The 1971 edition of the standard outlines specifications and design principles for sewage screening devices used in wastewater treatment plants. It details requirements for both manually and mechanically cleaned screens, encompassing materials, construction, installation, and operational methods to optimize the removal of solids from sewage streams. This specification serves as a vital reference for professionals engaged in the engineering, installation, and upkeep of sewage screening equipment in municipal and industrial settings.
Overview
The 1971 edition of the standard outlines specifications and design principles for sewage screening devices used in wastewater treatment plants. It details requirements for both manually and mechanically cleaned screens, encompassing materials, construction, installation, and operational methods to optimize the removal of solids from sewage streams. This specification serves as a vital reference for professionals engaged in the engineering, installation, and upkeep of sewage screening equipment in municipal and industrial settings.
Audience
Contents
Structure
This section defines the scope of the standard and presents a detailed table of recommended materials for various parts of sewage screening equipment, along with applicable Indian Standards for each. Materials for civil construction, gates, floats, rake arms, teeth, shafts, electrical components, structural steel, bearings, cables, housings, and reduction gears are included to ensure durability and compliance.
Clarifies important terminology used within the standard related to sewage screens, supplemented by a tabulated list of component parts and their corresponding material recommendations and IS references to maintain clarity and uniform understanding.
Details the materials specified for each part of the sewage screen assembly, emphasizing adherence to Indian Standards for concrete, steel, plastics, electrical equipment, and other materials to guarantee robustness and corrosion resistance.
Outlines criteria for the proper siting and installation of sewage screens, including requirements for physical separation within buildings, ventilation systems to prevent gas accumulation, lighting considerations, and disposal protocols for screenings.
Provides design guidance including recommendations for mechanical versus manual screens based on flow rates, material usage, and general construction principles to optimize performance and maintenance.
Focuses on manually operated coarse screens, highlighting design features such as platform requirements, drainage provisions, tool accessibility, and typical dimensional values for effective manual cleaning.
Describes mechanically cleaned screens featuring automatic raking devices, discussing design flexibility, flow thresholds for use, screen opening sizes, rake frequency, and operational parameters to ensure efficient automatic cleaning.
Specifies the painting system to be applied on steel components, including primer and top coat materials, number of coats, timing of application, and adherence to relevant standards to protect against corrosion.
Details equipment and methods for the collection and hygienic disposal of screenings from sewage screens, including recommended containers based on plant size and approved disposal techniques such as sanitary landfill and incineration.
Frequently Asked
The standard specifies materials such as concrete, brick, and stone masonry for civil works; cast iron and steel for gates; corrosion-resistant plastics for floats; fabricated structural steel and cast iron for rake arms and frames; cast steel for teeth; cold finished steel for shafts; electrical components complying with IS standards for motors and switches; bronze bearings; steel ropes and chains; mild steel for sheet housing; and steel gears and reduction mechanisms. These materials ensure structural integrity and resistance to environmental factors.
Manual screens should be installed at an inclination between 45° and 60° relative to the horizontal to facilitate easier manual cleaning. Mechanical screens, especially flat straight types, are recommended to have an inclination ranging from 60° to 90° to optimize self-cleaning efficiency. The raking mechanisms vary accordingly, including revolving types for curved screens, reciprocating for straight screens, and endless revolving types.
Raking mechanisms must be rigid to prevent deflection and maintain continuous engagement of rake teeth with the screen surface. The standard allows for revolving, reciprocating, or endless revolving types depending on screen shape. The rake speed should not exceed 3 meters per minute. An auxiliary switch should be provided for manual operation if needed. Additionally, overload protection devices must be installed to disengage the rake automatically if obstruction or jamming occurs, and sectional rake combs are recommended for easier maintenance.
Mechanically cleaned screens require three-phase induction motors with a minimum rating of 0.5 kW, conforming to IS 325 or IS 996. Motors should be totally enclosed, fan-cooled types suitable for outdoor use. The drive unit must include oil-immersed reduction gearing with anti-friction bearings. Safety devices such as magnetic starters, no-volt release, and overload protection are mandatory. The drive chain or belt must be enclosed within a sheet metal guard at least 2 mm thick. Outdoor motors should also have protective louvered covers. Controls should be conveniently located, with push-button controls near the motor and centralized controls optional for large installations.
The standard recommends using rubber-tyred tippers with a minimum capacity of 140 liters for collecting screenings. For large-scale plants, trailers are advised, while cleanable wheelbarrows are suitable for smaller facilities. Accepted disposal methods include sanitary landfilling and incineration to ensure hygienic handling and minimize environmental impact.
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