1 Ozone - BAC depth treatment processes (O3-BAC)
Ozone - BAC depth treatment of drinking water purification technology is called the second generation of water purification technology, ozone - biological activated carbon technology uses ozone oxidation and biological activated carbon filter combined with the method, the ozone chemical oxidation, ozone sterilization, activated carbon adsorption physicochemical and biological oxidative degradation four technologies into one. Its main purpose is to further conventional treatment after the removal of organic contaminants, chlorine disinfection byproduct precursors as well as ammonia, reducing the water BDOC and AOC, ensure that the chemical stability and biological stability of the water purification process.
Ozone is the allotropic form of oxygen, formula O3, the norm was gas, light blue, with special odor; Ozone is one of the strongest oxidants in nature, with broad-spectrum microbicidal effect, its faster than chlorine disinfection. Ozone in the water after dosing, there are three main role, on the one hand the direct degradation of organic matter, reducing the pool of activated carbon into the organic load; the one hand, the degradation of organic molecules for small organic molecules, changing the molecular weight distribution of organic compounds in water, improve water and organics biodegradability, which will help to strengthen the follow-up of activated carbon adsorption process for small and medium molecular weight organics degradation; the last role is to follow the process and oxygenation of activated carbon, activated carbon in favor of aerobic microbial growth.
Activated carbon can be used almost any substance containing carbon as raw material to manufacture, including wood, sawdust, coal, peat, shell, stone, bagasse, bone, oil foot, leather waste, paper mill waste, etc., recently some countries tend to manufacture granular activated carbon from natural coal and coke. The main feature is the large surface area of activated carbon and tectonic belt pores, thus showing good adsorption properties. Two kinds of powdered activated carbon charcoal and activated carbon divided particles of difference between the two different particle sizes, the adsorption performance is no essential difference. Activated carbon as a porous material that can adsorb low concentrations in water, otherwise it is difficult to remove the material, at the same time, you can also remove the water turbidity, odor, color and improve the taste of water, and can be effectively adsorbed synthetic detergent , anionic surfactant active substance; Activated carbon also has a catalytic oxidation of ozone to the hydroxyl radical, the resulting oxygen gas, to increase dissolved oxygen in water (DO) concentration. Activated carbon gap, large specific surface area, can quickly adsorption of dissolved organic matter, but also to the enrichment of microorganisms in the water. Granular activated carbon adsorption of dissolved organic matter, but for some less volatile, difficult biodegradable polymer molecular weight of 10,000 or more difficult to adsorb and remove organic matter, but also by the adsorption properties of organic functional groups and molecular structure carried by the impact. Ozone potential characteristics of high, easy to many readily biodegradable organic matter is decomposed into many smaller more biodegradable or more low molecular weight organic compounds containing oxygen, thereby changing the morphology and properties of organic compounds, it is easily activated carbon adsorption removed, and dissolved organic matter adsorbed carbon bed for maintaining microbial life activities provide a nutrient source. Also, because the ozone sufficient oxygen, carbon bed in a large number of aerobic bacteria growth and reproduction, there is enough time to low molecular weight organic compounds adsorbed biodegradable, so it biofilm formation in the carbon bed. The biofilm biological oxidation and biological degradation of the dual role of adsorption, and activated carbon pores organic matter is decomposed through the backwash, activated carbon adsorption pore vacated position, restoring organic matter and oxygen adsorption capacity. Activated carbon adsorption of organic compounds in water and microbial oxidation and decomposition are happening one after another, oxidative microbial decomposition, so that the adsorption capacity of the activated carbon have been restored, while the activated carbon adsorption also allows access to a wealth of microbial nutrients and oxygen, both of which promote each other, form a relatively stable state, a stable treatment effect, thereby greatly extending the activated carbon regeneration cycle. Activated carbon attached denitrifying bacteria can also be converted ammonia compounds in the water, reducing the concentration of water NH3- N.
Ozone - BAC depth of the water treatment process (O3-BAC) refers to the combination of ozone and activated carbon adsorption of water treatment, activated carbon adsorption to take after the first ozonation and activated carbon surface growth of microbial biodegradation, the completion of the water organic effectively remove contaminants, which combines ozone oxidation, disinfection, activated carbon adsorption and microbial oxidation of physical action as a whole, give full play to their strengths, and promote each other, has made the removal of organic pollutants multiple effects, so as to achieve the purpose of purifying water quality depth . Ozone - biological activated carbon filter combined process can effectively degrade and removal of organic compounds, pesticides, algae, remove the smell, odor, color, removal of some heavy metals, cyanide, radioactive substances, such as ammonia. 2 Ozone - BAC deep water technology advantages and disadvantages
Advantages: ozone - biological activated carbon filter process is the physical chemistry of activated carbon adsorption, ozone chemical oxidation, biological oxidation degradation and ozone sterilization technology as one of four compared with traditional water treatment process, has obvious advantages,
Mainly reflected in:
① conventional chlorination of the water treatment process of Ames mutagenicity test results are mostly positive, while ozone - BAC treated as negative;
② ozone - activated carbon process for removal of organic pollutants by more than 50%, an increase of 15 to 20 percentage points higher than conventional treatment;
③ improve the color and odor removal, improving sensory indicators;
④ improve the iron and manganese removal;
⑤ can remove ammonia to about 90%, ammonia and nitrite in water can be bio-oxidized to nitrate, thereby reducing the amount of chlorine after chlorination, reducing the generation of trihalomethanes and other disinfection byproducts;
⑥ effectively remove AOC, protein ammonia, improve biological stability of treated water, improve water quality in the pipe network.
Also ozone and activated carbon used in combination, you can also extend the operating life of the activated carbon to reduce operating costs.
Cons: Although ozone - biological activated carbon filter for advanced treatment technology to control pollution and improve water quality of drinking water quality has played a good role, but there are limitations.
① presence of ozone oxidation treatment of drinking water ozone utilization rate, lack of oxidation and other defects;
② can efficiently degrade the ozone containing an unsaturated bond or partially aromatic organic pollutants, and for part of the stability of the organic contaminants (such as pesticides, halogenated hydrocarbons and nitro compounds, etc.) is difficult to oxidative degradation. Ozone some degradation of organic matter confined to the parent compound and structural changes may generate more toxic and not easily biodegradable charcoal intermediate oxidation products;
③ ozone oxidation of organic molecules can be small organic molecules, but research has shown that the molecular mass of activated carbon adsorption of organic 500 ~ 3000Da better removal efficiency, while large and small molecules of organic matter removal less effective. After ozonation smaller molecular weight organics, activated carbon adsorption will not help;
When ④ When water containing bromide (Br-), ozonation will generate bromate (BrO3-) and brominated trihalomethanes (Br-THM) and other harmful byproducts, have a great impact on human health.
3 Ozone - BAC deep water technology application at home and abroad
Activated Carbon ozone water treatment process as early as 1961 in the West German city of Dusseldorf Amestaad water put into use. From the later 1960s, ozone - biological activated carbon technology gradually in Europe, USA, Canada, Japan and other developed countries are widely applied to the depth of micro-polluted water treatment, and achieved good results for the purification of drinking water to various pollutants ; Applications developing countries the most widely used in Israel, South Africa, Namibia. One representative of a water plant in Bremen, Germany, Miao Mannerheim water, water 梅里苏瓦茨 France, Switzerland, Zurich Rigby Lake plant, the city of Los Angeles and Tokyo Waterworks Japanese gold stare waterworks Chai Island Waterworks Osaka and Australia Edeope water plant.
Kanamachi waterworks in Tokyo City, Japan, the existing water supply capacity of approximately 1.6 million m3 / d, accounting for 23% of Tokyo Waterworks Bureau of the total water supply, serving a population of about 2.5 million, raw water from the Tone River water. Since 1972, as a result of the urbanization process accelerated Tone River, Kanamachi waterworks access to raw water is seriously contaminated, especially in the summer, the water has a very serious musty. After an investigation, Tokyo Waterworks Bureau found that the main cause of musty source material is two methylisoborneol (2- MIB). From the beginning of 1984, the net water trying to use powdered activated carbon to remove musty, but due to changes in raw water dimethylisoxazole borneol concentration quickly, powdered activated carbon is difficult to effectively remove the odor. From 1984 to 1990, Tokyo Waterworks Bureau in-depth treatment process pilot test study. June 1992 in Kanamachi waterworks built a charcoal depth of the ozone treatment process, treated water for 260,000 m3 / d, accounting for about one sixth of the total water supply capacity. Water sucked conventional water treatment factory and later mixed with water depth treatment of uniform external supply, water quality is good and there is no smell. Advanced treatment process, the ozone activated carbon pool is designed after the sedimentation tank, front filter, the purpose of this design is based on activated carbon technology they believe will increase the factory ozone water turbidity, so after sand filtration in addition to the depth to handle the increased turbidity . Ozone contact tank is divided into five pools, the effective depth of 6.0m, ozone contact time 12min, ozone maximum dosage of 3mg / L, general dosage of lmg / L, depending on the water quality; other ozone contact tank division for the three-stage, each segment ozonated air dosing ratio of 3: 2: 1, activated charcoal filter layer height of 2.5m, EBCT for 15min, usually every three to four days backwash once. Joint use of air and water backwash, usually the first joint air and water recoil 4min, then water recoil 10min. Years of operating experience proved ozone - biological activated carbon filter process not only effectively removes musty problems, but also can effectively reduce the concentration of ammonia nitrogen, UV260 value (as the water used in Japan UV260 UV absorption peaks have alternative arguments amount of organic matter ), a non-ionic surfactant concentration, and trihalomethane precursors (THMPFP) concentration.
In Osaka City, Japan Kunijima water also established ozone Activated Carbon Process. Kunijima existing water supply capacity of 1.18 million m3 / d, where the system is 670,000 m3 / d, the next line of 510,000 m3 / d, from the raw water from Lake Biwa Yodogawa. In recent years, due to the impact of water quality deterioration, odor increases, Osaka City Waterworks Bureau in March 1998 under the Department of Engineering of the transformation and expansion. After the completion of advanced treatment process is mainly between the sand filter and clean the pool adds a ozone activated carbon process, and in front of the sand filter increases the ozone dosing device, namely ozone. Fill in the amount of ozone 0.7mg / L, filtered water filling rate of ozone 1.0mg / L. The department or the original conventional treatment processes. After comparative study found that the depth of treatment on the basis of conventional treatment can significantly reduce the odor value 83%, 33% lower DOC concentration, KMNO4 reduce consumption by 54%, reduce TTHM concentration of 41%. Operating experience also shows that ozone - BAC facilitate removal of ammonia and lower manganese content in the water.
Victoria 1997 Australia Edenhope built the first use of ozone water activated carbon technology in the country, water from wallace lake water. wallace long-term contamination of the lake's blue-green algae, eutrophication serious, lake DOC concentration is particularly high, with an average of about 20mg / L, the water treatment capacity of 8000m3 / d, after ozone treatment after a biological activated carbon depth, water reached Australian water quality specifications. Ozone - BAC joint process has been more widely used in the United States. Clemens, Michigan, Hill City Water, Hai Siming water, EH Ardre branch water, water and Highland Park, California Goleta water are used ozone - Biological Activated Carbon Process. For the United States Recommended activated carbon filter parameters: activated carbon particle size 0.5 ~ 1.0mm, uniformity coefficient of 1.5 to 2.5, a density of 1.35 ~ 1.37g / cm3, the filtration rate is 7.5 ~ 15m / h, the filter layer depth of 1.8 to 3.6m, backwashing strength of 30 ~ 39m3 / (m2 · h). US to use more water to flow under gravity activated carbon filter bed. Each water before using granular activated carbon filter has a mix, flocculation, sedimentation, sand filtration and other processes, GAC is generally used for adsorption.
The earliest ozone in urban water industry - BAC technology into production practice is Beijing Tamura landscape plant, commissioned in 1985. Then in Beijing Yanshan Petrochemical water, living water Jiujiang refinery, Nanjing Refinery, Daqing Petrochemical Plant, Kunming Water Company water south sixth branch, Zhoujiadu waterworks, Shenzhen Meilin Waterworks, Hangzhou Nanxingqiao Waterworks and Tongxiang water applications such as orchards bridge ozone - biological activated carbon treatment process. 2004 production of the Guangzhou South Island is the largest of the waterworks of ozone - biological activated carbon water, daily water supply capacity of 100 tons.
Beijing Tamura landscape plant is China's earlier use of ozone - biological activated carbon technology, modern water, treated water for 170,000 m3 / d, is Beijing's first access to surface water (Guanting) of waterworks. Raw water after conventional treatment, they were ozonation - BAC deep purification. Design ozone dosage is 2mg / L, contact time l0min, activated carbon filter carbon thickness 1.5m, the filtration rate of 10m / h. Water quality: color less than 5 degrees, the same as sniffing and odor, turbidity is less than 2NTU, NO2-N from 0.03 down to 0.01mg / L, CODMn from 4mg / L reduced to 3mg / L or so.
Kunming Dianchi Lake water company for water with low turbidity high algal characteristics, by the end of 1996 in the sixth branch of applied water south of ozone - biological activated carbon treatment process, the size of 100 000 m3 / d. Raw water through coagulation, flotation, filtration, ozone contact reaction, biological activated carbon filtration, ozone exposure 10min, biological activated carbon filter filtration rate of 8.27m / h. After running the operation, finished water turbidity of less than 0.5NTU, chroma less than 5 degrees; UV254 and CODMn removal were 42% and 50%.
2000 Shanghai Waterworks for Zhoujiadu engineered, built two parallel processing, one of the pre-ozone + conventional treatment using ozone + + activated carbon, another bio-ceramic filter using conventional treatment + + + ozone activated carbon. Waterworks July 20, 2001 began to run continuously, filling volume control in the pre-ozone 0.76 ~ 3mg / L, generally about 2mg / L, a flow rate of 250m3 / h, the contact time was 4min; ozone to contact through the pipeline microporous diffuser with micro-bubbles form pool full contact with water, the contact time is 10min, each pool by 6: 2: 2 ratio divided into three dosing, filling the amount of ozone in accordance with the quality of the case may be, the general control plus fluence of 1 ~ 2mg / L, more than ozone is 0.01 ~ 0.11mg / L. Pretreatment of water can reduce the color and UV absorbance of more than 30%, reduce ammonia, iron, manganese and nitrite about 20%, and can increase the dissolved oxygen of about 42.59%. Oxygen consumption and turbidity removal for less than 10%; color after ozone, UV absorbance removal rates of 2% to 40% and 8% to 24%; for ammonia removal rate of 7% to 57% ; removal rate of oxygen consumption of 13% to 16%. Zhoujiadu advanced treatment process to increase the variable cost of production than the conventional treatment of the original 0.24 yuan / m3, after the adoption of economic operation, the cost is reduced by about 20%
Water Corporation Hangzhou in Hangzhou Nanxingqiao water using ozone Activated Carbon Process transformation of the original water, the process in October 2004 put into operation, the scale of 100 000 m3 / d. Rehabilitation programs including pre-mixed before adding paragraph ozone contact tank, activated carbon filter and ozone contact tank behind the increase in the biological filter. Pre-ozone maximum dosage by lmg / L design, the total contact time was 5min, the effective contact time of 3min, the effective depth of 6m; ozone maximum dosage by 2mg / L design, the total contact time was 10min, and arranged in the order of 3 a contact chamber, the contact time was 2,4,6min, ozone sub 3:00 was added to three parallel exposure to indoor; activated carbon filter layer thickness of 2m, effective grain by 0.65 ~ 0.75mm, using amorphous carbon from coal crushing, require Iodine value greater than 1000mg / g, methylene blue value is greater than 200mg / g, design empty bed residence time of 11.55min, corresponding filtration rate of 10.4m / h, filter backwash water will adopt after the first air impact. Advanced treatment process for turbidity, color, ammonia, nitrite nitrogen, the average removal rate was 99.49% CODMn, 94.76%, 75.31%, 46.73% and 67.49%. Tongxiang City, Zhejiang Province, orchards bridge water depth of activated carbon treatment process using ozone technology into production in 2003, water scale is 80,000 m3 / d. Raw water through biological pretreatment. Biological contact oxidation pretreatment process is mainly to remove the ammonia, the average removal rate of more than 70%, the removal of part of the color, such as oxygen consumption, thereby reducing the load on the follow-up process: after a period of time to run, mature biofilms after ozone Activated Carbon Treatment Process for CODMn, UV254; and ammonia removal rates up to 40%, 63%, 79%, good water quality and to meet drinking water standards.
Guangzhou South Island water supply design size 1 million m3 / d, the use of ozone - BAC is by far the largest of ozone - biological activated carbon water. South Island main process parameters ozone water treatment system is as follows: ozone mass fraction of 7% to 10%, the pre-ozone dosage of 0.5 ~ 1.5mg / L, contact time is not less than 4min; primary ozone dosage is 1.0 ~ 2.5mg / L, contact time is not less than 10min, the main ozone contact tank effluent requirements for ozone concentrations over 0.2 ~ 0.4mg / L. Pre / primary ozone transfer efficiency in the water is not less than 95%. A pre-ozone contact tank, setting four completely separate pool of ozone exposure response line, each line set up an ozone dosing point, the pre-catalytic system uses ozone venturi jet aeration of ozone gas diffusion; primary ozone l contact tank holder, set the pool six fully independent ozone exposure reaction paylines set three ozone dosing point, according to the proportion of ozone dosage, respectively, accounted for 60%, 20%, 20%, the main reaction of ozone exposure system in the form of microporous aeration of . South Island water using granular activated carbon filter main technical indicators: methylene blue adsorption value of not less than 180mg / g, iodine adsorption value of not less than 950mg / g, phenol adsorption value of not less than 150mg / g, not more than 12% ash; Activated carbon particle Φ1.5 ± 0.2mm. Biological activated carbon unit monthly average removal CODMn and ammonia were 29% and 71%.
Ozone - BAC depth of the water treatment process after numerous proved, both from chemical stability and biological stability of the water purification process point of view, or from the perspective of economic running costs, can all be used as drinking water purification section comprehensive promotion of second-generation water purification technology. How to solve a number of limitations need to improve its water treatment workers, the majority of research in the future to further explore the use of.
1 Ozone - BAC depth treatment processes (O3-BAC)