Section 630. Filtration

A. Rotary drums. The following rates of vacuum filtration, in pounds of dry solids per square foot of drum filter area per hour, for various types of sludge, may be considered conventional loading with proper prior sludge conditioning. A variable speed drive shall be provided.

Type of Treatment Process Producing Sludge Prior to Stabilization	Pounds of Dry Solids Per Square Foot Per Hour Minimum - Maximum
a. Primary	4 - 6
b. Primary and Contact Reactor	3 - 5
c. Primary and Suspended Growth Reactor	3 - 4

1. Unless dual trains are provided, the following appurtenant equipment shall be provided in duplicate with necessary connecting piping, and electrical controls to allow equipment alternation. Spare filter fabric shall be provided except when metal coils are utilized.

a. Feed pump.

b. Vacuum pump.

c. Filtrate pump.

2. Wetted parts should be constructed of corrosion-resistant material. Drum and agitator assemblies shall be equipped with variable speed drives and provisions for altering the liquid level shall be made.

3. Vacuum pumps having a capacity of at least 1.5 cfm per square foot for metal-covered drums should be provided. Vacuum receivers are required with dry type vacuum pumps.

4. Each filter shall be fed by a separate feed pump to ensure a proper feed rate. Filtrate pumps must be of adequate capacity to pump the maximum amount of liquid to be removed from the sludge.

5. Careful consideration to filter washing and variable sludge pickup depth should be made.

B. Plate and frame presses. Actual performance data developed from similar operational characteristics should be utilized for design. The impact that anticipated sludge variability will have on the design variables for the press as well as chemical conditioning shall be addressed. Appropriate scale-up factors shall be utilized for full size designs if pilot scale testing is done in lieu of full-scale testing.

1. The following appurtenant equipment shall be considered for duplicate operation unless multiple units are provided:

a. Feed pump.

b. Air compressor.

c. Washwater booster pump.

2. The following spare appurtenances shall be provided where multiple units are not installed:

a. At least one extra plate for every ten required for startup, but a total of not less than two extra plates required.

b. One complete filter fabric set.

c. Closure drive system.

d. Feed pump (when duplicates are not provided).

e. Air compressor (when duplicates are not provided).

f. Washwater booster pump (when duplicates are not provided).

3. Filter feed pumps shall be capable of a combination of initial high flow, low pressure filling followed by sustained periods of operating at 100 to 225 psi. An integral pressure vessel to produce this initial high volume flow should be considered. Operating pressures less than 225 psi will be considered if actual performance data using similar sludges is provided.

4. Provisions for cake breaking to protect or enhance downline process shall be incorporated where necessary.

5. Crane or monorail services capable of removing the plates should be considered. In some installations, the capability to remove other press parts should also be considered.

6. Provision for a high pressure water or acid wash system to clean the filter shall be considered. Booster pumping should be addressed.

C. Belt presses. Actual performance data developed from similar operational characteristics should be utilized for design. The impact that anticipated sludge variability will have on the design variables for the press as well as chemical conditioning shall be addressed. A second belt filter press or an approved backup method of dewatering shall be required whenever a single belt press is operated 60 hours or more within any consecutive five day period or the average daily flow received at the treatment works equals or exceeds four mgd. Appropriate scale-up factors shall be utilized for full-size designs if pilot plant testing is performed in lieu of full-scale testing.

1. The following appurtenant equipment shall be considered for duplicate operation unless multiple units are provided:

a. Feed pump.

b. Washwater booster pump.

2. Requirements for spare appurtenances should include the following:

a. Complete set of belts.

b. One set of bearings for each type of press bearing.

c. Tensioning and tracking sensors.

d. One set of wash nozzles.

e. Doctor blade.

f. Conditioning or flocculation drive equipment if duplicate units are not provided.

3. A polymer selection methodology, accounting for sludge variability and anticipated sludge loading to the press shall be provided.

4. Sludge feed shall be as constant as possible to eliminate difficulties in polymer addition and press operation. The range in feed variability shall be identified and equalization shall be provided as necessary. A method for uniform sludge dispersion on the belt shall be provided. Grinders for the sludge feed to the flocculation system shall be considered. Thickening of the feed sludge should be an integral part of the design of the filter press. Separate thickening or dual purpose thickening will be considered on a case-by-case basis.

5. The filter press design shall consider the following:

a. Variable belt speed mechanism.

b. Belt tracking and belt tensioning equipment.

c. Belt replacement availability based on evaluation of the belt equipment selection especially if the weave, material, width, or thickness cannot be reasonably duplicated.

6. Rollers specified for the press design should provide:

a. Rubber coating or other protective finish.

b. Maximum frame and roller deflection and operating tension.

c. Roller bearings that are watertight and rated for a B-10 life of 100,000 hours.

7. The washwater system should provide for:

a. High pressure washwater for each belt with a specified operating pressure.

b. Booster pumps if necessary.

c. Spray wash systems designed to be cleaned without interference with the system operation.

d. Particular care in nozzle selections and optional nozzle cleaning systems when recycled wastewater is used for belt washing.

e. Replaceable spray nozzles.

f. Spray curtains.

D. Additional design features to be considered include:

a. Drip trays under the press and under the thickener to readily remove filtrate if gravity belt thickening is employed.

b. Adequate clearance to the side and floor for maintenance and removal of the dewatered sludge.

c. Location of all electrical panels or other materials that are subject to corrosion out of the area of the press.

d. Adjustable doctor blade clearance.

Historical Notes

Former 12VAC5-581-690 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-630, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.