Section 217.248 - Sludge Thickening(a) If a sludge thickening system is used, the following criteria are required: (1) Capacity. The maximum monthly sludge production rate must be used as the basis for sludge thickening system sizing and design.(2) Flexibility. (A) A sludge thickening system must have a bypass to the digester.(B) A wastewater treatment facility with a design flow greater than 1.0 million gallons per day must have:(i) at least two sludge thickening units;(ii) an alternate means of sludge thickening; or(iii) an alternate sludge disposal method.(b) Specific Requirements for a Mechanical Gravity Thickener.(1) Equipment Features. (A) A mechanical gravity thickener must have: (i) a low-speed stirring mechanism for continuous mixing and flocculation;(ii) sufficient sludge storage, or sufficient additional storage in other external tanks; and(iii) a means of controlling the rate of sludge withdrawal.(B) A mechanical gravity thickener must use either a chemical addition or dilution water feed system.(C) A scraper mechanical train must be capable of withstanding any expected torque load. The working torque load must not exceed 10% of the manufacturer's recommended torque load.(2) Design Basis. (A) The design of a mechanical thickener must be justified in the engineering report.(B) The executive director may require data from a pilot study or similar mechanical gravity thickener operating under similar conditions.(C) The mechanical gravity thickener surface loading rate must be at least 400 gallons per day per square foot, but not more than 800 gallons per day per square foot.(D) The minimum side water depth for a mechanical gravity thickener is 10 feet.(E) A circular mechanical gravity thickener must have a minimum bottom slope of 1.5 inches per foot.(F) The peripheral velocity of a scraper must be at least 15 feet per minute but no more than 20 feet per minute.(G) A mechanical gravity thickener must prevent short-circuiting.(c) Specific Requirements for a Dissolved Air Flotation (DAF) Basin. (1) Equipment Features. (A) A DAF basin must have a bottom scraper that functions independently of the surface skimmer.(B) A recycle pressurization system for a DAF basin must use effluent instead of potable water.(C) A DAF basin must have a polymer feed system that meets the requirements of § 217.247(r) of this title (relating to Chemical Pretreatment of Sludge).(D) A DAF basin must be located in a covered building with positive air ventilation.(2) Design Basis. (A) The design of a DAF basin must be justified in the engineering report.(B) The executive director may require data from a pilot study or similar DAF basin operating under similar conditions.(C) The hydraulic loading rate must not exceed 2.0 gallons per minute per square foot.(D) The solids loading rate must be at least 1.0 pound per hour per square foot, but not more than 4.0 pounds per hour per square foot.(E) The air to solids weight ratio must be at least 0.02, but not more than 0.04.(F) A retention tank system must have a minimum pressure of 40 pounds per square inch, gauge.(G) A skimmer must have multiple or variable speeds that allow an operational range of at least 1.0 foot per minute, but not more than 25.0 feet per minute.(d) Specific Requirements for a Centrifugal Thickener.(1) The design of a centrifugal thickener must be justified in the engineering report.(2) The executive director may require data from a pilot study or data from a similar centrifugal thickener operating under similar conditions.(3) A centrifugal thickener must be preceded by pretreatment to prevent plugging of a nozzle or excessive wear in the bowl.(4) The centrate is subject to the requirements of § 217.242 of this title (relating to Control of Sludge and Supernatant Volumes).(e) Specific Requirements for a Gravity Belt Thickener. (1) Equipment Features. (A) A gravity belt thickener must include a wash water system capable of providing 60 gallons per minute of flow per meter of belt width at a pressure of at least 60 pounds per square inch. Booster pumps may be used.(B) A gravity belt thickener must include a polymer feed system that meets the requirements of § 217.247(r) of this title.(C) A filtrate drainage system must be sized to remove the full hydraulic capacity of a gravity belt thickener without accumulation or ponding of filtrate.(2) Design Basis. Unless otherwise justified in the engineering report, gravity belt thickener sizing must be based upon : (A) a maximum solids loading of 1,250 pounds per meter of belt width; or(B) a maximum hydraulic loading of 250 gallons per minute per meter of belt width.(3) Gravity belt thickener filtrate is subject to the requirements of § 217.242 of this title.30 Tex. Admin. Code § 217.248
The provisions of this §217.248 adopted to be effective August 28, 2008, 33 TexReg 6843; Amended by Texas Register, Volume 40, Number 47, November 20, 2015, TexReg 8336, eff. 12/4/2015