Following are the various types of troubles which occasionally occur at the site and operation of trickling filters: 1. Odour Nuisance 2. Ponding Nuisance 3. The Fly Nuisance.
Trouble # 1. Odour Nuisance:
It is used due to anaerobic decomposition, sludging and undesirable growth. The odour nuisance can be eliminated by preventing the conditions responsible for it.
Following are the main remedies for the prevention of the odour nuisance:
(i) The effluent obtained from the filter can be recirculated to continue aerobic condition and prevent anaerobic condition.
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(ii) The upper portion of the sewage can be kept fresh by its chlorination.
(iii) The sewage can be kept in aerobic condition by chlorinating it before primary settling treatment.
Trouble # 2. Ponding Nuisance:
When all the voids of the trickling filters are filled up due to choking by heavy fungus or other suspended matters, the sewage cannot pass through the filter and accumulate at the surface in the shape of a pond. Due to ponding nuisance the sewage cannot pass through the filter and the treatment work is stopped.
The ponding nuisance can be prevented and removed by the following methods:
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(i) By drying the filter media for 15 to 48 hours by exposing it to the sun and loosening the aggregate with steel bars.
(ii) By washing and flushing the filter media with high velocity water jet and simultaneously loosening the aggregate with steel bars.
(iii) By flooding the filter top with water and allowing to stand for 24 hours. Within this period the impurities filled in the voids of the filter media shall be washed down.
(iv) By applying heavy dose of chlorine or chlorinated lime upto a residual of 5 ppm in the filter influent for 2-6 hours after every 2-3 days. The chlorinated influent should be recirculated for opening the voids of the filter.
Trouble # 3. The Fly Nuisance:
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This is the major trouble at the site of sewage treatment plants. The operation of the trickling filters is done at very low rate. Small moth-like files breed and are; developed at the sites. This filter fly is also known as ‘Psychoda’. The very small size can enter through the window mesh or screens and enter into the nose, mouth, ears and eyes of the people and animals, and causes great trouble to them.
The life of filter fly is about 22 days at 15.5°C, but with the increase in temperature its life decreases. At 29°C its life is only 7 days. The filter fly also interferes with the working of filter, as it reaches in the filter media and chokes it. In its larval stage, it is found in gelatinous film covering the filter.
Following are the main methods of preventing fly nuisance:
(i) By chlorinating the sewage, the chlorine will kill all the larva and the fly.
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(ii) By adding insecticides such as D.D.T. in the sewage and sprinkling it from time to time on the ground and on the site of the treatment units.
(iii) Flooding of filter once a day within each breeding cycle of the fly.
(iv) By sprinkling lime at the site and at all possible places, where its larva are breeding.