GR1009924B - Waste treatment and diapers pre-treatment unit for the recovery of reusable materials and the production of gaseous biofuels and soil improvers - Google Patents

Abstract

The invention relates to a holistic approach process using disposable diapers in the production of gaseous biofuels and soil conditioners. Said process involves: the pretreatment of disposable diapers or personal hygienic products for the recovery of reusable plastics, the separation of biodegradable materials in the form of hydrolyzate from plastics streams, the separation of the superabsorbent polymer, the merge of the hydrolyzate with other biodegradable organic waste such as foodstuff unfit for human consumption (ABT), for the production of gaseous biofuels such as methane (ch4), hydrogen (h2) and / or mixtures thereof and the production of compost with the use of anaerobic runoff. An alternative process is also presented herein, using the disposable diaper hydrolyzate as the sole supply for the production a soil improver via the anaerobic reactor’s runoff as well as of gaseous biofuels such as methane (ch4), hydrogen (h2) and / or mixtures thereof.

Description

Method of waste treatment and pre-treatment of disposable diapers for the recovery of reusable materials and the production of gaseous biofuels and soil conditioner.

DESCRIPTION

FIELD OF THE PATENT

The present invention relates to the pre-treatment of disposable diapers for the recovery of reusable plastics and the separation of their biodegradable components and to methods of treating them together with other biodegradable organic wastes, or as a single feed stream, through anaerobic digestion and composting of the solid fraction of the anaerobic runoff. Disposable diapers include both infant and adult incontinence products, which differ primarily in their percentage of cellulose content.

BACKGROUND OF THE PATENT

A major problem in urban areas is the production of solid waste and its treatment, as, at least in Europe, various guidelines have been issued on solid waste management. European Directive 2008/98/EC defines the following hierarchy in waste management: prevention, preparation for re-use, recycling, other forms of recovery (such as energy recovery) and disposal, while Directive 1999/31/EC of 31 April 1999 regarding with landfilling of waste places significant limitations on the disposal of biodegradable materials in landfills. According to the latest directive, by 2016 biodegradable municipal waste ending up in landfills should have been reduced to 35% of the total quantity (by weight) of biodegradable municipal waste produced in 1995 (reference year). Disposable diapers are convenient for consumers, but they are characterized by a short shelf life. In Europe, in 2013 for example, the estimated amount of used disposable diapers was 4 million tons, corresponding to 1.7 % of total municipal waste and 0.5 % of total solid waste.

Diapers usually consist of a four-layer structure that allows for the transport and distribution of moisture in a basic absorbent layer. The first layer, which is in contact with the skin, is usually made of polypropylene (PP) and rarely of polylactic acid (PLA) and allows rapid transfer of fluids to the next layer. The next layer is called the acquisition and distribution layer (ACD), it absorbs and stores liquids before they diffuse into the absorbent layer of the diaper, while at the same time ensuring their spread over a larger area to maintain the low humidity of the diaper. previous layer. Super absorbent polymers (SUPP) require a short period of time to fully absorb all the liquid. Therefore, the presence and effectiveness of the DPF plays an important role in moisture management. The SPD usually consists of PP, PLA and nonwoven fabrics. The third and most important layer is an absorbent layer, consisting of a superabsorbent polymer (SUPP) as well as a mixture of cellulose fibers (fluffy pulp). The YAP can absorb large amounts of liquid compared to its mass (up to 1000% of its weight in the case of water) and swell. Common PAHs are generally white hygroscopic materials that resemble sugar (Zohuriaan-Mehr & Kabiri, 2008). This material is mainly responsible for the absorbency of the diaper. The final layer (backsheet layer) provides a liquid-impermeable barrier to limit moisture within the diaper structure and is primarily composed of polyethylene (PE), polyester, or nonwoven fabric. A small percentage of adhesives, dyes/prints and tapes can also be found in most diapers (EDANA, 2015). The composition of the diaper changes according to the use for which it is intended. Baby diapers contain a significantly smaller fraction of organic matter compared to adult diapers, while at the same time their percentage of PAD is twice that of adult diapers. Disposable diapers are sold in different sizes for different user weights. The biodegradable part of a used disposable diaper consists primarily of organic matter, including cellulosic (fluffy) pulp, feces, and urine. According to experimental and published data (Col aI . , 2013), the average weight of a clean baby diaper is about 40 g, while the average weight of a used baby diaper is 170 g (same data).

Although organic materials are present in a significant proportion in this type of waste, they are still disposed of in landfills or incinerated (Coet al . , Various methods have

recommended for the treatment of waste such as disposable nappies. In U.S. Pat. No. 5,558,745 issued in 1996 on September 24, Conway et al describe a processing method for absorbent sanitary products with the purpose of utilizing the resulting materials for recycling or reuse. They use a solid fraction disinfection stage with antimicrobial agents, a solid fraction separation stage with hydro-cyclones, posi-flow centrifugal cleaners and core cleaners, a stage where the reticulated superabsorbent polymer is separated from the cellulosic fraction using similar processes and filtration.

In U.S. Pat. No. 5,429,31 1 issued Jul 4, 1995, Y Cina and E Parag also describe a methodology for separating the cellulosic content of used diapers for recycling. This particular patent focuses on the selective collection of cellulose on a rough surface by separating water and effluents.

Other patents that have been developed that are primarily aimed at recovering materials from disposable diapers or similar materials are: U.S. Pat. No. 5,618,003 issued in 1997 on Apr. 8, DE 19821473 A1 issued in 1998 on Nov. 25, US Patent No. 8,979,005 B2 issued 2015 Mar. 17, and US Patent No. 4,500,040 issued in 1985 on February 19.

The present invention describes a method that involves the pretreatment and processing of disposable diapers and other organic biodegradable materials for their utilization as feedstock to produce gaseous biofuels, soil conditioner and a separate stream of plastics for recycling.

DESCRIPTION OF THE PROPOSED ARRANGEMENT FOR THE PROCESS

Fig. 1A shows a diagram of the process, including the pre-treatment of disposable diapers (DSDs), the anaerobic treatment of their biodegradable fraction together with other organic wastes, non-edible food (NDF) is illustrated as an example, and the utilization of anaerobic runoff for the production of soil conditioner. It should be noted that the individual elements of the process are devices and machines with known and established methods of operation, unless otherwise stated.

In particular, in Fig. 1A the elements included are: (1) refrigerator, (2) crusher, (3) grinding machine, (4) shredder, (5) washing device, (6) tank for collecting the washing runoff, ( 7) settling tank, (8) YAP collector, (9) pasteurizer/hydrolysis tank, (10) acid feed tank, (11) base feed tank, (12) feed tank, (13) oxygenating reactor, (14) methanogenic reactor , (15) rapid water heater, (16) solid/liquid separator, (17) composter.

The first stage of the process consists of the physical pre-treatment of ABT and PMX which can optionally be kept in a refrigerator (1) in order to avoid unpleasant odors and preserve their physicochemical characteristics. Normally, ABTs and PMCs can be processed directly after collection or kept in closed containers prior to processing. The particle size of the pre-treated waste must be small enough for the remainder of the process to be operable. This is achieved in two or more sub-processes, one for MSW and one or more for other biodegradable wastes, ABT is shown as an example. The ABT or similar materials are fed to a crusher (2) which produces a product with a reduced particle size (5-8 mm) and are then further processed with a milling machine or similar device (3) which results in the production of a material which looks like a paste (0.075-0.15 mm particle size). Before further processing, PMCs should be cut into small pieces using a slicer or similar device (4). The shredded disposable diapers are fed to a washer (5) where they are washed with tap water and chemical reagents that cause the LAP to dehydrate and shrink in volume to aid its subsequent separation from biodegradable materials. Reagents that can be used for this purpose are alkali metals, alkaline earth metals, aluminum, ferrous copper, ferric iron and zinc. Typically, MgCl2 and CaCl2 are used, taking into account the cost of the reagents, the safety of personnel in handling them, and the possible negative effects they may have on anaerobic digestion. In any case, other reagents and combinations thereof should not be considered excluded from this process. Plastics are typically recovered from the inside of the washer (5) after one or more wash cycles due to their particle size compared to the aggregated MSW and other biodegradable materials that pass through the wash drum holes. The temperature of the water used during the washing step should not exceed the melting temperature of the plastics, paints, glues and other materials of the diaper. The stream containing the NAP, cellulose fibers and faeces/urine is collected in a tank (6) and then fed to a settling tank (7) usually using a pump or similar equipment. There, with proper agitation, the cellulose fibers remain in suspension, while the YAP remains at the bottom of the tank. Then, the SAF is removed by removing an appropriate amount of water-SAF mixture from the bottom of the settling tank into a separate tank equipped with a bag filter or other solids separation device, the SAF collection vessel (8). The YAP is assembled in the YAP collector, while the liquid and cellulose fibers from (7) and (8) are fed to a pasteurization/hydrolysis tank (9). This device optionally functions as a pasteurizer, depending on the nature of the organic waste to be treated and the legislation governing its treatment, e.g. animal by-products and meat fall into this category for EU countries, according to regulation (EE) No 142/201 1. Similarly, the nature of the waste to be treated indicates whether hydrolysis is required and the device will be used for this the purpose. The ABT paste is then added to the liquid cellulose mixture and, after adding a sufficient amount of acid from the corresponding feed tank (10), depending on the pH value of the mixture, the mixture is heated at 70 °C for 1 hour or at different conditions duration and temperature that could provide the same effect. The mixture is then cooled and the pH adjusted by addition of base from the base feed tank (11). Finally, through a second pump or similar device, the pre-treated material is fed to the anaerobic digestion unit. The 2nd stage of the process is anaerobic digestion. The pre-treated material from PMXs and ABTs or other biodegradable material is mixed in a homogenizer (mixing tank) (shown in Fig. 1A as two separate feed tanks) (12) and automatically pumped to an oxygenating reactor (13). The effluent of the acidogenic reactor is then pumped to the methanogenic reactor (14). At this point, it should be noted that the anaerobic digestion process can operate either as a two-stage system, i.e. a separate oxygen reactor followed by a methanogen reactor, or in a single stage (one reactor), bypassing the oxygen reactor, depending on the characteristics of the raw material to be processed. The produced biofuels can be exploited for various applications, such as the production of electricity and thermal energy using a combustion engine for combined heat and power (CHP) by burning the mixture of biofuels (methane and hydrogen) after appropriate treatment (e.g. desulfurization etc.), supply to the central natural gas distribution system, use as automobile fuel after compression, etc. The water circulator rapid-fire heater (15), or other hot water supply device, is used to regulate the temperature of both the methanogen and oxygen reactor. The hot water circulates in the double walls of the reactors or in heat transfer devices to the contents of the reactors, such as for example heat exchangers or hot water transfer ducts. Hot water can also be provided to heat reactors (e.g. in full-scale units) by recovering heat from the combustion of the produced biofuels. The final stage of the process is the management of the effluent stream anaerobically with or without solids separation. In the first case, the methanogenic reactor effluent (anaerobic effluent) is fed to a solid/liquid separator (16) to produce two separate streams, namely one with an increased solids concentration (typically 15-25 wt% solids) and one liquid stream containing the components of anaerobic effluent after solids separation. The digestate produced by the reactor could alternatively be treated as a single stream without solid/liquid separation for applications such as liquid lubrication. The liquid stream after solids separation can be directed directly to the sewer system or can be used as a liquid fertilizer with or without further treatment, such as treatment through filtration membranes. Dewatered sludge (solid fraction of anaerobic effluent) can be used directly as compost material or suitably mixed with other organic residues or dry material/bulking agent such as wood pellets and composted in piles or other suitable configurations. In the case of using a mechanical composter, it can operate manually or fully automatically and be continuous or intermittent. All stages of the processes are controlled by specific operating times that depend on the hydraulic residence time of the methanogen and oxygen reactor, among other parameters.

An alternative to the above arrangement is illustrated in Fig. 1B where only PMXs are used as process feed. The difference of this proposed process is that (9) pasteurization/hydrolysis tank, (10) acid feed tank, (11) base feed tank are usually absent, as there is no need for pasteurization/hydrolysis of PMX hydrolyzate and pH adjustment. In addition, (13) the acidogenic reactor and (14) the methanogenic reactor are replaced by an Up Flow Anaerobic Sludge Blanket Reactor (UASB) or other high rate type bioreactor (18) for biogas production.

It should be noted that various sensors measuring temperature, pH, gas analyzers and/or other measuring devices could be used in the process and could be connected to monitoring and recording devices to control the operating parameters. Two examples are given to better understand the process.

EXAMPLE I

Used baby diapers from a kindergarten in Greece and unfit food (UNF) from a Greek Super Market chain were collected and used as raw material for the waste treatment plant. ABTs consisted of various fruits and vegetables that cannot be sold. The operating scenario of this example is: 18 diapers per day, 3 liters of tap water per diaper, 36 kg ABT per day, 2 days hydraulic residence time in the oxygenating reactor and 20 days in the methanogenic reactor at a constant operating temperature of 37 ± 0.2 °C. For this amount of PMX and the corresponding amount of YAP, 47.7 g of CaCl2*2H2O and 192.06 g of MgCl2*6H2O were used for the pre-treatment. The results of 97 days of operation showed 75.3 % COD removal and 93.7 % carbohydrate degradation, while H2 and CH4 production reached satisfactory levels. Biogas production was stable at 0.65 L CH4/(L reactor d) (12.9 L CH4/L feed) with methane corresponding to 62.2% of the biogas produced by the methanogenic reactor, while the yield of the oxygenating reactor in H2 reached 0.86 L H2 / L feed -

EXAMPLE II

Used adult diapers from a nursing home in Spain and unfit food (UNF) from a Spanish Super Market chain were collected and used as raw material for the waste treatment plant. FFAs consisted of non-edible meats, fish, confectionery, bread and vegetables. The operating scenario of this example is: 6 diapers per day, 10 L tap water per diaper, 5.22 kg ABT per day, 2 days hydraulic residence time in the oxygen reactor and 20 days in the methanogen reactor at an operating temperature of 37 ± 0.2 °C. For this amount of PMX and the corresponding amount of YAP, 17.49 g of CaCl2*2H2O and 70.42 g of MgCl2*6H2O were used for the pretreatment. The removal of COD and carbohydrates was also at satisfactory levels, of 67.6 % and 97.1 % respectively. The hydrogen production in the oxygenating reactor reached 0.74 L H2/(Lreactor d) (1.47 L H2/L feed), while the methane productivity was 0.56 L C H 4/(Lreactor d) (11.15 L CH4/L feed).

Although the foregoing examples presented by the inventors show the optimal operating conditions of the process of the invention, the application of the above invention is not limited thereto. It is stated that various additions, modifications and rearrangements of the conditions of the present invention may be made without departing from the scope and purpose of the original idea of the invention.

Claims (14)

1. A method of waste treatment and pre-treatment of disposable diapers for the recovery of reusable materials and the production of gaseous biofuels and soil conditioner through anaerobic digestion of their biodegradable content comprising the following steps: - the mechanical treatment of the waste in order to facilitate the biological process that follows, - the pretreatment of disposable diapers in order to separate reusable plastics and superabsorbent polymer (SUPP) that could cause problems in bioreactors due to its swelling, - the biological process of anaerobic digestion, - the production of soil conditioner from the solid fraction of the effluent of the anaerobic reactor (anaerobic effluent). 2. A waste treatment method according to claim 1, wherein an aqueous solution of at least one of the metals of the main groups or transition elements of the periodic table can be used in various proportions to pre-treat the diapers and de-swell the YAP as a pre-treatment for the anaerobic digestion that follows. 3. A waste treatment method according to claim 1, in which the YAP is separated from the cellulosic hydrolyzate produced by the pretreatment of the disposable diapers in the settling tank. 4. A waste treatment method according to claim 1, in which cellulose from disposable diapers and/or cellulose hydrolyzate can be hydrolyzed regardless of whether organic or inorganic acids or enzymes are added, under suitable temperature and time conditions in the pasteurizer/tank hydrolysis. 5. A waste treatment method according to claim 1, in which waste can be pasteurized regardless of whether organic or inorganic acids or enzymes are added, under appropriate temperature and time conditions in the pasteurizer/hydrolysis tank. A waste treatment method according to claim 1, in which base can be added to the pasteurizer/hydrolysis tank to adjust the pH value. 7. A waste treatment method according to claim 1, wherein anaerobic digestion of PMX hydrolyzate together with other biodegradable organic waste is carried out in one stage (using one reactor) or two stages (using two reactors) or more stages where the reactors they are interconnected. 8. A waste treatment method according to claim 1, in which only PMX hydrolyzate is used as raw material for the anaerobic digestion, which can be carried out in one stage (using one reactor) or two stages (using two reactors ) or more stages where the reactors are interconnected. 9. A waste treatment method according to claim 1, wherein at least 0.5 L of water is added per diaper in order to facilitate the washing process and the separation of YAP, plastics and cellulose. 10. A waste treatment method according to claim 1, wherein the biodegradable organic waste as well as the inedible food is mechanically treated to reduce its size to facilitate its flow through the pipes and its biological treatment. A waste treatment method according to claim 1, wherein the anaerobic digestion is carried out in mesophilic or thermophilic conditions. 12. A waste treatment method according to claim 1, wherein the disposable diapers can be co-digested with other biodegradable organic waste in various proportions. 13. A waste treatment method according to claim 1, wherein the organic fraction of the waste is used to produce gaseous biofuels, the plastics fraction can be recycled and the solid fraction of the anaerobic effluent can be used to produce soil conditioner. 14. A waste treatment method according to claim 1, wherein in addition to the solid fraction of the anaerobic effluent, other organic residues and/or bulking agents are added, including lignocellulosic waste and wood, or pellets.