3.10 Example: Small-Scale Trickling Filter for Pre-treated Wastewater in Morocco
In Morocco, a small trickling filter was installed to receive pre-treated wastewater. The filter had a volume of 9.5 m3 (3 m high, 2 m diameter). It was built using bricks, stainless steel pipes and plastic net. For filter media, pipes commonly used for electric cable installations were cut into small pieces (ca 5 cm in length). A specific surface area of 250 m2/m3 was calculated.
On the surface of the filter, the up-flow wastewater sprinkler system based on perforated stainless-steel tubes was installed.
Holes (4 – 5 mm diameter) were added to the pipes (every 30 cm).
A test was carried out to determine the impact of the hydraulic loading rate on the removal efficiency for BOD and COD. The results are presented in the following table:
| Test 1 with HLR = 24 m3/d | Test 2 with HLR = 84 m3/d | |||
| Inflow | Outflow | Inflow | Outflow | |
| BOD (mg/L) | 183 | 19 | 180 | 35 |
| COD (mg/L) | 500 | 58 | 511 | 118 |
The results show that the treatment performance is slightly higher at lower hydraulic loading rates:
- Test 1 (low HLR): 88% BOD removal and 90% COD removal
- Test 2 (high HLR): 81% BOD removal and 77% COD removal
