# US 2016/0257592 A1 · System and method for treating wastewater and resulting primary and biological sludge > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2016/0257592 A1 - Document ID: US20160257592A1 - Status: Published application - Kind: A1 - Application number: 15/058,559 - Filed: 2016-03-02 - Published: 2016-09-08 - Earliest claimed: 2015-03-02 - Assignees: Veolia Water Solutions & Technologies Support - Applicants: Veolia Water Solutions and Technologies Support - Inventors: Richard W. DiMassimo; Soren J. Hojsgaard - Web page: https://patentgrep.com/patent/US20160257592A1 ## CPC - C02F 11/04: Anaerobic treatment; Production of methane by such processes - C02F 11/18: by thermal conditioning (by pyrolysis C02F11/10) - C02F 11/185: {by pasteurisation} - C02F 1/025: {Thermal hydrolysis} - C02F 11/12: by de-watering, drying or thickening - C02F 2301/043: Treatment of partial or bypass streams - C02F 2301/046: Recirculation with an external loop - C02F 2301/066: Overpressure, high pressure - C02F 2303/06: Sludge reduction, e.g. by lysis - C02F: TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE (separation in general B01D; special arrangements on waterborne vessels of installations for treating water, waste water or sewage, e.g. for producing fresh water, B63J; adding materials to water to prevent corrosion C23F; treating radioactively-contaminated liquids G21F9/04; regeneration of reactants for recirculation into processes, see the relevant places for the processes) ## Abstract A method of treating primary sludge and activated sludge produced by a wastewater system is disclosed. A portion of the activated sludge is wasted to form biological sludge. The biological sludge is thermally hydrolyzed. The method entails cooling the thermally hydrolyzed biological sludge by mixing primary sludge with the thermally hydrolyzed biological sludge. Thereafter, the combined sludge is directed through a pasteurization process and then to an anaerobic digester which performs anaerobic digestion of the combined sludge. ## Claims ### Claim 1 A method of treating wastewater and resulting sludge comprising: subjecting the wastewater to primary treatment and producing primary sludge; after subjecting the wastewater to primary treatment, subjecting the wastewater to biological treatment and producing biological sludge; directing the biological sludge to a thermal hydrolysis unit and subjecting the biological sludge to a thermal hydrolysis process and producing thermally hydrolyzed biological sludge; mixing the primary sludge and thermally hydrolyzed biological sludge in a pressurized structure at a pressure greater than atmospheric pressure to form a sludge mixture; cooling the thermally hydrolyzed biological sludge in the pressurized structure by transferring sensible heat from the thermally hydrolyzed biological sludge to the primary sludge; transferring the mixture of primary sludge and thermally hydrolyzed biological sludge from the pressurized structure to a pasteurization unit and subjecting the sludge mixture to a pasteurization process; and after pasteurizing the mixture of sludge, transferring the mixture of thermally hydrolyzed biological sludge and primary sludge from the pasteurization unit to an anaerobic digester and subjecting the mixture of sludge to anaerobic digestion. ### Claim 2 (depends on 1) The method of claim 1 including reducing the temperature of the thermally hydrolyzed sludge by at least 80° C. by transferring sensible heat from the thermally hydrolyzed sludge to the primary sludge prior to the sludge mixture reaching the pasteurization unit. ### Claim 3 (depends on 1) The method of claim 1 wherein the pressurized structure includes a pressurized line leading from the thermal hydrolysis unit and wherein there are no heat exchangers engaged with the pressurized line; and the method includes transferring the thermally hydrolyzed biological sludge from the thermal hydrolysis unit through the pressurized line; and feeding the primary sludge into the pressurized line where the primary sludge and thermally hydrolyzed biological sludge are mixed and wherein substantially all cooling of the thermally hydrolyzed biological sludge is achieved by transferring sensible heat from the thermally hydrolyzed biological sludge to the primary sludge without the aid of heat exchangers engaged with the pressurized line. ### Claim 4 (depends on 1) The method of claim 1 including moving the thermally hydrolyzed biological sludge from the thermal hydrolysis unit into and through the pressurized structure that is operatively connected to a pressure-maintaining pump that is disposed downstream of the thermal hydrolysis unit and upstream from the pasteurization unit; wherein the pressure-maintaining pump maintains a pressure greater than atmospheric pressure in the pressurized structure between the thermal hydrolysis unit and the pump; and the method includes feeding the primary sludge into the pressurized structure at a point between the thermal hydrolysis unit and the pressure-maintaining pump and mixing thermally hydrolyzed biological sludge with the primary sludge in the pressurized structure. ### Claim 5 (depends on 4) The method of claim 4 wherein neither the thermally hydrolyzed biological sludge nor the sludge mixture is cooled by heat exchangers upstream of the pasteurization unit. ### Claim 6 (depends on 1) The method of claim 1 wherein subjecting the wastewater to primary and biological treatment produces a treated effluent and wherein the method includes mixing at least a portion of the treated effluent with the thermally hydrolyzed biological sludge or sludge mixture. ### Claim 7 A method of treating wastewater and resulting sludge comprising: subjecting the wastewater to primary treatment and producing primary sludge; after subjecting the wastewater to primary treatment, subjecting the wastewater to biological treatment and producing biological sludge; directing the biological sludge to a thermal hydrolysis unit and subjecting the biological sludge to a thermal hydrolysis process and producing thermally hydrolyzed biological sludge; bypassing the thermal hydrolysis unit with the primary sludge and not subjecting the primary sludge to the thermal hydrolysis process; wherein the temperature of the non-thermally hydrolyzed primary sludge is lower than the temperature of the thermally hydrolyzed biological sludge; after thermally hydrolyzing the biological sludge, mixing the thermally hydrolyzed biological sludge with the non-thermally hydrolyzed primary sludge to form a sludge mixture and transferring sensible heat from the thermally hydrolyzed biological sludge to the non-thermally hydrolyzed primary sludge in order to raise the temperature of the non-thermally hydrolyzed sludge and lower the temperature of the thermally hydrolyzed biological sludge; after mixing the thermally hydrolyzed biological sludge with the non-thermally hydrolyzed primary sludge, directing the sludge mixture to a pasteurization unit and pasteurizing the mixture of thermally hydrolyzed biological sludge and non-thermally hydrolyzed primary sludge in the pasteurization unit at a temperature of at least 70° C. for a period of at least 20 minutes; and after pasteurizing the mixture of sludge, transferring the mixture of thermally hydrolyzed biological sludge and non-thermally hydrolyzed primary sludge from the pasteurization unit to an anaerobic digester and subjecting the mixture of sludge to anaerobic digestion. ### Claim 8 (depends on 7) The method of claim 7 wherein subjecting the wastewater to primary and biological treatment produces a treated effluent, and wherein the method includes mixing at least a portion of the treated effluent with the thermally hydrolyzed biological sludge. ### Claim 9 (depends on 7) The method of claim 7 including pre-heating the non-thermally hydrolyzed primary sludge prior to the non-thermally hydrolyzed primary sludge being mixed with the thermally hydrolyzed biological sludge. ### Claim 10 (depends on 7) The method of claim 7 wherein subjecting the wastewater to primary and biological treatment produces a treated effluent, and mixing at least a portion of the treated effluent with the thermally hydrolyzed biological sludge; and including pre-heating the non-thermally hydrolyzed primary sludge prior to the non-thermally hydrolyzed primary sludge being mixed with the thermally hydrolyzed biological sludge. ### Claim 11 (depends on 7) The method of claim 7 including maintaining the temperature of the sludge mixture at 70° C. or higher prior to the sludge mixture entering the pasteurization unit by controlling one or more process variables that include: (1) the volumetric flow rate of the thermally hydrolyzed biological sludge, (2) the volumetric flow rate of the non-thermally hydrolyzed primary sludge, and (3) the temperature of the non-thermally hydrolyzed primary sludge. ### Claim 12 (depends on 7) The method of claim 7 wherein the pasteurization unit includes three batch reactors and the method include directing the sludge mixture to the three batch reactors and subjecting the sludge mixture to a pasteurization process in the three batch reactors. ### Claim 13 A system for treating wastewater and resulting sludge comprising: a primary treatment unit for treating wastewater and producing primary sludge; a biological wastewater treatment unit disposed downstream of the primary treatment unit and wherein the biological wastewater treatment unit produces biological sludge; a thermal hydrolysis unit operatively connected in the system for receiving biological sludge and thermally hydrolyzing the biological sludge; a pasteurization unit disposed downstream of the thermal hydrolysis unit; a pressurized line leading from the thermal hydrolysis unit for conveying the thermally hydrolyzed biological sludge from the thermal hydrolysis unit and wherein the pressure within the pressurized line is greater than atmospheric pressure; a primary sludge feed line for conveying primary sludge and communicatively connected to the pressurized line for conveying primary sludge into the pressurized line; wherein the primary sludge feed line bypasses the thermal hydrolysis unit resulting in the primary sludge not being subjected to thermal hydrolysis; a pump for pumping primary sludge through the primary sludge feed line into the pressurized line where the thermally hydrolyzed biological sludge and primary sludge are mixed to form a sludge mixture; wherein there is an absence of heat exchangers associated with the pressurized line such that the thermally hydrolyzed biological sludge being conveyed in the pressurized line is not cooled by heat exchangers and wherein the pressurized line is configured such that substantially all cooling of the thermally hydrolyzed biological sludge is accomplished by transferring sensible heat from the thermally hydrolyzed biological sludge to the primary sludge in the pressurized line; wherein the system is operative to transfer the sludge mixture from the pressurized line to the pasteurization unit where both the thermally hydrolyzed biological sludge and primary sludge undergo a pasteurization process; and an anaerobic digester disposed downstream from the pasteurization unit for receiving the mixture of sludge and performing an anaerobic digestion process on the mixture of sludge. ### Claim 14 (depends on 13) The system of claim 13 wherein a pressure-maintaining pump is operatively associated with the pressurized line and disposed downstream from the thermal hydrolysis unit for maintaining a pressure greater than atmospheric pressure in the pressurized line, and wherein the primary sludge feed line joins the pressurized line at a point between the thermal hydrolysis unit and the pressure-maintaining pump such that primary sludge is mixed with the thermally hydrolyzed biological sludge prior to the thermally hydrolyzed biological sludge being discharged from the pressure-maintaining pump. ### Claim 15 (depends on 14) The system of claim 14 wherein the primary treatment unit and the biological wastewater treatment unit produce a treated effluent and wherein the system includes a treated effluent feed line that is communicatively connected to the pressurized line at a point between the thermal hydrolysis unit and the pressure-maintaining pump. ### Claim 16 (depends on 13) The system of claim 13 including a heat exchanger associated with the primary sludge feed line for heating the primary sludge prior to the primary sludge being mixed with the thermally hydrolyzed biological sludge. ### Claim 17 (depends on 13) The system of claim 13 further including: wherein a pressure-maintaining pump is operatively associated with the pressurized line and disposed downstream from the thermal hydrolysis unit for maintaining a pressure greater than atmospheric pressure in the pressurized line, and wherein the primary sludge feed line joins the pressurized line at a point between the thermal hydrolysis unit and the pressure-maintaining pump such that primary sludge is mixed with the thermally hydrolyzed biological sludge prior to the thermally hydrolyzed biological sludge being discharged from the pressure-maintaining pump; wherein the primary treatment unit and the biological wastewater treatment unit produce a treated effluent and wherein the system includes a treated effluent feed line that is communicatively connected to the pressurized line at a point between the thermal hydrolysis unit and the pressure-maintaining pump; including a heat exchanger associated with the primary sludge feed line for heating the primary sludge prior to the primary sludge being mixed with the thermally hydrolyzed biological sludge; and one or more dewatering devices disposed upstream of the thermal hydrolysis unit and operative to receive biological sludge and to dewater the biological sludge; and wherein the one or more dewatering devices are operative in first and second modes wherein the first mode dewatered activated sludge is directed from the dewatering device to the thermal hydrolysis unit and in the second mode, the dewatered biological sludge is directed to a mixing tank and mixed with the primary sludge prior to the primary sludge being fed into the pressurized line. ### Claim 18 (depends on 1) The method of claim 1 further including: subjecting the wastewater to primary and biological treatment produces a treated effluent and wherein the method includes mixing at least a portion of the treated effluent with the thermally hydrolyzed biological sludge or sludge mixture; reducing the temperature of the thermally hydrolyzed sludge by at least 80° C. by transferring sensible heat from the thermally hydrolyzed sludge to the primary sludge prior to the sludge mixture reaching the pasteurization unit; wherein the pressurized structure includes a pressurized line leading from the thermal hydrolysis unit and wherein there are no heat exchangers engaged with the pressurized line; and the method includes transferring the thermally hydrolyzed biological sludge from the thermal hydrolysis unit through the pressurized line; and feeding the primary sludge into the pressurized line where the primary sludge and thermally hydrolyzed biological sludge are mixed and wherein substantially all cooling of the thermally hydrolyzed biological sludge is achieved by transferring sensible heat from the thermally hydrolyzed biological sludge to the primary sludge without the aid of heat exchangers engaged with the pressurized line; moving the thermally hydrolyzed biological sludge from the thermal hydrolysis unit into and through the pressurized structure that is operatively connected to a pressure-maintaining pump that is disposed downstream of the thermal hydrolysis unit and upstream from the pasteurization unit; wherein the pressure-maintaining pump maintains a pressure greater than atmospheric pressure in the pressurized structure between the thermal hydrolysis unit and the pump; and the method includes feeding the primary sludge into the pressurized structure at a point between the thermal hydrolysis unit and the pressure-maintaining pump and mixing thermally hydrolyzed biological sludge with the primary sludge in the pressurized structure; and wherein neither the thermally hydrolyzed biological sludge nor the sludge mixture is cooled by heat exchangers upstream of the pasteurization unit. ### Claim 19 (depends on 1) The method of claim 1 wherein the method includes first and second modes of operation; and wherein prior to directing the biological sludge to the thermal hydrolysis unit, the method includes directing the biological sludge to one or more dewatering devices and dewatering the biological sludge; and in the first mode of operation the method includes directing the dewatered biological sludge to the thermal hydrolysis unit and in the second mode of operation at least a portion of the dewatered sludge is directed to a mixing tank and mixed with the primary sludge prior to the primary sludge reaching the pressurized structure. ### Claim 20 (depends on 1) The method of claim 1 further including cooling the thermal hydrolyzed sludge by mixing treated effluent produced by the biological treatment with the thermal hydrolyzed sludge.