4.8 Example: Intermittent Sand Filter as Tertiary Treatment Step in Ben Sergao, Morocco

Effluent Management 4 Overview of Post-Treatment Techniques: Sand Filtration 4.8 Example: Intermittent Sand Filter as Tertiary Treatment Step in Ben Sergao, Morocco

*Small Sand Filter as Secondary Treatment in a Wastewater Treatment Plant, Ben Sergao, Morocco.*

In Ben Sergao, Morocco, a system was designed consisting of a settler for primary treatment, a trickling filter for the secondary step, and an intermittent sand filter for tertiary treatment.

Due to the low strength of wastewater after the pre-treatment by trickling filter, a higher hydraulic loading rate of 0.357 m³/m²/d (instead of 0.1 m³/m²/d) was possible. The resulting design saved space and cost whilst ensuring that the water is safe for reuse in terms of pathogens and helminth eggs.

During the operation, feeding was done 5 days per week, and the filter was left to rest for 2 days over the weekends.

The cylindrical sand filter had a diameter of 1.6 m and an area of 2 m² a filter medium of 0.2 m pea gravel and 1.5 m sand.

The following performance parameters were recorded for the whole system.

Parameter	Treatment Performance
Parameter	Settler	Trickling Filter	Sand filter	Total
TSS	64.6%	83.7%	90.2%	99.4%
COD	52.6%	76.8%	64%	96%
BOD₅	56.4%	79%	87.7%	98.9%
Helminths (eggs/100mL)	47			0
Coliforms (/100mL)	5.1⁶			170

Treatment Performance of the Filter

Specifically for the intermittent sand filter, the following values for TSS, COD and BOD₅ were measured:

Parameter	In	Out
TSS (mg/L)	23.5	2.3
COD (mg/L)	118	42.5
BOD₅(mg/L)	36.5	4.5

Treatment Performance of Intermittent Sand Filter

The objective was the removal of pathogens and helminth eggs. The results showed that the treatment realised a complete removal of helminth eggs, and the effluent was safe for discharge.

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