Application of excess activated sludge ozonation in an SBR Plant. Effects on substrate fractioning and solids production

This paper provides new insights on the application of the ozonation process for the reduction of the activated sludge production in a sequencing batch reactor (SBR). The study was performed in two identical lab-scale SBRs plant, one for experimental activities (Exp SBR) and one used as control (Control SBR), both fed with domestic sewage. A fraction of the activated sludge collected from the Exp SBR at the end of the aerobic react phase was periodically subjected to ozonation for 30 minutes at three different specific dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and then recirculated before the beginning of the following cycle.Recirculation of the ozonated sludge to the Exp SBR did not appreciably affect the efficiency of the biological nitrogen and carbon removal processes. Nonetheless, an improvement of the denitrification kinetic was observed. Mixed liquor volatile and suspended solids (MLSS and MLVSS, respectively) concentrations in the reactor decreased significantly with time for long term application of the ozonation treatment. Kinetic batch tests on unstressed sludge taken from Control SBR indicated that the different oxidant dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and durations of the ozonation process (10, 20 and 30 minutes) used remarkably affected chemical oxygen demand (COD) and organic nitrogen fractioning. In particular, soluble and biodegradable fractions seemed to be higher at lower dosage and longer contact time.     

Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability.

The purpose of this study was to evaluate the influence of partial ozonation of return activated sludge on settling properties and dewaterability of sludge. Sequencing batch reactors with two sets of aerobic and alternating anoxic/aerobic conditions were used. In each set, one reactor served as a control and the other was subject to the ozone treatment (doses in the range of 0.016-0.080 mg O3/mg TSS of initial excess sludge). The level of total suspended solids (TSS) in each reactor was controlled at 1,800 mg/l. To evaluate settleability and dewaterability, settling kinetic studies, sludge volume index (SVI) and capillary suction time test (CST) were used. For extraction and quantifying sludge biopolymers, thermal-ethanolic extraction was employed. The ratio of bound-to-total extracellular polymer substances (EPS) was higher for the strictly aerobic reactor than for the alternating anoxic/aerobic one, indicating the stronger structure of the aerobic flocs. After ozone treatment, the fraction of bound EPS was released and solubilized, increasing soluble EPS. Increased apparent food-to-microorganism (F/M) ratio favoured production of EPS in ozonated reactors, enhancing flocculation, which had potential to improve settling. Dewaterability, measured by CST test, was better in alternating anoxic/aerobic reactors than in aerobic ones, indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation.     

饮用水处理中不同滤料除氨氮效果及需氧量研究

对比研究了活性无烟煤、活性炭、石英砂以及无烟煤4种滤料过滤去除饮用水中氨氮的效果及其与需氧量的关系。试验结果表明,当氨氮低于2 mg/L时,4种滤料过滤都能够有效去除氨氮,水中溶解氧逐渐耗尽;当氨氮浓度高于2 mg/L时,4种滤料的去除率均有所下降,但相比石英砂和无烟煤而言,活性无烟煤和活性炭过滤能够更有效地去除氨氮。纯氧曝气能够将溶解氧浓度提高到25 mg/L,从而大幅度改善4种滤料对氨氮的去除效果;活性无烟煤和活性炭过滤可将大部分氨氮转化为硝酸盐,但石英砂和无烟煤过滤则会发生亚硝酸盐积累现象。在活性无烟煤和活性炭过滤去除氨氮过程中,氨氮去除量与溶解氧的平均比例为1∶4.25,略低于理论值。这种定量关系对于生物过滤去除氨氮工艺的设计和运行具有指导意义。     

Effect of ozonation on sludge reduction in a SBR plant.

This paper provides new insights on the application of the ozonation process for the reduction of activated sludge production in a Sequencing Batch Reactor. The study was performed on two identical lab-scale SBRs plant, fed with domestic sewage: a fraction (1/3 of the working volume) of the activated sludge from one reactor (Exp SBR) was periodically subjected to ozonation for 30 minutes at 0.05 g O(3)/gSS and then recirculated before the beginning of the cycle; the other reactor was used as control and therefore managed at the same sludge retention time but without the application of ozonation. The effects of the recirculation of the ozonated sludge to the Exp SBR were evaluated in terms of biological nitrogen and carbon removal efficiencies, Mixed Liquor Volatile and Suspended Solids (MLSS and MLVSS, respectively) concentrations, effluent quality and sludge settleability. Besides, characterization of the ozonated sludge was carried out for different oxidant dosages (0.05, 0.07 and 0.37 g O(3)/gSS) and durations of the ozonation process (10, 20 and 30 minutes). The results show that at 0.05 g O(3)/gSS and 30 minutes contact time MLVSS as well as MLVSS/MLSS ratio do not change appreciably. Ozone dosage must be increased much further to obtain a relevant effect.     

载锰污泥活性炭催化臭氧氧化草酸废水的研究

为研究在催化臭氧化过程中,载锰污泥活性炭对草酸废水降解的催化效果,以及为污泥的资源化探索一条新途径,本实验采用连续流臭氧氧化实验,通过单因素实验方法考察了载锰污泥活性炭催化臭氧化反应的主要影响因素及最佳反应条件,同时对催化臭氧化反应机理进行了探讨。结果表明:在臭氧浓度为5.0 mg/L,载锰污泥活性炭投加量为100 mg/L,pH值为3.5的最佳反应条件下,60 min内草酸的去除率最高达91.2%。叔丁醇对草酸降解具有抑制作用,催化臭氧化反应符合羟基自由基的反应机制。该方法的处理效果较为明显,对评价催化臭氧法的效果具有较明显的参考价值。     

Observations on ozone treatment of excess sludge.

This work experimentally studied the effects of ozonation treatment on waste sludge. During the treatment process, various parameters characterizing sludge were investigated. A substantial reduction in the volume of sludge and the release of intracellular and extracellular materials were observed. With the increase of ozone dose, the settleability and water content of sludge improved obviously, but the filterability of sludge deteriorated drastically. In addition, the evolution of particle size was evaluated, which proved the breakup of sludge flocs and cells. There existed a threshold of ozone dose which was 0.04 gO(3)/gMLSS in this work. Above the threshold, the soluble chemical oxygen demand (SCOD), protein, carbohydrate, total nitrogen and total phosphorus in supernatant increased remarkably and the electron transport system (ETS) sludge activity decreased. Organic nitrogen and organic phosphorus occupied the main part of total nitrogen and total phosphorus in the supernatant.     

The basics of oxidants in water treatment. Part B: ozone reactions.

The oxidation of organic and inorganic compounds during ozonation can occur via ozone or OH radicals or a combination thereof. Ozone is an electrophile with a high selectivity. The reactions of ozone with inorganic compounds are typically fast and occur by an oxygen atom transfer reaction. Organic micropollutants are oxidised with ozone selectively. Ozone reacts mainly with double bonds, activated aromatic systems and non-protonated amines. The kinetics of direct ozone reactions depend strongly on the speciation (acid-base, metal complexation). The reaction of OH radicals with the majority of inorganic and organic compounds is nearly diffusion-controlled. The degree of oxidation by ozone and OH radicals is given by the corresponding kinetics and the ratio of the concentration of the two oxidants. Product formation from the ozonation of organic micropollutants has only been established for a few compounds. Numerous organic and inorganic ozonation disinfection/oxidation byproducts have been identified. The byproduct of main concern is bromate, which is formed in bromide-containing waters. A low drinking water standard of 10 microgL(-1) has been set for bromate. In certain cases (bromide > approximately 50 microgL(-1)), it may be necessary to use control measures to lower bromate formation (lowering of pH, ammonia addition, chlorination-ammonia process).     

The discharged excess sludge treated by Oligochaeta.

To overcome unstable worm growth, a new worm-reactor was developed for oligochaete growth. The bench scale of this worm-reactor was used to treat the discharged excess sludge from a pilot activated sludge system, and experiments were carried out to investigate the sludge reduction induced by Oligochaeta. Due to difficult getting free-swimming worms such as Aeolosoma hemprichicii and Nais elinguis, Tubifex tubifex was thus selected and inoculated in Reactor 1 at the start-up phase except the control reactor (Reactor 2). Tubifex occurred in Reactor 1 throughout the operation period after its inoculation, and mainly attached on the carriers and aggregated on the bottom of the worm-reactor. Free-swimming worms such as Aeolosoma hemprichicii, Nais elinguis, and Aulophorus furcatus were found in both reactors since the 35th day. Microscopic investigation showed that these free-swimming worms naturally produced in the pilot activated sludge system, and entered into both reactors along the discharged sludge. Results clearly showed that the average sludge reduction in Reactor 1 was 59%, much higher than that in the control. The characteristics of sludge settling was improved by worm growth, but was not too much. High ammonia nitrogen concentration in influent sludge was toxic to worms, and then inhibited worm growth. Both the total inorganic nitrogen and phosphorus releases into effluent sludge were observed in Reactor 1, but such increases were not heavy.     

Changes in waste stabilisation pond performance resulting from the retrofit of activated sludge treatment upstream: part I--water quality issues.

This paper describes changes in effluent quality occurring before and after an upgrade to the Bolivar Wastewater Treatment Plant in South Australia. Trickling filters (TF) were replaced with an activated sludge (AS) plant, prior to tertiary treatment using waste stabilisation ponds (WSPs). The water quality in the WSPs following the upgrade was significantly improved. Reductions in total and soluble BOD, COD, TKN, suspended solids and organic nitrogen were recorded and the predominant form of inorganic nitrogen changed from NH(4)-N to NO(2)/NO(3)-N. The reduction in ammonium and potentially toxic free ammonia removed a control upon the growth of zooplankton, which may have contributed to decreases in algal biomass in the final ponds and consequently lower dissolved oxygen. Additionally, changes in inorganic nitrogen speciation contributed to a slightly elevated pH which reduced numbers of faecal coliforms in WSPs. The AS pretreated influent recorded significantly lower inorganic molar N:P ratio (10-4:1) compared to those fed with TF effluent (17-13:1). Algae within the WSPs may now be nitrogen limited, a condition which may favour the growth of nitrogen-fixing cyanobacteria. The decrease in algal biomass and in dissolved oxygen levels may enhance sedimentary denitrification, further driving the system towards nitrogen limitation.     

Advanced oxidation of commercial textile biocides in aqueous solution: effects on acute toxicity and biomass inhibition.

In the present study, the decomposition of two biocides used in the textile finishing process with Advanced Oxidation Processes (AOPs) has been studied. Different AOPs, i.e O3/OH-, TiO2/UV-A and Fe2+/H2O2 have been used representing mutually combined components of the chemically and photochemically driven advanced oxidation systems. The course of reaction was examined by changes in chemical oxygen demand (COD), total organic carbon (TOC) and acute toxicity towards the water flea Daphnia magna (assessed in terms of the effective dilution ratio LD50). Particular attention has been paid to determine the inhibitory effect of raw and ozonated biocides on biological activated sludge consortium at concentrations typically encountered in textile finishing effluents. Significant oxidation and mineralization of both biocides could be achieved employing ozonation at pH = 11.5 and heterogeneous photocatalysis (TiO2/UV-A) at pH = 5.0, whereas Fenton's reagent appeared to be less effective in COD and acute toxicity abatement.     

The effect of operational conditions on the hydrodynamic characteristics of the sludge bed in UASB reactors

This work aims to evaluate the hydrodynamic properties of the sludge bed of Upflow Anaerobic Sludge Blanket (UASB) reactors based on its settleability and expansion characteristics. The methodologies used for the evaluation of the settleability of aerobic activated sludge, and for the expansibility of a sludge bed of Expanded Granular Sludge Bed reactors and Fluidised Bed Reactors were adapted and applied to the particular characteristics of the sludge of UASB reactors. An easy-to-build experimental set-up was developed to assess the parameters necessary for the equations of settleability and of expansibility. The results obtained from the sludges of seven differently operated reactors show that, for the treatment of low strength wastewater, settleability increased and expansibility decreased at decreased hydraulic retention time, from 6 to 1 h, and/or increased influent concentrations, from 136 to approximately 800 mg chemical oxygen demand/L. The results also show that it is useless to design an UASB reactor with a longer hydraulic retention time to cope with hydraulic shock loads, as a more expansible sludge will develop at such condition.     

Screening of chemical oxidation processes and other methods for decolorization of urine for its re-use as toilet-flush liquid in ecological sanitation systems.

Because of its potential use as fertilizer, urine ("yellow water") is a resource originating from sanitation. Its separate collection in no-mix toilets is a beneficial aspect of ecological (source control) sanitation. In order to avoid dilution of the fertilizing nutrients with toilet flush water, the utilization of yellow water as toilet flush liquid seems to be advantageous. To be accepted for this purpose, urine has to be decolorized (and also deodorized). In this study activated carbon adsorption, irradiation with UV light of different wavelengths, the advanced oxidation processes ultrasound, UV/H2O2, and photocatalytic oxidation have failed to decolorize urine. Biological treatment caused brown colour of the treated urine. Only ozonation was successful in colour removal, although it did not affect TOC. In spite of darkening of yellow water during biological treatment (generation of humic substances), smaller ozone doses were required for decolorizing the biologically pre-treated urine than for original urine. Photocatalytic oxidation of biologically treated urine also removed brown colour, but the original yellow colour remained. In ozonated urine, yellow colour was reconstituted unless hydrogen peroxide was added. In addition to colour removal, ozone contributed to deodorization as a consequence of ammonia stripping and probably of phenol oxidation.     

Are standard wastewater treatment plant design methods suitable for any municipal wastewater?

The design and operational parameters of an activated sludge system were analyzed treating the municipal wastewaters in Istanbul. The design methods of ATV131, Metcalf & Eddy together with model simulations were compared with actual plant operational data. The activated sludge model parameters were determined using 3-month dynamic data for the biological nutrient removal plant. The ATV131 method yielded closer sludge production, total oxygen requirement and effluent nitrogen levels to the real plant after adopting correct influent chemical oxygen demand (COD) fractionation. The enhanced biological phosphorus removal (EBPR) could not easily be predicted with ATV131 method due to low volatile fatty acids (VFA) potential.     

Recalcitrant COD degradation by an integrated system of ozonation and membrane bioreactor.

In order to treat wastewater to a low residual COD-concentration such as 125 mg/L, classical biological treatment is not sufficient for many types of industry. This research focused on the integrated treatment of the wastewater of the paper industry, with a membrane bioreactor (MBR) and an oxidation step. The optimal configuration was examined. Screening tests with different types of oxidation showed that ozonation after biological treatment could reduce the COD with 40% with an ozone dose of 0.4-0.8g O3/g COD. BOD/COD ratio could be increased up to 0.19. Neither combination of ozone with UV and/or hydrogen peroxide nor the process H2O2/UV or (photo-)Fenton reagents gave any improvement in COD reduction or BOD increase, unless the doses were very high. Based on these results, an integrated system MBR-ozonation was designed, with recirculation of MBR effluent over ozonation. This test showed that reduction of COD up to 125 mg/L immediately behind the MBR required a lot of ozone. A technically feasible solution was to discharge the water after an extra ozonation step, which resulted in a high total ozone dosage. The alternative, the consecutive treatment activated sludge-ozonation-activated sludge, did not give a better COD-removal with the same ozone dose as the integrated concept. The economic evaluation proves that the integrated chemical and biological treatment is expensive for the paper industry if a low discharge limit of COD has to be complied with.     

Removal of endocrine-disrupting chemicals by ozonation in sewage treatment.

Treatment experiments by two laboratory scale semi-batch reactors and a demonstration scale process were both carried out to evaluate endocrine disrupting chemical removal characteristics by ozonation in sewage treatment. In the semi-batch mode experiments, secondary effluent and primary effluen of sewage treatment plants were ozonated respectively. Behaviour of brominated by-products was also evaluated. The results based on these studies indicated that estrogenicity in wastewater can be removed by ozonation effectively. The condition of ozonation until dissolved ozone concentration increased to 0.1 mg/L, which corresponded to 1 mgO3/mgC and 0.4 mgO3/mgC of ozone consumption per initial DOC for secondary effluent and primary effluent, respectively, is proposed as an appropriate operational condition for efficient removal of EDCs as well as UV254 and SUVA without production of brominated by-products.     

曝气条件对侧流活性污泥水解工艺脱氮性能和微生物的影响

通过改变传统厌氧/缺氧/好氧（A²/O）反应器和侧流活性污泥水解（SSH）反应器的曝气强度和溶解氧（DO）浓度,考察了曝气条件对脱氮性能的影响,并对比研究了微生物群落结构的变化规律。结果表明：相较于高DO阶段,两组反应器在中低DO阶段有更好的脱氮效果。在相同进水条件下,SSH反应器的脱氮性能优于A²/O反应器,且出水满足一级A标准。高通量测序结果表明,中低DO浓度更有利于脱氮微生物的生长。相对于A²/O反应器,SSH反应器中反硝化微生物的相对丰度更高。因此,合理控制曝气条件维持中低DO浓度有利于SSH工艺达到良好的脱氮性能及脱氮微生物的生长。     

Ozonation and reductive deiodination of iopromide to reduce the environmental burden of iodinated X-ray contrast media.

The potential of ozonation for the removal of iodinated X-ray contrast media (ICM) with focus on the oxidation products was examined. Iopromide used as model compound was dissolved in tap water, respectively in the effluent of a membrane bioreactor and was ozonated. Ozone (10 mg/L) was continuously introduced into a semi-batch reactor (35 L/h). After 30 minutes the ozone concentration was increased to 30 mg/L. In all experiments the iopromide concentration decreased very fast, whereas the decrease of the amount of organic bound iodine (AOI) was much lower. The concentration of iodate, the inorganic oxidation product increases with time, depending on the AOI decrease. The data clearly show that the ozonation of iopromide using a common applied ozone dosage leads to the formation of numerous iodinated transformation products, which are detectable by LC-ESI-MS. As an alternative treatment, especially for the treatment of urine or hospital waste water, the source for the contamination, it was tested if iopromide can be deiodinated by zero-valent iron. First experiments done in stirred batch reactors using iopromide dissolved in ultra pure water and urine with an initial pH of 2 showed that iopromide can be deiodinated completely by zero-valent iron. Even in contaminated urine collected in a hospital a deiodination of ICM was possible. Kinetic studies at constant pH showed that the deiodination can be described by pseudo-first order for equal iopromide and iron concentrations. The observed rate constant kobs increased with decreasing pH with a maximum at pH 3 with 4.76x10(-4) s(-1). The concentration of iopromide can be decreased by ozonation and by the reductive dehalogenation. In case of ozonation iodinated organic compounds are the main reaction products, whereas the reductive dehalogenation leads to transformation products which are not iodinated and are thus most probable biodegradable.     

Biological treatability of raw and ozonated synthetic penicillin formulation effluent.

Chemical pre-treatment of synthetic Procaine Penicillin G (PPG) effluent with ozone (applied dose = 1440 mg/h; treatment duration = 60 min) at pH = 7 was investigated. Successive biological treatability studies were performed with raw, ozonated penicillin formulation effluent and synthetic readily biodegradable substrate as simulated domestic wastewater. The PPG effluent additions were adjusted to constitute approximately 30% of the total COD in the reactor. Ozonation of PPG effluent resulted in practically complete removal of the parent pollutant accompanied by 40% COD abatement. Speaking for the raw PPG effluent, prolonged acclimation periods were necessary to obtain significant COD removal efficiencies. Batch activated sludge treatment experiments and respirometric studies have demonstrated that the selection of true retention time is extremely crucial for having high amount of slowly hydrolysable substrate or complex wastewater, like pharmaceutical effluent. The effect of ozonation time on biological treatability performance of PPG has been evaluated in the study. Pre-ozonation of PPG effluent did not improve its ultimate biodegradability.     

Long-term effects of the ozonation of the sludge recycling stream on excess sludge reduction and biomass activity at full-scale

This paper presents a full-scale experience of sludge minimization by means of short contact time ozonation in a wastewater treatment plant (WWTP) mainly fed on textile wastewater. The WWTP performance over a 3-year operational data series was analysed and compared with a two-year operation with sludge ozonation. Lab-scale respirometric tests were also performed to characterize biomass activity upstream and downstream of the ozone contact reactor. Results suggest that sludge ozonation: (1) is capable of decreasing excess sludge production by 17%; (2) partially decreases both N removal, by lowering the denitrification capacity, and P removal, by reducing biomass synthesis; (3) increases the decay rate from the typical value of 0.62 d(-1) to 1.3 d(-1); (4) decreases the heterotrophic growth yield from the typical value of 0.67 to 0.58 gCOD/gCOD.     

Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor.

Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation.