Control and optimization of nitrifying communities for nitritation from domestic wastewater at room temperatures

To achieve nitritation from complete-nitrification seed sludge at room temperature of 19 ± 1 °C, a lab-scale sequencing batch reactor (SBR) treating domestic wastewater with low C/N ratios was operated to investigate the control and optimization of nitrifying communities. Ammonia oxidizing bacteria (AOB) dominance was enhanced through the combination of low DO concentrations (<1.0 mg/L) and preset short-cycle control of aeration time. Nitritation was successfully established with NO₂^?-N/NO_x^?-N over 95%. To avoid the adverse impact of low DO concentrations on AOB activities, DO concentrations were increased to 1–2 mg/L. At the normal DO levels and temperatures, on-line control strategy of aerobic durations maintained the stability of nitritation with nitrite accumulation rate over 95% and ammonia removal above 97%. Fluorescence in-situ hybridization (FISH) analysis presented that the maximal percentage of AOB in biomass reached 10.9% and nitrite oxidizing bacteria (NOB) were washed out.     

Partial nitrification to nitrite using low dissolved oxygen concentration as the main selection factor

Partial nitrification to nitrite (nitritation) can be achieved in a continuous process without sludge retention by wash out of nitrite oxidising bacteria (NOB) while retaining ammonia oxidising bacteria (AOB), at elevated temperatures (the SHARON process) and, as demonstrated in this paper, also at low dissolved oxygen (DO) concentrations. Enriched AOB was attained at a low DO concentration (0.4 mg l⁻¹) and a dilution rate of 0.42 day⁻¹ in a continuous process. A higher oxygen affinity of AOB compared to NOB seemed critical to achieving this. This was verified by determining the oxygen half saturation constant, K _o, with similar oxygen mass transfer resistances for enriched AOB and NOB as 0.033 ± 0.003 mg l⁻¹ and 0.43 ± 0.08 mg l⁻¹, respectively. However, the extent of nitritation attained was found to be highly sensitive to process upsets.     

Denitrification of nitrified and non-nitrified swine lagoon wastewater in the suspended sludge layer of treatment wetlands

One method for managing livestock-wastewater N is the use of treatment wetlands. The objectives of this study were to (1) assess the magnitude of denitrification enzyme activity (DEA) in the suspended sludge layers of bulrush and cattail treatment wetlands, and (2) evaluate the impact of nitrogen pretreatment on DEA in the suspended sludge layer. The study used four wetland cells (3.6 m × 33.5 m) with two cells connected in series. Each wetland series received either untreated or partially nitrified swine wastewater from a single-cell anaerobic lagoon. The DEA of the suspended sludge layers of the constructed wetlands was measured by the acetylene inhibition method. The control DEA treatment for the sludge layer had a mean rate of 18 μg N₂O-N g^?1 sludge h^?1. Moreover, the potential DEA (nitrate-N and glucose-C added) mean was very large, 121 μg N₂O-N g^?1 sludge h^?1. These DEA rates are consistent with the previously reported high levels of nitrogen removal by denitrification from these wetlands, especially when the wastewater was partially nitrified. Stepwise regression using distance within the wetland, wastewater nitrate, and wastewater ammonia explained much of the variation in DEA rates. In both bulrush and cattail wetlands, there were zones of very high potential DEA.     

Operation of partial nitrification to nitrite of landfill leachate and its performance with respect to different oxygen conditions

The coupled system of partial nitrification and anaerobic ammonium oxidation (Anammox) is efficient in nitrogen removal from wastewater. In this study, the effect of different oxygen concentrations on partial nitrification performance with a sequencing batch reactor (SBR) was investigated. Results indicate that, partial nitrification of landfill leachate could be successfully achieved under the 1.0–2.0 mg L⁻¹ dissolved oxygen (DO) condition after 118 d long-term operation, and that the effluent is suitable for an Anammox reactor. Further decreasing or increasing the DO concentration, however, would lead to a decay of nitrification performance. Additionally, the MLSS concentration in the reactor increased with increasing DO concentration. Respirometric assays suggest that low DO conditions (<2 mg L⁻¹) favor the ammonia-oxidizing bacteria (AOB) and significantly inhibit nitrite oxidizing bacteria (NOB) and aerobic heterotrophic bacteria (AHB); whereas high DO conditions (>3 mg L⁻¹) allow AHB to dominate and significantly inhibit AOB. Therefore, the optimal condition for partial nitrification of landfill leachate is 1.0–2.0 mg L⁻¹ DO concentration.     

Urine nitrification with a synthetic microbial community

During long-term extra-terrestrial missions, food is limited and waste is generated. By recycling valuable nutrients from this waste via regenerative life support systems, food can be produced in space. Astronauts’ urine can, for instance, be nitrified by micro-organisms into a liquid nitrate fertilizer for plant growth in space. Due to stringent conditions in space, microbial communities need to be be defined (gnotobiotic); therefore, synthetic rather than mixed microbial communities are preferred. For urine nitrification, synthetic communities face challenges, such as from salinity, ureolysis, and organics.In this study, a synthetic microbial community containing an AOB (Nitrosomonas europaea), NOB (Nitrobacter winogradskyi), and three ureolytic heterotrophs (Pseudomonas fluorescens, Acidovorax delafieldii, and Delftia acidovorans) was compiled and evaluated for these challenges. In reactor 1, salt adaptation of the ammonium-fed AOB and NOB co-culture was possible up to 45 mS cm⁻¹, which resembled undiluted nitrified urine, while maintaining a 44 ± 10 mg NH₄⁺–N L⁻¹ d⁻¹ removal rate. In reactor 2, the nitrifiers and ureolytic heterotrophs were fed with urine and achieved a 15 ± 6 mg NO₃⁻–N L⁻¹ d⁻¹ production rate for 1% and 10% synthetic and fresh real urine, respectively. Batch activity tests with this community using fresh real urine even reached 29 ± 3 mg N L⁻¹ d⁻¹. Organics removal in the reactor (69 ± 15%) should be optimized to generate a nitrate fertilizer for future space applications.     

Nitrification rates in a saline medium at different dissolved oxygen concentrations

A kinetic study was carried out in a saline medium to assess the effect of O₂ on the two-step nitrification process: for the first nitritation step, 2–26 mg dissolved O₂ (DO) l^–1 was used and for the second nitratation step, 0.5–24 mg DO l^–1 was used. Nitritation rate was measured in the presence of sodium azide so as to inhibit nitratation. Ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacterial in the mixed culture were determined by 16 S rRNA hybridization. The affinity constants for oxygen O₂ of the AOB and the NOB were 1.66 mg O₂ l^–1 and 3 mg O₂ l^–1 respectively. The larger than the previously reported values of these constants might be due to the high salt content in the medium. High O₂ concentrations did inhibit the nitrification rate.     

Alkalinity and dissolved oxygen as controlling parameters for ammonia removal through partial nitritation and ANAMMOX in a single-stage bioreactor

The oxidation of ammonia to dinitrogen through partial nitritation and anaerobic ammonium oxidation (ANAMMOX) in a single-stage bioreactor is based on suppressing the nitratation process. The single-stage process operated on a laboratory-scale fixed film bioreactor achieved ammonia removal of 0.7 kg NH₄-N/(m³ day) at 4 h hydraulic retention time (HRT) by controlling the nitratation process through a ‘three-way control mechanism’ comprising control of electron donor (nitrite), electron acceptor (oxygen) and carbon source (bicarbonate). The control of alkalinity and dissolved oxygen (DO) concentrations in feed to maintain an alkalinity to ammonia ratio of less than 8 and DO loading of less than 0.06 mg O/(mg N day), respectively, was necessary for inhibiting nitratation and enhancing partial nitritation and ANAMMOX. Therefore, feed alkalinity along with DO concentrations are critical controlling parameters in a single-stage biological process for nitrogen removal.     

Removal of triethylamine from synthetic wastewater by acclimated mixed bacteria cultures

This aim of this study was to remove triethylamine by a biological method, as well as to understand the ability of mixed bacteria cultures to treat a triethylamine compound from synthetic wastewater. The mixed bacteria cultures could not remove triethylamine, whether the activated sludge came from an acrylonitrile–butadiene–styrene resin manufactured wastewater treatment system or a waterborne polyurethane resin manufactured wastewater treatment system. When the mixed bacteria cultures were acclimated to triethylamine, they could utilize 650 mg l⁻¹ triethylamine for growth. When the initial triethylamine concentration was below 200 mg l⁻¹, the triethylamine removal efficiency could reach 100%. The triethylamine removal rate of the acclimated GMIX sludge was faster than the acclimated EMIX sludge.     

Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules

Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were 0.21 g chemical oxygen demand (COD) g⁻¹ N, 0.09 h⁻¹, and 9.1 mg N L⁻¹, respectively, whereas the corresponding values for NOB were 0.05 g COD g⁻¹ N, 0.11 h⁻¹, and 4.85 mg N L⁻¹, respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules.     

Effects of vegetation,limestone and aeration on nitritation,anammox and denitrification in wetland treatment systems

Integration of partial nitrification (nitritation) and anaerobic ammonium oxidation (anammox) in constructed wetlands creates a sustainable design for nitrogen removal. Three wetland treatment systems were operated with synthetic wastewater (60 mg NH₃–N L^?1) in a batch mode of fill – 1-week reaction – drain. Each treatment system had a surface flow wetland (unplanted, planted, and planted plus aerated, respectively) with a rooting substrate of sandy loam and limestone pellets, followed by an unplanted subsurface flow wetland. Meanwhile, three surface flow wetlands with a substrate of sandy loam and pavestone were operated in parallel to the former surface flow wetlands. Influent and effluent were monitored weekly for five cycles. Aeration reduced nitrogen removal due to hindered nitrate reduction. Vegetation maintained pH near neutral and moderate dissolved oxygen, significantly improved ammonia removal by anammox, and had higher TN removal due to coexistence of anammox and denitrification in anaerobic biofilm layers. Nitrite production was at a peak at the residence time of 4–5 d. Relative to pavestone, limestone increased the nitrite mass production peak by 97%. The subsurface flow wetlands removed nitrogen via nitritation and anammox, having an anammox activity of up to 2.4 g N m^?3 d^?1 over a startup operation of two months.     

Anaerobic granule development for removal of pentachlorophenol in an upflow anaerobic sludge blanket (UASB) reactor

The granulation process using synthetic wastewater containing pentachlorophenol (PCP) in four 1.1 l laboratory scale upflow anaerobic sludge blanket (UASB) reactors was studied, and the anaerobic biotransformation of PCP during the granulation process investigated. After 110 days granular sludge was developed and up to 160 and 180 mg/l of PCP was added into the reactors R1 and R2, respectively, when they were inoculated with acclimated anaerobic sludge from an anaerobic digester of a citric acid plant. The inoculum was predominately composed of bacilli and filamentous bacteria. Granulation did not occur in reactors R3 and R4 which were inoculated with acclimated anaerobic sludge from aerobic sludge of the municipal sewage treatment plant which consisted mainly of cocci. Despite similar bacilli in the granule, the filamentous bacteria from reactor R1 were thicker than those of reactor R2. The granular sludge had a maximum diameter of 2.5 and 2.2 mm, and SMA of 1.44 and 1.32 gCOD/gTVS per day for reactors R1 and R2, respectively. Over 98% chemical oxygen demand (COD) removal rate and 99% of PCP removal rate were achieved when reactors R1 and R2 were operated at PCP and COD loading rates of 150 and 7.5 g/l per day, respectively. H₂-producing acetogens were the dominant anaerobes in the granular sludge.     

NOB suppression and adaptation strategies in the partial nitrification–Anammox process for a poultry manure anaerobic digester

Poultry manure contains high levels of ammonia, which result in a suboptimal bioconversion to methane in anaerobic digesters (AD). A simultaneous process of nitrification, Anammox and denitrification (SNAD) in a continuous granular bubble column reactor to treat the anaerobically digested poultry manure was implemented. Thus, two strategies to achieve high efficiencies were proposed in this study: (1) ammonia overload to suppress nitrite oxidizing bacteria (NOB) and (2) gradual adaptation of the partial nitrification–Anammox (PN–A) biomass to organic matter. During the NOB-suppression stage, microbial and physical biomass characterizations were performed and the NOB abundance decreased from 31.3% to 3.3%. During the adaptation stage, with a nitrogen loading rate of 0.34 g L⁻¹ d⁻¹, a hydraulic retention time of 1.24 d and an influent COD/N ratio of 2.63 ± 0.02, a maximum ammonia and total nitrogen removal of 100% and 91.68% were achieved, respectively. The relative abundances of the aerobic and the anaerobic ammonia-oxidizing bacteria were greater than 35% and 40% respectively, during the study. These strategies provided useful design tools for the efficient removal of nitrogen species in the presence of organic matter.     

Optimized immobilization of activated sludge in poly(ethylene glycol) gels by UV technology

Conventional methods for immobilization of microorganisms in hydrogel are not very efficient and cost-effective. Ultraviolet (UV) technology, a rapid method for hydrogel preparation in ambient environment, was applied to immobilize activated sludge in poly(ethylene glycol) (PEG) gel carriers synthesized from PEG pre-polymer. Conditions for cell immobilization were optimized by selecting suitable UV photoinitiators, crosslinker concentrations, and protection gas. The optimum conditions are the following: 12% PEG pre-polymer with 1% MBA and 0.1% DEAP. More than 90% of ammonia was reduced, and 75% of the total organic compound was removed after treating 40 and 10 mg/L synthetic ammonia wastewater with different C/N ratios in 5 h under aeration conditions. Ammonia degradation increased with increasing C/N ratios, and the scanning electron microscopy images revealed that the immobilized beads had porous structures dominantly filled with nitrifiers. The bioactivity of the immobilized activated sludge was maintained during immobilization by UV technology.     

A unified model of ammonium oxidation rate at various initial ammonium strength and active ammonium oxidizer concentrations

This paper attempts to provide insight into the biological ammonium oxidation process applied to high-strength ammonium wastewater treatment. The ammonium oxidation process has been investigated at various ammonium and biomass concentrations. Using the oxygen uptake rate (OUR) method, a proportion of both active ammonium oxidizers (AAO) and nitrite oxidizers to the total suspended solids were separately estimated, and then tested to normalize the ammonium oxidation rate at various ammonium strengths and AAO concentrations. High-ammonium strength showed no significant inhibition to ammonium oxidation due to high-AAO concentration. It was demonstrated that the key factor deciding the specific ammonium oxidation rate was the ratio of ammonium concentration to the active nitrifiers (AN) concentration, but not the sole-variable such as initial ammonium concentration and AN concentration. Contois model was screened to suitably fit the ammonium oxidation kinetics under the high-ammonium loading condition, resulting in a half-saturation constant of 0.028 mg N mg^?1 AAO and a maximum specific ammonium oxidation rate of 3.56 g N g^?1 AAO d^?1.     

Performance of the Columbia,Missouri, treatment wetland

Constructed treatment wetlands have served the City of Columbia, MO, for fourteen years. Four free water surface wetland units in series, comprised of 23 cells, are an addition to the activated sludge wastewater treatment plant, for the purpose of added biochemical oxygen demand (BOD) and total suspended solids (TSS) control. The system operates year-round, and supplies water to the Eagle Bluffs Conservation Area for wetland maintenance. The cattail wetlands processed an average of 57,000 m³/d, at a water depth of 20 cm. The resulting detention time was approximately 2 days, and the hydraulic loading was 13 cm/d. Water temperatures were warm leaving the treatment plant and in the wetlands in winter, because of the short detention. The period of record average carbonaceous biochemical oxygen demand (CBOD) leaving the wetlands was 5.0 mg/L, and the TSS was 14.7 mg/L. Dissolved oxygen was depressed in summer, likely because of the high sediment demand. Nutrient concentrations were only minimally reduced, total nitrogen (TN) by 22% and total phosphorus (TP) by 6%. However, load reductions were maximal, 98 t/yr for nitrogen, and 3.6 t/yr for phosphorus. Fecal coliforms were reduced by 98%, and E. coli by 95%. First order rate coefficients were high for CBOD (64 m/yr), nitrate (61 m/yr) and organic nitrogen (42 m/yr), but relatively low for ammonia (8 m/yr) and phosphorus (5.7 m/yr). Nitrogen removal was strongly affected by vegetative uptake. Sediment accretion in the wetland inlets was substantial, at 1.6 cm/yr in the inlets to the upstream wetland units. Muskrats caused vegetation damage, and waterfowl use was high in winter, causing TSS excursions.     

Partial nitrification under limited dissolved oxygen conditions

Partial nitrification to nitrite is technically feasible and economically favourable, especially when wastewaters contained high ammonium concentrations or low C/N ratios. Partial nitrification can be obtained by selectively inhibiting nitrite-oxidizing bacteria (NOB) through appropriate regulation of the pH, temperature and dissolved oxygen (DO) concentrations. The effect of pH, DO levels and temperature on ammonia oxidation rate and nitrite accumulation was investigated in order to determine the optimal conditions for partial nitrification of synthetic wastewater with high ammonia concentration. The experiments performed at low DO levels to lower the total oxygen needed in the nitrification step, which means great saving in aeration. During the start-up stage pH and DO were set at 7.0–7.4 and 0.5 mg/l, respectively. The reactor was operated until complete partial nitrification was achieved. The effect of pH, DO on partial nitrification was studied, as pH was kept at 6.5, 7.5, 8.5, 9.5 and DO at 0.5±0.2, 1.5±0.2 and 2.5±0.2 mg/l, and temperature at 30 °C. The influence of temperature on k_a value was studied by keeping pH=7.5, DO=1.5 mg/l and temperature was controlled at 12, 20 and 30 °C, respectively. The results showed that partial nitrification to nitrite was steadily obtained and the optimal operational parameters were pH=7.5, DO=1.5 mg/l, T=30 °C based on ammonia oxidation rate and nitrite accumulation rate. The maximum k_a was achieved and to be 115.1×10⁻³ mg NH₄⁺–N (mg VSS h)⁻¹ under this condition.     

Optimization of biological treatment of paper mill effluent in a sequencing batch reactor

Laboratory scale research on the effects of operating parameters, including mixed liquor suspended solid (MLSS) concentration, volumetric exchange rate (VER), aeration time, temperature and daily operation cycle on biological treatment of the pulp and paper mill effluent was studied using four 4 l sequencing batch reactors (SBR). The results revealed that chemical oxygen demand (COD) removal efficiency was up to 93.1 ± 0.3% and the volumetric loading reached 1.9 kg BOD m⁻³ day⁻¹ under optimal operating conditions. The treatment performance of organic removal by the SBR system remained stable during the operation. The effluent quality was satisfied with the discharge standard set by the local authority and the filamentous bulking problem was solved. At the same time, the sludge settleability, in terms of sludge volume index (SVI), was improved to the healthy level (SVI = 52.7 ± 1.3 ml g⁻¹).     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Role and characteristics of problematic biofilms within the removal and mobility of trace metals in a pilot-scale membrane bioreactor

The characteristics of problematic biofilms (i.e., fouling and clogging layers) were studied with regards to the removal and fate of trace metals (contents well under 100 μg/L) during the long-term operation of a pilot-scale membrane bioreactor for the treatment of real wastewaters from a large industrial area.Results showed that clogging layer was more effective than suspended activated sludge in the biosorption of As > Zn > Ni > Cd > Sb > Fe > Se due to the synergic effects of extracellular polymeric compounds and metal-resistant bacteria. In fact the selective microbial speciation of the phylum of Bacteroidetes, which is highly resistant to heavy metals, was observed in the clogging sludge in spite of the very low concentration of dissolved metals in the bioreactor.Compared to the suspended activated sludge, the clogging layer enhanced the biosorption of very toxic substances such as As, Cd and Ni. In fact, the metal contents were respectively: 7.9–7.4 vs. 690–840 μgAs/kgTS; 1.5–2.2 vs. 149–219 μgCd/kgTS; 58.8–71.7 vs. 227–298 μgNi/kgTS. Then, the potential desorption of metals during the membrane acid cleanings was estimated as relevant as 10–15% of the metals associated to the clogging sludge. The combined effects of pH and the selected microbial community, and the minor effect of the redox potential, let us conclude on the major importance of bio-sorption/desorption mechanisms with respect to bio-precipitation/dissolution.     

Stereoselective biocatalytic hydride transfer to substituted acetophenones by the yeast Metschnikowia koreensis

Freely suspended and variously entrapped viable cells of the yeast Metschnikowia koreensis were examined for the asymmetric reduction of prochiral acetophenone. A ketone substrate at 25 mM can be converted (92%) to the corresponding alcohol within 3 h using freely suspended cells [46 mg/mL dry cell weight (DCW)] at pH 9 (Tris buffer, 50 mM), 25 °C, in an agitated reactor (200 rpm). The reaction displayed an excellent stereoselectivity of >99%. Supplementation of the reaction mixture with glucose (20 g/L) greatly enhanced the rate of the bioreduction reaction likely because of improved cofactor recycling in the cells. The cells could successfully reduce various acetophenones substituted with electron withdrawing groups on the phenyl ring, particularly at the para-position compared to ortho- or meta-substituted acetophenones. The ketone reductase of M. koreensis showed Prelog-selectivity as the reaction exclusively yielded (S)-alcohols. The thermostability and the substrate tolerance of the yeast were improved by immobilization in calcium alginate beads. Immobilization reduced the effectiveness factor only slightly.