Title of Invention : A method for processing of biodegradable wastes and/or mixed wastes with content of biodegradable matter, especially industrial and municipal biodegradable wastes and mixed municipal wastes

Technical Field

[0001 ] Present invention relates to a method for processing of biodegradable wastes and/or mixed wastes with content of biodegradable matter, especially industrial and municipal biodegradable wastes and mixed municipal wastes.

Background Art

[0002] Industrial and municipal wastewaters are led to wastewater treatment plants.

After mechanical pre-treatment, the wastewater passes to the biological stage, where during the decomposition of organic matter by microorganisms the biomass of microorganisms increases, part of which is subsequently discharged as excess sludge - biological sludge is formed. Excess biological sludge from the wastewater treatment is separated by concentration - sedimentation, and is further processed in a digestion process where aerobic or anaerobic digestion of biodegradable sludge takes place, also called sludge digestion and/or

stabilization. Sludge stabilization is a process in which the biodegradable sludge resulting from the wastewater treatment process decomposes in a controlled manner, reaches high biochemical stability - it stabilizes (it is no longer actively decomposing). The sludge management of wastewater treatment plants is currently technologically adapted solely to the treatment of biodegradable sludge originating from treatment of wastewaters containing mainly dissolved organic matter.

[0003] Solid floating wastes that are trapped on rakes during mechanical

pretreatment of wastewater, so-called rakings, are currently disposed of almost exclusively by landfilling. [0004] At present, biodegradable industrial and municipal wastes are typically recovered in the form of compost and sometimes recovered in biogas plants that use green matter as the feedstock.

[0005] Mixed wastes, especially mixed municipal wastes are sorted at present only partially, they contain up to 50% of biodegradable municipal wastes and water. Mixed municipal wastes are currently disposed of mainly by landfilling. Even in areas where biodegradable waste is currently collected separately, mixed municipal waste still contains a significant portion of biodegradable wastes that are disposed of by landfilling, which, for the biodegradable matter, is inefficient and environmentally inappropriate.

[0006] The object of the present invention is therefore to provide a method for

processing of biodegradable wastes and/or mixed wastes containing

biodegradable matter so as to maximize the efficient use of biodegradable matter, in particular from mixed wastes, and to significantly reduce the amount of waste going to landfills.

Summary of Invention

[0007] Said object of maximal efficient use of biodegradable matter is achieved by a method for processing of biodegradable municipal wastes and/or mixed municipal wastes with content of biodegradable substances according to the present invention. The method is characterized that the biodegradable wastes and/or mixed wastes with content of biodegradable matter are crushed to a fraction of up to 300 mm, the biodegradable matter is separated from the crushed wastes by pulperization or by pressing in the form of pulpous suspension. Then, undesirable solid matter is separated from the pulpous suspension. Such treated pulpous suspension is exposed to the ultrasound with frequency 20 kHz to 100 kHz, intensity of from 25 to 50 W/cm ² , while sonication dose of the ultrasound, depending on composition of the biodegradable matter, is to reach 1 to 9 kWh/m ³ of the treated suspension.

[0008] Ultrasonic micro cavitation pretreats biodegradable wastes into the state of pumpable suspension by disrupting the cell structures of plant, animal and bacterial origin. Such treated suspension formed by pretreated biodegradable wastes is a substrate that can be applied without significant modifications to the technology to the biological stage of wastewater treatment - into the sludge stabilization process at the wastewater treatment plant.

[0009] Activated sludge formed in the biological stage of wastewater treatment in wastewater treatment plants is preferably mixed into the pulpous suspension prior to ultrasonication.

[0010] Depending on needs and composition of the suspension, alkaline agents from the group Ca(OH)2, NaOH, KOH can be preferably added to the suspension or to the suspension mixed with the sludge to adjust pH of the suspension to the pH of 9 to 10.

Description of Embodiments

[0011 ] Biodegradable wastes and/or mixed wastes with content of biodegradable matter are reduced to a fraction of up to 300 mm. Biodegradable wastes and/or mixed wastes with content of biodegradable matter are mainly industrial and municipal biodegradable wastes and mixed municipal wastes, where these wastes can advantageously include rakings trapped on the rakes during mechanical pretreatment of waste waters. Preferably, metals can be separated by induction and magnetically from the reduced waste, while these can be recycled. Biodegradable matter in the form of pulpous suspension is separated from such reduced wastes either by pulperizing, in a pulper, or by pressing in a special press. Preferably, a light fraction, usable as a solid alternative fuel, can be separated from the waste residue which has not been transformed into the pulpous suspension, on the basis of the specific weight. The pulpous suspension is purified in gravity or centrifugal separator such that small residues of light and heavy impurities such as small pieces of wood, sand, glass, metals, bones, plastic, and the like are separated from the suspension.

[0012] Subsequently, obtained pulpous suspension produced either separately, or after mixing with excess sludge from wastewater treatment, before entering the process of aerobic or anaerobic digestion, i.e. the process of sludge stabilization is led, e.g. by pumping through a pipe, through a device emitting ultrasonic waves into the suspension. The ultrasound used has frequency of 20 kHz to 100 kHz, intensity of from 25 to 50 W/cm ² , while the sonication dose of the ultrasound is to be 1 to 9 kWh/m ³ of the treated suspension depending on the composition of the biodegradable matter. Ultrasonic waves cause micro cavitation in suspension, while resulting implosion causes high temperatures and pressure waves (up to 5000 °C, and 500 bar). High temperature and pressure shockwaves disrupt the cell walls of plant, animal and bacterial cells. Also, the structure of organic matter is disrupted and clusters of biodegradable matter in the aqueous solution are dispersed. As the result of disruption of organic structures of biodegradable matter and clusters, organic matter contained in the suspension, or the mixture of the suspension with excess activated sludge from wastewater treatment, decompose in digesters more rapidly and to a greater extent, whole generating more biogas compared to present state (up to 30%) and after the process of sludge stabilization is finished, less stabilized sludge, thus less dry matter, remains at the output. Due to the loss of organic matter in the stabilized sludge, the process of sludge dewatering is also more efficient.

[0013] In order to increase efficiency of the method and to speed it up, prior to

application of the ultrasound alkaline agents from the group Ca(OH)2, NaOH,

KOH can be added to the suspension to adjust pH of the suspension to the pH 9 to 10, whereby alkaline hydrolysis occurs. Ultrasonic waves in combination with alkaline hydrolysis are particularly efficient also on material with content of cellulose and other hardly degradable organic matter as well as on cells of microorganisms contained in the wastes.

[0014] Due to alkaline hydrolysis and/or ultrasonic resonance, the suspension, or the suspension mixed with sludge is homogenized, treated and sanitized to a form a substrate containing mainly dissolved organic matter having properties similar to activated biodegradable sludge from wastewater treatment. The substrate has physical and biological transformation characteristics (standardized properties and composition) similar to sludge from wastewater treatment.

Dry matter: 9-12%

Water content: 88-91 %

Loss on ingnition of dry matter: >80% No fragments of plastics

No sand and neither stones > 250 pm

[0015] The substrate can be used, for example, for the production of biogas and after digestion, resulting digestate can be used, for example, for the production of fertilizer supplements, all this without a change of the process technology of sludge stabilization at the wastewater treatment plant.

[0016] The suspension treated by the ultrasound, or the combination of alkaline

hydrolysis and ultrasound, can be produced outside wastewater treatment plants and then transported to the wastewater treatment plants for recovery in the process of sludge stabilization. Likewise, the technology can be provided directly in a wastewater treatment plant, where the suspension made from biodegradable industrial and municipal wastes and/or mixed municipal wastes is then

transported to the process by pipelines or tank vehicles, while the process can also preferably use the excess activated sludge from the biological process of wastewater treatment as described above.

[0017] The method of treatment and recovery of biodegradable municipal and other wastes and/or mixed municipal wastes with content of biodegradable matter in the waste water treatment technology, or biogas stations allows to reduce the time required for decomposition of organic substances, i.e. for sludge

stabilization, to increase usable capacity of digesters, i.e. it is possible to recover more efficiently more of organic suspension and/or sludge, to increase the efficiency of biogas production in sludge management of wastewater treatment plants or biogas stations where more biogas is produced from specific unit of raw material, to reduce the amount digestate at the output, to increase rate of dewatering of digestate - less residual organic matter in digestate means less bound water, to save the environment, where the recovery of biodegradable wastes will reduce production of greenhouse gases, to recover up to 50% of mixed municipal waste, to reduce costs of sorting and recovery of biodegradable wastes.

Industrial Applicability [0018] The method according to this invention is the most efficiently used in particular for the processing of biodegradable industrial and municipal wastes and/or mixed municipal wastes with content of biodegradable matter, together with the operation of waste water treatment plants.

[0019] Efficiency of the installation is due to thorough use of existing capacities of wastewater treatment plants, the use of organic matter from industrial and urban environments, and due to the reduction of resulting waste substances compared to current processes. Thus, the objective of the waste management program, the reduction of the amount of landfilled waste as well as higher energy production in the form of biogas from the produced organic pollution will be achieved. |