Anaerobic-aerobic treatment of purified terephthalic acid (PTA) effluent; a techno-economic alternative to two-stage aerobic process

Anaerobically-digested sludge disintegration by transition metal ions-activated peroxymonosulfate (PMS): Comparison between Co2+, Cu2+, Fe2+ and Mn2

This study investigates anaerobically-digested sludge (ADS) disintegration by activated peroxymonosulfate (PMS) with transition metal ions of Co²⁺, Cu²⁺, Fe²⁺, and Mn²⁺ (PMS-Me²⁺). The activating performances of Me²⁺ are quantitatively compared by capillary suction time (CST), extracellular polymeric substances (EPS), bound water content (BWC), particle size distribution, and metal speciation. At Me²⁺ dose of 1.2 mmol/g VSS, PMS-Fe²⁺ and PMS-Cu²⁺ achieve the lowest normalized CST, i.e., CST/CST₀, of 0.47, and the higher normalized CST values of 0.71 and 0.74 are observed for PMS-Mn²⁺ and PMS-Co²⁺, respectively. BWC shows little extent of decrease upon PMS-Me²⁺ oxidation, and the most significant decrease from 89.5% to 88.3% is observed for PMS-Mn²⁺. PMS-Co²⁺ contributes to the decrease of DOC in total EPS fractions (DOC_tot) from 698.0 mg/L to 496.6 mg/L, whereas the increased DOC_tot to 713.6, 734.4, and 755.0 mg/L is observed with the introduction of Cu²⁺, Fe²⁺, and Mn²⁺, respectively. Fe²⁺ tends to transform to Fe³⁺ and the coagulation effect increases the median particle diameter (D₅₀) from 15.8 μm to 91.1 μm. Comparatively, much lower D₅₀ values of below 20.0 μm are observed for other divalent ions. The European Community Bureau of Reference (BCR) sequential extraction method is used to analyze the metal speciation in ADS sediment after PMS-Me²⁺ disintegration. The dominant species of Co and Mn are acid extractable fractions with the ratios of 91.0% and 87.3%, whereas the main Fe and Cu species are observed to be residual and oxidizable fractions. The pre-captured Me²⁺ ions with 50-days aging interestingly exhibit activating efficacy towards PMS, and CST values were observed to decrease by 11.5%, 30.5%, 11.8%, and 27.3% with the presence of pre-captured Co²⁺, Cu²⁺, Fe²⁺, and Mn²⁺ at 1.2 mmol/g VSS. This study proposes the potentially valuable strategy for the disintegration and dewatering of sludge with high contents of transition metal ions.

Impact of salinity on anaerobic microbial community structure in high organic loading purified terephthalic acid wastewater treatment system

To investigate the effect of salinity (1% sodium chloride) on anaerobic microbial community structure in high strength telephthalic wastewater treatment system, the performances of anaerobic-aerobic process and the shifts of microbial community in anaerobic tank were studied and determined. Results showed that the chemical oxygen demand (COD) removal in the whole process remained above 90%. And the effluent concentrations of targeted pollutants were lower than 10 mg/L, other than para-toluic acid (PT, 38.09 mg/L). However, methane production significantly decreased compared to no salinity situation. This might be due to the inhibition of salinity on methanogens, which hindered the conversion of acetate to methane. Furthermore, the dominant genus in bacterial level changed from Tepidisphaera to Syntrophus, which facilitated the syntrophic association with hydrogenotrophic methanogens. The prevailed archaea remained acetoclastic Methanothrix above 90%. Therefore, the salinity on anaerobic microbial community structure mainly reflects in the methanogen process, remarkably decreasing methane production.

Selective adsorption of Co(II)/Mn(II) by zeolites from purified terephthalic acid wastewater containing dissolved aromatic organic compounds and metal ions

Selective separation and recovery of Co(II)/Mn(II) from purified terephthalic acid (PTA) production wastewater is very important to reduce the Co(II)/Mn(II) catalysts consumption and control the pollutant discharge. This work employed zeolites NaA, NaX, and HZSM-5 with different pore sizes and Na(I) contents to selectively separate and recover Co(II)/Mn(II) from PTA wastewater and to understand the adsorption mechanism. It is found that only NaA can exclusively adsorb Co(II)/Mn(II) through ion-exchange without adsorbing any aromatic organic compound (AOC); oppositely, HZSM-5 shows the highest adsorption capacity for AOCs but almost no adsorption for Co(II)/Mn(II); and NaX exhibits moderate adsorption capacities for both Co(II)/Mn(II) and AOCs. Moreover, pH can significantly impact the adsorption of both Co(II)/Mn(II) and AOCs due to the competitive adsorption between H(I) and Co(II)/Mn(II) and the electrostatic repulsion between AOCs and zeolites. The adsorption kinetics, isotherms, and thermodynamics were also investigated to lay a good basis for process development. Importantly, bench-scale experiments for simulating the industrial operation were carried out, and the results show that the adsorption capacity of the NaA particles for Co(II)/Mn(II) from the industrial PTA wastewater is 9.1/8.6 mg/g, respectively, without adsorbing any AOC. Therefore, an efficient strategy to selectively separate and recover Co(II)/Mn(II) from PTA wastewater was successfully developed.

High-efficiency treatment of PTA wastewater using a biogas jet assisted anaerobic fluidized bed reactor

In this paper, a new type of biogas jet assisted anaerobic fluidized bed reactor loaded with a polypropylene carrier has been proposed. There was a clear improvement in the fluidized state due to the biogas assisted input when the gas/water ratio was set at 1:3 with a suitable carrier loading of 60%. When the circulating water flow is 30 L/min assisted with biogas 10 L/min, the mixing time shortens from 26 to 18 s. The performance of anaerobic biodegradation on wastewater treatment was improved largely. The chemical oxygen demand (COD) and terepthallic acid removal efficiencies were at 85.4% and 84%, respectively, at hydraulic retention time of 20 h, even when the influent COD concentration was as high as 4224 mg/L. In addition, plenty of microorganisms, attached to the carriers and assumed to be the reason behind the organic biodegradation efficiency of the proposed system, were observed using scanning electron microscopy.

Treatment of purified terephthalic acid wastewater using a bio-waste-adsorbent bagasse fly ash (BFA)

Purified terephthalic acid (PTA) plant of a petrochemical unit generates wastewater having high pollution load. Acid treatment of this wastewater reduces the chemical oxygen demand (COD) load by more than 50%, still leaving substantial COD load (>1500 mg/L) which should be removed. The present study reports on the use of a bio-waste-adsorbent bagasse fly ash (BFA) for the reduction of COD and other recalcitrant acids from this wastewater. The BFA showed basic character and was mesoporous with a BET specific surface area of 82.4 m²/g. Optimum conditions for the adsorptive treatment of acid-pretreated PTA wastewater were found to be as follows: initial pH (pH_i) = 4, BFA dosage = 15 g/L, and contact time = 3 h. Adsorption treatment resulted in 58.2% removal of COD, 96.3% removal of terephthalic acid (TA), and 99.9% removal of benzoic acid (BA). TA and BA were removed from the pretreated PTA wastewater through precipitation and sedimentation of un-dissociated acid molecules inside the mesopores of the BFA. The results showed that the COD removed by the BFA followed pseudo-second-order kinetics. Equilibrium sorption data were best correlated by the Freundlich isotherm. The process of adsorptive removal of COD was found to be exothermic. The change in the Gibbs free energy was found to be negative, suggesting that the adsorption process is spontaneous and feasible for the treatment of PTA wastewater.

A novel fast mass transfer anaerobic inner loop fluidized bed biofilm reactor for PTA wastewater treatment

In this paper, a fast mass transfer anaerobic inner loop fluidized bed biofilm reactor (ILFBBR) was developed to improve purified terephthalic acid (PTA) wastewater treatment. The emphasis of this study was on the start-up mode of the anaerobic ILFBBR, the hydraulic loadings and the operation stability. The biological morphology of the anaerobic biofilm in the reactors was also analyzed. The anaerobic column could operate successfully for 46 days due to the pre-aerating process. The anaerobic column had the capacity to resist shock loadings and maintained a high stable chemical oxygen demand (COD) and terephthalic acid removal rates at a hydraulic retention time of 5-10 h, even under conditions of organic volumetric loadings as high as 28.8 kg COD·m(-3).d(-1). The scanning electron microscope analysis of the anaerobic carrier demonstrated that clusters of prokaryotes grew inside of pores and that the filaments generated by pre-aeration contributed to the anaerobic biofilm formation and stability.

Application of sequential expanded granular sludge bed reactors for biodegradation of acetate, benzoate, terephtalate and p-toluate in purified terephtalic acid production wastewater

The anaerobic degradation of four major constituents from purified terephtalic acid production wastewater in sequential two expanded granular sludge bed (EGSB) reactors was studied. The performance of the system was evaluated in terms of chemical oxygen demand (COD) removal efficiencies, methane production, stability, granular sludge adaptability as well as reversion of bacterial inhibition. With volumetric loading rates of 1.9-25 kg-COD m(-3) d(-1) and terephtalate and p-toluate of 584-821 mg L(-1), average removal efficiencies of 97.6% and 75.2% were achieved in the EGSB reactors, respectively. In these conditions, gas production reached a total methane production rate of 0.33 L g-COD(-1) in the two-stage EGSB reactor system. The disturbance of the EGSB reactors was observed at a feed concentration above around 6.9 g-COD L(-1) because of higher influent COD concentration compared to other experiments.

454-Pyrosequencing Reveals Microbial Community Structure and Composition in a Mesophilic UAFB System Treating PTA Wastewater

To well understand the community structure and composition of mesophilic microorganisms in anaerobic system fed with PTA wastewater, an up-flow anaerobic fixed bed reactor was continuously run at 33 and 37 °C for 75 and 60 days, respectively. Both fluorescence in situ hybridization analysis and 454-pyrosequencing were applied to investigate the microbial distinction within mesophilic ranges. A preferable performance was achieved at 37 than 33 °C. The taxonomic complexities of two samples were further compared at phylum, class, and genus levels. Notably, microbial diversity differed a lot and the change of populations was observed mainly in the shared OTUs. Genus level analysis showed that when temperature was increased to 37 °C, the abundance of Thauera and Hydrogenophaga (β-Proteobacteria) decreased by 93.75 and 61.47 %, respectively, whereas that of Syntrophorhabdus (δ-Proteobacteria) increased from 4.93 to 16.01 %. Furthermore, the dominant archaeal Methanobacterium at both temperatures indicated the prevailing contribution of hydrogenotrophic methanogens in mesophilic anaerobic system.

Sequential anaerobic-aerobic treatment of pharmaceutical wastewater with high salinity

In this study, pharmaceutical wastewater with high total dissolved solids (TDSs) and chemical oxygen demand (COD) content was treated through a sequential anaerobic-aerobic treatment process. For the anaerobic process, an up-flow anaerobic sludge blanket (UASB) was applied, and a COD removal efficiency of 41.3±2.2% was achieved with an organic loading rate of 8.11±0.31gCOD/L/d and a hydraulic retention time of 48h. To evaluate the salinity effect on the anaerobic process, salts in the wastewater were removed by ion exchange resin, and adverse effect of salinity was observed with a TDS concentration above 14.92g/L. To improve the anaerobic effluent quality, the UASB effluent was further treated by a membrane bioreactor (MBR) and a sequencing batch reactor (SBR). Both the UASB+MBR and UASB+SBR systems achieved excellent organic removal efficiency, with respective COD removal of 94.7% and 91.8%. The UASB+MBR system showed better performance in both organic removal and nitrification.

Pulse respirometry in two-phase partitioning bioreactors: case study of terephthalic acid biodegradation

Two-phase partitioning bioreactors (TPPBs) are based on the addition of an organic phase, often called vector, to a bioreactor in order to increase mass transfer of oxygen or gaseous substrates from the gaseous phase to the aqueous phase. In TPPBs, like in any other reactor design, the characterization of the bioprocess is often required for design, control, and operation purposes. Pulse respirometry is a method that allows for microbial processes characterization through the determination of several stoichiometric and kinetic parameters with relatively little experimental effort. Despite its interest and its previous application in countless applications, pulse respirometry has never been applied in TPPBs. In this work, pulse respirometry was assessed in a model TPPB degrading terephthalic acid and using Elvax™ as solid vector to enhance oxygen transfer. The results indicated that the addition of 10 to 20% Elvax increased oxygen transfer by up to 97%, compared to control with no vector. Pulse respirometry was successfully applied and allowed for the determination of the growth yield, the substrate affinity constant, and the maximum growth rate, within other. It is concluded that pulse respirometry is a useful method, not only for the characterization of processes in TPPBs but also for the selection of a vector within several brands commercially available.

Simultaneous removal of carbon and nutrients from an industrial estate wastewater in a single up-flow aerobic/anoxic sludge bed (UAASB) bioreactor

Simultaneous removal of carbon and nutrients (CNP) in a single bioreactor is highly significant for energy consumption and control of reactor volume. Basically, nutrients removal is dependant to the ratio of biochemical oxygen demand to chemical oxygen demand (BOD₅/COD). Thus, in this study the treatment of an industrial estate wastewater with low BOD₅/COD ratio in an up-flow aerobic/anoxic sludge bed (UAASB) bioreactor, with an intermittent regime in aeration and discharge, was investigated. Hydraulic retention time (HRT) of 12-36 h and aeration time of 40-60 min/h were selected as the operating variables to analyze, optimize and model the process. In order to analyze the process, 13 dependent parameters as the process responses were studied. From the results, it was found, increasing HRT decreases the CNP removal efficiencies. However, by increasing the BOD₅ fraction of the feed, the total COD (TCOD), slowly biodegradable COD (sbCOD), readily biodegradable COD (rbCOD), total nitrogen (TN), and total phosphorus (TP) removal efficiencies were remarkably increased. Population of heterotrophic, nitrifying and denitrifying bacteria showed good agreement with the results obtained for TCOD and TN removal. The optimum conditions were determined as 12-15 h and 40-60 min/h for HRT and aeration time respectively.

Treatment of thin stillage in a high-rate anaerobic fluidized bed bioreactor (AFBR)

The primary objective of this work was to investigate the treatability of thin stillage as a by-product of bioethanol production plants using an anaerobic fluidized bed bioreactor (AFBR) employing zeolite with average diameter of (d(m)) of 425-610 μm and specific surface area (SSA) of 26.5m(2)/g as the carrier media. Despite the very high strength of thin stillage with chemical oxygen demand of 130,000 mg TCOD/L and suspended solids of 47,000 mg TSS/L, the AFBR showed up to 88% TCOD and 78% TSS removal at very high organic and solids loading rates (OLR and SLR) of 29 kg COD/m(3)d and 10.5 kg TSS/m(3)d respectively and hydraulic retention time (HRT) of 3.5 days. Methane production rates of up to 160 L/d at the steady state equivalent to 40 L(CH4)/L(thin stillage)d and biogas production rate per reactor volume of 15.8L(gas)/L(reactor)d were achieved.

Pretreatment of petrochemical wastewater by coagulation and flocculation and the sludge characteristics

In the present study, coagulation-flocculation was investigated as a pretreatment process for the treatment of purified terephthalic acid (PTA) wastewater. The effect of various inorganic and organic coagulants on the treatment of wastewater collected from flow equalization tank of an effluent treatment plant was studied. The settling and filtration characteristics of the sludge were also studied. The jar tests revealed that the wastewater was best treated when 3000 mg l(-1) of ferric chloride was dosed at pH 5.6. At optimum conditions, COD of the wastewater was reduced by 75.5%. The results of the gravity filtration of the treated wastewater showed that the addition of cationic polyacrylamide (175 mg l(-1)) to ferric chloride coagulation improved the filtration characteristics and reduced the specific cake resistance. Scanning electron microscopy and energy dispersive spectroscopy studies were also conducted to know the sludge structure and composition, respectively. Thermal analysis of the sludge showed that the oxidation of the sludges in the present study is a three step process. However, with the addition of C-PAA to ferric chloride coagulation system, the oxidation was found to be a two step process.