Integrated process for the production of bio-oil from sludge coming from a wastewater purification plant

Abstract

Integrated process for the production of bio-oil from sludge coming from a wastewater purification plant comprising the following steps: (a) sending wastewater to said purification plant obtaining sludge; (b) subjecting the sludge obtained in said step (a) to liquefaction, obtaining a mixture Including an oily phase consisting of bio-oil, a solid phase and an aqueous phase; (c) sending the aqueous phase obtained in said step (b) to said purification plant. The bio-oil (or bio-crude) thus obtained can be advantageously used in the production of bio-fuels which can be used as such, or in a mixture with other automotive fuels. Otherwise, said bio-oil (or bio-crude) can be used as such (bio-fuel), or in a mixture with fossil fuels (combustible oil, coal, etc.), for the generation of electric energy or heat.

Claims

1. Integrated process for the production of bio-oil from sludge coming from a wastewater purification plant, comprising the following steps: (a) sending wastewater to said purification plant obtaining sludge; (b) directly subjecting the sludge obtained in said step (a) to liquefaction obtaining a mixture comprising an oily phase consisting of bio-oil, a solid phase and an aqueous phase; and (c) sending the aqueous phase obtained in said step (b) to said purification plant.

2. Integrated process according to claim 1, wherein said sludge is selected from primary sludge, biologic sludge produced in purification plants of civil and/or industrial wastewater, or mixtures thereof.

3. Integrated process according to claim 1, wherein said sludge is used in a mixture with other materials selected from the group consisting of: urban solid waste selected from organic material coming from the sorted waste collection, organic material selected from not sorted urban solid waste, or mixtures thereof; or mixtures of said organic material with pruning cut-offs and/or agricultural residue; residue and/or scraps coming from agricultural and/or zootechnical activities; residue and/or scraps coming from the agricultural/food industry; residue and/or scraps coming from agricultural processes, from forestation and/or from silviculture; and oily by-products such as oils and/or fats, coming from the preliminary treatment of wastewater; mixtures thereof.

4. Integrated process according to claim 3, wherein said sludge is used in a mixture with oily by-products coming from the preliminary treatment of wastewater.

5. Integrated process according to claim 3, wherein said urban solid waste, and/or said residue and/or scraps coming from agricultural and/or zootechnical activities, and/or said residue and/or scraps coming from the agricultural/food industry, and/or said residue and/or scraps coming from agricultural processes, from forestation and/or from silviculture, or mixtures thereof, are treated by subjecting them to a preliminary grinding or size-sorting process before subjecting them to the liquefaction step (b).

6. Integrated process according to claim 1, wherein said liquefaction step (b) is carried out at a temperature ranging from 150 C. to 350 C.

7. Integrated process according to claim 6, wherein said liquefaction step (b) is carried out at a temperature ranging from 250 C. to 320 C.

8. Integrated process according to claim 1, wherein said liquefaction step (b) is carried out at a pressure ranging from 5 bar to 170 bar.

9. Integrated process according to claim 8, wherein said liquefaction step (b) is carried out at a pressure ranging from 35 bar to 120 bar.

10. Integrated process according to claim 1, wherein said liquefaction step (b) is carried out for a time ranging from 5 minutes to 240 minutes.

11. Integrated process according to claim 10, wherein said liquefaction step (b) is carried out for a time ranging from 15 minutes to 180 minutes.

12. Integrated process according to claim 1, wherein said oily phase, said solid phase and said aqueous phase included in the mixture obtained in said step (b) are separated by gravitational separation, filtering, or centrifugation.

13. Integrated process for the production of bio-oil from sludge coming from a wastewater purification plant, consisting essentially of: (a) sending wastewater to said purification plant obtaining sludge; (b) subjecting the sludge obtained in said step (a) to liquefaction obtaining a mixture comprising an oily phase consisting of bio-oil, a solid phase and an aqueous phase; and (c) sending the aqueous phase obtained in said step (b) to said purification plant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will in any case be more evident from the following detailed description of preferred embodiments of the same, given purely as a non-limiting example, with reference to the attached drawings, wherein:

(2) FIG. 1, for comparison, shows an embodiment of a civil wastewater purification plant; and

(3) FIG. 2 shows an embodiment of a purification plant to implement the integrated process object of the invention.

(4) According to a typical implementation of the purification process of civil wastewater, illustrated in FIG. 1, urban wastewater is fed to a preliminary treatment (for example, coarse solid screening, grit removal, oil separation) obtaining oils and/or fats, which are fed to a processing plant of industrial wastewater, and an aqueous phase which is sent to wastewater processing, obtaining sludge which can be used, for example, for composting, or as additives for cements, and water for irrigation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) According to a typical implementation of the integrated process object of the present invention, urban wastewater is sent to a preliminary treatment (for example, coarse solid screening, grit removal, oil separation) obtaining oils and/or fats and a first aqueous phase. Said first aqueous phase is sent to wastewater treatment obtaining water for irrigation and sludge. The sludge thus obtained, in a mixture with the oils and/or the fats obtained from said preliminary treatment, is sent to the liquefaction step obtaining a mixture including an oily phase consisting of bio-oil, a solid phase and a second aqueous phase. Said mixture is fed to the phase separation step obtaining: an oily phase consisting of bio-oil, a solid phase comprising organic and/or inorganic residues and a second aqueous phase comprising part of the dissolved organic material coming from said sludge and other inorganic compounds (for example, nitrates, phosphates, carbonates). Said solid phase can be disposed of in a landfill, or it can be exploited by direct combustion obtaining heat and/or electric energy which can be used in said liquefaction step (b), and ashes which can be sent to the landfill, or it can be used as inorganic starting material in the building industry, or in the ceramic industry. Said second aqueous phase is directly sent to the wastewater processing.

(6) During liquefaction a gaseous phase (not shown in FIG. 2) comprising CO.sub.2, gaseous hydrocarbons having from 1 to 4 carbon atoms, or other gases is also produced, which phase can be separated, for example, by depressurisation of the pressurised vessel in which said liquefaction is carried out, before sending the mixture (oily phase+solid phase+second aqueous phase) obtained after liquefaction to the phase separation section. The gaseous phase thus obtained can be fed to further processing in order to exploit the combustible organic component thereof.

(7) The bio-oil thus obtained can be fed to subsequent processing phases to transform it, for example, into bio-fuel through further treatments, for example, hydrogenation or cracking (not shown In FIG. 2).

(8) In order to better understand the present invention and to put into practice the same, in the following some non-limiting illustrative examples of the same are reported.

EXAMPLE 1 (COMPARATIVE)

(9) A reference plant for urban wastewater purification (white and black waters, rainwaters) has been used, which processes 100 million m.sup.3/year of wastewater. The wastewater has undergone a preliminary treatment flowing through coarse solid screening, grit removal and oil separation sections. From these sections there have been obtained, among the other by-products, about 282 ton/year of oils and fats which have been sent to processing plant of industrial wastewater and a first aqueous phase. Said first aqueous phase has been sent to wastewater processing obtaining sludge and purified water for irrigation. The sludge obtained from the above-said processing (aerobic bacterial oxidation) has been collected obtaining 46,000 ton/year of sludge (at 32% dry contents) which have been sent for composting.

EXAMPLE 2 (INVENTION)

(10) A purification plant of urban wastewater (white and black waters, rainwaters) has been used, which processes 100 million m.sup.3/year of wastewater, integrated with a bio-oil production plant through a liquefaction step.

(11) The 46,000 ton/year of wet sludge and the 282 ton/year of oils and fats have been unified and sent, continuously, to the liquefaction step, i.e. to a tubular reactor. The liquefaction step has been carried out at 310 C. (reactor inner temperature), at 110 bar (reactor inner pressure), for about 1 hour.

(12) The reaction crude has been separated, continuously, in a gravitational separator, obtaining the following phases: an aqueous phase (i.e. second aqueous phase) (31,100 ton/year) which has been sent directly to said purification plant of urban wastewater and which has turned out to be equal to 0.03% in volume compared to the total volume of the wastewater processed in said purification plant (said sending implied no change in the performance of said purification plant, since waters fully complying with the specifications required by the law have been obtained); a solid phase consisting of a solid residue (7,916 ton/year) which has been sent to a waste-to-energy plant (said solid phase has turned out to represent 17% by weight compared to the total weight of the solids which should have been processed in a purification plant non integrated with the production of bio-oil according with the present invention); an oily phase consisting of bio-oil (5,690 ton/yearequal to about 118 barrels/day) usable in the automotive field; a gaseous phase which has been sent to energy exploitation based on the residual calorific power thereof.

EXAMPLE 3 (INVENTION)

(13) An urban wastewater purification plant (white and black waters, rainwater) has been used, which processes 100 million m3/year of wastewater integrated with a plant for the production of bio-oil through a liquefaction step. The amount of urban waters is produced by an urban area having about 1-million population equivalent. Said urban area produces also, as sorted waste collection, about 90,000 ton/year of organic fraction of solid urban waste (FORSU) at 35% dry contents.

(14) The 46,000 ton/year of wet sludge, the 282 ton/year of oils and fats and the 90,000 ton/year of FORSU have been unified and sent, continuously, to the liquefaction step, i.e. to a tubular reactor. The liquefaction step has been carried out at 310 C. (reactor inner temperature), at 110 bar (reactor inner pressure), for about 1 hour.

(15) The reaction crude has been separated, continuously, In a gravitational separator, obtaining the following phases: an aqueous phase (i.e. second aqueous phase) (94,300 ton/year) which has been sent directly to said purification plant of urban wastewater and which has turned out to be equal to 0.08% in volume compared to the total volume of the wastewater processed in said purification plant (said sending implied no change in the performance of said purification plant, since waters fully complying with the specifications required by the law have been obtained); a solid phase consisting of a solid residue (13,435 ton/year) which has been sent to a waste-to-energy plant (said solid phase has turned out to represent 10% by weight compared to the total weight of the solids which should have been processed in a purification plant non integrated with the production of bio-oil and with the sorted waste collection (FORSU) according to the present invention); an oily phase consisting of bio-oil (24,494 ton/yearequal to about 500 barrels/day) usable in the automotive field; a gaseous phase which has been sent to energy exploitation based on the residual calorific power thereof.

EXAMPLE 4

(16) In a laboratory plant with active sludge (volume: 4 litres) the sludge coming from a purification plant of urban wastewater containing 6 g/litre of MLTSS (total suspended solids) has been loaded.

(17) Then the system has been fed with a liquid substrate which simulates the domestic sewage having the following characteristics: saccharose=0.4 g/litre; buffer solution at pH=7; loading COD (Chemical Oxygen Demand)=320 mg/litre.

(18) Once a constant degrading capacity (acclimatisation) has been verified, the charge to be purified has been added with the second aqueous phase coming from the liquefaction of the sludge+oils and fats obtained as described in Example 2, at a concentration of 0.03% compared to the total aqueous charge (sludge load equal to 0.016 Kg.sub.BOD/Kg.sub.MLTSS).

(19) The whole has been maintained at room temperature for 7 days, controlling the purifying capacity of the system through the analysis of the outgoing COD. The purifying capacity of the system in the entire period has been kept, providing purified water complying with legal requirements with an outgoing COD well below 100 mg/litre.

(20) Then, both the flow rate and the concentration of the aqueous phase have been increased up to 0.1 Kg.sub.BOD/Kg.sub.MLTSS, corresponding to a concentration of incoming waters equal to 0.3% compared to the total aqueous charge (i.e. 10 times above the initial one), in order to verify both the maximum working limit of the system and any load stress. The test has lasted in total about one month with no alteration in the purifying capacity of said purification plant of urban wastewater.