You are currently not logged in.
Biosolids Dewatering Overview
Purpose
The Belt filter press (BFP) removes water from conditioned sludge first by gravity fil­tration and then by squeezing it between two woven belt filters that retain the solids while filtrate passes through.

The purpose of the BFP and associated equipment is to reduce the quantity of di­gested sludge that must be handled after it is removed from the digesters, and to convert it from a liquid to a semisolid form. The offsite sludge drying beds are designed for dewatered sludge.
Theory of Operation
 The operator has 3 basic controls to the equipment to manipulate dewatering performance:

   1. Sludge feed rate – In general, the lower the gallons per square foot of belt area the drier the cake produced. Other factors can affect
       loading to the machine and resulting performance such as; sludge solids concentration, volatile %, amount of free water and rate of 
      draining, belt porosity, and belt condition.

   2. Polymer conditioning – Precise metering of polymer, polymer conditioning, mixing of polymer to sludge, and polymer application point will
       influence sludge flocculation. The ideal floc will allow water to freely drain in the gravity section, but maintain some adhesiveness when 
       in the pressure section of the machine.

   3. Belt speed – The operator can manipulate the detention time the sludge spends in each of the three dewatering zones listed below. 
      However, the operator cannot adjust the time spent in each zone independently unless the machine is provided an independent gravity
      drain belt. The operator must balance time spent in the pressure zone versus time needed for sludge to freely drain on the gravity zone.
      Too slow a belt speed will result in inefficient free water drainage on the gravity belt due to build up of solids. A belt speed that is to fast 
      may result in sufficient free water drainage, but insufficient time for remaining water to be squeezed from the sludge in the pressure zone.
Equipment
The WAS thickening system includes the following components:
  • Sludge feed/load pump
  • Sludge grinder
  • Polymer system
  • Washwater booster pump
  • Belt filter press
Description
The Sludge feed/load pump is a progressing cavity variable speed pump with an ad­justable flow rate of 50 to 200 gpm. Speed is modulated by a variable frequency drive located in the lower level of the solids building.

Sludge passes through rotating cutters in the grinder. Material that cannot pass through may occasionally jam the machine. It was supplied with its own control panel located adjacent to the machine, which has alarms and automatic features relating to jam­ming and unjamming.

The BFP is a 2‑meter Ashbrook‑Simon-Hartley Klampress with a hydraulic belt ten­sioning and belt alignment system. It is intended to receive blended digested primary and waste activated sludges with a concentration of 2.0 percent to 3.5 percent solids. It is intended to discharge dewatered sludge at a concentration of 15 to 20 percent solids.

The dewatered sludge is discharged from the press through a chute and an opening in the floor where it will fall into a truck below. A second opening in the floor has been provided for future conditions when a truck with a longer bed will be used. The layout has been arranged to accommodate a future conveyor belt to discharge the sludge into the second opening, spreading it more evenly in the longer truck. The intent is that the future conveyor belt would slide in and out from under the BFP discharge on a rail, so that both openings can be used.

There are two control panels associated with the BFP, both located adjacent to the machine. The first was supplied by the manufacturer of the BFP. It controls belt tensioning, belt alignment, the hydraulic power system, and other functions and alarms internal to the performance of the machine itself. Literature provided by the vendor should be consulted for information regarding the operation of this panel and the systems it controls.

A second control panel, LP‑8090, controls the interface between the BFP and associ­ated equipment, such as the washwater booster pumps, polymer pumps, and sludge feed/load pump.

The BFP requires a supply of belt filter washwater at 80 gpm and 85 to 120 psi. Two washwater booster pumps have been provided. Pump No. 2 is dedicated to the BFP and has a capacity of 80 gpm at 120 psi. Pump No. 1 has a lower capacity and is dedicated to the GBT. If Pump No. 2 fails, a piping interconnection will permit the use of Pump No. 1 for the BFP, but manual control from panel LP‑8080 will be required and inadequate belt washing may occur. The automatic valve in the pump discharge line will continue to shut the water supply on and off.
Sludge Feed/Load Pump6
The Sludge feed/load pump is a progressing cavity variable speed pump with an ad­justable flow rate of 50 to 200 gpm. Speed is modulated by a variable frequency drive located in the lower level of the solids building.  

Sludge Grinder 6
The grinder passes the sludge through rotating cutters. Material that cannot pass through may occasionally jam the machine. It was supplied with its own control panel located adjacent to the machine, which has alarms and automatic features relating to jam­ming and unjamming. The literature supplied by the vendor should be consulted for further operating information.
Polymer System 6
  The polymer feed unit is located in the Solids Handling Building.

The polymer system mixes and feeds dry polymer solution to the sludge feed lines for the GBT and belt filter press (BFP). The polymer solution mixes with the sludge and causes the solid particles in the sludge to agglomerate. This allows water to be removed more easily during sludge thickening and dewatering.
Washwater Booster Pump6
The BFP requires a supply of washwater of 80 gpm at 85 to 120 psi. Two washwater booster pumps have been provided. Pump No. 2 is dedicated to the BFP and has a capacity of 80 gpm at 120 psi. Pump No. 1 has a lower capacity and is dedicated to the GBT. If Pump No. 2 fails, a piping interconnection will permit the use of Pump No. 1 for the BFP, but manual control from panel LP‑8080 will be required and inadequate belt washing may occur. The automatic valve in the pump discharge line will continue to shut the water supply on and off.
Belt Filter Press6
  The BFP is a 2‑meter Ashbrook‑Simon-Hartley Klampress with a hydraulic belt ten­sioning and belt alignment system. It is intended to receive blended digested primary and waste activated sludges with a concentration of 2.0 percent to 3.5 percent solids. It is intended to discharge dewatered sludge at a concentration of 15 to 20 percent solids. 

Back To Top
Last Updated: 9/16/2013 11:27:52 AM
Version 4.0.1