Objective
To treat wastes from the mill before river or land application
Introduction
Palm Oil processing gives rise to highly polluting waste-water, known as
Palm Oil Mill Effluent (POME), which is often discarded in disposal ponds,
resulting in the leaching of contaminants that pollute the groundwater and
soil, and in the release of methane gas into the atmosphere. POME is an oily
wastewater generated by palm oil processing mills and consists of various
suspended components. This liquid waste combined with the wastes from
steriliser condensate and cooling water is called palm oil mill effluent
(POME). Based on the average data from the internet, for each ton of FFB (fresh
fruit bunches) processed, a standard palm oil mill generate about 1 tonne of
liquid waste with biochemical oxygen demand (BOD) 27 kg, chemical oxygen demand
(COD) 62 kg, suspended solids (SS) 35 kg and oil and grease 6 kg.
POME is a non-toxic waste, as no chemical is added during the oil
extraction process, but will pose environmental issues due to large oxygen
depleting capability in aquatic system due to organic and nutrient contents.
The high organic matter is due to the presence of different sugars such as arabinose,
xylose, glucose, galactose and manose. The suspended solids in the POME are
mainly oil-bearing cellulosic materials from the fruits. Since the POME is
non-toxic as no chemical is added in the oil extraction process, it is a good
source of nutrients for microorganisms.
Effluent waste come from:
Steriliser (condensate), hydrocyclone (water in the system), oil room
(sludge and dilution water).
Observation
Figure: Effluent treatment flow
In this mill, the treatment system using for effluent is ponding system.
It consist of holding pond, acidification pond, cooling pond, anaerobic pond
and irrigation pond. The sludge or the solid sediment are dried in the Geobag
to be used as fertiliser. The content from the irrigation ponds are not
released to the river but to trenches in the estate for land application. There
are no any chemical usage in the ponding system here.
The sludge from the deoiling tank will flows to the Holding pond. It
will goes through holding pond 1 and then 2. The third one is not using. After
that, the flow will go through 3 acidification pond. In the acidification
ponds, the content are thick and a layer of solid is covering the top. This
part has the strongest sourly smell. After that the content from acidification
ponds will goes through 4 cooling pond for further treatment. In cooling pond,
the content still looked much like the acidification pond. Then it will flow to
the anaerobic ponds, there are 4 anaerobic ponds. The third one looks cleanest
because the desludging is just carried out last year. There are few stirring
machine to give movement to the liquid and prevent the liquid to clogged up.
But only one machine is working and the others are tripped. From the 2nd
anaerobic pond, the bottom content will be pumped to the Geobag. This is to
clear up the accumulated sludge in the ponds. Some of it will be pumped into a
tank to be used as fertiliser in Paya Lang estate. The content in the Geobag
will be allowed to dry for 2 to 3 month. The dried content will then be used as
fertiliser for the estate. Lastly the content from anaerobic ponds will flow to
irrigation pond which is the last stage of the treatment. From the irrigation
pond, we can see the content is still black in colour but not viscous. Then the
effluent will be discharged to the trenches for land application.
DOE effluent discharging standard:
Land application: BOD < 500mg/l
River: BOD < 100mg/l
Figure: trenches
Figure:
Dried content in Geobags
Figure: The machine for stirring the pond
Figure: acidification pond
Operation
Proper retention time:
Ponds
|
Time
|
Holding pond
|
1.5 days
|
Acidification pond
|
3.5 days
|
Cooling pond
|
2 days
|
Anaerobic pond
|
28 days
|
Irrigation pond
|
3.5 days
|
Geobags
|
10 to 12 weeks
|
The table above is the proper retention time for the ponding system. But
due to insufficient capacity of the ponds, the retention time is not practice
in the system. The operation for the treatment system is that, once the level
of the ponds reach 1 or 2 feet below the land surfaces, the pumps will be
operated to pump the content to the next pond. By this, the retention time of
each pond are no following the proper retention time. This is because the pond
capacity is not sufficient to hold the effluent and have to move the content to
the next pond to prevent the pond from overflow.
Desludging
Due to the accumulation of deposited sludge at the bottom of the ponds,
ponds need to be maintained periodically through an activity commonly known as
desludging. The accumulation of sludge will reducing the ponds depth and
obstruct even flow. This will affect the efficiency of the ponds. Therefore,
desludging need to be carried out. The sludge will channelled to sludge drying
beds. The dried sludge are allwoed to dry can be used as fertiliser as it
contain high nutrient value.
Ponding system
Advantages:
Simple technology
Low construction cost and operating cost
Easy to maintain and operate
Skilled worker are not required
Acceptable treatment degree can be achieved
Disadvantages:
Require large land area
Unable to achieve high degree of treatment
Controlling and monitoring is difficult because of the pond size
Anaerobic treatment
A process which involves the breakdown of all organic matter by
microorganisms in the absence of oxygen or other oxidizing chemicals.
There are 3 stages;
Hydrolysis - complex organic molecules to simpler molecules by
hydrolytic microorganisms.
Acidogenesis - fermentation forming simpler organic compounds VFA
(Volatile FattyAcids).
Methanogenesis - VFA into methane and carbon dioxide.
Factor influencing anaerobic digestion
l Nutrient e.g. carbon, nitrogen, phosphorous,
l pH – between 7.0 and 7.2
l Redox potential – between – 520 and – 530 mV.
l Temperature – Mesophilic 35 to 40°C
l Thermophilic 55 to 60°C
l Toxic Substances.
Controlling and monitoring of anaerobic digestion
Constant and even feeding.
Minimize temperature fluctuation.
Well – mixing.
Regular monitoring on VFA, Alkalinity and gas composition.
Advantages:
Low operating cost
Smaller footprint
Low sludge production
High dewaterability and stabilized sludge
High tolerance to periods of unavailability of food
Disadvantages
High susceptibility of microorganism to man made- compounds
Low process stability
Low start up period
Aerobic treatment
Utilisation of oxygen by microbes to degrade and stabilise the organics
in wastewater.
Biosynthesis
Condition of Aerobic System
l pH
- 6.5 to 7.5
l Temperature – psychrophilic (12-18°C /
mesophilic m/o ( 25 - 40°C)
l Nutrients
l Oxygen – dissolved O2
l Proper mixing
Biochemical oxygen demand (BOD)
The amount of oxygen consumed during microbial utilization of organics
Facultative pond
-have long retention time, 50-60 days
-deeper and have 3 distinct layer, aerobic, facultative, anaerobic
-reduce significant amount of organic matter.
Aerobic (top zone): Aerobic bacteria consume organic matter releasing
ammonia, carbon dioxide, water, etc. Algae use carbon dioxide, ammonia and
phosphates in photosynthesis and metabolic processes and release oxygen during
photosynthesis.
Facultative (middle zone): The condition where fluctuates between
aerobic and anaerobic conditions. Facultative bacteria thrive and oxidize
organics in this zone where there is absence of minimal of oxygen.
Anaerobic (bottom zone): settled solids are consumed and biodegraded by
anaerobic bacteria in the absence of oxygen which release hydrogen sulfide,
carbon dioxide and methane.
Ponding system
- suspended growth or activated sludge
Suspended growth system, the microbial
responsible for waste breakdown are maintained
in suspension with the mainstream. The bacteria are free floating or suspension and air is bubbled through
liquid.
-attached growth or fixed film
In fixed film, microbial attach to an inert
medium
Advantages:
l Natural
l Low cost
l Highly efficient
l Tropical climate
l Load retention
l No mass removal
l Easy maintenance
Disadvantages:
l Long Hydraulic Retention Time
l Large Land Area
l High Solid Carry - Over
Figure: Geobags
Figure: Cooling pond
thanks for sharing
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