Oxic Treatment Research Articles

Anaerobic–anoxic–oxic biological treatment of high-strength, highly recalcitrant polyphenylene sulfide wastewater

This paper outlines an integrated anaerobic–anoxic–oxic (A2O) treatment scheme for high-strength, highly recalcitrant wastewater from the production of polyphenylene sulfide (PPS) resins and their composite chemicals. An integrated anaerobic granular sludge blanket (GSB) and anoxic–oxic (AO) reactor indicated that the A2O removed chemical oxygen demand (COD) of up to 7,043 mg/L with no adverse impact from high total dissolved solids (25,000 mg/L) on the GSB COD removal and effluent suspended solids. At a Total Kjeldahl Nitrogen (TKN) nitrification load of 0.11 g TKN/L.d and 400 mg NH3/L, almost 99 % of the NH3 was degraded with effluent NH3 < 5 mg/L, meeting the limit of 35 mg/L. High S2- levels of up to 1470 mg/L can be transformed through aerobic microbial degradation to meet a limit of 1.0 mg/L. With proper microbial acclimation and process designs, the integrated A2O scheme offers a resilient and robust treatment for high-strength recalcitrant PPS wastewater.

Redox-dependent surface passivation reduces phytolith solubility

Phytoliths are an important silicon (Si) source for plants due to their high solubility, yet some phytoliths are stable for centuries and used in paleosciences to reconstruct past vegetation. Here, we show that this discrepancy can be resolved by considering interactions of phytoliths with soil solution constituents. We tested the hypothesis that recurring alternating redox conditions reduce the solubility of phytoliths due to the formation of protective coatings. Phytoliths from rice plants were repeatedly exposed to solutions from a typical paddy soil under either exclusively oxic conditions or alternately anoxic−oxic conditions. Changes in solution chemistry and surface properties (chemical composition, ζ potential, surface area and porosity) of exposed phytoliths were linked to phytolith dissolution kinetics over 30 days (in 0.01 M CaCl2 at pH 7). We found that phytoliths exposed to alternating redox conditions accumulated iron and carbon at their surfaces, with changes in other properties being little. Dissolution rates decreased after exposure to soil solution regardless of redox conditions, but more pronounced under alternating redox conditions. After six exposure steps, the Si dissolution rate for the alternating redox treatment decreased by factor of 3.2 (oxic treatment: 2.1), with the Si release rate being negatively correlated with total iron contents. We conclude that alternating redox conditions can cause increased phytolith stability due to surface passivation and, in turn, reduced Si availability to plants.

Soil Redox Controls CO2, CH4 and N2O Efflux from White-Rot Fungi in Temperate Forest Ecosystems.

Microaerophilic white-rot fungi (WRF) are impacted by oxygen depletion because of fluctuating redox occurrence in southern temperate forest soils of Chile (1500–5000 mm year−1). How these conditions influence WRF survival has been scarcely examined. We explored the contributions of WRF to greenhouse gas (GHG) emissions of N2O and CH4 and soil organic C oxidation (CO2) in five sterilized and inoculated forest soils derived from various parent materials and climates. The soil was incubated for 20 days following (i) oxic, (ii) anoxic, and (iii) fluctuating redox conditions. Fungi contributed to 45% of the total GHG under redox fluctuating conditions, including the contribution of bacteria, while the opposite (26%) was valid for oxic treatment. On average, the highest gas emission (62%) was N2O for WRF under redox treatment, followed by anoxic (22%) and oxic (16%) treatments, while CO2 and CH4 emissions followed oxic > redox > anoxic. These data suggest that indigenous microbial WRF communities are well adapted to fluctuating redox milieu with a significant release of GHG emissions in humid temperate forests of the southern cone.

Internal phoshorus loading potential of a semiarid reservoir: an experimental study

Abstract: Aim To determine the internal P loading potential of semiarid tropical reservoir sediment while verifying the driving factors that affect P release rates. Methods An experiment was performed with water and sediment from the reservoir Boqueirão de Parelhas in Brazil. The effects of three variables on P release were studied: air temperature (region average of 28 °C and 32 °C, simulating an increase of 4 °C), pH (region average of pH 8, more acidic pH 6 and more alkaline pH 10) and oxygen (presence and absence). In addition, P fractionation analysis was performed on the P forms in the sediment. Results It was found that the minimum P release was in an oxic treatment at pH 6 and temperature 28 °C (0.22 mg m-2 d-1 ± 0.13) and the maximum P release in an anoxic treatment at pH 10 and temperature 32 °C (2.1 mg m-2 d-1 ± 0.15). The total P in the sediment was 597 mg kg-1, and the major P form in the sediment was NaOH-rP, the P bound to aluminum, corresponding to 42% of the total P. Conclusion These results allow us to confirm that the sediment of the Boqueirão reservoir is susceptible to the release of P bound to aluminum due to the prevalence of this form in its sediments concomitant with the high temperatures and alkaline pH of the water. This scenario can be aggravated by climate change.

Investigating microbial fuel cell aided bio-remediation of mixed phenolic contaminants under oxic and anoxic environments

The work focuses on the bioelectrochemical treatment of wastewater containing phenol and trichlorophenol in microbial fuel cells (MFC) with non-coated and PANI/SnO2 modified anodes respectively. The SnO2 and PANI/SnO2 nanocomposite synthesised were characterised using XRD and FTIR techniques. The results reflected that the efficiency of the system performing oxic treatment was better than the system performing anoxic treatment. The anoxic treatment of mixed phenolic contaminant using non-coated and coated electrodes yielded the highest power densities of 375.36 and 454.81 mW/m2 respectively while the maximum power densities under oxic treatment were 464.81 and 522.77 mW/m2 respectively. The consistently higher performance of oxic MFCs in terms of power generation and treatment efficiencies infers its higher potential in treating toxic phenolic contaminants. UV/Vis spectrophotometry and cyclic voltammetry (CV) also confirm better oxic treatment. Moreover, the electrochemical impedance spectroscopy (EIS) data further justified the higher oxic performance with reduced charge transfer and ohmic resistances. The study advocates MFC as a practically feasible alternative in treating recalcitrant chemical wastes with lower energy requirements.

Degradation of Tetrabromobisphenol A by Sulfidated Nanoscale Zerovalent Iron in a Dynamic Two-Step Anoxic/Oxic Process.

A dynamic two-step anoxic/oxic process using sulfidated nanoscale zerovalent iron (S-nZVI) was employed to degrade tetrabromobisphenol A (TBBPA). In the anoxic stage, TBBPA followed a four-step sequential debromination pathway and was completely transformed to bisphenol A (BPA) with the optimal S/Fe molar ratio of 0.3. S-nZVI inhibited H2 evolution and preserved the reducing capacity of Fe(0). Fe(0), rather than the formed FeS in S-nZVI, was responsible for TBBPA debromination. In the oxic stage, the product BPA was attacked by •OH, transformed to dihydroxybenzenes and benzoquinones, and eventually, achieved mineralization via ring-opening reactions. The sulfidation process facilitated •OH production through a two-electron transfer pathway by surface-bound Fe(II), in which structural Fe(II) in FeS and regenerated Fe(II) from Fe(III) reduction by Fe(0) played significant roles toward total BPA degradation. S-nZVI was transformed to S8 and α-FeOOH after the oxic treatment. After these two steps, complete degradation of TBBPA was achieved. This study demonstrated the feasibility that refractory contaminants could be completely degraded in the dynamic two-step anoxic/oxic process, thus broadening the utility of S-nZVI for environmental applications in water treatment.

Short exposure to oxygen and sulfide alter nitrification, denitrification, and DNRA activity in seasonally hypoxic estuarine sediments.

Increased organic loading to sediments from eutrophication often results in hypoxia, reduced nitrification and increased production of hydrogen sulfide, altering the balance between nitrogen removal and retention. We examined the effect of short-term exposure to various oxygen and sulfide concentrations on sediment nitrification, denitrification and DNRA from a chronically hypoxic basin in Roskilde Fjord, Denmark. Surprisingly, nitrification rates were highest in the hypoxic and anoxic treatments (about 5 μmol cm−3 d−1) and the high sulfide treatment was not significantly different than the oxic treatment. Denitrification in the hypoxic treatment was highest at 1.4 μmol cm−3 d−1 and significantly higher than the high sulfide treatment. For DNRA, the rate in high sulfide treatment was 2 μmol cm−3 d−1. This was significantly higher than all oxygen treatments that were near zero. In this system, nitrifiers rapidly recovered from conditions typically considered inhibiting, while denitrifiers had a more muted response. DNRA bacteria appear to depend on sulfide for nitrate reduction. Anammox was insignificant. Thus, in estuaries and coastal systems that experience short-term variations in oxygen and sulfide, capabilities of microbial communities are more diverse and tolerant of suboptimal conditions than some paradigms suggest.

Spectroscopic study on transformations of dissolved organic matter in coal-to-liquids wastewater under integrated chemical oxidation and biological treatment process

A large amount of wastewater containing various toxic organic contaminants is produced during coal-to-liquids process. In this study, several spectroscopic methods were used to monitor the transformation of organic pollutants during an integrated chemical oxidation and biological process. The results showed that the hydrophobic acid fraction increased after Fenton oxidation, which was likely due to the production of small-molecule organic acids. Soluble microbial products were generated during biological treatment processes, which were degraded after ozonation; meanwhile, the hydrophilic base and acid components increased. Ultraviolet-visible spectroscopic analysis indicated that peaks at the absorption wavelengths of 280 and 254nm, which are associated with aromatic substances, were detected in the raw water. The aromatic substances were gradually removed, becoming undetectable after biological aeration filter (BAF) treatment. Fourier transform infrared spectroscopy analysis revealed that the functional groups of phenols; benzene, toluene, ethylbenzene, and xylene (BTEX); aromatic hydrocarbons; aliphatic acids; aldehydes; and esters were present in raw wastewater. The organic substances were oxidized into small molecules after Fenton treatment. Aromatic hydrocarbons were effectively removed through bioadsorption and biodegradation after BAF process. Biodegradable organic matter was reduced and finally became undetectable after anoxic–oxic treatment in combination with a membrane bioreactor. Four fluorescent components were fractionated and obtained via excitation–emission matrix parallel factor analysis (EEM-PARAFAC). Dissolved organic matter fractionation in conjunction with EEM-PARAFAC was able to monitor more precisely the evolution of characteristic organic contaminants.

Occurrence, fate, and mass balance of different classes of pharmaceuticals and personal care products in an anaerobic-anoxic-oxic wastewater treatment plant in Xiamen, China

In this study, the occurrence and fate of 49 pharmaceuticals and personal care products (PPCPs) were investigated in an anaerobic-anoxic-oxic (A2/O) wastewater treatment plant (WWTP) for seven consecutive days using 24-h composite sampling technique. Special emphasis was placed to understand the distribution of PPCPs in dissolved and adsorbed phase, and to evaluate PPCP fate in different treatment units. Among the 49 PPCPs, 40 PPCPs in influent, 36 in effluent, 29 in sludge and 23 in suspended solids were detected at least once during sampling. Non-steroidal anti-inflammatory drugs (NSAIDs) and a stimulant were predominant PPCPs in influent whereas antibiotics were predominant in sludge, effluent and suspended solids. Removal efficiencies from the aqueous phase based on the dissolved PPCPs showed variable contribution in removing different PPCPs under screen and grit chamber, anaerobic treatment, anoxic treatment, oxic treatment and sedimentation-UV treatments, with the highest removal percentage by anaerobic process in terms of both individual and overall treatment. Mass load analysis showed that 352 g PPCPs enter the WWTP daily while 14.5 g and 58.1 g were discharged through effluent and excess sludge to the receiving sea water and soil applications, respectively. Mass balance analysis based on both aqueous and suspended PPCPs showed 280 g (79.4%) mass of influent PPCPs was lost along the wastewater treatment processes, mainly due to degradation/transformation.

Variations in toxicity of semi-coking wastewater treatment processes and their toxicity prediction

Chemical analyses and bioassays using Vibrio fischeri and Daphnia magna were conducted to evaluate comprehensively the variation of biotoxicity caused by contaminants in wastewater from a semi-coking wastewater treatment plant (WWTP). Pretreatment units (including an oil-water separator, a phenols extraction tower, an ammonia stripping tower, and a regulation tank) followed by treatment units (including anaerobic–oxic treatment units, coagulation-sedimentation treatment units, and an active carbon adsorption column) were employed in the semi-coking WWTP. Five benzenes, 11 phenols, and five polycyclic aromatic hydrocarbons (PAHs) were investigated as the dominant contaminants in semi-coking wastewater. Because of residual extractant, the phenols extraction process increased acute toxicity to V. fischeri and immobilization and lethal toxicity to D. magna. The acute toxicity of pretreated wastewater to V. fischeri was still higher than that of raw semi-coking wastewater, even though 90.0% of benzenes, 94.8% of phenols, and 81.0% of PAHs were removed. After wastewater pretreatment, phenols and PAHs were mainly removed by anaerobic-oxic and coagulation-sedimentation treatment processes respectively, and a subsequent active carbon adsorption process further reduced the concentrations of all target chemicals to below detection limits. An effective biotoxicity reduction was found during the coagulation-sedimentation and active carbon adsorption treatment processes. The concentration addition model can be applied for toxicity prediction of wastewater from the semi-coking WWTP. The deviation between the measured and predicted toxicity results may result from the effects of compounds not detectable by instrumental analyses, the synergistic effect of detected contaminants, or possible transformation products.

UASB-A/O-BAF treatment of high strength wastewater: a case study for soybean protein wastewater

During the soybean protein production process, a large amount of wastewater is being produced. Currently in China, the soybean protein wastewater produced everyday has reached over 60,000 m3. A technology to bring about a better wastewater treatment effect with reasonable cost of the wastewater treatment is expected to be employed. In the present study, with a view to enhancing the discharge water quality, a combined processing method incorporating a pretreatment unit, an upflow anaerobic sludge blanket (UASB) reactor, an anoxic–oxic treatment system, and a biological aerated filter (BAF), was employed. After a steady performance of all the wastewater treatment units, the facilities will have the capacity to can handle 1,000 m3 wastewater with the chemical oxygen demand (COD) of 18,000 mg/L each day. The total COD removal efficiency can reach 99.84%, and the final discharge water will contain a COD of 40 mg/L. The wastewater treatment cost amounts to only about 2 Yuan RMB/m3 wastewater. Additionally, the CH4 gas produced mainly from the UASB reactor is use to serve as the energy for the soybean protein production plant and thereby bring about a saving in the energy cost to the tune of about 3,500 Yuan RMB each day.

Experimental evidence of a low‐oxygen refuge for large zooplankton

We tested the hypothesis that hypoxic zones in the metalimnion and hypolimnion of lakes can provide a refuge against fish predation for large zooplankton. Experiments were run in a large indoor mesocosm system (Plön Plankton Towers). We compared mortality rates of Daphnia pulicaria due to free‐ranging fish in mesocosms with either oxic or hypoxic hypolimnia. In the presence of fish Daphnia moved down below the thermocline. Under hypoxic conditions their distribution peaked in the upper hypolimnion at a concentration of approximately 1 mg O2 L−1. In oxygen‐saturated hypolimnia Daphnia were distributed evenly. The mortality rate of Daphnia in the hypoxic treatment was only one third of that in the oxic treatment. The hypoxic habitat provided a refuge, as Daphnia tolerated lower oxygen concentrations than did fish. However, there may be demographic costs associated with living in low‐oxygen conditions. Hence, the importance of a hypoxic refuge under natural conditions will most likely depend on the trade‐off between predation risk and cost of living in hypoxic waters.

Inhibition of chemical dose in biological phosphorus and nitrogen removal in simultaneous chemical precipitation for phosphorus removal

A study on the influence of chemical dosing on biological phosphorus and nitrogen removal was carried out through batch experimental tests by lab-scale and a full-scale wastewater treatment plant (employing a typical anaerobic–anoxic–oxic treatment). Results indicated that the inhibition of aluminum salt on biological phosphorus release and uptake processes is significant, as well as the inhibition of aluminum salt on Ammonia-Oxidizing Bacteria (AOB) is dominantly observed in the nitrification process and is recoverability. The inhibition of iron salt in biological phosphorus and nitrogen removal is weak, and only the inhibition of iron salt on phosphorus release at anaerobic periods emerge under large dosing. Evidence shows persistent inhibition from the accumulation of chemical doses in sludge mass. Intermittent chemical dosing proves recommendable for simultaneous chemical phosphorus removal.

Oxygen stress in Salvinia natans: Interactive effects of oxygen availability and nitrogen source

The ability of Salvinia natans (L.) All. to tolerate growth in oxic, hypoxic and anoxic nutrient solutions when supplied with either NH 4 + or NO 3 − were studied in the laboratory to test the hypothesis that inorganic N-source affects the response of the plants to O 2 deprivation. The relative growth rate (RGR) was significantly reduced in the anoxic treatment, but in the hypoxic treatment RGR was only slightly affected. The NH 4 + fed plants generally had a higher shoot to root ratio than the NO 3 − fed plants, and highest in the anoxic treatment. Plants had more roots and larger leaves when supplied with NH 4 + as compared with NO 3 −, particularly in the oxic treatment, and root length was most affected by O 2 deprivation for NO 3 − fed plants. Cell walls in the endodermis, the bundle sheath and the cortex adjacent to endodermis developed thickened sclerenchymatous walls when deprived of O 2, and more so in plants supplied with NO 3 −. Plants lost chlorophylls, had lower rates of photosynthetic electron transport (ETR max) and lower quantum yields (Fv/Fm ratios) when grown in anoxic solutions, and the negative effects were mildest for NO 3 − fed plants suggesting that NO 3 − may be used as an alternative e −-acceptor in non-cyclic electron transport in the chloroplasts. Overall S. natans grew best on NH 4 +, but it also grew well on NO 3 −, and the O 2 stress symptoms differed somewhat between NH 4 + fed and NO 3 − fed plants. However, because N-form itself significantly influenced morphology and cell metabolism, it was impossible to conclusively identify the role of N-form for the O 2 stress reactions. S. natans is not well-adapted to grow in O 2 deficient waters and will not tolerate completely anoxic conditions as will prevail in waters receiving high loadings of organic pollutants such as livestock wastewater.

Three-step biological process for the treatment of the liquid fraction of cattle manure

The liquid fraction of cattle manure was subjected to a biological treatment combining anoxic–anaerobic and oxic processes in order to stabilize the organic matter and reduce nitrogen and phosphorus so as to avoid problems of pollution when applying it to the land. The anoxic process was carried out at 30°C in a CSTR reactor, the anaerobic process in a UASB reactor at 37°C and the oxic treatment in another CSTR at 20°C. The following results were obtained when working under optimum conditions (removal efficiencies in brackets): COD was reduced from 42 to 3.8g/L (>90%); total solids from 41 to 14 (67%); total volatile solids from 22 to 7.0 (68%); total Kjeldahl nitrogen from 2.2 to 0.1g/L (95%); NH4--N from 1.10 to 0.02g/L (98%) and Total-Phosphorus from 0.696 to 0.058g/L (92%). Nitrates, undetected in the liquid fraction of cattle manure, were present in the final effluent as a result of nitrification. To reduce the amount of nitrates, different recirculation rates were tested. The minimum nitrate concentration achieved was 127mg/L using a recirculation ratio of 4.

Effects of aluminum, iron, oxygen and nitrate additions on phosphorus release from the sediment of a Danish softwater lake

The effects of oxygen, aluminum, iron and nitrate additions on phosphate release from the sediment were evaluated in the softwater Lake Vedsted, Denmark, by a 34-day experiment with undisturbed sediment cores. Six treatments were applied: (1) Control - O2 (0–20% saturation), (2) O2 (100% saturation) (3) Al3+ – O2, (4) Fe3+ + O2, (5) Fe3+ – O2, and (6) NO3− – O2. Al2(SO4)3*18 H2O and FeCl3*4H2O were added in amounts that theoretically should immobilize the exchangeable P-pool in the top 5 cm of the sediment, while sodium nitrate concentrations were increased to 5 mg N l−1. The four treatments with metals or NO3− reduced the P efflux from the sediment significantly as compared to the suboxic control treatment. Mean accumulated P-release rates for suboxic treatments with Al3+, Fe3+, and NO3− were: –0.27 mmol m−2 (st. dev = 0.02 mmol m−2, N = 5), 0.58 mmol m−2 (st. dev = 0.30 mmol m−2, N = 5) and 1.40 mmol m−2 (st. dev = 0.14 mmol m−2, N = 5), respectively. The oxic treatment with Fe3+ had a P efflux of 0.36 mmol m−2 (st. dev = 0.08 mmol m−2, N = 5). The two highest P-release rates were observed in the control treatment and the treatment with O2 (14.50 mmol m−2 (st. dev = 3.90 mmol m−2, N = 5) and 2.31 mmol m−2 (st. dev = 0.80 mmol m−2, N = 5), respectively). In order to identify changes in the P and Fe binding sites in the sediment as caused by the treatments, a sequential P extraction procedure was applied on the sediment before and after the efflux experiment. Addition of O2, Fe3+ and NO3− to the sediment increased the amounts of oxidized Fe3+ and P→BD. Al3+ addition resulted in a lower fraction of P→BD but a correspondingly higher fraction of Al-bound P. Addition of Al3+ decreased the Fe-efflux from the suboxic sediment as well as the amount of oxidized Fe3+ in the sediment. This questions the use of Al compounds that contain sulfate because of the possible formation of FeS, which will restrict upward migration of Fe2+ and the formation of new Fe-oxides in the surface sediment. Instead, we suggest the use of AlCl3 for lake restoration purposes.

Modeling of recycling oxic and anoxic treatment system for swine wastewater using neural networks

A recycling reactor system operated under sequential anoxic and oxic conditions for the treatment of swine wastewater has been developed, in which piggery slurry is fermentatively and aerobically treated and then part of the effluent is recycled to the pigsty. This system significantly removes offensive smells (at both the pigsty and the treatment plant), BOD and others, and may be cost effective for small-scale farms. The most dominant heterotrophic were, in order,Alcaligenes faecalis, Brevundimonas diminuta andStreptococcus sp., while lactic acid bacteria were dominantly observed in the anoxic tank. We propose a novel monitoring system for a recycling piggery slurry treatment system through the use of neural networks. In this study, we tried to model the treatment process for each tank in the system (influent, fermentation, aeration, first sedimentation and fourth sedimentation tanks) based upon the population densities of the heterotrophic and lactic acid bacteria. Principal component analysis (PCA) was first applied to identify a relationship between input and output. The input would be microbial densities and the treatment parameters, such as population densities of heterotrophic and lactic acid bacteria, suspended solids (SS), COD, NH4+-N, or-tho-phosphorus (o-P), and total-phosphorus (T-P). Then multi-layer neural networks were employed to model the treatment process for each tank. PCA filtration of the input data as microbial densities was found to facilitate the modeling procedure for the system monitoring even with a relatively lower number of input. Neural networks independently trained for each treatment tank and their subsequent combined data analysis allowed a successful prediction of the treatment system for at least two days.

Design and economic aspects of activated carbon adsorption in relation to the effect of dissolved oxygen

AbstractPhenol and o‐c resol adsorption isotherms and columns were run under anoxic and oxic conditions. Both tests indicated that the adsorptive capacities under oxic conditions were 80%–160% higher than under anoxic conditions with very close agreement between the column and isotherm capacities. Throughput waste volumes processed in oxic columns were 70–169% higher than in anoxic columns. The economics of this oxygen‐induced enhancement in sorptive capacities was addressed. Savings of 30% and 50% in operational treatment cost were estimated for o‐cresol and phenol for parallel adsorber and serial schemes under oxic conditions while no differences between these two schemes in terms of the economics of this phenomenon were observed. Sensitivity analysis revealed that 15% and 30% loss of savings are incurred upon increasing the cost of GAC three‐fold, for phenol and o‐cresol respectively. The overall cost of oxic treatment was insensitive to the cost of oxygenation, exhibiting only a 14% increase for quadrupling the cost of oxygen. Higher oxic sorptive capacities not only results in greater savings of operational treatment costs but also less sensitivity to fluctuations in GAC and oxygenation costs.