UASB TECHNOLOGY FOR WASTE WATER TREATMENT
By
Dr Gautam Roy
Chief Executive Technical,
Envirad Projects Pvt.Ltd.,
6-Lakhanpur, Kanpur- 206024
Domestic/municipal wastewater and many industrial
effluents contain significant amounts of biodegradable
organic wastes. Organic pollutants are most economically
treated by biological methods, wherein microbes convert
them to inert biomass that can be precipitated out and
eliminated from the wastewater. Biological treatment is
essentially of two types- aerobic and anaerobic. In
comparison to aerobic biodegradation, anaerobic treatment,
where applicable, is often more advantageous.
One or the economic and effective anaerobic treatment
method is the UASB (Upflow Anerobic Sludge Blanket)
process. In a UASB Reactor wastewater is fed from the
bottom. As it flows upward through the reactor, organic
matter in the waste is degraded anaerobically by micro
organisms resident in the sludge blanket. Besides
converting organics to cell mass, biogas rich in methane is
produced as a by product. A Gas Liquid Solid
separator(GLSS) provided near the top of the reactor,
enables sludge to settle into the blanket, biogas to escape
into the dome at the top of the reactor, and treated
supernatant to flow out of the reactor. High sludge
concentration in sludge blanket and low concentration of
suspended solids in the reactor over flow are characteristic
features of a good UASBR.
The basic advantages of a UASBR over aerobic treatment
units are :
- UASBR in a compact unit, ideal for economic space utilization.
- UASB treatment process requires no external input of
energy. Even the required mixing is achieve by
upflowing waste water and rising gas bubbles.
- Nutrient requirement (i.e. N&P) is muc less than (about
half that needed ) for aerobic treatment.
- Residuals (i.e.sludge) generated by UASB treatmet are much less in amount and well digested, requiring
reduced sludge hanldling and causing much less odour
problems.
The UASBR comprises no mechanical or moving part
involving wear and tear. Thus it is virtually
maintenance free and involves few operational
problems. When properly designed and made, a
UASBR provides trouble-free service for many
years.
- Biogas, rich in methane, is generated as a valuable
by product. Methane produced is about 0.15 to 0.35
Nm3/kg COD destroyed.
- Owing to the compactness of UASBR , absence of
mechanical/moving components, energy
efficiency of the process, and reduced post-
treatment and sludge handling requirements,
both the capital cost and running cost of a
UASBR based treatment plant are
significantly less than for a fully aerobic teratment
plant.
- Once a UASBR has been put in operation,
acclimatised bacteria can survive without food in
the reactor for long durations. This enables easy
strartup of the UASBR after prolonged periods of
being out of operation.
- UASBR is a noiseless, closed and covered unit that is
aesthetically very satisfying.
UASBR APPLICATIONS:
UASB Technology has found applications worldwide,
in treating various types of wastewater. Among industries,
some popular applications are in the food processing and
producing industries, dairies and milk-processing units,
sugar mills, pulp and paper, breweries, distilleries, potato,
vegetable and fruit processing plants, soft drink plants,
tanneries and slaughterhouses. For complex industrial
wastes or adverse environmental conditions, however, a
pilot study or treatability assessment is desirable.
For municipal waste waters (Sewage) BOD removal of 60%
to 80% is normal under favourable conditions (influent
BOD >=140 mg/l. BOD/COD => 0.4, temperature 15-42 ºC,
etc.) Suspended solids may be also reduced in the
process, but some post-treatment (aerated lagoon or
stablization/polishing pond) is generally needed for BOD
removal to the desired degree.
Economics of UASBR Based Effluent Treatment Plants
| Type of Industry |
Waste Water at ETP Inlet |
Capital cost of ETP (in million rupees) |
Recurring Energy Saving in UASB-based ETP |
|---|
| Flow in cu. m. per day |
BOD Concentration (mg/l) |
BOD Load (kg/day) |
with UASBR |
with Mechanical Aeration |
Power |
Saving Rs. million/annum |
| Large Paper Mill with Recovery Boiler |
40,000 |
250 |
10,000 |
73 |
70 |
190 |
3.6 |
| 120,000 |
250 |
30,000 |
205 |
190 |
570 |
10.8 |
| Medium Agro based Paper Mill without Recovery Boiler |
2,000 | 1,800 | 3,600 | 11 | 12.6 |
130 | 2.5 |
| Domestic Sewage |
10,000 | 200 | 2,000 | 21 | 18 |
70 | 1.3 |
| 10,000 | 200 | 20,000 | 168 | 163 |
700 | 13.3 |
| Sugar Mill | 4,000 | 1,000 |
4,000 | 21.5 | 23.3 | 140 | 2.6 |
| Dairy | 1,000 | 1,200 | 1,200 |
6.5 | 7.8 | 30 | 0.5 |
| Slaughterhouse | 1,000 | 3,400 |
3,400 | 14.9 | 18.6 | 100 | 1.9 |