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.     

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.     

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.     

Intermittent Ozone Application in Aerobic Sludge Digestion

Excess biological sludge, WAS, produced during activated sludge process is a growing problem for the utilities owing to the stringent regulations now imposed worldwide. One method of handling the excess sludge is to digest it, to reduce its amount and to stabilize it. Aerobic digestion is particularly suitable for nutrient treating plants as sludge should not be exposed to anaerobiosis since this will lead to release of accumulated phosphorus. A novel and patented ozone-assisted aerobic sludge digestion process (PCT/TR2010/000213) is shown to appreciably shorten the 15–30-day aerobic digestion period and the extent of solids destroyed. WAS samples were ozonated for different periods in Erlenmeyer flasks, once a day, on each of four consecutive days. Flasks were continuously aerated between ozone applications. The MLVSS, MLSS, COD and OUR parameters were measured routinely during the course of four days of digestion in order to optimize the process. As a result 22.6%, 40%, 75% and 84% MLVSS reductions were obtained at total ozone applications of 0.42, 0.64, 0.85 and 1.27 mg O₃ g^?1 MLSS, at the end of the fourth day. Hence, it became possible to save on contact time as well as achieving a bio-solids digestion far exceeding the standard aerobic process, which is 40–50% in 15–30 days, at the expense of a minimum of ozone dose. The developed process is deemed superior over side-stream ozonation where ozone is applied to the return activated sludge, RAS, line; in that it does not cause any reduction in active biomass amount maintained in the aeration tank. Conversely, reduction in active biomass concentration results in reduced treatment efficiency.     

Effect of Ozone Pretreatment on Biodegradability Enhancement and Biogas Generation Potential From Biomethanated Distillery Effluent

The study evaluates the effect of ozone pretreatment on biodegradability enhancement of biomethanated distillery effluent. Results revealed that ozone pretreatment led to biodegradability index (BI = BOD/COD) enhancement up to 0.58 along with COD, color and toxicity reduction of up to 33%, 25% and 40%, respectively. Anaerobic digestion of pretreated effluent resulted in favorable biogas generation with methane content, yield and COD reduction of up to 62%, 39 mL/g COD and 57%, respectively. Kinetics of biogas generation determined by modified Gompertz model indicated methane production potential and production rate of 48.08 mL/g COD and 8.085 mL/g COD.day respectively under optimal conditions.     

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.     

Advanced Sewage Treatment with Ozone Under Excess Sludge Reduction,Disinfection and Removal of EDCs

A new advanced treatment system, which consists of biological nutrient removal process combined with reduction of excess sludge by ozonation and phosphorus recovery by crystallization and polishing-up ozonation process, was developed based on the fundamental studies and demonstrated by the demonstration plant set in AICHI EXPO 2005. Reduction of withdrawn excess sludge by 90% and phosphorus recovery by 70% were accomplished without any adverse effects on biological nutrient removal. The concentrations of SS, BOD, T-P and T-N in the effluent were less than 1.0, 3.0, 0.5 and 10 mg/L, respectively. EDCs were reduced to almost undetectable level and 2-log disinfection of Bacillus subtilis was established. The energy amount required for the operation was saved by 40% when compared with a conventional system to get the same level of water quality.     

工业污泥用于根瘤菌菌剂生产的新方法

接种根瘤菌技术在农业生产中应用广泛。根瘤菌菌剂的生产涉及两大因素：根瘤菌生长培养基和用于固体菌剂生产的载体。最近,全世界一种广泛存在的可再生废料——污水污泥正被研究用作接种根瘤菌剂生产的培养基和载体。研究表明,污泥通常含有足以维持根瘤菌生长的氮元素,其重金属含量也较低。并且可以通过污泥预处理或者添加营养素的方法优化其生长条件。同普通菌剂相比,污水污泥中生长的根瘤菌能够使植物进行有效的结瘤和固氮。这种接种根瘤菌剂生产的新方法为废料处理和菌剂生产提供了一种安全、经济、环保的选择。     

Sludge Pre-Treatment through Ozone Application: Alternative Sludge Reuse Possibilities for Recirculating Aquaculture System Optimization

Recirculating Aquaculture Systems (RAS) reduce water consumption by efficient filtration to maintain appropriate levels of accumulating compounds and sludge. Sludge is mechanically separated by drum filters and disposed of to the detriment of overall system water budgets. Dissolved nitrogen compounds are reduced via nitrification–denitrification filters, requiring commercial external carbon sources. The reuse of sludge after ozone pre-treatment may represent the next step in RAS optimization. The present study analyzes the content of sludge from RAS and tests ozonation as a pre-treatment for recycling as carbon source. The dissociative effect of ozone and the physicochemical changes due to ozonation lead to a significant increase in soluble carbon availability. Predominantly long-chain fatty acid (FA) (saturated and unsaturated) with 16 and 18 carbon atoms independently of the treatment were found in the profiles. Saturated FA concentrations in solution increased after 20, 40, and 60 min ozonation. The solid content of the sludge was practically unaffected by ozonation in terms of FA profile: only saturated FA slightly increases after 40 min treatment. The implications of these findings for denitrifying bacteria are discussed.

Abbreviations: Recirculating Aquaculture Systems (RAS); Advanced Oxidation Processes (AOPs)     

Sludge Ozonation and its Application to a New Advanced Wastewater Treatment Process with Sludge Disintegration

The applicability of sludge ozonation on wastewater treatment processes was investigated to reduce the amount of excess sludge without losing phosphorus removal efficiency. Solubilization degree per ozone consumption for general sludge was in the range from 2.4 to 5.8 gSS/O₃ and from 4.1 to 7.7 gCOD/gO₃. Around 80 to 90% of solubilized organics was biodegradable at a solubilization degree of 0.3. Based on the experimental results, a lab-scale plant with sludge ozonation and phosphorus crystallization was constructed to investigate the treatment performance. Amount of excess sludge was reduced by 93% with almost complete removal of soluble BOD and phosphorus removal efficiency of more than 80%. The percentage of the effluent COD_Cr discharge increased from 10% to 14–17% after installing ozonation and crystallization because of the formation of non-biodegradable organic substances in ozonation process. Energy consumption of the innovative advanced process is comparable or can be even smaller than that of the conventional anaerobic/oxic (A/O) process in spite of the installation of ozonation and crystallization.     

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.     

Automation of a Plant Treating Water With Ozone

The particularly powerful means supplied by commercial microcomputers made it possible to build this two–stage ozonation plant designed to ensure the chemical demand in oxidizing agent ofthe water in a first step and the viricidal action of this oxidizing agent ina second step. This plant was designed with one single ozone production unit and for quite variable flows of water tobe treated. Now, because such means are available, it is impossible to separate the design of acomplex ozonation plant from that of its automatic control system in particular since one cannot be looking for an economical and reliable system without conducting an overall analysis of the problem.     

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.     

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.     

Slurry Utilization and Impact of Mixing Ratio in Biogas Production

The anaerobic conversion of waste to biogas in a biogas digester is influenced by a number of factors including mixing ratios, type of substrate, temperature, organic loading rate, pH, and carbon/nitrogen ratio. The appropriate mixing ratio of water and animal waste leads to effective biogas yield. Different mixing ratios proposed in literature for various animal waste for improving biogas yield are reviewed. Characterization and application of animal slurry, the choice of animal slurry as suitable feedstock for biogas production, the storage of animal slurry, the agitation process of slurry as well as mixing ratios of animal slurry are evaluated.     

微波消解--FAAS测定污泥样品中的镉

采用微波消解—FAAS法测定污泥样品中的镉。研究了微波消解试样的最佳条件 ,与常压消解方法进行了对比实验 ,结果吻合。污泥中镉的检出限为 0 .0 1333mg/L ,样品测定的相对标准偏差 (N =6 )为 1.11%～ 2 .5 3% ,加标回收率为 97.8%～ 10 2 .3%。试验结果表明 ,该方法具有准确、快速、污染少的特点。     

Ozone Production: Economical Operation of a Cold Plasma Reactor

For a fixed value of the reduced electrical field, the economical operation of a cold plasma reactor generating ozone is determined by a particular value of the energy supplied by the field per molecule of reactant. Evidences are given in the ozone formation from air and oxygen. Moreover, influence of the flow and reduced electrical field upon the production is emphasized.     

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.     

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.     

Possibility of Improvement on Ozone Production by Using the Back-Corona Effect

Electrostatic precipitators’ problems and experimental results in point-to-plane or wire-to-cylinder systems indicate that the presence of a thin layer of porous dielectric material on the electrodes increases the discharge current for the same applied potential. This socalled Back-Corona effect, which generally reduces the sparking potential, depends on the active electrode polarity; nature, and thickness and porosity of the insulating layer; and position on the active or passive electrode of the deposited particles or insulating layer. In laboratory experiments in a point-to-plane device, with a dielectric porous layer on the plane, the current may be many times higher than its “normal” value (clean electrodes). In a DC negative wire-to-cylinder system, where the ozone concentration depends quasi directly on the discharge current, it appears possible to increase the ozone production, for the same running conditions (gas flow, electrical circuit, etc.).