WO2020139067A1

WO2020139067A1 - New external loop "air-lift" bioreactor for treating liquid effluent

Info

Publication number: WO2020139067A1
Application number: PCT/MA2019/000024
Authority: WO
Inventors: Reda ELKACMI; Mounir Bennajah
Original assignee: Université Sultan Moulay Slimane, Béni Mellal
Priority date: 2018-12-25
Filing date: 2019-12-05
Publication date: 2020-07-02
Also published as: MA44332B1; MA44332A1

Abstract

An innovative method for biological treatment has proven to be very effective and less expensive for treating various soluble and colloidal pollutants in agricultural, industrial and urban liquid waste. The present invention relates to an industrial device that allows degradation of the organic pollutant load of effluent by biological processing. The technique has been successfully tested in the case of liquid waste with a high biological load. The treatment was carried out in the presence of microalgae. The depollution of the waste in the external loop air-lift bioreactor that has been developed occurs with a continuous supply of the waste that is to be treated and through the contribution of oxygenation, for the first time using ventilation in this type of apparatus. The invention is focused on administering a significant amount of ambient air containing the oxygen and carbon dioxide that is required for biological treatment in the presence of microalgae. This contribution is provided, for the first time in this type of reactor, through ventilation that allows a pressure differential to be created between the outside and the inside of the reactor, which allows a considerable air flow to be routed towards the inside of the apparatus. Compared to the other treatment techniques that are applied in similar reactors, the present method has proven to be highly advantageous in terms of the effectiveness of the treatment and of energy consumption. For treating agricultural waste tested in a 35 litre capacity apparatus, COD reduction effectiveness of the order of 87.35% and a bleaching ratio of the order of 90.46% were recorded for energy consumption of 0.8 W/kg of COD eliminated over 12 hours of treatment.

Description

NEW AIR-LIFT BIOREACTOR WITH EXTERNAL LOOP FOR THE TREATMENT OF LIQUID EFFLUENTS

Summary :

An innovative biological treatment process has been shown to be very effective and less costly in treating different soluble and colloidal pollutants in agricultural, industrial and urban liquid discharges. The present invention consists of an industrial device which allows biological degradation of the organic pollutant load of the effluents. The technique has been successfully tested in the case of a liquid discharge with a high biological load. The treatment was carried out in the presence of microalgae. The depollution of discharges in the developed external loop gas siphon bioreactor is carried out by continuous supply of the discharges to be treated and by oxygenation, for the first time in this type of device with ventilation. The invention focuses on the administration of a large amount of ambient air containing oxygen and carbon dioxide necessary for biological treatment in the presence of microalgae. This contribution is ensured for the first time in this type of reactor by the ventilation ticket making it possible to create a vacuum between the outside and the inside of the reactor, which makes it possible to convey a considerable flow of air towards the inside the appliance.

Compared to other treatment techniques applied in similar reactors, the present process has proved to be very advantageous in terms of treatment efficiency and energy consumption. For the treatment of rejection of agricultural origin tested in a device with a capacity of 35 liters, a COD abatement efficiency of the order of 87.35% and a discoloration rate of the order of 90.46% were was recorded for an energy consumption of 0.8 W / kg COD eliminated during 12 hours of treatment. Originality and detailed description:

The treatment of organic matter and its elimination is an important discipline in the treatment of liquid discharges due to the large number of industrial pollutants "discharges" loaded with organic matter. The study conducted shed light on several scientific works concerning the treatment of organic matter by physical, biological and chemical processes. Biological oxidation remains an effective technique to achieve significant abatement yields given the low operating cost. In industrial practice, oxidation by oxygenation remains a cost-effective means of reducing organic matter due to the relatively low cost of operating the processing units. The availability of air and its oxygen content makes oxygenation with the supply of compressed air a process that is very popular in industry.

In this context, the present invention consists of an efficient treatment reactor for organic matter (COD, BOD5, coloring, turbidity, conductivity, salinity, etc.) which does not impose air compression for the treatment.

The need for oxygen and carbon dioxide necessary for biological treatment is provided by ventilation. The fan sized according to the reactor capacity makes it possible to create a density difference between the inside and the outside of the reactor, a supply of ambient air is ensured by means of a tube provided with a distributor at the end. The ambient air thus circulates from the outside to the inside of the reactor, the distributor is placed at an optimal height at the bottom of the Riser compartment, the bubbles produced in this compartment make it possible to create a density difference between the Riser and Downcomer compartments. . This difference in density causes an external circulation of the pollutant inside the device which allows an internal agitation highly favorable for the treatment. The supply of ambient air to the interior of the device allows, in addition to the hydrodynamic advantage relating to agitation, a supply of the biological medium with oxygen and carbon dioxide. Oxygen strongly activates the degradation of organic matter by oxidation while the carbon dioxide supplied combines with the fraction resulting from the oxidation of organic matter to activate the in situ development of microalgae. The treatment system being exposed to sunlight, it is therefore biologically effective especially if the process is carried out in an apparatus made of worms or plexiglass, Figure 1. Description of the geometry of the bioreactor:

- The total volume of the liquid in the reactor depends on the height h of the liquid in the separator, the device can therefore operate with a capacity ranging from 30 to 40 L. The height of the liquid in this area is h = 18 cm, height total is H = 22 cm.

- The 23.3 cm diameter Riser compartment at a height of 134 cm subdivided into two parts:

Hi = 109 cm: height of the straight section.

¾ = 25 cm: height of the conical lower part ensuring the junction between the two compartments.

- The Downcomer compartment has a diameter of 15.6 cm and a height of the order of HI + H ₄ = 469 cm with:

H4— 60 cm height of the lower part of the Downcomer compartment connecting its straight section to the lower inclined section of the reactor.

- The ratio of the sections of these two compartments (A _Dow ncomer / ARi _ser ) is 0.44. This geometric ratio allows optimal operation of the bioreactor for the case tested.

- The distance between the vertical axes of the two compartments Riser and Downcomer is 56 cm, this distance is a limit value which makes it possible to block the recirculation of air bubbles from the Riser to the Downcomer.

- The two Riser and Downcomer compartments are connected at the bottom by an inclined tube with a diameter of 15.6 cm and a length of 63.6 cm, which constitutes an extension of the Downcomer compartment.

- The air intake tube is made of stainless steel, length 1 m, thickness 2 mm and diameter 5 cm. The position of the tube inserted in the Riser compartment is variable. In our case, an optimal H2 value is found following an optimization study.

- Two bubble dispensers are welded to the end of a stainless steel tube, they are connected with a T-tube. Their diameter is 3 mm, they are each fitted with 67 high pressure nozzles.

- A fan with 9 rotating blades at a speed of 1500 rpm, this speed makes it possible to limit turbulence and ensure optimal agitation with an air flow of the order of 0.025 m ³ / s. - An electric regulator connected to a renewable energy source (solar panel or wind turbine) makes it possible to produce a sufficient amount of energy for the operation of the air extraction fan.

- The bioreactor is supplied and emptied at the bottom of the reactor at the level of the inclined section by means of a drain valve.

- The lower part of the Downcomer compartment is connected to a 4 cm diameter pipe, rising to the level of the liquid at the top of the separation chamber. This line is connected to a siphon, in order to maintain a stable level of the effluent in the reactor.

The agitation speed is an important parameter to control for the conduct of the treatment process. The turbulence created by the circulation of the liquid must be at its optimal value allowing a maximum of biological yield. Excessive turbulence has been shown to be unfavorable for treatment and may cause degradation of a fraction of the microalgae required for treatment. The speed of circulation of the rejects in the device is directly linked to the difference in density between the two compartments:

Liquid: Velocity of liquid in the reactor.

P _Riser : Density of liquid in the Riser compartment.

p Downcomer: Density of liquid in the Downcomer compartment.

This difference is caused by the supply of ambient air to the Riser level, the more the Riser compartment is loaded with air bubbles (vacuum rate or gas retention) the greater the difference in density and therefore the speed increases.

The circulation speed is linked to the ventilation speed, the size of the fan and its blades and especially the position of the air distributor in the Riser compartment. The use of a fan to provide ambient air to the reactor allows the treatment process to be easily connected to a renewable energy source. In this context, the ventilation in our reactor is normalized and the fan is sized in accordance with industrial standards, which is commonly used. This facilitates scaling up and allows ventilation in this process to be independent of the treatment. The speed of circulation therefore only becomes dependent on the position of the ambient air distributor. The position of the distributor is correlated with the speed of circulation of liquid according to the following relationship:

Uii quide _{, Down} : Speed of liquid in the Downcomer compartment.

hdis _P = (Hl + h) - H2: Dispersion height corresponds to the height of liquid above the distributors in the Riser compartment.

hmax ⁼ Hl + h = 127 cm: Maximum height of the dispersion corresponding to the low position of the electrodes in the Riser compartment.

In conventional treatment methods using gas-jet reactors [1, 2], ambient air is supplied by means of a compressor. The replacement of the compressor with a ventilation system in our case revealed a major energy advantage. This allowed a combined applicability of the treatment using conventional renewable energy sources, which was not economically viable in the case of a treatment system equipped with an air compressor especially in the context of applicability. industrial.

Example of application of the bioreactor for the treatment and detoxification of olive water.

The vegetable water, or vegetable water from the extraction of olive oil, presents an environmental nuisance, namely the acidification of the natural environment, the reduction of soil fertility and the disappearance of aquatic life. For this reason, these effluents were tested in our bioreactor in order to study the elimination of organic matter (COD) and the coloring. The sample was taken from a storage tank in a local crushing unit operating in a continuous system. Examination of the characteristics of this sample showed an initial COD of the order of 4.68 g O ₂ / I, BOD ₅ of approximately 10.49 g O ₂ / I and an absorbance (395 nm) corresponding to a initial coloration of 9.15.

The bioreactor subject of the invention used for the treatment of vegetable water in our case is that represented in FIG. 2. The volume of the rejection tested is 35 1, it circulates between the two compartments of the apparatus conveyed by a difference in density generated by an introduced air flow of about 0.025 m ³ / s. This flow value corresponds to a ventilation speed at 1,500 rpm. This air flow value was adopted to allow on the one hand to create a sufficient density difference between the two reactor compartments and therefore favorable agitation for the treatment (minimize the effect of the external diffusion of O 2). and on the other hand, bring and diffuse oxygen into the solution in order to degrade the organic matter. In the presence of atmospheric CO2, solar energy and dissolved salts, the treatment medium becomes favorable for the activity of microalgae (Chlorella vulgaris). The latter consume organic matter and release oxygen favorable for the degradation of the organic matter present in the effluent to be treated.

To determine the optimal speed Uii quide _{, Down} allowing proper operation and ensuring better effluent detoxification yields, three speeds were tested corresponding to the three distributor positions H2 = 84.15 cm, H2 '= 63.5 cm and H2 ”= 39.61 cm equivalent to the dispersion heights 1¾i = 42.85 cm, 1ID ₂ = 63.5 cm and ho ₃ = 87.39 cm.

Tests on the device have shown that effective reduction of COD and staining is found at liquid circulation speeds in the range 2.78 - 5.67 m / s.

In this context, a height H2 = 84.15 cm of distributor allowed an optimal internal circulation speed in the device allowing (Uii quide _{, Down} = 2.78 m / s) after 12 hours of treatment to reach a rate of elimination of the coloration of the order of 90.46% and a COD reduction of the order of 87.35% (FIG. 3). These yields have proven to be very satisfactory given the low electrical consumption of the device.

References:

1. Chisti, M. Y., & Moo-Young, M. (1987). Airlift reactors: characteristics, applications and design considerations. Chemical Engineering Communications, 60 1-6), 195-242.

2. Merchuk, J. C., & Gluz, M. (1999). Bioreactors, air-lift reactors. Gas, 1, 2.

Claims

1) Ventift external loop bioreactor for the treatment of liquid effluents based on the circulation of liquid effluent through the two sections of the device (Riser and Downcomer) by ventilation. A supply of ambient air is ensured by means of a tube fitted with a distributor inserted into the Riser compartment at an optimal depth ensuring an adequate circulation speed and high reduction rates.

2) ventilift external loop bioreactor according to claim 1, equipped with a tube which allows the generation of air bubbles which cause a circulation of the liquid. The location of the distributor is correlated with the circulation speed which facilitates the increase in scale and allows the ventilation in this process to be independent of treatment.

3) ventilift external loop bioreactor according to claims 1 and 2, coupled with a new renewable energy source, such as a photovoltaic or wind cell, to supply the ambient air extraction fan from the outside to the inside the appliance.

4) ventilift external loop bioreactor according to claims 1, 2 and 3, capable of ensuring the detoxification and treatment of liquid effluents in the presence of micoalgae.

5) Process for treating olive water in the external loop gazosiphon bioreactor is carried out according to the following steps: a- Extraction of air contained in the device by ventilation thus creating a vacuum allowing bubbles to be generated in situ. which cause the effluent to circulate in the device.

b- The oxygen supplied is used for the degradation of organic matter by oxidation. c- In the presence of solar radiation and dissolved nutrients, the carbon dioxide brought in from the outside combines with the fraction of DOC resulting from the oxidation of organic matter. This leads to the activation of in situ microalgae development.

d- Microalgae type (Chlorella vulgaris), consume organic matter and release oxygen favorable for the degradation of the pollutant load present in vegetable water. 6) Method according to claims 1, 2, 3, 4 and 5 is characterized for effluents with a high organic content such as urban waste water, textile waste, waste water from tanneries on a semi-pilot and industrial scale.