GB2401327A - Removing contaminants from a clarified liquid stream outlet in a settling tank - Google Patents

Abstract

A process for retaining solids in a treatment vessel while discharging a clarified liquor comprises a treatment vessel with an internal discharge pipe (1, Fig 1). In use, contaminated liquor enters the treatment vessel wherein a reaction takes place and suspended solids are allowed to settle at the bottom of the vessel. During the reaction and settling period some suspended solids collect in the discharge pipe and are periodically removed by a reverse flow of the clarified liquor. Preferably a pump 6 supplies a motive force to the clarified liquor which is either contained in a flushing tank 7 for removing suspended solids from the discharge pipe or held in main storage tanks. The contaminated liquor may comprise a leachate of rain water contaminated with chemicals and organic material mixed with bacteria and air. Advantageously suspended solids in the treated leachate are reduced and can therefore be discharged to a sewer or water course.

Description

Description

LTW discharge line clearing process The invention relates to a process which allows the discharge of clarified liquor from a treatment vessel without transfer of any solids.

When rain water percolates through the layers of waste it becomes contaminated with chemicals and organic matter. This water is called leachate. A leachate treatment works (LTW) is a plant designed to biologically treat the leachate emanating from a landfill site.

The chemicals contained within the leachate constitute an environmental hazard and must not contaminate any local water courses. To facilitate this, a biological treatment process is used. This involves introducing various strains of bacteria which consume the various chemicals and organic matter.

The process involves supplying the bacteria with the right quantities of food (leachate) and air (Fig 1). After a set amount of time, this mixture of leachate and bacteria is allowed to settle and all the suspended solids eventually precipitate to the bottom (Fig 2).

The leachate that remains is relatively contaminant free and can be discharged to a local sewer or watercourse. The discharge is via the internal run off pipe 1 (Fig 1). The problem is that during the reaction phase of the process and the subsequent settling period, suspended solids collect in this run off pipe (Fig 2).

Whilst the remainder of the leachate can settle out, the leachate trapped in the run off pipe 1 will settle in the pipe. This cannot be allowed to happen because the solids would then be discharged to sewer.

During the settlement period, a small amount of solids will settle in the vertical run off pipe (Fig 2). After a set amount of the settling period has taken place, the discharge pump 6 clears the settled solids out of the run off pipe 1 by reversing the motor direction (Fig 3).

The pump must be supplied with water in order that it can flush the pipe clear.

To that effect, a separate flushing tank 7 is used. This tank is filled with treated effluent during the discharge phase so that after a flushing (Fig 5), the subsequent discharge re-fills the tank (Fig 6).

After the run off pipe has been cleared, the leachate then settles for the remainder of the settlement period. The clarified leachate is then discharged, fills up the small flushing tank (Fig 6), with the balance of the treated leachate being discharged into the main treated leachate storage tanks.

Claims (3)

1. Claims 1. A process for retaining solids in a treatment vessel while

   discharging clarified liquor.
2. 2. A process as claimed in claim 1 which allows discharge of clarified liquor from a treatment vessel using a submerged vertical run off pipe without transfer of any solids previously suspended in the liquor.
3. 3. A process as claimed in claim 1 and 2 which uses a pump and a separate tank of treated liquor as a means of flushing the run off pipe of any solids.