Enrichment of a K-strategist microbial population able to biodegrade p-nitrophenol in a sequencing batch reactor

Impacts of sugarcane industrial effluent as an alternate source of irrigation on growth, chlorophyll contents and antioxidants of different canola varieties

The sugarcane industry often utilizes effluent for irrigation purposes; however, its intricate composition and elevated metal contaminants pose a potential risk of soil and crop contamination. Consequently, it is imperative to employ effective strategies to ensure the safe utilization of this resource for crop cultivation. One such strategy involves the dilution of sugarcane industry effluent. Dilution is a practical approach to mitigate its toxicity, minimizing its adverse impact on soil and crop health. That's why the current study explored the best dilution of sugarcane industrial effluent (SW) for cultivating canola varieties. A total of 15 canola varieties were cultivated 0%, 20%, 40%, 60%, 80%, and 100% SW. Results showed that 60% SW Faisalabad Canola and Punjab Canola improved germination, shoot length, root length, shoot fresh and dry weight, root fresh and dry weight, and chlorophyll contents compared to other treatments and control. AARI Canola and CON-III showed poor growth and chlorophyll contents under 60%SW. Dunkled and Oscar cultivars showed moderate improvement in growth and chlorophyll contents under 60SW. The 60% SW can be recommended for maximum growth benefits in canola cultivars, specifically Faisalabad Canola and Punjab Canola. At 20SW, the root dry weight of Faisalabad Canola increased by 2.7%, while Punjab Canola increased by 3.4%. Canola showed the highest increase in POD activity compared to the control, with a 55.45% increase, followed by Sandal Canola, with a 43.26% increase. However, additional field-level experiments are needed to determine the best cultivars suitable for optimal growth under 80SW and 60SW irrigation conditions.

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

The r/K selection theory and its application in biological wastewater treatment processes

Understanding the characteristics of functional organisms is the key to managing and updating biological processes for wastewater treatment. This review, for the first time, systematically characterized two typical types of strategists in wastewater treatment ecosystems via the r/K selection theory and provided novel strategies for selectively enriching microbial community. Functional organisms involved in nitrification (e.g., Nitrosomonas and Nitrosococcus), anammox (Candidatus Brocadia), and methanogenesis (Methanosarcinaceae) are identified as r-strategists with fast growth capacities and low substrate affinities. These r-strategists can achieve high pollutant removal loading rates. On the other hand, other organisms such as Nitrosospira spp., Candidatus Kuenenia, and Methanosaetaceae, are characterized as K-strategists with slow growth rates but high substrate affinities, which can decrease the pollutant concentration to low levels. More importantly, K-strategists may play crucial roles in the biodegradation of recalcitrant organic pollutants. The food-to-microorganism ratio, mass transfer, cell size, and biomass morphology are the key factors determining the selection of r-/K-strategists. These factors can be related with operating parameters (e.g., solids and hydraulic retention time), biomass morphology (biofilm or granules), and operating modes (continuous-flow or sequencing batch), etc., to achieve the efficient acclimation of targeted r-/K-strategists. For practical applications, the concept of substrate flux was put forward to further benefit the selective enrichment of r-/K-strategists, fulfilling effective management and improvement of engineered pollution control bioprocesses. Finally, the future perspectives regarding the development of the r/K selection theory in wastewater treatment processes were discussed.

Effect of Nitrate and Perchlorate on Selenate Reduction in a Sequencing Batch Reactor

Selenate removal from a water body is being vigorously debated owing to severe health impact, but inhibitions of coexisting anions have been reported. To suggest a viable treatment option, this study investigates the effect of nitrate and perchlorate on selenate reduction in a laboratory-scale sequencing batch reactor. The experimental design tests how competing electron acceptors (NO3− and ClO4−) and electron donor (acetate) limitations affect selenate reduction in the reactor. Results show that the reactor achieves almost complete selenate reduction within the initial concentration ranges of 0.1–1 mM by enriching selenate-reducing bacteria with appropriate temperature (30 °C) and acclimation period (50 days). We monitored simultaneous selenate and nitrate reduction in the reactor without specific inhibition due to a difference in microbial growth strategy related to electron donor status. Lack of perchlorate-reducing bacteria makes perchlorate addition (0.2 mM) not to be closely associated with dissimilative perchlorate reduction. These results provide information that can help us to understand the effect of competing electron acceptors on selenate reduction and the kinetics of potential parallel reactions in the reactor.

Simultaneous p-nitrophenol and nitrogen removal in PNP wastewater treatment: Comparison of two integrated membrane-aerated bioreactor systems

The chemical p-nitrophenol (PNP) is a priority pollutant, and PNP wastewater is highly toxic and resistant to biodegradation. The traditional physical and chemical methods (adsorption, extraction, and oxidation) for treating PNP wastewater have the disadvantages of complicated processes, high costs and secondary pollution generation. In this study, two integrated membrane-aerated bioreactor systems (RA and RB) with anoxic and aerated zones were constructed to enhance PNP biodegradation. The results showed that a helical silicone rubber membrane module displayed a high oxygen supply rate under a low membrane aeration pressure, and the hydraulic flow state of the reactor approached ideal mixing. At an influent PNP concentration of 500 mg/L, the average removal rates of PNP, chemical oxygen demand (COD) and total nitrogen (TN) reached 95.86%, 89.77%, and 94.81%, respectively, for RA and 89.48%, 74.26% and 64.78%, respectively, for RB, indicating efficient simultaneous PNP and nitrogen removal. Compared with that of RB, the pre-anoxic zone in RA not only performed detoxification pretreatment but also enhanced PNP degradation and denitrification effects, which relieved the biological treatment burden of the subsequent aerated zone. Based on these comprehensive analyses of reactor performance, the hydroquinone pathway might be the main route in the aerobic degradation of PNP.

Adsorptive removal of organics from aqueous phase by acid-activated coal fly ash: preparation, adsorption, and Fenton regenerative valorization of "spent" adsorbent

Raw coal fly ash was activated to an adsorbent by sulfuric acid impregnation. The activation condition, the adsorption capacity, and the regenerative valorization of the adsorbent were studied. The results show that the optimal preparation conditions of the adsorbent are [H₂SO₄] = 1 mol L^-1, activation time = 30 min, the ratio of coal fly ash to acid = 1:20 (g:mL), calcination temperature = 100 °C. The adsorption of p-nitrophenol on the adsorbent accords with the pseudo-second-order kinetic equation and the adsorption rate constant is 0.089 g mg^-1 min^-1. The adsorption on this adsorbent can be considered enough after 35 min, when the corresponding adsorption capacity is 1.07 mg g^-1 (85.6% of p-nitrophenol removal). Compared with raw coal fly ash, the adsorbent has a stable adsorption performance at low pH range (pH = 1-6) and the adsorption of p-nitrophenol is an exothermic process. Ninety minutes is required for the regenerative valorization of saturated adsorbent by Fenton process. The regenerative valorization for this saturated adsorbent can reach 89% under the optimal proposed conditions (30 °C, pH = 3, [H₂O₂] = 5.0 mmol L^-1, [Fe²⁺] = 5.5 mmol L^-1). Within 15 experimental runs, the adsorbent has a better and better stability with the increase of experimental runs. Finally, the mechanism of activating coal fly ash is proposed, being verified by the results of the SEM and BET test.

Bioaugmentation of strain Methylobacterium sp. C1 towards p-nitrophenol removal with broad spectrum coaggregating bacteria in sequencing batch biofilm reactors

This work was conducted in order to evaluate an instance of bioaugmentation, namely, the addition of a novel p-nitrophenol (PNP)-degrading bacterium Methylobacterium sp. C1 coaggregated with two other broad-spectrum coaggregating strains (Bacillus megaterium T1 and Bacillus cereus G5) within sequence batch biofilm reactors (SBBRs). Results showed that biofilms consisting of C1 and coaggregating bacteria were resistant to shock loads and were more efficient at PNP removal. High-throughput sequencing data revealed that biofilms formed in the presence of the coaggregating bacteria demonstrated greater microbial diversity. These results suggest that broad-spectrum coaggregating bacteria may be capable of mediating the immobilization of exogenous degrading bacteria into biofilms, rendering them more resistant to toxic compounds and environmental stresses. This represents the first attempt to assess the bioaugmentation of PNP-contaminated wastewater treatment through the utilization of broad-spectrum coaggregating bacteria.

Study on preparation conditions of coal fly ash catalyst and catalytic mechanism in a heterogeneous Fenton-like process

The heterogeneous Fenton-like process catalyzed by H₂SO₄-modified coal fly ash can treat organic wastewater effectively.

Catalytic oxidation of organic pollutants in wastewater via a Fenton-like process under the catalysis of HNO3-modified coal fly ash

Organic wastewater can be treated effectively via a heterogeneous Fenton-like process under the catalysis of HNO₃-modified coal fly ash.

Kinetic and microbiological characterization of aerobic granules performing partial nitritation of a low-strength wastewater at 10 °C

A granular airlift reactor enriched in ammonia oxidizing bacteria (AOB) was operated at 10 °C performing stable partial nitritation in the long-term. The reactor treated a synthetic low-strength influent during 250 days with an average nitrogen loading rate of 0.63 ± 0.06 g N L(-1) d(-1). Nitrate production was barely detected, being the average concentration in the effluent of 0.6 ± 0.3 mg N-NO3 L(-1). Furthermore, a suitable effluent for a subsequent reactor performing the anammox process was achieved. A maximum specific growth rate as high as 0.63 ± 0.05 d(-1) was determined by performing kinetic experiments with the granular sludge in a chemostat and fitting the results to the Monod model. Pyrosequencing analysis showed a high enrichment in AOB (41 and 65% of the population were identified as Nitrosomonas genus on day 98 and 233, respectively) and an effective repression of nitrite oxidizing bacteria in the long-term. Pyrosequencing analysis also identified the coexistence of nitrifying bacteria and heterotrophic psychrotolerant microorganisms in the granular sludge. Some psychrotolerant microorganisms are producers of cryoprotective extracellular polymeric substances that could explain the better survival of the whole consortia at cold temperatures.

Sequentially alternating pollutant scenarios of phenolic compounds in a continuous aerobic granular sludge reactor performing simultaneous partial nitritation and o-cresol biodegradation

Industrial wastewater treatment plants must operate properly during the transient-state conditions often found in the industrial production. This study presents the performance of simultaneous partial nitritation and o-cresol biodegradation in a continuous aerobic granular reactor under sequentially alternating pollutant (SAP) scenarios. Three SAP scenarios were imposed during the operation of the granular reactor. In each one, a secondary recalcitrant compound (either p-nitrophenol (PNP), phenol or 2-chlorophenol (2CP)) were added for a short period of time to the regular influent containing only ammonium and o-cresol. Partial nitritation and o-cresol biodegradation were not inhibited by the presence of PNP or phenol and both compounds were fully biodegraded. On the contrary, the presence of 2CP strongly inhibited both processes within 2days. However, the reactor was recovered in a few days. These findings demonstrate that treatment of complex industrial wastewaters with variable influent composition is feasible in a continuous aerobic granular reactor.

Partial nitritation and o-cresol removal with aerobic granular biomass in a continuous airlift reactor

Several chemical industries produce wastewaters containing both, ammonium and phenolic compounds. As an alternative to treat this kind of complex industrial wastewaters, this study presents the simultaneous partial nitritation and o-cresol biodegradation in a continuous airlift reactor using aerobic granular biomass. An aerobic granular sludge was developed in the airlift reactor for treating a high-strength ammonium wastewater containing 950 ± 25 mg N-NH4(+) L(-1). Then, the airlift reactor was bioaugmented with a p-nitrophenol-degrading activated sludge and o-cresol was added progressively to the ammonium feed to achieve 100 mg L(-1). The results showed that stable partial nitritation and full biodegradation of o-cresol were simultaneously maintained obtaining a suitable effluent for a subsequent anammox reactor. Moreover, two o-cresol shock-load events with concentrations of 300 and 1000 mg L(-1) were applied to assess the capabilities of the system. Despite these shock load events, the partial nitritation process was kept stable and o-cresol was totally biodegraded. Fluorescence in situ hybridization technique was used to identify the heterotrophic bacteria related to o-cresol biodegradation and the ammonia oxidising bacteria along the granules.

Simultaneous nitritation and p-nitrophenol removal using aerobic granular biomass in a continuous airlift reactor

The chemical and petrochemical industries produce wastewaters containing ammonium and phenolic compounds. Biological treatment of these wastewaters could be problematic due to the possible inhibitory effects exerted by phenolic compounds. The feasibility of performing simultaneous nitritation and p-nitrophenol (PNP) biodegradation using a continuous aerobic granular reactor was evaluated. A nitrifying granular sludge was bioaugmented with a PNP-degrading floccular sludge, while PNP was progressively added to the feed containing a high ammonium concentration. Nitritation was sustained throughout the operational period with ca. 85% of ammonium oxidation and less than 0.3% of nitrate in the effluent. PNP biodegradation was unstable and the oxygen limiting condition was found to be the main explanation for this unsteadiness. An increase in dissolved oxygen concentration from 2.0 to 4.5 mg O2 L(-1) significantly enhanced PNP removal, achieving total elimination. Acinetobacter genus and ammonia-oxidising bacteria were the predominant bacteria species in the granular biomass.

Aerobic biodegradation of a mixture of monosubstituted phenols in a sequencing batch reactor

A sequencing batch reactor (SBR) was inoculated with p-nitrophenol-degrading activated sludge to biodegrade a mixture of monosubstituted phenols: p-nitrophenol (PNP), PNP and o-cresol; and PNP, o-cresol and o-chlorophenol. Settling times were progressively decreased to promote biomass granulation. PNP was completely biodegraded. The PNP and o-cresol mixture was also biodegraded although some transitory accumulation of intermediates occurred (mainly hydroquinone and catechol). o-Chlorophenol was not biodegraded and resulted in inhibition of o-cresol and PNP biodegradation and complete failure of the SBR within a few days. The biomass had very good settling properties when a settling time of 1 min was applied: sludge volume index (SVI₅) below 50 mL g(-1), SVI₅/SVI₃₀ ratio of 1 and average particle size of 200 μm.

Strategies to evaluate biodegradability: application to chlorinated herbicides

The biodegradability of nitrochlorinated (diuron and atrazine) and chlorophenoxy herbicides (2,4-D and MCPA) has been studied through several bioassays using different testing times and biomass/substrate ratios. A fast biodegradability test using unacclimated activated sludge yielded no biodegradation of the herbicides in 24 h. The inherent biodegradability test gave degradation percentages of around 20-30% for the nitrochlorinated herbicides and almost complete removal of the chlorophenoxy compounds. Long-term biodegradability assays were performed using sequencing batch reactor (SBR) and sequencing batch membrane bioreactor (SB-MBR). Fixed concentrations of each herbicide below the corresponding EC50 value for activated sludge were used (30 mg L(-1) for diuron and atrazine and 50 mg L(-1) for 2,4-D and MCPA). No signs of herbicide degradation appeared before 35 days in the case of diuron and atrazine and 21 days for 2,4-D, whereas MCPA was partially degraded since the early stages. Around 25-36% degradation of the nitrochlorinated herbicides and 53-77% of the chlorophenoxy ones was achieved after 180 and 135 days, respectively, in SBR, whereas complete disappearance of 2,4-D was reached after 80 days in SB-MBR.

Study on the aerobic biodegradability and degradation kinetics of 3-NP; 2,4-DNP and 2,6-DNP

Four biodegradability tests (BOD(5)/COD ratio, production of carbon dioxide, relative oxygen uptake rate and relative enzymatic activity) were used to determine the aerobic biodegradability of 3-nitrophenol (3-NP), 2,4-dinitrophenol (2,4-DNP) and 2,6-dinitrophenol (2,6-DNP). Furthermore, biodegradation kinetics of the compounds was investigated in sequencing batch reactors both in the presence of glucose (co-substrate) and with nitrophenol as the sole carbon source. Among the three tested compounds, 3-NP showed the best biodegradability while 2,6-DNP was the most difficult to be biodegraded. The Haldane equation was applied to the kinetic test data of the nitrophenols. The kinetic constants are as follows: the maximum specific degradation rate (K(max)), the saturation constants (K(S)) and the inhibition constants (K(I)) were in the range of 0.005-2.98 mg(mgSS d)(-1), 1.5-51.9 mg L(-1) and 1.8-95.8 mg L(-1), respectively. The presence of glucose enhanced the degradation of the nitrophenols at low glucose concentrations. The degradation of 3-NP was found to be accelerated with the increasing of glucose concentrations from 0 to 660 mg L(-1). At high (1320-2000 mg L(-1)) glucose concentrations, the degradation rate of 3-NP was reduced and the K(max) of 3-NP was even lower than the value obtained in the absence of glucose, suggesting that high concentrations of co-substrate could inhibit 3-NP biodegradation. At 2,4-DNP concentration of 30 mg L(-1), the K(max) of 2,4-DNP with glucose as co-substrate was about 30 times the value with 2,4-DNP as sole substrate. 2,6-DNP preformed high toxicity in the case of sole carbon source degradation and the kinetic data was hardly obtained.

Bioaugmentation for treating transient or continuous p-nitrophenol shock loads in an aerobic sequencing batch reactor

Bioaugmentation with an enriched microbial population was applied in an aerobic sequencing batch reactor (SBR) receiving transient or continuous shock loads of p-nitrophenol (PNP). The effect of the amount of biomass added for bioaugmentation was assessed by using two different dosages (2% or 5% w/w of the total biomass in the seeded SBR). In both cases, total PNP removal was achieved during the transient PNP shock load occurring after bioaugmentation. However, after a long PNP starvation period the only experiment still showing total PNP removal during a second PNP shock load was the one where a dosage of 5% w/w was applied. The results suggested that the dosage is a key factor for the implementation of a successful bioaugmentation strategy. In addition, the performance of a bioaugmented SBR receiving a continuous PNP shock load was enhanced when compared to a non-bioaugmented SBR.

Kinetics of aerobic biodegradation of dihydroxybenzenes by a p-nitrophenol-degrading activated sludge

The aerobic biodegradation of the three dihydroxybenzene isomers (catechol, resorcinol and hydroquinone) by an activated sludge acclimated to consume p-nitrophenol (PNP) was studied through batch respirometric tests. The PNP-degrading biomass was able to consume each isomer as the sole organic carbon source, as well as, mixtures of two or three dihydroxybenzenes. However, the biodegradation rates were significantly different for each isomer and were highly influenced by the simultaneous presence of the other dihydroxybenzenes in binary or ternary mixtures. In general, hydroquinone was the isomer consumed at the fastest rate while the consumption rate of resorcinol was the slowest one. The kinetics of aerobic biodegradation of hydroquinone and catechol were successfully described by a Haldane model. The values of the kinetic coefficients showed that the affinity of PNP-degrading biomass for both isomers was low while catechol caused less substrate inhibition than hydroquinone.

Aromatic organic contaminant removal from an aqueous environment by p(4-VP)-based materials

p(4-vinylpyridine) (p(4-VP)) hydrogels were prepared in bulk (macro, 5 × 6 mm) and in nanosizes (370 nm) dimensions. The prepared hydrogels were used to remove organic aromatic contaminates such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), phenol (Ph) and nitrobenzene (NB) from an aqueous environment. Important parameters affecting the absorption phenomena, such as the initial concentration of the organic species and the absorbent, absorption rate, absorption capacity, pH and the temperature of the medium, were evaluated for both hydrogel sizes. The absorption capacity of bulk and microgels were found to be 4-NP>2-NP>Ph>NB. Furthermore, p(4-VP) microgels were embedded in poly(acrylamide) (p(AAm)) bulk hydrogel as a microgel-hydrogel interpenetrating polymer network and proved to be very practical in overcoming the difficulty of using the microgels in real applications. Moreover, it was demonstrated that separately prepared magnetic ferrite particles inserted inside p(4-VP) microgels during synthesis allowed for trouble-free removal of p(4-VP)-magnetic composite microgels from the aqueous environment by an externally applied magnetic field upon completion of their task.

Biodegradation of p-nitrophenol using Arthrobacter chlorophenolicus A6 in a novel upflow packed bed reactor

A novel packed bed reactor (PBR) was designed with cross flow aeration at multiple ports along the depth to improve the hydrodynamic conditions of the reactor, and the biodegradation efficiency of Arthrobacter chlorophenolicus A6 on p-nitrophenol (PNP) removal in PBR at different PNP loading rates were evaluated. The novel PBR was designed to improve the hydrodynamic features such as mixing time profile (t(m95)), oxygen mass transfer coefficient (k(L)a), and overall gas hold up capacity (ɛ(G)) of the reactor. PNP concentration in the influent was varied between 600 and 1400 mg l(-1) whereas the hydraulic retention time (HRT) in the reactor was varied between 18 and 7.5h. Complete removal of PNP was achieved in the reactor up to a PNP loading rate of 2787 mg l(-1)d(-1). More than 99.9% removal of PNP was achieved in the reactor for an influent concentration of 1400 mg l(-1) and at 18 h HRT. In the present study, PNP was utilized as sole source of carbon and energy by A. chlorophenolicus A6. Furthermore, the bioreactor showed good compatibility in handling shock loading of PNP.

Modelling the pH dependence of the kinetics of aerobic p-nitrophenol biodegradation

There are a number of publications in the literature that might indicate a connection between pH and the kinetics of the aerobic p-nitrophenol (PNP) biodegradation. In this study two hypotheses were postulated to elucidate the kinetics dependence on pH: (i) the substrate inhibition does not depend on the pH value, therefore the half-saturation coefficient and the substrate inhibition constant will be the same at any pH and (ii) the substrate inhibition depends on the pH value, therefore the half-saturation coefficient and the substrate inhibition constant will have a different value depending on the pH. A PNP-degrading activated sludge was used to carry out three batch respirometric experiments at different pH values: 6.5±0.1, 7.0±0.1, 8.0±0.1. The ability to describe the experimental results with the kinetic models derived from both postulated hypotheses was quantitatively evaluated through the norm of the prediction error array. The time course of specific oxygen uptake rate and PNP concentration was satisfactorily described by a Haldane kinetics that includes the pH effect, based on the PNP acid-base equilibrium, on the kinetic parameters. The results suggest that the nonionised form of PNP is the real substrate and also the inhibitor of the aerobic PNP biodegradation.