Trickling Filters
What Are Trickling Filters?

Process
Organic material from liquid is adsorbed onto the slime layer whose outer portions degraded by aerobic micro-organisms. As they grow thickness of slime layer increases & oxygen is consumed before it penetrates full depth. Hence micro-organisms enter into an endogenous phase of growth & lose ability to cling to the media surface. Liquid then washes the slime off the media & a new slime layer begins to grow. Losing of slime layer is known as “sloughing”
Factors Considered In Design
Distribution System
- Consists of distributor arms mounted on a pivot in the centre,
- These are hollow through which water is discharged over the filter bed
- For uniform distribution the flowrate per unit of length should be proportional to the radius from the center
- Head loss is in the range of (0.6 –1.5 m)
- Dosing tanks must ensure that minimum flow is sufficient to rotate the distributor & discharge all waters from nozzles
Filter Media
- A material having high surface area per unit volume , does not clog easily
- Media can be rock , plastic , pvc
- Stones less than 25mm not be used as they do not provide sufficient pore space
- Calculation of media depth
Underdrains & Airflow
These are waste water collection systems that collects the filtered waste water & solids discharged from the filter packing. They ventilate the filter by aproviding air for the micro-organisms by being open atleast to a circumferential channel. Should be designed such that forced air vibrations can be added later
Air flow:
- Natural draft
- Forced air ventilator
Advantages
- Because of their large air-water interface can remove co2,h2s, n2 & other gases
- A portion of liquid in underdrain system is recycled:
- It improves the treatment efficiency
- To dilute strength of incoming wastewater
- To maintain enough wetting of slime layer
- Prevents ponding in filter
- Suitable for shock loads
- Low running cost