Literature Review & Summary Report Design Basis Memorandum St. Johns River Water Management District Contract # SK940AA
BCI Project No. 19-15089 September 2007 Page 33
1) Requires much less dewatering equipment 2) Requires less labor/operator effort 3) Very basic, low-tech operation 4) Usually the most inexpensive dewatering approach 5) Effective containment
1) Typically requires expensive polymer addition to pre-condition sludge 2) Geo-tube solids are not as “dry” as filter press, belt press or centrifuge “cake”, therefore, much less waste volume reduction 3) Does not meet the required PFT and/or dryness/compaction specs on many sludge streams 4) Susceptible to cloth blinding by many sludge streams (oil and/or high biological content are most difficult) 5) Requires a large amount of real-estate 6) Requires a long period of time to dewater 7) Can be adversely impacted by local climate conditions (high humidity/rain) 8) Relatively “sloppy” and not feasible on hazardous sludge streams 9) Requires extensive preparation/construction of tube lay- down and drainage area/system
Confined Disposal Area
Placement of sediments in a confined disposal area offers several advantages. Foremost is the elimination of mechanical dewatering equipment necessitated by an accelerated process approach. Sediments are pumped directly from the dredge to a disposal area and are allowed to passively dewater while supernatant is decanted and returned to the lake. Maintenance requirements and operator expertise are minimal as the approach is basic with limited technology. 1) Increasing the concentration of solids in the sludge blanket 2) Increasing the settling rate of solids 3) Reducing sensitivity to temperature & flow fluctuations 4) Efficient use of disposal areas due to improved thickening and dewatering 5) Substantially increased clarity of recovered water
Confined disposal areas can require vast acreages to provide sufficient storage. In addition engineered dams may be required, with the associated construction costs. Pumping logistics are to be considered with the generally increased distance, and as with most dewatering technologies chemical treatment is necessary to enhance settlement. Consideration must also be given to sludge reuse timing as drying cannot occur until compartment filling is complete and the supernatant is removed.
The cost of Polymer application must be considered in the choice of a dewatering system. Additionally, the disposition of released water must be considered. For water returning to a lake or stream environment, polymers should be investigated for wildlife toxicity.
Table 3 Dewatering Technologies Advantages and Disadvantages
Miratech A Division of Ten Cate Nicolon