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I HAVE SHARED ALL MY PRACTICAL WATER TREATMENT EXPERIENCES WITH SOLVED EXAMPLE HERE SO THAT ANYBODY CAN USE IT.
SEARCH THIS BLOG BELOW FOR ENVO ,COMPACT STP,ETP,STP,FMR,MBBR,SAFF,IRON,ARSENIC,FLUORIDE,FILTER,RO,UASB,BIO GAS,AERATION TANK,SETTLING TANK,DOSING,AMC.
Biomethanation is a process by which organic material is microbiologically converted under anaerobic conditions to biogas. Three main physiological groups of microorganisms are involved: fermenting bacteria, organic acid oxidizing bacteria, and methanogenic archaea. Microorganisms degrade organic matter via cascades of biochemical conversions to methane and carbon dioxide. Syntrophic relationships between hydrogen producers (acetogens) and hydrogen scavengers (homoacetogens, hydrogenotrophic methanogens, etc.) are critical to the process. Determination of practical and theoretical methane potential is very important for design for optimal process design, configuration, and effective evaluation of economic feasibility. A wide variety of process applications for biomethanation of wastewaters, slurries, and solid waste have been developed. They utilize different reactor types (fully mixed, plug-flow, biofilm, UASB, etc.) and process conditions (retention times, loading rates, temperatures, etc.) in order to maximize the energy output from the waste and also to decrease retention time and enhance process stability. Biomethanation has strong potential for the production of energy from organic residues and wastes. It will help to reduce the use of fossil fuels and thus reduce CO(2) emission.
Anaerobic digestion can be performed as a batch process or a continuous process. In a batch system biomass is added to the reactor at the start of the process. The reactor is then sealed for the duration of the process. In its simplest form batch processing needs inoculation with already processed material to start the anaerobic digestion. In a typical scenario, biogas production will be formed with a normal distribution pattern over time. Operators can use this fact to determine when they believe the process of digestion of the organic matter has completed. There can be severe odour issues if a batch reactor is opened and emptied before the process is well completed. A more advanced type of batch approach has limited the odour issues by integrating anaerobic digestion with in-vessel composting. In this approach inoculation takes place through the use of recirculated degasified percolate. After anaerobic digestion has completed, the biomass is kept in the reactor which is then used for in-vessel composting before it is opened [28] As the batch digestion is simple and requires less equipment and lower levels of design work, it is typically a cheaper form of digestion.[29] Using more than one batch reactor at a plant can ensure constant production of biogas.
In continuous digestion processes, organic matter is constantly added (continuous complete mixed) or added in stages to the reactor (continuous plug flow; first in – first out). Here, the end products are constantly or periodically removed, resulting in constant production of biogas. A single or multiple digesters in sequence may be used. Examples of this form of anaerobic digestion include continuous stirred-tank reactors, upflow anaerobic sludge blankets, expanded granular sludge beds and internal circulation reactors.[30][31]
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
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.
If input COD is 5000 – 15000 mg/L or more, the design method should be used based on Organic Loading Rate
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
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.
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:
Initial pumping
Screening and degritting
Main UASB reactor
Gas collection and conversion or conveyance
Sludge drying bed
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 configuration
Rectangular or circular. Rectangular shape is preferred
Depth
4.5 to 5.0 m for sewage.
Width or diameter
To limit lengths of inlet laterals to around 10-12 m for facilitating uniform flow distribution and sludge withdrawal.
Length
As necessary.
Inlet feed
gravity 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 depth
2 to 2.5 m for sewage. More depth is needed for stronger wastes.
Deflector/GLSS
This 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 compartment
2.0-2.5 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.
HRT
8-10 hours at average flow (minimum 4 hours at peak flow)
SRT
30-50 days or more
Sludge blanket concentration (average)
15-30 kg VSS per m3. About 70 kg TSS per m3.
Organic loading on sludge blanket
0.3-1.0 kg COD/kg VSS day (even upto 10 kg COD/ kg VSS day for agro-industrial wastes).
Volumetric organic loading
1-3 kg COD/m3 day for domestic sewage (10-15 kg COD/m3 day for agro-industrial wastes)
BOD/COD removal efficiency
Sewage 75-85% for BOD. 74-78% for COD.
Inlet points
Minimum 1 point per 3.7-4.0 m2 floor area.
Flow regime
Either constant rate for pumped inflows or typically fluctuating flows for gravity systems.
Upflow velocity
About 0.5 m/h at average flow, or 1.2 m/h at peak flow, whichever is low.
Sludge production
0.15-0.25 kg TS per m3 sewage treated.
Sludge drying time
Seven days (in India)
Gas production
Theoretical 0.38 m3/kg COD removed. Actual 0.1-0.3 m3per kg COD removed.
Gas utilization
Method of use is optional. 1 m3 biogas with 75% methane content is equivalent to 1.4 kWh electricity.
Nutrients nitrogen and phosphorus removal
5 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
Environmental Entrepreneur,Green Biz.NRN Murthy of Infosys says that we Indians are weak in execution.We need to realize the need and practice of gud project management. Form a group of competent Managers,Give them responsibilities and review the project from day One.
