlorophyll a fluorescence parameters were temperature dominated, while some other parameters were salt dominated. We have also observed additive effects for parameters like antenna size heterogeneity. An important observation was that in high temperature alone, the K-step was observed at 40 °C, while in case of dual stress, the K-step was observed at 45 °C, while the Chl a fluorescence transient of 40 °C?+?0.5 M?NaCl was quite similar to 35 °C transient curve. In the presence of salt, K-step was observed at higher temperature suggesting a protection of OEC by salt. Plants are under dual stress, but effect of temperature stress is less severe in presence of salt stress. Thus, we can say that salt stress caused partial prevention from high temperature stress but it did not cause complete protection of PS II.     

Characterization and immobilization of a novel SGNH hydrolase (Est24) from Sinorhizobium meliloti

A novel oligomeric SGNH hydrolase (Est24) from Sinorhizobium meliloti was identified, actively expressed in Escherichia coli, characterized, and immobilized for industrial application. Sequence analysis of Est24 revealed a putative catalytic triad (Ser¹³-Asp¹⁶³-His¹⁶⁹), with moderate homology to other SGNH hydrolases. Est24 was more active toward short-chain esters, such as p-nitrophenyl acetate, butyrate, and valerate, while the S13A mutant completely lost its activity. Moreover, the activity of Est24 toward α- and β-naphthyl acetate, and enantioselectivity on (R)- and (S)-methyl-3-hydroxy-2-methylpropionate were tested. Est24 exhibited optimum activity at mesophilic temperature ranges (45–55 °C), and slightly alkaline pH (8.0). Structural and mutagenesis studies revealed critical residues involved in the formation of a catalytic triad and substrate-binding pocket. Cross-linked enzyme aggregates (CLEAs) of Est24 with and without amyloid fibrils were prepared, and amyloid fibril-linked Est24 with amyloid fibrils retained 83 % of its initial activity after 1 h of incubation at 60 °C. The high thermal stability of immobilized Est24 highlights its potential in the pharmaceutical and chemical industries.     

Test of Porous Ceramic Material for the Immobilisation of Predominant Nitrifying Bacteria and for the Improvement of the AAO Process

The efficiency of nitrification in a fixed bed reactor was compared to that found in an activated sludge reactor to determine their sensitivity to changing loads and lower temperatures. Two structurally identical lab‐scale systems, using the anaerobic/anoxic/aerobic (AAO) process to remove nitrogen and phosphorus simultaneously, were operated in parallel with secondary clarifiers and sludge return. The first aerobic system was operated as an activated sludge reactor, the second system as a fixed bed reactor. The aerobic fixed bed reactor was filled with porous ceramic materials for the immobilisation of predominantly nitrifying bacteria. The removal efficiencies of 99 % NH₄⁺‐N, 90 % DOC, and 98 % PO₄^3–‐P for normal loads of 0.11 g/L d DOC, 0.06 g/L d NH₄⁺‐N, and 0.0054 g/L d PO₄^3–‐P were achieved for both systems. However, the system with an aerobic fixed bed reactor was characterised by the following advantages over the system with an activated sludge reactor: a shorter time to reach almost complete nitrification, a higher nitrification rate at higher loads of NH₄⁺‐N and a lower sensitivity of nitrification at lower temperatures down to 12 °C.     

Characterization of a novel micro-pressure swirl reactor for removal of chemical oxygen demand and total nitrogen from domestic wastewater at low temperature

A novel micro-pressure swirl reactor (MPSR) was designed and applied to treat domestic wastewater at low temperature by acclimating microbial biomass with steadily decreasing temperature from 15 to 3 °C. Chemical oxygen demand (COD) was constantly removed by 85% and maintained below 50 mg L^?1 in the effluent during the process. When the air flow was controlled at 0.2 m³ h^?1, a swirl circulation was formed in the reactor, which created a dissolved oxygen (DO) gradient with a low DO zone in the center and a high DO zone in the periphery for denitrification and nitrification. 81% of total nitrogen was removed by this reactor, in which ammonium was reduced by over 90%. However, denitrification was less effective because of the presence of low levels of oxygen. The progressively decreasing temperature favored acclimation of psychrophilic bacteria in the reactor, which replaced mesophilic bacteria in the process of treatment.     

Molecular characterization of mesophilic and thermophilic sulfate reducing microbial communities in expanded granular sludge bed (EGSB) reactors

The microbial communities established in mesophilic and thermophilic expanded granular sludge bed reactors operated with sulfate as the electron acceptor were analyzed using 16S rRNA targeted molecular methods, including denaturing gradient gel electrophoresis, cloning, and phylogenetic analysis. Bacterial and archaeal communities were examined over 450 days of operation treating ethanol (thermophilic reactor) or ethanol and later a simulated semiconductor manufacturing wastewater containing citrate, isopropanol, and polyethylene glycol 300 (mesophilic reactor), with and without the addition of copper(II). Analysis, of PCR-amplified 16S rRNA gene fragments using denaturing gradient gel electrophoresis revealed a defined shift in microbial diversity in both reactors following a change in substrate composition (mesophilic reactor) and in temperature of operation from 30°C to 55°C (thermophilic reactor). The addition of copper(II) to the influent of both reactors did not noticeably affect the composition of the bacterial or archaeal communities, which is in agreement with the very low soluble copper concentrations (3–310 μg l⁻¹) present in the reactor contents as a consequence of extensive precipitation of copper with biogenic sulfides. Furthermore, clone library analysis confirmed the phylogenetic diversity of sulfate-reducing consortia in mesophilic and thermophilic sulfidogenic reactors operated with simple substrates.     

Simultaneous energy recovery and autotrophic nitrogen removal from sewage at moderately low temperatures

This study assessed the technical feasibility of treating sewage with a combination of direct anaerobic treatment and autotrophic nitrogen removal, while simultaneously achieving energy recovery and nitrogen removal under moderately low temperatures. The concentrations of ammonia, nitrite, and COD in effluent were below 1, 0.1, and 30 mg/L, respectively. In the up-flow, anaerobic sludge fixed-bed, there was no obvious change observed in the total methane production at temperatures of 35?±?1 °C, 28?±?1 °C, 24?±?3 °C, and 17?±?3 °C, with the accumulation of volatile fatty acids occurring with decreasing temperatures. The control strategy employed in this study achieved a stable effluent with equimolar concentrations of nitrite and ammonium, coupled with high nitrite accumulation (>97 %) in the partial nitrification sequencing batch reactor system at moderately low temperatures. In the anaerobic ammonium oxidation (anammox) reactor, a short hydraulic retention time of 0.96 h, with a nitrogen removal rate of 0.83 kgN/(m³/day) was achieved at 12–15 °C. At low temperatures, the corresponding fluorescence in situ hybridization image revealed a high amount of anammox bacteria. This study demonstrates that efficient nitrogen removal and energy recovery from sewage at moderately low temperatures can be achieved by utilizing a combined system. Additionally, this system has the potential to become energy-neutral or even energy-producing.     

Dual anaerobic co-digestion of sewage sludge and confectionery waste

Three configurations for a dual digestion system were examined. The units were based on three 5 l completely stirred tank reactors (CSTR). A first-stage thermophilic digester was used to provide the feed to each of the two second-stage mesophilic (35°C) digesters. Using a mixture of sewage sludge and strong confectionery waste, the thermophilic digester was operated at 55°C with a hydraulic retention time of 4 h. The mesophilic digesters were operated at hydraulic retention times of 8, 12 and 15 days. In terms of the reduction of volatile solids (VS), the three dual digestion configurations were similar but were more effective than the single-stage reactor which was used as a control. However, based on the specific methane yield (m³ CH₄/kg VS removed), the configuration with a first stage operating at 55°C and a secondary digester at 35°C with a hydraulic retention time of 12 days was the most effective. This configuration also maintained a more stable pH, irrespective of the quality of the feed sludge.