Key figures and costs

 

Production costs

 

Production costs and especially labour costs for an existing process depend mainly on the real liability and the performance of the equipments.

 

CODECAL^®  enables a decrease of production costs :

• by suppressing equipments asking for high maintenance costs and subject to frequent breakdowns : post-liming and transfer equipments for centrifuge processes and milk of lime preparation for plate filter presses,
• by improvement of the performances : filtrability and treated volume by batch in case of filter press, D.S. treated pro production hour in case of centrifuge process.

Reagents costs

 

Reagents use for dewatering depending on process are mainly :

• polymers as powder or as emultion with a consumption of 3 to 20 kg pro ton D.S., 
• iron chloride with a consumption of 3 to 15 % on D.S. content,
• lime as quicklime or as hydrated lime with a consumption of 5 to 100 % on D.S.; contrary to other reagents, lime consumption will not only depend on process but also on desired dewatered sludge (quality structure, angle of repose, long storage capacity, odours).

CODECAL^®  enables :

• either to reduce reagents consumption and consequently reagents costs at equivalent sludge quality,
• or to reduce sludge volumes and increase quality at equal reagents cost but with a recycling cost reduction. 

 

Recycling costs

 

Recycling costs of dewatered sludge usually represent the larger part of total costs, compared to i.e. reagents costs.  It depends on :

• the recycling path (route) 
• the total volume of sludge produced pro ton of D.S. in the sludge.

Recycling paths

 

Recycling costs are variable depending on country, region and location, but in average :

• Direct agricultural recycling remains the cheapest solution (15 to 30 Euros per ton of sludge).
• Composting is the intermediate solution, of which the cost depends to a large extent on the distance between production site and composting unit (30 to 80 Euros per ton).
• Incineration or co-incineration in electrical power plants or cement kilns are the most costly solutions (50 to 100 Euros per ton). The high cost is partially explained by the need to dry sludge prior to incineration.
• Landfilling (100 Euros per ton) is a solution which is less used, as it will only be allowed to landfill ultimate waste which cannot be recycled anymore. 
   

Volume of sludge produced by volume of D.S.

 

This ratio depends on the dewatering process, on its efficiency and on the added reagents.

 

For a centrifuge dewatering with polymers, without liming, production will be of :

• 4 tons of dewatered sludge pro ton of D.S., if dewatered sludge after centrifuge is of 25% D.S.,
• 5 tons of dewatered sludge pro ton of D.S., if D.S. content after centrifuge is of 20%,
• 6.7 tons of dewatered sludge pro ton of D.S., if D.S. content after centrifuge is of 15%.

 

The recycling cost pro ton D.S. varies in this case from 80 to 134 Euros per ton D.S. for one type of process with a recycling cost at 20 Euros per ton, and of 160 to 268 Euros per ton D.S. for a recycling path at 40 Euros per ton of sludge.  These costs have to be compared to the liming process with a i.e. 30% liming, of which cost would be between 30 and 45 Euros per ton D.S. depending on the cost for the lime.  Liming cost will be compensated to a very large extent by the savings on the recycling route when volume of sludge is reduced or if the quality of sludge enables to recycle through a cheaper recycling route.

 

Post-liming increases in all cases the volume of sludge produced per ton of D.S. but in a lesser proportion.  In the case of a centrifuge process with a D.S. content of 20% of the dewatering and a liming rate of 30% of D.S., ratio will be between 5.3 compared to 5 without liming, or an increase of 6%. But in this case, liming may enable direct agricultural recycling instead of composting, for example.  For the case hereabove and for recycling routes of respective 20 Euros per ton of sludge for direct agricultural recycling and of 40 Euros per ton of sludge for composting, the extra cost for liming is of 40 Euros  per ton D.S. for the lime and of 6 Euros per ton D.S. on the volume increase, or a maximum of 46 Euros per ton D.S. to compare to 100 Euros per ton D.S. of extra cost for composting compared to direct agricultural recycling.

Potential savings when using CODECAL^® 

 

1.  In post-liming

CODECAL^®  enables to decrease reagents consumption of 20 to 30% for an equivalent sludge quality; in fact, volume of dewatered sludge is reduced of 2 to 5% depending on the liming dosage.

 

2.  In pre-liming on filter press

Using hydrated lime and iron chloride is a largely used process. Sludge obtained is perfectly homogeneous and usually recycled without problem in the cheapest recycling route, which is direct agricultural recycling.
CODECAL^®  process does in this case not bring any savings by changing the recycling path.  Nevertheless CODECAL^®  enables to decrease production costs (by-pass of the milk of lime, increase of the productivity) and to reduce the volume of dewatered sludge to recycle (increase of the D.S. content).

 

3.  In pre-liming on centrifuge

Pre-liming on centrifuge is usually not efficient when using quicklime or hydrated lime.
But on the contrary, CODECAL^®  enables to produce perfectly homogeneous and well structured sludge.
Sludge volume reduction will depend on the mineralisation effect by CODECAL^®  on the treated liquid sludge : in the best cases, volume of dewatered sludge will even be smaller than the one obtained by a centrifuge process without lime.
The most significant savings are obtained when quality of sludge may enable direct agricultural recycling without any problems due to sludge structure and/or sludge smell.
When agricultural recycling is already practiced, pre-liming with CODECAL^®  on centrifuge will secure this recycling path in terms of quality and by decreasing in the same time the volume and the cost of the used reagents (polymers, iron chloride and lime).

Costs simulation of differnet processes for specific cases

Every sludge treatment plant is a specific case.  CARMEUSE has developed simulation tools to apprehend sludge process costs pro ton of recycled D.S. of sludge of which you will find a few examples under the heading Cases studies