Activated sludge process coupled with intermittent ozonation for sludge yield reduction and effluent water quality control

BACKGROUND: Ozone is applied in wastewater treatment for effluent water quality improvement (post‐ozonation) as well as for excess sludge reduction (in the recirculation line). There is some evidence that ozone dosed directly to aerobic biooxidation (ABO) process enhances degradation of recalcitrant compounds into intermediates, following their biodegradation in the same reactor. However, no information regarding the influence of ozone on sludge yield in this system was found. Therefore, the current work aimed to evaluate the effect of ozone on the sludge yield when ozone is dosed directly to the ABO process. In addition, batch and continuous treatment schemes for phenolic wastewater treatment are compared. RESULTS: The results revealed that an optimal ozone dose of ～30 mgO₃ L^?1 day^?1 reduced the sludge yield by ～50%, while effluent water quality in terms of total chemical oxygen demand (TCOD), compared with a conventional ABO process, was improved by 35.5 ± 3.6%. Slight improvement in soluble COD removal at the same ozone dose was also detected. The toxicity of effluent water was reduced as the ozone dose was increased. CONCLUSIONS: In an integrated ozonation‐ABO process it is possible to simultaneously reduce sludge yield and to improve effluent water quality, as COD and toxicity are reduced. Copyright © 2011 Society of Chemical Industry     

臭氧氧化与序批式好氧活性污泥法组合工艺的污泥减量化效果

该文研究了臭氧技术应用于剩余污泥处理过程中臭氧利用率及污泥的可生化性随时间的变化,组建了臭氧氧化与序批式好氧活性污泥法结合的联合工艺。将臭氧单元处理过的污泥全部回流至曝气池与污水进行合并处理,考察了不同臭氧投加量下联合工艺中剩余污泥的产量和污水处理效果。结果表明,当处理污泥浓度为4 000 mg/L,污泥体积为3 L,臭氧进气浓度为6.5 mg/L,气量为6 L/min时,前20 min的臭氧利用率几乎为100%,随后利用率逐渐降低;污泥的可生化性先降低,而后逐渐升高,在30 min时达到最大,其后又开始下降;当臭氧投加量为0.078 kg O3/kg MLSS时,联合工艺的污泥增长率几乎为0,同时出水水质相对对照组没有明显变化。     

活性炭负载Fe~(3+)催化臭氧氧化水中双酚A

采用浸渍法在活性炭上负载铁制备催化剂Fe/AC,用于催化臭氧氧化水中内分泌干扰物双酚A(BPA),研究了Fe/AC/O3体系的协同效应,探讨了Fe/AC投加浓度、臭氧浓度和BPA初始浓度等工艺参数的作用规律,并分析了Fe/AC/O3体系在不同pH值下的催化反应机制。结果表明,在Fe/AC/O3体系下,反应60 min后,BPA和COD的去除率分别为97.44%和69.47%,效果明显优于臭氧体系的70.15%、30.89%和活性炭体系的14.69%、7.53%之和,具有明显的协同作用;Fe/AC/O3体系降解BPA符合一级反应动力学,当Fe/AC的投加浓度为5.0 g/L,臭氧浓度为15.0 mg/L,BPA初始浓度为50.0 mg/L时,Fe/AC/O3体系降解BPA的反应速率常数为0.05972 min-1;其反应机制受溶液pH值的影响,在酸性条件下是吸附和臭氧直接氧化共同作用,而在碱性条件下以·OH间接氧化为主,活性炭上负载的Fe3+促进了·OH的生成,大大提高了BPA的反应效率和矿化率。     

Integration of continuous biological and chemical (ozone) treatment of domestic wastewater: 1. Biodegradation and post‐ozonation

The continuous treatment of domestic wastewater by an activated sludge process and by an integrated biological–chemical (ozone) oxidation process were studied in this work. Chemical oxygen demand (COD), biochemical oxygen demand (BOD), absorbance at 254 nm (UV₂₅₄) and nitrogenous compound content were the parameters followed in order to evaluate the performance of the two processes. Experimental data showed that both UV₂₅₄ and COD reductions are improved in the combined biological–chemical oxidation procedure. Thus, reductions of 59.1% and 37.2% corresponding to COD and UV₂₅₄, respectively were observed after the biological process (hydraulic retention time = 5 h; mixed liquor volatile suspended solids concentration = 3142 g m⁻³) compared with 71.0% and 78.4% obtained when a post‐ozonation step ( D _O3 = 41.7 g m⁻³) was included. During conventional activated sludge treatment, appropriate nitrification levels are only achieved with high hydraulic retention time and/or biomass concentration. Ozonation after the secondary treatment, however, allows improved nitrogen content reduction with total nitrite elimination. Post‐ozonation also leads to a higher biodegradability of the treated wastewater. Thus, the ultimate BOD/COD ratio goes from 0.16 after biological oxidation to 0.34 after post‐ozonation with 41.7 g O₃ m⁻³. © 1999 Society of Chemical Industry     

Effect of Ozonation on Biodegradability Characteristics of Surplus Activated Sludge

The study investigates the effect of sludge ozonation on solid matter species, disintegration properties, sludge components, and solubilization characteristics under different operating conditions. Ozonation of surplus activated sludge samples taken from the secondary settling tank of a domestic wastewater treatment plant indicates that soluble nitrogen, phosphorus and COD concentrations proliferate as a consequence of extending the ozone feeding time. A steady increase both in soluble nitrogen concentration and ratio of organic phosphorus to soluble phosphorus is observed through ozonation where specific ozone doses range between 4 and 11 mg O₃/g SS. Combined treatment of chemical oxidation and aerobic biodegradation to surplus activated sludge is also applied to improve the biodegradability of organic matter by partial chemical oxidative pretreatment with as little specific ozone consumption as possible. The partial oxidation by integrated ozonation is operated as a pre-oxidation step for the subsequent biological degradation, due to the fact that the competition with biological degradation in removing biodegradable organic compounds is avoided and most probably a more biodegradable sludge composition is obtained by means of ozonation. Combined treatment of chemical oxidation and aerobic biodegradation conducted to scrutinize the synergic effect of the coupled treatment system reveals that TS and COD removal efficiencies of ozonated sludge samples cannot be improved beyond the third aerobic biodegradation step.     

Incidence of an Ozonation Stage on the Treatment of Cherry Stillage by Activated Sludge

This article presents a laboratory study of the ozonation of diluted cherry stillage, a high-strength wastewater. Influence of variables, kinetics, and the effects of an ozonation stage coupled with the biological treatment by activated sludge are addressed. Single activated sludge processing was shown effective to remove biological oxygen demand (BOD) and chemical oxygen demand (COD) but polyphenols were reduced to a lesser extent. On the other hand, direct wastewater ozonation did not reduce COD and total organic carbon (TOC) appreciably, and foaming problems were experienced when a high gas flow rate was applied. However, polyphenols and UV₂₅₄ absorbance decreased substantially by means of ozonation. To best achieve complete cherry stillage purification, two ways of coupling ozonation with activated sludge are proposed. Ozonation prior to activated sludge is advised for high-concentration wastewater to reduce polyphenol concentration, thus removing inhibiting effects. For wastewater with low polyphenol concentration the sequence activated sludge–ozonation–activated sludge is preferred to enhance the overall process performance in terms of oxidation efficiency and sludge settling.     

臭氧尾气回用对曝气池污泥影响研究

将活性污泥分别在14.68、30.72、43.84 mg/L 3种臭氧浓度下进行氧化,同时以纯氧曝气作为平行实验,考察臭氧尾气对活性污泥的影响。结果表明,污泥经纯氧曝气后,在反应时间内并无明显变化,但在臭氧氧化过程中,污泥ATP下降,同时上清液中COD、TP、TN上升,且臭氧浓度越高,变化速率越大,其原因为污泥发生了溶胞现象;臭氧氧化后,污泥MLSS、MLVSS减少,污泥呼吸速率下降,但沉降性得到改善,同样随着臭氧浓度的升高,变化更为显著。经14.68、30.72 mg/L臭氧氧化后的污泥,其硝化能力、生化能力与反应前并无明显差距,而经43.84 mg/L臭氧氧化后污泥的硝化能力、生化能力明显弱于反应前。     

Ozone Application for the Improvement of UASB Reactor Effluent I. Physical-Chemical and Biological Appraisal

Ozonation can improve the effluent characteristics of UASB (upflow anaerobic sludge blanket) reactors treating domestic sewage, by removing organic matter, solids, surfactants, color and microorganisms. In Brazil, part of the effluent of a 120 msup3; UASB reactor, fed with screened domestic sewage at an hydraulic retention time of 7 hours, was post-treated in a two-column ozonation system of 300 liters total volume. With a contact time of 50 minutes and ozone application dosage of 16.7 mg/L, the following removals were obtained at the ozonation step: 51‰ BOD, 56‰COD, 76‰ TSS, 62‰ color, and 91‰ surfactants. Pathogens and indicator organisms were inactivated to over 99.9‰. Ozonation completely destroyed Salmonella, protozoa cysts and helminth eggs and larvae.     

Effect of Ozonation on Activated Sludge Solubilization and Mineralization

New strategies for sludge stabilization and mineralization need to be developed since the use of sludge in agriculture is debatable and sludge incineration cannot be a systematic solution. Minimization of sludge production should be preferred. In this work, the effect of ozone on activated sludge solubilization and mineralization during batch experiments is assessed by establishing carbon and ozone mass balances. After extended ozonation of the sludge, more than 90% of the particulate carbon is modified. Depending on the experimental conditions, from 15 to 50% is found in a soluble form and from 35% to 95% was mineralized. The VSS/SS ratio decreases from 86% to less than 50% illustrating the sludge mineralization. The initial rate of ozone consumption by the sludge is very high (estimated value: 30 mgO₃/g VSS.min) and corresponds to high rates of carbon solubilization and mineralization. More than 50% of the carbon obtained after ozonation is found to be readily biodegradable using a short-term BOD procedure.     

Degradation of methylene blue in aqueous solution by ozone-based processes

The aim of this study was to compare the efficiency of conventional ozonation and catalytic ozonation (ozone/activated carbon (O₃/AC) and ozone/TiO₂/activated carbon (O₃/TiO₂/AC)) in the degradation of methylene blue (MB) component from MB aqueous solution. The removal rates of color and chemical oxygen demand (COD_Cr) were assessed to screen the most appropriate oxidative process of MB treatment. In this experiment conditions, the color was completely disappeared in the presence of TiO₂/AC catalyst, after 40 min of reaction time. However, only ozone system still existed 11.8% MB in aqueous solution, while in case of O₃/AC system MB of 4.6% was not removed. In the COD removal experiment, the catalytic ozonation process showed a superior performance, compared to that of the conventional ozonation. COD removal efficiency was significantly promoted in the presence of catalysts such as AC and TiO₂. O₃/TiO₂/AC was found to be the most effective approach to eliminating the color and enhancing COD removal efficiency. The catalyst of TiO₂/AC was characterized by using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).     

Enhancing Biodegradability of Textile Wastewater by Ozonation Processes: Optimization with Response Surface Methodology

ABSTRACT

In this study, an ozonation process was used to increase biodegradability of textile wastewater by considering chemical oxygen demand (COD) and color removal. Response surface methodology was applied in order to determine the significance of independent variables which are initial pH, reaction time and ozone dose. While a biological oxygen demand (BOD)/COD rate of 0.315 was obtained at optimum conditions, which are pH 9, 75 min of reaction time and 26 mg/L ozone dose, color and COD removal was obtained at 74% and 39%, respectively. BOD/COD ratio value increased from 0.18 to 0.32 by ozonation process. In addition, k coefficient for BOD also increased from 0.21 to 0.30 d^?1.     

BAF-O_3组合工艺深度处理炼化含盐污水工业应用

臭氧催化氧化与曝气生物滤池的联合工艺可用于炼油厂含盐污水的深度处理。惠州炼化分公司采用BAF-O3组合工艺对含盐二级生化出水进行深度处理改造。运行结果表明,在进水COD浓度平均值97.9mg/L,臭氧催化氧化池和臭氧接触氧化塔的臭氧投加量分别为80~90 mg/L、30~20 mg/L的条件下,装置总出水COD浓度均值为43.5 mg/L,满足污水COD≤50 mg/L的限值要求,COD总去除率达到55.57%。BAF单元前置后,其COD去除率提高,COD去除量由2.71 mg/L提高至9.5 mg/L,经分析主要系生物絮凝作用;由于活性炭罐和BAF单元对悬浮物的有效过滤,有利于保护后续的臭氧催化氧化单元。     

Biological Nitrogen Removal Using the Supernatant of Ozonized Sludge as Extra Carbon Source

A sludge ozonation process with lab-scale anaerobic/oxic (A/O) system was used to investigate the utilization of the ozonized sludge (OS) supernatant as extra carbon source for denitrification. The optimal ozone dose for the sludge ozonation was 0.2 gO₃/gSS. The concentrations of SCOD, BOD, NH₃-N and TN in the supernatant increased respectively at this ozone dose. In the meantime, the sludge was significantly reduced. The OS supernatant had negative effect on nitrification because of low pH and alkalinity. After alkalinity adjustment, the A/O with the OS supernatant as the extra carbon source achieved a nitrogen removal rate of 78%, which was very close to the control experiment using glucose (79%).     

Granulation of sludge under different loads of a glycerol fraction from biodiesel production

The aim of the research was to evaluate the possibility of using the crude glycerol fraction from biodiesel manufacturing processes for granular sludge production. The experiment was carried out simultaneously in four sequencing batch reactors (SBRs) at different carbon loads: 0.2 ± 0.08, 0.6 ± 0.16, 1.1 ± 0.27, and 1.3 ± 0.35 g COD/g TSS per cycle (COD – chemical oxygen demand, TSS – total suspended solids). Granulation did not occur in the reactor with the lowest organic carbon load. In the remaining reactors small granules began to appear after 25 cycles of reactor operation. In all reactors the efficiency of carbon removal remained at ca. 80%. The highest granular sludge production per cycle was 0.31 ± 0.28 g TSS/L; it was obtained at an organic load of 1.1 ± 0.27 g COD/g TSS per cycle. Most of the introduced COD was removed in the reactors during the first 5 h of aeration; the COD removal rate was correlated with the organic load and varied from 123.12 to 472.76 mg COD per litre and hour. Practical applications: With the increasing production of biodiesel fuel a problem arises with the utilization of glycerol that is a by‐product of the process. By‐product glycerol fraction from small agricultural installations is usually contaminated. Its composition varies depending on parameters of the transesterification process and it is unprofitable to purify it. In the present research we investigated one possible way of dealing with the by‐product. The glycerol fraction was successfully used as a carbon source for the production of aerobic granular sludge. The granules obtained can be used as a seed sludge in granule‐based reactors, or can be cofired with coal or directly combusted. Since aerobic granular sludge is one of the most promising technologies investigated during the last few years it appears to possess high utility.     

Effect of Ozone on Viability of Activated Sludge Detected by Oxygen Uptake Rate (OUR) and Adenosine-5′-triphosphate (ATP) Measurement

The current study focused on treatment of phenolic wastewater using an integrated process – dosing of ozone directly to activated sludge. The main goal was to analyze the effect of ozonation on viability of activated sludge in different systems – activated sludge in distilled water and activated sludge in wastewater. Two viability detection methods, oxygen uptake (OUR) rate and adenosine-5'-triphosphate measurement (ATP), were compared. The linear correlation between ATP and OUR measurements in studied range was found to be good (r² = 0.90). In case of ozonation of activated sludge in wastewater, ozone doses up to 42 mgO₃·gMLVSS^?1 did not influence the viability of sludge. In addition, contrary to ozonation of sludge in distilled water, soluble COD was reduced by 15.6% (at ozone dose of 42 mgO₃·gMLVSS^?1).     

Development of the wastewater reclamation and reusing system with a submerged membrane bioreactor combined bio-filtration

Recently there have been many wastewater treatment processes combining different units of process to improve the dissolving and suspension of pollutants in water. The submerged membrane bioreactor (SMBR) system uses a membrane that can produce high quality water for reusing with minimal land demand, instead of using secondary clarifier as biological treatment, sand filters, ozonation, GAC or disinfection processes as a tertiary treatment. For the development of the bio-filter membrane bioreactor (BMB) system as a submerged membrane bioreactor in this study the new wastewater treatment system will consist of a rapid bio-filter clarifier, a bioreactor and a hollow fiber membrane and plate membrane, to help find the optimal process to meet the regulations for reused water. This study was performed to evaluate the BMB reusing system, made up of a rapid bio-filter clarifier, an activated sludge bioreactor and a membrane module. The rapid bio-filter clarifier replaced a conventional primary sedimentation and removed SS, BOD and COD to 40, 20, and 20%, while the turbidity and color were removed by 30 and 10% respectively. This means that the rapid bio-filter clarifier having an HRT value 5.2 min can replace the conventional primary sedimentation of the HRT value of 1.5–2.5 h. Also the BMB reusing system could achieve the effluent quality of BOD < 5 mg/L, COD < 10 mg/L, turbidity < 0.5 NTU, and color < 20 unit respectively, and total coliforms did not appear. This means this system can meet water quality standard for water reusing systems. The flux of the plate membrane and hollow Fiber membrane were 120–140 L/m² h bar and 60–90 L/m² h bar; much more water could permeate the plate type membrane than hollow fiber type membrane. Plus the total resistance of hollow fiber type membrane was higher than plate type membrane.     

Decomposition of excess sludge in a membrane bioreactor using a turbulent jet flow ozone contactor

We have investigated the decomposition of excess sludge generated in a membrane bioreactor using a turbulent jet flow ozone contactor (TJC), which induced both hydrodynamic cavitation and ozonation reactions. We monitored the effects of various TJC operating parameters on the properties of the sludge, including the particle sizes, the particle size distribution, and the levels of soluble COD, total COD, and mixed liquor suspended solids. The TJC enhanced the degree of sludge reduction while consuming less energy, relative to conventional ozonation treatment systems, because of the synergic effects of hydrodynamic cavitation and ozonation. The hydrodynamic cavitation generated in the TJC increased the ozone mass transfer efficiency, which in turn promoted the rate of disintegration and solubilization of the sludge particles.     

Application of Individual and Simultaneous Ozonation and Adsorption Processes in Batch and Fixed-Bed Reactors for Phenol Removal

Ozonation, adsorption onto activated carbon and catalytic ozonation in batch and in a fixed-bed reactor for the removal/degradation of phenol and COD were investigated. In the case of batch ozonation the oxidation capacity was greater than 6.9 g of phenol/g O₃, while the continuous ozonation system degraded 40% of the phenol and reduced the COD by 27.9%. The adsorption process provided over 99% removal for phenol and COD; however, it treated only 5 L compared with 17 L for the combined process, which also increased the total area and pore volume of the activated carbon, due to the formation of pores and a widening of micropores.     

The Optimization of Ozonation and Biological Activated Carbon (BAC) in a Water Reclamation Context

A pilot plant study showed that an ozone dosage of about 4 mg/l before filtration and BAC led to the most cost-effective COD removal in the reclamation of water from activated sludge effluent. The combination in the reclamation of water from activated sludge effluent. The combination of ozonation, filtration and BAC could maintain a least COD removal fraction of 30 per cent for more than three times as long an inter–reactivation period as for filtration and BAC without ozonation. Filtration has not been found to contribute significantly to the COD removal by the above combination of process units.     

微气泡臭氧催化氧化深度处理化工园区废水研究

以酸/碱改性和Cu负载活性炭为催化剂,采用微气泡催化臭氧氧化深度处理化工园区废水。结果表明,经该工艺处理后,出水COD降至20 mg/L以下,发光抑制率降至-1.2%~-7.3%,B/C升至0.29~0.37,消除了废水生物毒性,并提高了废水可生化性。硝酸改性并负载Cu组分活性炭具有更强的催化活性,COD去除率和去除负荷分别可达70.8%和0.478 kg/(m~3·d),臭氧利用率为97.5%,催化臭氧氧化反应效率为0.554 mg COD/mgO_3。