Treatment MeasuresLitter Traps : Life Cycle Costs
More Information
Life cycle costs are a combination of the installation and maintenance costs. To determine the life cycle costs the estimated duration of the project needs to be determined (eg. 20 or 25 years) or if the trap is to control pollutants during the development phase only it may be 3-10 years.
This is used to extrapolate the annual operating costs to project life costs. Below are more details on estimating the costs.
To estimate the life cycle costs for a litter trap the installation costs and the annual operating costs (for the project duration) are combined.
This can be simply performed for all traps and then, with consideration to the other influences (social, political etc.), the most appropriate trap can be selected.
To estimate life cycle costs:
- Determine the project life (n: years)
- Estimate the installation cost (including supply, installation and ancillary works)
- Estimate the annual operating cost (including collection and disposal)
- Estimate the Equivalent Annual Cost by estimating the Net Present Cost of the project and dividing by the project duration
NPC ($) = Installation ($) + [ n x annual maintenance ($)]
EAC ($/year) = NPC ($)/ duration (years)
Installation
To estimate the installation costs there a number of local issues that will need to be considered. These include the:
- design flow rate,
- size and configuration of the trap (with regard to site constraints),
- hydraulic impedance and the requirements for operation, and
- safety and other construction issues.
If any of the below factors can not be adequately satisfied by a particular trap it should be deemed as potentially inappropriate for that location.
Maintenance Costs
Maintenance costs can be more difficult (but are sometimes the most critical variable) to estimate than the installation costs. Variances of the techniques used, the amount of material removed and the unknown nature of the pollutants exported from a catchment. In many cases maintenance costs are the most significant cost of a treatment measure. It is therefore imperative to carefully consider the maintenance requirements and estimated costs when selecting litter traps.
One important step is to check with previous installations by contacting current owners of the litter trap and asking their annual costs (vendors can usually supply contact information).
All maintenance activities should be developed that require no manual handling of collected pollutants because of safety concerns with hazardous material.
Below is a list of maintenance considerations that should be applied to all litter traps. They are divided into the maintenance equipment, ancillary works, disposal of collected pollutants and safety issues.
Disposal costs
Disposal costs will vary depending on whether the collected material is retained in wet or dry conditions (ie. either under water or left so it can drain). Handling of wet material is more expensive and will require sealed handling vehicles.
- Is the material in a wet or dry condition and what cost implications are there?
- Are there particular hazardous materials that may be collected and will they require special disposal requirements (eg. contaminated waste -what cost implications are there?
- What is the expected load of material and what are the likely disposal costs?
Loads can be estimated using the decision support system developed by the CRCCH (see references) which requires rainfall and land-use information. In the event there are no other data, the values in following table should be adopted for Melbourne conditions. Note that litter and gross pollutants (litter and vegetation) are listed, this is because the disposal costs are dependent on the gross pollutant load rather than just the litter component. No litter traps can distinguish between litter and organic material therefore, in order to remove litter they must also collect debris in the same way.
* Gross pollutant loads should be used to estimate disposal costs.
APPROXIMATE LITTER & GROSS POLLUTANT LOADING RATES FOR MELBOURNE
| LANDUSE TYPE | LITTER¹ Volume (Litre/ha/year) |
LITTER¹ Mass² (kg/ha/year) |
GROSS POLLUTANTS³ Volume (Litre/ha/year) |
GROSS POLLUTANTS³ Mass² (kg/ha/year) |
|---|---|---|---|---|
| Commercial | 210 | 56 | 530 | 135 |
| Residential | 50 | 13 | 280 | 71 |
| Light-industrial | 100 | 25 | 150 | 39 |
|
¹ litter is defined as anthropogenic materials larger then 5 mm ² mass is a wet mass, ie. the mass expected when removed from a litter trap ³ gross pollutants contain vegetation as well as anthropogenic litter |
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- Do existing installations of a particular trap have comparable maintenance costs to the estimate above? - if not should an adjustment be made?
Occupational Health and Safety
- Is there any manual handling of pollutants and what will safety and equipment cost?
- Is entering the device required for maintenance and operating purposes - will this require confined space entry? What cost implications does this have on the maintenance cycle (for example, minimum of three people on site, safety equipment such as gas detectors, harnesses, ventilation fans and emergency oxygen)
- Are adequate safety features built into the design (eg. adequate step irons and inspection ports) or will these be an additional cost?
Costing Sheet - Selecting Litter Traps
Costs estimates for the life cycle of all litter traps considered should be performed. The check-list is to help identify all costs that may be involved during the life span of the trap. This total life cost can then be compared between different traps and the most suitable trap selected, also with consideration to the pollutant removal performance.