UASB anaerobic reactors

I. Summarize

Wastewater anaerobic biological technology because of its huge processing power and potential application prospect, has been water treatment technology research hot spot. From the traditional anaerobic contact technology development to now widely popular UASB process, wastewater anaerobic treatment technology has become increasingly mature.
 Anaerobic biological treatment as use of anaerobic sex of the metabolism of microbial characteristics, no need to provide foreign energy conditions to be restored by organic matter as hydrogen body, at the same time create energy value of the methane gas. Anaerobic biological treatment method not only apply to high concentration organic wastewater, feed the highest concentration of BOD tens of thousands of mg/l, also can be used in low concentration of organic wastewater, such as urban sewage and waste water.

 Anaerobic biological treatment process low energy consumption; Organic volume load high, average for 5-10 kgCOD/m3. D, the highest can be up to 30 to 50 kgCOD/m3. D.; Excess sludge quantity is little; Anaerobic bacteria nutritional needs of resistance, low toxic organic matter degradation of strong, can be high molecular weight; Impact resistance load ability; The output of the methane is a kind of clean energy.
    In all the social advocate recycling economy, paying attention to the implementation of industrial waste resources recycling today, anaerobic biological treatment is obviously can make wastewater reuse the optimization of process. In recent years, wastewater anaerobic treatment technology developing very rapidly, and all kinds of new technology, new method appear constantly, including anaerobic contact method, ShengLiuShi anaerobic sludge bed, archives plate anaerobic method, anaerobic bio-filter, anaerobic expansion bed and fluidized bed, and the third generation of anaerobic process EGSB and IC anaerobic reactors, developing very rapidly.
   And ShengLiuShi Anaerobic Sludge Bed UASB (Up-flow Anaerobic Sludge Bed, note: hereinafter referred to as UASB) process because of the Anaerobic filter and Anaerobic activated Sludge of double characteristics, as can the pollutant in sewage into renewable clean energy--kind of a technology. For different amount of sewage containing solid adaptability is strong, and its structure, operation maintenance management relatively simple, cost are relatively low, technology is mature, and are increasingly being sewage treatment industry attention, widely welcome and application.

This paper is to the UASB operation mechanism and technical characteristics and the design of the UASB start-up are described.

II.The origin of the UASB
  In 1971, the Netherlands Wagner's NingGen (Wageningen) agricultural university Latin case (Lettinga) professor through the physical structure design, use the gravitational field for different density material works in difference, invented the three-phase separator. Make active sludge retention time and waste water retention time separation, formed ShangLiuShi anaerobic sludge bed (UASB) of the prototype reactor. In 1974, the Netherlands in its CSM 6 m3 reactor beet sugar refinery wastewater treatment, found the active sludge formation mechanism of their own immobilized biological gather body structure, namely the granular sludge (granular sludge). The emergence of granular sludge, not only promote to as a representative of the second generation UASB anaerobic reactors applications and development, but also for the third generation of the birth of anaerobic reactors to lay the foundation.

III.UASB Working principle

  UASB include: sludge reaction district, gas to liquid solid three-phase separator (including precipitation area) the gas chamber of three parts. In the bottom of the reaction to retain a large number of anaerobic sludge, has good performance and coagulation precipitate performance of the sludge layer sludge in formation. To deal with sewage from anaerobic sludge bed bottom sludge layer into and sludge in the mixed contact, the microbial decompose sewage sludge of organic matter, put it into the methane gas. Methane bubbles form with a small constantly released, tiny bubbles rise in process, and constantly merger, and gradually form a larger bubble, in the sludge bed because of the biogas stir to form a sludge concentration is the thin sludge and water up into the three-phase separator together, the reflection of the biogas met separator plates, bends to the reflection board around, and across the water into the gas chamber, concentrated in the gas chamber methane, with a catheter and export of solid-liquid mixture into the three-phase separator passes reflection of the precipitation area, the sewage sludge happen flocculation, particle increase gradually, and by gravity settlement. Precipitation to the wall and the inclined slough inclined wall slid back into anaerobic reaction zone, the accumulation of the reaction of the sludge, and sludge separation of water after treatment from precipitation area of the overflow weir upper overflow, and then discharge sludge bed.

The basic requirements:

(1) for sludge flocculation provide favorable physical, chemical, and mechanical condition, anaerobic sludge to obtain and maintain good precipitation performance;

(2) good sludge bed often can form a fairly stable biological phase, maintain certain micro ecology environment, can resist strong anti-disturbance force, a larger body has good precipitation flocculant performance, so as to improve the equipment within the sludge concentration;

(3) through the in sludge bed equipment installed in a precipitation area, make fine particles in the sludge precipitation in sludge layer further flocculation and precipitation, and then back into the sludge in bed.
        IV.Flow condition and sludge distribution in UASB

The flow pattern in the UASB is very complex, the response of the flow pattern and gas production and reaction district highly relevant, generally speaking, the lower sludge layer reaction zone within the gas production because of the results, in part, by the gas of the cross section is more, forming the rising air, drive part mixture (refers to the sludge and the water) for upward movement. At the same time, the gas, water flow around the medium is downward motion, cause reverse mix, the flow patterns of short cause water flow. Away from the rise in gas, water areas tend to form blind Angle. In the corner place also has some of the gas production, form sludge and water slow and weak mix, so in sludge layer formed in different degree of mixed zone, the mixed zone size and short flows related degree. Suspended layer in the mixture, the movement of money because gas fluid drive at a higher rate up and down to form strong mix. In the gas production under the circumstances of less, sometimes sludge layer and suspended layer have distinct boundary, and in gas production more cases, the interface is not obvious. The test shows that the water in the precipitation is pushing streaming, but precipitation area still have a dead zone and the mixed zone.  
   UASB sludge concentration and equipment in the organic load rate of relevant. Is processing sugar wastewater test, distribution and the load of sludge UASB within the relationship. Can be seen from the graph sludge layer sludge concentration than suspended layer sludge concentration is high, suspended layer of sludge concentration smaller upper part and the poor that close to completely mixed flow pattern, the response of the sludge awarded, when organic load high sludge layer and suspended layer boundary is not obvious. Test showed that the sewage through the bottom 0.4 0.6 m height, has 90% of the organic matter be converted. This shows anaerobic sludge has a very high activity, change have long argued that anaerobic treatment process of slow concept. In anaerobic sludge, the accumulation has a large high anaerobic sludge is the equipment has great ability to deal with the main reason, and that, in turn, to have good performance of the sludge precipitation.  
    High volume UASB organic load rate, the main reason is that in the equipment, especially by sludge layer has a large amount of anaerobic sludge. Process stability and efficiency depends to a great extent on generation has good performance and high methane settlement activity of sludge, especially granular sludge. And in contrast, if the reaction of the sludge to loose flocculating form body existence, often appear floating sludge loss, not in higher load UASB next and stable operation.

According to the shape of the sludge formed within the UASB and achieve COD volume load, can will sludge process-roughly divided into three operation period:  
(1) vaccination start-up: from the inoculation to start in the sludge bed load up to five kgCOD COD volume/m3. D or so, the running period of sludge sedimentation performance generally;

(2) granular sludge formation: this operation period features a small granular sludge began to appear, when sludge bed the total amount within the total amount VSS SS and fall to lowest this operation period end namely, the running period of sludge sedimentation performance not too good;

(3) granular sludge mature period: the operation period is characteristic of granular sludge formed a large, bottom-up gradually filled the entire UASB. When sludge bed load capacity to 16 kgCOD/m3. D above, can think of granular sludge already cultivating mature. The operation period of sludge sedimentation is very good.  
         V.Peripherals settling pond to prevent loss of sludge
  Though within the liquid-solid UASB of three-phase separator, the mixture into the precipitation area has the gas before separation, but because the sludge precipitation area still had high methanogenesis activity, continue in the precipitation gas production; Or because impact load and the water quality suddenly change, may make the sludge bulking reaction, and the results precipitation area solid-liquid separation not beautiful, sludge and influence the loss occurred in water and sludge bed sludge concentration. In order to reduce the water with the water into the suspended, external another have a set of sediment basins, the sludge precipitation down backflow to the sludge bed inside.

The benefits of the external traps set:

(1) return sludge can accelerate the accumulation of sludge, reducing starting cycle;

(2) removing suspended solids, improve water quality of water;

(3) when occasionally happen a lot bleaching mud, improve the visibility, can prompt recycling sludge keep process stability;

(4) return sludge can be further decomposed, can reduce surplus sludge quantity.  
VI.Design of UASB

    The process design is mainly UASB calculated the volume of gas production, UASB and surplus sludge quantity, the nutritional requirements of balance.
  The pool of circular shape UASB, square, rectangle.Sludge bed height is commonly 3 to 8 m, multi-purpose reinforced concrete building. When the sewage in organic content is higher, the precipitation area and reaction to the small volume ratio, the reaction can be used and precipitation area of the same size and shape pool. When the sewage in organic content is low, the need large area precipitation, in order to guarantee the reaction a certain height, the reaction of can not be too big, it can use the reaction area is less than precipitation areas, namely sludge bed upper part is greater than the bottom of the pool area form.
Gas liquid-solid three-phase separator is an important part of the UASB, it to the normal operation of the sludge bed and the good water up very important role, so when the design shall be given special attention. According to experience, should meet the following three-phase separator requirements:

1, mixed liquid into the precipitation district of close, will be one of the bubble must be emergence, prevent bubbles into precipitation area influence precipitation;

2, the precipitation inclined wall Angle can be greater than about 45 degree Angle;

 3, and the surface precipitation hydraulic load should be in 0.7 m3 / m2. H the following, into the precipitation area before, through the sedimentation tank low velocity is not more than the seam of 2 m/m2. H;

4, in a set of the liquid gas in the interface of the spirit of the sludge to properly make submerged in water;

5, should prevent set the produce the large amount of foam in gas.

2, 3 two conditions can be by choosing the proper the precipitation depth of the board to meet-area.

For low concentration sewage, mainly using limit surface to control the hydraulic loading; For moderate levels and high concentration of sewage, in extremely high load, the unit of release of the cross section, the volume of a gas can be a critical index. But until now achievements of both at home and abroad show that as long as the load rate of not more than 20 kgCOD/m3. D, do not see more than UASB height 10 m reports, third generation except anaerobic reactors.

The sludge and the separation of liquid based on sludge flocculation and sedimentation and filtration role. So in the operation process, should as far as possible to create sludge can form the flocculation settlement hydraulic conditions, make the sludge has good flocculation and precipitation performance, not only for the work of the separator is very important, for the whole of organic material removal rate is even more crucial.
Special attention should be paid to avoid bubble into precipitation area, want to make solid, liquid into the precipitation area with bubbles before they good separation. In the air-liquid surface formation scum can force some bubble into precipitation area, in the design so must consider:   

(1) the adoption of appropriate technical measures, as far as possible to avoid the formation condition of scum, preventing the formation of sludge layer;

(2) must have derided the scum on facilities or device, in sludge reaction district once appear under the condition of scum, can prompt damage the formation of sludge layer, or can promptly eliminate scum.

As mentioned above, the sewage and sludge in UASB mixed by rising water flow and is in the fermentation process of produce bubbles to finish. Therefore, generally USES more water, make water evenly distributed in bed on the cross, the key is to uniform-even a quantity.

According to the calculation of UASB volume general organic matter volume load or hydraulic retention time. When the design can be through the test parameters or similar wastewater decision reference design and operation parameters. 
                             VII.Start of UASB
1, Sludge domestication

UASB start-up equipment is difficult to acquire a large settlement of the good performance of anaerobic granular sludge. The best way to tame, general need three to six months, if, by the device itself accumulate, put into production, the longest period can be as long as 1-2 years. Practice shows that the additive a small amount of the carrier, the attachment to anaerobic bacteria, promote the formation of the initial granular sludge; The sludge floe significant than than light-easily; Methane high activity than the anaerobic sludge can shorten the start-up.

2, starting operation points

(1) the best a dosing plenty of inoculation;

(2) the initial from sludge bed comes out of the sludge can not return, in order to make special light and finely sludge suspended from with continuous sludge bed eduction body outside, the relatively heavy activated sludge in accumulated in bed, and promote their proliferation gradually achieve the toro rosso;

(3) launch at low concentration COD waste water, not necessarily can let the sludge-speed;

(4) first sludge load rate generally in 0.1 0.2 kgCOD/kgTSS. D or so more appropriate;

(5) in the original sewage there and anaerobic decomposition out of the DuoZhong volatile acid has failed to effectively before decomposition, should not be optional improve organic volume load, the need to track observation and water samples tests;

(6) the biodegradable COD removal would reach 70-80%, can gradually increase the load rate of organic volume;

(7) in order to promote toro rosso sludge, the minimum air tower of the reaction speed cannot lower than 1 m/d, use a higher surface hydraulic loading helpful for little granular sludge and sludge flocculation separate, make small granular sludge and for large particle.  
          VIII.UASB Process advantages and disadvantages 
The main advantage of UASB is:

1 and in high concentration UASB sludge, the average sludge concentration of 20 to 40 gVSS / 1;

2, organic high load, hydraulic retention time is short, the fermentation temperature, volume for 10 kgCOD load general/m3. D or so;

3, no mixed mixing equipment, rely on in the fermentation process of biogas generated from the rising motion, make the sludge bed sludge in the upper part of the state of suspension, the lower part of the sludge layer also have some degree of stirring;

4, sludge bed not to fill the carrier, save cost and avoid the problems occur because of packing wall;

5, with UASB three-phase separator, usually do not set traps, separated by precipitation area of sludge back to the sludge bed reaction zone, can usually do not set return sludge equipment.  
The major disadvantage is:

1, suspended in water to appropriately control, is unfavorable and exorbitant, general control in 100 mg/l the following;

2, sludge bed has short flow phenomenon, influence processing ability;

3, a sudden change of water quality and load more sensitive, impact resistance is a bit poor.  
IX.UASB process range

Mainly application:

1. The slightly polluted raw water biological pretreatment. Remove the raw water in ammonia nitrogen, oxygen consumption material, improve the drinking water biological stability;

2. Water treatment. Further removes sewage treatment plant level 2 water of ammonia nitrogen and SS to urban sewage reuse landscape environment water water quality standards;

3. The sewage treatment. Formation DuoZhong combination process, realize the organic matter degradation, remove SS and COD, PO4-P role.

Apply to starch wastewater, alcohol wastewater and other light industry food of high concentration organic wastewater treatment.

X.UASB reactor notes to order

1. The unit in order before should provide detailed order water quality material.

2. Our factory can be based on user provide water quality, water and the floor plan, design the system engineering layout and with water fixtures size figure.

3. Our factory can be based on user needs to make special model of water quality and special equipment.

This instruction is only for your reference.

For improvement of equipment, the product is different from the instruction, without further notice, please forgive me!