ES2203259A1 - Organic waste bioreactor includes temperature gauges with oxygen, carbon dioxide and ammonia concentration logging and a ventilation system - Google Patents

Abstract

Organic waste bioreactor has a steel container with a lightweight adiabatic loading and off-loading door and a false floor made of wood containing conical holes. Nine temperature gauges analyze and log the oxygen, carbon dioxide and ammonia concentrations, for automatic control of the reaction.

Description

Organic waste bioreactor.

The large amount of waste to be treated and its variability, the diversity of technologies with competition between them and the need to try a way to manage globally waste, forces to specify the conditions to apply and parameters to assess in each specific case. The present invention allows experimentation with different residues, as well as different mixtures with plant material and more proportions suitable for an optimal composting process of that material in conditions comparable to the composting tunnels of industrial use.

Background of the invention

While it is true that virtually almost all of the Organic waste can be composted, it is also true that no it has always been possible to do it in the most correct conditions because:

to)

the inconvenience that generate

b)

the quality of Final product

c)

efficiency in the energy and time consumption

There have been many experiences to improve the process (Logsdon, 1992; Stentiford et al. , 1990; Storm et al. , 1982; Youngberg, 1990) by varying humidity, particle size, C / N ratio, temperature, the presence of oxygen, etc ... But transferring these results to the current industrial tunnels with a capacity greater than 100 m ^ 3 and even close to 1000, has a number of difficulties. In the first place they are not exactly versatile nor do they have the necessary instrumentation to be able to obtain sufficiently precise conclusions. And on the other hand it would be an excessive energy, material and labor cost to experiment with those volumes.

That is why a lot of research has been done in small laboratory reactors of tens of liters capacity, with some exception of 200 liters (Marugg et al. , 1993), and in which experiences of extraordinary interest have been obtained, trying to reproduce the composting ecosystem (Hogan, Miller & Finstein, 1989) in perfectly insulated containers in which the temperature, pressure and the flow of air that is incorporated and all the exhaust gases are thoroughly controlled. The thermal and respiratory evolution of the materials is observed and quantified (Marugg et al. , 1993) and the losses of mass and production of CO_2 (Mato, 1992), as well as the behavior of many residues (Storm, Monis & Finstein, 1982) with different particle sizes (Dominguez, 1996). But there is a big problem when extrapolating these investigations to industrial tunnels since the conditions and dimensions of the mass are different.

Description

The present invention relates to a reactor of biodegradation of organic waste coming especially from industrial treatment plants, characterized by their size which allows an interpretation of the results at scale industrial, as well as for its great usefulness for research scientific due to all the variables of the degradative process They are controlled.

The reactor elements consist of a drawer 3 meters long, 1.20 wide and 1.20 high, and walls of sandwich steel plate with polyurethane filling 2 cm thick. The structure that will give form and consistency to Drawer is built in steel. It has two doors: one superior for loading, and a side for unloading. Inwardly the drawer will have a false floor made with wooden slats with conical holes left by a lower ventilation chamber.

Inside the drawer there are 9 probes of temperature that also take a sample of gases from the same point where they measure These gas samples are conducted to a box with multiplexed solenoid valves in a single outlet to the cabinet where the O_2, CO_2 and NH_3 analyzers are located. All  these measurements are collected by a programmed automaton that controls the development of the process and memorizes all the data (Figure 1).

The ventilation system (figure 2) is composed of a circuit of pipes that thanks to a set of 6 valves allow to establish a suction or blow action in The inside of the drawer. As we open three valves and close the another three, we will establish one circuit or another of the following form: opening those marked AA, AR and AS, and closing the BB, BR and BS will draw air from the drawer; closing AA, AR and AS, and opening BB, BR and BS will blow air into the interior (figure 2).

The ventilation system is connected to the drawer through two holes, one upper and one lower. The air It is driven by a high pressure centrifugal fan. The automaton also controls the fan operating cycle;  collects the values of temperature and relative humidity of the air that enters and leaves the reactor, as well as the flow and its pressure.

Inside the drawer there is also a simple irrigation system for waste consisting of a small pump and a pipe with sprinklers located at distances regular.

The composting tunnel brings together the following terms:

to)

Dimensions almost Industrial

b)

Capacity of process a wide range of materials and waste.

c)

Versatility operational

d)

Ability to measure and control all the variables.

and)

possibility of measurement and analysis of the exhaust gases.

F)

possibility of leachate measurement and analysis.

g)

Ability to vary working conditions to facilitate the conservation of nitrogen.

h)

Continuous weighing and measurement for the determination of mass and volume reduction respectively.

i)

Resources informatics to help perform the balance of water, nitrogen, masses, etc ...

j)

Elements of energy management.

The measures of the drawer are fundamental for the the fact that the effects of a critical mass for the thermal and biological inertia. And the porosity variations to as decomposition progresses and the consequences of compaction

In some of these effects the density of material (which is one of the factors that determines the loss of load) is decisive for the calculation of tunnel dimensions, and especially to define the characteristics of the fan. For the Therefore, although the values of an industrial tunnel will not be reached, may approach the maximum.

It is also possible to expand the drawer entries for mechanical loading and therefore adapt them to the measurements of a small mechanical shovel. And about everything, that maintains proportions close to those of the tunnels industrial, that although they are very varied keep each other some margins And in this tunnel, unlike other systems, The entire mass is considered a homogeneous set, although the Length is limited by the fact that the measuring elements and control collect reference values at almost any point of the material.

The width and altitude of the industrial tunnels most usual are between 4 and 6 meters with lengths between 10 and 25 meters, always keeping certain proportions While these measures can be overcome, it is not It is advisable to build larger tunnels because of the difficulty It would mean being able to control them correctly.

There is also the fact that a tunnel of concrete, which is the material that is normally used, is not a container of all adiabatic, although its dimensions and low thermal conductivity of the materials that are usually composted, retains heat very well and allows thermal inertia necessary.

Considering all of the above, you reach the conclusion that with a height and width about 150 cm useful and a length between 3 and 4 meters, would result in a volume of the order of 7 m ^ 3, which is an adequate volume for a tunnel. This is a much more manageable volume in the experimental field, but already It has dimensions in which thermal inertia and losses loading are similar to those of large tunnels and results allow to be extrapolated to constructions industrial (Figures 1 and 3).

Brief description of the drawings

In the form of three schemes we have tried to facilitate understanding of the bioreactor design. In this way in figure 1 we have a schematic side view from the drawer, where the ventilation chamber can be distinguished, bottom (1) and the points where the nine probes of temperature (2) and they also take the gas samples (3). Also the boxes of the solenoid valves have been represented (4), that of the gas analyzer (5) and that of the automaton (6). In a side of the drawer is located the ventilation system with both inputs to the interior (7 and 8), and the centrifugal fan (9).

Figure 2 is a diagram of a front view of the bioreactor ventilation system. They are represented the six valves that form the suction circuits (with letter A) and blowing (with letter B), as well as those that are opening adjustable (AR and BR), and all / nothing (AA, AS, BB, and BS). Equally the two entrances to the upper and lower parts of the drawer (7 and 8) and the centrifugal fan (9).

Figure 3 is a three-dimensional scheme of only the bioreactor drawer (10) where the loading door (11) of the waste to be composted. Are not drawn neither the ventilation system, nor the valve boxes, gas analyzer or automaton.

Embodiment

Most of the organic waste and mixtures adjusting the configuration more suitable for each material in such a way that the tunnel elements can be easily adapted to different mixtures, at your granulometry, water content, decomposibility, ...

It is convenient to test the materials that alone or in certain mixtures they are not advisable to compose industrial, but that in the tunnel will give us valuable information of its characteristics and thus be able to determine under what conditions It could be processed.

There are materials of high C / N ratio, consisting basically of lignins and celluloses, which would take long time to decompose under normal conditions, but which are fundamental in the composition of humic substances. But carbon can also be more easily degradable and It is the one that serves as an energy source for microorganisms and ends peeling in the form of CO_2. Of the other materials, the that have a low C / N ratio, in general they break down quickly and are very energetic, providing the basic material for The multiplication of organisms.

As regards the structure, either by its constitution or by the measurement of the particle, some materials they remain fluffy allowing the passage of air while others are easily compacted so that microbial activity It is hindered by the lack of oxygen.

We can also find materials organic with water contents of more than 90% and others extremely dry

From this information and others experiences, it is possible to determine the possible mixtures to adjust the porosity, C / N ratio, carbon availability, humidity and therefore the optimum activity level. Depending on the  types and volumes of materials you can search for a new component to acquire a level of sponge without which it would be Impossible to make good composting. And at the same time it is sought with this new material correct the other elementary factors, such as high humidity and low C / N ratio, adding a dry sponge with a high C / N ratio.

Although the most usual structuring is to try which achieves low humidity and high C / N structure ligno-cellulosic, to obtain less humid mixtures and favor the formation of humic substances, you can also give excess use of inert materials such as plastics, ceramic and pieces of tire that separate at the end of the process And they are reused.

In order to experiment as described, We incorporate five fundamental conditions of versatility:

a) Centrifugal pressure and flow fan adjustable, oversized within rational margins, to be able to treat materials that due to their low porosity produce a considerable load loss, or others that due to its high activity requires a higher air flow.

b) Reversible air flow direction (Finstein, 1993), allowing servo valves to aspirate the gases, forcing entry through the outside area, or drive through the base collecting those from the top.

The main advantage of the first case is that it is not it is necessary that the tunnel is so hermetic since the leaks that can occur would not affect the mass because they would be outside air that would penetrate the dough without problems. Too facilitates the incorporation of irrigation water into the dough, little thing problematic given the permeability of most materials.

The second case involves total tightness and that any serious leakage of process gases would give bad odors or They would produce other problems. As for the blowing system It implies a number of advantages. First of all the fact that the air enters the theoretically hotter part, tends to heat the coldest surface and therefore to homogenize the temperature. Second, there is a slight tendency to sponge the material and uncover the air intake holes. If I dont know Recirculates, with the fan blowing clean air is passed, while that aspiring process gases are passed with the consequent corrosion problems

What is important is to be able to determine for each material or mixture which of the two systems produce a more homogeneous distribution of temperatures and oxygenation

c) Air recirculation / renewal in desired proportions through the regulating valves that connect the tunnel with the outside on one side and with the biofilter on the other, allowing partial or total air renewal of the tunnel to obtain the desired temperature and oxygenation or recirculate to conserve temperature and / or nitrogen (figure two).

d) Under the mass there is a series of slats of interchangeable wood of different sizes and arrangement of holes, which creates a lower air chamber and that allows study the optimal distribution of input and output of gases from the mass, because due to the large volume of industrial tunnels It is important to try to achieve the temperature conditions, oxygen, humidity, etc ... as homogeneous as possible (figures 1 and 3).

e) Great versatility and flexibility of elements of measurement and control. There are many more probes than in any tunnel Industrial and endless distribution possibilities. Three systems to control the air flow: stopping and turning on the fan, regulating the flow rate with the servo-activated valves and regulating fan speed. Three types of analysis of gases: oxygen, to ensure a sufficient level; CO_2, what It is the best indicator of the biological activity of the process; Y NH_3, which reports other aspects of the activity and allows know if you are missing, giving the opportunity to take some decision to try to avoid it. While it is true that with just one standard control system could be enough, we have a great flexibility to experience all possible actions to choose the most appropriate for each case, and to measure the effects in the most appropriate and accurate way. And all this equipment supported by a powerful and flexible program capable systems optimize and control the process the way preset and capture and analyze all the information that is can extract (figure 1).

There are some variables that are measured from the mass of the material and other ducts. It is evident that in the measures such as O_2 or temperature, the value really significant is the one that can be obtained from the dough, and better if It does in points distributed all over it. It would be simpler and facilitate the duration and maintenance of the probes if measured outside the tunnel. If this experimental tunnel is raised measure in and out at many points, it is to be able to establish correlations and significant points that simplify and reduce industrial construction and reduce its maintenance.

Of these measures, some would serve to control the process regulation elements and others will be Security, informative or reference.

It would also be possible to measure the air conditions of the outside, especially the temperature and humidity, that the program of regulation would use them as a reference. And how is the CO_2 analyzer, with a minimum cost could also be measured the environmental, since although in principle it is usually stable, so  Control the influence of some external factor.

It is noteworthy that the points of temperature and gas measurement match, since its relationship allows to draw significant conclusions from the march of the process in these places.

The fundamental control element is air, by which the oxygen contribution and the regulation of the temperature at the desired point in each phase of the process. Regulating the opening of the different valves and the engine speed of the turbine through the computer program, determining the flow of recirculation and renewal air with the corresponding exit to the biofilter.

At the beginning of decomposition, a moderate ventilation to maintain a sufficient oxygen ratio, it helps to reach the desired temperature more easily since Microbial activity is accelerated. On other occasions it will be necessary overvent to stop excessive acceleration in order to anticipate when the program detects a high speed of warming that could later be difficult to control. A higher temperature could inactivate bioxidation. It will also have to be regulated to maintain a maximum temperature productivity that allows the presence of thermophilic colonies and mesophilic in the proportion of maximum decomposition efficiency. OR recirculate to avoid cooling, always trying to keep the optimum point

It may be convenient to recirculate to retain the ammonia, or ventilate to remove it as is the case of the substrate For mushrooms. In each phase, and depending on the material, it is possible to determine an optimum humidity point. Although the margins They are usually wide, dryness can inactivate microorganisms getting to stop the process. And a very dry end material can give problems when rewetting it.

Excess moisture can also stop the process, since water occupies the air and material spaces can enter anaerobiosis, with complications and negatives consequences that entails.

By regulating the irrigation flow we intend to maintain the desired humidity level, although probably, depending on the material, the efficiency of this operation is not the highest, since it is difficult to incorporate water due to the low permeability of the dough And if it is contributed in excess we will end up losing it by runoff When air circulates by aspiration, from the surface into the dough, it can help it to penetrate.

The contribution of water also has an impact on the regulation of the temperature since although the air cools by exchange, the greatest cooling potential is provided by the heat of evaporation of water from the dough.

Industrial application

Apart from the obvious use of this bioreactor for sludge treatment produced in sewage treatment plants coming from industries, quickly, efficiently, cheaply and not pollutant, there are other features of the invention that have Other possible applications.

Most of the materials that are composted they release a high amount of heat, mainly in the First stages of the process. This fact, along with the high production of CO_2, allows to consider the use in greenhouses attached to the plant that would contribute their waste to Compost and use the produced substrate.

The fact is that few experiences have been made directed (Díaz, Golueke & Savage, 1986) to the use of this energy, probably due to transport difficulties Due to its low level. And therefore to the unfavorable relationship between costs and performance.

A study of the type of vegetable and the growing season, but without a doubt that the temperature and contribution of CO_2 from the biofilter outlet air, regulated properly, it could increase the production of certain plants. And so fix part of the carbon instead of releasing it to the atmosphere. Trials of serving the material obtained from greenhouse plants as biofilter

Since compost is a low price product, energy costs, although not high, can affect the economic performance of the plant. Good computer management of the phases of more electrical consumption and motor synchronism could reduce the cost of electric energy by accessing the cheaper rates and lower power factors.

This proposal is based on the inertia of the process which allows to program the maximum number of motors that work at same time and they stay on at the time due to the electrical overload they produce. And if they are to be hired rates of different blocks such as night, etc ..., plan them with the most energetic control actions of the process occur with the cheapest rates.

The power factor assumes a fixed part considerable bill of electricity and is supposed to of being the sum of all the consumption elements of the plant. But properly managed can reduce the cost between half and the third part and cheaper connections and lines electric.

An indirect way, but it could be the most important, to stabilize energy and make composting profitable from research with the experimental tunnel, it is determine the optimal conditions of the process parameters to try to obtain an optimal product in the minimum time.

Claims (2)

1. Bioreactor composting organic waste, experimental type, equipped with 9 temperature probes and three gas analyzers (CO_2, O_2 and NH_3), all connected to a PLC, characterized by being able to use any of these four parameters (temperature , CO_2, O_2 and NH_3) as control parameters of the ventilation system, and for taking the sample of are for gas analysis at exactly the same point inside the mass where the temperature measurement is performed. 2. Organic waste bioreactor, according to claim 1, equipped with a ventilation system consisting of a centrifugal motor and a maze of pipes with 6 servo-operated valves (4 digital and 2 proportional), characterized by allowing air flow inversion ( ascending or descending) inside the composting mass according to the disposition that these valves adopt, and for being able to ventilate with a mixture of outside air and interior air, in the desired proportion, according to the position in which the two proportional valves servo-activated ventilation system. These characteristics allow to control the ventilation of the dough in composting in three different non-exclusive ways: air blowing / aspirating, motor speed variation and air recirculation / renewal.