Requirements for sludge de-watering equipment, Part 2: Vacuum filtration equipment
1983 Edition

This section defines the extent of application for vacuum filtration equipment in sludge dewatering operations, emphasizing alignment with global standards while catering to Indian field conditions (Clause 0.6). It mandates rounding off test outcomes following IS 2-1960 standards to maintain consistent significant figures (Clause 0.7). The filter leaf test (Appendix A) is introduced here as a method for assessing filter media performance by evaluating different fabric types, forms, drying durations, and chemical conditioning to maximize filtration efficiency (Clause 3.1). No specific formulas or tables are included in this section; detailed testing procedures appear in subsequent parts.

This segment specifies the dimensional attributes of vacuum filters, commonly described by diameter and length (e.g., 150 mm × 600 mm). It prescribes the use of mild steel or stainless steel for filter casings and components with corrosion resistance as a key criterion. Filter media typically consist of wire mesh or perforated plates. Construction must adhere to welding and joint standards per IS codes to ensure integrity and durability. Uniformity in perforations or mesh openings is essential for consistent filtration performance. End caps and flanges should be securely attached and sealed to prevent leaks. Internal surfaces are to be smooth to avoid blockages, and designs should facilitate straightforward maintenance and cleaning.

The design and sizing of vacuum filters depend primarily on the volume of sludge slurry requiring filtration per unit time. The Leaf Filter Test (Appendix A) aids in selecting the appropriate filter media and determining necessary sludge conditioning. Operational parameters include vacuum levels of 500 to 650 mm Hg and drum peripheral speeds ranging from 7 to 40 revolutions per hour. Agitators maintain slurry homogeneity, while cake removal is achieved via scrapers, strings, or belts integrated with the filter medium. Drum size and sector quantity are adjusted based on filtration rates and cake thickness. Structural and lining materials are chosen for durability and chemical resistance. The filter area can be calculated using the formula A = Q / v, where Q is the slurry flow rate and v is the filtration velocity derived from leaf tests.

This section elaborates on the leaf test procedure for evaluating filter media. The objective is to assess the impact of different fabric types, fabric forms, drying intervals, and chemical conditioning on filtration yield. Sludge conditioning is performed in containers ranging from 9 to 25 liters, followed by immersion of the filter leaf in the slurry. Vacuum is applied with varying intensity and duration, after which the cake is dried for a predetermined time. Measurements taken include cake weight, moisture content, thickness, and ease of separation, as well as filtrate volume and suspended solids concentration. These data assist in optimizing the filter medium and chemical dosing to enhance vacuum filtration efficiency.

While detailed formulas or tables are not explicitly provided, this section outlines key operational and maintenance recommendations. The filter leaf test is instrumental in optimizing filter media and chemical conditioning. Chemical doses should be adjusted based on sludge properties to maximize filtration yield. Routine inspections involve checking filter cloth integrity, monitoring vacuum pressure and flow rates, and performing regular cleaning or replacement of filter media. A typical maintenance schedule includes daily vacuum and leak checks, weekly cloth inspections and cleaning, monthly chemical dosing assessments, and quarterly leaf tests. The filter yield can be expressed as the ratio of dry solids in the cake to the volume of sludge filtered.

Although specific formulas or tables are not provided, general installation recommendations include ensuring a firm, level foundation capable of supporting equipment weight and dynamic forces. Vacuum pumps should be positioned near the filter unit to minimize losses in vacuum lines. Piping must be of suitable diameter with airtight connections to reduce pressure drops. Electrical supply should be stable, properly earthed, and equipped with overload protection. Adequate drainage for filtrate and condensate is essential. Safety features such as pressure relief valves and emergency stop controls are mandatory. Results from tests and calculations should be rounded in accordance with IS 2:1960.

Performance assessments focus on maximizing filter yield through optimal selection of filter media and chemical conditioning, as per Appendix A (Clause 3.1). The filter leaf test is repeated multiple times to evaluate filtration efficiency, cake dryness, and throughput. Typical parameters monitored include filter yield, cake moisture content, drying time, and chemical dosing levels. The iterative process involves fabric selection, chemical conditioning, filter testing, yield measurement, and moisture evaluation until parameters are optimized. Detailed chemical and fabric specifications are available within the standard.

This appendix describes the method to evaluate the influence of fabric types, fabric forms, drying durations, and chemical dosing on filter performance. Sludge is conditioned in containers of 9 to 25 liters. The filter leaf is submerged in the slurry, and vacuum is applied with variations in pressure and time. Following vacuum filtration, the leaf is removed and the cake is dried for a fixed period. Measurements taken include cake weight, moisture content, thickness, and separability, along with filtrate volume and suspended solids concentration. The filter size is specified by diameter and length. The filter yield is calculated as the dry cake weight per unit area of the filter leaf.