Trickling Filters & Advantages

Trickling Filters

What Are Trickling Filters?

•Fungi

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