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Thursday, December 03, 2015

Design of UASBR Upflow Anaerobic Sludge Blanket Reactor

 These are the 4 top applications of the UASB reactors:
  • Breweries and beverage industry
  • Distilleries and fermentation industry
  • Food Industry, Slaughter Houses.
  • Pulp and paper
Together, these four industrial sectors account for 87% of the applications. However, the applications of the technology are rapidly expanding, including:
1.      treatment of chemical and petrochemical industry effluents
2.      textile industry wastewater
3.      landfill leachates
4.      Conversions in the sulfur cycle and removal of metals.


YOU NEED AN EXPERT WITH SPECIFIC INDUSTRY WISE EXPERIENCE TO DESIGN A PROPER UASBR SYSTEM. 

The UASB reactor can be designed as circular or rectangular. Modular design can be preferred when the volume of reactor exceeds about 400 m3. It is necessary to select proper range of operating parameters for design, such as, OLR, SLR, superficial liquid upflow velocity (referred as liquid upflow velocity), and HRT. The literature recommendations for all these parameters and design procedure to account these recommendations are given below.

What is Upflow Anaerobic Sludge Blanket?
Upflow anaerobic sludge blanket, or UASB, is a form of anaerobic (oxygen-free) digester used in wastewater treatment. It is a methane-producing digester which uses an anaerobic process and forming a blanket of granular sludge and is processed by anaerobic microorganism.
UASB was developed in 1970s by Letinga in the Netherlands. It is essentially a suspended growth system in which proper hydraulic retention time (HRT) and organic loading rate (OLR) is maintained in order to facilitate the dense biomass aggregation known as granulation.
How to Design UASB Pond
About a week ago, I asked the appointed vendor who will design and supply wastewater treatment unit about design calculation of UASB pond. The design of UASB pond is a function of:
  • COD input of wastewater
  • Flow of wastewater
  • Organic loading rate
  • Hydraulic retention time
Organic loading rate is a measure of the biological conversion capacity of the anaerobic digestionsystem. It is expressed in kg Chemical Oxygen Demand (COD) or Volatile Solids (VS) per cubic meter of reactor. A relatively high organic loading rate facilitated the formation of anaeronic granules in UASB systems.
In general, there are two ways to design an UASB reactor.
  1. If input COD is 5000 – 15000 mg/L or more, the design method should be used based on Organic Loading Rate
  2. If input COD less than 5000 mg/L, the design method should be based on velocity
Let’s take an example.
Data
Waste water input flow rate (Q) = 62.5 m3/day
COD = 15,000 mg/L = 15 kg/m3
Organic loading rate = 5.5 kg COD/m3.day (I found that organic loading rate is sometimes state of art in wastewater treatment design. Some vendors may have already had the data)
Volume of tank = Q x C /OLR = 62.5 x 15 / 5.5 = 170 m3
Note: the above volume is the actual volume. You need to add more volume (as void volume).
Calculating an UASB Tank Based on Velocity

When input COD < 5,000 mg/l, using the method base on ORL is not effective in operation process because the granular sludge will be hardly formed. Therefore, the design criteria must be:
Up-flow velocity V Ј 0,5 m/h. Hydraulic retention time HRT і 4 h Chosen in table 1, the height of sludge is Hs = 3 – 5 m The height of setting area HSe і 1.2 m The volume of the UASB reactor: W = Q x HRTThe area of the UASB reactor: A = V / Q


GSL Separator Design

Slope of the separator bottom from 45 – 60oFree surface in the aperture between the gas collectors: 15 – 20% of reactor area.Height of separator from 1.5 – 2 m
The baffles to be installed beneath the gas domes should overlap the edge of the domes over a distance from 10 – 20 cm
Construct material: In the anaerobic conditions of an UASB reactor, there is a risk of corrosion in two main situations:
Some H2S gas can pass the GSL separator and accumulate above the water level in the top of the reactor. This will be oxidized to sulphate by oxygen in the air to form Sulphuric Acid that will in turn cause corrosion of both concrete and steel. Below the water level: Calcium Oxide, (CaO), in concrete can be dissolve with by Carbon Dioxide, (CO2), in the liquid in low pH conditions. To avoid these problems, the material used to construct the UASB reactor should be corrosion resistant, such as stainless steel or plastics, or be provided with proper surface coatings, (e.g. coated concrete rather than coated steel, plastic covered with impregnated hardwood for the settler, plastic fortified plywood, etc).

YOU NEED ONE TECHNICAL PERSON WITH EXPERIENCE TO RUN A PROPER UASBR SYSTEM.

Operation & Maintenance (O&M)

Operation criteria: The optimum pH range is from 6.6 to 7.6 The wastewater temperatures should not be < 5 °C because low temperatures can impede the hydrolysis rate of phase 1 and the activity of methanogenic bacteria. Therefore in winter season, methane gas may be needed to heat the wastewater to be treated in the reactor.
Always maintain the ratio of COD : N : P = 350 : 5 : 1 If there is a deficiency of some of these nutrients in the wastewater nutrient addition must be made to sustain the micro-organisms. Chemicals that are frequently used to add nutrients (N, P) are NH4H2PO4, KH2PO4, (NH4)2CO3…
Suspended solid (SS) can affect the anaerobic process in many ways:
Formation of scum layers and foaming due to the presence of insoluble components with floating properties, like fats and lipids. Retarding or even completely obstructing the formation of sludge granules. Entrapment of granular sludge in a layer of adsorbed insoluble matter and sometimes also falling apart (disintegration) of granular sludge. A sudden and almost complete wash-out of the sludge present in reactor Decline of the overall methanogenic activity of the sludge due to accumulation of SS Therefore, the SS concentration in the feed to the reactor should not exceed 500 mg/l In phase 2 and 3 the pH will be reduced and the buffer capacity of wastewater may have to be increased to provide alkalinity of 1000 – 5000 mg/l CaCO3

Start-up:

 An UASB reactor requires a long time for start-up, e.g. from 2 – 3 weeks in good conditions (t > 20oC) and sometimes the start-up can take up to 3 – 4 months. In start-up process, hydraulic loading must be Ј 50% of the design hydraulic loading.
The start-up of the UASB reactor can be considered to be complete once a satisfactory performance of the system has been reached at its design load.
Source: http://nptel.ac.in/courses/105104102/Lecture%2032.htm

UASB Units
UASB type units are one in which no special media have to be used since the sludge granules themselves act as the 'media' and stay in suspension. UASB system is not patented. A typical arrangement of a UASB type treatment plant for municipal sewage would be as follows:
  1. Initial pumping
  2. Screening and degritting
  3. Main UASB reactor
  4. Gas collection and conversion or conveyance
  5. Sludge drying bed
  6. Post treatment facility
In the UASB process, the whole waste is passed through the anaerobic reactor in an upflow mode, with a hydraulic retention time (HRT) of only about 8-10 hours at average flow. No prior sedimentation is required. The anaerobic unit does not need to be filled with stones or any other media; the upflowing sewage itself forms millions of small "granules" or particles of sludge which are held in suspension and provide a large surface area on which organic matter can attach and undergo biodegradation. A high solid retention time (SRT) of 30-50 or more days occurs within the unit. No mixers or aerators are required. The gas produced can be collected and used if desired. Anaerobic systems function satisfactorily when temperatures inside the reactor are above 18-20°C. Excess sludge is removed from time to time through a separate pipe and sent to a simple sand bed for drying.
Design Approach
Size of Reactor: Generally, UASBs are considered where temperature in the reactors will be above 20°C. At equilibrium condition, sludge withdrawn has to be equal to sludge produced daily. The sludge produced daily depends on the characteristics of the raw wastewater since it is the sum total of (i) the new VSS produced as a result of BOD removal, the yield coefficient being assumed as 0.1 g VSS/ g BOD removed, (ii) the non-degradable residue of the VSS coming in the inflow assuming 40% of the VSS are degraded and residue is 60%, and (iii) Ash received in the inflow, namely TSS-VSS mg/l. Thus, at steady state conditions,
SRT= Total sludge present in reactor, kg          Sludge withdrawn per day, kg/d
     = 30 to 50 days.
Another parameter is HRT which is given by:
HRT= Reactor volume, m3 
         Flow rate, m3/h
     = 8 to 10 h or more at average flow.
The reactor volume has to be so chosen that the desired SRT value is achieved. This is done by solving for HRT from SRT equation assuming (i) depth of reactor (ii) the effective depth of the sludge blanket, and (iii) the average concentration of sludge in the blanket (70 kg/m3). The full depth of the reactor for treating low BOD municipal sewage is often 4.5 to 5.0 m of which the sludge blanket itself may be 2.0 to 2.5 m depth. For high BOD wastes, the depth of both the sludge blanket and the reactor may have to be increased so that the organic loading on solids may be kept within the prescribed range.
Once the size of the reactor is fixed, the upflow velocity can be determined from
Upflow velocity m/h = Reactor height
                                     HRT, h
Using average flow rate one gets the average HRT while the peak flow rate gives the minimum HRT at which minimum exposure to treatment occurs. In order to retain any flocculent sludge in reactor at all times, experience has shown that the upflow velocity should not be more than 0.5 m/h at average flow and not more than 1.2 m/h at peak flow. At higher velocities, carry over of solids might occur and effluent quality may be deteriorated. The feed inlet system is next designed so that the required length and width of the UASB reactor are determined.
The settling compartment is formed by the sloping hoods for gas collection. The depth of the compartment is 2.0 to 2.5 m and the surface overflow rate kept at 20 to 28 m3/m2-day (1 to 1.2 m/h) at peak flow. The flow velocity through the aperture connecting the reaction zone with the settling compartment is limited to not more than 5 m/h at peak flow. Due attention has to be paid to the geometry of the unit and to its hydraulics to ensure proper working of the "Gas-Liquid-Solid-Separator (GLSS)" the gas collection hood, the incoming flow distribution to get spatial uniformity and the outflowing effluent.

Physical Parameters

A single module can handle 10 to 15 MLD of sewage. For large flows a number of modules could be provided. Some physical details of a typical UASB reactor module are given below:

Reactor configurationRectangular or circular. Rectangular shape is preferred
Depth4.5 to 5.0 m for sewage.
Width or diameterTo limit lengths of inlet laterals to around 10-12 m for facilitating uniform flow distribution and sludge withdrawal.
LengthAs necessary.
Inlet feedgravity feed from top (preferred for municipal sewage) or pumped feed from bottom through manifold and laterals (preferred in case of soluble industrial wastewaters).
Sludge blanket depth2 to 2.5 m for sewage. More depth is needed for stronger wastes.
Deflector/GLSSThis is a deflector beam which together with the gas hood (slope 60) forms a "gas-liquid-solid-separator" (GLSS) letting the gas go to the gas collection channel at top, while the liquid rises into the settler compartment and the sludge solids fall back into the sludge compartment. The flow velocity through the aperture connecting the reaction zone with the settling compartmentt is generally limited to about 5m/h at peak flow.
Settler compartment2.0-2.5 m in depth. Surface overflow rate equals 20-28 m3/m2/d at peak flow.

Process Design Parameters

A few process design parameters for UASBs are listed below for municipal sewages with BOD about 200-300 mg/l and temperatures above 20°C.

HRT8-10 hours at average flow (minimum 4 hours at peak flow)
SRT30-50 days or more
Sludge blanket concentration (average)15-30 kg VSS per m3. About 70 kg TSS per m3.
Organic loading on sludge blanket0.3-1.0 kg COD/kg VSS day (even upto 10 kg COD/ kg VSS day for agro-industrial wastes).
Volumetric organic loading1-3 kg COD/m3 day for domestic sewage (10-15 kg COD/m3 day for agro-industrial wastes)
BOD/COD removal efficiencySewage 75-85% for BOD. 74-78% for COD.
Inlet pointsMinimum 1 point per 3.7-4.0 m2 floor area.
Flow regimeEither constant rate for pumped inflows or typically fluctuating flows for gravity systems.
Upflow velocityAbout 0.5 m/h at average flow, or 1.2 m/h at peak flow, whichever is low.
Sludge production0.15-0.25 kg TS per m3 sewage treated.
Sludge drying timeSeven days (in India)
Gas productionTheoretical 0.38 m3/kg COD removed. Actual 0.1-0.3 m3per kg COD removed.
Gas utilizationMethod of use is optional. 1 m3 biogas with 75% methane content is equivalent to 1.4 kWh electricity.
Nutrients nitrogen and phosphorus removal5 to 10% only.

HOW TO DESIGN BIO GAS HOLDER
GAS PRODUCTION & POWER GENERATION:

The gas flowing upward with the liquid will be prevented from escaping with the treated flow by GLSS and beam deflector, which will divert it to the gas collector domes. The gas produced shall be passed through 100 mm dia FRP pipe for individual domes and collected at a common point for each reactor by a common header of 200 mm dia pipe from where it will conveyed to the gas holder for constant flow to the gasomete generator or flaring in open atmosphere at about 6 meter above ground level.

Quantity of Gas Production:

PARAMETER
INLET OF UASB
OUTLET OF UASB
REMOVAL IN UASB
BOD
1700 ppm
340 ppm
80%
COD
3300 ppm
1320 ppm
60%
TSS
1800 ppm
450 ppm
75%

FLOW IN UASB = 1500 KLD (Taking full future capacity into account)

Influent COD@ 3300 ppm = 4950 Kg
Effluent COD = 1980 Kg
COD removed in a day = 2970 kg
Bio gas produced @ 0.1 cu mtr per kg of COD removed = 297 cu mtr per day.

Capacity of gas holder:
The primary purpose of a gas holder is to adjust the difference in the rate of gas production and consumption. As bio gas enters or leaves, the holder rises or falls  by guide rails.
Provide a gas holder of 300 cu mtr capacity.

POWER GENERATION:
The bio gas produced in UASB process should be utilized for production of electric power. The amount of electric power generated shall be as under:
Bio Gas production = 297 cu mtr /day
Methane content (65.75%) = 195.28 cu mtr
Calorific value =28.9 MJ/N.cu mtr
Energy content 195.28x28.9x273/(273+30)=5048 MJ/Day
Generator efficiency--- 30%
Electricity generated =0.3x5048x1000000/3600x1000
                                      = 420.66
Electric power generated = 420.66x0.04167=17.5289 kw  say17 kw 
                                     = 1.25x 17= 21.25 kva.
We can go for a gas engine of capacity 10 KW . If any gas is left , it will be flared or supplied to staff quarters.
NOTE: A 56 mld UASB plant having  Inlet COD =400 ppm can safely run a 45 KW gas engine.

                              INDIAN STANDARDS


ENVO PROJECT"S FIRST UASBR PROJECT WAS IN 2005. SOME OF OUR PROJECT PHOTOS



VIDEO OF THE PLANT

Our Project photo and Video in our facebook page https://www.facebook.com/envoprojects


                                                         Some Of the UASB Projects


NAME OF COMPANY
SCOPE OF WORK
Year
HMA FROZEN FOOD EXPORTS,AGRA
SLAUGHTER HOUSE ETP  WITH UASB,450KLD
2007
AL HAMD FROZEN FOODS, ALIGARH
ETP PROJECT, 200 KLD UASB
2004
Bhola baba Dairy Ind Limited,Aligarh
1 MLD ETP with UASB         
2007
SARASWATI SUGAR MILLS,HARYANA
Suger mill ETP Project,UASB,500KLD
1998
Namaste India Dairy, Kanpur, UP
1MLD DAIRY ETP Project with UASB
2010
Malhotra Gelatine and Bones,Unnao
Rendering plant ETP Project with UASB,1MLD
2010
AOV Exports, Unnao,UP
Slaughter House ETP Project with UASB,750KLD
2010
Mash Agro Pvt Ltd, Unnao
Slaughter house ETP with UASB, 1 MLD
2013
Rustam Foods, Unnao, UP
Slaughter house ETP with UASB, 1 MLD
2013
Al Laham Food Exports,Khurja,UP.
Slaughter House ETP with UASB,750 KLD
2014
Al  Huda Frozen Foods, Khurja
Slaughter House ETP with UASB,750 KLD
2014
Al Halal Foods (Link Lock Company),Aligarh
Slaughter House ETP with UASB,1 MLD
2015
Al Ammar Exports, Aligarh
Slaughter House ETP with UASB,600 KLD
2015
Agrotec Foods Ltd, Kanpur
Food processing waste, 200 KLD,UASB
2015
Bholebaba  Dairy,Kanpur
500KLD DAIRY ETP Project with UASB
2016


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