Activated Sludge Inhibition Test Research Articles

Kinetics of ciprofloxacin removal using a sequential two-step ozonation-biotreatment process

The main objective of this reported research is to develop an efficient treatment method for pharmaceutical wastewater by combining ozonation and biological treatment. The antibiotic ciprofloxacin (CIP) was used to prepare synthetic pharmaceutical wastewater. The effect of ozonation on wastewater was assessed by antibacterial activity and biodegradability index. The inhibitory effect of raw and ozone pre-treated wastewater on biomass oxygen uptake was examined and compared with that of biodegradable non-inhibitory compound (sodium acetate). The raw and ozone pre-treated wastewater were used in batch bioreactor experiments. It was found that the pre-treatment by ozone increased the biodegradability index from 0.13 to 0.32 and reduced the antibacterial activity of wastewater. The activated sludge inhibition test showed that a total of 77% and 46% inhibition in raw wastewater and ozone pre-treated wastewater, respectively. This result were corroborated by the substrate removal kinetic models, that the ozone-treated wastewater has more biodegradable compounds through the enhanced biomass growth in the batch bioreactor. The combined ozonation and biological treatment removed 82.5% of Chemical Oxygen Demand (COD), whereas 38% of COD was removed in biological treatment alone. The two-step treatment (ozonation and biological) process was applied to real pharmaceutical wastewater and the treatment efficiency was evaluated.

Activation of persulfate by a novel magnetic CuFe2O4/Bi2O3 composite for lomefloxacin degradation

In this paper, magnetic CuFe2O4/Bi2O3 composite was successfully fabricated by a simple sol–gel combustion method with an excellent activity in the activation of persulfate (PS) for lomefloxacin (LOM) degradation. The surface morphology and structure characterizations of CuFe2O4/Bi2O3 were carried out by X-ray diffraction, scanning electron microscope, transmission electron microscope, N2 physical adsorption/desorption and vibration magnetometer measurements. The CuFe2O4/Bi2O3 synthesized exhibited high catalytic activity and good stability, it could degrade 77.19% of LOM at the natural pH (6.08), more efficient than CuFe2O4. Subsequently, the catalytic performances of CuFe2O4/Bi2O3 during LOM degradation were studied comprehensively under different initial conditions (catalyst dosage (0.6–1.8 g/L), PS dosage (0.6–1.8 g/L), initial pH value (3.0–11.0)). Also, the main active radicals (SO4− and OH) were determined by the radical scavenging experiment, which indicated that OH had a higher contribution to remove LOM than SO4− in CuFe2O4/Bi2O3/PS system. Moreover, the mechanism of the CuFe2O4/Bi2O3/PS system for LOM degradation was further proposed and the possible degradation pathways of LOM in CuFe2O4/Bi2O3/PS system were deduced. Furthermore, activated sludge inhibition test was performed to determine the variation of toxicity of the LOM during the degradation process. In a word, the CuFe2O4/Bi2O3 catalyst has a high catalytic efficiency and a short degradation period, indicating that it was a promising catalyst towards LOM wastewater treatment, which had a great potential in environmental protection.

Implementation of continuously electro-generated Fe3O4 nanoparticles for activation of persulfate to decompose amoxicillin antibiotic in aquatic media: UV254 and ultrasound intensification

In the present investigation, the treatment of amoxicillin (AMX)-polluted water by the activated persulfate (PS) was considered. As a novel research, continuously electro-generated magnetite (Fe3O4) nanoparticles (CEMNPs) were utilized as the activator of PS in an electrochemical medium. The PS/CEMNPs displayed a remarkable enhancement in the decomposition of AMX molecules up to 72.6% compared with lonely PS (24.8%) and CEMNPs (13.4%). On the basis of pseudo-first order reaction rate constants, the synergy percent of about 70% was achieved due to the combination of PS with CEMNPs. The adverse influence of free radical-scavenging compounds on the efficiency of the PS/CEMNPs process was in the following order: carbonate < chloride < tert-butyl alcohol < ethanol. Overall, these results proved the main role of free radical species in degrading AMX. The implementation of ultrasound (US) enhanced the performance of the PS/CEMNPs process. Nevertheless, the highest degradation efficiency of about 94% was achieved when UV254 lamp was joined the PS/CEMNPs system. Under UV254 and US irradiation, the results showed significant potential of the PS/CEMNPs process for degrading AMX antibiotic and generating low toxic effluent based on the activated sludge inhibition test. However, more time is needed to achieve the acceptable mineralization.

Degradation of Acid Orange 7 by an ultrasound/ZnO-GAC/persulfate process

Abstract Granular activated carbon (GAC) supported ZnO catalyst (ZnO-GAC) was prepared to activate persulfate (PS) for the decolorization of Acid Orange 7 (AO7) in the presence of ultrasonic irradiation (US). The effects of initial pH, PS concentration, catalyst dosage, initial dye concentration, and reaction temperature were investigated. The results showed that the decolorization efficiency increased with the increase of catalyst dosage and temperature, but decreased with the increase of initial dye concentration and initial pH, and the optimal PS concentration for color removal was 0.5 g L−1. Radical quenching tests were performed by using ethanol, tert-butanol and phenol to verify the formation of sulfate radicals and hydroxyl radicals in the US/ZnO-GAC/PS process. Under the optimal conditions, 91.2% of decolorization was achieved and 83.1% of TOC was removed after 60 min treatment. Activated sludge inhibition tests were carried out to monitor the change of toxicity during the treatment of AO7 solution.

The mechanism and efficiency of MnO2 activated persulfate process coupled with electrolysis

Pure three-dimensional manganese oxides (MnO2) were successfully synthesized by a simple one-step hydrothermal process. The obtained particles were characterized via XRD, BET, SEM, XPS and FTIR techniques. To enhance the efficiency of heterogeneous catalytic process, a facile and effective electrochemical method was introduced. The degradation of C. I. Acid Orange 7 (AO7) as the target pollutant in aqueous solution by an oxidation system involving MnO2 activated peroxydisulfate (PDS) coupled with electrochemical method is reported herein. Influences of some key reaction parameters such as initial pH (pH0), current density, initial AO7 concentration, dosage of MnO2 and anions (Cl−, NO3−, HCO3− and H2PO4−) were investigated. The cyclic voltammetry (CV) was performed to investigate the charge transfer process occurred at the surface of catalyst. LC-MS/MS analysis was applied to identify degradation intermediates and a plausible degradation mechanism is proposed accordingly. Activated sludge inhibition tests were carried out to evaluate the change of toxicity of the dye solution in the oxidation process. The inorganic by-products such as NO2−, NO3−, and NH4+ along with AO7 degradation were also identified. The stability of MnO2 catalyst was evaluated by recycling experiments and the electrical energy consumption was also investigated. Radical quenching tests with several scavengers (methanol, tert-butyl alcohol, 1,4-benzoquinone and phenol) were performed to clarify the dominating reactive species participating in this oxidation process and the underlying mechanisms involving the generation of radical from the proposed electro-assisted heterogeneous activated PDS system were identified.

The UV/peroxymonosulfate process for the mineralization of artificial sweetener sucralose

As one of non-nutritive and commonly used artificial sweeteners, sucralose (SUC) is now ubiquitous and detected in aquatic environments, which has already been recognized as an emerging contaminant. The mineralization of SUC in aqueous media by UV/peroxymonosulfate (PMS) process is investigated herein. Influences of several operating parameters, including pH, oxidant concentration and initial SUC concentration, on SUC mineralization were evaluated. Changing the pH from 3 to 9 had a weak effect on the mineralization of SUC, but the mineralization efficiency dropped sharply at pH 11. Nearly complete mineralization (>95%) of SUC was achieved after 60min treatment with 3.780mM oxidant at neutral pH. Both hydroxyl and sulfate radicals were demonstrated to participate in the oxidation of SUC according to EPR analysis. Under neutral pH condition, the presence of inorganic anion such as Cl−, NO3− or NO2− exhibited a varied inhibition effect on the mineralization efficiency with the order being NO2−>NO3−>Cl−. Activated sludge inhibition tests and Daphnia magna acute immobilization tests were performed to evaluate the detoxification efficiency of the UV/PMS process. The by-products formed were identified using LC–MS technique and a possible pathway of SUC degradation was proposed. In summary, the obtained result provides meaningful information on the application of UV/PMS process for the mineralization of SUC or other artificial sweeteners.

Degradation of C. I. Acid Orange 7 in aqueous solution by a novel electro/Fe3O4/PDS process

The decolorization of C. I. Acid Orange 7 (AO7) in aqueous solution by Fe3O4 activated peroxydisulfate (PDS) oxidation in an electrochemical reactor (EC/Fe3O4/PDS process) was performed in this study. Various parameters were investigated to optimize the process, including initial pH, current density, PDS concentration and Fe3O4 dosage. The stability of Fe3O4 particles was observed by recycle experiments. The X-ray photoelectron spectroscopy (XPS) was applied to investigate the surface properties of Fe3O4 before and after reaction. GC–MS analysis was employed to identify the intermediate products and a plausible degradation pathway of AO7 was proposed. The change of acute toxicity during the treatment was investigated by activated sludge inhibition test. The TOC removal efficiency was 30.0% in a 90min reaction.

Toxicity and Biodegradability Behavior of Xenobiotic Chemicals Before and After Ozonation: A Case Study with Commercial Textile Tannins

Ozonation of a natural tannin (NT; CODo = 1195 mg/L; TOCo = 342 mg/L; BOD5,o = 86 mg/L) and a synthetic tannin ST; CODo = 465 mg/L; TOCo = 55 mg/L; BOD5,o = 6 mg/L) being frequently applied in the polyamide dyeing process was investigated. Synthetic wastewater samples containing these tannins individually were prepared and subjected to ozonation at varying ozone doses (625– 1250 mgO3/L wastewater), at pH = 3.5 (the application pH of tannins) and pH = 7.0 at an ozone dose of 1125 mgO3/L wastewater. The collective environmental parameters COD, TOC, BOD5, UV254 and UV280 (UV absorbance at 254 nm and 280 nm, representing aromatic and unsaturated moieties, respectively) were followed during ozonation. Changes in the biodegradability of the tannins were evaluated in terms of BOD5 measurements conducted before and after ozonation. In addition, activated sludge inhibition tests employing heterotrophic biomass were run to elucidate the inhibitory effect of raw and ozonated textile tannins towards activated sludge biomass. Partial oxidation (45% COD removal at an ozone dose of 750 mg O3/L wastewater and pH = 3.5) of ST was sufficient to achieve elimination of its inhibitory effect towards heterotrophic biomass and acceptable biodegradability improvement, whereas the inhibitory effect and biodegradability of NT could not be reduced via ozonation under the same reaction conditions.

Treatability of cefazolin antibiotic formulation effluent with O3 and O3/H2O2 processes

The effect of applying ozonation and perozonation to antibiotic cefazolin-Na formulation effluents were investigated in this study. Twenty minutes of ozonation at a rate of 1,500 mg/L-h was observed to remove COD by 38%, whereas a COD removal efficiency of 40% was achieved via H2O2 enhanced ozonation (same conditions + 31.25 mM H2O2). Both of the pretreatment alternatives were monitored to elevate the BOD5/COD ratio from 0.01 to 0.08. The initially inert COD was reduced by 38% using ozonation and by 60% employing H2O2 enhanced ozonation. In terms of the lowest achievable effluent COD levels after bio-treatment, ozonation was observed to yield a residual COD of 205 mgL(-1), while a residual COD of 135 mgL(-1) was involved for perozonation. According to the results of acute toxicity on Phaedactylum tricornutum, ozonated and perozonated samples exhibited more toxicity than the untreated effluent after 4 days. The activated sludge inhibition test demonstrated that both of the pretreatment alternatives efficiently eliminated the inhibition of investigated formulation effluent.

Pre-Ozonation of Commercial Textile Tannins: Effects on Biodegradability and Toxicity

The effect of ozonation on the biodegradability and acute toxicity of two frequently used textile dye assisting chemicals, namely natural tannin (NT) having an initial chemical oxygen demand (COD0) of 1195 mg L−1; initial total organic carbon (TOC0) of 342 mg L−1; initial 5th-day biochemical oxygen demand (BOD5,0) of 86 mg L−1; initial ultraviolet absorbance at 280 nm wavelength (UV280,0) of 32.2 cm−1; initial ultraviolet absorbance at 254 nm wavelength (UV254,0) of 19.35 cm−1 and synthetic tannin (ST); with a COD0 of 465 mg L−1; TOC0 of 155 mg L−1; BOD5,0 of 6 mg L−1; UV280,0 of 11.78 cm−1; UV254,0 of 13.74 cm−1 was investigated. Synthetic wastewater bearing these tannin formulations was individually prepared and subjected to ozonation at varying doses (500 and 1000 mg h−1), and pHs (3.5 and 7.0) to elucidate the effect of ozone dose and pH on oxidation efficiency. Changes in the environmental sum parameters chemical oxygen demand (COD), total organic carbon (TOC), 5th-day biochemical oxygen demand (BOD5), ultraviolet absorbance at 280 nm wavelength (UV280) and ultraviolet absorbance at 254 nm wavelength (UV254), the latter two representing the aromaticity and double bonds of the studied textile tannins, respectively, were monitored during the course of ozonation. In the second part of the study, the biodegradability and acute toxicity of the raw and pre-ozonated textile tannins were evaluated in terms of the BOD5 parameter and an activated sludge inhibition test, respectively. Results indicated no significant changes in acute toxicity for NT, whereas the inhibitory effect of ST could be completely eliminated after 40 min ozonation at a rate of 1000 mg h−1 (i.e., at a specific ozone dose of 1.4 mg O3 (mg COD0)−1 and a pH of 3.5. In conclusion, pre-ozonation appeared to be potential pretreatment option to achieve complete detoxification and a fair biodegradability improvement of the otherwise refractory synthetic tannin.

Effect of Perozonation on Biodegradability and Toxicity of a Penicillin Formulation Effluent

The pretreatment of synthetic penicillin formulation effluent containing Procain Penicillin G (PPG) with the O3/H2O2 process (applied ozone dose = 1440 mg h−1 treatment time = 60 minutes; pH 7; H2O2 = 10 mM) was investigated. The effect of chemical pretreatment was assessed on the basis of acute toxicity and biodegradability with activated sludge using water flea Daphnia magna toxicity and activated sludge inhibition tests. Biological treatability studies were performed with a mixture of untreated or pretreated PPG effluent (25% on volume basis) and synthetic domestic wastewater simulating readily biodegradable organic substrate to simulate the characteristics of domestic wastewater (75% on volume basis). Pretreatment of PPG effluent the O3/H2O2 process resulted in more than 70% chemical oxygen demand (COD) removal and a 50% decrease in the acute toxicity towards Daphnia magna. On the other hand, biodegradation of untreated PPG effluent needed prolonged acclimation periods to obtain a significant biological COD removal (= 80%). Pretreatment employing the O3/H2O2 process not only decreased the ultimate biodegradability of PPG effluent but also increased its inhibitory effects on activated sludge treatment speculatively due to the formation of less biodegradable oxidation by-products.

Acid dyebath effluent pretreatment using Fenton's reagent: Process optimization, reaction kinetics and effects on acute toxicity

Fenton's reagent (Fe 2+/H 2O 2) is known as one of the most effective and most often employed advanced oxidation process (AOPs) for the treatment of textile dyes and dyehouse effluent. In the present study, a synthetic acid dyebath effluent (SADB) bearing two azo and one anthraquinone dye together with two dye auxiliaries was subjected to pretreatment with Fenton's reagent. Firstly, initial Fe 2+ and H 2O 2 concentrations as well as pH were optimized to achieve highest COD and color removals during Fenton's treatment of SADB. In the second stage of the experimental work, kinetic studies were conducted to elucidate the effect of operating temperature (20 °C < T < 60 °C) on COD, color abatement and H 2O 2 consumption kinetics. Obtained results indicated that 30% COD and practically complete color removal (99%) could be achieved at T = 50 °C. The kinetic studies revealed that a strong correlation existed between COD removal and H 2O 2 utilization rates. In the final part of the study, the acute toxicity of raw (untreated) and pretreated SADB on heterotrophic biomass was investigated employing a modified (COD-balanced), activated sludge inhibition test. The toxicity experiments demonstrated that the inhibitory effect of SADB towards sewage sludge could be completely eliminated when the effluent was pretreated with Fenton's reagent.

Rapid Activated Sludge Respiration Inhibition Test Performed by CO2 Producing Rate Using a Carbon Dioxide Sensor

The rapid activated sludge inhibition test (rapid ASRI) is one of the promising bioassays to evaluate environmental risk to the ecosystem caused by various pollutants. To improve the sensitivity and stability of ASRI, the CO2 producing rate (CPR) using a carbon dioxide gas sensor was employed to examine the respiration activity of activated sludge and to compare it to that by the conventional activated sludge respiration inhibition test using oxygen uptake rate (OUR) by EC50 values derived from dose response curve. Detection of respiratory activity based on CPR has higher reliability and sensitivity than that of OUR. It should be noted that the sensitivity of CPR for evaluating toxicity is sufficiently high in terms of derived dose response curve of some model environmental pollutants and the resultant EC50 values.

Acid mine-drainage toxicity testing

The BOD inhibition test, the activated sludge respiration inhibition test, and the Microtox® Bioassay procedure were examined for their potential as rapid toxicity screening methods for acid mine drainage (AMD) and for setting toxicity threshold levels in receiving waters. The BOD inhibition test proved to be unsuitable due to the high chemical oxygen demand of the toxicant. The long incubation time (minimum 5 d at 20°C) allowed growth of chemo-autotrophic bacteria and resulted in excessive flocculation and precipitation of metals, making accurate and meaningful measurements of inhibition impossible. The activated sludge respiration inhibition test was successful in measuring AMD toxicity, and for deriving toxicity threshold levels for the basic heterotrophic community in surface waters. However, it is a very time-consuming technique and is not sensitive enough to be used as a routine screening technique. The variability in toxicity was found to be due to the availability of metals as well as the effect of pH on metabolism. Simple linear models were derived to estimate inhibition within surface waters. Prediction of the inhibition caused by AMD can be made as long as the pH of the river water after mixing and the dilution of the AMD are known. Most accurate predictions are made using equations for specific pH ranges, but a useful estimation of inhibition can be obtained using the general equation: inhibition (%) = -2.34 pH + 6.41 AMD (%) + 22.1. The Microtox® Bioassay method, although expensive, was rapid and simple to use. It was the most sensitive test of the three, with the toxic response of marine bacteria increasing notably from 5 to 15 min due to the presence of bivalent metals in the toxicant. The problem of repeatability and reproducibility encountered with the activated sludge inhibition test was overcome with the highly standardised Microtox® method, making it an ideal screening method for AMD. However, the advantage of the activated sludge inhibition test is that the types of heterotrophic micro-organisms found in activated sludge are similar to those found in receiving waters such as the Avoca River and so more meaningful toxicity threshold values can be obtained.