Regression Modeling of Ozonation Process in Wastewater Treatment Plants for Reduction of Waste Activated Sludge

This research was based on the hypothesis that waste activated sludge (WAS) from municipal wastewater treatment plants can be reduced by ozonation of excess biosolids to induce cell lysis and by promoting utilization of intracellular products released by ozonation of biosolids in the aeration basins. In this research, mathematical modeling studies were performed in order to define process design and major components of ozonation. The main purpose of the model simulations was to evaluate the effect of operational parameters of the ozonation system (such as dosage and duration of ozonation) and to determine the amount of solids to be ozonated in order to achieve desired mass reductions in WAS. This modeling study focused on identification of design parameters and their suggested range of operation. The model presented in this study does not intend to detail and analyze the impact of the scientific variables in the ozonation mechanism, nor does it try to model the biosolids destruction mechanisms when ozonation is applied. The computer model simulations indicated that zero biosolids yield conditions can be achieved if more biosolids than was grown on the influent wastewater was processed through the ozonation system. The simulations suggested that zero biosolids yield conditions can be observed if 2.4 times as much biosolids as was grown on the influent wastewater was processed through the ozonation column, with a daily R of about 0.08 mg O₃/mg TSS-day. Furthermore, zero biosolids yield conditions can also be observed if only the amount of waste biosolids grown on the influent wastewater was processed through the ozonation column with a higher average daily R of 0.2 mg O₃/mg TSS-day.     

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.     

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.     

Feasibility of Sludge Ozonation for Stabilization and Conditioning

A pilot-scale sludge treatment plant was built to investigate the feasibility of ozonation processes for waste activated sludge treatment. Ozonation of wastewater sludge resulted in mass reduction by mineralization as well as by supernatant and filtrate recycle. Another advantage of sludge ozonation is a significant improvement of settleability and dewaterability. Experimental results showed that mass reduction of 70% and volume reduction of 85% compared with the control sludge was achieved through the sludge ozonation at a dose of 0.5?gO₃/gDS. It is also interesting to note that the filterability deteriorates up to ozone dose of 0.2?gO₃/gDS and then improves considerably at a higher ozone dose. The filterability could be improved by chemical conditioning even at a low ozone dose. The economic feasibility by cost analysis reveals that ozonation processes can be more economical than other alternative processes for sludge treatment and disposal at small-sized wastewater treatment plants.     

Systematic Analysis of the Biochemical Characteristics of Activated Sludge During Ozonation for Lowering of Biomass Production

Properties of activated sludge during ozonation were analyzed. The structure and surface characteristics altered with the increase of ozone dosage. At low ozone dosage, the floc structure was completely dismantled. Floc fragments reformed through reflocculation at an ozone dosage greater than 0.20 g O₃·g^?1 mixed liquor suspended solids (MLSS). Inactivation of microorganisms in the activated sludge mixture was caused by ozonation. Microbial growth decreased by up to 65% compared to the control. Simultaneously, 92.5% of nucleotide and 97.4% of protein in microbial cells of the sludge were released. Organic substance, nitrogen and phosphorus were released from the sludge during the ozonation process. The initial value of soluble chemical oxygen demand (SCOD) was 72 mg·L^?1. When the ozone dosage was 0.12 g O₃·g^?1 MLSS, the value of SCOD rapidly reached 925 mg·L^?1, increased by almost 12-fold. Simultaneously, 54.7% of MLSS was reduced. The composition of MLSS was changed, indicating that the inner water of cells and volatile organic substance decreased during the ozonation process.     

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.     

Ozonation within an Activated Sludge System for Azo Dye Removal by Partial Oxidation and Biodegradation

Pre-ozonation is often uneconomical for typical wastewaters with varied mixtures of organic compounds as more biodegradables than non-biodegradables are oxidized, all requiring ozone. The concept developed in this paper is ozonation within an activated sludge system to oxidize recalcitrant substances to more degradable forms and byproducts and to immediately assimilate or biodegrade these within the biological system. The focus was on a novel method of combining ozonation and biological treatment in one integrated unit without adversely affecting the bacterial population responsible for the biological degradation. An azo dye, spiked into the wastewater feed was used to study removal of a recalcitrant compound in a biological system.     

The Influence of Ozone,Oxygen and Chlorine on Biolocical Activity on Biological Activated Carbon

A laboratory study was conducted into the effects of the treatment of activated sludge effluent with different oxidants on the biodegradability of the organic substances. It was found that, under the experimental conditions described, ozone increased the biodegradability, whereas chlorine had no apparent significant effect. The effect of continuous oxidative pretreataent of activated sludge effluent on microbial populations and the biological activated carbon used subsequently in the process also was studied. It was found that ozone, particularly at a dosage of about 5 mg/L promoted biological activity, while chlorine and oxygen (in addition to the dissolved oxygen already in the effluent) had no significant effect on the biological population size.     

Reduction of Excess Sludge Produced by Biological Treatment Processes: Effect of Ozonation on Biomass and on Sludge∗

The excess sludge produced during biological treatment of wastewater can be reduced by treating this sludge with ozone in a specific reactor and recycling it to the biological facility. This increases the biodegradability of the inert fractions of the sludge without deteriorating the activity of the microorganisms. Ozone reacts only within the film zone near the gas/liquid interface: it is assumed that the size of the microflocs of active microorganisms is greater than the effective thickness of the film, thus protecting them from ozone. This coupled treatment produces treated water having satisfactory characteristics and a residual excess sludge that has an extremely high settling capability.     

Application of Ozonation and Biotreatment for Forest Industry Wastewater

This research is focused on the integrated process for the treatment of bleached Kraft pulp mill effluents. Pre-ozonation of softwood and hardwood combined bleaching effluents at alkaline pH resulted in 50 and 44% COD abatement, respectively. Segregation of highly polluted streams of bleaching process can be recommended to reduce the cost of treatment since the COD removal yield of CEH effluents was higher than combined bleaching effluents. Moreover, biodegradability of CEH effluents in terms of BOD₅/COD ratio was increased from 0.16 to 0.32. Noticeable color removal was achieved by pre-ozonation of the CEH stage and combined bleaching effluents. Pre-ozonation enhanced the performance of subsequent algal treatment in the sequential batch reactor (SBR) and activated sludge treatment. Algae have a higher ability to degrade AOX producing compounds together with a high COD removal rate. Although pre-ozonation increased the abatement rate of COD of SBR, the AOX removal rate remained constant as 87%.     

Combined Ozone Pretreatment and Anaerobic Digestion for the Reduction of Biological Sludge Production in Wastewater Treatment

The ever-increasing amount of solid waste generated by wastewater treatment plants highlights emerging economic and environmental issues. In order to develop new processes producing less sludge, the use of ozone combined with anaerobic digestion was investigated for waste activated sludge treatment. This paper was aimed at evaluating the impact of ozone pretreatment on anaerobic digestion and particularly the enhancement of biogas production. Sludge solubilization was estimated in terms of modification of chemical oxygen demand, solids and nitrogen. Batch anaerobic digestion highlighted the enhancement of ozonated sludge biodegradability. Ozonation led to an increase in biogas production. The ozone dose of 0.15 g O₃/g total solids resulted in a considerable increase in the soluble COD ratio from 4% to 37%. This ozone dose achieved the highest increase in biogas production: 2.4 times greater than without chemical pretreatment.     

Ozonation of Primary Sludge and Digested Sludge to Increase Methane Production in a Chemically Enhanced Primary Treatment Facility

The purpose of this research was the investigation of the ozonation of sludge as a method to improve anaerobic digestion performance in a chemically enhanced primary treatment facility. Batch tests were conducted to evaluate the effect of ozonation on the physicochemical characteristics of both primary and digested sludge. Then, the performance of semi-continuous anaerobic digesters in combination with ozone treatment was investigated (pre-ozonation and post-ozonation). Ozonation of primary sludge did not increase the soluble COD nor the biodegradable COD, but resulted in the mineralization of a fraction of the organic matter into CO₂. However, the ozonation of anaerobic digested sludge resulted in an increase in soluble COD and biodegradable COD and in a small level of mineralization at the dose of 90 mg O₃/g COD. Pre-ozonation of primary sludge was not effective in enhancing the performance of the anaerobic digester. The coupling of ozonation and anaerobic digestion by means of the post-ozonation of digested sludge was found to be effective in improving methane production (+16%), for COD removal efficiency and for the dewaterability of anaerobic digesters compared to the control digester.     

Ozonation of Cyanide Catalyzed by Activated Carbon

In this work, the removal of cyanide from aqueous solutions was accomplished by using the synergetic effect of activated carbon and an oxidizing agent. A basic-character coconut shell activated carbon (CAC) was used; experiments were conducted in a semi-batch reactor, at 25 °C, initial pH of 11.5, and using cyanide solutions with initial concentration up to 1200 mg/mL. In particular, the beneficial effect of an oxidizing agent such as air, oxygen or ozone on the removal of cyanide by CAC was evaluated. At the optimum operating conditions found in this study, 1200 mg/mL of cyanide were totally decomposed in about 3 h, by using 1 g of CAC and about 2 mgO₃/min. The experimental results were rationalized based on different mechanisms reported in the literature. The findings provide the basis to optimize the removal of cyanide from aqueous solutions in mining or metallurgical effluents by using the synergetic effect of CAC and ozone.     

Ozonation as a Pre-treatment for Anaerobic Digestion of Waste-Activated Sludge: Effect of the Ozone Doses

The aim of the present study was to improve the anaerobic biodegradability of waste-activated sludge by using ozonation. The effect of different ozone doses was assessed in terms of biogas production, maximum biogas production rate, and concentration of amino acids and long-chain fatty acids in the waste-activated sludge. Four different doses were used: 0.043 gO₃ g_TSS^?1, 0.063 gO₃ g_TSS^?1, 0.080 gO₃ g_TSS^?1, and 0.100 gO₃ g_TSS^?1. The lower doses resulted in biogas production increases and a higher maximum biogas production rate in the anaerobic digestion of waste-activated sludge, while the contrary occurred at higher doses. The amino acids and long-chain fatty acids concentrations decreased when the ozone dose increased. The correlation with the ozone dose was nonlinear for amino acids and linear for long-chain fatty acids. The reaction products of long-chain fatty acids (aldehydes) are proposed as the cause of inhibition observed in the anaerobic digestion of waste-activated sludge treated with higher ozone doses.     

活性炭催化剂臭氧催化氧化处理废水的研究进展

介绍了近年来国内外活性炭催化剂臭氧催化氧化的研究结果,对活性炭及金属负载型活性炭催化剂的反应机理进行了总结。讨论了非均相臭氧催化氧化过程中活性炭的主要作用,活性炭催化剂的表面物化性质、pH值、温度在臭氧催化氧化过程中的影响规律。并提出活性炭催化剂的降解机理以及催化剂性质与有机污染物的化学结构之间的关系还需要进一步的研究。     

Improving the Biodegradation of Organic Pollutants with Ozonation during Biological Wastewater Treatment

Pre-ozonation is often used to enhance the biodegradability of recalcitrant compounds prior to biological treatment of wastewater. A usual shortcoming of such an approach is wasting ozone on other compounds that are already biodegradable. This research followed a groundbreaking approach of degrading a recalcitrant substance with ozone during biological treatment. Two parallel bench-top activated sludge processes were fed a synthetic wastewater containing typical biodegradable substances and also methylene blue at 5 mg/L. Ozone was applied continuously and directly into one of the activated sludge units at 17 mg/L based on inflow rate. The methylene blue was removed by 95%?in the ozonated process compared with just 40%?removal in the non-ozonated control. The removal in the activated sludge without ozonation was demonstrated to be mainly due to biosorption. The ozone oxidation reaction by-products were analyzed using GC-MS on volatile substances collected in the headspace above ozonated samples of methylene blue and most found to be biodegradable. These by-products are expected to be degraded and assimilated in the same process unit together with the other biodegradables in the feed stream by the activated sludge process. The reaction rate with organic substances depleted the dissolved ozone at such a rate that the inactivation of the treatment bacteria (and protozoa) was minimal, mostly affecting the filamentous bacteria. A concern that ozone, as a powerful disinfectant, could inhibit or kill the beneficial bacteria in the activated sludge process was proven to be incorrect.     

Effect of Ozonation on Degradation of Organochlorine Compounds in Biosludge of Pulp and Paper Industry

The waste-activated sludge in the pulp and paper industry has been classified as hazardous waste due to the presence of organochlorine compounds. The fate of organochlorine compounds during ozonation of biosludge as well as subsequent treatment in activated sludge process has been studied. Ozonation of biosludge at 45.3 ± 2.1 mg O₃/g dry solid dosage resulted in 23 ± 2 and 26 ± 4% removal of adsorbable organic halides and extractable organic halides compounds, respectively. Out of 12 chlorophenolic compounds identified by USEPA for regulation, 10 compounds were detected in the biosludge and 19–68% removal of the individual compounds was observed during ozonation. High molecular weight chlorinated compounds were decomposed to low molecular weight ones with partial dechlorination. The ozonation followed by biological treatment can remove more than 80% of organochlorine compounds.     

Comparison of Activated Carbon and Hydrophobic Zeolite Efficiencies in 2,4-Dichlorophenol Advanced Ozonation

This study aims at comparing the removal of 2,4-dichlorophenol (2,4-DCP) by 3 methods; adsorption using hydrophobic zeolite (faujasite) or activated carbon (S-23 and L-27), conventional ozonation and hybrid adsorption/ozonation treatment. On the one hand, the three materials correctly adsorb 2,4-DCP; however the adsorption kinetics using zeolite is very low. On the other hand, ozonation totally removes 2,4-DCP after 1 h experiment and the simultaneous combination of adsorbent and ozone does not change the 2,4-DCP degradation. But, though ozonation and hybrid process appear to be equivalent for 2,4-DCP removal, activated carbons are able to decompose ozone and to improve chemical oxygen demand (COD) removal, whereas the zeolite does not show this catalytic effect. Similar results were also observed in a former study with nitrobenzene. Adsorbent degradation is evaluated by Brunauer, Emmet and Teller (BET) and differential thermogravimetric (DTG) analysis, which evidence that Faujasite and S-23 activated carbon are resistant to ozone exposure whereas the pore volume and the surface area of L-27 activated carbon decrease during ozonation.     

Domestic and Industrial Wastewater Treatment with Ozonated Activated Sludge

Poor sludge settleability is a problem encountered in many activated sludge wastewater treatment plants. This study was aimed at combatting the unwanted biological growths at the root of this phenomenon with ozone. Ozone dosed directly into the aeration basins of small activated sludge pilot plants treating both domestic and synthetic fuel wastewaters led to a substantial reduction of the bulking problem even at dosages as low as 6 to 10 mg/L. Ozone did not interfere in the delicate nutrient removal processes and significantly enhanced effluent quality.     

污泥粉煤灰混合制备活性炭及其性能研究

为提高以污泥制备的活性炭的吸附性能,采用化学活化方法将污泥、粉煤灰混合制备活性炭并研究其吸附性能。研究表明,在污泥、粉煤灰和ZnCl2质量比为10∶3∶4、活化温度为500℃、活化时间为80 min条件下,制备的活性炭吸附性能最佳,其比表面积为459.56 m2/g,总孔面积为0.32 mL/g,碘值为376.17 mg/g。以污泥和粉煤灰制备活性炭技术在废水治理领域具有良好的工业应用前景。