NO346325B1

NO346325B1 - Reactor and method for the treatment of wet organic waste, such as black water from households, manure, sludge and slurries

Info

Publication number: NO346325B1
Application number: NO20191472A
Authority: NO
Inventors: Daniel Todt
Original assignee: Jets As
Priority date: 2019-12-11
Filing date: 2019-12-11
Publication date: 2022-06-07
Also published as: WO2021118365A1; NO20191472A1

Description

The present invention relates to an anaerobic reactor for the treatment of wet organic wastes such as black water from households, manure, sludge and slurries including a closed vessel or housing preferably provided with a detachable lid, further including an inlet for the wet organic waste, an outlet for purified water and an outlet for produced gas. The invention also includes a method of operating such reactor.

Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion. Anaerobic digestion is used as part of the process to treat biodegradable waste and sewage sludge.

Anaerobic digestion is widely used as a source of renewable energy. The process produces a biogas, consisting of methane and carbon dioxide, and traces of other ‘contaminant’ gases. This biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. The nutrientrich digestible also produced can be used as fertilizer.

Anaerobic digestion can be performed as a batch process or a continuous process. In a batch system, biomass is added to the reactor at the start of the process. The reactor is then sealed for the duration of the process.

In continuous digestion processes, organic matter is constantly added (continuous complete mixed) or added in stages to the reactor (continuous plug flow; first in – first out). Here, the end products are constantly or periodically removed, resulting in constant production of biogas. A single or multiple digester in sequence may be used. Examples of this form of anaerobic digestion include continuous stirred tank reactors (CSTR), upflow anaerobic sludge blankets (UASB), expanded granular sludge bed (EGSB) and internal circulation reactors (IC reactor). Another abbreviation which is often seen is ABR, anaerobic baffle reactor, which was originally designed to take advantage of the UASB principle while being able to handle feeds with high particulate contents, but it has not been as efficient as intended.

An example of an anaerobic reactor is shown in DE 3604415 A1. It includes a cylindrical, closed reactor vessel which is subdivided by further concentrically arranged cylinders into a plurality of stages, which, depending on the direction of flow, have overruns at the top end or overflow ducts at the bottom end. When biogas is produced from highly organically polluted waste waters, e.g., three stages are situated in the reactor through which flow passes successively. In the inner stage the hydrolysis takes place, in the middle stage acid formation takes place and in the outer stage the methane formation takes place. The untreated water is continuously introduced into the inner stage from below by a feed pipe. Pre-clarified water collects after passing through all stages in an annular duct and is taken off via a connection branch. It is fed into an annular outer space via feed branches, where degassing takes place. The gases produced from the outlet orifices of the reactor, are fed jointly for suitable further processing. The degassed liquid passes into a sedimentary device where the entrained sludge is separated off and returned from there to the reactor, while the clarified waste water collects in an annular duct and is taken off via an outlet pipe. This known process includes several stages where the wet organic waste to be treated passes over several thresholds by overflow arrangements. Such flow regime contributes to the build-up of floating sludge that eventually will cause clogging of the reactor.

From WO2018135952A1 it is known an apparatus and method for treatment of wet organic matter for producing biogas, comprising a closed reactor for anaerobic digestion of wet organic matter. The reactor comprises two vertical tubes, an outer tube defining a first chamber encircling an inner tube which is divided into a first region and a second region of a second reactor chamber by a vertical partitioning wall. The first reactor chamber comprises a particle retaining unit connecting the first and second reactor chamber. The anaerobic reactor exhibits a top discharge pipe for gas generated in either of the two chambers of the reactor. The purpose of the particle retaining unit is to hold back floating particles reaching the surface of the waste water in the reactor, forming a floating layer. By holding back the floating organic material the intention is to prolong the residence time of such material and thereby provide sufficient time to digest it.

However, tests with black water from toilets have shown that the particle retaining unit is not functioning according to its intention with substrates having a high content of particulate matter. A thick layer of floating sludge is formed over time which is not digested and this layer eventually is clogging the water outlet of the reactor and needs to be removed. Such removal is a cumbersome and expensive operation making the reactor useless and not suited for commercial exploitation.

With the present invention is provided an anaerobic ABR type reactor where the problems related to build up of floating sludge is prevented by effective redirection and recirculation of the floating particles to the waste water feed to prolong the retention time for these particles and thereby completing the digestion of the biomass of the waste water feed.

The invention is characterized by the features as defined in the independent claims 1, 9 and 13.

Preferred embodiments are further defined in the dependent claims 2 – 8, method claims 10 – 12, and use claim 14.

The invention will now be further described by way of example and with reference to the drawings where:

Fig. 1 shows a principle sketch in cross section of a reactor according to the invention,

Fig. 2 shows a sketch of the same reactor from above, along section line B – B in Fig.1,

Fig. 3 shows the same reactor as in Figs.1 and 2 under ordinary operation, and

Fig.4 further shows the reactor as shown in Figs.1 and 2 under recirculating operation.

An example of an anaerobic reactor 20 according to the invention for the treatment of wet organic waste is shown in Figs. 1 and 2. It includes an outer casing or vessel 10 with a lid 11 forming a closed volume, but being provided with an outlet 12 for gas produced by the reactor. The vessel may be of any shape such as circular as shown in Fig. 2, oval, square, rectangular or polygonal. The reactor is divided by a partition wall 1 into two or more chambers (see use claims below). A first chamber I and a second chamber II, where the first chamber I at its lower end is provided with an inlet 8 for the organic waste feed and chamber II which at its upper end is provided with an outlet 7 for purified water. Chamber I is provided with a separation device such as a 3-phase separator 2 as shown in Fig.1, which is formed by v-shaped plates, and is integrated in the partition wall 1 below inflow openings 6 for the inflow of (partly digested) organic feed from chamber I to chamber II. Above the 3-phase separator 2, partly overlapping the separator, is further provided a slanted deflection plate 3 with a vertical upper part 19 which stretches across the vessel 10. This plate 3, 19 is designed to deflect upwardly floating organic particles towards a circular or polygonal collection funnel 14 at the opposite side of chamber I and at the same time reducing the open surface area of the floating sludge in chamber I. The collection funnel 14 as such is a plate stretching across chamber I as shown in Fig.2. A vertical duct 5 connected to an opening in the plate forming the circulation opening is provided to enable circulation of the partly digested organic waste mixed with floating sludge as is further explained below. With the vertical part on the outside of the reactor, the duct 5 also functions as a trap, preventing gas of escaping from the reactor.

By the arrangement of the integrated 3-phase separator 2 and deflection plate 3 as shown in Figs 1 and 2, there is a longitudinal slit 15 through which the partly digested wet organic waste passes from chamber I towards chamber II. The openings 6 at the upper part of the partition wall 1 (all together 3 openings as shown in Fig.2) are each connected with a vertical duct 13 stretching towards the bottom of chamber II and thereby passing the partly digested waste to the bottom of the chamber. In conjunction with each vertical duct 13 and inlet 6, there is provided a flanged opening 23 for inspection and cleaning/hosing of the inlet and duct in case of blockage. Even though Fig. 2 shows 3 openings and ducts 6, 13, 23, the reactor according to the invention may be provided with one, two or more than three such ducts/openings.

The inlet 8 of the reactor formed by a pipe stub 16 is equipped with a horizontal plate 9 to ensure horizontal distribution of the wet organic waste feed into chamber I. Further chamber I as well as chamber II are provided with outlets 17 and 18 in the bottom to extract precipitate that is produced during the digestion process.

The anaerobic reactor 20 as described above is working in two different modes, 1) an operating mode and 2) a recirculation mode as described below and with reference to Figs. 3 and 4: Wet organic waste such as black water is fed to the reactor, preferably by a pumping means 21 from a feed buffer tank (not shown), through the reactor inlet 8 and is distributed along the bottom of chamber I. Under normal operation, mode 1) as illustrated by the arrows in Fig.3, the wet organic waste passes slowly upwards in chamber I, being slowly digested and then passing the slit 15 via the separator 2 and further through the overflow inlets 6 and still further down through the ducts 13 and into chamber II at its bottom. Here, the partly digested wet organic waste continues the digestion process towards the outlet 7 of the chamber and is finally led out through the outlet 7, preferably mostly as purified water. However, any particles passing the outlet 7, are separated in a downstream trap or collector/filter (not further shown) and is returned to the inlet 8 of the reactor by pumping means (not shown). Under the anaerobic process taking place in chambers I and II, gas that is produced is evacuated through the gas outlet 12, while digested particles with higher density precipitates at the bottom of the chambers and are extracted/ tapped at regular, required intervals. On the other hand, lighter particles with lower density are separated by the 3-phase separator 2 and are further deflected to the surface towards the recirculation opening 14.

As to the recirculation mode of operation, mode 2), illustrated by the arrows as shown in Fig. 4, circulation of the wet organic waste is obtained by means of an externally provided pump 22 connected to the suction duct 5 through a piping loop (not further shown) and further connected to the inlet 8 of the reactor 20. The wet organic waste, including light organic particles being deflected by the sloped plate 3 and floating towards the surface, is sucked into the upper inlet 14 of chamber I by the pump and is returned to the reactor inlet 8 and distributed along the bottom of the chamber I by the horizontal plate 9. By this pumping activity, forced circulation is obtained and the nondigested sludge forming particles floating on the surface are returned to chamber I, thereby obtaining prolonged residence time in the reactor. The pump may be of any type, but preferably the applicants own Vacuumarator® liquid ring screw pump with macerator is well suited since it effectively breaks down the floating sludge to very fine particles.

The recirculation operation is preferably controlled by a PLC based on an algorithm calculating the instant detected load of the reactor. If the operating load of the reactor is high (higher circulation volume of wet organic waste), less recirculation is needed than when the load is low to ensure sufficient “stirring” of the biomass within the reactor at all time. The recirculation operation needs to be optimized for each reactor based on different factors such as reactor size, the type and consistence of the wet organic waste and the instant load. However, preferably the waste feed and recirculation will be performed as pulsations lasting between 10 – 100 seconds and at intervals of 10 – 90 minutes. In extreme situations, when there is no wet organic waste fed to the reactor, which may be the case for black water installations outside the tourist season, only the recirculation, mode 2) takes place until all organic material is digested.

Even though the recirculation operation preferably may be controlled by a PLC based on the instant load detected, as described above, the reactor may be operated based on other data control means and further using some kind of detector such as ultra sound, radar or possibly photo detector to reveal build up of sludge on the surface in chamber I and then trigger the recirculation mode operation based on such detection.

Depending on different parameters and factors such as capacity requirements, type of wet organic waste and purification requirements, the use of a reactor according to the invention may include two or more reactors connected in series or in parallel, or the chambers of the reactors may be connected in series or parallel.

Claims

1. Anaerobic reactor for the treatment of wet organic wastes, such as black water from households, manure, sludge and slurries, including a closed vessel or housing (10) preferably provided with a detachable lid, further including an inlet (8) for the wet organic waste and an outlet (7) for purified water and an outlet (12) for produced gas,

c h a r a c t e r i s e d i n t h a t

the reactor is divided by a partition wall (1) into at least two chambers, a first chamber I and a second chamber II, interlinked by an inflow arrangement (6, 13), where the first chamber I at its lower end is provided with the inlet (8) for the organic waste feed and the chamber II at its upper end is provided with the outlet (7) for purified water, and where the first chamber I is provided with a 3-phase separator (2) and means (3, 14, 5) for recirculation of floating particles/sludge in the first chamber I, wherein the means (3, 14, 5) for recirculation include a slanted deflection plate (3) provided above the 3-phase separator (2).

2. Anaerobic reactor according to claim 1,

c h a r a c t e r i s e d i n t h a t the inflow arrangement includes one or more overflow inlets(6) at the upper part of the partition wall (1), each connected with a vertical duct (13) stretching towards the bottom of chamber II and thereby passing the partly digested waste to the bottom of chamber II.

3. Anaerobic reactor according to claim 2,

c h a r a c t e r i s e d i n t h a t in conjunction with each vertical duct (13) and the one or more overflow inlets (6), there is provided a flanged opening (23) for inspection and cleaning/hosing of the inlet and duct in case of build-up of floating particles/sludge.

4. Anaerobic reactor according to any of claims 1 - 3,

c h a r a c t e r i s e d i n that the 3-phase separator (2) is integrated in the partition wall (1) below the one or more overflow inlets (6) for the inflow of organic feed from chamber I to chamber II.

5. Anaerobic reactor according to claim 4,

c h a r a c t e r i s e d i n t h a t the 3-phase separator (2) is protruding outwards from the partition wall (1) in a v-shaped form.

6. Anaerobic reactor according to claims 1 - 5,

c h a r a c t e r i s e d i n t h a t the slanted deflection plate (3) provided above the 3-phase separator (2), has a vertical upper part (19), the slanted deflection plate (3) partly overlapping the separator, which stretches across the vessel or housing (10) and which is designed to deflect upwardly floating organic particles towards a circular or polygonal collection funnel (14) at the opposite side of chamber I and at the same time reducing the open surface area of the floating particles/sludge in chamber I.

7. Anaerobic reactor according to claim 6,

c h a r a c t e r i s e d i n t h a t the collection funnel (14) as such is a plate stretching across chamber I and where a vertical duct (5) is connected to an opening in a plate (14) and further to the outside of the vessel or housing (10).

8. Anaerobic reactor according to claims 1 - 7,

c h a r a c t e r i s e d i n t h a t the recirculation of the floating particles/sludge in chamber I is obtained by means of an external pump (22) connected with its suction side to the duct (5) and further connected to the inlet (8) of the reactor at its pressure side whereby the recirculated fluid is returned to the bottom end of chamber I.

9. Method of operating an anaerobic reactor as defined in the device claims 1 – 8,

c h a r a c t e r i s e d i n t h a t the anaerobic reactor (20) is operated sequentially in two modes; an operating mode where the wet organic waste flows from the inlet (8) through the first chamber I, past the 3-phase separator, and further through the overflow inlets (6) and through the second chamber II to the outlet (7), and a second, recirculation mode where the floating

particle/sludge is deflected by the plate (3) towards the recirculation outlet (14) and is fed back to the first chamber I by means of the pump (22).

10. Method of operating an anaerobic reactor according to claim 9,

c h a r a c t e r i s e d i n t h a t the operation of the reacor is preferably controlled based on an algorithm calculating the instant detected load of the reactor.

11. Method of operating an anaerobic reactor according to claims 9 and 10,

c h a r a c t e r i s e d i n t h a t the waste feed and recirculation mode of operation is performed as pulsations.

12. Method of operating an anaerobic reactor according to claims 9 and 10,

c h a r a c t e r i s e d i n t h a t reactor is operated based on a detector such as ultra sound, radar or photo detector to reveal build-up of floating particles/sludge on the surface in chamber I and then trigger the recirculation mode operation based on such detection.

13. Use of a reactor according to claims 1 – 8 or method claims 9 - 12 including two or more reactors connected in series or parallel to increase capacity or performance.

14. Use of a reactor according to claims 1 – 8 or method claims 9 - 12 including two or more reactors where the respective chambers I or II are connected in series or in parallel.