DSE
Civil/Environmental
- Sep 23, 2004
- 1
We are working with a small Village on evaluating the operation of their WWTP. Treatment units are two aeration cells, storage cell, two 1.8 acre sand beds with shallow under drains (5-7 feet deep), and deep under drains ( 27 feet deep).
The WWTP went into operation in the early 90’s and receives a flow of approximately 150,000 gpd. Three years ago the sand beds started to clog and water started to pond within each sand bed.
The sand was evaluated by a geotechnical firm and was concluded to meet class II sand. In addition, the shallow under drains were exposed and were found to be in a septic anaerobic condition (black with orange spots, Iron Bacteria??).
As a short term solution, an air compressor was used to introduce air into the existing under drains in an attempt to loosen material surrounding the under drains that currently hinders drainage of the sand beds.
As a mid Term, additional under drains were installed between the existing under drains to aid in draining the sand beds.
The long term solution was to construct another sand bed to allow for additional sand bed capacity that would better flows of wastewater, and allow each sand bed ample time to dry decreasing the chances of the under drains becoming clogged.
Three years after installation of the new drains, the WWTP is experiencing the same problem again. Sample fom before and after the sand bed indicated iron not detected before the sand bed and at 0.97 mg/l after, and ph is 7-8.
In light of the above, it is greatly appreciated if someone can provide me with some input or leads to follow ... Has anyone ever experienced a similar problem
The WWTP went into operation in the early 90’s and receives a flow of approximately 150,000 gpd. Three years ago the sand beds started to clog and water started to pond within each sand bed.
The sand was evaluated by a geotechnical firm and was concluded to meet class II sand. In addition, the shallow under drains were exposed and were found to be in a septic anaerobic condition (black with orange spots, Iron Bacteria??).
As a short term solution, an air compressor was used to introduce air into the existing under drains in an attempt to loosen material surrounding the under drains that currently hinders drainage of the sand beds.
As a mid Term, additional under drains were installed between the existing under drains to aid in draining the sand beds.
The long term solution was to construct another sand bed to allow for additional sand bed capacity that would better flows of wastewater, and allow each sand bed ample time to dry decreasing the chances of the under drains becoming clogged.
Three years after installation of the new drains, the WWTP is experiencing the same problem again. Sample fom before and after the sand bed indicated iron not detected before the sand bed and at 0.97 mg/l after, and ph is 7-8.
In light of the above, it is greatly appreciated if someone can provide me with some input or leads to follow ... Has anyone ever experienced a similar problem