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; Anaerobic treatment of wastewaterThe anaerobic treatment of wastewater from food, beverages and pharmaceutical industries has many advantages compared to other treatment methods: · Energy consumption is very low with anaerobic treatment. For example no oxygen has to be supplied, or extensive mixing has to take place. · Most of the organic material in the waste water is converted into biogas, which can be combusted for the purpose of energy or steam production. The energy can be used in the production plant or can be supplied to the power net. · Sludge production in anaerobic treatment is very low, because most of the organic material is converted into biogas, not in sludge. Furthermore, the anaerobic sludge is stabilised and can be easily dewatered by gravity. The sludge can be used for starting up new anaerobic reactors, or can be wasted on the land. Sludge handling costs are therefor minimal. · the anaerobic sludge can be easily stored and conserved, which simplifies second start-ups after production stops or periods with reduced organic loading rates. · Investment costs are low, because high reactor loading rates and short retention times are applied. Furthermore, the design and construction of an anaerobic reactor is simple, which further reduces the costs. Anaerobic treatment is most commonly applied as a pre-treatment, because normally high concentrated waste waters are treated. The effluents form the anaerobic treatment still contain some organic material, despite the very high removal efficiencies. Furthermore nutrients are only partly removed, so post-treatment will be necessary in many cases. 2 The development of the Pre-fermerEIMS BV developed an anaerobic reactor of the Upflow Anaerobic Sludge Blanket (UASB) type. The UASB reactor proved to be a very suitable and satisfying reactor for the treatment of a range of different wastewater’s. Depending on the type of wastewater, the UASB reactor can be combined with the sedimentation buffer tank. Many (agro-industrial) wastewater’s contain high amount of solids that can be removed in this tank. The UASB reactor and the sedimentation buffer tank developed by EIMS is protected as one system under the name Pre-fermer. Pre comes from ‘pre’-treatment or preliminary wastewater purification. FERMER is a pun on fermenter, a different designation for an anaerobic reactor. 3 Types of wastewater suitable for the Pre-fermerThe Pre-fermer is suitable for the treatment of a wide range of different types of wastewater. Both high-strength industrial waste waters and domestic waste water can be treated, however the specific reactor design and construction will be different for each type of wastewater. Types of wastewater: 1. food industries, such as potato processing industries; 2. paper mills; 3. pharmaceutical industries, 4. beverage production facilities, 5. breweries; 6. sugar and sugar derivatives production facilities; 7. domestic wastewater. 4 System description of the Pre-fermerThe raw waste water will be physically/mechanically pre-treated by means of a screen for grid removal, a sand catcher, a drum screen and other equipment if necessary. The pre-fermer system consists of a:
· Sedimentation buffer tank · Neutralisation tank · UASB reactor · Biogas handling system
The Pre-fermer has a number of advantages compared to
other anaerobic pre-treatment systems. ·
The Pre-fermer combines the following anaerobic wastewater
treatment targets: -
a high COD and TSS removal performance and a high biogas performance;
-
an optimal combination of water inlet points and water recycling
in the UASB reactor to generate a homogeneous expanded sludge blanket; -
an optimal separation of the sludge, wastewater and biogas
through the round three phases separators; ·
The Pre-fermer has a storage capacity in the sedimentation
buffer tank by means of a floating rim. The effluent discharge from the
tank can be controlled. ·
In the sedimentation buffer tank settling of solids and some
acidification occurs, which makes the waste water more easily anaerobic
biodegradable. ·
The application of a neutralisation tank improves the performance
of the system by neutralising the wastewater before entering the reactor
and by maintaining continuous upflow velocities in the reactor. Fluctuations
in the waste water flow do not result in changes in the flow through the
reactor. ·
A high pressure storage tank is one of the devices of the
biogas handling system. Methane gas can be stored in this tank while CO2
and H2S are removed from the biogas in liquid form. The caloric
value of the biogas gas will be highly increased. The H2S can
be neutralised with caustic soda in a de-sulphurisation installation; ·
The sedimentation buffer tank and the UASB reactor are completely
insulated. Heat release devices are provided in the space underneath the
cone of the sedimentation buffer for warm summer periods; ·
The Pre-fermer is equipped with extended managing and control
devices. The operator has the possibility to change and control most of
the process variables such as the flow over the sedimentation buffer, the
flow over the UASB reactor, the sludge load in the UASB, the solids removal
frequency and quantity from the sedimentation buffer, the pH of the UASB
influent, the temperature in the sedimentation buffer etc.; ·
The investment costs in the Pre-fermer are low because of
the simple, sophisticated and flexible design and the exquisite material
choice with a minimum on mechanical devices; ·
The savings on running costs as a consequence of the use of
the Pre-fermer is high, because of the low operational costs, while the
revenues of steam or electricity generation and the revenues on sales of
solids as cattle feed and sludge as fertiliser are high; ·
The productivity of the Pre-fermer given as the Internal Rate
of Return on Investment IRR is high compared with other wastewater treatment
systems; ·
The Pre-fermer contributes to the sustainable plant management
because of the generation of renewable energy in the form of biogas from
wastewater; The Pre-fermer is constructed under the product guarantee
for all system devices and for the system as a whole for a period of time
at least equal to the term of the lease contract made up for the design
build project realisation. The process guarantee includes a performance bond regarding
the COD and TSS removal efficiencies can be provided in the framework of
the design build contract of the Pre-fermer. After the provision of the product guarantee and the
performance bond the operational costs and revenues have been safe guarded.
Therefore the return on net revenues of the department of the enterprise
that installed the Pre-fermer will be guaranteed. |
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