Accessible Sand Filters: Procedures & Schedules

1. Every 3 months:

a) rake and level filter surface to prevent ponding

b) remove vegetation on filter surface

c) if alternating filters, redirect flow to the other filter by operating diversion valve

d) for filters which follow septic tanks, monitor effluent biochemical oxygen demand, suspended solids, fecal coliforms

2. Replace top 2-4 inches of sand annually.

These recommendations are conservative. Typically the sand should not need to be removed every year. Sand filters almost always follow a septic tank unless they are used for polishing effluent after a technology such as a lagoon or constructed wetland. Sand filters which are used for polishing typically serve multiple homes and may directly discharge.

Accessible Sand Filters: Personnel & Contracted Work

Labor:

• trained person
• $6/hr
• 10 man-hrs/yr./filter

For filters following septic tanks, chemical analysis:

• contract 4 samples/yr.
• $28/sample

Chemical analysis is typically a requirement for systems that discharge.

Accessible Sand Filters: Parts, Supplies & Equipment

Parts and Supplies:

Sand:

• non-recirculating 0.06 cubic ft/gpd/yr. @ $5/cubic ft
• recirculating 0.03 cubic ft/gpd/yr. @ $5/cubic ft

Equipment:

• rake, shovel: $44/2 yrs
• Total: $12/1 yr.

Power: none

Accessible Sand Filters: Example Annual Costs Per Home

Labor:	10 man-hrs/filter * $6/man-hr * 1 filters / 30 homes =	$ 2.00
Equipment:	$22.00 / 30 homes =	$ 0.73
Sand:
	(non-recirculating filters) 0.06 cu ft/gpd * 333 gpd/home * $5/cu ft 30 homes w/non-recirculating filters / 30 homes =	$99.90
	(recirculation filters) 0.03 cu ft/gpd * 333 gpd/home * $5/cu ft * 0 homes w/recirculating filters / 30 homes =	$ 0.00
Total:	(First Quarter 1982) =	$102.63

 

Updated Total:	Total	OMR	1982 OMR
	$102.63	* 3.49	/ 3.44	= $104.13

Accessible Sand Filters: Operational Problems

Accessible sand filters are applicable to single or multiple home use, for surface discharge of effluent. Effluent quality is high but experience with these systems is limited.

Recirculation is a recent modification that employs a small sump pump such as a septic tank effluent pump). EPA (1980c) describes the systems.

Odor is inherent to non-recirculating types. Proper design and strict control of recirculation is critical with the recirculating filters to avoid plugging, ponding, or odors due to an aerobic conditions.

Both types clog after a period of use and must be serviced.

Accessible Sand Filters: O&M Requirements

The filter itself requires periodic raking and leveling to break up any surface mat, prevent ponding, and assure even wastewater distribution over filter surface. When the sand depth falls below 24 inches, the top 2 to 4 inches should be replaced.

These tasks may require 10 man-hours per home per year (EPA, 1980c) in addition to maintenance of pump and septic tank or other prior treatment units (solids must not enter filter). Sand availability may be a problem in some areas, in which case transportation costs will increase.

The example presents costs for one non-recirculating filter which is used as tertiary treatment following, for example, an aerated package plant servicing 30 homes. Sand is seen to be a very significant expense.

Sand filter technology has progressed quite a bit in the last 10 years. The latest recommendations require sand (or crushed glass) that meets rigorous size specifications. This may increase the price if sand needs to be transported over long distances.